JP3246206B2 - 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]

Absorbs NO _X when the air-fuel ratio is lean of the Related Art inflowing exhaust gas, the _the NO _X absorbent when the air-fuel ratio of the exhaust gas flowing emits NO _X inhaled and becomes rich in the engine exhaust passage as arranged, and usually to the rich air-fuel ratio of the mixture supplied into the engine cylinder is in when releasing the NO _X from _the NO _X absorbent while maintaining the air-fuel mixture fed into the engine cylinder to the lean air-fuel ratio A known internal combustion engine is known (PCT International Publication WO 93/0736).
No. 3).

[0003]

However, when the air-fuel mixture supplied to the engine cylinder is simply switched between the lean air-fuel ratio and the rich air-fuel ratio, the output torque of the engine becomes large due to a change in the air-fuel ratio at the time of the switching. And a large shock occurs.

[0004]

Means for Solving the Problems] According to the first invention to solve the above problems, the air-fuel ratio of the inflowing exhaust gas absorbs the NO _X when the lean air-fuel ratio of the exhaust gas flowing N that releases absorbed NO _x when rich
The O _X absorbent disposed in an engine exhaust passage, the air-fuel mixture to when releasing the NO _X from _the NO _X absorbent with allowed to absorb NO _X in _the NO _X absorbent when burned lean mixture from lean again to return to the lean after the rich to temporarily switched, the transition from the lean air-fuel mixture to the rich air-fuel mixture
Sometimes engine output torque gradually increases and rich mixing
Engine output torque gradually changes from lean to lean
And shifted from a rich mixture to a lean mixture.
The engine output torque gradually changes from lean to rich
The engine output torque gradually changes during the transition to
In remote long internal combustion engine, switching the air-fuel mixture at the time of NO _X released
To prevent fluctuations in engine output torque due to
Engine output torque when transitioning from rich mixture to rich mixture
And gradually decrease the engine output torque by
Engine output torque during transition from rich to lean
Comprising an outgoing <br/> force torque changing means for gradually increasing the decrement only engine output torque of the torque, increases from the rich air-fuel mixture in the engine output torque by the output torque change means when a transition to the lean air-fuel mixture gradually changed period is longer than the decrease gradual change period of the engine output torque by the output torque change means at the time of the transition to the rich air-fuel mixture from the lean air-fuel mixture.

According to a second aspect of the present invention, in order to solve the above-mentioned problem, in the first aspect, the output torque changing means gradually retards the ignition timing at the time of transition from the lean mixture to the rich mixture. The engine output torque is changed by gradually advancing the ignition timing at the transition from the rich mixture to the lean mixture, and the gradual change period of the ignition advance action at the transition from the rich mixture to the lean mixture Is set longer than the gradual change period of the ignition retarding effect when the mixture is shifted from the lean mixture to the rich mixture.

According to a third aspect of the present invention, in order to solve the above-mentioned problems, in the second aspect of the present invention, the ignition timing at the time of transition from the lean air-fuel mixture to the rich air-fuel mixture is retarded at a substantially constant rate. Then, the advance ratio of the ignition timing at the time of transition from the rich mixture to the lean mixture is increased with time. According to the fourth aspect of the present invention, in order to solve the above-mentioned problem , the air-fuel
Exhaust gas the ratio absorbs NO _X when the lean, flows
The air-fuel ratio of vinegar to release the NO _X absorbed and becomes rich
The NO _X absorbent is placed in the engine exhaust passage,
The NO _X Shi absorb the NO _X absorbent when burned the
To when releasing the NO _X from _the NO _X absorbent with Mel
Temporarily switches the mixture from lean to rich, then
In an internal combustion engine that is made to return to lean again, NO _X
Changes in engine output torque due to switching of air-fuel mixture during discharge
Temporarily retarding the ignition timing when should be released NO _X from _the NO _X absorbent in order to prevent movement, and gradually the degree of rich after rich mixture transition from lean mixture during the transition to the rich air-fuel mixture While maintaining the predetermined rich mixture after the reduction, the degree of lean after the transition from the lean mixture to the lean mixture is gradually reduced during the transition from the rich mixture to the lean mixture, and then maintained at the predetermined lean mixture. ,
The gradual change period of the lean degree after the transition from the rich mixture to the lean mixture is longer than the gradual change period of the rich degree after the transition from the lean mixture to the rich mixture.

According to a fifth aspect of the present invention, in order to solve the above-mentioned problems, in the fourth aspect of the invention, the degree of richness after the transition from the lean air-fuel mixture to the rich air-fuel mixture is reduced at a substantially constant rate. The rate of decrease in the degree of lean after the transition from rich to lean is increased with time. According to a sixth aspect of the present invention, in order to solve the above problems, the first aspect of the present invention provides
An intake air amount reducing means for reducing an intake air amount supplied into the combustion chamber when NO _X is to be released from the O _X absorbent is provided.

[0008]

[Action] _the NO _X absorbent air mixture so as to release the NO _X switched gradually changes the output torque of the engine when from lean to rich from, whereas engine when the air-fuel mixture was again returned from rich to lean There is an internal combustion engine in which the output torque of the internal combustion engine gradually changes over a longer period of time than when switching from lean to rich. Lippo from lean mixture in order to suppress the fluctuation of the engine output torque based on the switching action of the mixture during NO _X released in such an internal combustion engine in the first aspect of the invention
When the engine shifts to the air-fuel mixture, the engine
Output torque is gradually reduced and rich mixture
Only the decrease in engine output torque when transitioning to a lean mixture
An output torque changing means for gradually increasing the engine output torque is provided, and the rich air-fuel mixture is changed in accordance with the difference in the engine output torque gradually changing period based on the switching operation of the air-fuel mixture from lean to rich and from rich to lean. When the engine shifts to the lean mixture, the output torque
Reduction of engine output torque by output torque changing means when the increased gradual change period shifts from lean to rich
It is longer than the period of slight change.

