JP3203931B2 - 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 purifying apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art When the air-fuel ratio of inflowing exhaust gas is lean,
NO_xAnd the air-fuel ratio of the exhaust gas
NO absorbed at stoichiometric air-fuel ratio or rich_xEmit
NO _xThe absorbent is placed in the engine exhaust passage, and NO_xabsorption
NO from agent_xWhen it should be released into the engine cylinder.
The air-fuel ratio of the supplied mixture is changed from lean to stoichiometric or
Switch for a predetermined period of time, and then
An internal combustion engine that returns the air-fuel ratio to lean again is known.
is there.

[0003] However since in the lubricating oil of the fuel and the engine contains sulfur, the exhaust gas contains SO _x, this SO _x is absorbed in _the NO _x absorbent with NO _x. However, this SO _x is NO air-fuel ratio of the exhaust gas flowing into _x absorbent when the temperature of the NO _x absorbent even if the rich low is not released from the NO _x absorbent, therefore NO _x SO in absorbent The amount of _x will gradually increase. However the amount of the NO _x when the amount of the SO _x in the absorber increases _the NO _x absorbent can absorb NO _x is decreased gradually,
Eventually, the NO _x absorbent can hardly absorb NO _x .

[0004]_xWhen the temperature of the absorbent rises
NO_xRich air-fuel ratio of exhaust gas flowing into absorbent
And NO_xAbsorbent to SO_xWas released
An internal combustion engine has already been proposed by the present applicant (Japanese Patent Application
5-162778). NO_xAbsorbed by absorbent
SO_xEstimate the quantity, this SO_xThe amount is acceptable
When exceeding, NO by electric heater_xThe temperature of the absorbent
Raise and NO _xExhaust gas empties into the absorbent
NO with rich fuel ratio_xAbsorbent to SO_xRelease
The proposed internal combustion engine has already been proposed by the applicant.
(See Japanese Patent Application No. 4-216145).

[0005]

[0005] Meanwhile high temperature of the NO _x absorbent is regardless of the amount of SO _x is absorbed in the NO _x absorbent in the internal combustion engine described in JP above Hei 5-162778 If possible, the air-fuel ratio of the exhaust gas flowing into the NO _x absorbent is made rich. Thus the air-fuel ratio when even the exhaust gas NO _x almost SO _x absorption agent is not absorbed is to be made rich, the fuel consumption means that the waste fuel is consumed in such a case Is increased.

On the other hand, always electric heater is caused to heat when the internal combustion engine described in Japanese Patent Application No. 4-216145 described above should be released NO _x from the NO _x absorbent. However, if the temperature of the NO _x absorbent is originally high, is released SO _x purposely from _the NO _x absorbent even without heating the electric heater, thus wasteful power consumption for heating the electric heater in an internal combustion engine There is a problem that is.

[0007]

[0008]

[0009]

In order to solve the above problems, according to the present invention SUMMARY OF THE INVENTION The air-fuel ratio of the exhaust gas flowing absorbs NO _x when the lean air-fuel ratio is the stoichiometric air of the exhaust gas flowing in fuel ratio or an internal combustion engine arranged to _the NO _x absorbent to release the absorbed NO _x in the engine exhaust passage when the rich, and amount of SO _x estimating means for estimating the amount of SO _x is absorbed in the NO _x absorbent, temperature detecting means for detecting a representative temperature representing the temperature of the NO _x absorbent, the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent is absorbed in _the NO _x absorbent when the lean or the stoichiometric air-fuel ratio and heating means for raising the temperature of the NO _x absorbent when amount of SO _x is allowable amount exceeding and representative temperature is lower than a predetermined set temperature estimated, the temperature of the NO _x absorbent is the temperature increase device When the temperature rises O and _x air-fuel ratio of the exhaust gas flowing into the absorbent rich temporarily are provided with air-fuel ratio control means for releasing the SO _x from _the NO _x absorbent.

Further, when in order to solve the above problems, according to the present invention, does not exceed the temperature at which the temperature is representative temperature be allowed Atsushi Nobori predetermined of the NO _x absorbent by the above-mentioned Atsushi Nobori means Prohibition means is provided for prohibiting rich control of the air-fuel ratio by the air-fuel ratio control means. Further, in order to solve the above problems, according to the present invention, the air-fuel ratio of the inflowing exhaust gas absorbs the NO _x when the lean air-fuel ratio of the inflowing exhaust gas absorbed when the stoichiometric air-fuel ratio or rich in an internal combustion engine arranged to _the NO _x absorbent to release the NO _x in the engine exhaust passage, the amount of SO _x estimating means for estimating the amount of SO _x is absorbed in the NO _x absorbent, NO _x
Temperature detecting means for detecting a representative temperature representing the temperature of the absorbent, SO _x amount when the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent is estimated to be absorbed in _the NO _x absorbent when the rich There when exceeding the allowable amount and representative temperature is lower than the set temperature predetermined are and a Atsushi Nobori means for raising the temperature of the NO _x absorbent.

Furthermore, in order to solve the above problems, according to the present invention, heating means described above is to increase the temperature of the NO _x absorbent by retarding the ignition timing.

[0012]

[0013]

[Action] In the first invention, NO when the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent is lean or the stoichiometric air-fuel ratio
temperature of the NO _x absorbent when _the amount of SO _x estimated to be absorbed in the _x absorbent is lower than the set temperature representative temperature is predetermined to represent a temperature of exceeding the permissible amount and _the NO _x absorbent is The air-fuel ratio of the exhaust gas which is raised and flows into the NO _x absorbent is temporarily made rich, and at this time, SO _x is released from the NO _x absorbent.

[0014] In the second invention, the air-fuel ratio is not rich temporarily when the representative temperature even if the temperature is made to increase the temperature of _the NO _x absorbent does not exceed a predetermined temperature.
In the third invention, SO _x amount when the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent is estimated to be absorbed in _the NO _x absorbent when the rich exceeds the permissible amount and _the NO _x absorbent When the representative temperature representing the temperature is lower than a predetermined set temperature, the temperature of the NO _x absorbent is increased, and at this time, SO _x is released from the NO _x absorbent. No.
In the fourth invention, NO is set by retarding the ignition timing.
_x The temperature of the absorbent is increased.

[0015]

Referring to FIG. 1, 1 is an engine body, 2 is a piston, 3 is a combustion chamber, 4 is a spark plug, 5 is an intake valve, 6 is an intake port, 7 is an exhaust valve, and 8 is an exhaust port. Show. The intake port 6 is connected to a surge tank 10 via a corresponding branch pipe 9, and a fuel injection valve 11 for injecting fuel into the intake port 6 is attached to each branch pipe 9. The surge tank 10 is connected to an air cleaner 13 via an intake duct 12, and a throttle valve 14 is arranged in the intake duct 12. On the other hand, the exhaust port 8 is connected via an exhaust manifold 15 and an exhaust pipe 16 to a casing 17 containing a NO _x absorbent 18.

