JP2001065388A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impede a misfire due to purge action of fuel vapor. SOLUTION: Fuel vapor generated in a fuel tank 26 is purged in an engine intake passage. When the concentration of a mixture around a spark plug 7 is judged to be the limit concentration or more at ignition time when the fuel vapor is purged, a purge is stopped, a purge amount is decreased, injection timing is advanced, or ignition timing is delayed so as to decrease concentration of the mixture around the spark plug 7 at ignition time below the limit concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for an internal combustion engine.

[0002]

2. Description of the Related Art There is known an internal combustion engine in which fuel vapor generated in a fuel tank is purged into an engine intake passage, and at this time, a fuel injection amount is controlled so that an air-fuel ratio becomes a target air-fuel ratio. See JP-A-5-52139).

[0003]

In an internal combustion engine in which an air-fuel mixture is ignited by a spark plug, misfire occurs if the air-fuel mixture formed around the spark plug is too rich. Therefore, in an internal combustion engine provided with an ignition plug, it is necessary that the concentration of the air-fuel mixture formed around the ignition plug does not become higher than the concentration causing misfire.

However, when the fuel vapor is purged into the engine intake passage, the concentration of the air-fuel mixture formed around the ignition plug by the fuel vapor increases, and as a result, the concentration of the air-fuel mixture formed around the ignition plug becomes misfiring. May be higher than the concentration that causes In such a case, a misfire will occur, and therefore, it is necessary to take some measures.

[0005]

In a first aspect of the present invention, there is provided an internal combustion engine in which an ignition plug is disposed in a combustion chamber and fuel vapor generated in a fuel tank is purged into an engine intake passage. When there is a possibility that the concentration of the air-fuel mixture around the spark plug at the time of ignition may become higher than a predetermined concentration at the time of ignition, the ignition timing or the air-fuel mixture is reduced so that the concentration of the air-fuel mixture around the spark plug at the time of ignition decreases. Is controlled.

In the second invention, in the first invention,
Determining means for determining whether the concentration of the air-fuel mixture around the ignition plug when purging the fuel vapor is equal to or higher than a predetermined limit concentration at the time of ignition; and And control means for controlling the ignition timing or the concentration of the air-fuel mixture so that the concentration of the air-fuel mixture around the ignition plug at the time of ignition becomes equal to or lower than the limit concentration.

In the third invention, in the second invention,
When it is determined that the concentration of the air-fuel mixture around the ignition plug becomes equal to or higher than the limit concentration at the time of ignition, the control means stops the purging operation of the fuel vapor or reduces the purge amount of the fuel vapor. In a fourth aspect based on the second aspect, the control means advances the fuel injection timing into the combustion chamber or delays the ignition timing when it is determined that the concentration of the air-fuel mixture around the ignition plug becomes higher than the limit concentration at the time of ignition. I am trying to do it.

[0008] In a fifth invention, in the second invention,
Fuel is injected into the combustion chamber during the engine intake passage or intake stroke to form a homogeneous mixture, and then fuel is injected into the combustion chamber at the end of the compression stroke to cause the mixture to enter a limited region around the spark plug. When it is determined that the concentration of the air-fuel mixture around the spark plug becomes greater than or equal to the limit concentration at the time of ignition in the case where the air-fuel mixture formed in the limited region around the spark plug is ignited by the spark plug, The control means reduces the amount of fuel injected into the combustion chamber in the engine intake passage or during the intake stroke.

In the sixth invention, in the second invention,
In a case where fuel is injected into the combustion chamber during the engine intake passage or during the intake stroke to form a homogeneous mixture, and the homogeneous mixture is ignited by an ignition plug, the concentration of the mixture around the ignition plug is ignited. When it is determined at times that the concentration becomes equal to or higher than the limit concentration, the control means reduces the amount of fuel injected into the combustion chamber in the engine intake passage or during the intake stroke.

[0010] In a seventh invention, in the second invention,
A stratified operation in which a mixture formed in a limited area around the ignition plug is ignited by the ignition plug and a homogeneous mixture operation in which the homogeneous mixture is ignited by the ignition plug are selectively performed, and the stratified operation is performed. When it is determined that the concentration of the mixture around the spark plug becomes equal to or higher than the limit concentration at the time of ignition, the control means switches the operation from the stratified operation to the homogeneous mixture operation.

According to an eighth aspect, in the first aspect,
When the air-fuel ratio of the inflowing exhaust gas lean absorbs NO _x contained in the exhaust gas, the _the NO _x absorbent to release the NO _x when the air-fuel ratio of the exhaust gas is absorbed and becomes the stoichiometric air-fuel ratio or rich flowing Placed in the engine exhaust passage, NO _x
So that the amount obtained by subtracting the fuel vapor amount from a predetermined fuel injection quantity of fuel injection quantity of when to release the NO _x from the absorbent.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes an engine body, 2 denotes a cylinder block, 3 denotes a cylinder head, 4 denotes a piston, 5 denotes a combustion chamber, and 6 denotes a peripheral portion of an inner wall surface of the cylinder head 3. Fuel injection valve, 7 is the cylinder head 3
, An ignition plug, 8 an intake valve, 9 an intake port, 10 an exhaust valve, and 11 an exhaust port. The intake port 9 is connected to a surge tank 13 via a corresponding intake branch pipe 12, and the surge tank 13 is connected to an air cleaner 15 via an intake duct 14. A throttle valve 17 driven by a step motor 16 is arranged in the intake duct 14. On the other hand, the exhaust port 11 is connected to an exhaust manifold 18. Exhaust manifold 18
And the surge tank 13 are connected to each other through an exhaust gas recirculation (hereinafter referred to as EGR) passage 19, and the EGR passage 1
An electronically controlled EGR control valve 20 is arranged in 9.