The second invention is applicable to a case where the engine output increases when the air-fuel mixture is switched from lean to rich, and the ignition timing is gradually increased when the air-fuel mixture is shifted from the lean air-fuel mixture to the rich air-fuel mixture. And the ignition timing is gradually advanced at the time of transition from the rich mixture to the lean mixture. At this time, the engine output torque gradually changes based on the switching action of the mixture from lean to rich and rich to lean. In accordance with the difference between the rich and lean air-fuel mixtures, the gradual change period of the ignition advancing action should be longer than the gradual change of the ignition retarding action when the air-fuel mixture transitions from lean to rich. ing.

In the third aspect of the invention, the ignition timing at the time of transition from the lean mixture to the rich mixture is determined in accordance with the gradual change of the engine output torque based on the switching operation of the mixture from lean to rich and from rich to lean. The ignition timing is retarded at a substantially constant rate, and the advance rate of the ignition timing at the time of transition from the rich mixture to the lean mixture is increased with time.

[0011] The fourth invention is an invention which is applicable when the engine output is increased when switching the air-fuel mixture from lean to rich, temporary ignition timing when should be released NO _X from _the NO _X absorbent At the time of transition from the lean mixture to the rich mixture, the degree of richness after the transition to the rich mixture is gradually reduced, and then maintained at a predetermined rich mixture. During the transition to the lean mixture, the degree of lean is gradually reduced after the transition to the lean mixture, and then maintained at a predetermined lean mixture.
After the transition from the rich mixture to the lean mixture according to the difference in the gradual change period of the engine output torque based on the switching operation to the lean, the gradual change period of the lean degree after the transition from the lean mixture to the rich mixture It is longer than the gradual change period of the rich degree.

According to a fifth aspect of the present invention, the degree of the richness after the transition from the lean air-fuel mixture to the rich air-fuel mixture is determined in accordance with the gradual change of the engine output torque based on the switching operation of the air-fuel mixture from the lean air-fuel mixture to the rich air-fuel mixture. It is reduced at a substantially constant rate, and the rate of decrease in the degree of lean after the transition from rich to lean is increased over time.

[0013] In the sixth invention, the NO _x absorbent is converted to NO _x
The amount of intake air fed into the combustion chamber from _the NO _X absorbent to suppress the variation itself of the engine output torque when releasing the NO _X when switched to a rich air-fuel mixture to when releasing from lean to Is reduced.

[0014]

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 intake duct 12 upstream of the throttle valve 14 and the surge tank 10 are connected to a bypass passage 19.
The idle rotation speed control valve 20 is disposed in the bypass passage 19.

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 21 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 21 is input to an input port 35 via an AD converter 37. . The input port 35 is connected to a rotation speed sensor 22 that generates an output pulse representing the engine rotation speed. On the other hand, output port 3
6 is connected to the ignition plug 4, the fuel injection valve 11 and the idle speed control valve 20 via the corresponding drive circuit 38. The opening of the idle speed control valve 20 is such that the idling speed is equal to the target speed during idling operation. The idle rotation speed control valve 20 is maintained at a constant opening, for example, in a fully open state except during the idling operation.

In the internal combustion engine shown in FIG. 1, the fuel injection time TAU is calculated based on, for example, the following equation. TAU = K · TP Here, TP indicates a basic fuel injection time, and K indicates a correction coefficient. The basic fuel injection time TP indicates a fuel injection time required to make the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder a stoichiometric air-fuel ratio. The basic fuel injection time TP is obtained in advance by an experiment, and the absolute pressure PM in the surge tank 10 is determined.
As a function of the engine speed N, it is stored in the ROM 32 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, when K <1.0, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder becomes larger than the stoichiometric air-fuel ratio, that is, lean, and when K> 1.0, the air-fuel ratio is supplied into the engine cylinder. The air-fuel ratio of the air-fuel mixture is smaller than the stoichiometric air-fuel ratio, that is, rich.

The target air-fuel ratio of the air-fuel mixture to be supplied to the engine cylinder, that is, the value of the correction coefficient K is changed according to the operating state of the engine. In the embodiment according to the present invention, it is basically shown in FIG. As described above, it is predetermined as a function of the absolute pressure PM in the surge tank 10 and the engine speed N. That is, as shown in FIG. 3, K <1.0 in the low-load operation region on the lower load side than the solid line R, that is, the air-fuel mixture is lean, and K in the high-load operation region between the solid line R and the solid line S. = 1.
0, that is, the air-fuel ratio of the air-fuel mixture is the stoichiometric air-fuel ratio, and K> 1.0, that is, the air-fuel mixture is rich in the full load operation region on the higher load side than the solid line S.