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 an input port 35 mutually connected by a bidirectional bus 31. And an output port 36. A pressure sensor 19 that generates an output voltage proportional to the absolute pressure in the surge tank 10 is disposed in the surge tank 10, and the output voltage of the pressure sensor 19
The data is input to the input port 35 via the D converter 37. A throttle switch 20 that is turned on when the throttle opening reaches an idling opening is attached to the throttle valve 14, and an output signal of the throttle switch 20 is input to an input port 35. An air-fuel ratio sensor 21 is disposed in the exhaust manifold 15, and an output voltage of the air-fuel ratio sensor 21 is input to an input port 35 via a corresponding AD converter 37. An exhaust temperature sensor 22 that generates an output voltage proportional to the temperature of exhaust gas flowing through the exhaust pipe 16 is mounted in the exhaust pipe 16 near the input portion of the casing 17.
The output voltage of the exhaust gas temperature sensor 22 is input to the input port 35 via the corresponding AD converter 37. Engine body 1
A water temperature sensor 23 that generates an output voltage proportional to the engine cooling water temperature is attached to the input port. The output voltage of the water temperature sensor 23 is input to an input port 35 via a corresponding AD converter 37. The input port 35 is connected to a rotation speed sensor 24 that generates an output pulse indicating the engine rotation speed. On the other hand, the output port 36 is connected to the ignition plug 4 and the fuel injection valve 11 via a corresponding drive circuit 38, respectively.

In the internal combustion engine shown in FIG. 1, the fuel injection time TAU is calculated based on, for example, the following equation. TAU = f · TP · K · FAF where f is a constant, TP is a basic fuel injection time, K is a correction coefficient, and FAF is a feedback correction coefficient. The basic fuel injection time TP indicates a fuel injection time required for setting the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder to the stoichiometric air-fuel ratio. The basic fuel injection time TP is obtained by an experiment in advance, and is stored in advance in the ROM 32 as a function of the absolute pressure PM in the surge tank 10 and the engine speed N in the form of a map as shown in FIG. The correction coefficient K is a coefficient for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder. If K = 1.0, the air-fuel mixture supplied to the engine cylinder becomes the stoichiometric air-fuel ratio. On the other hand, K <
At 1.0, the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder becomes larger than the stoichiometric air-fuel ratio, that is, lean, and when K> 1.0, the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder becomes empty. The fuel ratio becomes smaller than the stoichiometric air-fuel ratio, that is, becomes rich.

The feedback correction coefficient FAF is basically equal to the output signal of the air-fuel ratio sensor 21 when K = 1.0, that is, when the air-fuel ratio of the air-fuel mixture supplied to the engine cylinder is to be the stoichiometric air-fuel ratio. It is a coefficient for making the air-fuel ratio accurately match the stoichiometric air-fuel ratio based on the above. The feedback correction coefficient FAF moves up and down about 1.0.
This FAF decreases when the mixture becomes rich, and increases when the mixture becomes lean. In addition, K <1.0 or K>
When it is 1.0, the FAF is fixed at 1.0.

The target air-fuel ratio of the air-fuel mixture to be supplied into the engine cylinder, that is, the value of the correction coefficient K is changed according to the operating condition of the engine. In the embodiment according to the present invention, the correction coefficient K after the completion of warm-up is set. Is predetermined in the surge tank 10 as a function of the absolute pressure PM and the engine speed N as shown in FIG. That is, as shown in FIG. 3, in the low-load operation region on the lower-load side than the solid line R, K <
1.0, that is, the air-fuel mixture is lean, and in the high load operation region between the solid line R and the solid line S, K = 1.0, that is, the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio, and the load is higher than the solid line S. In the full load operation region on the side, K> 1.0, that is, the air-fuel mixture is made rich. Further, during idling operation, K = 1.0, that is, the stoichiometric air-fuel ratio.

On the other hand, the correction coefficient K is changed according to the engine cooling water temperature TW before the completion of the warm-up, as shown in FIG. That is, the warm-up before completion (TW <TW _o) The lower the engine coolant temperature TW correction coefficient K (K ≧ 1.0) is large. Before the completion of warm-up (TW <TW _o ), the correction coefficient K is calculated from the relationship shown in FIG.
For TW _o ), the correction coefficient K is calculated from the relationship shown in FIG.

The optimum ignition timing θ has been determined in advance by an experiment as a function of the absolute pressure PM in the surge tank 10 and the engine speed N. The optimum ignition timing θ is shown in the form of a map as shown in FIG. It is stored in the ROM 32 in advance.
FIG. 6 schematically shows the concentrations of representative components in the exhaust gas discharged from the combustion chamber 3. As can be seen from FIG. 6, the concentration of unburned HC and CO in the exhaust gas discharged from the combustion chamber 3 increases as the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 increases, and the concentration of the exhaust gas from the combustion chamber 3 increases. 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 contained in casing 17_x
The absorbent 18 uses, for example, alumina as a carrier, and on this carrier,
For example, potassium K, sodium Na, lithium Li,
Alkali metals such as Cs, barium Ba, cal
Alkaline earths such as calcium Ca, lanthanum La,
At least one selected from rare earths such as thorium Y
And a noble metal such as platinum Pt. organ
Intake passage and NO_xProvided in the exhaust passage upstream of the absorbent 18
The ratio of supplied air and fuel (hydrocarbon) is set to NO _xabsorption
When this is referred to as the air-fuel ratio of the exhaust gas flowing into the agent 18, this NO_x
When the air-fuel ratio of the inflowing exhaust gas is lean, the absorbent 18
NO_xAnd reduce the oxygen concentration in the incoming exhaust gas
And absorbed NO_xReleases NO_xPerform the absorption and release action of
U. Note that NO_xFuel in the exhaust passage upstream of the absorbent 18
(Hydrocarbons) or inflow and exhaust when air is not supplied
The air-fuel ratio of the gas-gas is the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3.
Ratio, and in this case NO_xAbsorbent 18 burns
When the air-fuel ratio of the mixture supplied to the firing chamber 3 is lean
Is NO_xIn the air-fuel mixture supplied into the combustion chamber 3
NO absorbed when oxygen concentration decreases_xTo release
Become.

If the above-mentioned NO _x absorbent 18 is arranged in the exhaust passage of the engine, the NO _x absorbent 18 actually acts to absorb and release NO _x , but the detailed mechanism of the absorption and release action is not clear. There is also. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, when the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is made lean and the inflowing exhaust gas becomes lean, the oxygen concentration in the inflowing exhaust gas greatly increases, and FIG. these oxygen O ₂ as shown is O ₂ ^- or O ^{2 -} is in the form of adhering to the surface of the platinum Pt. Meanwhile, O ₂ NO in the inflowing exhaust gas on the surface of the platinum Pt ^- or reacts with O ^2-, N
O ₂ (2NO + O ₂ → 2NO ₂ ). Next, a part of the generated NO ₂ is absorbed in the absorbent while being oxidized on the platinum Pt, and combined with the barium oxide BaO as shown in FIG.
Nitrate ions NO as shown in (A) ₃ ^- is diffused in the absorbent in the form of. In this way, NO _x is absorbed in the NO _x absorbent 18.

