JP3353650B2 - Catalyst poisoning regeneration equipment for internal combustion engines - Google Patents

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 Exhaust gas upstream of a certain position in an exhaust passage
Total fuel supplied in the passage, combustion chamber, and intake passage
The ratio of the total amount of air to the amount of fuel
The air-fuel ratio has been conventionally used to burn lean air-fuel mixtures.
In the internal combustion engine, the air-fuel
NO when ratio is lean_XNO_TwoAbsorbed in the form of
NO absorbed when the oxygen concentration in the exhaust gas becomes low_X
Releases NO_XAn absorber is placed in the engine exhaust passage and N
O_XFor supplying the reducing agent into the exhaust passage upstream of the absorbent
A reducing agent injection valve is provided, and the reducing agent is supplied from the reducing agent injection valve.
NO by temporarily supplying_XFlows into the absorbent
Make the air-fuel ratio of the exhaust gas rich temporarily _XFrom absorbent material
NO absorbed_XAnd released N
O_XThere is known an internal combustion engine configured to reduce the pressure.

[0003] By the way, are also included, for example, NO not only NO ₂ to NO _X in the exhaust gas, the NO is NO _X
It is absorbed after being oxidized to NO ₂ in the absorbent. However, for example, NO, when the temperature of the NO _X absorbent is low
It can not be satisfactorily absorbed NO _X because the oxidation reaction of is less likely to occur. Therefore, the exhaust gas purification device an oxidation catalyst is arranged in the NO _X absorbent in the engine exhaust passage upstream of are known (P
CT International Publication WO93 / 8383).

[0004] 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 the absorbent. However not released from the NO _X absorbent even if the air-fuel ratio of the sulfur containing components is the exhaust gas flowing into the NO _X absorbent simply rich, therefore the amount of sulfur in NO _X absorbent to be increased gradually Become. However the amount of the NO _X when the amount of sulfur in the absorbent material in increases NO _X absorbent can absorb NO _X is reduced gradually, finally NO _X absorbent can hardly be absorbed NO _X.

[0005] However, if the concentration of oxygen in the exhaust gas flowing into the NO _X absorbent is reduced when the temperature of the NO _X absorbent is high, the absorbed sulfur is released in the form of SO ₂ , for example. On the other hand, the reducing agent is supplied to the reducing agent to the NO _X absorbent is oxidized in NO _X absorbent, the temperature of the NO _X absorbent is increased by the reaction heat, moreover in the exhaust gas flowing into the NO _X absorbent Oxygen concentration decreases. Therefore, the reducing agent is supplied to the exhaust gas
It is considered that if the air-fuel ratio of the exhaust gas flowing into the _X absorbent is temporarily made rich, the sulfur absorbed from the NO _X absorbent can be released.

[0006]

[SUMMARY OF THE INVENTION However, in the exhaust purification apparatus described above oxidation catalyst is disposed in the exhaust passage between the reducing agent injection valve and NO _X absorbent, i.e. supplied from the reducing agent injection valve reduction NO agent after flowing through the oxidation catalyst
It reaches the _X absorber. As a result, most of the supplied reducing agent from the reducing agent injection valve is to be oxidized in the oxidation catalyst, i.e. almost done without oxidation reaction of the reducing agent in the NO _X absorbent, thus the temperature of the NO _X absorbent there is a problem that it is impossible to release the sulfur component is sufficiently increased that in order to release the sulfur is absorbed from the nO _X absorbent can not be satisfactorily.

[0007]

According To solve the above problems SUMMARY OF THE INVENTION to the first invention, the air-fuel ratio of the exhaust flowing absorbs NO _X when the lean, low oxygen concentration in the inflowing exhaust gas the the NO _X absorbent releases the NO _X that is absorbed disposed engine exhaust passage, the NO _X absorbent disposed an oxidation catalyst in the exhaust passage upstream, reduced to the exhaust passage of the oxidation catalyst upstream agent in the first reducing agent an internal combustion engine equipped with a supply means for supplying, comprising a second reducing agent supply means for supplying a reducing agent into the exhaust passage between the oxidizing catalyst and the NO _X absorbent, when the NO _X absorbent to emit sulfur that is absorbed is so as to temporarily supply the reducing agent from the second reducing agent supply means. That is, in the first invention, when the sulfur component absorbed from the NO _X absorbent is to be released, the reducing agent directly reaches the NO _X absorbent without flowing through the oxidation catalyst. reaction will be occurring in the NO _X absorbent, the temperature of the NO _X absorbent is surely increased, sulfur is sufficiently released from the NO _X absorbent.

Further, in the first aspect according to the second invention, NO _X which is absorbed from the NO _X absorbent
Is to be released, the reducing agent supply operation by the second reducing agent supply unit is prohibited, and the reducing agent is temporarily supplied from the first reducing agent supply unit. Temperature of the NO _X absorbent when supplying a reducing agent from a second reducing agent supplying means as described above is high, NO even after stopping the reducing agent supply operation of the second reducing agent supply means
_{The X} absorber is kept at a high temperature. However the temperature of the NO _X absorbent becomes the NO _X absorbing capacity decreases high. So 2
Th In the invention, when it should perform NO _X release action which are relatively frequent prohibits reducing agent supply operation of the second reducing agent supply means, temporarily reducing agent supply operation by the first reducing agent supply means To do it.

