JP3077492B2 - 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_xThe air-fuel ratio of the mixture
At a fixed air-fuel ratio or rich predetermined time
The air-fuel ratio of the mixture back to lean again.
An internal combustion engine is known (International Publication W093 / 0).
No. 7363).

[0003]

However, when the air-fuel ratio of the air-fuel mixture is switched from lean to the stoichiometric air-fuel ratio or rich, and then the air-fuel ratio of the air-fuel mixture is again switched to lean, the torque changes when these air-fuel ratios are switched. Occurs. On the other hand, in an internal combustion engine equipped with an automatic transmission, a torque change occurs during a shift operation, and in an internal combustion engine equipped with an automatic transmission equipped with a lock-up mechanism, a torque change occurs even when the lock-up mechanism is turned on and off. Occurs. Thus automatic transmission internal combustion engine equipped with a, or or the stoichiometric air-fuel ratio temporarily from lean air-fuel ratio in order to release the NO _x from the NO _x absorbent in an internal combustion engine provided with the automatic transmission equipped with a lockup mechanism If the switching is made rich, there is a problem that the frequency of torque change increases.

[0004]

Means for Solving the Problems] According to the present invention in order to solve the above problems, comprises an automatic transmission, absorbs NO _x when the air-fuel ratio of the inflowing exhaust gas is lean, flows exhaust in the air-fuel ratio is stoichiometric or rich engine arranged to _the NO _x absorbent to release the absorbed NO _x in the engine exhaust passage when the gas, _the NO _x absorbent when the lean air-fuel mixture is burned N absorbed by
And _the amount of NO _x estimating means for estimating a O _x amount, mixing should be burned in the engine when it exceeds the first set value _the amount of NO _x is a predetermined estimated to be absorbed in _the NO _x absorbent a first air-fuel ratio switching means for switching the air-fuel ratio of the gas from the lean temporarily rich, NO _x amount estimated to be absorbed in _the NO _x absorbent is small predetermined than the first set value When the shift operation of the automatic transmission is performed when it is larger than the second set value, the air-fuel ratio of the air-fuel mixture to be burned during the shift operation of the automatic transmission is temporarily switched from lean to rich. Air-fuel ratio switching means.

Further, according to the present invention, the above problems are solved.
Automatic transmission with lock-up mechanism
And when the air-fuel ratio of the inflowing exhaust gas is lean, NO
_xAnd the air-fuel ratio of the inflowing exhaust gas is
Is NO absorbed when rich_xReleases NO_xSucking
In an internal combustion engine in which a sorbent is placed in the engine exhaust passage,
NO when the fuel-air mixture is burning_xAbsorbent
NO absorbed by_xNO to estimate the amount_xQuantity estimation means;
NO_xNO presumed to be absorbed by the absorbent _xQuantity
When the engine exceeds a first preset value
The air-fuel ratio of the mixture to be burned from lean to rich temporarily
First air-fuel ratio switching means for selectively switching, NO_xFor absorbent
NO presumed to be absorbed_xThe amount is the first set value
Is smaller than a predetermined second set value.
The lock-up mechanism was switched on and off
Occasionally, during the on / off switching action of the lock-up mechanism,
Temporarily increase the air-fuel ratio of the mixture to be burned from lean to rich
And second air-fuel ratio switching means for switching.

In order to further solve the above problems, according to the present invention, comprises an automatic transmission, the air-fuel ratio of the inflowing exhaust gas is absorbed NO _x when the lean air-fuel ratio of the exhaust gas flowing in stoichiometric 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, NO lean air-fuel mixture is absorbed in _the NO _x absorbent when being burned and _the amount of NO _x estimating means for estimating the _x amount, the operating state of the engine is predetermined when the amount of NO _x estimated to be absorbed in _the NO _x absorbent exceeds a predetermined set value A first air-fuel ratio control means for temporarily making the air-fuel ratio of the air-fuel mixture to be burned in the engine when the engine becomes an operating state; and a case where the operating state of the engine is not the above-mentioned predetermined operating state. _the NO _x absorbent even Fuel mixture to be burned during the shifting action of the automatic transmission when the amount of NO _x estimated to be absorbed the shifting action of the automatic transmission is performed when greater than the predetermined set value And second air-fuel ratio control means for temporarily making the air-fuel ratio rich.

Further, according to the present invention, the above problems are solved.
Automatic transmission with lock-up mechanism
And when the air-fuel ratio of the inflowing exhaust gas is lean, NO
_xAnd the air-fuel ratio of the inflowing exhaust gas is
Is NO absorbed when rich_xReleases NO_xSucking
In an internal combustion engine in which a sorbent is placed in the engine exhaust passage,
NO when the fuel-air mixture is burning_xAbsorbent
NO absorbed by_xNO to estimate the amount_xQuantity estimation means;
NO_xNO presumed to be absorbed by the absorbent _xQuantity
The engine operation status is exceeded when the preset value is exceeded.
When the engine is in a predetermined operating state,
To temporarily enrich the air-fuel ratio of the air-fuel mixture to be burned
The air-fuel ratio control means and the operating state of the engine are determined in advance as described above.
NO even if the operating state is not_xFor absorbent
NO presumed to be absorbed_xThe quantity is predetermined
When the value is larger than the set value, the lock-up
When the switching operation is performed, the lock-up mechanism is turned on.
.Temporarily set air-fuel ratio of air-fuel mixture to be burned during off-switching action
And second air-fuel ratio control means for enriching the air-fuel ratio.
You.