As long as the oxygen concentration in the incoming exhaust gas is high, platinum
NO on Pt surface_TwoIs generated, and the NO_xAbsorption capacity
NO unless power is saturated_TwoIs absorbed in the absorbent and nitric acid
Ion NO_Three ^-Is generated. In contrast, the inflow exhaust gas
NO in the oxygen concentration in the_TwoWhen the amount of
The reaction is reversed (NO_Three ^-→ NO_Two) And thus suck
Nitrate ion NO in the collector_Three ^-Is NO_TwoFrom the absorbent in the form of
Released. That is, the oxygen concentration in the inflow exhaust gas decreases.
NO_xNO from absorbent 18_xWill be released
You. As shown in FIG. 6, the degree of lean of the incoming exhaust gas
Lower the oxygen concentration in the incoming exhaust gas
If the degree of leanness of the inflow exhaust gas is reduced,
NO even if the air-fuel ratio of the exhaust gas is lean_xAbsorbent 18
From NO _xWill be released.

On the other hand, at this time, the mixture supplied into the combustion chamber 3 is
The air-fuel ratio of aiki is enriched and the air-fuel ratio of
When it becomes rich, as shown in FIG.
The unburned HC and CO are discharged, and the unburned HC and CO are white.
Oxygen O on gold Pt_Two ^-Or O ^2-Reacts with and oxidizes
It is. Also, when the air-fuel ratio of the inflowing exhaust gas becomes rich,
The oxygen concentration in the exhaust gas is extremely low,
From NO_TwoIs released and this NO_TwoIs shown in FIG.
Reacts with unburned HC and CO to reduce
You. In this way, NO on the surface of platinum Pt_TwoExists
When exhausted, NO from the absorbent one after another_TwoIs released
You. Therefore, if the air-fuel ratio of the inflow exhaust gas is made rich,
NO in between_xNO from absorbent 18_xIs released
And

That is, the air-fuel ratio of the inflowing exhaust gas is made rich.
First, unburned HC and CO are converted to O on platinum Pt._Two ^-or
Is O^2-And immediately oxidized, then platinum
O on Pt_Two ^-Or O^2-Is consumed but unburned HC,
If CO remains, this unburned HC and CO will absorb
NO released from_xAnd NO emitted from the engine _x
Is reduced. Therefore, the air-fuel ratio of the inflow exhaust gas is reset.
NO in a short time_xAbsorbed by absorbent 18
NO_xIs released, and the released NO
_xNO in the atmosphere due to reduction_xIs discharged
It can be blocked. NO_xAbsorbent
18 has a function of a reduction catalyst, so that
NO even if the air-fuel ratio is stoichiometric_xReleased from absorbent 18
NO_xIs reduced. However, inflow and exhaust
NO if the air-fuel ratio of the gas is the stoichiometric air-fuel ratio_xabsorption
NO from agent 18_xIs released only gradually
_xTotal NO absorbed in absorbent 18_xTo release
Takes a little longer.

As described above, when the lean air-fuel mixture is burned, NO _x is absorbed by the NO _x absorbent 18. However there is a limit to the absorption of NO _x capacity of the NO _x absorbent 18, _the NO _x absorbent 18 when saturation absorption of NO _x capacity of the NO _x absorbent 18 is not E longer absorb NO _x.
Therefore NO absorption _of NO _x capacity of the _x absorbent 18 must be released the NO _x from the NO _x absorbent 18 before the saturation, how much to _the NO _x absorbent 18 to the NO _x
Needs to be estimated. Then this N
A method for estimating the O _x absorption amount will be described.

[0029] is _the amount of NO _x absorbed per unit time per _the NO _x absorbent 18 to _the amount of NO _x discharged from the higher unit time per engine becomes higher the engine load increases when the lean air-fuel mixture is burned Increases and the higher the engine speed, the more NO is discharged from the engine per unit time.
NO _{x to x} amount is absorbed per unit time _the NO _x absorbent 18 in order to increase is increased. Therefore, NO per unit time
amount of NO _x absorbed in the _x absorbent 18 becomes a function of the engine load and the engine speed. In this case, the engine load is absolute pressure PM and the engine speed N of the absolute amount of NO _x that have at pressure representative absorbed in unit time per _the NO _x absorbent 18 since it is the surge tank 10 in the surge tank 10 Is a function of Therefore, in the embodiment according to the present invention, NO _x per unit time
Absolute pressure PM of the amount of NO _x NOXA that is absorbed by the absorbent 18
And as a function of the engine speed N obtained by experiments in advance,
Figure this amount of NO _x NOXA as a function of PM and N 8
It is stored in the ROM 32 in advance in the form of a map shown in FIG.

Meanwhile, although the air-fuel ratio of the mixture fed into the engine cylinder NO _x is released from the NO _x absorbent 18 becomes the stoichiometric air-fuel ratio or rich _the NO _x releasing amount at this time primarily exhaust gas Affected by volume and air-fuel ratio. That is, NO of _the amount of NO _x amount exhaust gas is discharged from the higher per unit time _the NO _x absorbent 18 increases increases, the air-fuel ratio is discharged from the higher per unit time _the NO _x absorbent 18 becomes rich
_x amount increases. In this case, the amount of exhaust gas, that is, the amount of intake air, can be represented by the product of the engine speed N and the absolute pressure PM in the surge tank 10. Therefore, as shown in FIG. _the amount of NO _x NOXD released from _the NO _x absorbent 18 increases as N · PM increases. Further, since the air-fuel ratio corresponds to a value of the correction coefficient K NO _x amount NOXD released from per unit time _the NO _x absorbent 18 as shown in FIG. 8 (C) increases as the value of K increases I do. _The amount of NO _x NOXD released from the unit time per _the NO _x absorbent 18 in advance in the form of a map shown in FIG. 9 (A) as a function of N · PM and K ROM 3
2 is stored.

Further, _the NO _x absorbent 18 nitrate ions NO ₃ and the absorbent temperature is high in ^- that _the NO _x releasing rate from _the NO _x absorbent 18 is increased so easily decomposed. In this case, since the temperature of the NO _x absorbent 18 is almost proportional to the exhaust gas, the NO _x release rate Kf as shown in FIG.
Increases as the exhaust gas temperature TE increases. Therefore N
When the O _x release rate Kf is taken into consideration, N
Amount of NO _x released from the O _x absorbent 18 will be represented by the product of the NOXD and _the NO _x releasing factor Kf shown in FIG. 9 (A).

As described above, the lean mixture burns.
NO per unit time _xNOXA absorption
And a mixture of stoichiometric air-fuel ratio or rich mixture
NO per unit time when burned_xThe amount released
NO because it is expressed by Kf · NOXD_xAbsorbed by absorbent 18
NO presumed to be collected_xThe quantity ΣNOX is expressed by the following equation.
Will be forgotten.

ΣNOX = ΣNOX + NOXA−Kf · NOXD As described above, when the lean air-fuel mixture (K <1.0) is being burned, NO _x is absorbed by the NO _x absorbent 18 and the stoichiometric air-fuel mixture ( K = 1.0) or N when rich mixture (K> 1.0) is being burned.
NO _x is released from the O absorbent 18. Therefore NO lean mixture when the air-combustion is continued _the NO _x absorbent 18
_x Absorption capacity will be saturated. Therefore, in this embodiment of the present invention exceeded the allowable amount N _max of _the amount of NO _x ΣNOX the lean mixture combustion is absorbed continuously performed in _the NO _x absorbent 18 is predetermined as shown in FIG. 10 In this case, the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is made rich. If the air-fuel ratio of the air-fuel mixture is made rich, NO _x is released from the NO _x absorbent 18, so that ΣNOX decreases sharply, and ΣNOX decreases to the lower limit N _min.
When the air-fuel ratio of the mixture decreases, the air-fuel ratio returns to lean again.