Further, in the first aspect according to the third invention, starting the reducing agent supply operation according to the second reducing agent supply means when it should emit sulfur which is absorbed from the NO _X absorbent Prior to the first
The reducing agent supply means temporarily supplies the reducing agent. When the temperature of the NO _X absorbent is low in some cases even if supplying the reducing agent hardly occurs the oxidation reaction of the reducing agent from the second reducing agent supply means. On the other hand, when the reducing agent is supplied from the first reducing agent supply unit, the temperature of the exhaust gas flowing into the NO _X absorbent is increased, and as a result, the oxidation reaction of the reducing agent in the NO _X absorbent is likely to occur. Therefore, in the third invention, when the sulfur content absorbed from the NO _X absorbent is to be released, first, the reducing agent supply operation by the first reducing agent supply unit is started, and then the reduction by the second reducing agent supply unit is started. The agent supply operation is started.

According to a fourth aspect of the present invention, in the first aspect, the second reducing agent supply means supplies the reducing agent intermittently. That is, in the fourth invention, the second
Is because the reducing agent from the reducing agent supply means is prevented from continuously supplying oxidation reaction in the NO _X absorbent is prevented to occur continuously and therefore the NO _X absorbent becomes excessively high temperature Will be blocked.

[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 an engine body, 2 is a piston, 3 is a combustion chamber, 4 is a fuel injection valve for directly injecting fuel into the combustion chamber 3, 5 is an intake valve, 6 is an intake port, and 7 is an exhaust valve. , 8 indicate exhaust ports, respectively. The intake port 6 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 8 is connected to the exhaust manifold 13 and the exhaust pipe 1.
4, the casing 16 is connected to a casing 16 containing an oxidation catalyst 15, and the casing 16 is connected via an exhaust pipe 17 to a casing 19 containing a NO _X absorbent 18.

A first reducing agent injection valve 21 for supplying a reducing agent into the exhaust pipe 14 is disposed in the exhaust pipe 14, and a first reducing agent injection valve 21 is provided in the exhaust pipe 17 for supplying the reducing agent into the exhaust pipe 17. The second reducing agent injection valve 22 is disposed. These reducing agent injection valves 21 and 22 are connected to pumps 24 and 25 whose discharge sides are connected to a fuel tank 23. 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, in the diesel engine of FIG. 1, the same fuel as the engine fuel injected from the fuel injection valve 4, that is, light oil, is injected from the reducing agent injection valves 21 and 22. As a result, no additional reductant tank for reductant supply is required. The pumps 24 and 25 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, and a B-RAM which is always supplied with power by a bidirectional bus 31. (Backup RAM) 33a, CPU
(Microprocessor) 34, input port 35 and output port 36. A temperature sensor 37 for generating an output voltage proportional to the temperature of the exhaust gas flowing through the exhaust pipe 17 is attached to the exhaust pipe 17 adjacent to the inflow end of the NO _X absorbent 18.
A stepping amount sensor 39 that generates an output voltage proportional to the stepping amount of the pedal is mounted. The output voltages of the temperature sensor 37 and the depression amount sensor 39 are input to the input port 35 via the corresponding AD converters 40, respectively. The input port 35 is connected to a vehicle speed sensor 41 that generates an output pulse at a cycle proportional to the vehicle speed, and a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 degrees. The CPU 34 calculates the engine speed based on the output pulse of the crank angle sensor 42. On the other hand, the output port 36 is connected to the pumps 24 and 25 via the corresponding drive circuit 43, respectively.

The oxidation catalyst 15 uses, for example, zeolite as a carrier, and platinum Pt, palladium Pd, ceria C
eO ₂ , lanthanum cobalt perovskite LaCoO ₃
At least one selected from the group consisting of On the other hand, the NO _X absorbent 18 uses, for example, cordierite or alumina as a carrier, and, for example, potassium K, sodium Na, lithium Li, cesium C
Alkali metals such as s, barium Ba, calcium C
At least one selected from alkaline earths such as a and rare earths such as lanthanum La and yttrium Y and a noble metal such as platinum Pt are supported. This NO _X absorbent 18 is used when the air-fuel ratio of the inflowing exhaust gas is lean.
Absorbs O _X, perform absorption and release action of the NO _X that releases NO _X to the oxygen concentration in the exhaust gas absorbed and reduced to flow.

If the NO _X absorbing material 18 is arranged in the engine exhaust passage, the NO _X absorbing material 18 actually performs the NO _X absorbing / releasing action, but the detailed mechanism of the NO _X absorbing / releasing action is not clear. is there. 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 air-fuel ratio of the exhaust gas flowing flows considerably becomes lean is increased by a large margin, these oxygen O ₂ as shown in FIG. 2 (A) 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 exhaust gas that flows in reacts with O ₂ ⁻ or O ²⁻ on the surface of platinum Pt to become NO ₂ (2NO + O ₂ → 2NO).
₂ ). Then part of the produced NO ₂ while bonding with the barium oxide BaO is absorbed by the absorbent material within while being further oxidized on the platinum Pt, 2 nitrate ions NO ₃ as shown in (A) ^- of Diffuses into the absorbent in the form. In this way, NO _X is absorbed in the NO _X absorbent 18.

The NO ₂ is produced on the surface of the platinum Pt so long as the oxygen concentration is high 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 absorber nitrate ions NO ₃ ^- Is generated. On the other hand, when the oxygen concentration in the exhaust gas that flows in decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the opposite direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ions NO ₃ ⁻ in the absorbent material. There are released from the absorbent in the form of NO _2. That is, the oxygen concentration in the inflowing exhaust gas are released NO _X from NO _X absorbent 18 when lowered. If the degree of leanness of the inflowing exhaust gas decreases, the oxygen concentration in the inflowing exhaust gas decreases. Therefore, if the degree of leanness of the inflowing exhaust gas decreases, the NO _x absorbent 18
O _X is to be released.