[0008]

In any of the first to fourth aspects of the invention, it is possible to synchronize the automatic transmission or the lock-up mechanism with the on / off switching operation as much as possible. and to perform the air-fuel ratio of the switching action for _the NO _x releasing from NO absorbent.

That is, in the first aspect, basically, when the lean air-fuel mixture is being burned, the estimated absorption NO _x
If the amount is far beyond the second set value the air-fuel ratio is estimated absorption amount of NO _x but is temporarily rich air-fuel mixture is smaller than the first set value when it exceeds the first set value air-fuel ratio of the mixture is rich temporarily for synchronization with the shifting action of the automatic transmission _the NO _x releasing.

[0010] The second invention is basically an air-fuel ratio is temporarily of the mixture when the estimated absorption amount of NO _x when the lean air-fuel mixture is burned exceeds a first set value is estimated absorption amount of NO _x but is rich, the air-fuel mixture for synchronization to _the NO _x releasing for the first set value smaller second set value lockup mechanism on-off switching long as beyond than換作The air-fuel ratio is temporarily made rich.

Further, the air-fuel ratio of the mixture when the engine operating state becomes a predetermined operating condition when the third estimated absorption amount of NO _x is basically the invention is higher than a setting of _the NO _x releasing but in synchronization with the shifting action of the automatic transmission without an operating state in which the operating state has been determined in advance of the engine if exceeding the set value is the estimated amount of NO _x is rich temporarily Therefore, the air-fuel ratio of the air-fuel mixture is temporarily made rich.

Further, the air-fuel ratio of the mixture when the engine operating state becomes a predetermined operating condition when the fourth estimation absorbed amount of NO _x is basically the invention is higher than a setting NO There synchronously for on-off switching action of the lock-up mechanism may not be operating state operating condition is a predetermined engine if exceeding the set value is the estimated amount of NO _x is rich temporarily The air-fuel ratio of the mixture is temporarily enriched for _x release.

[0013]

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.

On the other hand, the crankshaft 19 of the engine is connected to an automatic transmission 20, and the output shaft 21 of the automatic transmission 20 is connected to driving wheels. The automatic transmission 20 includes a torque converter 22, and a lock-up mechanism 23 is provided in the torque converter 22. That is, the torque converter 22 is connected to the crankshaft 19 and rotates with the crankshaft 19,
Pump impeller 25 supported by pump cover 24
And a turbine runner 27 attached to an input shaft 26 of the automatic transmission 20, and a stator 28, and the rotational movement of the crankshaft 19 is controlled by the input shaft 26 via the pump cover 24, the pump impeller 25 and the turbine runner 27.
Is transmitted to

On the other hand, the lock-up mechanism 23 has an input shaft 26
And a lock-up clutch plate 28 movably mounted in the axial direction with respect to the input shaft 26 and rotating together with the input shaft 26. Normally, that is, at the time of lock-up off, the input shaft 2
6 through the oil passage in the lock-up clutch plate 28.
Pressurized oil is supplied into a room 29 between the pump cover 28 and the pump cover 28, and then the pressurized oil flowing out of the room 29 is fed into a room 30 around the pump impeller 25 and the turbine runner 27, and then the input shaft 26. It is discharged through an oil passage inside. At this time, since the pressure difference between the chambers 29 and 30 on both sides of the lock-up clutch plate 28 hardly occurs, the lock-up clutch 28 is
Therefore, at this time, the rotational force of the crankshaft 19 is transmitted through the pump cover 24, the pump impeller 25 and the turbine runner 27 to the input shaft 26.
Is transmitted to

On the other hand, when the lock-up is to be turned on, pressurized oil is supplied into the room 30 through an oil passage in the input shaft 26, and oil in the room 29 is discharged through an oil passage in the input shaft 26. Is done. At this time, the pressure in the room 30 becomes higher than the pressure in the room 29, and thus the lock-up clutch 28 is pressed against the inner peripheral surface of the pump cover 24 so that the crankshaft 19 and the input shaft 26 are at the same speed. It becomes a rotating directly connected state. The supply control of the oil into the chambers 29 and 30, that is, the on / off control of the lock-up mechanism 23 is controlled by a control valve provided in the automatic transmission 20, and this control valve controls the output signal of the electronic control unit 40. Controlled based on Also, a number of clutches for performing a shifting operation are provided in the automatic transmission 20.
These clutches are also controlled based on the output signal of the electronic control unit 40.

The electronic control unit 40 is composed of a digital computer, and a ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, and an input port 45 interconnected by a bidirectional bus 41. And an output port 46. A pressure sensor 31 for generating 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 31
The data is input to the input port 45 via the D converter 47. A throttle sensor 32 for generating an output voltage proportional to the throttle opening is attached to the throttle valve 14, and the output voltage of the throttle sensor 32 is applied to the corresponding AD converter 2
7 is input to the input port 45. Further, an air-fuel ratio sensor 33 is disposed in the exhaust manifold 15, and an output voltage of the air-fuel ratio sensor 33 is supplied to a corresponding AD converter 47.
Through the input port 45.