However, the exhaust gas contains SO _x , and the SO _x absorbent 18 contains not only NO _x but also SO _x
Is also absorbed. Absorption mechanism of the SO _x to the _the NO _x absorbent 18 is considered to be the same as the mechanism of absorption of NO _x. That is, assuming that platinum Pt and barium Ba are supported on the carrier as in the case of describing the NO _x absorption mechanism, as an example, when the air-fuel ratio of the inflowing exhaust gas is lean as described above, oxygen O ₂ Is O ₂
^- is attached to the surface of the platinum Pt in the form of inflow exhaust SO ₂ in the gas is O ₂ on the surface of the platinum Pt ^- reacts with SO ₃
Becomes Next, the generated SO ₃ is further oxidized on the platinum Pt, is absorbed in the absorbent, and is bonded to barium oxide BaO, and diffuses into the absorbent in the form of sulfate ions SO ₄ ^2- . Next, this sulfate ion SO ₄ ^2- is combined with barium ion Ba ²⁺ to form sulfate BaSO ₄ .

However, the sulfate BaSO ₄ hardly decomposes, and when the temperature of the NO _x absorbent 18 is low, NO
_{Even when} the air-fuel ratio of the exhaust gas flowing into the _x absorbent 18 is made rich, the sulfate BaSO ₄ remains without being decomposed. Therefore NO _x in absorbent 18 hours will be sulfate BaSO ₄ increases as elapses, thus _the NO _x absorbent 18 as to time has elapsed can absorb NO _x
The amount will be reduced. Therefore, it is necessary to release SO _x from the NO _x absorbent 18 before the amount of NO _x that can be absorbed by the NO _x absorbent 18 does not decrease so much. For that purpose, how much SO _x is absorbed by the NO _x absorbent 18 It is necessary to estimate what is being done. Next, an example of a method for estimating the SO _x absorption amount will be described.

NO_xWhen the temperature of the absorbent 18 is low,
The rich mixture will burn even if the
SO even if burned_xIs NO_xAbsorbed by absorbent 18
Will be collected. At this time, as the fuel injection amount increases, the unit time
SO emitted from the hit engine _xUnits for increasing quantity
NO per hour_xSO absorbed by the absorbent 18_xIncrease volume
The higher the engine speed, the higher the engine speed per unit time.
SO discharged from_xN per unit time due to increased volume
O_xSO absorbed by the absorbent 18_xIncrease. Therefore
NO per unit time_xSO absorbed by the absorbent 18_xQuantity S
As shown in FIG. 11 (A), OXA
Fuel injection time / engine speed).

On the other hand, NO_xWhen the temperature of the absorbent 18 is high
Rich in the air-fuel ratio of the mixture supplied to the engine cylinder
NO when_xAbsorbent 18 to SO_xIs released
SO at_xEmissions mainly depend on exhaust gas volume and air-fuel ratio
Receive. That is, as the amount of exhaust gas increases,
No_xSO released from absorbent 18_xThe amount increases,
NO per unit time as the air-fuel ratio becomes richer_xAbsorbent 1
SO released from 8 _xThe amount increases. In this case, the exhaust
The gas amount, that is, the intake air amount, depends on the engine speed N and the surge tank.
It can be represented by the product of the absolute pressure PM in 10
And therefore, as shown in FIG.
NO_xSO released from absorbent 18_xThe quantity SOXD is N
-Increases as PM increases. The air-fuel ratio is corrected
Since it corresponds to the value of coefficient K, it is shown in FIG.
NO per unit time_xS released from the absorbent 18
O_xThe quantity SOXD increases as the value of K increases. This
NO per unit time_xSO released from absorbent 18_x
The quantity SOXD is shown in FIG.
It is stored in the ROM 32 in advance in the form of a map shown.

As described above, NO_xAbsorbent 18
BaSO produced in the process _FourIs difficult to disassemble
NO_xThe temperature of the absorbent 18 is NO_xDetermined by absorbent 18
Set temperature TE_oDecomposes, for example, above 450 ° C
Sulfate ion SO_Four ^2-Is SO_ThreeReleased from the absorbent in the form of
You. In this case, NO_xAbsorbent 18 temperature is 450 ° C or higher
NO_xThe higher the temperature of the absorbent 18, the more NO_x
SO released from absorbent 18_xThe amount increases. Place
In this case, NO_xThe temperature of the absorbent 18 is the exhaust gas temperature TE
As shown in FIG. 12B,
Sea urchin SO_xThe release rate Kg is TE <TE_oIs zero and T
E ≧ TE_oBecomes larger as the exhaust gas temperature TE increases.
It becomes. Therefore SO_xIf the release rate Kg is taken into account
Is NO per unit time_xSO released from absorbent 18_x
The amounts are SOXD and SO shown in FIG._xRelease rate K
It will be expressed by the product with g.

The SO _x absorption amount per unit as described above time is represented by SOXA, SO _x release amount per unit time to be absorbed in _the NO _x absorbent 18 so represented by Kg · SOXD estimate amount of SO _x ΣSOX to be will be represented by the following equation. ΣSOX = ΣSOX + SOXA-Kg · SOXD estimated absorption amount ShigumaSOX of this SO _x is the estimated weight determined quite precisely. Therefore if it does not so much require stringency it can also be used operating time of the running distance and the engine of the vehicle as an estimated absorption amount ΣSOX of SO _x.

Next, referring to FIG. 13 to FIG._x
The method for releasing methane will be described. Figure 13 shows the lean mixture
SO during combustion_xThe amount ΣSOX is the allowable amount S
_maxAt this time, the exhaust gas temperature TE becomes equal to the set temperature TE._o
It shows the case where it is higher than. TE ≧ TE_oWhen
NO if the air-fuel ratio of the mixture is rich_xFrom absorbent 18
SO_xIs released. Therefore, in this case, SO_xQuantityΣS
OX is the allowable amount S_{ma x}If the air-fuel ratio of the mixture exceeds
Switching is made slightly richer than the fuel ratio. Air-fuel ratio of mixture
NO if slightly rich_xAbsorbent 18 to SO_xRelease
ΣSOX is reduced, and SO_xΣSOX is lower
Limit S_minWhen the air-fuel ratio of the mixture decreases to
Is returned to.

As can be seen from FIG. 11C, when the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio, the NO _x absorbent 18
_x is not released from _the NO _x absorbent 18 to release the SO _x must make the air-fuel ratio of the mixture rich. However the air-fuel ratio of the mixture of air-fuel ratio of the mixture so much from the standpoint of fuel consumption since not SO _x is released also in proportion to it by the rich care be slightly richer than the stoichiometric air-fuel ratio It will be preferable. Therefore, in the embodiment according to the present invention, as shown in FIG.
When O _x is to be released, the air-fuel ratio of the air-fuel mixture is maintained slightly rich.

