JP3374759B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine.

[0002]

2. Description of the Related Art The ratio of the total amount of fuel and the total amount of air supplied to the exhaust passage, the combustion chamber, and the intake passage upstream of a certain position in the exhaust passage is passed through that position. when referred to as air-fuel ratio of the exhaust gas, conventionally, in an internal combustion engine which is adapted allowed to combust a lean air-fuel mixture, air-fuel ratio of the exhaust flowing absorbs NO _X when the lean,
N absorbed when the oxygen concentration in the inflowing exhaust gas becomes low
A NO _X absorbent that releases O _X is placed in the engine exhaust passage, and the air-fuel ratio of the exhaust gas that flows into the NO _X absorbent is temporarily made rich to release the NO _X that is absorbed from the NO _X absorbent. There is known an internal combustion engine which is configured to reduce the released NO _x .

However, since sulfur is contained in the fuel and the lubricating oil of the engine, sulfur is contained in the exhaust gas, for example, S.
O _X contains is absorbed with the SO _X at be for example SO ₄ ^2-form NO _X in _the NO _X absorbent. However, this SO _X is not released from the NO _X absorbent even if the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent is simply made rich, so that the amount of SO _X in the NO _X absorbent gradually increases. Become. However the amount of the NO _X amount of SO _X in _the NO _X absorbent can absorb is _the NO _X absorbent Increasing decreases gradually and finally _the NO _X absorbent can hardly be absorbed NO _X.

Therefore, a sulfur content absorbent that absorbs the sulfur content in the inflowing exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean and releases the absorbed sulfur content when the oxygen concentration in the inflowing exhaust gas becomes low. An exhaust gas purification device is known in which the exhaust gas is arranged in the exhaust passage upstream of the NO _x absorbent (Japanese Patent Laid-Open No. 6-17).
3652 gazette). Sulfur content in the exhaust gas in the exhaust purifying apparatus is absorbed in sulfur absorbent, only NO _X is absorbed in _the NO _X absorbent.

[0005]

SO _X absorbent SO _X
Since this exhaust gas purification device has a limited absorption capacity,
O _X fuel ratio of the exhaust gas flowing into the absorbent temporarily made rich so that to release SO _X being absorbed from the SO _X absorbent. Considered In this case, since the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent becomes rich at this time SO _X released from the SO _X absorbent passes through _the NO _X absorbent without being absorbed in _the NO _X absorbent To be However, for example, NO _X immediately after the air-fuel ratio of the exhaust gas flowing is rich in absorbent has still residual oxygen to the surface of the NO _X absorbent, since the oxygen concentration in _the NO _X absorbent surface does not decrease Another problem is that SO _X is absorbed in the NO _X absorbent.

[0006]

Means for Solving the Problems] According to the first invention to solve the above problems, the air-fuel ratio of the exhaust flowing absorbs NO _X when the lean, the oxygen concentration in the inflowing exhaust gas decreases then place the _the NO _X absorbent to release the NO _X that is absorbed in the engine exhaust passage, arranging the sulfur absorbent to temporarily absorb sulfur content in the exhaust passage of the _the NO _X absorbent upstream combustion in the exhaust purification system of the engine, NO _X absorption
If the temperature of the sorbent is out of the sulfur absorption temperature range, NO _x absorption will occur.
The sorbent is designed to absorb almost no sulfur.
Ri, the temperature of the NO _X absorbent is so as to release the sulfur from the sulfur content absorber when outside sulfur absorption temperature range of the NO _X absorbent. That is, according to the inventor of the present application,
NO _X absorbent has a sulfur absorption temperature range,
If the temperature of the O _X absorbent in sulfur absorption temperature range N
O _X absorbent has been confirmed that does not absorb the sulfur. Therefore, in the first invention, the temperature of the NO _X absorbent is N
And so as to release the sulfur from the sulfur content absorber when the O _X absorbent outside sulfur absorption temperature range.

Further, in the first aspect according to the second invention, the release of sulfur from sulfur absorbent when the temperature of the NO _X absorbent is lower than the sulfur absorption temperature range of the NO _X absorbent I am trying. According to the third invention, in the second invention, the sulfur content absorbent absorbs the sulfur content when the air-fuel ratio of the inflowing exhaust gas is lean, and the temperature of the sulfur content absorbent is higher than the sulfur content release temperature. is adapted to release the sulfur component concentration of oxygen in the exhaust gas flowing when higher is absorbed to be lower, sulfur absorption temperature range of the temperature of the sulfur absorbent and _the NO _X absorbent is _the NO _X absorbent At a lower steady state, the air-fuel ratio of the exhaust gas flowing into the sulfur content absorbent is temporarily made rich or stoichiometric, and the temperature of the sulfur content absorbent is temporarily made higher than the sulfur content release temperature. As a result, the sulfur content absorbed from the sulfur content absorbent is released. That is, in the third aspect, when the temperature of the sulfur content absorbent is increased to release the sulfur content from the sulfur content absorbent, the temperature of the NO _x absorbent is raised to the SO _x absorption temperature range within a short time. As a result, the sulfur content is sufficiently released from the sulfur content absorbent.

According to the fourth invention, in the third invention, the sulfur content is released from the sulfur content absorbent at the time of starting the engine. That is, when the engine is started, the temperatures of the sulfur content absorbent and the NO _x absorbent are in a steady state which is lower than the sulfur content absorption temperature range of the NO _x absorbent. Therefore, in the fourth invention, the sulfur content is released from the sulfur content absorbent when the engine is started.

According to the fifth invention, in the second invention, the temperature of the NO _x absorbent is kept lower than the sulfur content absorption temperature range while releasing the sulfur content from the sulfur content absorbent. I have to. That is, in the fifth aspect, the sulfur content released from the sulfur content absorbent is NO.
Absolutely prevented from being absorbed by _X absorbent. Also, 6
Th In the fifth invention according to the invention are arranged a large heat capacity material in the exhaust passage between the sulfur absorbent and _the NO _X absorbent. That is, there is a possibility that the temperature of the exhaust gas flowing out this time from the sulfur absorber is increased when increasing the temperature of the sulfur absorbent temperature of the NO _X absorbent is raised to the sulfur absorption temperature range. Therefore, in the sixth aspect, the temperature of the sulfur absorbent and NO _X in the exhaust passage between the absorber arrange a large heat capacity body _the NO _X absorbent is to be kept low.

Further, in the first aspect according to the seventh invention, the release of sulfur from sulfur absorbent when the temperature of the NO _X absorbent is higher than the sulfur absorption temperature range of the NO _X absorbent I am trying. According to the eighth aspect, in the seventh aspect, the temperature of the NO _x absorbent is kept higher than the sulfur content absorption temperature range while the sulfur content is being released from the sulfur content absorbent. . That is, in the eighth aspect, the sulfur content released from the sulfur content absorbent is reliably prevented from being absorbed by the NO _x absorbent.

According to a ninth aspect of the present invention, in the eighth aspect, the internal combustion engine includes a plurality of cylinders divided into a pair of cylinder groups, and the combined exhaust passage for joining the exhaust gases of the cylinder groups to each other. An NO _x absorbent is placed inside the exhaust gas, and when the sulfur content is being released from the sulfur content absorbent, the air-fuel ratio of the exhaust gas from one of the pair of cylinder groups is made rich to form exhaust gas containing hydrocarbons. At the same time, the air-fuel ratio of the exhaust gas of the other cylinder group is made lean to form an exhaust gas containing oxygen, and the hydrocarbons in the exhaust gas and oxygen are reacted to generate NO.
The temperature of the _X absorbent is kept higher than the sulfur absorption temperature range. That is, in the ninth aspect, the temperature of the NO _X absorbent is controlled by controlling the air-fuel ratio of the exhaust gas of each cylinder group.

According to the tenth invention, the ninth invention
In the light, sulfur content absorbent and NO _XExhaust communication between absorbents
Place an oxidation catalyst in the passage and
NO by reacting with oxygen_XAdjust the temperature of the absorbent
Try to keep above the absorption temperature range
It That is, NO_XAbsorbent NO_XIncrease absorption capacity
NO to do_XNeed to increase the alkalinity of the absorbent
But no_XNO when the alkalinity of the absorbent is increased_XAbsorbent
Has a reduced oxidation capacity, which results in good hydrocarbon and oxygen
I can not get a reaction. Therefore, in the tenth invention, NO
_XBy placing an oxidation catalyst in the exhaust passage upstream of the absorbent,
The element and oxygen are made to react well.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the following embodiments, the present invention is applied to a spark ignition engine. However, the invention can also be applied to diesel engines. Also,
Although the following embodiment describes the case where the sulfur content is SO _X , the present invention can also treat other sulfur content.

Referring to FIG. 1, the engine body 1 is, for example, 4
Equipped with two 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 that directly injects fuel into the cylinder. On the other hand, each cylinder is connected to the S through the exhaust manifold 8.
It is connected to a casing 10 containing an O _X absorbent 9, and the casing 10 is connected via an exhaust pipe 11 to a casing 13 containing an NO _X absorbent 12. SO _X absorbent 9
Is provided with an electric heater 14, which is connected to a power supply 16 via a switch 15 which is normally kept off. Each fuel injection valve 7 and the switch 15 are controlled based on the output signal from the electronic control unit 20. The exhaust stroke sequence of the internal combustion engine of FIG. 1 is # 1- # 3- # 4- # 2.

The electronic control unit 20 is composed of a digital computer, and has a ROM (Read Only Memory) 22, a RAM (Random Access Memory) 23, a CPU (Microprocessor) 24 and a constant power which are connected to each other by a bidirectional bus 21. It is provided with a supplied B-RAM (backup RAM) 25, an input port 26 and an output port 27. A water temperature sensor 28 for generating an output voltage proportional to the engine cooling water temperature is attached to the engine body 1, and a pressure sensor 29 for generating an output voltage proportional to the pressure in the surge tank 3 is attached to the surge tank 3 for exhaust gas. A temperature sensor 30 that generates an output voltage proportional to the temperature of the exhaust gas flowing into the NO _X absorbent 12 is attached to the pipe 11. The output voltages of these sensors 28, 29, 30 are input to the input port 26 via the corresponding AD converters 31, respectively. Further, the input port 26 is connected to a rotation speed sensor 32 that generates an output pulse representing the engine rotation speed. The CPU 24 calculates the intake air amount based on the output voltage of the pressure sensor 28. On the other hand, the output port 27 is connected to each fuel injection valve 7 and the switch 15 via the corresponding drive circuit 33.

