JPH06229231A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce the fuel consumption rate during emission of SOX while preventing an NOX absorbent from being poisoned by sulfur. CONSTITUTION:An NOX absorbent 19 for absorbing NOX when the air-fuel ratio of inflow exhaust gas being lean, and for discharging absorbed NOX when the density of oxygen in the exhaust gas being decreased, is located in an engine exhaust passage, and an SOX absorbent 18 for absorbing SOX when the air-fuel ratio of inflow exhaust gas being lean, and for discharging absorbed SOX when it is rich is located in the engine exhaust passage, upstream of the NOX absorbent 19. The air-fuel ratio of the exhaust gas flowing into the SOX absorbent and the NOX absorbent 19 is made to be rich when SOX is discharged from the SOX absorbent and is to be discharged from the NOX absorbent 19, and the degree of richness at this time is made to be lower as the temperature of the SOX absorbent is higher.

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]

In the internal combustion engine which is adapted allowed to combust a lean air-fuel mixture, the air-fuel ratio of the inflowing exhaust gas is absorbed NO _x when the lean, the NO _x concentration of oxygen absorbed to decrease in the inflowing exhaust gas emission the _the NO _x absorbent arranged in the engine exhaust passage, the NO _x generated when burned lean mixture is absorbed by _the NO _x absorbent before the absorption of NO _x capacity of the NO _x absorbent is saturated to temporarily already proposed by the internal combustion engine is the applicant which is adapted to reduce the released NO _x with the release of NO _x in the rich from _the NO _x absorbent the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent Has been done.

However, in the fuel and the lubricating oil of the engine,
SO is included in the exhaust gas because it contains OH._XIncluded
Therefore, in this internal combustion engine, this SO_XAlso NO_xWhen
Both NO_xIt is absorbed by the absorbent. However, this SO
_XIs NO_xRich air-fuel ratio of exhaust gas flowing into the absorbent
Even if it is NO_xNot released from the absorbent and therefore NO_xabsorption
SO in the agent_XWill gradually increase. By the way
Is NO_xSO in absorbent_XNO when the amount of_xabsorption
NO that the agent can absorb_xGradually decreases, and finally N
O_xAbsorbent is NO_xCan hardly absorb
U Therefore NO _xSulfur in the engine exhaust passage upstream of the absorbent
Equipped with a trap, this sulfur trap allows exhaust gas
SO contained in_XThe internal combustion engine that captures
It has already been proposed by the applicant (Japanese Patent Application No. 4-2080).
90). In this internal combustion engine, the S discharged from the engine
O_XIs captured by the sulfur capture device, so NO_xabsorption
NO for the agent_xOnly will be absorbed.

[0004]

However, in this internal combustion engine, the SO _X captured by the sulfur trapping device is not released from the sulfur trapping device even if the air-fuel ratio of the exhaust gas flowing into the sulfur trapping device is made rich. Continues to be captured in the capture device. Therefore S by sulfur capture device
The amount of trapped O _X gradually increases, and when the SO _X trapping capacity of the sulfur trap becomes saturated, SO _X passes through the sulfur trap, so SO _X is absorbed by the NO _x absorbent and NO is absorbed.
_x The problem of progressive accumulation in the absorbent arises.

[0005]

According to the present invention, in order to solve the above problems, when the air-fuel ratio of the inflowing exhaust gas is lean, NO _x is absorbed and the oxygen concentration in the inflowing exhaust gas is increased. NO releases released NO _x
with placing the _x absorbent engine exhaust passage, the air-fuel ratio of the inflowing exhaust gas absorbs SO _X when a lean air-fuel ratio of the inflowing exhaust gas to release SO _X absorbed and becomes rich absorbing SO _X absorbent SO _X absorbent to SO _X in the exhaust gas discharged into the engine exhaust passage when being brought arranged to lean air-fuel mixture is combusted in _the NO _x absorbent in the engine exhaust passage upstream of In addition, NO _x in the exhaust gas is absorbed by the NO _x absorbent, and the SO _x absorbent absorbs S
SO _X absorbing the degree of rich at this time with the O _X from _the NO _x absorbent with releasing the when releasing the NO _x is an air-fuel ratio of the exhaust gas flowing into the SO _X absorbent and _the NO _x absorbent rich The higher the temperature of the agent, the smaller the agent.

[0006]

[Function] Exhaust when lean mixture is burned
SO in gas_XIs SO_XSO is absorbed by the absorbent_X
NO placed downstream of the absorbent_xNO for absorbent_xonly
Is absorbed. On the other hand, SO_XAbsorbent and NO_xAbsorbent
When the air-fuel ratio of the exhaust gas flowing into the engine is made rich, SO_X
SO absorbed by absorbent_XIs decomposed into SO _XLet go
Issued, NO_xNO from the absorbent_xIs released. this
If SO_XSO absorbed by absorbent_XDecomposition rate
Is SO_XThe higher the temperature of the absorbent, the faster
SO_XThe higher the temperature of the absorbent, the less rich
Even SO _XAbsorbent from SO_XIs released. Therefore
The degree of touch is SO_XThe higher the temperature of the absorbent, the smaller
To be done.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is an engine body, 2 is a piston
Ton, 3 is combustion chamber, 4 is spark plug, 5 is intake valve, 6 is intake
A port, 7 is an exhaust valve, and 8 is an exhaust port. Intake
Port 6 is connected to surge tank 10 via corresponding branch pipe 9.
Each of the branch pipes 9 is connected to the inside of the intake port 6 and burns.
A fuel injection valve 11 for injecting fuel is attached. Surger
Ink 10 includes intake duct 12 and air flow meter 13
Is connected to the air cleaner 14 through the intake duct 12
A throttle valve 15 is arranged inside. On the other hand, the exhaust port
8 through the exhaust manifold 16 and the exhaust pipe 17
O_XAbsorbent 18 and NO_xCase with built-in absorbent 19
Connected to the sing 20. SO_XAbsorbent 18 is NO_xSucking
It is located upstream of the sorbent 19, and in the embodiment shown in FIG.
Is SO _XAbsorbent 18 and NO_xIf the absorbent 19 is
Using a monolithic carrier made of Lumina as a unit
Has been formed.