FIG. 14 shows the combustion of a lean mixture.
Sometimes SO_xThe amount ΣSOX is the allowable amount S _maxAnd this
Exhaust gas temperature TE is the set temperature TE_oIndicates lower than
are doing. TE <TE_oThe air-fuel ratio of the mixture
NO_xAbsorbent 18 to SO_xIs released
No, NO_xAbsorbent 18 to SO_xIn order to release
SO_xThe temperature of the absorbent 18 must be increased. So
Here, in the embodiment according to the present invention, at this time, the ignition timing θ is retarded.
To increase the exhaust gas temperature,
NO_xThe temperature of the absorbent 18 is raised.

When the ignition timing θ is delayed when the stoichiometric air-fuel mixture or the rich air-fuel mixture is being burned, the normal exhaust gas temperature TE rises, but when the lean air-fuel mixture is being burned, the ignition timing θ is increased. Is delayed, the possibility of misfire is high. Therefore, when the lean air-fuel mixture is being burned, the ignition timing θ cannot be retarded. Also, the low and medium during load operation the lean air-fuel mixture is burned in some cases that do not also TE> TE _o as likened retarded spark timing θ due to the low amount of heat generated by combustion. Therefore, in this embodiment of the present invention of absorption of NO _x and slightly richer than the stoichiometric air-fuel ratio of the mixture as well as retarding the ignition timing θ when became ΣSOX ≧ S _max as indicated by the solid line in FIG. 14 so that to release sO _x, then returned to the air-fuel ratio of the mixture is again lean becomes ΣSOX ≦ S _min from agents 18. The ignition timing when the contrast ignition timing θ is retarded and the air-fuel ratio of the mixture does not become TE> TE _o slightly Over Time Δt as indicated by the chain line in FIG. 14 be rich The ignition timing is returned to the original timing after the retard control of θ is stopped, and at this time, the air-fuel ratio of the air-fuel mixture is returned to lean as indicated by the chain line. That is, in this case, the rich control of the air-fuel ratio is prohibited.

[0044] Figure 15 is amount of SO _x ΣSOX when the doing the combustion of the air-fuel mixture of the theoretical air-fuel ratio allowance S _max, and the
At this time the exhaust gas temperature TE indicates a higher than the set temperature TE _o. When the TE ≧ TE _o is SO _x is released from the NO _x absorbent 18 when the air-fuel ratio of the mixture rich. Thus the air-fuel ratio of the mixture and amount of SO _x ΣSOX in this case exceeds the permissible amount S _max is switched to the slightly richer than the stoichiometric air-fuel ratio. Since SO _x air-fuel ratio from _the NO _x absorbent 18 when slightly become rich air-fuel mixture is discharged ΣSOX decreases, SO _x amount ΣSOX is a lower limit amount S _min decreases the air-fuel ratio is again the stoichiometric air-fuel ratio of the mixture to Is returned to.

[0045] Figure 16 is the amount of SO _x ΣSOX when performing the combustion of the air-fuel mixture of the theoretical air-fuel ratio allowance S _max, and the
In this case shows a case where the exhaust gas temperature TE is lower than the set temperature TE _o. When TE <TE _o, the SO _x is not released from the NO _x absorbent 18 even if the air-fuel ratio of the air-fuel mixture is made rich, and the temperature of the SO _x absorbent 18 is required to release the SO _x from the NO _x absorbent 18. Must be higher. Therefore, in this case, the ignition timing θ is retarded so that TE> T
Stoichiometric nonsense the air-fuel ratio of the mixture as well as the E _o also is slightly release the SO _x from _the NO _x absorbent 18 to rich, then stops the retarding action of the ΣSOX ≦ S becomes _min and the ignition timing θ At the same time, the air-fuel ratio of the air-fuel mixture is returned to the stoichiometric air-fuel ratio again.

FIG. 17 shows the combustion of the rich mixture.
Sometimes SO_xThe amount ΣSOX is the allowable amount S _manAnd this
Exhaust gas temperature TE is the set temperature TE_oIndicates lower than
are doing. TE when burning rich mixture>
TE_oΣSOX will decrease if
ΣSOX ≧ S_manAnd therefore ΣSOX
≧ S_manBecomes TE <TE_oIt is time. This place
In this case, the ignition timing θ is retarded so that TE> TE_oAnd the following
ΣSOX ≦ S_min, The retarding effect of the ignition timing θ
Stopped.

[0047] It should be noted that, usually becomes a TE> TE _o When the ignition timing θ is retarded when the air-fuel mixture or a rich air-fuel mixture of the stoichiometric air-fuel ratio is burned. There is also, therefore not become within a predetermined time even when the ignition timing is retarded θ when the mixture of the theoretical air-fuel ratio is combusted with TE> TE _o However it does not become TE> TE _o optionally when the result is not also good, also in case of rich mixture is burned and TE> TE _o within a predetermined time when the ignition timing is retarded θ so as to prohibit the rich control of the air-fuel ratio when the the The retarding effect of the ignition timing may be stopped.

Also, as can be seen from FIG. 4, before the warm-up is completed, the air-fuel ratio of the air-fuel mixture is set to a rich or stoichiometric air-fuel ratio. If ΣSOX ≧ S _{man at} this time, the method shown in FIGS. As a result, SO _x is released from the NO _x absorbent 18. When the air-fuel mixture of a lean air-fuel mixture or the stoichiometric air-fuel ratio as described above is to be released SO _x when being burned air-fuel ratio of the mixture is slightly richer than the stoichiometric air-fuel ratio. In this case, the air-fuel ratio of the air-fuel mixture is feedback-controlled slightly richer than the stoichiometric air-fuel ratio based on the output of the air-fuel ratio sensor 21. Therefore, the feedback control of the air-fuel ratio will be described first with reference to FIGS.

As shown in FIG. 18, the air-fuel ratio sensor 21
Generates an output voltage V of about 0.9 (V) when the air-fuel mixture is rich, and 0.1 (V) when the air-fuel mixture is lean.
Output voltage V of the order. FIG. 19 shows feedback control of the air-fuel ratio performed based on the output signal of the air-fuel ratio sensor 21. The routine shown in FIG. 19 is performed by interruption every predetermined time.

Referring to FIG. 19, first, at step 5
At 0, it is determined whether or not a flag F indicating that the feedback control should be executed is set. When the flag F is not set, the processing cycle is completed, and therefore, at this time, the feedback control is not performed. On the other hand, when the flag F is set, the routine proceeds to step 51, where it is determined whether or not the output voltage V of the air-fuel ratio sensor 21 is lower than a reference voltage Vr of about 0.45 (V). When V ≦ Vr, that is, when the air-fuel ratio is lean, the routine proceeds to step 52, where the delay count value CD
L is decremented by one. Then step 53
Then, it is determined whether or not the delay count value CDL has become smaller than the minimum value TDR. When CDL <TDR, the routine proceeds to step 54, where CDL is set to TDR, and thereafter, the routine proceeds to step 55. Therefore, as shown in FIG.
When ≤ Vr, the delay count value CDL is gradually decreased, and then the CDL is maintained at the minimum value TDR.

On the other hand, when it is determined in step 51 that V> Vr, that is, when the air-fuel ratio is rich, the routine proceeds to step 56, where the delay count value CDL is incremented by one. Next, at step 57, it is determined whether or not the delay count value CDL has become larger than the maximum value TDL. When CDL> TDL, the routine proceeds to step 58, where CDL is set to TDL, and then at step 5
Go to 5. Therefore, as shown in FIG. 18, when V> Vr, the delay count value CDL is gradually increased, and then the CDL is maintained at the maximum value TDL.