On the other hand, the air-fuel ratio of the exhaust gas flowing in at this time is reset.
Switch, that is, for example, the reducing agent
Supply of fuel (HC) as fuel and this HC
Unburned HC and CO discharged from Pt are oxygen O on platinum Pt_Two
^-Or O^2-And oxidize. Also inflow
When the air-fuel ratio of the exhaust gas is increased, the acid
NO concentration from the absorber due to extremely low element concentration_TwoIs released
This NO_TwoIs HC, as shown in FIG.
It is reduced by reacting with CO. In this way, platinum
NO on Pt surface_TwoWhen no longer exists, the next
NO to next _TwoIs released. Therefore the inflow exhaust
If the air-fuel ratio of the air is made rich, NO_Xabsorption
NO from material 18_XWill be released.

When the air-fuel ratio of the exhaust gas flowing in this way becomes lean,
NO when_XIs NO_XAbsorbed by the absorbing material 18 and flows in
NO if the air-fuel ratio of exhaust_XIs NO_XAbsorbent
Emitted from 18 in a short time. Therefore, in FIG.
NO in the diesel engine shown _XNO of absorbent 18_Xabsorption
When the amount exceeds a certain amount, the air-fuel ratio of
Rich and NO_XNO from absorbent 18_XReleased
The released NO_XIs to be reduced.

By the way, in order to maintain reduced amount of NO _X discharged without being reduced from NO _X absorbent 18 is required to maintain a high NO _X absorbing capacity of the NO _X absorbent 18. However, the temperature of the NO _X absorbent 18 is low and NO _X absorbing capacity of the NO _X absorbent 18 has been confirmed to be reduced. Figure 3 is a NO _X absorption rate R of the NO _X absorbent 18 when the air-fuel ratio of the exhaust gas flowing is lean, and the temperature T of the exhaust gas flowing to the NO _X absorbent 18 representative of the temperature of the NO _X absorbent 18 2 shows the experimental results showing the relationship. As indicated with a broken line in FIG. 3, the temperature of the NO _X absorbent 18 is low and NO _X adsorbing capacity of the NO _X absorbent 18 decreases. As described above, the NO _x absorbent 18 has NO
_X from NO ₂ NO ₃ ^- is absorbed is oxidized to. However the oxidation of NO when the temperature decreases of the NO _X absorbent _{18 (2NO + O 2 → 2NO} 2) becomes inactive, NO _X absorption rate R of this for NO _X absorbent 18 is believed to decrease.

[0021] Therefore, NO _X in the diesel engine shown in FIG. 1
An oxidation catalyst 15 is provided in the exhaust passage upstream of the absorbent 18 to reduce
NO oxidation reaction even when the temperature is low O _X absorbent 18 so as to produce the active, thereby thereby ensuring a good NO _X absorption of the NO _X absorbent 18. As a result, it is possible to expand the temperature range in which NO _X absorption rate R is kept high as shown with a solid line in FIG. 3 to the low temperature side.

[0022] Incidentally, the the temperature of the NO _X absorbent 18 becomes higher NO _X absorption rate R drops is believed to be due to the following reason. That, NO _X in the absorbent material 18 to flow air-fuel ratio of the exhaust gas has been carried out and releasing action and absorption also NO _X a lean, NO _X absorption rate by high partial than NO _X release rate NO NO _X is absorbed in the _X absorbent 18. However, when the temperature of the NO _X absorbent 18 increases, the NO _X release speed becomes higher than the absorption speed, and thus the NO _X absorption rate R decreases.

In the diesel engine shown in FIG.
In the air-fuel ratio of the mixture burned is maintained lean than the stoichiometric air-fuel ratio, thus NO _X absorbent 18
The air-fuel ratio of the exhaust gas flowing into the inside is normally kept lean. Therefore, a first reducing agent injection valve 21 that injects fuel into the exhaust pipe 14 to temporarily make the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 18 rich or to perform a reducing agent is provided. . That is, the fuel from the first reducing agent injection valve 21 is supplied to the time to emit NO _X that is absorbed from the NO _X absorbent 18. The fuel is first oxidized reached the oxidation catalyst 15, thus NO _X absorbent 18
The oxygen concentration in the exhaust gas flowing into the NO _x absorbent 18 is reduced, that is, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 18 is made rich. At this time, partially oxidized HC is generated, and this HC is unburned HC and CO discharged from the combustion chamber 3.
Reducing the released NO _X from NO _X absorbent 18 with. Incidentally, NO is absorbed from the NO _X absorbent 18 _X
May be supplied continuously from the first reducing agent injection valve 21 when the fuel is to be discharged.
In the diesel engine of FIG. 1, fuel is intermittently supplied from the first reducing agent injection valve 21 in order to prevent the temperature of No. 5 from becoming excessively high.

[0024] it is possible to ensure a good absorption of the NO _X by providing such a NO _X absorbent 18 oxidation catalyst 15 upstream of the exhaust passage. However, the exhaust flowing includes a sulfur component, NO _X absorbent 18
Absorbs not only NO _x but also sulfur such as SO _x . It is considered that the mechanism of sulfur absorption by the NO _X absorbent 18 is the same as the mechanism of NO _X absorption.