In the internal combustion engine shown in FIG. 1, the fuel injection time TAU is calculated based on the following equation, for example. TAU = TP · (A / F) S / (A / F) T Here, TP is the basic fuel injection time, (A / F) T is the target air-fuel ratio, and (A / F) S is the theoretical air-fuel ratio ( = 14.6) respectively. The basic fuel injection time TP indicates the fuel injection time required to make the air-fuel ratio of the air-fuel mixture burned in the cylinder the stoichiometric air-fuel ratio. This basic fuel injection time TP is obtained in advance by experiments, and is stored in advance in the ROM 22 in the form of a map as shown in FIG. 2 as a function of the engine load Q / N (intake air amount Q / engine speed N) and the engine speed N. Remembered in.

On the other hand, the target air-fuel ratio (A / F) T is a target value of the air-fuel ratio of the air-fuel mixture burned in the cylinder. This target air-fuel ratio (A / F) T is usually lean, for example 22.0.
To be In the internal combustion engine of FIG. 1, the target air-fuel ratio (A /
F) T is the same for each cylinder, and therefore the fuel injection time TAU is also the same for each cylinder. The NO _X absorbent 12 contained in the casing 13 uses, for example, alumina as a carrier, and on this carrier, for example, potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, barium Ba, calcium Ca, or the like. At least one selected from alkaline earths, lanthanum La, rare earths such as yttrium Y, and platinum Pt,
A noble metal such as palladium Pd, rhodium Rh, or iridium Ir is supported. N air-fuel ratio of the _the NO _X absorbent 12 flows exhaust gas absorbs the NO _X when the lean, the oxygen concentration in the inflowing exhaust gas absorbed and reduced
The O _X performs the absorbing and releasing action of NO _X to be released. Note that NO
_When fuel or air is not supplied to the exhaust passage upstream of the _X absorbent 12, the air-fuel ratio of the exhaust flowing into the NO _X absorbent 12 is the sum of the amount of air to the total amount of fuel supplied to the combustion chamber of each cylinder. Match the ratio of.

If the above-mentioned NO _x absorbent 12 is arranged in the engine exhaust passage, this NO _x absorbent 12 actually performs the action of absorbing and releasing NO _x , but the detailed mechanism of this action of absorbing and releasing is not clear. There is also. However, it is considered that this absorbing / releasing action is performed by the mechanism shown in FIGS. 3 (A) and 3 (B). Next, regarding this mechanism, platinum Pt and barium Ba are formed on the carrier.
The explanation will be made taking as an example the case of supporting other precious metals,
The same mechanism can be obtained by using 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, and FIG.
As shown in (A), these oxygen O ₂ attaches to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ . On the other hand, NO in the inflowing exhaust gas 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, 3 nitric acid as shown in (A) ions NO ₃ ^- in Diffuses into the absorbent in the form. In this way 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. Oxygen concentration decreased with the amount of NO ₂ is lowered by reaction opposite direction in the exhaust gas flowing contrast (NO ₃ ^- → NO ₂₎ proceeds to, thus nitrate ions to the absorber NO ₃ ^- 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. If the lean degree of the inflowing exhaust gas is low, the oxygen concentration in the inflowing exhaust gas is low. Therefore, if the lean degree of the inflowing exhaust gas is low, the NO _x absorbent 12 to N is reduced.
O _X is to be released.

On the other hand, when the air-fuel ratio of the exhaust gas flowing in at this time is made rich, a large amount of unburned HC and CO are discharged from the engine, and these unburned HC and CO are oxygen O ₂ ⁻ or O ²⁻ on platinum Pt. It reacts with and is oxidized. Further, when the air-fuel ratio of the inflowing exhaust gas is made rich, NO ₂ is released from the absorbent because the oxygen concentration in the inflowing exhaust gas is extremely lowered, and this NO ₂ is not stored as shown in FIG. 3 (B). Burn H
It is reduced by reacting with C and CO. When NO ₂ is no longer present on the surface of platinum Pt in this way, NO ₂ is released one after another from the absorbent. Therefore, if the air-fuel ratio of the inflowing exhaust gas is made rich, NO _X will be reached in a short time.
NO _x will be released from the absorbent 12.

As described above, the target air-fuel ratio (A / F) T is
NO because it is usually lean_XExhaust flowing into the absorbent 12
The air-fuel ratio of the air is usually lean, so at this time
NO in the air_XIs NO_XIt is absorbed by the absorbent 12. By the way
But no_XAbsorbent 12 NO _XAbsorption capacity is limited
So no_XAbsorbent 12 NO_XBefore the absorption capacity is saturated
NO_XNO from absorbent 12_XNeed to be released.
Therefore, in the internal combustion engine shown in FIG._XAbsorbent 12 N
O_XIf the amount absorbed is greater than the preset amount
The target air-fuel ratio (A / F) T is temporarily rich, for example,
If 13.0 and NO_XExhaust air flowing into the absorbent 12
Temporarily enriches the fuel ratio, which results in NO_XAbsorbent 1
2 to NO_XI'm trying to release and reduce
It

However, the inflowing exhaust gas contains SO _X , and the NO _X absorbent 12 contains S as well as NO _X.
O _X is absorbed. It is considered that the mechanism of SO _X absorption into the NO _X absorbent 12 is the same as the mechanism of NO _X absorption. That is, platinum Pt and barium B are deposited on the carrier as in the case of explaining the NO _x absorption mechanism.
Taking the case of supporting a as an example, as described above, when the air-fuel ratio of the inflowing exhaust gas is lean, oxygen O
₂ is attached to the surface of platinum Pt in the form of O ₂ ⁻ or O ²⁻ , SO _x in the inflowing exhaust gas, for example SO ₂ is platinum Pt.
Reacts with O ₂ ⁻ or O ^{2 −} to form SO ₃ . Next, the produced SO ₃ is further oxidized on platinum Pt, absorbed in the absorbent and combined with barium oxide BaO, and diffused in the absorbent in the form of sulfate ion SO ₄ ²⁻ . Next, this sulfate ion SO ₄ ²⁻ combines with the barium ion Ba ²⁺ to form the sulfate salt BaSO ₄ .

However, this sulfate BaSO_FourIs decomposed
Slightly, even if the air-fuel ratio of the inflowing exhaust gas is simply made rich
Sulfate BaSO_FourRemains undecomposed. But
No_XSulfur is absorbed in the absorbent 12 as time passes.
BaSO salt_FourWill increase and thus the time
NO as time passes_XNO that can be absorbed by the absorbent 12 _X
The amount will decrease.

Therefore, in this embodiment, the NO _x absorbent 12 is used.
Are arranged SO _X absorbent 9 in the NO _X absorbent 12 upstream of the exhaust passage so as SO _X does not flow into. This SO _X
The absorbent 9 is SO when the air-fuel ratio of the inflowing exhaust gas is lean.
_X is absorbed, and when the temperature of the SO _X absorbent 9 is higher than the SO _X release temperature and the oxygen concentration in the inflowing exhaust gas decreases, the absorbed SO _X is released.

As described above, the air-fuel ratio of the exhaust gas discharged from the engine body 1 is usually lean, so the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 is usually lean. Therefore, the SO _X discharged from the engine body 1 is the SO _X absorbent 9
Thus, the NO _X absorbent 12 absorbs only NO _X. However there is a limit to SO _X absorbing capacity of the SO _X absorbent 9, it is necessary to release the SO _X from the SO _X absorbent 9 before SO _X absorbing capacity of the SO _X absorbent 9 becomes saturated. In this embodiment, SO _X absorbent 9 temporarily the temperature of the SO _X absorbent 9 when the SO _X amount that is absorbed becomes larger than setting a predetermined amount of the SO
Target air-fuel ratio (A / F) as well as higher than _X emission temperature
Temporarily rich and T, to temporarily rich air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 in the example 10.0, thereby so that to release SO _X from SO _X absorbent 9. It is also the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 when the SO _X absorbent 9 to emit SO _X in the stoichiometric air-fuel ratio but, from the SO _X absorbent 9 per this unit time The amount of SO _X released is small.

[0027] SO Since _X fuel ratio of the exhaust gas air-fuel ratio of the exhaust gas flowing into the absorbent 9 flows into _the NO _X absorbent 12 becomes rich becomes rich, SO _X at this time is released from the SO _X absorbent 9 is believed to pass through _the NO _X absorbent 12 without being absorbed in the NO _X absorbent 12. However, for example, immediately after the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 9 is switched from lean to rich, oxygen still remains on the surface of the NO _X absorbent 12, and the NO _X absorbent 1
The second surface SO _X released from the SO _X absorbent 9 for the oxygen concentration does not drop is absorbed in the NO _X absorbent 12. Alternatively, there is also the idea that the oxygen is contained in the exhaust air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 12 is SO _X into _the NO _X absorbent 12 even rich is absorbed to flow.

On the other hand, according to the inventor of the present application, when the temperature of the NO _x absorbent 12 is a certain temperature, the NO _x absorbent 12 is
It has been confirmed that does not absorb SO _X regardless of residual oxygen in the NO _X absorbent 12 or oxygen in the exhaust gas. FIG. 4 shows NO when the air-fuel ratio of the inflowing exhaust gas is rich.
₈ is an experimental result showing the relationship between the exhaust gas temperature TEX flowing into the _X absorbent 12 and the SO _X absorption rate RAS of the NO _X absorbent 12. This exhaust gas temperature TEX represents the temperature of the NO _X absorbent 12. As shown in FIG. 4, the NO _x absorbent 12
SO _x becomes NO _x absorbent 12 when the temperature is very low.
Not absorbed by. This is SO in the NO _x absorbent 12.
It is considered that this is because the oxidation reaction of _X hardly occurred. Next, when the temperature of the NO _x absorbent 12 rises, S
O _X absorptivity RAS is increased gradually. It is considered that this is because the SO _X oxidation reaction in the NO _X absorbent 12 becomes more active as the temperature of the NO _X absorbent 12 becomes higher, and the production of sulfate becomes more active. Further NO _X when the temperature of the absorbent 12 becomes high SO _X absorbing ratio RAS is lowered gradually. It is resolved as released from _the NO _X absorbent 12 is decomposed partially rapidly the once absorbed SO _X into _the NO _X absorbent 12 in the form of sulfate, the temperature of the NO _X absorbent 12 is higher It is considered that this is because the ratio of the sulfates to be increased. Further, when the temperature of the NO _x absorbent 12 rises, the SO _x is hardly absorbed by the NO _x absorbent 12. This is because the SO _X once absorbed by the NO _X absorbent 12 in the form of sulfate is decomposed very rapidly and the NO _X absorbent 1
It is considered that this is because it is released from 2.