The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, and a constant power source by a bidirectional bus 31. Connected backup RAM
33 a, an input port 35 and an output port 36. The air flow meter 13 generates an output voltage proportional to the intake air amount, and this output voltage is input to the input port 35 via the AD converter 37. A temperature sensor 21 that generates an output voltage proportional to the exhaust gas temperature is arranged in the exhaust pipe 17 upstream of the SO _X absorbent 18, and the output voltage of this temperature sensor 21 is input to an input port 35 via an AD converter 38. Is entered. Further, the input port 35 is connected to the rotation speed sensor 22 that generates an output pulse representing the engine rotation speed. On the other hand, the output port 36 is connected to the spark plug 4 and the fuel injection valve 11 via the corresponding drive circuit 39, respectively.

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 · K Here, TP represents the basic fuel injection time, and K represents the correction coefficient. The basic fuel injection time TP indicates the fuel injection time required to make the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder the stoichiometric air-fuel ratio. This basic fuel injection time TP is obtained by an experiment in advance, and the engine load Q / N
As a function of (intake air amount Q / engine speed N) and engine speed N, the ROM 3 is previously stored in the form of a map as shown in FIG.
It is stored in 2. The correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder, and if K = 1.0, the air-fuel mixture supplied to the engine cylinder becomes the stoichiometric air-fuel ratio. On the other hand, when K <1.0, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes larger than the theoretical air-fuel ratio, that is, becomes lean, and K> 1.0.
If so, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes smaller than the stoichiometric air-fuel ratio, that is, becomes rich.

The correction coefficient K is controlled according to the operating state of the engine, and FIG. 3 shows an embodiment of the control of the correction coefficient K. In the embodiment shown in FIG. 3, the correction coefficient K is gradually decreased as the engine cooling water temperature increases during warm-up operation, and when warm-up is completed, the correction coefficient K becomes a constant value smaller than 1.0, that is, the engine. The air-fuel ratio of the air-fuel mixture supplied into the cylinder is maintained lean. Next, when the acceleration operation is performed, the correction coefficient K is set to 1.0, that is, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is set to the stoichiometric air-fuel ratio,
If the full load operation is performed, the correction coefficient K is made larger than 1.0, that is, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is made rich. As can be seen from FIG. 3, in the embodiment shown in FIG. 3, the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder is maintained at a constant lean air-fuel ratio except during warm-up operation, acceleration operation and full load operation. Therefore, the lean air-fuel mixture is burned in most engine operating regions.

FIG. 4 schematically shows the concentrations of typical components in the exhaust gas discharged from the combustion chamber 3. As can be seen from FIG. 4, the concentrations of HC and CO in the exhaust gas discharged from the combustion chamber 3 increase as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes richer, and are discharged from the combustion chamber 3. The concentration of oxygen O ₂ in the exhaust gas increases as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes leaner.

NO _x contained in the casing 20
The absorbent 19 uses, for example, alumina as a carrier, and alkali metals such as potassium K, sodium Na, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, and rare earths such as lanthanum La and yttrium Y are used on the carrier. At least one selected from the above and a noble metal such as platinum Pt are supported. In addition, it is preferable to add lithium Li to the NO _x absorbent 19. NO of Toko to refer to the ratio of the engine intake passage and _the NO _x absorbent 19 the exhaust passage upstream of the supply air and fuel into the (hydrocarbon) and the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent 19
_x absorbent 19 absorbs the NO _x when the air-fuel ratio of the inflowing exhaust gas is lean, perform absorption and release action of the NO _x concentration of oxygen in the inflowing exhaust gas to release NO _x absorbed to decrease. When fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NO _x absorbent 19, the air-fuel ratio of the inflowing exhaust gas matches the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3, Thus absorbs NO _x when the air-fuel ratio of the mixture is _the NO _x absorbent 19 to be supplied into the combustion chamber 3 in this case is lean, lowering the oxygen concentration in the mixture fed into the combustion chamber 3 Then, the absorbed NO _x is released.

If the above-mentioned NO _x absorbent 19 is arranged in the exhaust passage of the engine, the NO _x absorbent 19 actually performs the NO _x absorption and release action, but the detailed mechanism of this absorption and release action is not clear. There is also. However, it is considered that this absorbing / releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking the case where platinum Pt and barium Ba are supported on the carrier as an example, 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), the oxygen O ₂ is O ₂ ⁻ or O _2.
It adheres to the surface of platinum Pt in the form of ^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 ). Next, a part of the generated NO ₂ is absorbed on the platinum Pt while being absorbed in the absorbent and combined with barium oxide BaO to be absorbed in the form of nitrate ion NO ₃ ⁻ as shown in FIG. 5 (A). Diffuses in the agent. In this way, NO _x is absorbed in the NO _x absorbent 19.

Platinum as long as the oxygen concentration in the inflowing exhaust gas is high
NO on the surface of Pt₂Is generated and the absorbent NO_xAbsorption capacity
NO unless power is saturated₂Is absorbed in the absorbent and nitric acid
Ionic NO₃ ^-Is generated. On the other hand, the inflow exhaust gas
NO in the oxygen₂When the production of
Reaction is in the opposite direction (NO₃ ^-→ NO₂), And thus suck
Nitrate ion NO in the sorbent₃ ^-Is NO₂From the absorbent in the form of
Is released. That is, the oxygen concentration in the inflowing exhaust gas decreases
And NO_xAbsorbent 19 to NO_xWill be released
It As shown in Fig. 4, the degree of leanness of the inflowing exhaust gas
The lower the value, the lower the oxygen concentration in the inflowing exhaust gas.
Even if the lean degree of the inflowing exhaust gas is lowered by
NO even if the air-fuel ratio of the exhaust gas is lean_xAbsorbent 19
To NO _xWill be released.