That is, in the same manner as when the NO _X absorption mechanism was described, platinum Pt and barium Ba were deposited on the support.
When the air-fuel ratio of the inflowing exhaust gas is lean as described above, the oxygen O2
Is attached to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ , and SO _X in the flowing exhaust gas, for example, SO ₂ reacts with O ₂ ⁻ or O ^{2− on} the surface of platinum Pt to form SO ₃ Becomes Then SO ₃ generated while bonding with the barium oxide BaO is absorbed by the absorbent material within while being further oxidized on platinum Pt, diffuses into the absorbent material in a sulfuric acid ion SO ₄ ^2-form. Next, this sulfate ion SO ₄ ^2- is combined with barium ion Ba ²⁺ to form sulfate BaSO ₄ .

However, this sulfate BaSO_FourDecomposes
It is difficult to make the air-fuel ratio of the inflowing exhaust gas rich
Sulfate BaSO_FourRemains undisassembled. But
NO_XAs time passes, sulfuric acid
Acid salt BaSO_FourWill increase, and thus the time
NO as time goes by_XNO that can be absorbed by the absorbent 18 _X
The amount will be reduced.

However, NO_XProduced in the absorbent 18
Sulfate BaSO_FourIs NO_XWhen the temperature of the absorbent 18 is high
Set the air-fuel ratio of exhaust flowing into the
Decomposes into sulfate ion SO_Four ^2-Is SO_ThreeAbsorbent in the form of
Released from On the other hand, NO _XSupplying a reducing agent to the absorbent 18
When supplied, this reducing agent becomes NO_XOxidation in absorber 18
(Combustion), resulting in NO_XAbove the temperature of the absorbent 18
As well as NO_XFlows into the absorbent 18
The exhaust gas air-fuel ratio can be made rich. So figure
In diesel engine No. 1, NO_XAbsorbed by the absorbing material 18
When the sulfur content exceeds a predetermined amount
NO_XBy temporarily supplying the reducing agent (HC) to the absorbent 18
NO_XSet the temperature of the absorbent 18 to NO_XSulfur from absorbent 18
Temporarily higher than required to release minutes
And NO_XThe air-fuel ratio of the exhaust gas flowing into the absorber 18 is
Temporarily rich, so NO_XAbsorbent 18
To release sulfur. Release at this time
SO_ThreeIs the HC, unburned HC, CO
SO immediately_TwoIt is reduced to.

It should be noted, NO _X absorbent air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 18 on whether the unit time to whether stoichiometric air-fuel ratio is rich when the NO _X absorbent to emit sulfur It is determined according to the amount of sulfur released from the fuel cell 18. However, in order to make the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 18 in order to release the sulfur that has been absorbed from the NO _X absorbent 18 rich, injecting a reducing agent from the first reducing agent injection valve 21 and even if NO _X absorbing material 1
8 cannot be raised sufficiently. That is,
As described above, most of the reducing agent supplied from the first reducing agent injection valve 21 first flows into the oxidation catalyst 15 and is oxidized, that is, almost no oxidation reaction of the reducing agent occurs in the NO _X absorbent 18. Therefore, the first reducing agent injection valve 2
Even if the reducing agent is supplied from No. 1, the temperature of the NO _x absorbent 18 cannot be sufficiently increased. In this case, the temperature of the exhaust gas flowing through the oxidation catalyst 15 is increased, and therefore, the temperature of the exhaust gas flowing into the NO _X absorbent 18 is increased. However, a large amount in the reducing agent supplied from the first reducing agent injection valve 21 becomes able to be used indirectly to increase the temperature of the NO _X absorbent 18, to sufficiently increase the temperature of the NO _X absorbent 18 Is inefficient because it requires a reducing agent.

[0029] Therefore, the second or additional reducing agent injection valve 22 into the exhaust pipe 17 between the oxidation catalyst 15 and the NO _X absorbent 18 provided in the embodiment according to the present invention, NO _X absorber 1
When sulfur is to be released from the nozzle 8, the reducing agent is supplied from the second reducing agent injection valve 22.
As a result, to increase since the reducing agent is directly fed to the NO _X absorbent 18 oxidation reaction of the reducing agent becomes to result in NO _X absorbent 18, thus the temperature of the NO _X absorbent 18 efficiently it can.

By the way, thus the case of providing a second reducing agent injection valve 22, so as to supply the reducing agent from the second reducing agent injection valve 22 when the NO _X absorbent 18 to be released the NO _X In this case, it is considered that it is not necessary to provide the first reducing agent injection valve 21. However, the temperature of the NO _X absorbent 18 in the oxidation reaction of the reducing agent occurs in NO _X absorbent 18 when directly supplying reducing agent from the second reducing agent injection valve 22 in the NO _X absorbent 18 becomes higher. However, the temperature of the NO _X absorbent 18 be stopped reducing agent supply operation does not decrease immediately, i.e. a while after the stop of the reducing agent supply operation is maintained at a high temperature. However, as described above with reference to FIG. 3, when the temperature of the NO _X absorbent 18 is high, the NO _X absorption capacity is reduced. Therefore, immediately after stopping the reducing agent supply operation, it is possible to absorb NO _X well. Can not. NO _X release effect is relatively so frequently carried out the NO _X absorbing capacity is decreased every time the NO _X release action is performed is not preferable.