As shown in FIG. 4, the SO _X absorption rate RAS
NO _X but the temperature range of greater _the NO _X absorbent 12 than zero
When referred to as the SO _X absorption temperature range of the absorbent 12, when the temperature of the NO _X absorbent 12 is within the SO _X absorption temperature range, even if the air-fuel ratio of the inflowing exhaust gas is rich, the NO _X absorbent 12 is SO Absorbs _X and the temperature of the NO _X absorbent 12 becomes SO
_X absorption temperature range and long regardless of residual oxygen or oxygen in the inflowing exhaust gas of the NO _X absorbent in 12 _the NO _X absorbent 12
Will not absorb SO _X.

That is, the temperature of the NO _x absorbent 12 is SO
When outside _X absorption temperature range to release the SO _X from the SO _X absorbent 9, or the temperature of the NO _X absorbent 12 is a SO _X release action from SO _X absorbent 9 when the SO _X absorption temperature range If prohibited, it is possible to prevent the SO _{X from} being absorbed by the NO _X absorbent 12. This is the basic idea of the present invention.

On the other hand, since the target air-fuel ratio (A / F) T is made rich when to emit NO _X that is absorbed from _the NO _X absorbent 12 as described above flows into the SO _X absorbent 9 exhaust The air-fuel ratio of is also made rich. However, at this time, the temperature of the NO _X absorbent 12 may be within the SO _X absorption temperature range, and at this time, the SO _X absorbent 9 to SO
_{When X} is released, this SO _X may be absorbed by the NO _X absorbent 12. Accordingly SO _X of SO _X absorbent 9
The release temperature during normal operation to be higher than the temperature range of SO _X absorbent 9 can take needs to SO _X from being released from the SO _X absorbent 9 during normal operation. In other words, by increasing the alkalinity of the SO _X absorbent 9 SO _X
Needs to be retained in the SO _x absorbent 9 in the form of a stable sulfate salt. As the SO _X absorbent that enables this, at least one selected from, for example, potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, and an alkaline earth such as calcium Ca on a carrier made of alumina. Tsuto, platinum Pt, palladium P
An absorbent carrying a noble metal such as d, rhodium Rh, or iridium Ir can be used.

The SO _X absorbing / releasing mechanism of the SO _X absorbent 9 is considered to be the same as the SO _X absorbing / releasing mechanism of the NO _X absorbent 12 as understood from the components of the SO _X absorbent 9. That is, platinum Pt and calcium Ca on the carrier
When the air-fuel ratio of the inflowing exhaust gas is lean, the SO _x in the inflowing exhaust gas will be explained.
For example, SO ₂ reacts with O ₂ ⁻ or O ^{2 − on} the surface of platinum Pt to become SO ₃ . Next, the generated SO ₃ is platinum P
While being further oxidized on t, it is absorbed in the absorbent and bound to calcium oxide CaO, and diffuses in the absorbent in the form of sulfate ion SO ₄ ²⁻ . Then this sulfate ion SO ₄ ^2-
Binds to calcium ions Ca ²⁺ and forms sulfate CaSO ₄
To generate. On the other hand, when the temperature of the SO _X absorbent 9 is SO
When the oxygen concentration in the inflowing exhaust gas decreases when the temperature is higher than the _X release temperature, the sulfate decomposes (CaSO ₄ → Ca ²⁺ + S
O ₄ ²⁻ ), and thus the sulfate ion SO ₄ ²⁻ in the absorbent is S
It is released from the absorbent in the form of O ₂ .

In the present embodiment, when the temperature of the NO _X absorbent 12 is lower than the SO _X absorption temperature range, the SO _X absorbent 9 is
To release SO _X from. That is, first, the temperature of the NO _X absorbent 12 is whether lower than SO _X absorption temperature range is determined when the SO _X absorbent 9 to emit SO _X. Temperature TEX of the exhaust gas flowing to the NO _X absorbent 12 as described above represents the temperature of the NO _X absorbent 12. Therefore, in the present embodiment, the exhaust temperature T
EX is so as to release the SO _X from the SO _X absorbent 9 when lower than the set temperature T1. The set temperature T1 is set to a temperature lower than the SO _X absorption temperature range of the NO _X absorbent 12, for example, 300 ° C.

[0034] Incidentally, even as the temperature of the NO _X absorbent 12 is cooled _the NO _X absorbent 12 to be lower than the SO _X absorption temperature range when the SO _X absorbent 9 to emit SO _X Good, but a cooling device is needed. On the other hand, in this embodiment, the temperature of the NO _X absorbent 12 is SO _X.
SO _X absorbent 9 to SO when the temperature is lower than the absorption temperature range
_{Since X} is emitted, no cooling device is required.

NO_XThe temperature of the absorbent 12 is SO_XAbsorption temperature
If it is determined that the value is lower than the range, then switch 1
5 is turned on and the electric heater 14 is turned on.
SO_XThe absorbent 9 is heated. As mentioned above
SO_XAbsorbent 9 SO_XThe discharge temperature during normal operation
SO_XIt is set higher than the temperature of the absorbent 9. did
So, at this time SO_XAir-fuel of exhaust flowing into the absorbent 9
Even if the ratio is rich, SO_XAbsorbent 9 to SO_XIs released
The fuel consumption rate will deteriorate. On the other hand, SO_XOf absorbent 9
After a certain period of time has passed since heating was started, SO_XSucking
The temperature of the sorbent 9 is SO_XJudged to be higher than the release temperature
can do. Therefore, in this embodiment, the SO_Xabsorption
When the heating of the agent 9 is started, the target air-fuel ratio (A / F)
Instead of immediately making T rich, SO_XOf absorbent 9
Target air-fuel ratio after a certain period of time has passed since heating was started
(A / F) T is made rich. In addition, S
O _XA certain time has passed since the heating of the absorbent 9 was started.
Later SO_XThe temperature of the absorbent 9 is, for example, 900 to 100
It is maintained at about 0 ° C.

When the SO _X absorbent 9 is heated in this way, the temperature of the exhaust gas flowing out from the SO _X absorbent 9 gradually rises, and as a result, the temperature T of the exhaust gas flowing into the NO _X absorbent 12 is increased.
EX may be higher than the set temperature T1. When the exhaust temperature TEX becomes higher than the set temperature T1, the temperature of the NO _x absorbent 12 falls within the SO _x absorption temperature range and the NO _x absorbent 12 may absorb the SO _x . Therefore, in this embodiment, so as to stop the SO _X release action from SO _X absorbent 9 when the exhaust gas temperature TEX is higher than the set temperature T1 when it is to release the SO _X from the SO _X absorbent 9 ing.

FIG. 5 shows the SO _X release control routine in this embodiment. This routine is executed by interruption every predetermined set time. Referring to FIG. 5, first, in step 50, the SO _X absorbent 9 to SO
It is determined whether or not the SO _X flag is set, which is set when _X is to be released and is reset otherwise. When the SO _X flag is reset, the routine proceeds to step 51, where the SO _X amount SS absorbed by the SO _X absorbent 9 is, for example, the engine operating state and the time during which the SO _X absorbent 9 releases SO _X. It is estimated based on and. In the following step 52, it is judged if the absorbed SO _X amount SS is larger than the set amount SS1. This set amount S
S1 is, for example, about 30% of the maximum amount of SO _X that the SO _X absorbent 9 can absorb. When SS ≦ SS1, the processing cycle is ended. On the other hand, when SS> SS1, the routine proceeds to step 53, where it is determined whether the temperature TEX of the exhaust gas flowing into the NO _X absorbent 12 is lower than the set temperature T1, that is, the temperature of the NO _X absorbent 12 is SO _X absorption. It is determined whether the temperature is lower than the temperature range. When TEX ≧ T1, that is, when the temperature of the NO _X absorbent 12 is within the SO _X absorption temperature range, the processing cycle is ended. On the other hand, TE
When X <T1, that is, the temperature of the NO _x absorbent 12 is S
If it is lower than the O _x absorption temperature range, then step 5
4, the switch 15 is turned on and the electric heater 14 is turned on.
There are turned on, thereby heating the SO _X absorbent 9 is started. In the following step 55, it is determined whether or not a certain time has passed since the switch 15 was turned on, that is, whether or not the temperature of the SO _X absorbent 9 has risen to the SO _X release temperature. When a certain time has not passed since the switch 15 was turned on, that is, the temperature of the SO _X absorbent 9 is S
When it is lower than the O _X release temperature, the processing cycle is ended. On the other hand, when a certain time has passed since the switch 15 was turned on, that is, the temperature of the SO _X absorbent 9 is S
When the temperature reaches the O _X release temperature, then step 56
And the SO _X flag is set. As will be described later, when the SO _X flag is set, the target air-fuel ratio (A / F) T
Are enriched and therefore SO _X absorbent 9 to SO _X
Is released.

The SO _X flag proceeds from step 50 when it is set in step 57, whether the SO _X flag has elapsed a predetermined time from setting, i.e. SO _X
It is determined whether or not the SO _X releasing action of the absorbent 9 is completed. When SO _X flag is not predetermined time has elapsed since the set, i.e., the routine goes to step 58 when the SO _X release action of SO _X absorbent 9 is not completed,
It is determined whether the temperature TEX of the exhaust gas flowing into the NO _X absorbent 12 is higher than the set temperature T1. When TEX ≦ T1, the processing cycle is ended. In contrast,
When a certain time has elapsed after the SO _X flag was set in step 57, that is, the SO _{X of the} SO _X absorbent 9
_{When the X-} releasing action is completed, and when TEX> T1 in step 58, then proceed to step 59,
The switch 15 is turned off. In the following step 60, S
O _X flag is reset. In the following step 61,
It is set when the _the NO _X absorbent 12 to be released the NO _X, otherwise NO _X flag is reset is reset. When the target air-fuel ratio (A / F) T is made rich in order to release SO _X from the SO _X absorbent 9, NO _X
Air-fuel ratio of the exhaust gas flowing into the absorbent 12 becomes rich, this time _the NO _X absorbent 12 from the NO _X is reduced is released. The time required to complete the NO _X release action of _the NO _X absorbent 12 is considerably shorter, thus _the NO _X absorbent when the SO _X release action of SO _X absorbent 9 is performed 1
The NO _x releasing action of 2 is completed. Therefore, when the SO _X releasing action of the SO _X absorbent 9 is performed, step 61
Then, the NO _x flag is reset or the reset state is maintained.

