JP2000145436A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) Abstract: large amount of the NO _X is prevented from caused to bypass _the NO _X absorbent. SOLUTION] _the NO _X absorbent 12 is disposed in the engine exhaust passage, arranging the SO _X absorbent 9 in the NO _X absorbent 12 upstream of the exhaust passage. Branches the bypass passage 24 for bypassing the _the NO _X absorbent 12 from the exhaust passage between the SO _X absorbent 9 and _the NO _X absorbent 12, of the NO _X absorbent 12 or the bypass passage 24 to the branch portion of the bypass passage 24 A switching valve 17 that allows exhaust gas to flow into one of them is arranged. And that the temperature of the SO _X absorbent 9 higher than the SO _X release temperature when the engine load is higher than the allowable maximum load when the absorbed SO _X amount of SO _X absorbent 9 becomes larger than the set value, S
The air-fuel ratio of the exhaust gas flowing into the O _X absorbent 9 prohibit and be rich from SO _X absorbent 9 with SO _X is prevented from being released, the exhaust flows into _the NO _X absorbent 12 The switching valve 17 is held at the position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine.

[0002]

Absorbs NO _X flowing when the air-fuel ratio of the exhaust gas of the Prior Art inflow is lean, NO _X absorbent to the engine exhaust passage in which the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed to decrease And the SO _X absorbent is NO _X
Placed absorbent in the engine exhaust passage upstream of, SO _X absorbent air-fuel ratio of the exhaust gas flowing flows when the lean SO _X
It absorbs the temperature of SO _X absorbent releases SO _X in which the air-fuel ratio of the exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich flowing when higher than SO _X release temperature, SO _X absorbent and NO _X absorbent NO _X from the engine exhaust passage located between
Absorbent arranged switching valve for flowing the exhaust in one of _the NO _X absorbent or the bypass passage to the branch portion of the bypass passage with branches a bypass passage bypassing the, S
When SO _X is to be released from the O _X absorbent, the switching valve is switched to a position where exhaust gas flows into the bypass passage, and SO _X is discharged.
2. Description of the Related Art An exhaust gas purifying apparatus for an internal combustion engine for enriching the air-fuel ratio of exhaust gas flowing into an _X absorbent is known (Japanese Patent No. 2605580).
Reference). Released from SO _X absorbent SO _X is N
O flowing into the _X absorbent is likely to be absorbed in the NO _X absorbent when. Therefore, in the exhaust emission control device, SO when should emit SO _X from _X absorbent SO _X when to emit SO _X from the absorbent by switching the switching valve to a position where the exhaust flows into the bypass passage SO _X is NO _X It is designed to bypass the absorbent.

[0003]

SUMMARY OF THE INVENTION In this exhaust gas purifying apparatus,
Is SO_XAbsorbent temperature depends on engine operating conditions, to be precise
Determined according to the engine operating state determined by the vehicle operator
Can be Therefore, SO _XThe temperature of the absorbent is SO_Xrelease
The reason why the temperature is higher than the temperature is, for example, that the engine load has increased.
That is, when the engine load is high, SO_XAbsorbent
SO_XA release action takes place. However, engine load
Emission from the engine when the pressure rises_XAs the volume increases
Nevertheless, this large amount of NO_XIs N through the bypass passage
O_XThe absorbent is bypassed and thus a large amount of NO_XTo
NO_XThe problem is that it cannot be reduced and purified with an absorbent.
You.

[0004]

[MEANS FOR SOLVING THE PROBLEMS]
According to the first aspect, the air-fuel ratio of the inflowing exhaust gas is low.
NO when flowing in_XAbsorbs the
NO absorbed when oxygen concentration decreases_XReleases NO_X
The absorbent is arranged in the engine exhaust passage and the SO_Xabsorption
NO agent_XArranged in the engine exhaust passage upstream of the absorbent,
_XAbsorbent flows in when the air-fuel ratio of the incoming exhaust gas is lean
SO_XAbsorbs SO_XThe temperature of the absorbent is SO_Xrelease
The air-fuel ratio of the exhaust gas that flows in when it is higher than the temperature is stoichiometric
Absorbed SO when ratio or rich_XTo release SO
_XAbsorbent and NO_XEngine exhaust passage located between the absorbent
From NO_XFork the bypass passage to bypass the absorbent
And NO at the branch of the bypass passage_XAbsorbent or ba
A switching valve that allows exhaust gas to flow into one of the
Place and SO_XAbsorbent to SO_XWhen to release
Switch the switching valve to the position where exhaust gas flows into the bypass passage
In an exhaust gas purifying apparatus for an internal combustion engine,
_XA temperature control means for controlling the temperature of the absorbent;
_XAbsorbent to SO_XShould be released when temperature control
SO by means_XThe temperature of the absorbent is SO_XThan the release temperature
High and SO_XTheory of air-fuel ratio of exhaust gas flowing into absorbent
Make the air-fuel ratio or rich, and exhaust the bypass passage
The switching valve is switched to the position where it flows into the
When it is higher than the load, the temperature control means_Xabsorption
Agent temperature SO_XHigher than the release temperature and SO
_XThe air-fuel ratio of the exhaust gas flowing into the absorbent
And prohibiting at least one of
The exhaust is NO_XHolds switching valve at the position where it flows into the absorbent
I am trying to do it. That is, in the first invention, the engine
From a large amount of NO_XIs released when SO_XAbsorbent or
SO_XIs prevented from being released and NO_XSucking
Guided to a collector. Therefore, a large amount of NO_XIs NO_XSucking
Bypassing the sorbent is prevented.