In step 55, it is determined whether or not the sign of the delay count value CDL has been inverted from positive to negative or from negative to positive between the previous processing cycle and the current processing cycle. When the sign of the delay count value CDL is inverted, the process proceeds to step 59 to determine whether the inversion is from positive to negative.
That is, it is determined whether or not the inversion is from rich to lean. Step 60 when reversing from rich to lean
Then, the rich skip value RSR is added to the feedback correction coefficient FAF, and thus the FAF is rapidly increased by the rich skip value RSR as shown in FIG. On the other hand, when the inversion is performed from lean to rich, the routine proceeds to step 61, where the lean skip value RSL is subtracted from the FAF, and thus the FAF is sharply reduced by the lean skip value RSL as shown in FIG.

On the other hand, when it is determined in step 55 that the sign of the delay count value CDL has not been inverted, the routine proceeds to step 62, where it is determined whether or not the delay count value CDL is negative. When CDL ≦ 0, the routine proceeds to step 63, where the rich integral value KIR (KIR <RSR) is added to the feedback correction coefficient FAF, and the FAF is gradually increased as shown in FIG. On the other hand, when CDL> 0, the routine proceeds to step 64, where the lean integral value KIL is subtracted from the FAF, and thus the FAF is gradually reduced as shown in FIG.

By adopting such a feedback control method, as can be seen from FIG. 18, even if the air-fuel ratio temporarily becomes lean, the FAF can be prevented from being affected by this. FIG. 20A shows a case where the air-fuel ratio is maintained at the stoichiometric air-fuel ratio. At this time, the actual air-fuel ratio moves up and down around the stoichiometric air-fuel ratio of 14.6. Therefore, at this time, the average value of the actual air-fuel ratio becomes the stoichiometric air-fuel ratio of 14.6. On the other hand, FIG. 20B shows a case where the rich integral value KIR is made larger than the lean integral value KIL. In this case, the actual air-fuel ratio fluctuates while leaning toward the rich side as a whole, and the rich time and the rich degree during this time are larger than the lean time and the lean degree during this time. Therefore, at this time, the average value of the air-fuel ratio is slightly richer than the stoichiometric air-fuel ratio. Therefore, in the embodiment according to the present invention, the average value of the air-fuel ratio is made slightly richer than the stoichiometric air-fuel ratio by making the rich integral value KIR larger than the lean integral value KIL.

In order to make the average value of the air-fuel ratio slightly richer than the stoichiometric air-fuel ratio, the rich skip value RSR shown in FIG. 18 may be made larger than the lean skip value RSL, and the minimum value shown in FIG. The absolute value of the value TDR may be larger than the maximum value TDL. FIGS. 21 to 26 show a routine for executing the air-fuel ratio control, and this routine is executed by interruption every predetermined time.

Referring to FIGS. 21 and 22, first, at step 100, the basic fuel injection time TP is calculated from the map shown in FIG. Next, at step 101, the ignition timing θ is calculated from the map shown in FIG. Next, at step 102, it is determined whether or not the fuel supply is stopped during the deceleration operation. If the fuel supply has not been stopped, the routine proceeds to step 103, where it is determined whether or not the idle switch 20 is on, that is, the throttle valve 1
It is determined whether or not 4 is the idling opening. If the idle switch 20 is not on, step 105
The correction coefficient K is calculated from the engine cooling water temperature TW based on the relationship shown in FIG. 4 or from the operating state of the engine based on the relationship shown in FIG. Next, the routine proceeds to step 106. On the other hand, in step 103, the idle switch 2
When 0 is turned on, the routine proceeds to step 104, where K =
1.0, and then proceeds to step 106.

In step 106, it is determined whether or not the correction coefficient K is larger than 1.0. When K> 1.0, that is, when the rich air-fuel mixture is to be burned, the routine proceeds to step 110. On the other hand, if K ≦ 1.0, step 10
Proceeding to 7, it is determined whether or not K <1.0. K <
If it is not 1.0, that is, if the air-fuel mixture having the stoichiometric air-fuel ratio is to be burned, the routine proceeds to step 109. On the other hand, when K <1.0, that is, when the lean air-fuel mixture is to be burned, the routine proceeds to step 108.

The routine of the air-fuel ratio control 1 shown in step 108 is shown in FIGS. 23 and 24, and the routine of the air-fuel ratio control II shown in step 109 is shown in FIG. Air-fuel ratio control II
The routine for I is shown in FIG. In these routines, whether or not to perform feedback control and a final correction coefficient K are determined as described later. When these routines are completed, the routine proceeds to step 111.

In step 111, the fuel injection time TAU is calculated based on the following equation. TAU = f.TP.K.FAF Next, at step 112, it is determined whether or not K <1.0. When K <1.0, that is, when the lean air-fuel mixture is being burned, the routine proceeds to step 113, where FIG.
Absorption of NO _x amount NOXA from the map shown in (A) is calculated, then SO _x absorption amount SOXA shown in FIG. 11 (A) is calculated proceeds to step 114. Next, at step 115 NO _x emissions NOXD is made zero, then at step 116 is the release of SO _x amount SOXD is zero the process proceeds to step 117.

On the other hand, in step 112, K ≧
When it is determined to be 1.0, that is, when the air-fuel mixture or the rich air-fuel mixture of the stoichiometric air-fuel ratio is being burned, the routine proceeds to step 118, where NO is determined from the map shown in FIG.
_{The x} release amount NOXD is calculated.
(B) NO _x emission rate Kf shown in are calculated. Next, at step 120, SO _{x is obtained} from the map shown in FIG.
Emissions SOXD is calculated, and then release SO _x ratio Kg is calculated as shown in step 121 FIG. 12 (B). Next, at step 122, the NO _x absorption amount NOXA is made zero, then at step 123, the SO _x absorption amount SOXA is made zero, and then the routine proceeds to step 117.

[0061] amount of NO _x ΣNOX is estimated to be absorbed on the basis of step 117 the following equation is calculated. ΣNOX = ΣNOX + NOXA−Kf · NOXD Next, at step 124, it is determined whether or not ΣNOX <0. If ΣNOX <0, the routine proceeds to step 125, where ΣNOX = 0, and then to step 126. In step 126, the SO _x amount ΣSOX estimated to be absorbed is calculated based on the following equation.

ΣSOX = ΣSOX + SOXA−Kg · SOXD Next, at step 127, it is determined whether ΣSOX <0, and if ΣSOX <0, the routine proceeds to step 128, where ΣSOX = 0, and the processing cycle is completed. On the other hand, when it is determined in step 102 that the supply of fuel has been stopped, the routine proceeds to step 129, where a stop flag described later is reset, and then the processing cycle is completed.

Next, the routine of the air-fuel ratio control I executed when the lean air-fuel mixture is to be burned will be described with reference to FIGS. Referring to FIGS. 23 and 24, first, at step 200, it is determined whether or not the stop flag is set. Since the normal stop flag has been reset, the process proceeds to step 201 and SO _x
It is determined whether the flag 2 is set. Normally, the SO _x flag 2 is reset, so that step 20
Whether SO _x flag 1 has been set or not proceed to 2. Usually SO _x flag 1 jumps to step 203 because it is reset.