As shown in FIG. 1, the internal combustion engine is activated carbon 2
1 is provided. The canister 22 has a fuel vapor chamber 23 and an atmosphere chamber 24 on both sides of the activated carbon 21, respectively. The fuel vapor chamber 23 is on the one hand a conduit 25
To the fuel tank 26, and on the other hand a conduit 27
Through the surge tank 13. A purge control valve 28 controlled by an output signal of the electronic control unit 40 is disposed in the conduit 27. The fuel vapor generated in the fuel tank 26 is sent into the canister 22 via the conduit 25 and is adsorbed on the activated carbon 21. Purge control valve 2
When the valve 8 is opened, air is sent from the atmosphere chamber 24 through the activated carbon 21 and into the conduit 27. When the air passes through the activated carbon 21, the fuel vapor adsorbed on the activated carbon 21 is desorbed from the activated carbon 21, so that the air containing the fuel vapor, that is, the purge gas, enters the surge tank 13 through the conduit 27. Purged.

The exhaust manifold 18 has a catalytic converter 29
is connected to a, in the catalyst converter 29a NO _x
An absorbent 29 is arranged. The electronic control unit 40 is composed of a digital computer, and a ROM (Read Only Memory) 4 interconnected by a bidirectional bus 41.
2, RAM (random access memory) 43, CPU
(Microprocessor) 44, input port 45 and output port 46 are provided. A concentration sensor 30 for detecting the concentration of the purged fuel vapor is disposed in the surge tank 13, and the output voltage of the concentration sensor 30 is input to the input port 45 via the corresponding AD converter 47. The input port 45 receives the output signal of the atmospheric pressure sensor 31 for detecting the atmospheric pressure.
Is entered via A load sensor 33 that generates an output voltage proportional to the amount of depression L of the accelerator pedal 32 is connected to the accelerator pedal 32, and the output voltage of the load sensor 33 is input to an input port 45 via a corresponding AD converter 47. . The input port 45 is connected to a crank angle sensor 34 that generates an output pulse every time the crankshaft rotates, for example, by 30 °. An air-fuel ratio sensor 35 is disposed in the exhaust manifold 18, and an output signal of the air-fuel ratio sensor 35 is input to an input port 45 via a corresponding AD converter 47. On the other hand, the output port 46 is connected to the fuel injection valve 6, the ignition plug 7, the step motor 16, the EGR control valve 20, and the purge control valve 28 via the corresponding drive circuit 48.

[0015] Figure 2 is a fuel injection amount Q1, Q2, Q (= Q 1
+ Q ₂ ), the injection start timing θS1, θS2, the injection completion timing θE1, θE2, and the average air-fuel ratio A in the combustion chamber 5.
/ F. In FIG. 2, the horizontal axis L indicates the amount of depression of the accelerator pedal 32, that is, the required load.
When the required load L as can be seen from Figure 2 is lower than L ₁ is the fuel injection Q2 is performed between θE2 from θS2 of the end of the compression stroke. At this time, the average air-fuel ratio A / F is considerably lean. Required load L first fuel injection Q1 is performed between θE1 from the beginning of the intake stroke of θS1 when between L ₁ and L _2, then the second fuel in between θS2 of θE2 of the end of the compression stroke Injection Q2 is performed. At this time, the air-fuel ratio A / F is lean. When the required load L is greater than L ₂ the fuel injection Q1 is performed between θE1 from the beginning of the intake stroke of the? S1. At this time, in the region where the required load L is low, the average air-fuel ratio A / F is lean, and the required load L
Becomes higher, the average air-fuel ratio A / F becomes the stoichiometric air-fuel ratio, and if the required load L further increases, the average air-fuel ratio A / F becomes rich. The operation region where the fuel injection Q2 is performed only at the end of the compression stroke, the operation region where the fuel injections Q1 and Q2 are performed twice, and the fuel injection Q only at the beginning of the intake stroke.
The operation range in which 1 is performed is not determined only by the required load L, but is actually determined by the required load L and the engine speed.

FIG. 3 shows that the fuel injection Q2 is performed only when the required load L is smaller than L ₁ (FIG. 2), ie, only at the end of the compression stroke.
Is performed. In this case, the fuel is injected from the fuel injection valve 6 toward the bottom wall surface of the cavity 5 a formed on the top surface of the piston 4. This fuel is guided by the peripheral wall surface of the cavity 5a toward the spark plug 7,
Thereby, an air-fuel mixture G is formed around the ignition plug 7 as shown in FIG. In the embodiment according to the present invention, the space in the combustion chamber 5 around the air-fuel mixture G is filled with air or a mixed gas of air and EGR gas. Therefore, when the required load L is smaller than L ₁ (FIG. 2). The mixture G is formed in a limited area in the combustion chamber 5. Less than,
Such a state is called a strong stratification operation state.