Further, in the first aspect according to the second aspect, the engine load is the maximum allowed when lower than the load temperature control means by SO _X the temperature of the absorbent SO _X higher than release temperature vital SO _X The air-fuel ratio of the exhaust gas flowing into the absorbent is allowed to be stoichiometric or rich. That is, in the second invention, when the NO _X amount discharged from the engine is small, the SO _X absorbent changes the SO _X
Can be released.

[0006] In order to solve the above-mentioned problems, a third method has been proposed.
According to the invention, the SO_XSO absorbed in the absorbent_Xamount
And this SO_XVolume is greater than a predetermined set volume
When the engine load is lower than the maximum allowable load
Is controlled by the temperature control means. _XThe temperature of the absorbent is SO_XRelease
Higher than the outlet temperature and SO_XOf exhaust gas flowing into the absorbent
Make the air-fuel ratio stoichiometric or rich and exhaust
Switch the switching valve to the position where it flows into the bypass passage
are doing. That is, in the third invention, SO_XFor absorbent
SO absorbed_XThe amount is larger than the set amount and the engine is
SO when the load is lower than the maximum allowable load_XS from absorbent
O_XIs released, at which time SO_XIs NO _XBypass absorbent
I'm sullen.

According to a fourth aspect, in the first or second aspect, the amount of SO _X flowing out of the SO _X absorbent in the exhaust passage between the SO _X absorbent and the NO _X absorbent is detected. the sO _X sensor arranged, and to switch the switching valve to a position where the exhaust flows into the bypass passage when sO _X amount detected by the sO _X sensor is larger than the allowable maximum sO _X amount. That is, in the fourth invention, SO
_{When the} amount of SO _X flowing out of the _X absorbent is larger than the maximum allowable SO _X amount, the SO _X bypasses the NO _X absorbent.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an engine body 1 has, for example, four cylinders. Each cylinder is connected to a surge tank 3 via a corresponding intake branch pipe 2, and the surge tank 3 is connected to an air cleaner 5 via an intake duct 4. A throttle valve 6 is arranged in the intake duct 4.
Each cylinder is provided with a fuel injection valve 7 for directly injecting fuel into the combustion chamber. On the other hand, each cylinder is connected via a common exhaust manifold 8 to a casing 10 containing a SO _X absorbent 9, and an outlet of the casing 10 is connected to an exhaust pipe 1.
1 and a casing 13 containing a NO _X absorbent 12
Linked to A bypass passage 14 branches from an inlet 13 a of the casing 13, and the bypass passage 14 is connected to an exhaust pipe 15 connected to an outlet of the casing 13. A switching valve 17 controlled by an actuator 16 is disposed at a branch of the bypass passage 14 from the inlet 13 a of the casing 13. The switching valve 17 and the bypass closed position to fully open the inlet portion of the inlet portion of the bypass passage 14 as shown by the solid line in FIG. 1 by the actuator 16 to the closed vital _the NO _X absorbent 12, shown in dashed lines in FIG. 1 The position is controlled to one of a bypass open position in which the inlet to the NO _X absorbent 12 is closed and the inlet of the bypass passage 14 is fully opened. In the present embodiment, during normal operation, the switching valve 17 is held at the bypass closed position.

The electronic control unit 20 is composed of a digital computer, and a ROM (read only memory) 22, a RAM (random access memory) 23, a CPU (microprocessor) 24, and a constant power supply connected to each other by a bidirectional bus 21. It has a supplied B-RAM (backup RAM) 25, an input port 26 and an output port 27. A pressure sensor 28 that generates an output voltage proportional to the absolute pressure in the surge tank 3 is attached to the surge tank 3, and an output voltage that is proportional to the temperature of exhaust flowing through the exhaust pipe 11 is generated in the exhaust pipe 11. A temperature sensor 29 and an SO _X sensor 30 that generates an output voltage proportional to the amount of SO _X in the exhaust gas flowing through the exhaust pipe 11 are attached. The absolute pressure in the surge tank 3 detected by the pressure sensor 28 indicates the engine load, and the temperature of the exhaust gas detected by the temperature sensor 29 indicates the temperature TCAT of the SO _X absorbent 9. These sensors 28, 29,
The output voltages of 30 are input to the input ports 26 via the corresponding AD converters 31. Also, input port 2
A rotation speed sensor 32 for generating an output pulse representing the engine rotation speed N is connected to 6. On the other hand, the output port 27 is connected to each fuel injection valve 7 and the actuator 16 via the corresponding drive circuit 33.

In this embodiment, the fuel injection time TAU (i) of the i-th cylinder is calculated based on the following equation. TAU (i) = TP · (1 + K (i)) Here, TP represents the basic fuel injection time, and K (i) represents the correction coefficient of the i-th cylinder.

The basic fuel injection time TP is a fuel injection time required to bring the air-fuel ratio of the air-fuel mixture burned in each cylinder to the stoichiometric air-fuel ratio, and is obtained in advance by an experiment.
The basic fuel injection time TP is stored in advance in the ROM 22 in the form of a map shown in FIG. 2 as a function of the absolute pressure PM in the surge tank 3 and the engine speed N. Correction coefficient K
(I) is a coefficient for controlling the air-fuel ratio of the air-fuel mixture burned in the i-th cylinder. If K (i) = 0, the air-fuel ratio of the air-fuel mixture burned in the i-th cylinder is the stoichiometric air-fuel ratio. Becomes On the other hand, if K (i) <0, the air-fuel ratio of the air-fuel mixture burned in the i-th cylinder becomes larger than the stoichiometric air-fuel ratio, that is, lean, and if K (i)> 0, the i-th cylinder The air-fuel ratio of the air-fuel mixture burned at the time becomes smaller than the stoichiometric air-fuel ratio, that is, becomes rich.