On the other hand, at this time, if the air-fuel mixture supplied to the combustion chamber 3 is made rich and the air-fuel ratio of the inflowing exhaust gas becomes rich, a large amount of H is emitted from the engine as shown in FIG.
C and CO are discharged, and HC and CO are platinum Pt
It is oxidized by reacting with the oxygen O ₂ ⁻ or O ^{2 −} above.
Further, when the air-fuel ratio of the inflowing exhaust gas becomes rich, the oxygen concentration in the inflowing exhaust gas drops extremely, so
O ₂ is released, and this NO ₂ is reduced by reacting with HC and CO as shown in FIG. 5 (B). 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 NO _x from the NO _x absorbent 19 in a short time when the air-fuel ratio of the inflowing exhaust gas is made rich, that is released.

That is, the air-fuel ratio of the inflowing exhaust gas is made rich.
Then, first of all, HC and CO are already O on platinum Pt.₂ ^-or
Is O^2-Reacts immediately and is oxidized, then platinum
O on Pt₂ ^-Or O^2-Is consumed even if is consumed,
If CO remains, it is an absorbent due to HC and CO.
NO released from_xAnd NO emitted from the engine _x
Is reduced. Therefore, the air-fuel ratio of the inflowing exhaust gas is
No in a short time if you switch_xAbsorbed by absorbent 19
NO_xIs released, and this released NO
_xNO is reduced to the atmosphere_xIs discharged
You will be able to prevent it. Also, NO_xAbsorbent
Since 19 has the function of a reduction catalyst,
NO even if the air-fuel ratio is the theoretical air-fuel ratio_xRelease from absorbent 19
NO done_xIs reduced. However, inflow and outflow
NO when the air-fuel ratio of air gas is set to the theoretical air-fuel ratio_xabsorption
Agent 19 to NO_xNO is released only gradually
_xAll NO absorbed in the absorbent 19_xTo release
Takes a little longer.

By the way, as described above, the inflow of exhaust gas is
If the leanness of the fuel ratio is reduced,
NO even if the air-fuel ratio is lean_xAbsorbent 19 to NO_x
Is released. Therefore NO_xAbsorbent 19 to NO_xLet go
To release it, reduce the oxygen concentration in the exhaust gas
It will be good. However, NO_xAbsorbent 19 to NO _x
If the air-fuel ratio of the inflowing exhaust gas is lean even if
NO_xNO in absorbent 19_xIs not reduced, so
NO in this case_xNO downstream of the absorbent 19_xReduce
A catalytic converter or NO_xDownstream of absorbent 19
It is necessary to supply a reducing agent. Of course NO like this_x
NO downstream of the absorbent 19_xCan be reduced
But rather NO_xN in the absorbent 19
O_xIs preferably reduced. Implementation according to the invention
NO in the example_xAbsorbent 19 to NO _xWhen to release
Is the stoichiometric air-fuel ratio or rich
And thereby NO_xNO released from absorbent 19
_xNO_xTry to reduce in the absorbent 19
It

An embodiment according to the present invention as shown in FIG.
In the warm-up operation and full load operation,
The supplied air-fuel mixture is rich and mixed during acceleration operation.
Aiki is assumed to be the theoretical air-fuel ratio, but most other operating areas
In the region, the lean mixture is burned in the combustion chamber 3.
Be done. In this case, it is burned in the combustion chamber 3.
The air-fuel ratio of the air-fuel mixture is almost 18.0 or higher, which is shown in Fig. 1.
In a preferred embodiment, a lean mixture with an air-fuel ratio of 20 to 24 is used.
Qi is burned. When the air-fuel ratio becomes 18.0 or more
Three-way catalysts have reducing properties even under lean air-fuel ratios.
Even if NO _xCan not be fully returned, obey
NO under lean air-fuel ratio like this_xTo reduce
It is not possible to use a three-way catalyst. Also, the air-fuel ratio is 1
NO even if it is 8.0 or more_xAs a catalyst capable of reducing C
There is a u-zeolite catalyst, but this Cu-zeolite catalyst
Uses this Cu-zeolite catalyst because it lacks heat resistance
It is not preferable to have it. So after all,
NO when the air-fuel ratio is 18.0 or higher_xBook to purify
NO used in the invention_xUse absorbent 19
There is no other way.

In the embodiment according to the present invention, as described above, the air-fuel mixture supplied into the combustion chamber 3 is rich during full-load operation, and the air-fuel mixture has a stoichiometric air-fuel ratio during acceleration operation. NO _x during acceleration and acceleration
NO _x will be released from the absorbent 19. However while lean mixture is combusted as such full load operation or acceleration operation is NO _x from the NO _x absorbent 19 only at the time and acceleration operation full load operation the less frequently performed release NO _x absorbent 19
The NO _x absorption capacity due to is saturated, and thus N
The O _x absorbent 19 cannot absorb NO _x . Thus when the lean air-fuel mixture is burned continuously air-fuel ratio periodically or rich of the inflowing exhaust gas or the air-fuel ratio of the inflowing exhaust gas is periodically to the stoichiometric air-fuel ratio _the NO _x absorbent 19 it is necessary to periodically release the NO _x from.

[0021] Incidentally, the exhaust gas contains SO _X, the _the NO _x absorbent 19 well NO _x SO _X
Is also absorbed. It is considered that the SO _x absorption mechanism into the NO _x absorbent 19 is the same as the NO _x absorption mechanism. That is, similar to the case of explaining the NO _x absorption mechanism, the case of supporting platinum Pt and barium Ba on the carrier will be described as an example. As described above, when the air-fuel ratio of the inflowing exhaust gas is lean, the oxygen O ₂ Is O ₂
^- or O is deposited on the surface of the platinum Pt in ^2-form, SO ₂ in the inflowing exhaust gas on the surface of the platinum Pt O ₂ ^- or O ^2-
And becomes SO ₃ . Then, a part of the generated SO ₃ is further oxidized on the platinum Pt, absorbed in the absorbent and bonded to the barium oxide BaO, and the sulfate ion SO 3
Stable sulfate BaSO ₄ that diffuses into the absorbent in the form of ^4-
Generates ₄ .