On the other hand, a rotation speed sensor for generating an output pulse indicating the rotation speed of the input shaft 26 and a rotation speed sensor for generating an output pulse indicating the rotation speed of the output shaft 21 are arranged in the automatic transmission 20. The output pulses of these rotation speed sensors are input to an input port 45. The input port 45 is connected to a rotation speed sensor 34 that generates an output pulse representing the engine rotation speed. On the other hand, the output port 46
Are connected to the ignition plug 4, the fuel injection valve 11, and a control valve for lock-up control and a clutch for shift control disposed in the automatic transmission 20 via corresponding drive circuits 48, 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 is the mixing supplied to the engine cylinder. It shows the fuel injection time required to make the air-fuel ratio of the air 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 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 K = 1.
When 0, that is, when the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder is to be the stoichiometric air-fuel ratio, a coefficient for making the air-fuel ratio accurately match the stoichiometric air-fuel ratio based on the output signal of the air-fuel ratio sensor 33 It is. This feedback correction coefficient FAF
Moves up and down about 1.0, and this FAF
Decreases when the mixture becomes rich, and increases when the mixture becomes lean. When K <1.0 or K> 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 state of the engine.
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 exhaust passage of the engine, 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 platinum Pt and barium Ba supported on a carrier as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.

That is, the inflow exhaust gas becomes considerably lean.
And the oxygen concentration in the inflowing exhaust gas greatly increased, and FIG.
As shown in FIG._TwoIs O_Two ^-Or O
^2-On the surface of platinum Pt. On the other hand, inflow exhaust
NO in the gas becomes O 2 on the surface of platinum Pt._Two ^-Or O^2-When
React, NO_Two(2NO + O_Two→ 2NO_Two). Next
NO generated_TwoIs partially oxidized on platinum Pt
Is absorbed in the absorbent and does not bind to barium oxide BaO.
As shown in FIG. 5A, nitrate ions NO_Three ^-of
It diffuses into the absorbent in form. NO in this way_xIs NO
_xIt is absorbed in the absorbent 18.

The oxygen concentration in the inflowing exhaust gas is generated NO ₂ on the surface of as high as platinum Pt, as long as NO ₂ of absorption of NO _x capacity of the absorbent is not saturated is absorbed in the absorbent and nitrate ions NO ₃ ^- Is generated. On the other hand, when the oxygen concentration in the inflowing exhaust gas decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the opposite direction (NO ₃ ⁻ → NO ₂ ), thus the nitrate ion NO ₃ ⁻ in the absorbent. There are released from the absorbent in the form of NO _2. That is, when the oxygen concentration in the inflowing exhaust gas decreases, NO _x from the NO _x absorbent 18 is released. As shown in FIG. 4, if the degree of leanness of the inflowing exhaust gas decreases, the oxygen concentration in the inflowing exhaust gas decreases. Therefore, if the degree of leanness of the inflowing exhaust gas decreases, the air-fuel ratio of the inflowing exhaust gas decreases. Even NO _x absorbent 1
8 will release NO _x .

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, a large amount of unburned H
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 is extremely reduced, so that NO ₂ is released from the absorbent, and this NO ₂ is unreacted as shown in FIG. It is reduced by reacting with the fuel HC and CO.
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.

[0028] That is, when the air-fuel ratio of the inflowing exhaust gas is rich First the unburned HC, CO are O ₂ on the platinum Pt ^- or O ^{2 -} immediately be reacted with oxidized and then O on the platinum Pt Unburned H even if ₂ ^- or O ^2- is consumed
C, CO is any remaining This unburned HC, discharged from the NO _x and engine released from the absorbent by CO N
O _x is reduced. Thus _the NO _x absorbed in _the NO _x absorbent 18 in a short period of time if the air-fuel ratio of the inflowing exhaust gas is made rich is released, yet NO to the atmosphere for the released NO _x is reduced _x can be prevented from being discharged. Furthermore, _the NO _x absorbent 18 is NO _x because the has function even if the air-fuel ratio of the inflowing exhaust gas the stoichiometric air-fuel ratio emitted from _the NO _x absorbent 18 of the reduction catalyst is made to reduction. However, when the air-fuel ratio of the inflowing exhaust gas is set to the stoichiometric air-fuel ratio, NO _x
Since NO _x is gradually released from the absorbent 18, it takes a slightly longer time to release all the NO _x absorbed in the NO _x absorbent 18.

As described above, the lean mixture burns.
NO_xIs NO_xIt is absorbed by the absorbent 18. Only
NO_xNO of absorbent 18_xLimited absorption capacity
Yes, NO_xNO of absorbent 18_xIf the absorption capacity is saturated
NO_xAbsorbent 18 is no longer NO_xCan not be absorbed.
Therefore NO_xNO of absorbent 18_xBefore the absorption capacity is saturated
NO_xNO from absorbent 18_xNeed to be released
For that, NO _xHow much NO in the absorbent 18_x
Needs to be estimated. Then this N
O_xA method for estimating the amount of absorption will be described.