On the other hand, when the reducing agent is supplied from the first reducing agent injection valve 21 as described above, the reducing agent is supplied to the oxidation catalyst 15.
Therefore, the temperature of the NO _x absorbent 18 is prevented from becoming excessively high. So, NO _X
When NO _X is to be released from the absorbent 18, the reducing agent supply action from the second reducing agent injection valve 22 is prohibited, and the first
The reducing agent is supplied from the reducing agent injection valve 21. As a result, the temperature of the NO _X absorbent 18 is prevented from becoming excessively high, it is possible to maintain a high NO _X absorbing capacity of the NO _X absorbent 18.

That is, generally speaking, the NO _x absorbent 1
8 to release the absorbed NO _X , the reducing agent supply operation of the second reducing agent injection valve 22 is prohibited, and the reducing agent supply operation of the first reducing agent injection valve 21 is performed.
And to perform the reducing agent supply operation of the second reducing agent injection valve 22 when the NO _X absorbent 18 to emit sulfur being absorbed.

Note that NO_XAbsorbed from the absorbent 18
Second reducing agent injection valve when sulfur is to be released
Although the fuel may be continuously supplied from 22,
NO _XPrevents the temperature of the absorbent 18 from becoming too high
Therefore, in the diesel engine shown in FIG.
2 to supply fuel intermittently. Sand
That is, for example, fuel is injected only for 2 seconds every 5 seconds.

FIG. 4A is an experimental result showing the SO ₂ concentration C (SO ₂ ) in the exhaust gas released from the NO _X absorbent 18 when the reducing agent is supplied from the second reducing agent injection valve 22. FIG. 4B is an experimental result showing the SO ₂ concentration C (SO ₂ ) in the exhaust gas discharged from the NO _X absorbent 18 when the reducing agent is supplied from the first reducing agent injection valve 21. . FIG.
In (A) and FIG. 4 (B) TI, TO indicates the temperature of the exhaust gas flowing out of the respective NO _X absorbent 18 to a temperature of the exhaust gas flowing and NO _X absorbent 18, Q (H
C) indicates the amount of reducing agent injected from the reducing agent injection valves 21 and 22. In addition, time zero is equal to the reducing agent injection valves 21 and 22.
Shows the time at which the reducing agent injection action from is started.
As can be seen from FIGS. 4A and 4B, when the reducing agent is supplied from the second reducing agent injection valve 22, the sulfur component can be quickly released from the NO _X absorbent 18.
Therefore, the time required for the sulfur release action and the amount of the reducing agent can be reduced.

The sulfur containing components release effect is actually absorbed carried out but the NO _X absorbent 18 when the sulfur containing components which is absorbed in the NO _X absorbent 18 exceeds a certain amount of such NO _X absorbent 18 been is difficult to detect the amount of sulfur, therefore the amount of sulfur that is absorbed in the NO _X absorbent 18 is estimated forced. However, the amount of sulfur absorbed by the NO _X absorbent 18 depends on the vehicle travel distance, and therefore, the NO _X absorbent 18
It is possible to estimate the amount of sulfur that has been absorbed. Therefore, NO _X absorbent 18 when exceeding the predetermined value accumulated running distance has been determined in advance in the diesel engine shown in FIG. 1
It is determined that the amount of sulfur absorbed inside exceeds a certain amount.

Next, the sulfur release control in the diesel engine of FIG. 1 will be described in more detail with reference to FIG. The routine of FIG. 5 is executed by interruption every predetermined set time. Referring to FIG. 5, is set when the NO _X absorbent 18 to emit sulfur, first, at step 50, the sulfur content releasing flag is reset is set when should stop the sulfur containing components release effect Is determined. When the sulfur release flag is reset, the routine proceeds to step 51, where the vehicle travel distance L0 from the previous processing cycle to the current processing cycle is calculated from the output pulse of the vehicle speed sensor 41. In the following step 52, the vehicle travel distance L0 is added to the accumulated travel distance L. In the following step 53, it is determined whether or not the accumulated traveling distance L is larger than a predetermined constant value L1. N when L ≦ L1
O _X absorbent sulfur content absorbed in 18 is determined to still less the processing cycle is ended. On the other hand, L> L
If it is 1, then the routine proceeds to step 54, where the exhaust gas temperature T
However, the reducing agent supplied from the second reducing agent injection valve 22 is N
O _X absorbent 18 temperature is favorably oxidized in T1 (for example 300 ° C.) higher it is determined whether than. T ≦ T
If it is 1, the processing cycle ends. That is, T ≦
A reducing agent supply operation of the second reducing agent injection valve 22 is determined that the reducing agent supplied from the second reducing agent injection valve 22 is discharged from the NO _X absorbent 18 without being oxidized at the time of T1 Stop. On the other hand, when T> T1, the second
Of reducing agent supplied from the reducing agent injection valve 22 is determined to be better oxidized in NO _X absorbent 18, and then sulfur containing components release flag is set the routine proceeds to step 55.
That is, when L> L1 and T> T1, the sulfur release action is performed.

When the sulfur release flag is set, the process proceeds from step 50 to step 56, where the counter C representing the time during which the sulfur release flag is set is incremented by one. In the following step 57, it is determined whether or not the counter C is larger than the fixed value C1. C ≦
At the time of C1, the processing cycle ends. On the other hand, C
If> C1, that is, if the sulfur release operation has been performed for a certain period of time, then the routine proceeds to step 58, where the sulfur release flag is reset. In the following step 59, the accumulated traveling distance L and the counter C are cleared. Next, the processing cycle ends.