FIG. 4 schematically shows the concentration of typical components in the exhaust gas discharged from the combustion chamber 3. As can be seen from FIG. 4, 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-described NO _X absorbent 18 is arranged in the engine exhaust passage, the NO _X absorbent 18 actually performs the absorption and release of NO _X , but the detailed mechanism of the absorption and release is not clear. There is also. However, it is considered that this absorption / release action is performed by a mechanism as shown in 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 inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases.
These oxygen O ₂ as shown in (A) is O ₂ ^- or O
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 the platinum Pt to become NO 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 is absorbed in the form of nitrate ion NO ₃ ⁻ as shown in FIG. Diffuses into agent. 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
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. 4, 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, when the air-fuel mixture supplied into the combustion chamber 3 is made rich and the air-fuel ratio of the inflowing exhaust gas becomes rich, as shown in FIG.
C and CO are discharged, and these unburned HC and CO are converted to platinum Pt.
It reacts with the above oxygen O ₂ ^- or O ^2- to be oxidized.
Further, when the air-fuel ratio of the inflowing exhaust gas becomes rich, the oxygen concentration in the inflowing exhaust gas extremely decreases.
O ₂ is released, and this NO ₂ is reduced by reacting with unburned HC and CO as shown in FIG. 5 (B). In this way, when NO ₂ is no longer present on the surface of platinum Pt, NO ₂ is released from the absorbent one after another. Therefore NO _X from _the NO _X absorbent 18 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.
First, unburned HC and CO are converted to O on platinum Pt._Two ^-or
Is O^2-Immediately oxidized and then platinum
O on Pt_Two ^-Or O^2-Is consumed but unburned HC,
If CO remains, the unburned HC and CO make it an absorbent
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 NO _X absorbing capacity of the NO _X absorbent 18, _the NO _X absorbent 18 when saturation NO _X absorbing capacity of the NO _X absorbent 18 is not E longer absorb NO _X.
Therefore NO NO _X absorbing capacity of the _X absorbent 18 must emit NO _X from _the NO _X absorbent 18 before the saturation degree of the NO _X in _the NO _X absorbent 18 in order that
Needs to be estimated. Then this N
Described O _X absorption of estimation method.

[0026] is _the amount of NO _X absorbed in 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 is increased _{to X} amount is absorbed per unit time _the NO _X absorbent 18 to increase. Therefore, NO per unit time
_The amount of NO _X absorbed by the _X absorbent 18 is 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 in the amount of NO _X is surge tank 10 which is absorbed per unit time _the NO _X absorbent 18 it is possible to represent with an absolute pressure in the surge tank 10 Is a function of Therefore, in the embodiment according to the present invention, NO _X
Absolute pressure PM and _the amount of NO _X NOXA absorbed in absorbent 18
And as a function of the engine speed N obtained by experiments in advance,
Figure The amount of NO _X NOXA as a function of PM and N 6
It is stored in the ROM 32 in advance in the form of a map shown in FIG.

On the other hand, 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 NO _X emission amount at this time primarily exhaust gas Affected by volume and air-fuel ratio. That is, NO of _the amount of NO _X amount of 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, and 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. 6 (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. 7 (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 ^- is NO _X emission rate from _the NO _X absorbent 18 is increased so easily decomposed. In this case, NO since the temperature of the _X absorbent 18 is proportional to substantially exhaust gas as shown in FIG. 7 (B) NO _X emission rate Kf
Increases as the exhaust gas temperature T increases. Therefore NO
_{When the X} release rate Kf is taken into consideration, NO per unit time
_The NO _X amount released from the _X absorbent 18 is represented by the product of NOXD and the NO _X release rate Kf shown in FIG. In the embodiment according to the present invention, the exhaust gas temperature T is determined in advance as a function of the absolute pressure PM in the surge tank 10 and the engine speed N in the form of a map shown in FIG.
It is stored in M32.

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, in the embodiment according to the present invention, basically, FIG.
The air-fuel ratio is controlled according to the value of the correction coefficient K distinguished by the solid lines R and S. Accordingly, in the region on the lower load side than the solid line R in FIG. 3, the lean mixture (K <1.0) is burned, and at this time, NO _X is absorbed by the NO _X absorbent 18. However, if the lean mixture continues to burn, N
The NO _X absorption capacity of the O _X absorbent 18 is saturated, and thus the NO _X absorbent 18 cannot absorb NO _X. Accordingly, in this embodiment according to the present invention is burned lean air-fuel mixture continues _the NO _X absorbent 18
_The amount of NO _X ΣNOX is estimated to be absorbed is set NO _X release flag when it exceeds the upper limit value MAX predetermined for, rich switched mixture from lean when the NO _X release flag is set Thus, NO _X is released from the NO _X absorbent 18.

That is, as shown in FIG. 8, when the lean air-fuel mixture is combusted, the NO _X amount ΣNOX gradually increases, and when the NO _X amount ΣNOX exceeds the upper limit value MAX, the NO _X release flag is set. You. Air-fuel ratio of the mixture with NO _X releasing flag is set is changed from lean to rich. Since the air-fuel ratio of the mixture is released of the NO _X is started from is switched from lean to rich _the NO _X absorbent 18 _the amount of NO _X ΣNOX is rapidly decreased, the amount of NO _X ΣNOX reaches the lower limit value MIN NO _{The X} release flag is reset. When the NO _X release flag is reset, the air-fuel ratio of the air-fuel mixture is returned from rich to lean again. Such releasing action of the NO _X by the NO _X release flag is in the embodiment according to the present invention is controlled, thus a description will be given of the control of the NO _X release flag with reference to the first, Figure 9. The routine shown in FIG. 9 is executed by interruption every predetermined time.

Referring to FIG. 9, first of all, step 50 is executed.
NO _X releasing flag whether been set or not in. If the NO _X release flag has not been set, the routine proceeds to step 51, where it is determined whether the NO _X amount ΣNOX has exceeded the upper limit MAX. If と き に は NOX ≦ MAX, the routine jumps to step 55.こ れ
NOX> becomes MAX when NO _X release flag proceeds to step 52 is set, then the routine proceeds to step 55. N
When O _X release flag is set, at the next processing cycle proceeds from step 50 to step 53 in _the amount of NO _X ΣNO
It is determined whether or not X has become equal to or less than the lower limit, and ΣNOX ≧
If it is MIN, the process jumps to step 55. On the other hand, if ΣNOX <MIN, the routine proceeds to step 54, where N
O _X release flag is reset, then the routine proceeds to step 55.