However, this sulfate BaSO ₄ is stable and difficult to decompose, and even if the air-fuel ratio of the inflowing exhaust gas is made rich, the sulfate BaSO ₄ remains without being decomposed. Thus will be sulfates BaSO ₄ increases as NO _x time to absorbent 19. elapses, that _the amount of NO _{x the} NO _x absorbent 19 can absorb as thus to time has elapsed is reduced Become.

[0023] Therefore, in this embodiment of the present invention absorbs SO _X when the air-fuel ratio of the exhaust gas flowing to not flow into the SO _X into _the NO _x absorbent 19 is lean, the air-fuel ratio of the exhaust gas flowing The SO _X absorbent 18 that releases the absorbed SO _X when it becomes rich is arranged upstream of the NO _X absorbent 19. This SO _X absorbent 18 is the SO _X absorbent 18
When the air-fuel ratio of the exhaust gas flowing into the engine is lean, SO _X
At the same time, NO _{x is} also absorbed, but when the air-fuel ratio of the exhaust gas flowing into the SO _x absorbent 18 is made rich, not only the absorbed NO _x but also the absorbed SO _x is released.

As described above, when the NO _x absorbent 19 is SO
_{When X} is absorbed, stable sulfate BaSO ₄ is formed. As a result, SO _X is not released from the NO _x absorbent 19 even if the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 19 is made rich. Therefore, when the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 18 is made rich, the SO _X absorbent 18
Absorbed SO in order to release SO _X from
As present in the absorbent in the state where no stable sulfates BaSO ₄ as it is generated either, or sulfate BaSO ₄ to be present in the absorbent in the form of ^- O _X is sulfate ion SO ₄ ² It is necessary to As the SO _X absorbent 18 that enables this, iron Fe, manganese Mn, nickel Ni, tin Sn, titanium T are formed on a carrier made of alumina.
An absorbent carrying at least one selected from transition metals such as i and lithium Li can be used. In this case, it has been found that the absorbent in which lithium Li is supported on a carrier made of alumina is most preferable.

In this SO _X absorbent 18, SO _X absorbent 1
When the air-fuel ratio of the exhaust gas flowing into 8 is lean, SO ₂ contained in the exhaust gas is absorbed in the absorbent in the form of sulfate ion SO ₄ ²⁻ while being oxidized on the surface of the absorbent, and then the absorbent. Diffused in. In this case, if platinum Pt is supported on the carrier of the SO _X absorbent 18, SO ₂ easily sticks to the platinum Pt in the form of SO ₃ ^2- , and thus SO ₂
Is easily absorbed in the absorbent in the form of sulfate ion SO ₄ ²⁻ . Therefore, in order to promote the absorption of SO ₂ , it is preferable to support platinum Pt on the carrier of the SO _X absorbent 18. As described above, when the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 18 becomes lean, the SO _X becomes SO _X absorbent 18
Therefore, the NO _x absorbent 19 provided downstream of the SO _x absorbent 18 absorbs only NO _x .

On the other hand, as described above, SO_XIn absorbent 18
SO absorbed_XIs sulfate ion SO _Four ^2-Inside the absorbent in the form of
Sulfate BaS that has diffused into or is unstable
O_FourHas become. Therefore SO_XFlowing into the absorbent 18
When the air-fuel ratio of exhaust gas becomes rich, SO_XIn absorbent 18
SO absorbed_XIs SO_XReleased from absorbent 18
Will be. NO at this time_xAbsorbent 19 to N
O_xIs released.

By the way, as described above, the NO _x absorbent 19
In reaction with NO ₂ on the platinum Pt surface is not present immediately ^- advances in the direction of _{(NO 3 → NO 2),} NO x is immediately released from the absorbent. When the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent 19 is made rich, NO ₂ on the platinum Pt surface is immediately reduced by HC and CO, so NO ₂ on the platinum Pt surface immediately disappears, and thus As shown in FIG. 6, NO _x is released from the NO _x absorbent 19 within a short time. That is, the NO _x release rate of the NO _x absorbent 19 is considerably high.

[0028] In contrast SO _X SO _X absorbed in the absorbent 18 is absorbed in _the NO _x absorbent 19 NO
_It is more stable than _x and is difficult to decompose, so this SO
Decomposition of _X does not occur unless the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 18 rich. That is, when the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 18 is made rich, SO
SO _X in the _X absorbent 18 is decomposed and released from the absorbent. This decomposition rate is considerably slow, and therefore, as shown in FIG. 6, even if the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 18 is made rich, it takes a long time compared to NO _X until the release of SO _X is completed. Will be required. That is, the SO _x release rate is considerably slower than the NO _x release rate.

On the other hand, decomposition of SO _X absorbed in the inside SO _X absorbent 18 is dependent on the temperature of the SO _X absorbent 18, the temperature of the SO _X absorbent 18 becomes hard to break down as low. Thus without non when SO _X is decomposed fuel ratio of the exhaust gas temperature of the SO _X absorbent 18 flows into the SO _X absorbent 18 as lower rich, SO _X is not released from the SO _X absorbent 18 and thus It will be. Figure 7 is SO
The relationship between the air-fuel ratio A / F of the inflowing exhaust gas where the _X absorbent 18 can release SO _X and the temperature T of the SO _X absorbent 18 is shown. To release SO _X from FIG 7 it can be seen that should the air-fuel ratio of the exhaust gas flowing into the more SO _X absorbent 18 temperature T of the SO _X absorbent 18 is lowered rich.