When the air-fuel ratio of the inflowing exhaust gas is lean, the SO _X absorbent 9 absorbs NO _X together with SO _X.
The absorbed NO _X is released from SO _X absorbent 9 with SO _X when SO _X release action of SO _X absorbent 9 is reduced. FIG. 6 shows a NO _X release control routine in this embodiment. This routine is executed by interruption every predetermined set time. Referring to FIG. 6, first, at step 70, it is judged if the NO _X flag is set or not. NO _X flag routine goes to step 71 when it is reset, NO _X absorbent and _the amount of NO _X SN, for example, the engine operating state that is absorbed in 12, NO _X time absorbent 12 from NO _X is released It is estimated based on and. In the following step 72, it is judged if the absorbed NO _X amount SN is larger than the set amount SN1. This set amount SN1 is, for example, the NO _X absorbent 12
Is about 30% of the maximum amount of NO _x that can be absorbed by. SN ≦ S
When it is N1, the processing cycle is ended. In contrast,
If SN> SN1, then proceed to step 73, where N
O _X flag is set. NO _X flag when is set the target air-fuel ratio (A / F) T as described below is made rich, therefore _the NO _X absorbent 12 from the NO _X is reduced is released.

The NO _X flag proceeds to step 74 from step 70 when it is set, NO _X flag whether a predetermined time has passed since a time is set, i.e. NO _X
It is determined whether or not the NO _x releasing action of the absorbent 12 is completed. When NO _X flag is not predetermined time has elapsed since the set, i.e., the processing cycle is ended when NO _X release action of _the NO _X absorbent 12 is not completed. In contrast, NO when _{the X} flag predetermined time has elapsed since the set, i.e. NO _X absorbent 12 NO _X
When the releasing action is completed, the routine proceeds to step 75, where the NO _X flag is reset.

FIG. 7 shows the fuel injection time T in this embodiment.
The calculation routine of AU is shown. This routine is executed by interruption for each preset crank angle. Referring to FIG. 7, first, at step 80, the basic fuel injection time TP is calculated from the map of FIG. In the following step 81, it is judged if the SO _X flag is set. If the SO _X flag is set, then the routine proceeds to step 82, where the target air-fuel ratio (A / F) T
Is set to 10.0. Then, it proceeds to step 86.
On the other hand, when the SO _X flag is reset, then the routine proceeds to step 83, where it is judged if the NO _X flag is set or not. When the NO _X flag is set, then the routine proceeds to step 84, where the target air-fuel ratio (A / F) T is set to 13.0. Then, it proceeds to step 86. On the other hand, when the NO _X flag is reset, the routine proceeds to step 85, where the target air-fuel ratio (A / F) T is set to 22.0. Then, it proceeds to step 86.

In step 86, the fuel injection time TAU is calculated based on the following equation. TAU = TP · (A / F) S / (A / F) T From each fuel injection valve 7, fuel injection is performed by TAU.
Next, another embodiment will be described. In this embodiment, the fuel injection time TAU is calculated by the following two methods. That is, the engine speed N is a predetermined set speed N1, for example, 400 r. p. Immediately after the engine starts lower than m, the starting fuel injection time TPS is calculated based on the engine cooling water temperature THW, and this TPS is the fuel injection time TAU.
It is said that This starting fuel injection time TPS is the fuel injection time necessary for promptly starting the engine, and FIG.
As shown in (3), it increases as the engine cooling water temperature decreases. The starting fuel injection time TPS is previously obtained by an experiment and is stored in advance in the ROM 22 in the form of the map shown in FIG.

On the other hand, the engine speed N is the set speed N
When it becomes higher than 1, the fuel injection time TAU is calculated based on the following equation. TAU = TP * KW * (A / F) S / (A / F) T Here, KW represents the warm-up increase correction coefficient. This warm-up increase correction coefficient KW is for stabilizing the combustion during engine warm-up operation, and as shown in FIG.
When the HW reaches the threshold temperature T2, for example 60 ° C. or higher, 1.
It is maintained at 0. The warm-up increase correction coefficient KW has been previously obtained through experiments, and is stored in advance in the ROM in the form of the map shown in FIG.
It is stored in 22.

When the fuel injection time TAU is set to the starting fuel injection time TPS, the air-fuel ratio of the air-fuel mixture burned in the cylinder at this time becomes rich. On the other hand, when the engine cooling water temperature THW is lower than the threshold temperature T2, the target air-fuel ratio (A / F) T is maintained at the stoichiometric air-fuel ratio (A / F) S.
At this time, since the warm-up increase correction coefficient KW is larger than 1.0, the air-fuel ratio of the air-fuel mixture burned in the cylinder at this time also becomes rich. Therefore, the air-fuel ratio of the air-fuel mixture burned in the cylinder is kept rich at the time of starting the engine from when the engine starting is started until the engine cooling water temperature THW becomes equal to or higher than the threshold temperature T2.

[0045] Incidentally, similarly to the above embodiment in this embodiment, are the SO _X absorbent 9 when the temperature of the NO _X absorbent 12 is lower than the SO _X absorption temperature range so as to release the SO _X . In the above-described embodiment, when the temperature of the NO _X absorbent 12 is lower than the SO _X absorption temperature range, SO 2
From _X absorbent 9 SO _X is released, the temperature of the NO _X absorbent 12 is SO _X release action of SO _X absorbent 9 becomes in the SO _X absorption temperature range is stopped. However, NO _X absorbent 1
Since the second temperature may vary NO _X temperature of the absorbent 12 even for a short time to start the SO _X release action of SO _X absorbent 9 that is lower than the temporarily SO _X absorption temperature range temperature of the nO _X absorbent 12 of which is may be enhanced up to sO _X absorption temperature range, it is impossible to release this case sO _X sufficiently sO _X from the absorbent 9. Also, N
Since O _X absorbent 12 temperature temperature of the exhaust gas discharged from the SO _X absorbent 9 becomes high when the temperature of the SO _X absorbent 9 be lower than SO _X absorption temperature range is high, this case NO There is a possibility that the temperature of the _X absorbent 12 may be raised to within the SO _X absorption temperature range within a short time.

Meanwhile, when the temperature of the NO _X absorbent 12 is at a low steady-state than SO _X absorption temperature range, even if the SO _X release action from SO _X absorbent 9 this time NO
The temperature of the _X absorbent 12 is not raised to the SO _X absorption temperature range within a short time. Moreover, until the SO _X absorption temperature range while the temperature of _the NO _X absorbent 12 in a short time even when the temperature of the SO _X absorbent 9 is at a low steady-state than SO _X absorption temperature range of the NO _X absorbent 12 It cannot be raised. Therefore, in this embodiment, the SO _X absorbent 9 and N
The temperature of the O _x absorbent 12 is the same as the SO _{x of} the NO _x absorbent 12.
SO _X when in a steady state below the _X absorption temperature range
SO _X is released from the absorbent 9. As a result, it becomes possible to sufficiently release SO _X from the SO _X absorbent 9.

By the way, when the engine is started, the SO _X absorbent 9
And NO temperature _X absorbent 12 are both, NO _X absorbent 1
It is in a steady state lower than the SO _x absorption temperature range of No. 2. Further, as described above, when the engine is started, the air-fuel ratio of the air-fuel mixture burned in the cylinder is made rich, so that the SO _X
The air-fuel ratio of the exhaust gas flowing into the absorbent 9 is rich. Therefore, in the present embodiment, when the engine is started, the electric heater 1
4 is turned on to heat the SO _X absorbent 9, which causes S
SO _X is released from the O _X absorbent 9.
Thus, in the present embodiment, the SO _X absorbent 9 to the SO _X
Does not require special control of the target air-fuel ratio (A / F) T for releasing.

FIG. 10 shows the SO _X release control routine in this embodiment. This routine is executed by interruption every predetermined set time. Referring to FIG. 10, first, at step 90, the engine cooling water temperature THW
It is determined whether the temperature is lower than the threshold temperature T2, that is, whether the engine is currently being started. When THW <T2, that is, when the engine is currently started, the routine proceeds to step 91, where the SO _X absorbed by the SO _X absorbent 9 is absorbed.
_It is determined whether the _X amount SS is larger than the set amount SS1. When the SS> SS1, the routine goes to step 92, the electric heater 14 switch 15 is turned on is turned on, thereby heating the SO _X absorbent 9 is started. Step 93 In the switch 15 continues whether predetermined time has elapsed since the ON, that is, whether SO _X release action of SO _X absorbent 9 has been completed or not. When the switch 15 is not a predetermined time has elapsed since the ON, i.e., the routine goes to step 94 when the SO _X release action of SO _X absorbent 9 is not completed, NO _X
The temperature TEX of the exhaust gas flowing into the absorbent 12 is the set temperature T1.
Is higher than the above. When TEX ≦ T1, the processing cycle is ended.

On the other hand, in step 91 SS ≦
When SS1, the switch 15 is turned off in step 93.
When a certain period of time has passed since the_X
Absorbent 9 SO_XWhen the release action is complete, and
When TEX> T1 at step 94, the next step
Proceeding to step 95, the switch 15 is turned off. On the other hand,
When THW ≧ T2 at step 90, the next step
Prop 96, SO _XSO absorbed by absorbent 9
_XAfter estimating the quantity SS, proceed to step 95.

11 and 12 show a routine for calculating the fuel injection time TAU in this embodiment. This routine is executed by interruption for each preset crank angle. In this embodiment as well, the NO _X release control routine shown in FIG. 6 is executed. Referring to FIGS. 11 and 12, first, at step 100, it is judged if the engine speed N is lower than the set speed N1. When N <N1, the process proceeds to step 101,
The starting fuel injection time TPS is calculated from the map of FIG. In the following step 102, this TPS is set as the fuel injection time TAU.