[0030] 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 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 _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, 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 amount 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 ^- 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 substantially proportional to the exhaust gas, the NO _x release rate Kf as shown in FIG.
Increases as the exhaust gas temperature T increases. Therefore NO
_{When the x} release rate Kf is taken into consideration, NO per unit time
amount of NO _x released from the _x absorbent 18 will be represented by the product of the NOXD and _the NO _x releasing factor Kf shown in FIG. 7 (A). 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 the 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, FIG.
The air-fuel ratio is controlled according to the value of the correction coefficient K distinguished by the solid lines R and S. Therefore, in the region on the lower load side than the solid line R in FIG. 3, the lean mixture (K <1.0) is burned, so that NO _x is absorbed by the NO _x absorbent 18 and the load is higher than the solid line R in FIG. In the region on the side, a mixture having a stoichiometric air-fuel ratio (K = 1.0) or a rich mixture (K> 1.
0) is burned, so that the NO _x absorbent 18
_x will be released. Therefore, NO _x in which the low load operation and the high load operation are alternately repeated with the solid line R in FIG.
When the NO _x absorption capacity of the absorbent 18 does not saturate and thus the lean mixture is burned, the NO _x
NO _x absorption agent 18 is to be well absorbed.

[0035] However, NO _x absorption capacity of and lean mixture combustion is continuously performed _the NO _x absorbent 18 will be saturated. Thus during the lean mixture combustion is when more than the amount that _the amount of NO _x ΣNOX being absorbed in the NO _x absorbent 18 is made lean mixture combustion is continuously reaches a predetermined, in the embodiment according to the present invention, or The air-fuel ratio of the air-fuel mixture supplied into the combustion chamber 3 is temporarily made rich during a predetermined specific operating state such as a deceleration operation or an idling operation.

FIG. 8 schematically shows an example of the area of each shift speed of the automatic transmission 20 and the lock-up ON area. In the example shown in FIG. 8, the range of each shift speed and the lock-up ON region are a function of the opening degree of the throttle valve 14 and the vehicle speed. Therefore, each shift speed (first speed) is determined based on the opening degree of the throttle valve 14 and the vehicle speed. (First speed, third speed, and fourth speed) and the ON / OFF switching action of the lock-up mechanism 23. In this case, the throttle opening is obtained from the output signal of the throttle sensor 32, and the vehicle speed is obtained from the output shaft 2.
It is calculated from the number of rotations of 1.

FIGS. 9 to 13 show a first embodiment according to the present invention. First setting of the amount of NO _x ΣNOX being absorbed in the NO _x absorbent 18 when the combustion of the lean air-fuel mixture is continuously performed As can be seen from Figure 9 predefined in the first embodiment When the value exceeds MAX1, the air-fuel ratio of the air-fuel mixture is made rich (K> 1.0). NOX amount NOX to _the NO _x releasing action is started from a mixed air-fuel ratio of the air becomes rich _the NO _x absorbent 18 is rapidly reduced, and then the air-fuel ratio of the mixture and _the amount of NO _x ΣNOX is zero It is switched from rich to lean again.

Further, NO _x amount in the first embodiment ΣN
When OX is larger than a second set value MAX2 smaller than the first set value MAX1, the air-fuel ratio of the air-fuel mixture is temporarily made rich even when the shift operation of the automatic transmission 20 is performed, and NO _The effect of releasing NO _x from the _x absorbent 18 is performed. That is, as shown in FIG. 9, when the shift I is performed, ΣNOX <MAX2, so that the air-fuel ratio of the air-fuel mixture is not made rich, but when the shift II is performed, ΣNOX>
Since the gear ratio is MAX2, the air-fuel ratio of the air-fuel mixture is temporarily made rich when the shift II is performed. Although not shown in FIG. 9 is _the amount of NO _x ΣNOX second set value M
The air-fuel ratio of the air-fuel mixture is also temporarily made rich when the on / off switching action of the lock-up mechanism 23 is performed when it is larger than AX2.

When the shifting operation of the automatic transmission 20 or the on / off switching operation of the lock-up mechanism 23 is performed, the output torque of the automatic transmission 20 changes. Therefore, if the air-fuel ratio of the air-fuel mixture is temporarily made rich at this time, the change in the output torque generated when the air-fuel ratio of the air-fuel mixture is made rich temporarily, and the shift operation of the automatic transmission 20 or the lock-up mechanism 23 And the change of the output torque generated when the on / off switching operation is performed, so that the frequency of occurrence of the output torque change can be reduced. Therefore the first
In the embodiment, the second operation is performed in order to increase the frequency at which the air-fuel ratio of the air-fuel mixture is temporarily made rich when the shift operation of the automatic transmission 20 or the on / off switching operation of the lock-up mechanism 23 is performed. The set value MAX2 is set to a value smaller than the first set value MAX1.

FIG. 10 shows a routine for switching the set values MAX1 and MAX2. Set value MAX for _the amount of NO _x ΣNOX, first, at step 100, referring to FIG. 10 is a second set value MAX2
Is determined. When MAX is not MAX2, that is, when MAX = MAX1, the routine proceeds to step 101, where the gear position of the automatic transmission 20 is changed from the first gear to the second gear.
It is determined whether a shift request has been issued to switch from the second speed to the third speed, the third speed to the fourth speed, the fourth speed to the third speed, the third speed to the second speed, or the second speed to the first speed. When the shift request has not been issued, the routine proceeds to step 102, where the lock-up mechanism 2
It is determined whether or not a request for switching from ON to OFF or from OFF to ON has been issued. When the switching request has not been issued, the routine proceeds to step 103, where the set value MAX is set to the second value.
, And then returns to step 100 again.