In the embodiment according to the invention, NO _x and SO
_The air-fuel mixture supplied to the combustion chamber 3 to release _X is periodically made rich, and FIG. 8 shows the timing at which the air-fuel mixture is made rich in this way. Note that in FIG. 8 P shows the timing of releasing the NO _x from the NO _x absorbent 19, Q is a timing for releasing SO _X from SO _X absorbent 18. As can be seen from FIG. 8, the period for enriching the air-fuel mixture to release NO _x from the NO _x absorbent 19 is quite short, and the air-fuel mixture is enriched once every few minutes. On the other hand, since the amount of SO _x contained in the exhaust gas is much smaller than the amount of NO _x , it takes a considerable time for the SO _x absorbent 18 to be saturated with SO _x . Therefore, the period for enriching the air-fuel mixture in order to release the SO _X from the SO _X absorbent 18 is considerably long, and the air-fuel mixture is enriched, for example, once every several hours.

By the way, inside the combustion chamber 3 as shown in FIG.
NO when the air-fuel ratio of the air-fuel mixture supplied to
_xIs NO in a short time_xReleased from absorbent 19,
SO _XSorbent 18 to SO_XBy the time is released
Takes more time. Therefore SO_XMixed to release
No time to keep feeling rich_xTo emit
Much longer than the time the mixture remains rich. An example
For example NO_xThe mixture is rich for several seconds when releasing
Whereas SO_XWhen releasing the
It will be rich for a few minutes. SO like this_XEmit
Sometimes the mixture becomes rich over a long period of time
SO like_XThe mixture is rich due to the release of
The fuel consumption increases drastically due to the long cycle
There is nothing to do.

FIG. 9 shows rich control of the air-fuel mixture when NO _x is released (P in FIG. 8). Note that Kt represents a correction coefficient for the basic fuel injection time TP. As shown in FIG. 9, when NO _x is to be released from the NO _x absorbent 19, the correction coefficient Kt is increased to KK (> 1.0) so that the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is increased. It is made rich and then kept in this rich state for C ₁ hour. Next, the correction coefficient Kt is gradually decreased, and then the correction coefficient Kt is maintained at 1.0, that is, the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is maintained at the stoichiometric air-fuel ratio. Next, when C ₂ hours have elapsed after the rich control was started, the correction coefficient Kt is made smaller than 1.0 again, and the combustion of the lean mixture is started again.

The air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is
NO when rich (Kt = KK) _xAbsorbed in absorbent 19
Most of the NO_xIs released rapidly. Corrector
Value of several KK and time C₁At this time O on platinum Pt₂
^-Or O^2-Consumed and all NO_xNeeded to reduce
Stipulated to generate a large amount of HC and CO
It In this case, the exhaust gas temperature rises and NO_xAbsorbent 1
The higher the temperature of 9, the more NO_xReleased from absorbent 19
NO_xThe amount of Therefore, as shown in FIG.
As described above, the value of the correction coefficient KK increases as the exhaust gas temperature T increases.
And the time C is increased as shown in FIG. 10 (B).₁
Is shortened as the exhaust gas temperature T increases. Note that the figure
Relationship between the correction coefficient KK shown in 10 (A) and the exhaust gas temperature T
And time C shown in FIG.₁And the exhaust gas temperature T
The relationship is stored in the ROM 32 in advance.

On the other hand, as described above, when the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 becomes rich (Kt = KK), N
Most of the NO _x absorbed in the O _x absorbent 19 is rapidly released, and after that, even if the air-fuel ratio is made rich, N
NO _x is released little by little from the O _x absorbent 19. Therefore, if the air-fuel ratio is kept rich, HC, CO
Will be released into the atmosphere. Therefore, as shown in FIG. 9, after the air-fuel ratio is made rich (Kt = KK), the degree of rich is gradually decreased, and then the air-fuel ratio is maintained at the stoichiometric air-fuel ratio (Kt = 1.0) to NO _x. The NO _x gradually released from the absorbent 18 is gradually reduced.

When the air-fuel ratio is made rich, NO _x
The amount of the NO _x amount of the NO _x released from the absorbent 19 is released from the more then _the NO _x absorbent 19 often less, therefore _the NO _x absorbent 19 is shorter the time until you release the NO _x I will get sick. As described above, the higher the exhaust gas temperature T, the larger the amount of NO _x released from the NO _x absorbent 19 when the air-fuel ratio is made richer, and therefore the amount shown in FIG.
As shown by 0 (C), the time C ₂ from when the air-fuel ratio is made rich to when it is returned to lean again is made shorter as the exhaust gas temperature T becomes higher. Note that the time C shown in FIG.
The relationship between ₂ and the exhaust gas temperature T is stored in the ROM 32 in advance.

In this way, KK, C ₁ and C ₂ are controlled according to the exhaust gas temperature T, and when the exhaust gas temperature T is high, the correction coefficient Kt changes in the pattern shown by the solid line in FIG. When is low, it changes in the pattern shown by the broken line in FIG. In this case, the air-fuel mixture hardly SO _X is released from the SO _X absorbent 18 to buy time for which a rich short, only _the NO _x releasing action from substantially _the NO _x absorbent 19 Done.

FIG. 11 shows the case of releasing SO _X (see FIG. 8).
Q) shows rich control of air-fuel mixture. As shown in FIG. 11, even when SO _X is to be released from the SO _X absorbent 18, the correction coefficient Kt is increased to KK (> 1.0) so that the air-fuel mixture supplied to the combustion chamber 3 becomes empty. The fuel ratio is made rich and then kept in this rich state for C ₁ hour. Next, the correction coefficient Kt is gradually decreased, and then the correction coefficient Kt is kept at Ko (> 1.0), that is, the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is kept rich. That is, when SO _X is to be released, first, the air-fuel mixture is greatly enriched to the first rich degree (Kt = KK), and thereafter, the first rich degree (Kt = KK).
The second rich degree (Kt = Ko) smaller than KK) is maintained. Next, when C ₂ hours have elapsed after the rich control was started, the correction coefficient Kt is made smaller than 1.0 again, and the combustion of the lean mixture is started again. In addition, SO
The time C ₂ for releasing _X is considerably longer than the time C ₂ for releasing NO _x shown in FIG. 9, and is, for example, about 3 to 10 minutes.