In the strong stratified operation state shown in FIG. 3, the mixture G formed around the spark plug 7 is ignited by the spark plug 7. In this case, if the mixture G is too rich, a misfire will occur. On the other hand, as described above, the required load L is L ₁
Fuel injection is divided into two times when it is between the L _2. In this case, a homogeneous lean mixture is formed in the combustion chamber 5 by the first fuel injection Q1 performed at the beginning of the intake stroke. Next, an air-fuel mixture having an optimum concentration is formed around the ignition plug 7 by the second fuel injection Q2 performed at the end of the compression stroke. This air-fuel mixture is ignited by the spark plug 7, and the ignition flame causes the lean air-fuel mixture to burn. Hereinafter, such a state is referred to as a weak stratification operation state. In this case as well, if the mixture formed around the ignition plug 7 is too rich, misfire will occur.

Meanwhile, the required load L has uniform mixture of lean or stoichiometric or rich air-fuel ratio is formed in the combustion chamber 5 as is shown in Figure 2 when greater than L _2, the homogeneous air-fuel mixture It is ignited by the spark plug 7. Hereinafter, such a state is referred to as a homogeneous mixture operation state. In this case as well, if the mixture formed around the ignition plug 7 is too rich, misfire will occur.

Incidentally, the target opening TA of the throttle valve 17 and the target opening E of the EGR control valve 20 during the strong stratification operation.
G, the ignition timing θI, the duty ratio DU of the control pulse of the purge control valve 28, the injection amount Q2, and the injection start timing θS2
As shown in FIGS. 4 (A) to 4 (F), R is determined in advance in the form of a map as a function of the required load L and the engine speed N.
It is stored in the OM42. In this case, the injection completion timing θE2 is calculated based on the injection start timing θS2, the injection amount Q2, and the engine speed N.

Further, the target opening TA of the throttle valve 17 and the target opening E of the EGR control valve 20 during the weak stratification operation.
G, the ignition timing θI, the duty ratio DU of the control pulse of the purge control valve 28, the injection start timing θS2, and the injection amount Q1
As shown in FIGS. 5 (A) to 5 (F), R is previously determined in the form of a map as a function of the required load L and the engine speed N.
It is stored in the OM42. Note that the injection amount Q2 is constant, and the injection completion timing θE2 is calculated based on the injection start timing θS2, the injection amount Q2, and the engine speed N. The injection start timing θS1 is fixed, and the injection completion timing θ
E1 is calculated based on the injection start timing θS1, the injection amount Q1, and the engine speed N.

On the other hand, the target opening TA of the throttle valve 17, the target opening EG of the EGR control valve 20, the ignition timing θI, the duty ratio DU of the control pulse of the purge control valve 28, and the injection amount Q1 during the homogeneous mixture operation are as follows. As shown in FIGS. 6A to 6E, the required load L and the engine speed N are respectively shown.
Is stored in the ROM 42 in advance in the form of a map as a function of. The injection start timing θS1 is fixed, and the injection completion timing θE1 is calculated based on the injection start timing θS1, the injection amount Q1, and the engine speed N.

In the embodiment according to the present invention, FIG.
(A)-(F), FIGS. 5 (A)-(F), FIG. 6 (A)-
Based on the map shown in (E), the opening of the throttle valve 17, the opening of the EGR control valve 20, the ignition timing, the duty ratio of the control pulse of the purge control valve 28, the injection amount Q
1, Q2, injection start timings θS1, θS2, and injection completion timings θE1, θE2.

By the way, even if the duty ratio DU of the control pulse of the purge control valve 28 is constant, that is, even if the purge gas amount is constant, the amount of fuel vapor generated in the fuel tank 26 and adsorbed by the activated carbon 21 The amount of fuel vapor purged into the surge tank 13 varies depending on the amount of fuel vapor being supplied. Therefore, even if the duty ratio DU of the control pulse of the purge control valve 28 is determined according to the maps of FIGS. 4 (D), 5 (D) and 6 (D), the amount of fuel vapor supplied into the combustion chamber 5 varies. I do. In this case, when the amount of the fuel vapor supplied into the combustion chamber 5 is large, the mixture formed around the ignition plug 7 becomes rich, thus causing a misfire. Further, even when the purge amount is increased so that the adsorption capacity of the activated carbon 21 is not saturated, the air-fuel mixture formed around the ignition plug 7 becomes thick, thus causing a misfire.

In the present invention, various measures are taken in order to prevent the occurrence of such a misfire. It is to be noted that the mixture near the ignition plug 7 is most likely to be rich during the strong stratification operation, and then the mixture is likely to be too rich during the weak stratification operation. Therefore, measures have been taken in consideration of this. Next, a first embodiment will be described with reference to FIGS.

In this embodiment, when the stratified operation in which the mixture around the ignition plug 7 tends to be most concentrated is performed, the purging operation is stopped or the fuel in the intake air supplied into the combustion chamber 5 is stopped. When the vapor concentration exceeds the reference concentration, the purge action is stopped during the strong stratification operation. FIG.
Shows an operation control routine.

Referring to FIG. 7, first, at step 10
At 0, the purge execution determination shown in FIG. 8 or 9 is performed. Therefore, the purge execution control will be described first. In the example shown in FIG. 8, first, at step 110, it is determined whether or not a purge execution condition for purging the fuel vapor is satisfied. If the purge execution condition is satisfied, the routine proceeds to step 111, where a purge flag is set. On the other hand, when the purge execution condition is not satisfied, the routine proceeds to step 112, where the purge action of the fuel vapor is stopped, and then, in step 113, the purge flag is reset. Therefore, in this example, the purge flag is set when the purge execution condition is satisfied.