On the other hand, in step 100, N ≧ N
When it is 1, then the routine proceeds to step 103, where the basic fuel injection time TP is calculated from the map of FIG. In the following step 104, the warm-up increase correction coefficient KW is calculated from the map of FIG. In the following step 105, the engine cooling water temperature TH
It is determined whether W is lower than the threshold temperature T2, that is, whether the engine is currently being started. When THW <T2, that is, when the engine is currently started, the routine proceeds to step 106, where the target air-fuel ratio (A / F) T is set to the theoretical air-fuel ratio (A / F) S. Then, it proceeds to step 110. On the other hand, when THW ≧ T2, that is, when the engine is not currently started, the routine proceeds to step 107,
It is determined whether the NO _X flag is set.
If the NO _X flag is set, then the routine proceeds to step 108, where the target air-fuel ratio (A / F) T is set to 13.0. Then, it proceeds to step 110. On the contrary, when the NO _X flag is reset, the routine proceeds to step 109, where the target air-fuel ratio (A / F) T is 22.0.
Stipulated in. Then, it proceeds to step 110.

In step 110, the fuel injection time TAU is calculated based on the following equation. TAU = TP * KW * (A / F) S / (A / F) T FIG. 13 shows another embodiment. This embodiment differs from the above-mentioned embodiment in that a large heat capacity body 17 made of, for example, ceramic is provided between the SO _X absorbent 9 and the NO _X absorbent 12. The large thermal capacity member 17 is for maintaining a low temperature of the NO _X absorbent 12 when the temperature of the SO _X absorbent 9 is increased in order to release the SO _X from the SO _X absorbent 9. Preferably, the heat capacity of the large heat capacity body 17 is determined so that the temperature of the NO _X absorbent 12 is kept lower than the SO _X absorption temperature range until the SO _X releasing action of the SO _X absorbent 9 is completed. In this way S
That SO _X is absorbed is reliably prevented in the NO _X absorbent 12 during the O _X absorbent 9 SO _X is released.

The large heat capacity body 17 may be formed of, for example, a catalyst, or may be formed of a filter that collects fine particles in the inflowing exhaust gas. FIG. 14 shows another embodiment. Referring to FIG. 14, the cylinders of the engine body 1 are a first cylinder group 1a including first cylinder # 1 and fourth cylinder # 4 and a second cylinder group including second cylinder # 2 and third cylinder # 3.
Cylinder group 1b. As described above, since the exhaust stroke order of the engine body 1 is # 1- # 3- # 4- # 2, the cylinders of the engine are the first cylinder group and the second cylinder in which the exhaust stroke does not overlap the first cylinder group. It will be divided into the cylinder group and. The first cylinder group 1a includes a casing 10a containing a first SO _X absorbent 9a via an exhaust manifold 8a.
The second cylinder group 1b is connected to the casing 1 and the second SO _x absorbent 9b is contained in the casing 1 through the exhaust manifold 8b.
0b. These casings 10a and 10b are connected to a NO _x
It is connected to a casing 13 containing the absorbent 12. Further, as shown in FIG. 14, the SO _x absorbents 9a, 9
An oxidation catalyst, for example, a three-way catalyst 19a, 19b is housed in each of the casings 10a, 10b upstream of b.

By the way, even in this embodiment, during normal operation
The air-fuel ratio of the air-fuel mixture burned in each cylinder is lean.
Be done. At this time, the SO in the exhaust of the first cylinder group 1a_XIs the
SO of 1_XAbsorbed by the absorbent 9a, the second cylinder group 1b
SO in the exhaust_XIs the second SO _XAbsorbed by absorbent 9b,
Therefore NO_XNO for absorbent 12_XOnly absorbed
It

Then, the first SO_XAbsorbent 9a or No.
2 SO_XSO absorbed by absorbent 9b_XAmount set
NO when the amount exceeds_XThe temperature of the absorbent 12
SO _XIt is determined whether the temperature is lower than the absorption temperature range. N
O_XThe temperature of the absorbent 12 is SO _XLower than absorption temperature range
Sometimes SO_XAir-fuel of exhaust gas flowing into the absorbents 9a, 9b
The ratios are made rich and SO_XAbsorbent 9
The temperature of a and 9b is SO_XHigher than the emission temperature
And SO_XAbsorbed from absorbents 9a, 9b
SO_XIs released.

In this case, SO_XCapacity of absorbent 9a, 9b
In the embodiments described thus far_XAbsorbent 9
Can be made smaller than SO_XAbsorbent 9a,
9b SO_XIt is necessary to raise the discharge temperature quickly and sufficiently.
You can Therefore SO _XAbsorbents 9a, 9b to S
O_XCan be released promptly and sufficiently. one
However, in the present embodiment, SO_XAbsorbents 9a, 9b to SO
_XOf the exhaust gas emitted from each cylinder when it should be released
SO by controlling the air-fuel ratio_XOf the absorbents 9a, 9b
The temperature is raised. That is, a large amount of hydrocarbons in the exhaust
And a lot of oxygen O₂And these hydrocarbons and
Oxygen O₂And is SO_XAbsorbent 9a, 9b or SO_XSucking
SO when reacting upstream of sorbent 9a, 9b_XAbsorbent 9a, 9
The temperature of b can be increased. So in this embodiment
Is the first SO_XAbsorbent 9a to SO_XShould be released
When the first cylinder group 1a is exhausted from the first cylinder # 1.
The air-fuel ratio of the exhaust gas emitted is made lean and a large amount of oxygen O₂To
Of the exhaust gas that is emitted from the fourth cylinder # 4.
Exhaust containing a large amount of hydrocarbons is formed by making the air-fuel ratio rich
The exhaust gas from the first SO_XCombined upstream of absorbent 9a
Let hydrocarbon and oxygen O in mixed exhaust gas₂To react with
And the first SO_XThe temperature of the absorbent 9a is set to SO_XRelease temperature
I try to make it higher than the degree. Similarly, the second SO
_XAbsorbent 9b to SO_XSecond when to release
Of the exhaust gas discharged from the second cylinder # 2 of the cylinder group 1b of
Make the air-fuel ratio lean and use a large amount of oxygen O₂Forming exhaust containing
The rich air-fuel ratio of the exhaust gas discharged from the third cylinder # 3
To form exhaust containing large amounts of hydrocarbons
The second SO_XDuring the mixed exhaust with the upstream of the absorbent 9b
Oxygen O₂By reacting with a hydrocarbon
SO_XThe temperature of the absorbent 9b is set to SO_XAbove the release temperature
I am trying to do it.

That is, generally speaking, each cylinder group has a plurality of cylinders, and the air-fuel ratio of the exhaust gas discharged from a part of the cylinders of each cylinder group is made lean to form exhaust gas containing a large amount of oxygen. At the same time, the air-fuel ratio of the exhaust gas discharged from the remaining cylinders is made rich to form exhaust gas containing a large amount of hydrocarbons, and these exhaust gases are combined upstream of the SO _X absorbent to combine oxygen O ₂ and hydrocarbons in the mixed exhaust gas. By reacting with, the temperature of the SO _X absorbent is made higher than the SO _X release temperature.

However, as described above, SO_XAbsorbent 9
a and 9b are SO once absorbed_XMust be held securely
SO is necessary_XHigh alkalinity of absorbents 9a, 9b
And as a result SO_XOxidation of absorbents 9a, 9b
The ability is low. Therefore, a large amount of oxygen O₂And charring
Direct SO with hydrogen_XEven if led to the absorbents 9a and 9b, SO _X
The temperature of the absorbents 9a, 9b cannot be raised sufficiently
Yes.

Therefore, in this embodiment, the SO _X absorbent 9 is used.
Three-way catalysts 19a and 19b are arranged adjacent to each other on the upstream side of a and 9b, and oxygen O ₂ and hydrocarbons in the exhaust gas of the first cylinder group 1a are reacted in the three-way catalyst 19a, and the second cylinder group 1a
Oxygen O ₂ and hydrocarbon in the exhaust gas of b are made to react in the three-way catalyst 19b. As a result, SO _X
The temperature of the exhaust gas flowing into the absorbents 9a, 9b is raised and S
O _X absorbent 9a, the temperature of 9b is increased. Further, the three-way catalyst 19a, 19b is SO _X absorbent 9a, since it is arranged adjacent to 9b SO _X absorbent 9a, the temperature of 9b is certainly enhanced.

In this case, the first cylinder # is controlled so that the air-fuel ratio of the mixed exhaust flowing into the first SO _X absorbent 9a becomes rich.
If the air-fuel ratio of the exhaust gas discharged from the first and fourth cylinders # 4 is controlled, SO _X is released from the first SO _X absorbent 9a and the air-fuel ratio of the mixed exhaust gas that flows into the second SO _X absorbent 9b. No. 2 cylinder # 2 and No. 3 cylinder #
If the air-fuel ratio of the exhaust gas discharged from No. 3 is controlled, the second SO
SO _X is released from the _X absorbent 9b.

By the way, as described above, NO_XAbsorbent 1
The temperature of 2 is SO_XSO when outside the absorption temperature range_XAbsorbent
9a, 9b to SO_XNO is released_XAbsorbent 1
SO to 2_XIs never absorbed. However, N
O_XThe temperature of the absorbent 12 is SO _XOutside the absorption temperature range
A small amount of SO_XIs NO_XAbsorbed by the absorbent 12
It is possible. Also, SO_XInflow into absorbent 9a, 9b
A slight amount of SO when the air-fuel ratio of the exhaust gas is lean_X
Is SO_XSO without being absorbed by the absorbents 9a, 9b_X
NO flowing out from the absorbents 9a, 9b_XAbsorb to absorbent 12
It may be done. On the other hand, NO_XTemperature of absorbent 12
Is NO_XAbsorbent 12 SO_XWhen higher than the emission temperature
NO when the oxygen concentration in the inflowing exhaust gas decreases_XAbsorbent 1
SO absorbed from 2_XIs released. Then the truth
In the embodiment, SO_XSO of absorbent 9a, 9b_XRelease action
NO immediately after being stopped_XThe temperature of the absorbent 12 is set to N
O _XAbsorbent 12 SO_XHigher than the emission temperature
And NO_XRich the air-fuel ratio of the exhaust flowing into the absorbent 12.
And NO_XAbsorbent 12 to SO_XTo release
is doing.

[0062] the temperature of _the NO _X absorbent 12 NO _X absorbent 1
To higher than 2 SO _X release temperature, in the present embodiment to form an exhaust containing a large amount of oxygen O ₂ fuel ratio of the exhaust in the lean discharged from the first cylinder group 1a, the second The air-fuel ratio of the exhaust gas discharged from the cylinder group 1b is made rich to form exhaust gas containing a large amount of hydrocarbons.
In this case, the exhaust gas flowing into the three-way catalyst 19a contains a large amount of oxygen O ₂ but does not contain a large amount of hydrocarbons, and thus a large amount of oxygen O ₂ is almost consumed in the three-way catalyst 19a. Without reaching the NO _x absorbent 12, the NO _x absorbent 12 is reached. Similarly, the exhaust gas flowing into the three-way catalyst 19b contains a large amount of hydrocarbons but does not contain a large amount of oxygen O ₂ , so that a large amount of hydrocarbons is almost consumed in the three-way catalyst 19b. Without reaching the NO _x absorbent 12. Therefore, reacts with a large amount of oxygen O ₂ and a large amount of hydrocarbons in _the NO _X absorbent 12, the temperature of the NO _X absorbent 12 and thus can be made higher than its SO _X release temperature.