As described above, the S from the SO _x absorbent 18
The O _X release rate is considerably slow, and even if the air-fuel ratio of the air-fuel mixture is made extremely rich, the SO _X release rate does not increase in proportion thereto. That is, making the air-fuel ratio of the air-fuel mixture extremely rich only unnecessarily increases the fuel consumption amount. Therefore, when SO _X should be released, the air-fuel ratio of the air-fuel mixture is maintained at the lowest rich degree that can release NO _x satisfactorily, and this lowest rich degree is indicated by Ko in FIG. 11. Therefore, if the correction coefficient Kt is maintained at Ko, SO _X will be satisfactorily released from the SO _X absorbent 18. Nevertheless, when SO _X is to be released, the air-fuel mixture is first made extremely rich (Kt = KK). Next, the reason will be described.

SO_XCorrection coefficient Kt
If you keep Ko_XSO gradually from absorbent 18₂But
Is released. NO at this time_xAbsorbent 19 to NO
₂Is released, but because the degree of richness is small, NO_xSucking
NO from collecting agent 19₂Is gradually released. By the way
Like NO_xAbsorbent 19 to NO₂Is gradually released
SO when_XSO released from absorbent 18₂But
NO_xNO when flowing into the absorbent 19₂And SO₂Is anti
Response (SO₂+ NO₂→ SO₃+ NO), thus generated
SO₃Is SO_Four ^-In the form of NO_xAbsorbed in absorbent 19
Will be done. Such a reaction is NO₂Exist
Unless it exists, it does not occur, so NO_xSO in the absorbent 19
₂To prevent the absorption of SO_XAbsorbent 18
To SO ₂NO is released_xAbsorbent 19
To NO₂Need to be released. That
For SO as shown in FIG._XWhen to release
First, the air-fuel ratio of the air-fuel mixture is extremely rich (Kt =
KK).

That is, the air-fuel mixture is extremely rich (Kt = KK)
If set to NO_xAbsorbent 19 to most NO₂At once
Released, NO thereafter_xMost NO from absorbent 19
₂Is not released. Therefore, after that, the correction coefficient Kt becomes Ko.
SO when maintained_XReleased from absorbent 18
SO₂Is NO₂Does not react with SO ₂
Is NO_xThere is no risk of being absorbed by the absorbent 19.

As described above, when the air-fuel ratio of the air-fuel mixture becomes rich (Kt = KK), most of the NO _x absorbed in the NO _x absorbent 19 is rapidly released, at which time the exhaust gas temperature is high, Thus the amount of the NO _x which the temperature of _the NO _x absorbent 19 is released from the higher _the NO _x absorbent 19 is increased. Therefore, as shown in FIG.
The value of is increased as the exhaust gas temperature T increases, and
₁ becomes shorter as the exhaust gas temperature T increases. In addition,
The relationship between the correction coefficient KK and the exhaust gas temperature T shown in FIG. 12A and the relationship between the time C ₁ and the exhaust gas temperature T shown in FIG. 12B are stored in the ROM 32 in advance.

On the other hand, the air-fuel ratio of the air-fuel mixture is extremely rich (K
After t = KK), a relatively small rich degree (K
t = Ko), and at this time SO_XFrom absorbent 18
SO _XContinues to be released. At this time, as shown in FIG.
To SO_XThe temperature of the absorbent 18, that is, the exhaust gas temperature T becomes high.
The lower the air-fuel ratio A / F of the air-fuel mixture, the more SO_XEmit
You can keep it going. Therefore, in the embodiment according to the present invention,
Is the air-fuel ratio A / F of the air-fuel mixture as the exhaust gas temperature T increases.
Made smaller. That is, when the exhaust gas temperature T is high,
As shown by the solid line in 1, the value of Ko is relatively small.
If the exhaust gas temperature T is low, the
The value of Ko is made relatively large as indicated by the line. Figure
12 (C) shows the relationship between the value of Ko and the exhaust gas temperature T.
This relationship is stored in the ROM 32 in advance.
It

The air-fuel ratio of the air-fuel mixture is rich (Kt = K
The larger the amount of SO _X released from the SO _X absorbent 18 when maintained at o), the shorter the time until the SO _X absorbent 18 finishes releasing SO _X. As described above, the higher the exhaust gas temperature T, the faster the SO _X decomposition rate and the SO _X release rate. Therefore, FIG.
As shown in (3), the time C ₂ from when the air-fuel ratio is made rich to when it is returned to lean again is made shorter as the exhaust gas temperature T becomes higher. The relationship between the time C ₂ and the exhaust gas temperature T shown in FIG. 12D is stored in the ROM 32 in advance. As shown in FIGS. 10 and 12, each value KK, C
₁ , Ko and C ₂ are functions of the exhaust gas temperature T, and the exhaust gas temperature T is detected by the temperature sensor 21 in the embodiment according to the present invention. As described above, the exhaust gas temperature T can be directly detected, but can also be estimated from the intake air amount Q and the engine speed N. In this case, the relationship between the exhaust gas temperature T, the intake air amount Q, and the engine speed N is previously obtained by an experiment, and this relationship is preliminarily expressed in the form of a map as shown in FIG.
The exhaust gas temperature T may be calculated from this map by storing it in the OM 32.