In the present embodiment, during normal operation, the correction coefficient K (i) is maintained at -KL (KL> 0) in all cylinders, so that the air-fuel ratio of the air-fuel mixture burned in all cylinders is lean. Has been maintained. FIG. 3 schematically shows the concentrations of representative components in the exhaust gas discharged from the cylinder. As can be seen from FIG. 3, the amount of unburned HC and CO in the exhaust gas discharged from the cylinder increases as the air-fuel ratio of the air-fuel mixture burned in the cylinder becomes rich, and the oxygen O in the exhaust gas discharged from the cylinder increases. The amount of ₂ increases as the air-fuel ratio of the mixture fueled in the cylinder becomes leaner.

[0013] _the NO _X absorbent 12, for example alumina as a carrier, with, for example, on the carrier K, sodium N
a, at least one selected from alkali metals such as lithium Li and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y, and platinum Pt and palladium P
d, a noble metal such as rhodium Rh and iridium Ir are supported. The ratio of the total air amount to the total fuel amount and the total reducing agent amount supplied into the exhaust passage, the combustion chamber, and the intake passage upstream of a certain position in the exhaust passage is determined by the air-fuel ratio of the exhaust flowing through the position. when called, NO when the air-fuel ratio of the _the NO _X absorbent 12 is inflowing exhaust is lean
_{When the} concentration of oxygen in the exhaust gas that flows in is reduced by absorbing _X , the absorption and release of NO _X that releases the absorbed NO _X is performed. In the case where the fuel or air to _the NO _X absorbent 12 upstream of the exhaust passage is not supplied air-fuel ratio of the inflowing exhaust matches the ratio of the total air amount to the total amount of fuel supplied to the cylinders.

If the above-mentioned NO _X absorbent 12 is arranged in the exhaust passage of the engine, the NO _X absorbent 12 actually acts to absorb and release NO _X , but the detailed mechanism of the absorption and release is not clear. There is also. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIGS. 4 (A) and 4 (B). 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.

That is, when the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases.
As shown in (A), these oxygens O ₂ adhere to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ . 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 into the absorbent while being further oxidized on the platinum Pt, 4 nitrate as shown in (A) ions NO ₃ ^- in It diffuses into the absorbent in form. Thus N
O _X is absorbed in the NO _X absorbent 12.

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 that flows in decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ions NO ₃ ⁻ 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 _the NO _X absorbent 12 when lowered. The oxygen concentration in the exhaust gas lean degree of the exhaust gas flowing to flow the lower the lowered, thus from _the NO _X absorbent 12 when lowering the lean degree of the exhaust gas flowing N
O _X is to be released.

Meanwhile, at this time _the NO _X absorbent a large amount of HC is an air-fuel ratio of the exhaust gas flowing into the 12 during the exhaust as shown in Figure 3 when the rich, CO and which are formed with H
C and CO react with oxygen O ₂ ^- or O ^2- on platinum Pt to be oxidized. Further, when the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas extremely decreases, so that NO ₂ is released from the absorbent, and this NO ₂ is released from the HC as shown in FIG. , CO and reduced. In this way, NO _{2 is} deposited on the surface of platinum Pt.
When NO is no longer present, NO ₂ is released from the absorbent one after another. Therefore NO _X from _the NO _X absorbent 12 in a short time when the air-fuel ratio of the exhaust gas flowing into the rich is to be released.

As described above, during normal operation, the air-fuel ratio of the air-fuel mixture burned in all cylinders is kept lean, and the switching valve 17 is maintained at the bypass closed position. Thus, NO _X in the exhaust gas discharged from the cylinders during normal operation is directed to _the NO _X absorbent 12 _the NO _X absorbent 12
Is absorbed by However, the the NO _X absorbing capacity of the NO _X absorbent 12 is necessary to release the NO _X from _the NO _X absorbent 12 before the NO _X absorbing capacity of the NO _X absorbent 12 is saturated because there is a limit. Therefore, in the present embodiment, the absorbed NO _X amount of the NO _X absorbent 12 is obtained, and when the absorbed NO _X amount becomes larger than a predetermined set amount, the air-fuel ratio of the air-fuel mixture burned in all cylinders is temporarily determined. so that the reduction with is to be released from _the NO _X absorbent 12 is made rich NO _X.

[0019] That is, NO _X absorbent 12 from all the cylinders when to emit NO _X correction coefficient K (i) is K
N (> 0). However, the exhaust gas flowing into _the NO _X absorbent 12 since in the lubricating oil of the fuel and the engine contains sulfur includes sulfur content for example SO _X, is the NO _X absorbent 12 NO Not only _X but also SO _X is absorbed. This NO _X absorbent 12
The mechanism of absorption of SO _X into is considered to be the same as the mechanism of absorption of NO _X.

That is, the platinum Pt and the barium Ba are deposited on the carrier in the same manner as described for the NO _x absorption mechanism.
When the air-fuel ratio of the inflowing exhaust gas is lean as described above, the oxygen O ₂
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 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 ions SO ₄ ^2- . 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 simply enrich the air-fuel ratio of the inflowing exhaust
Sulfate BaSO_FourRemains undisassembled. But
NO_XAs time passes, sulfuric acid is contained in the absorbent 12.
Acid salt BaSO_FourIncrease, and thus the time
NO as time goes by_XNO that can be absorbed by the absorbent 12 _X
The amount will be reduced.

[0022] Therefore, in this embodiment, SO _X is arranged SO _X absorbent 9 in the NO _X absorbent 12 upstream of the exhaust passage so as not to flow into _the NO _X absorbent 12. This SO _X
When the air-fuel ratio of the inflowing exhaust gas is lean, the absorbent 9
_X is absorbed, and when the temperature of the SO _X absorbent 9 is higher than the SO _X release temperature and the concentration of oxygen in the exhaust gas flowing in decreases, the absorbed SO _X is released.