[0063] Thus, in the present embodiment, the air-fuel ratio of the exhaust gas discharged from the third cylinder # 3 and fourth cylinder # 4 is made rich when SO _X absorbent 9a, from 9b to emit SO _X . Also, from the NO _x absorbent 12 to the SO _x
The second cylinder group 1b, that is, 2
The air-fuel ratio of the exhaust gas discharged from the # 2 cylinder # 2 and the # 3 cylinder # 3 is made rich. Furthermore, the air-fuel ratio of the exhaust gas discharged from all the cylinders is made rich when the _the NO _X absorbent 12 to be released the NO _X. In order to make the air-fuel ratio of the exhaust gas discharged from the cylinder rich, in this embodiment, the secondary fuel injection is performed from the fuel injection valve 7 while maintaining the air-fuel ratio of the air-fuel mixture burned in the cylinder lean. There is. That is, in addition to the normal fuel injection performed in the engine intake stroke or the compression stroke, that is, the main fuel injection, the second fuel injection, that is, the secondary fuel injection is performed in the engine expansion stroke or the exhaust stroke.

[0064] SO _X absorbent 9a, the time to emit SO _X from 9b 3 cylinder # 3 of the secondary fuel injection time T
Secondary fuel injection time T of AUS (3) and No. 4 cylinder # 4
Each AUS (4) is set as TSS. The TSS is necessary to SO _X absorbent 9a, temperature SO _X absorbing higher than release temperature vital SO _X absorbent 9a of 9b, the air-fuel ratio of the exhaust gas mixture flowing into 9b rich example 10.0 This is the secondary fuel injection time. The TSS is previously obtained by an experiment, and for example, the engine load Q / N and the engine speed N
Is stored in the ROM 22 in advance in the form of a map as shown in FIG. In this case, the secondary fuel injection time TAUS (1) of the first cylinder # 1 and the secondary fuel injection time TAUS (2) of the second cylinder # 2 are set to zero.

On the other hand, when SO _X should be released from the NO _X absorbent 12, the secondary fuel injection time TAUS (2) of the second cylinder group 1b, that is, the second cylinder # 2, and the second fuel of the third cylinder # 3. Injection time TAUS (3) is TN
S. This TNS changes the temperature of the NO _x absorbent 12 to S
This is the secondary fuel injection time required for making the air-fuel ratio of the mixed exhaust flowing into the NO _X absorbent 12 higher than the O _X absorbing and releasing temperature and rich, for example, 10.0. The TNS is obtained in advance by experiments, and is stored in advance in the ROM 22 in the form of a map as shown in FIG. 15B as a function of the engine load Q / N and the engine speed N, for example. In this case, the secondary fuel injection time TAU of the first cylinder # 1
Secondary fuel injection time TAU of S (1) and No. 4 cylinder # 4
Each S (4) is set to zero.

[0066] NO _X from the absorbent 12 when it should emit NO _X is secondary fuel injection time for all the cylinders TAUS (i)
(I = 1, 2, 3, 4) is set as TNN. This TNN
Is the secondary fuel injection time required to make the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 12 rich, for example 13.0. The TNN has been obtained in advance by experiments, and as a function of the engine load Q / N and the engine speed N, for example, FIG.
It is stored in advance in the ROM 22 in the form of a map as shown in FIG.

16 and 17 show the present embodiment.
SO_XThe release control routine is shown. This routine is
It is executed by an interrupt at every preset time.
It It should be noted that in the present embodiment as well, NO shown in FIG._XEmission system
Your routine is executed. Please refer to FIG. 16 and FIG.
Then, first in step 120, NO_XAbsorbent 12 to S
O_XIs set when the
N-SO _XWhether or not the flag is set
To be determined. N-SO_XWhen the flag is reset
Then proceed to step 121, where SO_XAbsorbent 9
a, 9b to SO_XIs set when the
S-SO reset except for this_XFlag set
Is determined. S-SO_XFlag is reset
If it is not, then proceed to step 122,
SO of 1_XSO absorbed by absorbent 9a_XQuantity SSa
Is estimated. In the following step 123, absorbed SO_XQuantity S
It is determined whether or not Sa is larger than the set amount SSa1.
It This set amount SSa1 is, for example, SO_XAbsorbent 9a, 9
maximum SO that b can absorb_XIt is about 30% of the amount. First
SO_XAbsorbent 9a and second SO_XAbsorbent 9b is
Almost the same amount of SO_XIs considered to have been absorbed.
Either SO_XSO absorbed by absorbent_XQuantity
It is only necessary to determine whether it is larger than the set amount.
It Therefore, in this embodiment, the first SO_XSoak up in absorbent 9a
SO being stored_XEstimate the amount SSa_X
It is determined whether or not the amount SSa is larger than the set amount SSa1.
I am trying to do it.

When SSa≤SSa1, the processing cycle is ended. On the other hand, when SSa> SSa1, the routine proceeds to step 124, where it is determined whether or not the temperature TEX of the exhaust gas flowing into the NO _X absorbent 12 is lower than the set temperature T1, that is, the temperature of the NO _X absorbent 12 is SO _X absorption. It is determined whether the temperature is lower than the temperature range. When TEX ≧ T1, that is, when the temperature of the NO _X absorbent 12 is within the SO _X absorption temperature range, the processing cycle is ended. On the other hand, when TEX <T1, that is, when the temperature of the NO _X absorbent 12 is lower than the SO _X absorption temperature range, the routine proceeds to step 125, where the S-SO _X flag is set. As will be described later, when the S-SO _X flag is set, the air-fuel ratios of the mixed exhausts flowing into the SO _X absorbents 9a and 9b are made rich, so that the SO _X absorbent 9a, 9b
SO _x is released from 9b.

S-SO_XWhen the flag is set
From step 121 to step 126, S-SO_X
Whether or not a certain time has passed since the flag was set
Nozawa SO_XSO of absorbent 9a, 9b_XRelease action completed
Whether or not it is determined. S-SO_XFlag set
When a certain time has not passed since the _X
SO of absorbent 9a, 9b_XIf the release action is not complete
If so, proceed to step 127, where NO_XAbsorbent 12
The temperature TEX of the exhaust gas flowing into the engine is higher than the set temperature T1.
It is determined whether or not. If TEX≤T1, then
End the processing cycle. On the other hand, in step 126
S-SO_XA certain amount of time has passed since the flag was set
When I passed, SO_XSO of absorbent 9a, 9b_X
When the release action is complete, and in step 127
If TEX> T1, then proceed to step 128.
Only S-SO_XThe flag is reset. Subsequent steps
No in 129_XThe flag is reset. Continued step
N-SO in_XFlag is set.

N-SO_XWhen the flag is set
From step 120 to step 131, N-SO_X
Whether or not a certain time has passed since the flag was set
Nowa No_XAbsorbent 12 SO_XIs the release action complete?
It is determined whether or not. N-SO _XIs the flag set
When a certain time has not passed from, that is, NO_XAbsorbent
12 SO_XWhen the release action is not complete, the processing
Finish the icicle. On the other hand, N-SO_XThe flag is
When a certain time has passed since the
Go to page 132, N-SO_XThe flag is reset.

FIG. 18 shows a calculation routine of the main fuel injection time TAU and the secondary fuel injection time TAUS in this embodiment. This routine is executed by interruption for each preset crank angle. Referring to FIG. 18, first, at step 140, the basic fuel injection time TP is calculated from the map of FIG. Continued Step 141
Then, the target air-fuel ratio (A / F) T is set to 22.0, and in the following step 142, the main fuel injection time TAU is calculated (TAU = TP · (A / F) S / (A / F) T). In the following step 143, it is determined whether or not the N-SO _X flag is set. If the N-SO _X flag is set, then the routine proceeds to step 144, where FIG.
The TNS is calculated from the map of (B). In the following step 145, the secondary fuel injection times TAUS (1) and TAUS (4) of the first and fourth cylinders are set to zero, and the secondary fuel injection times TAUS (2) and TUS of the second and third cylinders TAUS (2), T are set.
AUS (3) becomes TNS.

On the other hand, when the N-SO _X flag is reset, the routine proceeds to step 146, where S-S
It is determined whether or not the _Ox flag is set. S
If the -SO _X flag is set, then the routine proceeds to step 147, where TSS is calculated from the map of FIG. In the following step 148, the first cylinder and the second cylinder
No. 2 cylinder fuel injection time TAUS (1), TAUS
(2) is set to zero, and the secondary fuel injection times TAUS (3) and TAUS (4) of the third and fourth cylinders are set to TSS.

On the other hand, when the S-SO _X flag is reset, the routine proceeds to step 149, where NO _X
It is determined whether or not the flag is set. NO _X
If the flag is set, then step 15
The process proceeds to 0 and the TNN is calculated from the map of FIG. In the following step 151, the secondary fuel injection time TAUS (i) of all cylinders is set to TNN. On the other hand, if the NO _X flag is reset, then step 15
In step 2, the secondary fuel injection time TAUS (i) of all cylinders is set to zero.

From the fuel injection valve 7 of the i-th cylinder, main fuel injection is performed only for TAU, and secondary fuel injection is performed only for TAUS (i). FIG. 19 shows another embodiment. The internal combustion engine shown in FIG. 19 differs from the internal combustion engine of FIG. 14 in the following points. That is, in the internal combustion engine shown in FIG. 19, the oxidation catalyst 160 is housed in the casing 13 upstream of the NO _X absorbent 12, and the three-way catalyst is not provided upstream of the SO _X absorbents 9a and 9b. Also, SO _X absorbent 9a, respectively 9b, electric heater 14a, and 14b are provided, the electric heater 14a, 14b switches 15a that are maintained in the normal off, it is connected to a common power supply 16 via the 15b ing. Further, an intake control valve 161 which is normally kept fully open is arranged in each intake branch pipe 2. First cylinder group 1
a, that is, the intake control valves 161 of the first cylinder and the fourth cylinder
Are driven by a common actuator 162a to have the same opening degree, and the intake control valves 161 of the second cylinder group 1b, that is, the second cylinder and the third cylinder are driven by a common actuator 162b to have the same opening degree. . Switches 15a and 15b and actuator 16
2a and 162b are connected to the output port 26 of the electronic control unit 20 via the corresponding drive circuit 33, and are controlled based on the output signal from the electronic control unit 20.