On the other hand, in the example shown in FIG. 9, first, at step 120, it is determined whether or not the purge execution condition is satisfied. When the purge execution condition is satisfied, the routine proceeds to step 121. In step 121, the density sensor 3
It is determined whether the concentration of the fuel vapor in the intake air detected by 0 is higher than a predetermined reference concentration K. When the concentration of the fuel vapor in the intake air is higher than the reference concentration K, the routine proceeds to step 122, where a purge flag is set, and the concentration of the fuel vapor in the intake air is reduced to the reference concentration K.
If it is lower than the above, the routine proceeds to step 123, where the purge flag is reset. On the other hand, when it is determined in step 120 that the purge execution condition is not satisfied, the routine proceeds to step 124, where the purge action of the fuel vapor is stopped, and then, in step 123, the purge flag is reset. Therefore, in this example, the purge flag is set when the concentration of the fuel vapor in the intake air becomes higher than the reference concentration K.

Returning to FIG. 7, in step 101, it is determined whether or not the operation is in the operation region in which the stratification operation is to be performed. On the other hand, when it is determined that the operation is not in the operation region where the strong stratification operation is performed, step 10
The routine proceeds to step 2 where it is determined whether or not the operating region is in the weak stratified operation. If it is in the operation region where the weak stratification operation is performed, the routine proceeds to step 300, where the weak stratification operation is performed.

In the strong stratification operation in step 200, the weak stratification operation in step 300, and the homogeneous mixture operation in step 400, injection control, ignition control, and purge control are performed based on the purge flag. However,
FIG. 7 shows basic operations of the strong stratification operation, the weak stratification operation, and the homogeneous mixture operation, and each control based on the purge flag is shown in FIGS. 10 to 20.

As shown in FIG. 7, in the basic operation of the strong stratification operation, first, in step A, the target opening TA of the throttle valve 17 is calculated from the map shown in FIG. Is the target opening degree TA. Next, at step B, the target opening EG of the EGR control valve 20 is calculated from the map shown in FIG. 4B, and the opening of the EGR control valve 20 is set to the target opening EG. Next, at step C, the injection amount Q2 is calculated from the map shown in FIG. 4E, and the injection start timing θ is obtained from the map shown in FIG.
S2 is calculated, and based on these, fuel injection is performed at the end of the compression stroke. Next, in step D, the ignition timing θI is determined from the map shown in FIG. 4C, and then in step E, the duty of the control pulse of the purge control valve 28 is determined from the map shown in FIG. 4D unless the purge action is stopped. DU is calculated.

On the other hand, in the basic operation of the weak stratification operation as shown in FIG.
The target opening TA of the throttle valve 17 is calculated from the map shown in Fig. 7, and the opening of the throttle valve 17 is used as the target opening TA. Next, at step B, the target opening degree EG of the EGR control valve 20 is calculated from the map shown in FIG.
The opening of the R control valve 20 is set to the target opening EG. Next, in step C, the injection start timing θS2 is calculated from the map shown in FIG. 5 (E), and the injection amount Q1 is calculated from the map shown in FIG. 5 (F). Based on these, the fuel injection is performed at the end of the intake stroke and the end of the compression stroke. Is performed. Then step D
5C, the ignition timing θI is determined from the map shown in FIG. 5C. Then, in step E, the duty DU of the control pulse of the purge control valve 28 is calculated from the map shown in FIG. 5D unless the purge action is stopped. Is done.

As shown in FIG. 7, in the basic operation of the homogeneous mixture operation, first in step A, FIG.
Based on the map shown in FIG.
A is calculated, and the opening of the throttle valve 17 is set as the target opening TA. Next, at step B, the target opening EG of the EGR control valve 20 is calculated from the map shown in FIG. 6B, and the opening of the EGR control valve 20 is set to this target opening EG. Next, at step C, the injection amount Q1 is calculated from the map shown in FIG. 6 (E), and based on this, the fuel injection is performed in the intake stroke. Next, in step D, the ignition timing θI is determined from the map shown in FIG. 6C, and then in step E, the duty of the control pulse of the purge control valve 28 is determined from the map shown in FIG. 6D unless the purge action is stopped. DU is calculated.

FIG. 10 shows a first example of the strong stratification operation performed in step 200 of FIG. In this example, steps A, B, C, and D are the same as steps A, B, C, and D shown in FIG. 7, and therefore, only step E will be described below. In step E, it is first determined in step 210 whether or not the purge flag is set. When the purge flag has not been set, the routine proceeds to step 212, where FIG.
Is calculated as the final duty ratio DU0. On the other hand, when it is determined that the purge flag is set, the routine proceeds to step 211, where the purging operation of the fuel vapor is stopped.
Therefore, when the purge execution determination shown in FIG. 8 is used, the purge operation of the fuel vapor is stopped when the strong stratification operation is performed, and when the purge execution determination shown in FIG. When the vapor concentration becomes higher than the reference concentration K, the purge operation of the fuel vapor is stopped.