As described above, the air-fuel ratio of the air-fuel mixture burned in all cylinders during normal operation is lean, so SO _X discharged from the cylinders is absorbed by the SO _X absorbent 9 and
_{The X} absorbent 12 absorbs only NO _X.
However there is a limit to SO _X absorbing capacity of the SO _X absorbent 9, S before SO _X absorbing capacity of the SO _X absorbent 9 becomes saturated
It is necessary to release SO _X from the O _X absorbent 9. Therefore, in the present embodiment, the absorbed SO _X amount of the SO _X absorbent 9 is determined, and when the absorbed SO _X amount exceeds a predetermined set amount, the temperature of the SO _X absorbent 9 is temporarily set to SO. _X
The air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 is temporarily made rich by making it higher than the release temperature, and the SO _X absorbent 9
And so as to release the SO _X from. Note that SO _X
The air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 when the absorbent 9 to emit SO _X may be the stoichiometric air-fuel ratio, but is released from the SO _X absorbent 9 per this unit time SO _X amount decreases.

By the way, SO_XExhaust flowing into absorbent 9
Contains a large amount of oxygen and a large amount of HC at the same time
And these oxygen and HC_XAnti-absorbent 9
SO with this heat of reaction to respond_XHeat absorbent 9
can do. In this case, SO_XFlows into absorbent 9
Air-fuel ratio is slightly richer than stoichiometric air-fuel ratio
If HC is SO_XHeating action of absorbent 9 and SO_X
It can be used effectively for the release action. on the other hand,
As shown in FIG. 3, the air-fuel mixture burned in the cylinder
If the air-fuel ratio is made rich, a large amount of HC is contained in the exhaust gas,
If lean, the exhaust will contain a large amount of oxygen. Therefore
In this embodiment, SO_XAbsorbent 9 to SO _XRelease
Combustion in cylinders # 1 and # 4 when should be
Enriching the air-fuel ratio of the air-fuel mixture
And the second cylinder # 2 and the third cylinder
Make the air-fuel ratio of the mixture burned in # 3 lean
Exhaust gas containing a large amount of oxygen is formed.
So that the air-fuel ratio of the combined exhaust is slightly rich
SO_XAbsorbent 9 is SO_XHeat to the release temperature, thereby
Ri SO_XAbsorbent 9 to SO_XTo release
You. In this way, the temperature of the exhaust gas discharged from the engine
Is low, SO_XAbsorbent 9 is SO_XHeat to release temperature
It is possible to do.

[0025] That Generally speaking, dividing the cylinder of the engine into a first cylinder group and second cylinder group, SO _X absorbent 9
The target air-fuel ratio of the mixed exhaust gas flowing into the cylinder is set slightly richer than the stoichiometric air-fuel ratio, and the target air-fuel ratio of the air-fuel mixture burned in the first cylinder group is set richer than the target air-fuel ratio of the mixed exhaust gas. The target air-fuel ratio of the air-fuel mixture burned in the second cylinder group is set to be lean with respect to the target air-fuel ratio of the mixed exhaust gas, and the air-fuel ratio of the air-fuel mixture burned in the first cylinder group and the second cylinder The target air-fuel ratio of the air-fuel mixture burned in the first cylinder group is such that the air-fuel ratio of the mixed exhaust gas becomes the target air-fuel ratio when the air-fuel ratio of the air-fuel mixture burned in the group is the corresponding target air-fuel ratio. This means that the target air-fuel ratio of the air-fuel mixture to be burned in the second cylinder group is set. Further, since the exhaust stroke order of the engine is # 1- # 3- # 4- # 2, in this embodiment,
The cylinders of the engine are divided into a first cylinder group and a second cylinder group in which the first cylinder group and the exhaust stroke do not overlap.

In this embodiment, the SO _X absorbent 9 is
_{When X} should be released, the correction coefficients K (1) and K (4) for the first and fourth cylinders are KS + a (KS, a>
0), and the correction coefficient K for the second and third cylinders
(2) and K (3) are set to -KS. Therefore, SO
The air-fuel ratio of the mixed exhaust gas flowing into the _X absorbent 9 is made rich by an amount corresponding to a small constant number a. Note that a =
If it is set to 0, the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 becomes the stoichiometric air-fuel ratio.

The SO _X absorbent 9 SO _X is sulfate ion SO ₄ the air-fuel ratio of the exhaust gas flowing from the SO _X absorbent 9 when the rich absorbed in order to SO _X is easily released to the It is necessary to be present in the absorbent in the form of ^2- , or even if the sulfate BaSO ₄ is produced, the sulfate BaSO ₄ is present in the absorbent in an unstable state. As the SO _X absorbent 9 which makes this possible, copper Cu, iron Fe, manganese M on a carrier made of alumina are used.
n, a transition metal such as nickel Ni, sodium Na,
An absorbent supporting at least one selected from titanium Ti and lithium Li can be used. Alternatively, relatively stable SO _X to be higher than _the NO _X absorbent 12 to alkalinity of the SO _X absorbent 9 in order to reliably absorbed SO _X into SO _X absorbent 9 in the SO _X absorbent 9 Some believe that it is better to keep in the form of sulfate. The SO _X absorbent which makes this possible is at least one selected from the group consisting of alkali metals such as potassium K, sodium Na, lithium Li and cesium Cs and alkaline earths such as calcium Ca on a carrier made of alumina. In addition, an absorbent carrying a noble metal such as platinum Pt, palladium Pd, rhodium Rh, and iridium Ir can be used.