On the other hand, if it is determined in step 101 that a shift request has been issued,
When it is determined in step 2 that a switching request has been issued, the routine proceeds to step 104, where the set value MAX is changed to the second set value MA.
X2. Step 10 when MAX = MAX2
From 0, the routine proceeds to step 105, where it is determined whether or not the shift operation has been completed, for example, because the rotational speed X of the input shaft 26 of the automatic transmission 20 has become equal to the rotational speed X of the output shaft 21. Step 1 when the shifting operation is not completed
In step 06, for example, since the engine speed has become equal to the speed of the input shaft 26, it is determined whether or not the switching operation of the lock-up mechanism 23 from off to on has been completed, or the engine speed and the input shaft 26 Since the difference from the rotation speed becomes larger than the predetermined difference, it is determined whether or not the switching operation of the lock-up mechanism 23 from on to off has been completed. If the switching action has not been completed, the process returns to step 100 again.

On the other hand, if it is determined in step 105 that the shifting operation has been completed, or if it is determined in step 106 that the switching operation has been completed, step 1 is executed.
In step 07, the set value MAX is set to the first set value MAX1. That is, MAX = MAX2 until a shift request is issued and the shift operation is completed, and MAX = MAX2 until a switch request is issued and the switch operation is completed.

FIGS. 11 to 13 show a routine for controlling the air-fuel ratio, and this routine is executed by interruption every predetermined time. Referring to FIGS. 11 to 13, first, at step 200, the basic fuel injection time TP is calculated from the map shown in FIG. Next, at step 201, a correction coefficient K is obtained from the relationship shown in FIG. 3 according to the operating state of the engine. Next, at step 202, it is determined whether or not the correction coefficient K is smaller than 1.0. When K <1.0, i.e. a lean air-fuel mixture when the operating state to be burning _the NO _x releasing showing a temporarily should be rich air-fuel ratio of the mixture for _the NO _x releasing proceeds to step 203 It is determined whether the flag has been set. When _the NO _x releasing flag has not been set, the routine proceeds to step 204.

In step 204, the mask shown in FIG.
NO per unit time from top_xThe absorption amount NOXA is calculated.
It is. Next, at step 205, NO_xNOXD released
Is set to zero, and then in step 206 the feedback
The lock correction coefficient FAF is fixed at 1.0. Next,
NO at step 207_xIt is assumed that it is absorbed by the absorbent 18.
NO to be set_xThe amount ΣNOX is equal to the set value MAX (= MAX1
Or, it is determined whether or not it is larger than MAX2). ΣN
If OX ≦ MAX, jump to step 209
You. On the other hand, if ΣNOX> MAX, step 2
Go to 08 and NO _xThe release flag is set, then
Proceed to step 209.

In step 209, the fuel injection time TAU is calculated based on the following equation. TAU = f · TP · K · FAF Next, at step 210, the NO _x absorbent 1 is obtained based on the following equation.
8 NO _x amount ΣNOX has been absorbed is calculated. ΣNOX = ΣNOX + NOXA−Kf · NOXD Next, at step 211, it is determined whether or not the NO _x amount ＸNOX has become negative. When ΣNOX <0, the routine proceeds to step 212, where ΣNOX is made zero. At this time, the lean mixture is fueled in the combustion chamber 3.

On the other hand, in step 203, NO_xrelease
If it is determined that the flag has been set, step 2
Go to 13 and NO_xIt is determined whether the quantity ΣNOX has become zero.
Separated. Step 215 when NOX = 0
The correction coefficient K is set to a predetermined value KK.
This value KK indicates that the air-fuel ratio of the air-fuel mixture is about 12.5 to 13.5.
The value is about 1.1 to 1.2. Next,
In step 216, the map shown in FIG.
Release NO_xThe quantity NOXD is calculated. Next,
In step 217, the relationship shown in FIG. 7B and the relationship shown in FIG.
NO from map _xThe release rate Kf is calculated, and then the step
In step 218, NO per unit time_xAbsorption NOXA is zero
It is said. Next, at step 219, feedback compensation is performed.
The positive coefficient FAF is fixed at 1.0, then step 20
Go to 9.

On the other hand, in step 213, ΣNOX =
If it is determined that the value has become 0, the process proceeds to step 214 and NO
_{The x} release flag is reset, and then the process proceeds to step 204. Switching Therefore .SIGMA.NOX> become MAX air between the air-fuel mixture to _the NO _x releasing flag is .SIGMA.NOX = 0 after the set is made rich, the air-fuel ratio of the mixture to become .SIGMA.NOX = 0 is from rich to lean Can be

On the other hand, in step 202, K ≧ 1.0
When it is judged in, NO _x releasing flag proceeds to step 220 is reset to the words when the air-fuel ratio of the mixture to be burned is stoichiometric or rich. In step 221 then released amount of NO _x NOXD per unit time from the map shown in FIG. 7 (A) is calculated. Then _the NO _x releasing factor Kf is calculated from the map shown in relation to FIG. 7 (C) shown in step 222 FIG. 7 (B), the then absorption of NO _x amount NOXA per unit step 223 time is made zero. Next, at step 224, the correction coefficient K is set to 1.
It is determined whether it is greater than zero. When K> 1.0, that is, when the operation state is such that the rich air-fuel mixture should be burned, the routine proceeds to step 226, where the feedback correction coefficient FAF
Is fixed at 1.0, and then the routine proceeds to step 209.