In any case, it is possible to prevent the mixture formed around the ignition plug 7 from becoming too rich, and thus to prevent misfiring. FIG.
Shows a second example of the strong stratification operation performed in step 200 of FIG. Note that, also in this example, steps A, B, C, and D are steps A, B, and C shown in FIG.
This is the same as C and D, so only step E will be described below.

In step E, it is first determined in step 220 whether the purge flag has been set. When the purge flag has not been set, the routine proceeds to step 222, where the duty ratio DU calculated from the map shown in FIG. 4D is made the final duty ratio DU0. On the other hand, when it is determined that the purge flag is set, the routine proceeds to step 221, and the duty ratio D calculated from the map shown in FIG.
The result of subtracting a predetermined value ΔDU from U is the final duty ratio DU0. That is, when the purge flag is set, the purge amount of the fuel vapor is reduced. Therefore, when the purge execution determination shown in FIG. 8 is used, the purge amount of the fuel vapor is reduced by performing the purge action, and when the purge execution determination shown in FIG. 9 is used, the fuel in the intake air is reduced. When the vapor concentration becomes higher than the reference concentration K, the purge amount of the fuel vapor is reduced.

In any case, it is possible to prevent the mixture formed around the spark plug 7 from becoming too rich, and thus to prevent misfire. FIG.
Shows a third example of the strong stratification operation performed in step 200 of FIG. In this example, steps A, B, D, and E correspond to steps A, B, D, and E shown in FIG.
This is the same as E, so that only step C will be described below.

In step C, it is first determined in step 230 whether the purge flag has been set. If the purge flag has not been set, the routine proceeds to step 232, where the injection start timing θS2 calculated from the map shown in FIG. 4F is set as the final injection start timing θS20. Next, at step 233, the injection amount Q2 is calculated. On the other hand, when it is determined that the purge flag is set, the routine proceeds to step 231, and the addition result obtained by adding the predetermined value ΔS to the injection start timing θS2 calculated from the map shown in FIG. Injection start timing θS20. That is, when the purge flag is set, the injection start timing θS2 is advanced.

Accordingly, when the purge execution determination shown in FIG. 8 is used, the injection start timing is advanced when the purge action is performed, and when the purge execution determination shown in FIG. 9 is used, the fuel in the intake air is reduced. When the vapor concentration becomes higher than the reference concentration K, the injection start timing is advanced. If the injection start timing is advanced, the injected fuel is dispersed over a wide range before the ignition is performed, and thus the mixture formed around the ignition plug 7 at the time of ignition becomes thin. Therefore, in any case, the spark plug 7
The mixture formed around it can be prevented from becoming too rich, and thus a misfire can be prevented.

FIG. 13 shows a fourth example of the strong stratification operation performed in step 200 of FIG. In this example, steps A, B, C, and E are the same as steps A, B, C, and E shown in FIG. 7, and therefore, only step D will be described below. In step D, it is first determined in step 240 whether the purge flag is set. When the purge flag has not been set, the routine proceeds to step 242, and FIG.
The ignition timing θI calculated from the map shown in FIG. On the other hand, when the purge flag is set, the routine proceeds to step 241, and FIG.
The subtraction result obtained by subtracting a predetermined value ΔI from the ignition timing θI calculated from the map shown in (C) is the final ignition timing θI. That is, when the purge flag is set, the ignition timing is delayed.

Therefore, when the purge execution judgment shown in FIG. 8 is used, the ignition timing is delayed when the purge action is performed, and when the purge execution judgment shown in FIG. 9 is used, the fuel in the intake air is When the vapor concentration becomes higher than the reference concentration K, the ignition timing is delayed. If the ignition timing is delayed, the injected fuel will be widely dispersed by the time the ignition is performed,
Thus, the mixture formed around the ignition plug 7 at the time of ignition becomes thin. Therefore, in any case, it is possible to prevent the mixture formed around the ignition plug 7 from becoming too rich.
Thus, misfire can be prevented from occurring.

FIG. 14 shows a first example of the weak stratification operation performed in step 300 of FIG. In this example, steps A, B, C, and D are the same as steps A, B, C, and D shown in FIG. 7, and therefore, only step E will be described below. In step E, it is first determined in step 310 whether the purge flag is set. When the purge flag has not been set, the process proceeds to step 312 and FIG.
Is calculated as the final duty ratio DU0. On the other hand, when it is determined that the purge flag is set, the routine proceeds to step 311 and the purging operation of the fuel vapor is stopped.
Therefore, when the purge execution determination shown in FIG. 8 is used, the purge action of the fuel vapor is stopped when the weak stratification operation is performed, and when the purge execution determination shown in FIG. When the vapor concentration becomes higher than the reference concentration K, the purge operation of the fuel vapor is stopped.

In any case, it is possible to prevent the air-fuel mixture formed around the ignition plug 7 from becoming too rich, and thus to prevent misfiring. FIG.
Shows a second example of the weak stratification operation performed in step 300 of FIG. Note that, also in this example, steps A, B, C, and D are steps A, B, and C shown in FIG.
This is the same as C and D, so only step E will be described below.