Next, one embodiment of NO _x and SO _x absorption / release control according to the present invention will be described with reference to FIGS. 14 to 16. 14 and 15 show a routine for calculating the correction coefficient KK at the time of rich control, and this routine is executed by interruption at regular time intervals. Referring to FIGS. 14 and 15, first, at step 50, it is judged if the correction coefficient K is smaller than 1.0, that is, if the lean air-fuel mixture is burned. K <
When 1.0, that is, when the lean air-fuel mixture is being burned, the routine proceeds to step 51, where the NO _x amount Wn absorbed in the NO _x absorbent 19 is calculated. That is, the NO _x amount discharged from the combustion chamber 3 increases as the intake air amount Q increases and increases as the engine load Q / N increases, so the NO _x amount Wn absorbed by the NO _x absorbent 19 is Wn.
And k ₁ · Q · Q / N (k ₁ is a constant).

Next, at step 52, the SO _X absorbent 18
The SO _X amount Ws absorbed in is calculated. That is, the SO _X amount discharged from the combustion chamber 3 increases as the intake air amount Q increases, so the SO _X amount Wn absorbed by the SO _X absorbent 18 is Wn and k ₂ · Q (k ₂ is a constant). Will be represented by the sum of and. This SO _X amount Ws is stored in the backup RAM 33a. Then SO _X release flag indicating that should be released in SO _X step 53 whether it is set or not. SO _X release flag is whether _the NO _x releasing flag showing that should be released NO _x proceeds to step 54 is set when not been set or not. When the NO _x release flag is not set, the routine proceeds to step 55.

At step 55, SO_XAbsorbed in absorbent 18
Is SO_XThe amount W is a preset amount Wso
It is determined whether or not it is larger than that. This set amount Wso is an example
SO_XMaximum SO that the absorbent 18 can absorb_XQuantity of 30
It is about a percentage. When Ws ≤ Wso, step
Proceed to 61. NO in step 61_xAbsorbed in absorbent 19
Is NO_xThe amount Wn is a predetermined set amount Wno
Is determined to be greater than or equal to. This set amount Wno is
For example, NO_xMaximum NO that the absorbent 19 can absorb _xQuantity 3
It is about 0%. When Wn ≦ Wno, the processing support
Complete the ukule.

On the other hand, in step 55, Ws> Wso
If it is determined that the condition is
_{The X} emission flag is set. Next, at step 57, the correction coefficient KK is calculated from the relationship shown in FIG.
Next, at step 58, the time C ₁ is calculated from the relationship shown in FIG. Next, in step 59, FIG.
The correction coefficient Ko is calculated from the relationship shown in (C), and then in step 60, the time C ₂ is calculated from the relationship shown in FIG.
Is calculated. The processing cycle is then completed. In addition,
The SO _X release flag is set and each value KK, C ₁ , K
When o and C ₂ are calculated, the air-fuel mixture is made rich as described later.

On the other hand, in step 61, Wn> Wno
If it is determined to be NO, the process proceeds to step 62 and NO.
_{The X} emission flag is set. Next, at step 63, the correction coefficient KK is calculated from the relationship shown in FIG.
Next, at step 64, the time C ₁ is calculated from the relationship shown in FIG. Next, in step 65, the correction coefficient Ko is set to 1.0, and then in step 66, the correction coefficient Ko is set to the value shown in FIG.
The time C ₂ is calculated from the relationship shown in (C). The processing cycle is then completed. When the NO _X release flag is set and the respective values KK, C ₁ , Ko, C ₂ are calculated, the air-fuel mixture is made rich as will be described later.

When the SO _x release flag or the NO _x release flag is set, the routine proceeds from step 53 or step 54 to step 67 where the count value C is incremented by 1. Next, at step 68, the count value C is the time C.
_It is determined whether it is smaller than ₁ . When C <C ₁ , the processing cycle is completed, so the correction coefficient is kept at KK for the time C ₁ . Next, when C ≧ C ₁ , the routine proceeds to step 69, where it is judged if the count value C is smaller than the time C ₂ . When C <C ₂ , step 70
Then, the constant value α is subtracted from the correction coefficient KK. Therefore, the value of the correction coefficient KK gradually decreases.

Next, at step 71, the correction coefficient KK is K
It is determined whether or not it becomes smaller than o. KK> Ko
In the case of, the processing cycle is completed, and when KK ≦ Ko, the routine proceeds to step 72, where KK is made Ko. Therefore KK =
After it becomes Ko, if the SO _{X is} released, the correction coefficient is Ko.
(> 1.0), and the correction coefficient is maintained at 1.0 when NO _{x is} released.

Next, when it is judged at step 69 that C ≧ C ₂ , the routine proceeds to step 73, where it is judged if the SO _X release flag is set or not. SO
_{When the X} release flag is set, step 74
Then, the SO _x release flag is reset. When the SO _X release flag is reset, combustion of the lean mixture is started again as described later. Next, at step 75, S
The SO _X amount Ws absorbed by the O _X absorbent 18 is made zero, and then the NO _x amount Wn absorbed by the NO _X absorbent 19 is made zero at step 77. Next, the count value C is set to zero.

On the other hand, if it is determined at step 73 that the SO _X release flag is not set, then the routine proceeds to step 76, at which the NO _X release flag is reset. N
When the O _X release flag is reset, the combustion of the lean mixture is started again as described later. Then step 77
Amount of NO _x W that is absorbed in the NO _x absorbent 19 in
n is set to zero. Next, the count value C is set to zero.

On the other hand, when it is judged at step 50 that K ≧ 1.0, that is, when the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder is the stoichiometric air-fuel ratio or rich, the routine proceeds to step 79, where K ≧ 1. It is determined whether or not the state of 0 has continued for a certain time t ₁ , for example, 10 seconds. K ≧ 1.0
When the state of _No. has not continued for the fixed time t ₁ , the processing cycle is completed, and when the state of K ≧ 1.0 has continued for the constant time t ₁ , the routine proceeds to step 80, where Wn is made zero. That is, if the time period during which the air-fuel mixture supplied to the engine cylinder is at the stoichiometric air-fuel ratio or rich continues for about 10 seconds, NO
Most of the NO _x absorbed in the _x absorbent 19 is considered to have been released, so that Wn is made zero in step 80 in this case.