SO_XAbsorbent 9 to SO_XShould release
Switch valve 17 is held in the bypass closed position when
And SO_XThe exhaust gas flowing out of the absorbent 9 is NO_XAbsorbent 12
Flows into. In this case, NO_XFlows into the absorbent 12
Since the air-fuel ratio of the exhaust gas is rich,_Xabsorption
SO released from agent 9_XIs NO_XAbsorbed by absorbent 12
NO without being_XIs considered to pass through the absorbent 12
You. However, for example, SO_XExhaust flowing into absorbent 9
Immediately after the air-fuel ratio is switched from lean to rich
O_XOxygen still remains on the surface of the absorbent 12 and NO
_XBecause the oxygen concentration has not decreased on the surface of the absorbent 12
SO_XSO released from absorbent 9_XIs NO_XAbsorbent 1
2 may be absorbed. Or in the exhaust that flows in
NO if contains oxygen_XExhaust flowing into the absorbent 12
NO even if the air-fuel ratio is rich _XSO in absorbent 12
_XThere is also the idea that is absorbed.

[0029] In this embodiment, SO when should emit SO _X from _X absorbent 9 switches the switching valve 17 to the bypass open position, thereby released from the SO _X absorbent 9 the SO _X is _the NO _X absorbent 12 so as not to flow. However, when the engine load is high, the switching valve 17
There a large amount of the NO _X is made to bypass the _the NO _X absorbent 12 is exhausted from the time the engine is switched to the bypass open position, reducing the large amount of the NO _X in _the NO _X absorbent 12 and thus, can not be purified.

Therefore, in the present embodiment, when the absolute pressure in the surge tank 3 representing the engine load is larger than a predetermined allowable maximum value, the switching valve 17 is maintained at the bypass closed position and flows into the SO _X absorbent 9. and making the air-fuel ratio of the exhaust gas rich, as sO _X both from sO _X absorbent 9 prohibits the that the temperature be higher than the sO _X release temperature of sO _X absorbent 9 is not released I have. Therefore, a large amount of the NO _X discharged from the engine is guided into _the NO _X absorbent 12, the reduction in _the NO _X absorbent 12 is purified.
Incidentally, SO _X fuel ratio of the exhaust gas flowing into the absorbent 9 and be rich and, SO _X the temperature of the absorbent 9 SO _X SO _X be prohibited at least one of the to be higher than release temperature It is possible to prevent SO _{X from} being released from the absorbent 9.

That is, in the present embodiment, the SO _X absorbent 9
When the absolute pressure in the surge tank 3 is larger than the allowable maximum value when the absorbed SO _X amount of the fuel cell exceeds the set amount, the switching valve 17 is held at the bypass closed position, and
The air-fuel ratio of the exhaust gas flowing into the _X absorbent 9 is kept lean, and the SO _X absorbent 9 is not heated. On the other hand, when the absorbed SO _X amount of the SO _X absorbent 9 becomes larger than the set amount and the absolute pressure in the surge tank 3 is smaller than the allowable maximum value, the switching valve 17 is switched to the bypass open position, At this time the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 is switched to rich, SO _X absorbent 9 is heated. The amount of NO _X discharged from the when the engine is small, therefore _the amount of NO _X to bypass the _the NO _X absorbent 12 is maintained small quantities.

[0032] In this way, SO _X release action of SO _X absorbent 9 when the absolute pressure in the surge tank 3 when absorbed SO _X amount becomes more than the set amount is smaller than the allowable maximum value takes place when to be is absorbed sO _X amount S of sO _X absorbent 9 when the absolute pressure in the surge tank 3 is greater than the allowable maximum value when it becomes more than a set amount
O _X release action necessarily may not be prohibited. Or,
Compared to the absolute pressure is frequently higher state than the allowable maximum value in the surge tank 3 when the amount absorbed SO _X becomes larger than the set amount, actually SO _X release action of SO _X absorbent 9 in this state May be reduced.

As described above, during normal operation, the switching valve 1
7 is maintained in the bypass closed position, and the air-fuel ratio of the air-fuel mixture burned in all cylinders is maintained lean. However, SO _X SO _X when the temperature is excessively high from the SO _X absorbent 9 of absorbent 9 air-fuel ratio of exhaust flowing into the even SO _X absorbent even lean 9 is released. Alternatively, if the temperature of the SO _X absorbent 9 is higher than the SO _X release temperature when the air-fuel ratio of the air-fuel mixture burned in all the cylinders to release NO _X from the NO _X absorbent 12 is higher than the SO _X release temperature, SO _X is released from the _X absorbent 9. Further, in the internal combustion engine so as to the air-fuel ratio of the mixture burned in all cylinders for example, at the time or during engine acceleration operation full load operation to rich, even not time to emit SO _X absorbent 9 SO _X SO _X can be released from the absorbent 9.
In this case, SO _X released from the switching valve 17 is held in the bypass closed position SO _X absorbent 9 is absorbed in the NO _X absorbent 12.

Therefore, in this embodiment, the SO_XAbsorbent 9
Outflow from SO_XSO to detect_XProviding a sensor 30,
SO during normal operation_XDetection S detected by sensor 30
O_XThe quantity is the maximum allowable SO_XSwitching valve 1 when larger than quantity
7 is switched to the bypass open position and SO_XReleased from absorbent 9
SO_XIs NO_XBypass the absorbent 12
I have. At this time, SO_XExhaust flowing into absorbent 9
Slightly rich air-fuel ratio and SO_XAbsorbent 9
To SO_XHeated to the release temperature, thereby producing SO _XAbsorbent
9 to SO_XIs to be released. as a result,
Exhaust is NO_XThe period during which the absorbent 12 can be bypassed is set to SO
_XIt can be used effectively for the release action.

Next, the present embodiment will be described in detail with reference to the time chart of FIG. At time a in FIG. 5, the absorbed SO _X amount SS of the SO _X absorbent 9 becomes larger than the set amount SS1. At this time, since the absolute pressure PM in the surge tank 3 is lower than the allowable maximum value PM1, the air-fuel ratio (A / F) I of the exhaust gas flowing into the SO _X absorbent 9 is switched from lean to rich, and the switching valve 17 is switched. The bypass close position is switched to the bypass open position. As a result, the SO _X absorbent 9 SO _X
Is released, and the SO _X amount DS detected by the SO _X sensor 30
Increase. As long as the absolute pressure PM is lower than the allowable maximum value PM1, the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 (A /
F) I is maintained rich, and the switching valve 17 is maintained at the bypass open position.