In step E, it is first determined in step 320 whether or not the purge flag has been set. If the purge flag has not been set, the routine proceeds to step 322, where the duty ratio DU calculated from the map shown in FIG. 5D is made the final duty ratio DU0. On the other hand, when it is determined that the purge flag is set, the routine proceeds to step 321 and the duty ratio D calculated from the map shown in FIG.
The result of subtracting a predetermined value ΔDU from U is the final duty ratio DU0. That is, when the purge flag is set, the purge amount of the fuel vapor is reduced. Therefore, when the purge execution determination shown in FIG. 8 is used, the purge amount of the fuel vapor is reduced by performing the purge action, and when the purge execution determination shown in FIG. 9 is used, the fuel in the intake air is reduced. When the vapor concentration becomes higher than the reference concentration K, the purge amount of the fuel vapor is reduced.

In any case, it is possible to prevent the mixture formed around the ignition plug 7 from becoming too rich, and thus to prevent misfire. FIG.
Shows a third example of the weak stratification operation performed in step 300 of FIG. In this example, steps A, B, D, and E correspond to steps A, B, D, and E shown in FIG.
This is the same as E, so that only step C will be described below.

In step C, it is first determined in step 330 whether or not the purge flag has been set. When the purge flag has not been set, the routine proceeds to step 332, where the injection start timing θS2 calculated from the map shown in FIG. 5E is set as the final injection start timing θS20. Next, at step 333, the injection amounts Q1 and Q2 are calculated. On the other hand, if it is determined that the purge flag has been set, then step 3
Proceeding to 31, the addition result obtained by adding the predetermined value ΔS to the injection start timing θS2 calculated from the map shown in FIG. 5 (E) is set as the final injection start timing θS20. That is, when the purge flag is set, the injection start timing θS2
Is hastened.

Therefore, when the purge execution judgment shown in FIG. 8 is used, the injection start timing is advanced when the purge action is performed, and when the purge execution judgment shown in FIG. 9 is used, the fuel in the intake air is reduced. When the vapor concentration becomes higher than the reference concentration K, the injection start timing is advanced. If the injection start timing is advanced, the injected fuel is dispersed over a wide range before the ignition is performed, and thus the mixture formed around the ignition plug 7 at the time of ignition becomes thin. Therefore, in any case, the spark plug 7
The mixture formed around it can be prevented from becoming too rich, and thus a misfire can be prevented.

FIG. 17 shows a fourth example of the weak stratification operation performed in step 300 of FIG. In this example, steps A, B, C, and E are the same as steps A, B, C, and E shown in FIG. 7, and therefore, only step D will be described below. In step D, it is first determined in step 340 whether or not the purge flag is set. When the purge flag has not been set, the routine proceeds to step 342, and FIG.
The ignition timing θI calculated from the map shown in FIG. On the other hand, when the purge flag is set, the routine proceeds to step 341 and proceeds to FIG.
The subtraction result obtained by subtracting a predetermined value ΔI from the ignition timing θI calculated from the map shown in (C) is the final ignition timing θI. That is, when the purge flag is set, the ignition timing is delayed. Therefore, when the purge execution determination shown in FIG. 8 is used, the ignition timing is delayed when the purge action is performed, and when the purge execution determination shown in FIG. 9 is used, the concentration of the fuel vapor in the intake air is reduced. Is the reference concentration K
When it becomes higher, the ignition timing is delayed.

When the ignition timing is delayed, the injected fuel is dispersed over a wide range before the ignition is performed, and thus the mixture formed around the ignition plug 7 at the time of ignition becomes thin. Therefore, in any case, it is possible to prevent the air-fuel mixture formed around the ignition plug 7 from becoming too rich, and thus to prevent misfire. FIG. 18 shows Step 4 of FIG.
7 shows a first example of a homogeneous mixture operation performed at 00. In this example, steps A, B, C, D
Are the same as steps A, B, C and D shown in FIG. 7, and therefore only step E will be described below.

In step E, it is first determined in step 410 whether the purge flag has been set. If the purge flag has not been set, the routine proceeds to step 412, where the duty ratio DU calculated from the map shown in FIG. 6D is made the final duty ratio DU0. On the other hand, when it is determined that the purge flag is set, the routine proceeds to step 411, where the duty ratio D calculated from the map shown in FIG.
The result of subtracting a predetermined value ΔDU from U is the final duty ratio DU0. That is, when the purge flag is set, the purge amount of the fuel vapor is reduced. Therefore, when the purge execution determination shown in FIG. 8 is used, the purge amount of the fuel vapor is reduced by performing the purge action, and when the purge execution determination shown in FIG. 9 is used, the fuel in the intake air is reduced. When the vapor concentration becomes higher than the reference concentration K, the purge amount of the fuel vapor is reduced.

In any case, it is possible to prevent the air-fuel mixture formed around the ignition plug 7 from becoming too rich, thereby preventing the occurrence of misfire. FIG.
Shows a second example of the homogeneous mixture operation performed in step 400 of FIG. In this example, steps A, B, C, and E correspond to steps A, B, and C shown in FIG.
This is the same as C and E, so only step D will be described below.

In step D, it is first determined in step 420 whether the purge flag has been set. When the purge flag has not been set, the routine proceeds to step 422, where the ignition timing θI calculated from the map shown in FIG. 6C is set as the final ignition timing θI0. On the other hand, when the purge flag is set, the routine proceeds to step 421, where a predetermined value Δ is calculated from the ignition timing θI calculated from the map shown in FIG.
The result of subtracting I is the final ignition timing θI. That is, when the purge flag is set, the ignition timing is delayed.