In step 55, it is determined whether the correction coefficient Kt for the basic fuel injection time TP is smaller than 1.0. When Kt <1.0, that is, when the operation state is such that the lean air-fuel mixture is to be burned, the routine proceeds to step 56, where FIG.
From the map shown in (A) per unit time NO _X absorption N
OXA is calculated. Next, at step 57 NO _X emissions NOXD is made zero, then the routine proceeds to step 61.
On the other hand, released amount of NO _X NOXD per unit time from the map shown in FIG. 7 (A) is calculated by the routine proceeds to step 58 when it is judged that Kt ≧ 1.0 in step 55. Then NO _X emission rate Kf is calculated from the map shown in relation to FIG. 7 (C) shown in step 59 FIG. 7 (B), the then NO _X absorption amount NOXA per unit step 60 time is made zero. Next, the routine proceeds to step 61.

The amount of NO _X ΣNOX is estimated to be absorbed in _the NO _X absorbent 18 on the basis of the step 61 following formula
Is calculated. .SIGMA.NOX = .SIGMA.NOX + whether NOXA-Kf · NOXD then _the amount of NO _X .SIGMA.NOX step 62 becomes negative is discriminated, are .SIGMA.NOX is zero the routine proceeds to step 63 when it is .SIGMA.NOX <0.

As described above, when the NO _X release flag is set, the air-fuel ratio of the air-fuel mixture is switched from lean to rich until the NO _X release flag is reset. However, when the air-fuel ratio of the air-fuel mixture is switched from lean to rich, a shock is generally generated in the vehicle because the engine output torque increases. Therefore, in the embodiment according to the present invention, as shown in FIG. 8, when the air-fuel ratio of the air-fuel mixture is switched from lean to rich as shown in FIG. The ignition timing is retarded in order to reduce the output torque by the amount of the increase. In this manner, the increase in the output torque due to the switching of the air-fuel ratio from lean to rich and the decrease in the output torque due to the retarding effect of the ignition timing are offset, so that the air-fuel ratio of the air-fuel mixture is changed from lean to rich. , The engine output torque does not fluctuate.

However, as described above, the ignition timing retard amount is calculated.
Even if the force torque does not fluctuate, it is actually empty
When the fuel ratio is switched from lean to rich, and when the air-fuel ratio
When returning from rich to lean again, the output torque changes.
Will move. Next, this will be described with reference to FIG.
I will explain. FIG. 10 is NO_XEmission flag set
Sometimes increase the fuel injection amount to increase the air-fuel ratio from lean to rich
The ignition timing is immediately retarded at the same time as switching to
NO _XWhen the release flag is reset, the fuel injection
When the air-fuel ratio is switched from rich to lean immediately after weight loss
At the same time, the ignition timing is immediately advanced to the original ignition timing.
Is shown. However, in this case, is the air-fuel ratio lean?
Even if it is switched to rich, it contributes to combustion in the combustion chamber 3.
The actual air-fuel ratio of the air-fuel mixture (hereinafter, as shown in FIG.
The air-fuel ratio is gradually increased as shown in FIG.
Does not change from lean to rich and changes the air-fuel ratio from rich
Even when switching to lean, the actual air-fuel ratio gradually changes from rich to
The actual air-fuel ratio as shown in FIG.
Output torque fluctuates while gradually changing from lean to rich
Output while the actual air-fuel ratio gradually changes from rich to lean
The torque will fluctuate.

That is, in the internal combustion engine as shown in FIG. 1, when the amount of injected fuel is increased in order to switch the mixture from lean to rich, the increased amount of injected fuel is not immediately supplied to the combustion chamber 3 as it is. Part of the increased amount of fuel adheres to the inner wall surface of the intake port 6. As a result, even if the amount of fuel injected into the intake port 6 is increased, the combustion chamber 3
The amount of fuel supplied into the fuel tank is not immediately increased, and thus the actual air-fuel ratio does not immediately change from lean to rich.

On the other hand, if the injected fuel is increased for a while, the equilibrium state is established in which the amount of the injected fuel deposited on the inner wall surface of the intake port 6 and the amount of the deposited fuel flowing into the combustion chamber 3 become equal. When the equilibrium state is reached, the fuel injection amount and the combustion chamber 3
And the amount of fuel flowing into the inside becomes equal. Therefore, the actual air-fuel ratio gradually changes from lean to rich from the start of increasing the amount of injected fuel to the point of reaching such an equilibrium state. As shown in FIG. 10, the time t ₁ from the start of increasing the amount of injected fuel until the actual air-fuel ratio falls to a constant rich air-fuel ratio, that is, the time t ₁ during which the actual air-fuel ratio is gradually changing is relatively short.

On the other hand, the mixture is changed from rich to lean.
Even if the injected fuel is reduced to return, initially before the injected fuel is reduced
About the same amount of adhered fuel continues to flow into the combustion chamber 3
Does not immediately decrease the total amount of fuel supplied into the combustion chamber 3.
No. Therefore, even if the injected fuel is reduced, the actual air-fuel ratio is immediately restored.
Does not change from lean to lean. Then, after a while, intake
The amount of injected fuel deposited on the inner wall surface of port 6 and the amount of deposited fuel
An equilibrium state where the amount of inflow into the combustion chamber 3 becomes equal,
Such a state of equilibrium is reached after the injection fuel is reduced.
Until the actual air-fuel ratio gradually changes from rich to lean.
Will be transformed. As shown in FIG.
After the start of weight reduction, the actual air-fuel ratio stabilizes to a certain lean air-fuel ratio
Time t_TwoThat is, the time t during which the actual air-fuel ratio gradually changes_Two
Is the time t ₁It is considerably longer than.

As described above, when the actual air-fuel ratio gradually changes from lean to rich and when the actual air-fuel ratio gradually changes from rich to lean, not only the time t ₁ and t ₂ during which the actual air-fuel ratio changes gradually but also gradually. The way of weird is quite different. That is, when the actual air-fuel ratio gradually changes from lean to rich, the actual air-fuel ratio decreases at a substantially constant rate, whereas when the actual air-fuel ratio gradually changes from rich to lean, the actual air-fuel ratio increases at that rate. Increase with time. The reason why the actual air-fuel ratio gradually changes when the air-fuel ratio gradually changes from lean to rich and when the actual air-fuel ratio gradually changes from rich to lean is considered to be as follows.