[0064] whether step 203 the amount of SO _x ΣSOX has exceeded the allowable value S _max is determined. ΣSOX ≦ S
When the value is _max, the routine proceeds to step 207, where the flag F is reset. Therefore, at this time, the feedback control of the air-fuel ratio is not performed. Next, at step 208, the feedback correction coefficient FAF is fixed at 1.0. Next, at step 209 NO _x flag whether it is set or not. Since usually NO _x flag has been reset proceeds to step 210. In step 210, N
O _x amount ΣNOX whether exceeds the allowable value N _max is determined. When ΣNOX ≦ _Nmax , step 1 in FIG.
Proceed to 11. At this time, the lean mixture is burned.

On the other hand, in step 210 ΣNOX>
When a determination is made that the N _max NO _x flag is set the routine proceeds to step 211. NO _x flag when is set correction coefficient K proceeds from step 209 to step 212, at the next processing cycle is a large constant value KK than 1.0. Thus, the air-fuel ratio of the air-fuel mixture is switched from lean to rich. Next, at step 213 NO _x amount ΣNOX is whether it is smaller than the lower limit value N _min is determined. Between .SIGMA.NOX> N _min jumps to step 111, NO _x flag is reset routine proceeds to step 214 becomes a .SIGMA.NOX ≦ N _min. Therefore, when NOX> _Nmax , as shown in FIG.
The air-fuel ratio of the air-fuel mixture is made rich until NOX ≦ N _min .

On the other hand, in step 203, ΣSOX>
Whether the exhaust gas temperature TE detected by the exhaust temperature sensor 22 proceeds when it is determined that becomes S _max in step 204 is higher than the set temperature TE _o is determined. TE> T
When E _o is SO _x flag 1 proceeds to step 205
There is set, step at the time of the TE ≦ TE _o 206
And the SO _x flag 2 is set.

When the SO _x flag 1 is set, that is, T
If E> TE _o , Steps 202 to 21
Proceeding to 5, the flag F is set. When the flag F is set, the feedback correction coefficient FAF is calculated in the feedback control routine shown in FIG. 19, and the air-fuel ratio feedback control is started. Then step 21
At 6, the correction coefficient K is fixed at 1.0. Sum of Next, at step 217 the reference rich integration value KIR _o a constant value k ₁ is set to the rich integration value KIR, then step 21
Subtraction result obtained by subtracting the predetermined value k ₂ from the reference lean integration value KIL _o At 8 is a lean integration value KIL. That is, the rich integral value KIR is increased, and the lean integral value KI is increased.
Since L is reduced, the air-fuel ratio of the air-fuel mixture is feedback-controlled slightly richer than the stoichiometric air-fuel ratio.

Next, at step 219, ΣSOX ≦ S
_It is determined whether or not _min has been reached. When ΣSOX> S _min , the routine jumps to step 111, where ΣSOX ≦ S
_When it reaches _min , the _routine proceeds to step 220, where the SO _x flag 1 is reset, and then proceeds to step 221, where the SO _x flag 2 is reset. Thus the air-fuel ratio of the mixture as illustrated in FIG. 13 If it is TE> TE _o when it is ΣSOX> S _max is slightly rich until ΣSOX ≦ S _min.

On the other hand, when the SO _x flag 2 is set,
That is, when TE ≦ TEo, the _routine proceeds from step 201 to step 222, where the ignition timing θ is retarded by α. Next
In SO _x flag 2 in step 223 whether a predetermined time Δt has elapsed since been set or not. If the fixed time Δt has not elapsed, the routine proceeds to step 215, and the air-fuel ratio of the air-fuel mixture is feedback-controlled to be slightly rich.

Next, when a predetermined time Δt has elapsed, step 2 is executed.
Whether it is TE> TE _o is it determined proceeds to 24. At this time, if TE> TE _o , the process proceeds to step 215, and at this time, the air-fuel ratio of the air-fuel mixture is maintained slightly rich until ΔSOX ≦ S _min as shown by the solid line in FIG. On the other hand, when it is determined that TE ≦ TE _o , the routine proceeds to step 225, where the stop flag is set. When the stop flag is set, the process jumps from step 200 to step 207, so that the retard control of the ignition timing θ is stopped and the air-fuel ratio of the air-fuel mixture is returned to lean as shown by a chain line in FIG.

Next, the routine of the air-fuel ratio control II executed when the air-fuel mixture having the stoichiometric air-fuel ratio is to be burned will be described with reference to FIG. Referring to FIG. 25, first, in step 300, the flag F is set. Flag F
Is set, the feedback correction coefficient FAF is calculated in the feedback control routine shown in FIG. 19, and the air-fuel ratio feedback control is started. Then whether SO _x flag 2 in step 301 is set or not. Usually SO _x flag 2 is whether because it is reset SO _x flag 1 proceeds to step 302 has been set or not. Since usually SO _x flag 1 is reset the process proceeds to step 303.

[0072] whether step 303 the amount of SO _x ΣSOX has exceeded the allowable value S _max is determined. ΣSOX ≦ S
When the value is _max, the process proceeds to step 304, where the rich integration value K
IR is the reference rich integration value KIR _o, then the lean integration value KIL is the reference lean integration value KIL _o proceeds to step 305. Next, at step 306, the stop flag is reset. At this time, the rich integral value KIR and the lean integral value KIL are respectively set to the reference value KI.
Since they are R _o and KIL _o , feedback control is performed so that the air-fuel ratio of the air-fuel mixture becomes the stoichiometric air-fuel ratio.

On the other hand, in step 303 ΣSOX>
Sum of when it is determined that becomes S _max proceeds to step 307 and the reference rich integration value KIR _o a constant value k ₁ is set to the rich integration value KIR, then a constant value k from step 308 in the reference lean integration value KIL _{o The} result of subtraction of ₂ is used as the lean integral value KIL. That is, the rich integral value K
Since the IR is increased and the lean integral value KIL is reduced, the air-fuel ratio of the air-fuel mixture is feedback-controlled to be slightly richer than the stoichiometric air-fuel ratio. Then whether higher than the detected exhaust gas temperature TE set temperature TE _o by the exhaust temperature sensor 22 at step 309 is determined. When TE> TE _o, the routine proceeds to step 310, where the SO _x flag 1 is set. When TE ≦ TE _o , the routine proceeds to step 311 and the SO _x flag 2 is set.

When the SO _x flag 1 is set, that is,
When TE> TE _o , Step 302 to Step 3
Proceeding to 13, it is determined whether or not ΣSOX ≦ S _min . When ΣSOX> S _min, the process jumps to step 306. When ΣSOX ≦ S _min , the process proceeds to step 314, where the SO _x flag 1 is reset. Then, the process proceeds to step 315, where the SO _x flag 2 is reset. Thus the air-fuel ratio of the mixture as shown in Figure 15 When it is TE> TE _o when it is ΣSOX> S _max is ΣSOX ≦ S
Slightly rich until _min .

On the other hand, when the SO _x flag 2 is set,
That is, when TE ≦ TEo, the _routine proceeds from step 301 to step 312, where a constant value α is subtracted from the ignition timing θ. That is, the ignition timing θ is retarded. Then step 3
Proceed to 13. Therefore, at this time, as shown in FIG. 16, the ignition timing θ is retarded until ΔNOX ≦ S _min , and the feedback control is performed so that the air-fuel ratio of the air-fuel mixture becomes slightly richer than the stoichiometric air-fuel ratio.