In this embodiment, the target air-fuel ratio is set for each cylinder. The target air-fuel ratio of the i-th cylinder is (A / F) T (i)
The fuel injection time TAU (i) of the i-th cylinder is expressed by the following equation. TAU (i) = TP ・ (A / F) S / (A / F) T
(I) Note that the secondary fuel injection is not performed in this embodiment.

[0076] The time to emit NO _X from _the NO _X absorbent 12 the target air-fuel ratio of all cylinders (A / F) T (i ) is rich, for example, 13.0. Further, at this time, the opening degree OP (i) of the intake control valves 161 of all the cylinders is set to the opening degree CLN smaller than the full opening degree. That is, when the intake air amount is large, a large amount of fuel is required to make the air-fuel ratio rich, which deteriorates the fuel consumption rate. Therefore, in the present embodiment, the intake control valve 161 of the cylinder with the target air-fuel ratio being rich is closed to reduce the intake air, thereby suppressing the deterioration of the fuel consumption rate. The opening CLN is, for example, the optimum opening of the intake control valve 161 for releasing NO _X from the NO _X absorbent 12, and is previously obtained by an experiment.

On the other hand, from the first SO _X absorbent 9a to SO _X
First SO _X absorbent 9a by the electric heater 14a switch 15a is turned on when it should emit the S
The first cylinder group 1a is heated while being heated to the O _X release temperature.
That is, the target air-fuel ratio (A / F) T (1) of the first cylinder # 1
And the target air-fuel ratio (A / F) T (4) of the fourth cylinder # 4 is made rich, for example 10.0. Furthermore, at this time 1
The opening degree OP (1) of the intake control valve 161 of the No. cylinder # 1 and the opening degree OP (4) of the intake control valve 161 of the No. 4 cylinder # 4 are set to the opening degree CLS smaller than the full opening. This opening degree CLS is, for example, the optimum opening degree of the intake control valve 161 for releasing SO _X from the SO _X absorbents 9a and 9b, and is obtained in advance by experiments.

Similarly, the second SO_XAbsorbent 9b to SO
_XSwitch 15b should be turned on when the
The electric heater 14b causes the second SO_XAbsorbent 9b
SO _XSecond cylinder group 1 while being heated to the discharge temperature
b, that is, the target air-fuel ratio (A / F) T of the second cylinder # 2
(2) and the target air-fuel ratio (A / F) T of the third cylinder # 3
(3) is made rich. Furthermore, at this time, the second cylinder #
Opening OP (2) of intake control valve 161 of No. 2 and No. 3 cylinder
The opening OP (3) of the intake control valve 161 of # 3 is CLS.
Be done.

Further, in this embodiment, the NO _x absorbent 12 is used.
Temperature is so high to release SO _X SO _X absorbent 9a, from 9b when than SO _X absorption temperature range. During normal engine operation, the temperature of the NO _x absorbent 12 is S
It rarely goes above the O _x absorption temperature range.
Therefore, in the present embodiment, the SO _X absorbents 9a, 9b to S
When O _X should be released, the NO _X absorbent 12 is heated to raise the temperature of the NO _X absorbent 12 above the SO _X absorption temperature range, and the SO _X releasing action of the SO _X absorbents 9a and 9b is performed. During this time, the temperature of the NO _X absorbent 12 is kept higher than the SO _X absorption temperature range.

As described above, NO_XInflow into absorbent 12
A large amount of oxygen O in the exhaust gas₂And a large amount of hydrocarbons
NO if yes_XThe temperature of the absorbent 12 can be increased
It On the other hand, for example, the first SO_XAbsorbent 9a to SO_XTo
First SO to release _XExhaust flowing into the absorbent 9a
When the air-fuel ratio of air is made rich, the first SO _X
The air-fuel ratio of the exhaust gas discharged from the absorbent 9a becomes rich.
That is, the first SO_XDischarged from absorbent 9a
The exhaust gas contains a large amount of hydrocarbons. According to
At this time, the second SO_XExhaust discharged from absorbent 9b
Makes the air-fuel ratio lean and creates a large amount of oxygen O₂NO_Xabsorption
NO if supplied to agent 12_XTo increase the temperature of the absorbent 12.
You will be able to

Therefore, in this embodiment, the SO _X releasing action of the first SO _X absorbent 9a and the S of the second SO _X absorbent 9b are reduced.
O _X release effect and without simultaneously either SO _X
When the SO _X releasing action of the absorbent is being performed, the air-fuel ratio of the exhaust gas flowing into the other SO _X absorbent is made lean. That, SO _X absorbent 9a, first, the time to release the SO _X from 9b, with the release of SO _X from the first SO _X absorbent 9a by the target air-fuel ratio of the first cylinder group 1a rich, the The target air-fuel ratio of the second cylinder group 1b is made lean. The large amount of hydrocarbons in the exhaust gas discharged from the first SO _X absorbent 9a and the large amount of oxygen O ₂ in the exhaust gas discharged from the second SO _X absorbent 9b then react in the oxidation catalyst 160, As a result, the temperature of the NO _X absorbent 12 is raised above the SO _X absorption temperature range. At this time, the air-fuel ratio of the mixed exhaust flowing into the NO _X absorbent 12 is made rich, so that the SO _X released from the first SO _X absorbent 9a is absorbed by the NO _X absorbent 12. It has been blocked. S of the first SO _X absorbent 9a
When the O _X releasing action is completed, then the second cylinder group 1
The second SO _x absorbent 9b is made rich by increasing the target air-fuel ratio of b.
SO _X is released from the engine and the target air-fuel ratio of the first cylinder group 1a is made lean. As a result, SO _X is released from the second SO _X absorbent 9b, and the temperature of the NO _X absorbent 12 is maintained higher than the SO _X absorption temperature range. At this time also, the air-fuel ratio of the mixed exhaust flowing into the NO _X absorbent 12 is made rich, so that the SO _X released from the second SO _X absorbent 9b is absorbed by the NO _X absorbent 12. Have been blocked.

By the way, as described above, the SO _X absorbent 9
a, the SO _X released from 9b is absorbed in the NO _X absorbent 12 is believed to be due to residual oxygen in _the NO _X absorbent 12. On the other hand, if the oxygen concentration in the exhaust flowing into the NO _x absorbent 12 is reduced, the NO _x absorbent 12
The amount of residual oxygen in the inside can be reduced. Therefore,
For example the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 12 to release the NO _X from _the NO _X absorbent 12 is that the residual oxygen amount in _the NO _X absorbent 12 when it is rich, is reduced. In this embodiment, NO _X immediately after the NO _X release action of the absorbent 12 is completed SO _X absorbent 9a, 9
and so as to release the SO _X b. From

On the other hand, as described above, when the exhaust gas flowing into the NO _x absorbent 12 contains oxygen, the SO _x absorbent 9
There is also an idea that the SO _x released from a and 9b is absorbed by the NO _x absorbent 12. Therefore, in this embodiment, N
O _X absorbent 12 is provided upstream to the oxidation catalyst 160 consumes oxygen O ₂ in the exhaust in the oxidation catalyst 160 when the SO _X is released SO _X absorbent 9a, from 9b, whereby _the NO _X absorbent The amount of oxygen flowing into 12 is made as small as possible. Preferably, NO _X absorbent 1
SO _X absorbent 9a so that hardly contained oxygen O ₂ in the exhaust gas flowing into the 2, for example, the target air-fuel ratio of the first cylinder group 1a or the second cylinder group 1b when the release of SO _X from 9b, Alternatively, the opening degree of the intake control valve 161 is determined.

[0084] Further, thus oxidizing ability of the NO _X absorbent 12 in the case of arranging the _the NO _X absorbent 12 upstream the oxidation catalyst 160 may be lower, increasing the alkalinity of the resulting _the NO _X absorbent 12 it is possible to increase the NO _X absorbing capacity of the NO _X absorbent 12 Te. 20 and 21 show NO _X and SO _X release control in this embodiment.
This routine is executed by interruption every predetermined set time.

Referring to FIGS. 20 and 21, first, the screen is
Second SO in step 170_XAbsorbent 9b to SO_XTo
Set when to release, reset otherwise
Second SO_XDetermines if the flag is set
Be done. Second SO_XWhen the flag is reset
Next, in step 171, the first SO_XAbsorbent 9a
To SO_XIs set when the
First SO reset_XIs the flag set
It is determined whether or not. First SO_XFlag is reset
If yes, then proceed to step 172, NO_Xabsorption
Agent 12 to NO _XSet when it should be released,
Other than reset NO_XFlag is set
It is determined whether or not. NO_XThe flag has been reset
If yes, then proceed to step 173, NO_XAbsorbent
NO absorbed in 12_XThe quantity SN is estimated. Continue
Absorption NO in step 174_XThe amount SN is the set amount SN1
It is determined whether or not it is larger than that. When SN ≦ SN1
Next, the routine proceeds to step 175, where the intake control valves 1 for all cylinders are
The opening degree OP (i) of 61 is FU indicating full opening. this
On the other hand, if SN> SN1, then step 176
Go to No_XFlag is set. Continued Step 1
At 77, the opening OP (i) of the intake control valves 161 of all cylinders is
CLN.

NO_XWhen the flag is set
Step 172 to step 178, NO_XFlag is
Whether or not a certain time has passed since being set, that is, N
O_XAbsorbent 12 NO_XDetermine if the release action is complete
Be separated. NO_XA certain amount of time has passed since the flag was set
When not having, namely NO_XAbsorbent 12 NO _X
If the release action is not complete, end the treatment cycle
To do. On the other hand, NO_XOne after the flag was set
When the fixed time has passed, that is, NO_XAbsorbent 12 NO
_XWhen the releasing action is completed, then go to step 179.
Go, NO_XThe flag is reset. Continued Step 1
The first SO at 80_XFlag is set. Continued step
181, the first cylinder group 1a, that is, the first cylinder group 1a
Openings OP (1), OP of the intake control valve 161 of the fourth cylinder
(4) is set to CLS, and the second cylinder group 1b, that is, No. 2
Opening OP of the intake control valve 161 of the cylinder and the third cylinder
(2) and OP (3) are maintained in the fully open FU.