That is, as described above, if the fuel injection amount is constant, the amount of the injected fuel adhered to the inner wall surface of the intake port 6 and
It can be considered that the amount of the adhering fuel flowing into the combustion chamber 3 is in an equilibrium state, and the injected fuel adhering to the inner wall surface of the intake port 6 flows into the combustion chamber 3 after a predetermined time.
Next, if the injected fuel is increased, the amount of the attached fuel is immediately increased, and the increased amount of the attached fuel starts flowing into the combustion chamber 3 after a predetermined time. Therefore, the actual air-fuel ratio when the injected fuel has been allowed to increase will vary from lean to a constant rich air-fuel ratio with a relatively short time t _1.

On the other hand, when the injected fuel is reduced, the equilibrium state is not attained unless the attached fuel that has already adhered before the injected fuel is reduced flows into the combustion chamber 3. In this case, it takes a certain time for the adhering fuel that has already adhered to flow into the combustion chamber 3, and the amount of the adhering fuel that flows into the combustion chamber 3 does not decrease unless the certain time has elapsed. since the actual air-fuel ratio becomes relatively long time t ₂ can take is to return to a certain lean air-fuel ratio from the rich. Immediately after the amount of injected fuel is reduced, a large amount of the deposited fuel continues to flow into the combustion chamber 3 until the flow of the large amount of the deposited fuel into the combustion chamber 3 is completed. Since the amount of adhering fuel flowing into the fuel cell 3 decreases, the rate of increase of the actual air-fuel ratio increases with time, as shown in FIG.

As described above, the actual air-fuel ratio is determined from the fuel injection amount.
The air-fuel ratio changes differently from the
Output torque does not fluctuate when switching from
In order to reduce the output torque by increasing the actual air-fuel ratio
Torque change means to reduce the output torque by the increase
Must be provided. FIG. 11 shows this torque changing means.
1 shows a first embodiment using ignition timing control. This second
NO in one embodiment_XAir-fuel ratio when release flag is set
Fuel injection so that the target air-fuel ratio becomes the target rich air-fuel ratio (Kt = KK).
The fire rate is increased immediately. On the other hand, NO_XRelease hula
When the ignition is set, the ignition timing is changed from θL to the target ignition timing θ.
Period for gradually changing the actual air-fuel ratio toward R₁For the same period as
It is retarded at a fixed rate. On the other hand, NO_XRelease flag reset
When set, the fuel injection amount is immediately reduced,
The ignition timing is from the target ignition timing θR to the original ignition timing θL.
Period of the actual air-fuel ratio _TwoGradually over the same period as
It is advanced. At this time, the ignition timing advance ratio is time
Over time, and thus is shown in FIG.
Output torque can be prevented from fluctuating
Will be. In the embodiment shown in FIG.
No time_XThe time since the release flag was reset
It is advanced in proportion to the cube of the overtime T.

FIGS. 12 and 13 show an injection and ignition control routine for executing the first embodiment, and this routine is executed by interruption every predetermined time. FIG.
With reference to FIG. 2 and FIG.
0, the basic fuel injection time TP from the map shown in FIG.
Is calculated. Next, at step 101, it is determined whether or not the NO _X release flag is set. Step when the NO _X release flag is not set 104
The correction coefficient K obtained from the relationship shown in FIG.
t. Next, at step 105, the basic fuel injection time TP is multiplied by Kt to obtain the fuel injection time TA.
U (= Kt · TP) is calculated. Then step 10
In step 6, it is determined whether or not an in-execution flag indicating that the NO _X release control is being executed is set. If the running flag is not set, step 118
The ignition timing θL determined by the operation state of the engine is set as the final ignition timing θ. This θL is the surge tank 1
It is stored in the ROM 32 in advance in the form of a map as a function of the absolute pressure PM in 0 and the engine speed N.

When the NO _X emission control is not performed, the air-fuel ratio of the air-fuel mixture becomes the air-fuel ratio determined by the correction coefficient K shown in FIG. 3, and the ignition timing θ at this time depends on the operating state of the engine. Ignition timing θL. On the other hand, N
O _X release flag is set by the setting value KK predetermined proceeds from step 101 to step 102 (>
1.0) is defined as Kt. The value of this set value KK can make the air-fuel ratio of the air-fuel mixture about 11.0 to 12.0, 1.25.
To about 1.35. Next, at step 103, the running flag is set, and then at step 105, the fuel injection time TAU is calculated. Therefore, when the NO _X release flag is set, the air-fuel ratio of the air-fuel mixture becomes 11.0 to 1
The fuel injection amount is immediately increased so as to achieve a rich air-fuel ratio of about 2.0.

[0046] Then whether because execution flag in step 106 is determined to be set NO _X release flag proceeds to step 107 has been set is discriminated again. When the NO _X release flag is set, the routine proceeds to step 108, where a predetermined constant value Δθ is added to the cumulative retard amount C. Next, at step 109, the final ignition timing θ is calculated by subtracting the accumulated retard amount C from θL. Next, at step 110, it is determined whether or not θ has become smaller than a predetermined ignition timing θR (FIG. 11). If θ <θR, the routine proceeds to step 111, where θR is set as the final ignition timing θ. You. The ignition timing θR is predetermined so that the output torque does not fluctuate even when Kt = KK by offsetting the increase in the output torque when Kt = KK, for example, the absolute pressure in the surge tank 10. It is stored in the ROM 32 in advance in the form of a function of PM and the engine speed N.