Next, will be described in more detail NO _X release control in the diesel engine of FIG. 1 with reference to FIG. The routine of FIG. 6 is executed by interruption every predetermined set time. Referring to FIG. 6, first, at step 60, it is determined whether or not the sulfur release flag set or reset in the routine of FIG. 5 is set. When the sulfur release flag is reset, the routine proceeds to step 61, where N
O from _X absorbent 18 is set when it should emit NO _X, whether NO _X release flag is reset when should stop the NO _X release action is set or not. When the NO _X release flag is reset, that is, when both the sulfur release flag and the NO _X release flag are reset, the routine proceeds to step 62. When the sulfur containing components release flag is also NO _X release flag is also reset has been air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 18 as described later lean, therefore at this time the NO _X absorbent 18 NO _X Absorption is taking place.

NO absorbed in the NO _X absorbent 18
Since it is difficult to directly determine the _X amount, that is, the absorbed NO _X amount S, the diesel engine shown in FIG. 1 estimates the absorbed NO _X amount S based on the engine operating state. That is, first _the amount of NO _X i.e. inflow amount of NO _X F flowing into the NO _X absorbent 18 per step 62 the unit time is calculated. As shown in FIG. 7A in which each curve shows the same inflow NO _X amount, the inflow NO _X amount F increases as the depression amount DEP of the accelerator pedal 38 increases, and increases as the engine speed N increases. Become. Therefore, in the diesel engine shown in FIG. 1, the inflow NO _X amount F is previously obtained by an experiment as a function of the depression amount DEP of the accelerator pedal 38 and the engine speed N, and based on the depression amount DEP of the accelerator pedal 38 and the engine speed N. And inflow N
The O _X amount F is to be calculated. The inflow NO _X amount F is stored in advance in the ROM 32 in the form of a map shown in FIG.
Is stored within. In the following step 63, the absorbed NO _X amount S is calculated based on the following equation.

S = S + F · DLT where DLT is the time from the previous routine to the present routine, and therefore F · DLT is the NO absorbed in the NO _X absorbent 18 from the previous routine to the present routine. _X amount is shown. In the following step 64, it is determined whether or not the absorbed NO _X amount S is larger than a predetermined set amount S1. The set amount S1 is, for example, about 30% of the maximum NO _X amount that can be absorbed by the NO _X absorbent 18. If S ≦ S1, the processing cycle is completed, and S>
NO _X releasing flag proceeds to step 65 if S1 is set. In the following step 66, the absorbed NO _X amount S when the NO _X release flag is set is set to the initial absorbed amount S0.
It is said.

NO_XWhen the release flag is set
The process proceeds from step 61 to step 67. NO_XRelease hula
Is set to NO as described later._XSucking
It is assumed that the air-fuel ratio of the exhaust flowing into the collecting material 18 is rich.
And therefore NO _XNO in the absorbent 18_XRelease
An action is performed. In step 67, a simple
NO per unit initial absorption_XReleased from the absorbent 18
NO_XAmount or release NO_XThe quantity D is calculated.

[0042] Figure 8 is released from the NO _X absorbent 18 in the unit initial absorption amount per unit time when the rich air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 18 NO _X
It is an experimental result showing the amount. In FIG. 8A, the solid line is N
O shows the case the temperature of the _X absorbent 18 is high, the dashed line shows the case temperature of the NO _X absorbent 18 is low, t is a rich air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 18 Shows the time since being. Temperature of the NO _X absorbent 18 becomes the degradation rate of the nitrate becomes high in NO _X absorbent 18 increases, thus the discharge amount of NO _X D exhaust temperature T is higher, as shown in many FIG 8 (A).
This released NO _X amount D is stored in the ROM 32 in advance in the form of a map shown in FIG. 8B as a function of the exhaust gas temperature T and the time t. In the following step 68, the absorbed NO _X amount S is calculated based on the following equation.

S = S−D · S0 · DLT Here, D · S0 is the NO _x absorption material 18 per unit time.
The amount of NO _X released from
T indicates the NO _X amount released from the NO _X absorbent 18 from the previous routine to the current routine. In the following step 69, it is determined whether or not the absorbed NO _X amount S is equal to or less than zero. If S> 0, the processing cycle is completed and S
If ≦ 0, the routine proceeds to step 70, where the NO _X release flag is reset.

On the other hand, also when the sulfur release flag is set, the process proceeds from step 60 to step 67. As described later, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 18 even when the sulfur containing components release flag is set is made rich, the thus NO _X absorbent 18 NO _X
A release action is taking place. Next, the reducing agent supply control in the diesel engine of FIG. 1 will be described in more detail with reference to FIG. The routine of FIG. 9 is executed by interruption every predetermined set time. Referring to FIG. 9, first, at step 80, it is determined whether or not the sulfur release flag is set. Whether NO _X release flag proceeds to step 81 when the sulfur containing components release flag is not set is set or not. When NO _X release flag is not set, i.e. the proceeds then to step 82 when also sulfur containing components release flag NO _X release flag is also not set 1
The reducing agent supply operation of the reducing agent injection valve 21 is stopped, and then the routine proceeds to step 83, where the reducing agent supply operation of the second reducing agent injection valve 22 is stopped. Next, the processing cycle ends.
Therefore, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 18 is made lean.

When the NO _X release flag is set, the routine proceeds from step 81 to step 84, where the reducing agent is intermittently supplied from the first reducing agent injection valve 21.
O _X release action is performed. At this time, the reducing agent supply operation of the second reducing agent injection valve 22 is stopped. on the other hand,
Step 8 when the sulfur release flag is set
From 0, the routine proceeds to step 85, where the reducing agent is intermittently supplied from the second reducing agent injection valve 22, so that the sulfur release operation is performed. At this time, the first reducing agent injection valve 2
No. 1 reducing agent supply operation is stopped.