Next, at time b, the detected SO _X amount DS
When There is smaller than the smaller set value DS2, SO _X in absorbent 9 it is absorbed SO _X is judged to have been mostly discharged, the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 (A /
F) I is returned to lean, and the switching valve 17 is returned to the bypass closed position. As a result, the absorbed SO _X amount SS increases again.

On the other hand, even when the absorbed SO _X amount SS becomes larger than the set amount SS1 as in the time c, when the absolute pressure PM is higher than the allowable maximum value PM1, the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 ( (A / F) I is maintained lean, and the switching valve 17 is maintained at the bypass closed position. Next, when the absolute pressure PM becomes lower than the permissible maximum value PM1 at time d, the air-fuel ratio (A / F) I of the exhaust gas flowing into the SO _X absorbent 9 is switched to rich, and the switching valve 17 is set to the bypass open position. Is switched to Next, when the absolute pressure PM becomes higher than the allowable maximum value PM1 at time e, the detection S
Also O _X amount DS is larger than the set value DS2, SO _X fuel ratio of the exhaust gas flowing into the absorbent 9 (A / F) I is returned to lean, the switching valve 17 is returned to the bypass closed position.

On the other hand, when the air-fuel ratio (A / F) I of the exhaust gas flowing into the SO _X absorbent 9 is maintained lean as in the time f and the switching valve 17 is maintained at the bypass closed position, the detected SO _{When the X} amount DS becomes larger than the allowable maximum SO _X amount DS1, even if the absolute pressure PM is higher than the allowable maximum value PM1 or the absorbed SO _X amount SS is smaller than the set amount SS1, the SO _X absorbent The air-fuel ratio (A / F) I of the exhaust gas flowing into the fuel cell 9 is switched to rich, and the switching valve 17 is switched to the bypass open position. Next, when the detected SO _X amount DS becomes smaller than the set value DS2 at time g, SO
The air-fuel ratio (A / F) I of the exhaust gas flowing into the _X absorbent 9 is returned to lean, and the switching valve 17 is returned to the bypass closed position.

FIG. 6 and FIG._XFlags and switching
4 shows a routine for controlling a valve. This luch
Is interrupted by a predetermined set time DLT.
Executed. Referring to FIG. 6 and FIG.
In top 40, SO_XWhether the flag is set or not
Is determined. This SO_XThe flag is SO_XAbsorbent 9 to S
O_XIs set when it should be released, otherwise it is reset.
Set. SO_XWhen the flag is reset
Then proceeds to step 41, where SO_XAbsorbent 9 absorption
SO_XThe quantity SS is calculated. That is, the absorption SO_XThe quantity is
SO emitted from engine 1_XUnit time depends on quantity
SO discharged from the engine 1_XThe amount is in the surge tank 3
It increases as the absolute pressure PM increases, and the engine speed N
It increases as it gets higher. Therefore, the previous luch
Between the current routine and this routine_XAbsorbed by the absorbent 9
SO_XThe quantity is LS, PM, N, DLT with LS as a constant
It is represented by Therefore, LS / PM / N / DLT is integrated.
SO by absorption_XI try to estimate the amount
(SS = SS + LS.PM.N.DLT). The next step
In step 42, the absorption SO_XVolume SS is greater than set volume SS1
It is determined whether it is good or not. This set amount SS1 is, for example, S
O_XThe maximum SO that can be absorbed by the absorbent 9 _X30 percent of quantity
About. Next step when SS> SS1
Proceeding to 43, the absolute pressure PM in the surge tank 3 is the allowable maximum
It is determined whether the pressure is higher than PM1. PM> PM1
, That is, when SS> SS1 and PM> PM1
Then proceed to step 44, where SO_XFlag set
Is done. In the following step 45, the switching valve 17 is opened by bypass.
Switch to position. On the other hand, in step 42, S
When S ≦ SS1, or in step 43, PM ≦ PM1
Then, the routine proceeds to step 46, where the detected SO_XQuantity D
S is the maximum allowable SO_XIt is determined whether the amount is greater than DS1.
It is. When DS ≦ DS1, the processing cycle ends.
You. If DS> DS1, then go to step 47.
Steps 44 and 4 after setting the compulsory flag.
Go to 5. This compulsory flag indicates that the absolute pressure PM is equal to the allowable maximum value P.
SO when higher than M1_XAbsorbent 9 to SO_XRelease
Set when it should be and reset otherwise
You.

When the SO _X flag is set, the process proceeds from step 40 to step 48, where the S _X
Counter value CS which represents the time O _X release action is being carried out
Is incremented by one. In the following step 49, the SO _X amount RS released from the SO _X absorbent 9 per unit time is calculated from the map of FIG. FIG. 8 (A)
As shown in the figure, the SO _X amount RS released from the SO _X absorbent 9 per unit time is determined by the temperature TCA of the SO _X absorbent 9.
When T is lower than the SO _X release temperature TR, it is maintained at almost zero. On the other hand, when TCAT> TR, RS increases as TCAT increases, and decreases as the counter value CS increases. This RS is a function of the temperature TCAT of the SO _X absorbent 9 and the counter value CS as shown in FIG.
Are stored in the ROM 22 in advance in the form of a map shown in FIG.