When the first SO _X flag is set, the routine proceeds from step 171 to step 182, where the first SO _X flag is set.
It is determined whether or not a fixed time has elapsed since the flag was set, that is, whether or not the SO _X releasing action of the first SO _X absorbent 9a has been completed. When a certain time has not passed since the first SO _X flag was set, that is, when the SO _X releasing action of the first SO _X absorbent 9a is not completed, the processing cycle is ended. On the other hand, the first SO
When _{the X} flag is a predetermined time elapsed since the set, i.e., the routine goes to step 183 when the SO _X release action of the first SO _X absorbent 9a is completed, the 1SO _X
The flag is reset. In the following step 184, the second
SO _X flag is set. In the following step 185, the opening degrees OP (1) and OP (4) of the intake control valves 161 of the first cylinder group 1a, that is, the first cylinder and the fourth cylinder are fully opened F.
U, which is the second cylinder group 1b, that is, the second cylinder and the third cylinder.
Opening OP (2), OP of the intake control valve 161 of the No. cylinder
(3) is set as CLS.

When the second SO _X flag is set, the routine proceeds from step 170 to step 186, where the second SO _X flag is set.
It is determined whether or not a fixed time has elapsed since the flag was set, that is, whether or not the SO _X releasing action of the second SO _X absorbent 9b has been completed. When a certain time has not elapsed since the second SO _X flag was set, that is, when the SO _X releasing action of the second SO _X absorbent 9b is not completed, the processing cycle is ended. In contrast, the second SO
When _{the X} flag predetermined time has elapsed since the set, that is, when the SO _X release action of the second SO _X absorbent 9b is completed and then proceeds to step 187, the 2SO _X
The flag is reset. In the following step 188, the opening degrees OP (i) of the intake control valves 161 of all cylinders are returned to full open FU.

FIG. 22 shows a routine for calculating the fuel injection time TAU (i) for the i-th cylinder in this embodiment.
This routine is executed by interruption for each preset crank angle. Referring to FIG. 22, first, at step 200, the basic fuel injection time T is calculated from the map of FIG.
P is calculated. In the following step 201, it is judged if the second SO _X flag is set. Second SO
_{If the X} flag is set then step 2
02, the target air-fuel ratio (A / F) T (1), (A / F) of the first cylinder group 1a, that is, the first cylinder and the fourth cylinder
T (4) is set to 22.0. In the following step 203, the target air-fuel ratios (A / F) T (2) and (A / F) T (3) of the second cylinder group 1b, that is, the second cylinder and the third cylinder, are set to 1
It is set to 0.0. Then, it proceeds to step 210.

On the other hand, when the second SO _X flag is reset, the routine proceeds to step 204, where the first S
It is determined whether or not the _Ox flag is set. If the first SO _X flag is set, then the routine proceeds to step 205, where the target air-fuel ratio (A / F) T (1), (A
/ F) T (4) is set to 10.0. Continued Step 20
6, the target air-fuel ratios (A / F) T (2), (A / F) T of the second cylinder group 1b, that is, the second cylinder and the third cylinder
(3) is set to 22.0. Then, it proceeds to step 210.

On the other hand, when the first SO _X flag is reset, then the routine proceeds to step 207, where NO _X
It is determined whether or not the flag is set. NO _X
If the flag is set then step 20
8, the target air-fuel ratio (A / F) T (i) of all cylinders is 1
It is set to 3.0. On the other hand, when the NO _X flag is reset, the routine proceeds to step 209, where the target air-fuel ratio (A / F) T (i) of all cylinders is set to 22.0.
Then, it proceeds to step 210.

In step 210, the fuel injection time TAU (i) of the i-th cylinder is calculated based on the following equation. TAU (i) = TP ・ (A / F) S / (A / F) T
(I) In the embodiments described above, for example, the air-fuel ratio of the air-fuel mixture burned in the cylinder is made rich in order to make the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent rich, or 2
Next fuel injection is performed. However, SO
_A secondary fuel injection valve is arranged in the exhaust passage upstream of the _X absorbent, and the secondary fuel is injected from this secondary fuel injection valve so that the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent becomes rich. You can also do it.

Further, in the embodiments described so far, the SO _X absorbent and the NO _X absorbent are arranged in series in the exhaust passage. However, as described above, the SO _X absorbing / releasing action of the SO _X absorbent is almost the same as the SO _X absorbing / releasing action of the NO _X absorbent. Therefore, when two NO _X absorbents are arranged in series in the exhaust passage. The present invention can also be applied to.

[0094]

When the temperature of the NO _x absorbent is outside the sulfur content absorption temperature range, the sulfur content is released from the sulfur content absorbent, so the sulfur content released from the sulfur content absorbent is NO _x.
It is possible to prevent absorption by the absorbent.

[Brief description of 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.

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

FIG. 4 is a diagram showing the SO _X absorption rate of a NO _X absorbent.

FIG. 5 is a flowchart for executing SO _X release control.

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

FIG. 7 is a flowchart for calculating a fuel injection time.

FIG. 8 is a diagram showing a map of a fuel injection time for starting.

FIG. 9 is a diagram showing a map of a warm-up increase correction coefficient.

FIG. 10 is a flowchart for executing SO _X release control according to another embodiment.

FIG. 11 is a flowchart for calculating a fuel injection time in another embodiment.

FIG. 12 is a flowchart for calculating a fuel injection time in another embodiment.

FIG. 13 is an overall view of an internal combustion engine according to still another embodiment.

FIG. 14 is an overall view of an internal combustion engine according to still another embodiment.

FIG. 15 is a diagram showing a map of secondary fuel injection time.

FIG. 16 is a flow chart for executing SO _X release control in the embodiment of FIG.

FIG. 17 is a flow chart for executing SO _X release control in the embodiment of FIG.

18 is a flowchart for calculating a main fuel injection time and a secondary fuel injection time in the embodiment of FIG.

FIG. 19 is an overall view of an internal combustion engine according to still another embodiment.

20 is NO _x and SO in the embodiment of FIG.
It is a flow chart for performing _X release control.

FIG. 21 is NO _x and SO in the embodiment of FIG.
It is a flow chart for performing _X release control.

22 is a flow chart for calculating a fuel injection time in the embodiment of FIG.

[Explanation of symbols]

1 ... Engine body 7 ... Fuel injection valve 8 ... Exhaust manifold 9 ... SO _X absorbent 12 ... NO _X absorbent 14 ... Electric heater

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takamitsu Asanuma 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor: Hiroshi Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. ( 72) Inventor Naoto Suzuki 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (56) References JP-A-11-107812 (JP, A) JP-A-6-229230 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) F01N 3/08-3/28

Claims (10)

(57) [Claims] 1. A fuel ratio of the exhaust gas flowing absorbs NO _X when the lean engine and _the NO _X absorbent to the oxygen concentration in the inflowing exhaust gas to release NO _X which is absorbed to decrease the exhaust passage disposed, in the exhaust purification system of an internal combustion engine arranged sulfur absorbent to temporarily absorb sulfur content in the exhaust passage of the _the NO _X absorbent upstream, the temperature of _the NO _X absorbent
Is outside the sulfur content absorption temperature range, the NO _x absorbent will
C min being adapted to absorb very little, the exhaust gas of the internal combustion engine the temperature so as to release the sulfur from the sulfur content absorber when outside sulfur absorption temperature range of the NO _X absorbent of the NO _X absorbent Purification device. Wherein the exhaust of an internal combustion engine according to claim 1 the temperature so as to release the sulfur from the sulfur content absorber is lower than the sulfur absorption temperature range of the NO _X absorbent of the NO _X absorbent Purification device. 3. The sulfur content absorbent absorbs sulfur content when the air-fuel ratio of the inflowing exhaust gas is lean, and the oxygen concentration in the exhaust gas that flows in when the temperature of the sulfur content absorbent is higher than the sulfur content release temperature. Releases absorbed sulfur content when the
And the air-fuel ratio of the exhaust gas flowing into the sulfur content absorbent when the temperature of the sulfur content absorbent and the NO _X absorbent is in a steady state lower than the sulfur content absorption temperature range of the NO _X absorbent. A sulfur content absorbed from the sulfur content absorbent is released by temporarily making the temperature of the sulfur content absorbent higher than the sulfur content release temperature while making the air rich or stoichiometric ratio. 2. An exhaust emission control device for an internal combustion engine according to 2. 4. The exhaust emission control device for an internal combustion engine according to claim 3, wherein the sulfur content is released from the sulfur content absorbent when the engine is started. 5. The exhaust gas purification of an internal combustion engine according to claim 2, wherein the temperature of the NO _x absorbent is kept lower than the sulfur content absorption temperature range when the sulfur content is being released from the sulfur content absorbent. apparatus. 6. The exhaust gas purification device for an internal combustion engine according to claim 5, wherein a large heat capacity body is arranged in the exhaust passage between the sulfur component absorbent and the NO _x absorbent. 7. The exhaust of an internal combustion engine according to claim 1 which is adapted to release sulfur from sulfur absorbent when the temperature of the NO _X absorbent is higher than the sulfur absorption temperature range of the NO _X absorbent Purification device. 8. The exhaust gas purification of an internal combustion engine according to claim 7, wherein the temperature of the NO _x absorbent is maintained higher than the sulfur content absorption temperature range while releasing the sulfur content from the sulfur content absorbent. apparatus. 9. An internal combustion engine is provided with a plurality of cylinders divided into a pair of cylinder groups, and a NO _x absorbent is arranged in a confluent exhaust passage that joins the exhaust gases of the respective cylinder groups to each other to absorb sulfur. While releasing sulfur from the agent, the air-fuel ratio of the exhaust gas of one cylinder group of the pair of cylinder groups is made rich to form exhaust gas containing hydrocarbons and the air-fuel ratio of the exhaust gas of the other cylinder group is made lean. The exhaust gas containing oxygen is formed to react the hydrocarbons in the exhaust gas with oxygen to keep the temperature of the NO _x absorbent above the sulfur content absorption temperature range. Exhaust gas purification device for internal combustion engine. 10. The temperature of the NO _x absorbent is adjusted by arranging an oxidation catalyst in the exhaust passage between the sulfur content absorbent and the NO _x absorbent, and reacting hydrocarbon and oxygen in the oxidation catalyst. The exhaust gas purification device for an internal combustion engine according to claim 9, wherein the exhaust gas purification device is maintained above the range.