[0046] During the exhaust of the diesel engine 1 way contains soot, the soot reduces the oxidative capacity of the oxidation catalyst 15 is deposited on the surface of the oxidation catalyst 15 and the NO _X absorbent 18, or NO reducing the NO _X absorbing capacity of the _X absorbent 18. However, as described above NO _X absorber 1
The first reducing agent injection valve 21 to perform the NO _X release action of 8
When the reducing agent is supplied from the reducing agent is burned in the oxidation catalyst 15, the reducing agent from the second reducing agent injection valve 22 to perform the sulfur releasing action of the NO _X absorbent 18 is supplied this The reducing agent is burned in the NO _x absorbent 18. Therefore, NO of the NO _X absorbent 18
Surface on soot combustion with the oxidation catalyst 15 _X release action is performed, is made to remove soot on the surface of the sulfur containing components release action of the NO _X absorbent 18 is made NO _X absorbent 18 is also burned, removed I'm sullen. Therefore, it is not necessary to provide a special device for removing soot deposited on the surface of the oxidation catalyst 15 and the NO _X absorbent 18 is a diesel engine of FIG.

FIG. 10 shows another embodiment. In the embodiment shown in FIG.
The intake throttle valve 45 driven by the valve is disposed. The actuator 44 is a drive circuit of the electronic control unit 30.
3 and is controlled based on an output signal from the electronic control unit 30. On the other hand, the intake throttle valve 45 is normally kept fully open.

Next, this embodiment will be described in detail with reference to FIG. Time to emit NO _X that is absorbed from the NO _X absorbent 18 in this embodiment, i.e. NO _X
When the release flag is set, the reducing agent supply operation of the second reducing agent injection valve 22 is prohibited, and the reducing agent supply operation of the first reducing agent injection valve 21 is performed. NO
_{When the} sulfur absorbed from the _X absorbent 18 is to be released, that is, when the NO _X release flag is set, the reducing agent supply operation of the second reducing agent injection valve 22 is performed.

[0049] However, for example, the NO oxidation reaction of the reducing agent when the temperature is low _X absorbent 18 (combustion) hardly occurs, thus also NO _X absorbed as to supply the reducing agent from the second reducing agent injection valve 22 at this time The temperature of the material 18 cannot be raised quickly. However reducing agent supplied from the first reducing agent injection valve 21 is relatively even at low temperatures is oxidized in the oxidation catalyst 15, the temperature of the exhaust gas flowing in the order in NO _X absorbent 18 becomes higher. Therefore, in the diesel engine shown in FIG. 10, when the sulfur content absorbed from the NO _X absorbent 18 is to be released, the first reducing agent is supplied before the second reducing agent injection valve 22 starts the reducing agent supply operation. The reducing agent is temporarily supplied from the injection valve 21.

That is, when the sulfur release flag is set as shown in FIG. 11, first, the reducing agent is supplied from the first reducing agent injection valve 21, and as a result, the NO _X absorbent 18
Is maintained above the temperature at which the oxidation reaction of the reducing agent occurs. Next, when a certain time (C2) has elapsed, the reducing agent supply operation of the second reducing agent injection valve 22 is started. As a result, the reducing agent supplied from the second reducing agent injection valve 22 becomes N
Come to be reliably oxidized in O _X absorbent 18,
That is, the reducing agent supplied from the second reducing agent injection valve 22 can be used efficiently for the sulfur release action. Further, even when the temperature of the NO _X absorbent 18 is low, the sulfur releasing action can be performed, that is, the temperature T1 in the routine of FIG. 5 can be set lower than the embodiment of FIG.

Since the reducing agent supply operation of the first reducing agent injection valve 21 is for raising the temperature of the NO _X absorbent 18 to a temperature required for oxidizing the reducing agent, the sulfur release flag is set. After a lapse of a predetermined time (C2), the reducing agent supply operation of the first reducing agent injection valve 21 is stopped. Meanwhile, the air-fuel ratio of the mixture burned in the diesel engine 1, the combustion chamber 3 as described above is maintained lean, thus NO _X absorbent 18
The air-fuel ratio of the exhaust gas flowing into the inside is normally kept lean. In this case, the amount of the reducing agent required to make the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 18 rich depends on the amount of oxygen flowing into the NO _X absorbent 18, that is, the amount of intake air. If the amount is reduced, the required amount of the reducing agent can be reduced. Therefore, in the diesel engine 10 to be the air-fuel ratio of the exhaust gas capable of reducing the intake throttle valve 45 to the intake air amount is arranged in an engine intake passage, flows into the NO _X absorbent 18 to rich or stoichiometric air-fuel ratio When
That is, so as to temporarily close the throttle valve 45 intake when it should emit NO _X or sulfur is absorbed from the NO _X absorbent 18.

[0052] In other words, the opening OP of the intake throttle valve 45 as shown in FIG. 11 is maintained in FL representing a normal full open, a small opening CL when NO _X release flag or sulfur containing components release flag is set Is done. In an internal combustion engine provided with a device for supplying EGR gas into the engine intake passage, the EGR gas amount may be increased in order to reduce the required reducing agent amount.