Next, when the NO _X release flag is reset, the routine proceeds from step 101 to step 104, where the correction coefficient K obtained from the relationship shown in FIG. 3 is set to Kt. Therefore, at this time, the mixture is immediately switched from the rich mixture to the lean mixture. On the other hand, [Delta] T the NO _X release flag is reset at step 107 to T proceeds to step 112
Is added. This T increases as the elapsed time from when the NO _X release flag is reset increases. Next, at step 113, the ignition timing θ is calculated based on the following equation.
Is calculated.

The theta = .theta.R is + T ³ thus ignition timing theta caused to advance in proportion to the cube of the elapsed time from when the NO _X release flag is reset NO _X release flag is reset. Next, at step 114, it is determined whether or not the ignition timing θ has become larger than the ignition timing θL determined by the operation state of the engine. θ
If> θL, the routine proceeds to step 115, where θL is set as the ignition timing θ. Next, in step 116, the running flag is reset, and then in step 117, C
And T are set to zero.

FIGS. 14 to 16 show a second embodiment according to the present invention. In this embodiment, as shown in FIG.
_{When the X} release flag is set, the ignition timing θ becomes θR
To θL, and when the NO _X release flag is reset, the ignition timing θ is immediately advanced from θL to θR. Furthermore, the actual air-fuel ratio is immediately switched from lean to rich, the fuel injection amount so switched in real actual air-fuel ratio from rich to lean when the NO _X release flag is reset when the NO _X release flag is set Is controlled.

[0050] That is, in this second embodiment when the NO _X release flag is set correction factor for the basic fuel injection time TP is larger once by a large margin to KKR (> KK), then the correction coefficient is gradual-change period t KKR at a constant rate during ₁
To KK. On the other hand, when the NO _X release flag is reset, the correction coefficient for the basic fuel injection time TP is temporarily reduced to KKL (<K), and then the correction coefficient is gradually reduced during the gradual change period t ₂ (> t ₁ ). So that the rate of increase increases with time.
It is increased from L to K. In the second embodiment, at this time, the correction coefficient is increased in proportion to the third power of the elapsed time Q from when the NO _X release flag is reset. In the second embodiment, fuel injection amount control is used as torque changing means.

FIGS. 15 and 16 show an injection and ignition control routine for executing the second embodiment. This routine is executed by interruption every predetermined time. FIG.
Referring to FIG. 5 and FIG.
0, the basic fuel injection time TP from the map shown in FIG.
Is calculated. Next, at step 20 1 NO _X release flag is whether it is set or not. Step when the NO _X release flag is not set 203
It is determined whether or not the execution flag indicating that the NO _X release control is being executed is set. If the running flag has not been set, the routine proceeds to step 215, where the correction coefficient K obtained from the relationship shown in FIG. 3 is set as Kt. Next, at step 216, the fuel injection time TAU (= Kt · TP) is calculated by multiplying the basic fuel injection time TP by Kt. Then whether step 217 NO _X release flag is set or not is determined again, NO _X releasing flag ignition timing θL determined by the operating state of the engine proceeds to step 219 when it is not set final ignition timing θ. This θL is previously stored in the ROM 32 in the form of a map as a function of the absolute pressure PM in the surge tank 10 and the engine speed N.
Is stored within.

When the NO _X emission control is not performed, the air-fuel ratio of the air-fuel mixture becomes the air-fuel ratio determined by the correction coefficient K shown in FIG. 3, and the ignition timing θ at this time depends on the operating state of the engine. Ignition timing θL. On the other hand, N
O _X release flag is running proceeds when set from step 201 to step 202 flag is set. If the execution flag is set whether NO _X release flag proceeds from step 203 to step 204 has been set it is discriminated again. Cumulative correction amount D proceeds to step 205 when the NO _X release flag is set
Is added to the predetermined value ΔK. Next, at step 206, the final correction coefficient Kt is calculated by subtracting the cumulative correction amount D from KKR (FIG. 14). Next, at step 207, it is determined whether or not Kt has become smaller than a predetermined set value KK (FIG. 14). When Kt <KK, the routine proceeds to step 208, where KK is made the final correction coefficient Kt. You. This set value K
The value of K is about 1.25 to 1.35, which can make the air-fuel ratio of the air-fuel mixture about 11.0 to 12.0. Next, at step 216, the fuel injection time TAU is calculated. Therefore, when the NO _X release flag is set, the air-fuel ratio of the air-fuel mixture becomes K
The fuel injection amount is immediately increased so as to have a rich air-fuel ratio corresponding to KR, and then the fuel injection amount is gradually reduced until the rich air-fuel ratio corresponding to KK is reached, that is, the degree of richness is gradually reduced. .

[0053] Since the following step 217 NO _X release flag is determined to be set willing ignition timing to step 218 theta is the .theta.R (Figure 14). The ignition timing θR is set in advance to a value such that the output torque does not fluctuate even when Kt = KK by offsetting the increase in the output torque when Kt = KK.
ROM in the form of a function of the absolute pressure PM and the engine speed N
32.

[0054] Then the NO _X release flag is reset ΔQ from step 204 to Q proceeds to step 209
Is added. This Q increases as the elapsed time from when the NO _X release flag is reset increases. Next, at step 210, the correction coefficient K is calculated based on the following equation.
t is calculated. Kt = KKL + Q ³ Therefore, the correction coefficient Kt is immediately reduced to KKL (FIG. 14) when the NO _X release flag is reset, and the correction coefficient Kt is set when the NO _X release flag is reset based on the value of KKL. Is increased in proportion to the third power of the elapsed time from. Next, at step 211, it is determined whether or not the correction coefficient Kt has become larger than the correction coefficient K determined by the operating state of the engine. When Kt> K, the routine proceeds to step 212, where K is set as the correction coefficient Kt. Next, at step 213, the running flag is reset, and then at step 214, D and Q are made zero. Next, the routine proceeds to step 216.