On the other hand, when K = 1.0, that is, when the air-fuel mixture having the stoichiometric air-fuel ratio is to be burned, the routine proceeds to step 224, where the feedback correction coefficient FAF is calculated based on the output signal of the air-fuel ratio sensor 33. Proceed to step 209. In step 224, when the air-fuel ratio sensor 33 detects that the air-fuel ratio has become rich, the FAF is decreased, and when it is detected that the air-fuel ratio has become lean, the FAF is increased. The air-fuel ratio will be maintained.

FIGS. 14 to 18 show a second embodiment according to the present invention. Empty mixture and deceleration operation is performed at this time in the second embodiment exceeds the set value MAX which is _the amount of NO _x ΣNOX being absorbed in the NO _x absorbent 18 As can be seen from Figure 14 a predetermined Rich fuel ratio (K> 1.0)
It is said. Then the air-fuel ratio of the mixture and _the amount of NO _x ΣNOX becomes zero is changed to a lean again rich. Although not shown in FIG. 14, the mixture of the air-fuel mixture is temporarily made rich similarly to the case where the idling operation is performed when ΣNOX> MAX.

In the second embodiment, the amount of NO _x ΣNO
Releasing action of the NO _x from the automatic air-fuel ratio of the mixture even when the speed change action is performed in the transmission 20 is temporarily made rich _the NO _x absorbent 18 when X is larger than the set value MAX is Done. That is, as shown in FIG. 9, when the shift I is performed, ＸNOx <MAX, so that the air-fuel ratio of the air-fuel mixture is not made rich, but when the shift II is performed,
Since NOX> MAX, when the shift II is performed, the air-fuel ratio of the air-fuel mixture is temporarily made rich. In addition,
Although not shown in Figure 9 but _the amount of NO _x ΣNOX set value M
When larger than AX, the lock-up mechanism 23 is turned on.
The air-fuel ratio of the air-fuel mixture is also temporarily made rich when the off-switching operation is performed.

As described above, in the second embodiment, when the shift operation of the automatic transmission 20 or the on / off switching operation of the lock-up mechanism 23 is performed (if ΣNOX> MAX, the air-fuel ratio of the air-fuel mixture is temporarily reduced). In this case, the frequency at which the torque change occurs can be reduced.
9 shows a routine for controlling the O _x release flag.

Referring to FIG. 15, first, in step 3
_The NO _x releasing flag in 00 whether has been set or not. In normal _the NO _x releasing flag since the reset process proceeds to step 301, whether the deceleration operation is started is determined. For example, when the engine speed is equal to or higher than a predetermined speed and the throttle valve 14 reaches the idling opening degree, it is determined that the deceleration operation has been started. If it is not during the deceleration operation, the routine proceeds to step 302, where it is determined whether or not the idling operation has been started. For example, when the engine speed is equal to or lower than the predetermined speed and the throttle valve 14 is at the idling opening, it is determined that the idling operation has been started. When the idling operation has not been started, the routine proceeds to step 303.

In step 303, the speed of the automatic transmission 20 is changed from the first gear to the second gear, the second gear to the third gear, the third gear to the fourth gear, the fourth gear to the third gear, the third gear to the second gear, or the second gear to the first gear. It is determined whether or not a shift request for switching to is issued. If a shift request has not been issued, the routine proceeds to step 304, where it is determined whether a request to switch the lockup mechanism 23 from on to off or from off to on has been issued. When the switching request has not been issued, the process returns to step 300 again.

On the other hand, when it is determined in step 301 that the deceleration operation has been started, or in step 3
If it is determined in step 02 that the idling operation has started, or if it is determined in step 303 that a shift request has been issued, or if it is determined in step 304 that a switching request has been issued, step 30 is performed.
5 willing amount of NO _x ΣNOX being absorbed in the NO _x absorbent 18 whether greater than the set value MAX or not. When ΣNOX ≦ MAX, the process returns to step 300 again. This .SIGMA.NOX> NO _x releasing flag proceeds becomes the MAX in step 306 is set for. Air-fuel ratio of the mixture with _the NO _x releasing flag is set as described later is made rich.

[0056] whether deceleration operation since the NO _x when releasing flag is set for example engine speed proceeds from step 300 to step 307 is below a predetermined rotational speed is completed is discriminated. If the deceleration operation has not been completed, the routine proceeds to step 308, where it is determined whether the idling operation has been completed, for example, because the throttle valve 14 has been opened. If the idling operation has not been completed, the routine proceeds to step 309, where the automatic transmission 2
Since the number of revolutions of the input shaft 26 of 0 becomes equal to the number of revolutions X reduction ratio of the output shaft 21, it is determined whether or not the shifting operation has been completed. If the shift operation has not been completed, the process proceeds to step 310 to determine whether or not the switching operation of the lock-up mechanism 23 from OFF to ON has been completed since the engine speed and the rotation speed of the input shaft 26 have become equal, for example. Alternatively, since the difference between the engine speed and the speed of the input shaft 26 has become larger than a predetermined difference, it is determined whether or not the switching operation of the lock-up mechanism 23 from on to off has been completed.
If the switching action has not been completed, step 300 is repeated.
Return to

On the other hand, when it is determined in step 307 that the deceleration operation has been completed, or when it is determined in step 308 that the idling operation has been completed, or when it is determined in step 309 that the shifting operation has been completed, when it is determined that the use switching action has been completed in step 310 NO _x releasing flag is reset routine proceeds to step 311. That is, during deceleration operation or during idling, or the shift request is set between _the NO _x releasing flag until until that shifting action is completed issued, or the switching request for issued by switching action completed Will be.