In the following step 50, the absorbed SO _X amount of the SO _X absorbent 9 is calculated (SS = SS−RS · DLT).
In a succeeding step 51, it is determined whether or not the detected SO _X amount is smaller than the set value DS2. When DS ≧ DS2, the process then proceeds to step 52, where it is determined whether the compulsory flag is set. When the compulsory flag is set, the processing cycle ends. When the compulsory flag has not been set, the process then proceeds to step 53,
It is determined whether the absolute pressure PM is higher than the allowable maximum value PM1. When PM ≧ PM1, the processing cycle ends.

On the other hand, in step 51, DS <DS2
Or when PM <PM1 in step 53, the process proceeds to step 54, where the SO _X flag is reset. In the following step 55, the switching valve 17 is returned to the bypass closed position. In the following step 56, the counter value CS is cleared. In the following step 57, the compulsory flag is reset or held in a reset state.

FIG. 9 shows NO_XA route to control the flags
Shows Chin. This routine has a predetermined setting
It is executed by interruption every time DLT. See FIG.
First, at step 60, SO_XFlag set
It is determined whether or not it has been performed. SO_XFlag set
If so, the processing cycle is terminated and SO_XHula
If the flag is reset, then go to step 61
Proceed, NO_XIt is determined whether the flag is set.
It is. This NO_XFlag is NO _XNO from absorbent 12_X
Is set when it should be released, and reset otherwise.
Is NO_XWhen the flag is reset
Next, the routine proceeds to step 62, where NO_XAbsorption N of absorbent 12
O_XThe quantity SN is calculated. That is, absorption NO_XQuantity is machine
NO emitted from Seki 1_XDepends on quantity, per unit time
NO emitted from engine 1_XThe amount should be within the surge tank 3
The engine speed N increases as the counter pressure PM increases.
It increases as it gets older. Therefore, the previous routine
NO from this routine to this routine_XAbsorbed by the absorbent 12
NO_XThe quantity is LN ・ PM ・ N ・ DLT with LN as a constant
It is represented by Therefore, LS / PM / N / DLT is integrated.
NO_XI try to estimate the amount
(SN = SN + LN.PM.N.DLT).

In the following step 63, the absorbed NO _X amount SN
Is larger than the set amount SN1. This set amount SN1 is, for example, about 30% of the maximum NO _X amount that the NO _X absorbent 12 can absorb. SN ≦ SN1
If, the processing cycle ends, and if SN> SN1, the routine proceeds to step 64, where the NO _X flag is set.

When the NO _X flag is set, the routine proceeds from step 61 to step 65, where a counter value C representing the time during which the NO _X absorbent 12 is performing the NO _X releasing action is performed.
N is incremented by one. In the following step 66, it is determined whether or not the counter value CN is larger than the set value CN1. When CN ≦ CN1, the processing cycle ends. When CN> CN1 determines that NO _X that is absorbed in the NO _X absorbent 12 is almost discharged and then resets the NO _X flag proceeds to step 67. In the following step 68, the count value CN is cleared.

FIG. 10 shows the fuel injection time TAU of the i-th cylinder.
9 shows a routine for calculating (i). This routine is executed by interruption every predetermined crank angle. Referring to FIG. 10, first, in step 70, the parameter i is repeatedly set to 1, 2, 3, and 4. In the following step 71, the basic fuel injection time TP is calculated from the map of FIG. In the following step 72, SO
It is determined whether the _X flag is set. SO
_{When the X} flag has been reset, the routine proceeds to step 73, where it is determined whether the NO _X flag has been set. When the NO _X flag is reset,
That is, when both the SO _X flag and the NO _X flag are reset, the routine proceeds to step 73, where the correction coefficients K (i) of all the cylinders are set to −KL. Then step 7
Proceed to 8.

On the other hand, when the NO _X flag is set in step 73, the process proceeds to step 75, where the correction coefficients K (i) of all the cylinders are set to KN. Next, the routine proceeds to step 78. On the other hand, when the SO _X flag is set in step 72, the process then proceeds to step 76,
Correction coefficients K (1) and K (4) for the first and fourth cylinders
Are KS + a. In the following step 77, 2
The correction coefficients K (2) and K (3) for the cylinder No. 3 and the cylinder No. 3 are set to −KS. Next, the routine proceeds to step 78.

In step 78, the fuel injection time TAU (i) is calculated based on the following equation. TAU (i) = TP · (1 + K (i)) The embodiments described above show the case where the present invention is applied to a spark ignition type internal combustion engine. However, the present invention can be applied to a diesel engine. In this case, a reducing agent supply device is provided in the exhaust passage upstream of the SO _X absorbent 9, and the reducing agent is supplied from the reducing agent supply device into the exhaust passage, so that the SO _X absorbent 9 or the NO _X absorbent 12 The air-fuel ratio of the exhaust gas flowing into the fuel cell can be made rich. Alternatively, the air-fuel ratio of the exhaust gas discharged from the cylinder can be made rich by injecting the fuel from the fuel injection valve 7 secondary during the engine explosion stroke or the exhaust stroke.

In the embodiments described above, a single SO _X absorbent 9 is provided. However,
For example arranged one SO _X absorbent to the first cylinder and the second cylinder can also be provided a different SO _X absorbent to the third cylinder and the fourth cylinder. In this case, the air-fuel ratio of the air-fuel mixture burned in the first and third cylinders is made rich, the air-fuel ratio of the air-fuel mixture burned in the second and fourth cylinders is made lean, and the mixture flows into each SO _X absorbent. By slightly making the air-fuel ratio of the mixed exhaust gas slightly rich, SO _X can be released from each SO _X absorbent.

In the embodiments described above, N
O _X absorbent also air-fuel ratio of the exhaust gas flowing to the NO _X absorbent or SO _X absorbent to release the NO _X or SO _X from SO _X absorbent is set to be the stoichiometric air-fuel ratio or rich. However, if the oxygen concentration in the inflowing exhaust gas is low, the air-fuel ratio of the inflowing exhaust gas may be made lean. In this case, a reducing agent such as HC adheres to the surface of the NO _X absorbent or SO _X absorbent, are believed to form a locally reducing atmosphere.