In the following step 217, it is determined that the NO _X release flag 217 has not been set, so that the routine proceeds to step 219. Therefore NO _X release flag is the ignition timing to be reset θ is switched immediately to θL from .theta.R.
17 to 19 show a third embodiment according to the present invention. The third embodiment basically uses ignition timing control as torque changing means as in the first embodiment. That is, the third the NO _X release flag is set in Example air is made to increase the fuel injection amount immediately so that the target rich air-fuel ratio (Kt = KK '), the target ignition timing from θL It is retarded at a constant rate with the same period a gradual change period t ₁ of the actual air-fuel ratio toward the ignition timing θR. On the other hand, if NO _X release flag is reset the fuel injection amount is made to decrease immediately, the ignition timing with the same period as the gradual-change period t ₂ of the actual air-fuel ratio toward the target ignition timing θR to the original ignition timing θL It is gradually advanced. At this time, the advance ratio of the ignition timing is increased with time.

[0056] If NO _X release flag is set idle speed control valve 20 is made to closed by a fixed degree of opening further in the third embodiment. When the idle speed control valve 20 is closed in this manner, the amount of intake air supplied into the combustion chamber 3 decreases, so that the amount of injected fuel to be increased to increase the air-fuel ratio of the air-fuel mixture to the same rich degree Can be reduced. As a result, the fluctuation amount of the actual air-fuel ratio also becomes small, and thus the fluctuation of the output torque can be further suppressed.

FIGS. 18 and 19 show an injection and ignition control routine for executing the third embodiment. This routine is executed by interruption every predetermined time. FIG.
Referring to FIG. 8 and FIG.
0, the basic fuel injection time TP from the map shown in FIG.
Is calculated. Next, at step 301, it is determined whether or not the NO _X release flag is set. If the NO _X release flag is not set, step 305
The correction coefficient K obtained from the relationship shown in FIG.
t. Next, at step 306, the idle speed control valve 20 is opened.

Next, at step 307, the basic fuel injection time TP is multiplied by Kt to obtain the fuel injection time TA.
U (= Kt · TP) is calculated. Then step 30
In step S8, it is determined whether or not the execution flag indicating that the NO _X emission control is being executed is set. Step 320 when the running flag is not set
The ignition timing θL determined by the operation state of the engine is set as the final ignition timing θ. This θL is the surge tank 1
It is stored in the ROM 32 in advance in the form of a map as a function of the absolute pressure PM in 0 and the engine speed N.

[0059] Thus is made to idle speed control valve 20 is opened when the controlled release of the NO _X is not performed, the air-fuel ratio of the mixture becomes an air-fuel ratio which is determined by the correction coefficient K shown in FIG. 3, this The ignition timing θ at this time is the ignition timing θL according to the operating state of the engine. On the other hand, NO _X when releasing flag is set a predetermined set value KK proceeds from step 301 to step 302 '(> 1.
0) is set to Kt. The value of this set value KK 'is about 1.1 to 1.25, which can make the air-fuel ratio of the air-fuel mixture about 12.0 to 13.0. Next, at step 303, the idle speed control valve 20 is closed. Next, at step 304, the running flag is set, and then at step 307, the fuel injection time TAU is calculated. Therefore NO _X release flag when set idle speed control valve 20 is immediately being made to closed, the fuel injection amount so that the air-fuel ratio becomes a rich air-fuel ratio of 12.0 from 13.0 of the mixture immediately Is increased.

[0060] Then whether because step 308 the execution flag is determined to be set NO _X release flag proceeds to step 309 has been set is discriminated again. When the NO _X release flag is set, the routine proceeds to step 310, where a predetermined constant value Δθ is added to the accumulated retard amount C. Next, at step 311, the final ignition timing θ is calculated by subtracting the accumulated retard amount C from θL. Next, at step 312, it is determined whether or not θ has become smaller than a predetermined ignition timing θR ′ (FIG. 17). When θ <θR ′, the routine proceeds to step 313, where θR ′ is set to the final ignition timing. θ. The ignition timing .theta.R 'is predetermined so that the output torque does not fluctuate even when Kt = KK' by offsetting the increase in the output torque when Kt = KK '. Is stored in the ROM 32 in advance in the form of a function of the absolute pressure PM and the engine speed N.

Next, when the NO _X release flag is reset, the routine proceeds from step 301 to step 305, where the correction coefficient K obtained from the relationship shown in FIG. 3 is set to Kt. Therefore, at this time, the mixture is immediately switched from the rich mixture to the lean mixture. Next, at step 306, the idle speed control valve 20 is opened. On the other hand, when the NO _X release flag is reset, the routine proceeds from step 309 to step 314, where ΔT is added to T. This T is NO
_It increases as the elapsed time from when the _X release flag is reset increases. Next, at step 315, the ignition timing θ is calculated based on the following equation.

[0062] θ = θR '+ is T ³ thus ignition timing theta caused to advance in proportion to the cube of the elapsed time from when the NO _X release flag is reset NO _X release flag is reset. Next, at step 316, it is determined whether or not the ignition timing θ has become larger than the ignition timing θL determined by the operation state of the engine. θ
If> θL, the routine proceeds to step 317, where θL is set as the ignition timing θ. Next, at step 318, the running flag is reset, and then at step 319 C
And T are set to zero.

The control of the idle speed control valve 20 can be applied to the second embodiment. As described above, in an internal combustion engine in which fuel is injected into the intake port 6, when the amount of injected fuel is increased, the output torque gradually changes at a substantially constant rate, and when the amount of injected fuel is reduced, the output torque increases. The rate of change of the torque changes over time over a relatively long time.
The present invention can be applied to any type of internal combustion engine that generates such a change in output torque. The present invention can be applied to such an internal combustion engine as long as the output torque changes as described above.