Therefore, when the purge execution judgment shown in FIG. 8 is used, the ignition timing is delayed when the purge action is performed, and when the purge execution judgment shown in FIG. 9 is used, the fuel in the intake air is When the vapor concentration becomes higher than the reference concentration K, the ignition timing is delayed. If the ignition timing is delayed, the injected fuel will be widely dispersed by the time the ignition is performed,
Thus, the mixture formed around the ignition plug 7 at the time of ignition becomes thin. Therefore, in any case, it is possible to prevent the mixture formed around the ignition plug 7 from becoming too rich.
Thus, misfire can be prevented from occurring.

Next, another embodiment will be described. As described above, during the weak stratification operation, a lean homogeneous mixture is formed in the combustion chamber 5 by the fuel injection Q1 during the intake stroke, and even during the homogeneous mixture operation, the homogeneous mixture is injected into the combustion chamber 5 by the fuel injection Q1. It is formed. On the other hand, the purged fuel vapor also forms a homogeneous mixture in the combustion chamber 5. Therefore, in the case where a homogeneous mixture is formed in the combustion chamber 5, if the injection amount is obtained by subtracting the fuel vapor amount from the injection amount Q1, the homogeneous mixture reduced by the decrease in the injection amount is changed by the fuel vapor. Therefore, the concentration of the homogeneous mixture in the combustion chamber 5 does not change regardless of the purge amount of the fuel vapor, regardless of whether the purge operation is performed. If the concentration of the homogeneous mixture in the combustion chamber 5 does not change, the concentration of the mixture around the ignition plug 7 does not change, and thus misfire can be prevented from occurring.

Therefore, in this embodiment, the amount obtained by subtracting the fuel vapor amount from the injection amount Q1 is used as the injection amount during the weak stratification operation and the homogeneous mixture operation. However, to do this, the fuel vapor amount must be calculated. Therefore, in this embodiment, as shown in FIG. 20, a pressure sensor 36 is disposed in the surge tank 13 and an air-fuel ratio sensor 37 is disposed in the conduit 27, based on the output signals of the pressure sensor 36 and the air-fuel ratio sensor 37. Thus, the amount of fuel vapor in the intake air is calculated. Next, a method of calculating the fuel vapor amount will be described.

FIG. 21 shows a purge gas flow rate per unit time when the purge control valve 28 is fully opened, that is, a fully opened purge gas flow rate PG100 (1 / sec). As shown in FIG. 21, the flow rate PG100 (l / sec) of the full-open purge gas is equal to the atmospheric pressure PA and the absolute pressure PM in the surge tank 13.
Is a function of the pressure difference (PA-PM). On the other hand, the purge control valve 28 is controlled based on the ratio of the time during which the purge control valve 28 should be opened within a certain time, that is, the duty ratio DU. As shown in FIG. 22, the purge gas flow rate (l / sec) per unit time is proportional to the duty ratio DU (%). Therefore, the actual purge gas flow rate (l / sec) per unit time can be calculated by multiplying the fully open purge gas flow rate (l / sec) shown in FIG. 21 by DU (%) / 100%.

On the other hand, the actual purge gas flow rate (l / sec) per unit time is changed to the fuel vapor concentration PV (g) in the purge gas.
/ L), the amount of fuel vapor purged per unit time (g / sec) is determined based on the following equation. EVQ = PG100 · PV · DU / 100 Here, the duty ratio DU is determined according to the operating state of the engine, and since the PG100 is obtained from the relationship shown in FIG. 21, the fuel vapor concentration PV (g / l) in the purge gas is If it is found, the fuel vapor amount EVQ will be found.

In the embodiment shown in FIG. 20, the fuel vapor concentration PV (g / l) is obtained from the air-fuel ratio A / F detected by the air-fuel ratio sensor 37. That is, the flow rate of the purge gas purged per unit time is PG (l / sec), and the amount of fuel vapor purged per unit time is FUEL (g / g).
sec), the fuel vapor concentration PV is expressed by the following equation. PV = FUEL (g / sec) / PG (1 / sec) Here, the air flow rate in the purge gas flow rate PG (1 / sec) is represented by A
Assuming that IR (l / sec) and the fuel vapor flow rate in the purge gas flow rate PG (l / sec) are FUEL (l / sec), the fuel vapor concentration PV is expressed by the following equation.

PV = FUEL (g / sec) / (AIR (l
/ Sec) + FUEL (l / sec)) Here, if the density of air is ρa (g / l) and the density of fuel is ρf (g / l), the above expression is as follows. PV = FUEL (g / sec) / (AIR (g / sec) / ρa
+ FUEL (g / sec) / ρf) When the denominator and the numerator on the right side of the above equation are divided by FUEL (g / sec), the above equation becomes as follows.

PV = 1 / (AIR (g / sec) / FUEL
(G / sec) / ρa + 1 / ρf Here, AIR (g / sec) / FUEL (g / sec) represents the air-fuel ratio of the purge gas. If this air-fuel ratio is A / F, the above equation is as follows: become. PV = 1 / ((A / F) / ρa + 1 / ρf) Therefore, if the air-fuel ratio A / F of the purge gas is known, the fuel vapor concentration PV can be obtained. In the embodiment shown in FIG. 20, the air-fuel ratio A / F of the purge gas is detected by the air-fuel ratio sensor 37. Therefore, the fuel vapor concentration PV (g / g) is calculated based on the air-fuel ratio A / F detected by the air-fuel ratio sensor 37.
l) can be obtained.