[0051]

SO _X released from the SO _X absorbent according to the present invention is N
A large amount of NO _X can be prevented from being diverted around the NO _X absorbent, while preventing flow into the O _X absorbent.

[Brief description of the drawings]

FIG. 1 is an overall view of an internal combustion engine.

FIG. 2 is a diagram showing a map of a basic fuel injection time TP.

FIG. 3 is a diagram schematically showing the concentrations of unburned HC, CO, and oxygen in exhaust gas discharged from an engine.

FIG. 4 is a diagram for explaining a sphere releasing action of NO _X.

FIG. 5 is a time chart for explaining the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent and the switching operation of the switching valve.

FIG. 6 is a flowchart for controlling a SO _X flag and a switching valve.

FIG. 7 is a flowchart for controlling a SO _X flag and a switching valve.

FIG. 8: S released from the SO _X absorbent per unit time
It is a diagram showing a map of O _X amount RS.

FIG. 9 is a flowchart for controlling a NO _X flag.

FIG. 10 is a flowchart for calculating a fuel injection time TAU (i).

[Explanation of symbols]

1 ... engine body 8 ... exhaust manifold 9 ... SO _X absorbent 12 ... NO _X absorbent 14 ... bypass passage 17 ... switching valve

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) F01N 3/24 F01N 3/24 R F02D 41/04 385 F02D 41/04 385 F term (reference) 3G091 AA12 AA13 AA17 AA18 AA24 AB01 AB06 AB11 BA01 BA11 BA32 BA33 CA12 CA13 CA18 CB02 DA03 DB06 DB10 DB11 EA01 EA03 EA06 EA17 EA18 EA20 EA31 EA33 FB10 FB1 1 PD01Z PD11Z PE01Z

Claims (4)

[Claims] 1. A fuel ratio of the exhaust gas flowing absorbs NO _X flowing into the case of the lean, NO _X absorbent to the engine exhaust passage in which the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed to decrease And the SO _X absorbent is NO _X
Placed absorbent in the engine exhaust passage upstream of, SO _X absorbent air-fuel ratio of the exhaust gas flowing flows when the lean SO _X
It absorbs the temperature of SO _X absorbent releases SO _X in which the air-fuel ratio of the exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich flowing when higher than SO _X release temperature, SO _X absorbent and NO _X absorbent NO _X from the engine exhaust passage located between
Absorbent arranged switching valve for flowing the exhaust in one of _the NO _X absorbent or the bypass passage to the branch portion of the bypass passage with branches a bypass passage bypassing the, S
In the exhaust purification system of O _X when to emit SO _X from the absorbent internal combustion engine so as to switch the switching valve to a position where the exhaust flows into the bypass passage, comprising a temperature control means for controlling the temperature of the SO _X absorbent and, SO _X absorbent temperature control means by SO _X the temperature of the absorbent SO _X flows into the high vital SO _X absorbent than release temperature the stoichiometric air-fuel ratio of the exhaust or when to emit SO _X from Switching the switching valve to a position where the exhaust gas flows into the bypass passage, and when the engine load is higher than the allowable maximum load, the temperature of the SO _X absorbent is made higher than the SO _X release temperature by the temperature control means. , while prohibiting at least one of the making the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent the stoichiometric air-fuel ratio or rich, position the exhaust flows into _the NO _X absorbent An exhaust purification system of an internal combustion engine which is adapted to hold the switching valve in. 2. When the engine load is lower than the allowable maximum load, the temperature of the SO _X absorbent is made higher than the SO _X release temperature by the temperature control means, and the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent is set to the stoichiometric air-fuel ratio. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus is allowed to be rich. Wherein the air-fuel ratio of the exhaust gas flowing absorbs NO _X flowing into the case of the lean, NO _X absorbent to the engine exhaust passage in which the oxygen concentration in the inflowing exhaust gas to release NO _X absorbed to decrease And the SO _X absorbent is NO _X
Placed absorbent in the engine exhaust passage upstream of, SO _X absorbent air-fuel ratio of the exhaust gas flowing flows when the lean SO _X
It absorbs the temperature of SO _X absorbent releases SO _X in which the air-fuel ratio of the exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich flowing when higher than SO _X release temperature, SO _X absorbent and NO _X absorbent NO _X from the engine exhaust passage located between
Absorbent arranged switching valve for flowing the exhaust in one of _the NO _X absorbent or the bypass passage to the branch portion of the bypass passage with branches a bypass passage bypassing the, S
In the exhaust purification system of O _X when to emit SO _X from the absorbent internal combustion engine so as to switch the switching valve to a position where the exhaust flows into the bypass passage, comprising a temperature control means for controlling the temperature of the SO _X absorbent and, SO _X absorbent seek SO _X amount absorbed in the, SO by the temperature control means when the SO _X amount engine load when it becomes more than a set amount that is determined in advance is lower than the allowable maximum load The temperature of the _X absorbent is higher than the SO _X release temperature, the air-fuel ratio of the exhaust flowing into the SO _X absorbent is set to the stoichiometric air-fuel ratio or rich, and the switching valve is switched to a position where the exhaust flows into the bypass passage. An exhaust gas purification device for an internal combustion engine that releases SO _X from a SO _X absorbent. 4. Place the SO _X sensor for detecting the SO _X amount flowing out from the SO _X absorbent in the exhaust passage between the SO _X absorbent and _the NO _X absorbent, detected by the SO _X sensor sO _X amount allowable maximum sO _X amount exhaust purification system of an internal combustion engine according to claim 1 or 2 so as to switch the switching valve to a position where the exhaust flows into the bypass passage when more than.