FIGS. 16 to 18 show a routine for controlling the air-fuel ratio, and this routine is executed by interruption every predetermined time. Referring to FIGS. 16 to 18, first, at step 400, the basic fuel injection time TP is calculated from the map shown in FIG. Next, at step 401, a correction coefficient K is obtained from the relationship shown in FIG. 3 according to the operating state of the engine. Next, at step 402, it is determined whether the correction coefficient K is smaller than 1.0.
If K ≦ 1.0, that is, if the operating state is to burn a lean air-fuel mixture or a stoichiometric air-fuel mixture, step 403 is executed.
Willing _the NO _x releasing flag is whether it is set or not. When the NO _x release flag is not set, the process proceeds to step 404.

At step 404, it is determined whether or not K = 1.0. If K is not 1.0, that is, if the operating state is such that the lean air-fuel mixture is to be burned, the routine proceeds to step 405, where the feedback correction coefficient FAF is fixed at 1.0. Next, at step 406 NO _x absorption amount NOXA is calculated monkey per unit time from the map shown in FIG. 6 (A). Next, at step 407 NO _x emissions NOXD is made zero, then the routine proceeds to step 408.

In step 408, the fuel injection time TAU is calculated based on the following equation. In TAU = f · TP · K · FAF then step 409, NO _x amount ΣNOX is calculated, which is absorbed in _the NO _x absorbent 18 on the basis of the following equation. .SIGMA.NOX = .SIGMA.NOX + whether NOXA-Kf · NOXD then _the amount of NO _x .SIGMA.NOX step 410 becomes negative is discriminated, are .SIGMA.NOX is zero proceeds to step 411 when it is .SIGMA.NOX <0. At this time, the lean mixture is burned in the combustion chamber 3.

On the other hand, at step 404, K = 1.0
Is determined, that is, in the operating state in which the air-fuel mixture having the stoichiometric air-fuel ratio is to be burned, the routine proceeds to step 412, where the feedback correction coefficient FAF is calculated based on the output signal of the air-fuel ratio sensor 33, and then proceeds to step 415. . In step 415 the calculated discharge amount of NO _x NOXD per unit time from the map shown in FIG. 7 (A), then _the NO _x releasing from the map shown in relation to FIG. 7 (C) shown in step 416 FIG. 7 (B) The rate Kf is calculated. Then absorption of NO _x amount NOXA per unit in step 417 the time is made zero, then the routine proceeds to step 408. At this time, in step 412, when the air-fuel ratio sensor 33 detects that the air-fuel ratio has become rich, the FAF is decreased, and
When it is detected that the air-fuel ratio has become lean, the FAF is increased, so that the air-fuel ratio is maintained at the stoichiometric air-fuel ratio.

On the other hand, at step 402, K> 1.0
If it is determined that, i.e. _the NO _x releasing flag proceeds to step 413 when the operating state to combust a rich mixture is reset. Next, at step 414, the feedback correction coefficient FAF is fixed at 1.0, and then the routine proceeds to step 415. On the other hand, when the NO _x release flag is set, the routine proceeds from step 403 to step 418, where it is determined whether or not the NO _x amount ΣNOx has become zero.
If ΣNOX = 0, the routine proceeds to step 420, where the correction coefficient K is set to a predetermined value KK. This value KK
Is a value of about 1.1 to 1.2 at which the air-fuel ratio of the air-fuel mixture becomes about 12.5 to 13.5. Then step 42
Released amount of NO _x NOXD per unit time from the map shown in is calculated in 1 Figure 7 (A). Then step 422
In _the NO _x releasing factor Kf is calculated from the map shown in FIG. 7 relationship and 7 shown in (B) (C), then step 423
In absorption of NO _x amount NOXA per unit time is made zero. Next, at step 424, the feedback correction coefficient FAF is fixed at 1.0, and then the routine proceeds to step 408.

Next, at step 418, ΣNOX =
If it is determined that the value has become 0, the process proceeds to step 419 and NO
_{The x} release flag is reset, then go to step 420. Therefore, after the NO _x release flag is set, ΣNO
Until X = 0, the air-fuel ratio of the air-fuel mixture is made rich,
When ΣNOX = 0, the air-fuel ratio of the air-fuel mixture is switched from rich to lean.

[0064]

According to the present invention, the output torque of the automatic transmission temporarily changes, whereby the frequency of occurrence of torque shock can be reduced.

[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 illustrating 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.

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

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

FIG. 8 is a diagram showing a gear position region and a lock-up ON region.

FIG. 9 is a time chart of air-fuel ratio control.

FIG. 10 is a flowchart for performing a setting value switching process.

FIG. 11 is a flowchart showing air-fuel ratio control.

FIG. 12 is a flowchart showing air-fuel ratio control.

FIG. 13 is a flowchart showing air-fuel ratio control.