[0064]

Outputted from _the NO _X absorbent according to the present invention when the air-fuel ratio of the mixture is switched from lean to rich so as to release the NO _X torque can be prevented from fluctuating. Also, 6
Th and thereby reduced the intake air amount at the time of NO _X emission as in the invention the variation of the output torque can be further suppressed.

[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 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. 5 is a diagram for explaining a NO _X absorption / release effect.

FIG. 6 is a diagram showing a NO _X absorption amount NOXA and the like.

FIG. 7 is a diagram showing a NO _X release amount NOXD and the like.

FIG. 8 is a time chart showing control of a NO _X release flag, and control of an air-fuel ratio and an ignition timing.

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

FIG. 10 is a flowchart for explaining the occurrence of a change in output torque.

FIG. 11 is a time chart showing a first embodiment of the NO _X release control.

FIG. 12 is a flowchart showing a first embodiment of the injection ignition control.

FIG. 13 is a flowchart showing a first embodiment of the injection ignition control.

FIG. 14 is a time chart showing a second embodiment of the NO _X release control.

FIG. 15 is a flowchart showing a second embodiment of the injection ignition control.

FIG. 16 is a flowchart showing a second embodiment of the injection ignition control.

FIG. 17 is a time chart showing a third embodiment of the NO _X release control.

FIG. 18 is a flowchart showing a third embodiment of the injection ignition control.

FIG. 19 is a flowchart showing a third embodiment of the injection ignition control.

[Explanation of symbols]

4 ... spark plug 11 ... Fuel injection valve 18 ... NO _X absorbent

Continued on the front page. (51) Int.Cl. ⁷ Identification code FI F02D 45/00 330 F02D 45/00 330 F02P 5/15 F02P 5/15 B (72) Inventor Tetsuro Kihara 1st Toyota Town, Toyota City, Toyota City, Aichi Prefecture Toyota (56) References JP-A-59-7774 (JP, A) JP-A-6-66135 (JP, A) JP-A-2-136526 (JP, A) JP-A-60-13953 (JP) JP, A) JP-A-59-194059 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08 F01N 3/24 F02D 41/14 F02D 43/00 F02D 45 / 00 F02P 5/15

Claims (6)

(57) [Claims] 1. A absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, the _the NO _X absorbent when the air-fuel ratio of the exhaust gas flowing emits NO _X absorbed and becomes rich in the engine exhaust passage arrangement and, NO with allowed to absorb NO _X in _the NO _X absorbent when burned lean mixture
_When NO _X should be released from the _X absorbent, the mixture is temporarily switched from lean to rich and then returned to lean again
The engine during the transition from lean to rich
As the force torque gradually increases, the lean
The engine output torque gradually decreases during the transition to
Engine output when transitioning from rich to lean
Force torque gradually changes from lean to rich
In the long inner <br/> combustion engine than the gradual-change period engine output torque when the migrated, or lean air-fuel mixture in order to prevent fluctuation in the engine output torque based on the switching action of the mixture during NO _X release
Increase in engine output torque when transitioning from
The engine output torque is gradually reduced and rich mixing is performed.
Engine output torque when transitioning from lean to lean
An output torque changing means for gradually increasing the engine output torque by an amount corresponding to the amount of the engine output torque by the output torque changing means when shifting from the rich mixture to the lean mixture.
Reduction of engine output torque by output torque changing means when the increased gradual change period shifts from lean to rich
An exhaust gas purification device for an internal combustion engine that has been made longer than the small gradual change period. 2. The output torque changing means gradually retards the ignition timing when transitioning from a lean mixture to a rich mixture, and gradually advances the ignition timing when transitioning from a rich mixture to a lean mixture. The engine output torque is changed by this, and the gradual change period of the ignition advancing action at the time of transition from the rich mixture to the lean mixture is the gradual change period of the ignition retarding action at the time of transition from the lean mixture to the rich mixture. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus is longer. 3. The ignition timing when a transition is made from a lean mixture to a rich mixture is retarded at a substantially constant rate,
3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the advance ratio of the ignition timing at the time of transition from the rich mixture to the lean mixture is increased with time. 4. When the air-fuel ratio of the inflowing exhaust gas is lean.
Absorbs Kiniwa NO _X, the air-fuel ratio of the inflowing exhaust gas is Li
The _the NO _X absorbent to release the absorbed NO _X to be a pitch
Located in the engine exhaust passage to burn lean mixture
Sometimes NO _X is absorbed by the NO _X absorbent and NO
Lee air-fuel mixture at the time from the _X absorbent should be released NO _X
Switch temporarily from rich to rich, then back to lean again
In the internal combustion engine was in Suyo, the air-fuel mixture at the time of NO _X emission
Ignition timing when the fluctuation of the engine output torque based on the switching action from _the NO _X absorbent in order to prevent the should be released NO _X
Temporarily retarded, and while maintaining the lean air-fuel mixture to a rich mixture to a predetermined after gradually reducing the degree of rich after rich mixture migrated during transition to the rich air-fuel mixture from rich mixture After the transition to the lean mixture, the lean degree is gradually reduced after the transition to the lean mixture, then maintained at a predetermined lean mixture, and the lean change period after the transition from the rich mixture to the lean mixture is maintained. The exhaust gas purifying apparatus for an internal combustion engine has a period longer than a period of gradually changing the degree of richness after a shift from a lean mixture to a rich mixture. 5. The degree of richness after a transition from a lean air-fuel mixture to a rich air-fuel mixture is reduced at a substantially constant rate.
5. The rate of decrease in the degree of lean after transition from rich to lean mixture is increased over time.
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 6. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising intake air amount reducing means for reducing the amount of intake air supplied into the combustion chamber when NO _X is to be released from the NO _X absorbent. .