Next, a routine of the air-fuel ratio control III executed when the rich air-fuel mixture is to be burned will be described with reference to FIG. Referring to FIG. 26, first, in step 400, the flag F is reset. Therefore, at this time, the feedback control of the air-fuel ratio is not performed. Next, at step 401, the feedback correction coefficient FAF
Is fixed at 1.0. Next, at step 402, SO
It is determined whether or not the _x flag is set. Since the normal SO _x flag is reset, step 403 is executed.
Proceed to. In step 403, amount of SO _x ΣSOX whether exceeds an allowable value S _max is determined. ΣSOX ≦ S _max
In the case of, the routine proceeds to step 406, where the stop flag is reset.

On the other hand, in step 403 ΣSOX>
Whether the exhaust gas temperature TE detected by the exhaust temperature sensor 22 proceeds when it is determined that becomes S _max in step 404 is higher than the set temperature TE _o is determined. TE> T
If _Eo, the process jumps to step 406, where TE ≦ T
SO _x flag is set the routine proceeds to step 405 when the E _o.

SO_xStep 4 when the flag is set
From 02 to step 407, a fixed value from ignition timing θ
α is subtracted. That is, the ignition timing θ is retarded. Next
In step 408, ΣSOX ≦ S_minWhether or not
Is determined. ΣSOX> S _minStep 4
Jump to 06, ΣSOX ≦ S_minWhen it comes
Proceed to 409 and SO_xThe flag is reset. Therefore
ΣSOX> S_maxWhen it becomes, it is shown in FIG.
Sea urchin SOX ≦ S_minThe ignition timing θ is retarded until
You.

[0079]

Can be released from without _the NO _x absorbent the use of waste fuel or waste power the NO _x absorbed in the absorbent was SO _x, according to the present invention.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing a correction coefficient K;

FIG. 4 is a diagram showing a correction coefficient K before warm-up is completed.

FIG. 5 is a diagram showing a map of ignition timing.

FIG. 6 shows unburned HC and C in exhaust gas discharged from the engine.
FIG. 3 is a diagram schematically showing the concentrations of O and oxygen.

FIG. 7 is a view for explaining the NO _x absorption / release action.

8 is a diagram showing the absorption of NO _x amount NOXA like.

9 is a diagram showing the _the NO _x releasing amount NOXD like.

FIG. 10 is a time chart for explaining NO _x release control.

11 is a diagram showing the SO _x absorption amount SOXA like.

12 is a diagram showing the release of SO _x amount SOXD like.

13 is a time chart showing the controlled release of the SO _x during lean mixture combustion.

FIG. 14 is a time chart showing SO _x release control during lean air-fuel mixture combustion.

Is a time chart showing the controlled release of the SO _x in FIG. 15 when the air-fuel mixture combustion of the stoichiometric air-fuel ratio.

FIG. 16 is a time chart showing SO _x release control during combustion of a mixture at a stoichiometric air-fuel ratio.

FIG. 17 is a time chart showing SO _x release control during rich mixture combustion.

FIG. 18 is a time chart showing changes in a feedback correction coefficient FAF.

FIG. 19 is a flowchart for performing feedback control.

FIG. 20 is a diagram showing a change in an air-fuel ratio.

FIG. 21 is a flowchart for executing air-fuel ratio control.

FIG. 22 is a flowchart for executing air-fuel ratio control.

FIG. 23 is a flowchart for executing air-fuel ratio control I.

FIG. 24 is a flowchart for executing air-fuel ratio control I.

FIG. 25 is a flowchart for executing air-fuel ratio control II.

FIG. 26 is a flowchart for executing air-fuel ratio control III.

[Explanation of symbols]

16 ... exhaust pipe 18 ... NO _x absorbent 21 ... air-fuel ratio sensor 22 ... exhaust gas temperature sensor

──────────────────────────────────────────────────の Continuation of front page (51) Int.Cl. ⁷ Identification code FI F01N 3/18 ZAB F02D 43/00 301B 3/24 ZAB 301E F02D 41/14 310 45/00 310R 43/00 301 F02P 5/15 B B01D 53/34 ZAB 45/00 310 129Z F02P 5/15 121Z (72) Inventor Tetsu Iguchi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Shinichi Takeshima Toyota Town, Toyota City, Aichi Prefecture 1 Toyota Motor Corporation (72) Inventor Takamitsu Asanuma 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Kiyoshi Nakanishi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (56) References JP-A-5-76771 (JP, A) JP-A-63-150441 (JP, A) JP-A-4 265414 (JP, A) JP flat 5-31326 (JP, A) JP flat 6-88518 (JP, A) WO 93/7363 (WO, A1) (58 ) investigated the field (Int.Cl. ⁷ , DB name) F02D 41/00-41/14 F02D 43/00-45/00

Claims (4)

(57) [Claims] 1. A absorbs NO _x when the air-fuel ratio of the inflowing exhaust gas is lean, the engine and _the NO _x absorbent air-fuel ratio of the exhaust gas to release the NO _x absorbed when the stoichiometric air-fuel ratio or rich flowing in an internal combustion engine disposed in the exhaust passage, and amount of SO _x estimating means for estimating the amount of SO _x is absorbed in the NO _x absorbent, the temperature detection means for detecting a representative temperature representing the temperature of the NO _x absorbent , SO _x estimated to be the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent is absorbed in _the NO _x absorbent when the lean or the stoichiometric air-fuel ratio
And heating means for raising the temperature of the NO _x absorbent when the amount allowable amount beyond and the representative temperature is lower than a predetermined set temperature, the temperature of the NO _x absorbent is made to heating by heating device S temporarily rich air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent from _the NO _x absorbent when the
An exhaust gas purification device for an internal combustion engine, comprising: air-fuel ratio control means for releasing O _x . Wherein prohibiting temperature of the NO _x absorbent by the Atsushi Nobori means is for inhibiting the rich control of the air-fuel ratio by the air-fuel ratio control means when said representative temperature be allowed Atsushi Nobori does not exceed a predetermined temperature an exhaust purification system of an internal combustion engine according to claim 1 provided with the means. Wherein absorbing the NO _x when the air-fuel ratio of the inflowing exhaust gas is lean, the engine and _the NO _x absorbent air-fuel ratio of the exhaust gas to release the NO _x absorbed when the stoichiometric air-fuel ratio or rich flowing in an internal combustion engine disposed in the exhaust passage, and amount of SO _x estimating means for estimating the amount of SO _x is absorbed in the NO _x absorbent, the temperature detection means for detecting a representative temperature representing the temperature of the NO _x absorbent , set temperature air-fuel ratio of the exhaust gas flowing into the NO _x absorbent and the representative temperature exceeds a amount of SO _x estimated to be absorbed in _the NO _x absorbent is permissible amount when the rich predetermined A temperature raising means for raising the temperature of the NO _x absorbent when the temperature is lower than the temperature. Wherein said Atsushi Nobori means is an exhaust purification system of an internal combustion engine according to any one of claims 1 to 3 to raise the temperature of the NO _x absorbent by retarding the ignition timing.