Next, at step 81, it is judged if the state of K> 1.0 has continued for a fixed time t ₂ (t ₂ > t ₁ ), for example, 10 minutes. The condition of K> 1.0 is a constant time t
_{2 If} not continued, complete the processing cycle and K>
When the state of 1.0 continues for a certain time t ₂ , the routine proceeds to step 82, where Ws is made zero. That is, it is considered that most of the SO _X absorbed in the SO _X absorbent 18 is released if the time period during which the air-fuel mixture supplied to the engine cylinder is rich is continued for about 10 minutes, and therefore, this SO _X is released. In this case, Ws is made zero in step 82.

FIG. 16 shows a routine for calculating the fuel injection time TAU, and this routine is repeatedly executed. Referring to FIG. 16, first, at step 90, the correction coefficient K is calculated. The correction coefficient K is set to, for example, 0.6 in the operating state where the lean air-fuel mixture should be burned.
Further, the correction coefficient K is a function of the engine cooling water temperature during the engine warm-up operation, and is made smaller as the engine cooling water temperature becomes higher in the range of K ≧ 1.0. The correction coefficient is set to 1.0 during acceleration operation, and the correction coefficient K is set to a value larger than 1.0 during full load operation.

Next, at step 91, the correction coefficient K is 1.
It is determined whether it is smaller than 0. When K ≧ 1.0, the routine proceeds to step 95, where K is set to Kt. On the other hand, when K <1.0, the routine proceeds to step 92, where it is judged if the SO _X release flag is set. SO
Step 9 when the _X release flag is not set
Then, the routine proceeds to step 3, where it is judged if the NO _x releasing flag is set. When the NO _x release flag is not set, the routine proceeds to step 95. Next, at step 96, the basic fuel injection time TP is calculated from the map shown in FIG. 2, and then at step 97, the fuel injection time TAU (= T
P · Kt) is calculated. Therefore, when K ≧ 1.0, or even when K <1.0, the SO _x release flag and NO _x are released.
When neither the release flag is set, the air-fuel ratio of the air-fuel mixture is set to the air-fuel ratio according to the correction coefficient K.

On the other hand, when the SO _x release flag or the NO _x release flag is set, the routine proceeds from step 92 or step 93 to step 94, where Kt is set to KK calculated by the routine shown in FIGS. 14 and 15. Next, through step 96, the fuel injection time TAU is calculated at step 97. Therefore, at this time, the air-fuel ratio of the air-fuel mixture is forcibly made rich.

FIG. 17 shows another embodiment. In this embodiment, the same components as those of the embodiment shown in FIG. 1 are designated by the same reference numerals. As shown in FIG. 17, in this embodiment, the exhaust manifold 16 is connected to the inlet of the casing 41 containing the SO _x absorbent 40, and the outlet of the casing 40 contains the NO _x absorbent 43 via the exhaust pipe 42. Casing 4
4 is connected to the inlet part. NO with SO _X is absorbed in the SO _X absorbent 40 when the lean air-fuel mixture is burned in the combustion chamber 3 in this embodiment
NO _x is absorbed by the _x absorbent 43. On the other hand, when the air-fuel mixture supplied into the combustion chamber 3 is made rich, the SO _X absorbent 4
SO _x is released from 0, NO _x absorbent 43 from NO _x
Is released.

[0059]

EFFECT OF THE INVENTION Even if a NO _x absorbent is used for a long time, NO _x
The high NO _x absorption capacity of the absorbent can be maintained.
Also, the degree of rich at this time is smaller as the temperature of the SO _X absorbent becomes higher when the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent to be released SO _X is rich. Therefore, it is possible to reduce the fuel consumption amount by the extent that the degree of richness is reduced.

[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 showing changes in a correction coefficient K.

FIG. 4 HC and C in exhaust gas emitted from the engine
It is a diagram which shows the concentration of O and oxygen roughly.

FIG. 5 is a diagram for explaining the action of absorbing and releasing NO _x .

FIG. 6 is a graph showing SO _x and NO _x release rates.

FIG. 7 is a graph showing SO _X release characteristics.

FIG. 8 is a diagram showing SO _x and NO _x release timings.

FIG. 9 is a diagram showing rich control at the time of releasing NO _x .

FIG. 10 is a diagram showing a relationship between various parameters and exhaust gas temperature.

FIG. 11 is a diagram showing rich control at the time of SO _X release.

FIG. 12 is a diagram showing a relationship between various parameters and exhaust gas temperature.

FIG. 13 is a diagram showing a map of exhaust gas temperature.

FIG. 14 is a flowchart for calculating a correction coefficient KK.

FIG. 15 is a flowchart for calculating a correction coefficient.

FIG. 16 is a flowchart for calculating a fuel injection time TAU.

FIG. 17 is an overall view showing another embodiment of the internal combustion engine.

[Explanation of symbols]

16 ... exhaust manifold 18, 40 ... SO _X absorbent 19,43 ... NO _x absorbent

Claims (1)

[Claims] 1. A absorbs NO _x when the air-fuel ratio of the inflowing exhaust gas is lean, the engine exhaust to _the NO _x absorbent to release the NO _x absorbed to decrease the oxygen concentration in the exhaust gas flowing while disposed within the passage, to absorb SO _X when the air-fuel ratio of the inflowing exhaust gas is lean, the air-fuel ratio of the inflowing exhaust gas is absorbed and becomes rich SO _X
SO in the exhaust gas discharged into the engine exhaust passage when the lean air-fuel mixture to SO _X absorbent disposed in _the NO _x absorbent in the engine exhaust passage upstream of the are burned releasing
Absorbs _X in SO _X absorbent and NO _{x in} exhaust gas
It was absorbed in _the NO _x absorbent, the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent and _the NO _x absorbent in when releasing the NO _x from the NO _x absorbent with releasing SO _X from SO _X absorbent An exhaust gas purification device for an internal combustion engine, which is made rich and is made smaller at this time as the temperature of the SO _X absorbent increases.