FIG. 12 shows a routine for executing the reducing agent supply control in the diesel engine of FIG. 10, and this routine is executed by interruption every predetermined set time. In this embodiment, the routines of FIGS. 5 and 6 are also executed. Referring to FIG. 12, first, at step 80, it is determined whether or not the sulfur release flag is set. Whether NO _X release flag proceeds to step 81 when the sulfur containing components release flag is not set is set or not. When the NO _X release flag is not set,
That opening OP of willing intake throttle valve 45 is then in step 81a when also sulfur containing components release flag NO _X release flag is also not set is fully opened FL. Next, proceeding to step 82, the reducing agent supply operation of the first reducing agent injection valve 21 is stopped, and then proceeding to step 83, the reducing agent supply operation of the second reducing agent injection valve 22 is stopped. Next, the processing cycle ends. Therefore, NO _X absorber 1
The air-fuel ratio of the exhaust gas flowing into the inside 8 is made lean.

NO_XWhen the release flag is set
Proceeding from step 81 to step 81b, the intake throttle valve 4
The opening OP of 5 is set as the small opening CL. Then step 8
Proceeding to 4, the reducing agent is intermittent from the first reducing agent injection valve 21
And therefore NO _XA release action takes place. What
At this time, the reducing agent supply action of the second reducing agent injection valve 22
Has been stopped.

On the other hand, when the sulfur release flag is set, the routine proceeds from step 80 to step 80a, where the opening OP of the intake throttle valve 45 is set to the small opening CL. Next, the routine proceeds to step 80b, where a counter C (see FIG. 5) indicating the time since the sulfur release flag was set is set to a constant value C.
It is determined whether it is greater than two. When the process proceeds to step 80b for the first time after the sulfur release flag is set, C ≦ C2, so that the process proceeds to step 84, where the reducing agent is intermittently supplied from the first reducing agent injection valve 21. On the other hand, when C> C2, the routine proceeds to step 80c, where the reducing agent supply action of the first reducing agent injection valve 21 is stopped, and then proceeds to step 85, where the reducing agent is intermittently supplied from the second reducing agent injection valve 22. Supplied.

In the embodiment described above, the temperature sensor 37 is provided in the exhaust pipe 17 to obtain the exhaust gas temperature T. However, when the exhaust gas temperature T is changed to the engine operating state,
For example, it can be obtained based on the depression amount DEP of the accelerator pedal 38 and the engine speed N. Further, in the embodiment described so far, the first reducing agent injection valve 21 is disposed in the exhaust pipe 14 to supply the reducing agent into the exhaust passage upstream of the oxidation catalyst 15, and the first reducing agent Injection valve 2
The fuel is injected from one. However,
It is also possible to supply the reducing agent into the exhaust passage upstream of the oxidation catalyst 15 by injecting the fuel secondary from the fuel injection valve 4 to the engine expansion stroke or the exhaust stroke. Alternatively, in the spark ignition type internal combustion engine, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 3 can be made rich.

[0057]

[Effect of the Invention] while ensuring a good NO _X absorbing capacity of the NO _X absorbent is absorbed in the NO _X absorbent was the sulfur content can be sufficiently released.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining a NO _X absorption / release effect.

FIG. 3 is a graph showing a relationship between an NO _X absorption rate and an exhaust gas temperature.

FIG. 4 is an experimental result showing a change with time of the SO ₂ concentration in the exhaust gas discharged from the NO _X absorbent.

FIG. 5 is a flowchart for executing sulfur release control.

FIG. 6 is a flowchart for executing NO _X release control.

FIG. 7 is a diagram showing an inflow NO _X amount F;

FIG. 8 is a diagram showing a released NO _X amount D.

FIG. 9 is a flowchart for executing a reducing agent supply control.

FIG. 10 is an overall view of a diesel engine showing another embodiment.

FIG. 11 is a time chart for explaining the embodiment in FIG. 10;

FIG. 12 is a flowchart for executing a reducing agent supply control in the embodiment of FIG. 10;

[Explanation of symbols]

13 ... exhaust manifold 15 ... oxidizing catalyst 18 ... NO _X absorbent 21 ... first reducing agent injection valve 22 ... second reducing agent injection valve

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Toshimitsu Takahashi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-8-200048 (JP, A) JP-A-7-217474 JP-A-6-336916 (JP, A) JP-A-6-336914 (JP, A) JP-A-6-307230 (JP, A) JP-A-6-200737 (JP, A) Kaihei 5-214926 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) F01N 3/08-3/20

Claims (4)

(57) [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 NO _X absorbent to the engine exhaust passage arranged, the NO _X absorbent disposed an oxidation catalyst in the exhaust passage upstream, in the first reducing agent an internal combustion engine equipped with a supply means for supplying a reducing agent into the exhaust passage of the oxidation catalyst upstream, A second reducing agent supplying means for supplying a reducing agent into an exhaust passage between the oxidation catalyst and the NO _x absorbent; and a second reducing agent supply means for releasing sulfur absorbed from the NO _x absorbent. A catalyst poisoning regeneration device that temporarily supplies a reducing agent from a reducing agent supply unit. 2. The N absorbed by the NO _X absorbent.
When the O _X to be released according to claim 1 which is adapted to temporarily supply the reducing agent from the first reducing agent supplying means as well as prohibiting a reducing agent supply operation according to the second reducing agent supply means Catalyst poisoning regeneration equipment. 3. The first reducing agent supply means prior to starting the reducing agent supply operation by the second reducing agent supply means when the sulfur content absorbed from the NO _X absorbent is to be released. The catalyst poisoning regeneration device according to claim 1, wherein the reducing agent is temporarily supplied from the reactor. 4. The catalyst poisoning regeneration apparatus according to claim 1, wherein said second reducing agent supply means intermittently supplies the reducing agent.