FIG. 14 is a time chart of air-fuel ratio control.

FIG. 15 is a flowchart for controlling a NO _x release flag.

FIG. 16 is a flowchart showing air-fuel ratio control.

FIG. 17 is a flowchart showing air-fuel ratio control.

FIG. 18 is a flowchart showing air-fuel ratio control.

[Explanation of symbols]

16 ... exhaust pipe 18 ... NO _x absorbent 20 ... automatic transmission 23 ... lock-up mechanism

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI F01N 3/18 ZAB F01N 3/24 ZABR 3/24 ZAB F02D 29/00 C F02D 29/00 B01D 53/34 129Z (56) Reference Document JP-A-5-263917 (JP, A) JP-A-64-45933 (JP, A) JP-A-5-306641 (JP, A) JP-A-62-25555 (JP, A) JP-A-6-23555 173742 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/04 305

Claims (4)

(57) [Claims] 1. A comprising an automatic transmission, the air-fuel ratio of the inflowing exhaust gas is absorbed NO _x when the lean, release the NO _x air-fuel ratio of the exhaust gas is absorbed when the stoichiometric air-fuel ratio or rich flowing in an internal combustion engine arranged to _the NO _x absorbent in the engine exhaust passage to the amount of NO _x estimating means lean air-fuel mixture to estimate the amount of NO _x absorbed in _the NO _x absorbent when being burned, NO the rich temporarily switching the air-fuel ratio of the mixture to be burned from the lean in the engine when it exceeds the first set value _the amount of NO _x is a predetermined estimated to be absorbed in the _x absorbent and 1 of the air-fuel ratio switching means, the automatic transmission when _the amount of NO _x estimated to be absorbed in _the NO _x absorbent is higher than a second set value predetermined smaller than the first set value When the shifting action of Exhaust purification system for an internal combustion engine and a second air-fuel ratio switching means for switching the air-fuel ratio of the mixture to be burned during the shifting action of the transmission from the lean temporarily rich. 2. A comprising an automatic transmission that includes a lock-up mechanism, the air-fuel ratio of the inflowing exhaust gas is absorbed NO _x when the lean, when the air-fuel ratio of the inflowing exhaust gas of the stoichiometric air-fuel ratio or rich is NO that releases absorbed NO _x
In an internal combustion engine arranged to _x absorbent engine exhaust passage, NO _x when the lean air-fuel mixture is burned
And _the amount of NO _x estimating means for estimating the amount of NO _x absorbed in the absorbent, is estimated to be absorbed in _the NO _x absorbent NO
a first air-fuel ratio switching means for switching the air-fuel ratio of the mixture to be rich temporarily from lean combustion in the engine when it exceeds the first set _{value x} amount is predetermined in _the NO _x absorbent lockup when the amount of NO _x estimated to be absorbed second set on and off switching for換作the lockup mechanism when greater than value is performed which is determined smaller advance than the first set value A second air-fuel ratio switching device for temporarily switching an air-fuel ratio of an air-fuel mixture to be burned from lean to rich during an on / off switching operation of the mechanism. Comprising a wherein the automatic transmission, the air-fuel ratio of the inflowing exhaust gas is absorbed NO _x when the lean, release the NO _x air-fuel ratio of the exhaust gas is absorbed when the stoichiometric air-fuel ratio or rich flowing in an internal combustion engine arranged to _the NO _x absorbent in the engine exhaust passage to the amount of NO _x estimating means lean air-fuel mixture to estimate the amount of NO _x absorbed in _the NO _x absorbent when being burned, NO mixture to be burned in the engine when the operating condition of the engine becomes a predetermined operating condition when the amount of NO _x estimated to be absorbed in the _x absorbent exceeds a predetermined set value a first air-fuel ratio control means for temporarily rich air-fuel ratio of the air, the operating state of the engine is absorbed in _the nO _x absorbent even if not predetermined operating state of the estimated pre-determined amount of NO _x is A second air-fuel ratio control means for temporarily enriching the air-fuel ratio of the air-fuel mixture to be burned during the speed-changing operation of the automatic transmission when the speed-changing operation of the automatic transmission is performed when the value is larger than the set value. An exhaust gas purification device for an internal combustion engine, comprising: 4. An automatic transmission having a lock-up mechanism.
Equipped, when the air-fuel ratio of the inflowing exhaust gas is lean
NO_xAnd the air-fuel ratio of the exhaust gas that flows in is stoichiometric
NO absorbed when ratio or rich_xReleases NO
_xIn an internal combustion engine with an absorbent placed in the engine exhaust passage
NO when the lean mixture is being burned_x
NO absorbed by the absorbent_xNO to estimate the amount_xHand
Dan and NO_xNO presumed to be absorbed by the absorbent
_xWhen the amount exceeds the preset value, the engine
When the operating state becomes a predetermined operating state, the engine
Air-fuel ratio of air-fuel mixture to be burned
The first air-fuel ratio control means that performs
NO even if it is not the predetermined operating state _xSucking
NO presumed to be absorbed in the absorbent_xQuantity is predetermined
When the lock-up mechanism is
When the lock-up mechanism is
Reduce the air-fuel ratio of the mixture to be burned during the on / off switching action.
Second air-fuel ratio control means for making the air-fuel ratio richer
An exhaust gas purification device for an internal combustion engine.