On the other hand, assuming that the engine has four cylinders, the fuel vapor is supplied to each cylinder at every 180 ° crank angle, ie, every half rotation, so that the fuel vapor amount EV supplied to each cylinder is
Qt (g) is expressed as follows. EVQt (g) = EVQ / (N (rpm) / 60) · 2
= EVQ · (30 / N) Therefore, the amount of fuel injected into each cylinder is (Q1−EVQt)
It is said.

FIG. 23 shows the weak stratification operation performed in step 300 of FIG. Steps A, B, D, and E in FIG. 23 are the same as steps A, B, D, and E shown in FIG. 7, and therefore, only step C will be described below. In step C, first, in step 350, the duty ratio DU is calculated from the map shown in FIG. Next, at step 351, the full open purge rate PG 100 is calculated from the relationship shown in FIG. Next, at step 352, the fuel vapor concentration PV is calculated based on the output signal of the air-fuel ratio sensor 37.
Next, at step 353, the fuel vapor amount EVQ (g / sec) is calculated based on the following equation.

EVQ = PG100.PV.DU / 100 Next, at step 354, the fuel vapor amount EVQt (= EVQ.30 / N) supplied to each cylinder is calculated. Next, at step 355, the result of subtracting EVQt from the injection amount Q1 calculated from the map shown in FIG. 5 (F) is used as the final injection amount Q1. Next, at step 356, the injection start timing θS2 is calculated.

As described above, from the injection amount Q1 to the fuel vapor amount E
Since VQt is subtracted, the air-fuel mixture around the spark plug 7 does not become too rich even if the purging operation is performed, and thus misfire can be prevented from occurring. FIG. 24 shows a homogeneous mixture operation performed in step 400 of FIG. Each step A, FIG.
Steps B, D, and E are the same as steps A, B, D, and E shown in FIG. 7, and thus only step C will be described below.

In step C, first, in step 430, the duty ratio DU is calculated from the map shown in FIG. Next, at step 431, FIG.
Is calculated from the relationship shown in FIG.
Next, at step 432, the fuel vapor concentration PV is calculated based on the output signal of the air-fuel ratio sensor 37. Next, at step 433, the fuel vapor amount EVQ is calculated based on the following equation.
(G / sec) is calculated.

EVQ = PG100.PV.DU / 100 Next, at step 434, the fuel vapor amount EVQt (= EVQ.30 / N) supplied to each cylinder is calculated. Next, at step 435, the result of subtracting EVQt from the injection amount Q1 calculated from the map shown in FIG. 6E is used as the final injection amount Q1.

As described above, from the injection amount Q1 to the fuel vapor amount E
Since VQt is subtracted, the air-fuel mixture around the spark plug 7 does not become too rich even if the purging operation is performed, and thus misfire can be prevented from occurring. 23 and 24, only the fuel injection Q2 performed at the end of the compression stroke is performed by the fuel injection valve 6.
As shown in FIG. 25, a fuel injection valve 38 for performing fuel injection toward the inside of the intake port 9 may be separately provided, and the fuel injection Q1 may be performed from the fuel injection valve 38.

Next, still another embodiment will be described with reference to FIG. As described above, when the fuel vapor is purged, misfire is most likely to occur during strong stratification operation, and then misfire is likely to occur during weak stratification operation. Thus, in this embodiment, when the purge flag is set when the strong stratification operation or the weak stratification operation is performed, that is, when the purge action is performed (FIG. 8), or the concentration of the fuel vapor in the intake air is higher than the reference concentration K. Is higher (Fig. 9),
The operation is switched to the homogeneous mixture operation.

That is, referring to FIG. 26, first, at step 100, a purge execution judgment is made. This purge execution determination is performed by the routine shown in FIG. 8 or FIG. Next, at step 130, it is determined whether or not the operation is in the operation range in which the homogeneous mixture operation is performed. On the other hand, when it is determined that the operation is not in the operation range where the homogeneous mixture operation is performed, step 13
Proceeding to 1, it is determined whether or not the purge flag has been set.

When the purge flag is set, the routine proceeds to step 400, where the homogeneous mixture operation is performed. On the other hand, when the purge flag is not set, the routine proceeds to step 132, where it is determined whether or not the operation is in the operation region where the strong stratification operation is performed. When the operation is in the operation region where the strong stratification operation is performed, the process proceeds to step 200, and the operation proceeds to step 300.

As described above, in this embodiment, if the purge flag is set during the stratification operation, the operation is switched to the homogeneous mixture operation, and if the purge flag is reset, the operation is returned to the stratification operation again. At this time, it is preferable to provide hysteresis for this switching operation. That is, for example, it is preferable that the purge flag is set when the concentration of the fuel vapor exceeds the reference concentration K, and the purge flag is reset when the concentration of the fuel vapor falls below a value smaller than the reference concentration K.

Next, still another embodiment will be described with reference to FIG. In this embodiment, the values of the duty ratios DU shown in FIG. 4D during the strong stratification operation and the values shown in FIG. 5 ( The value of each duty ratio DU shown in D) is set smaller than the corresponding value of each duty ratio DU during the homogeneous mixture operation shown in FIG. 6D.

That is, although it is considered that FIG. 27 does not need to be particularly described, first, at step 140, it is determined whether or not the operating region is for performing the homogeneous mixture operation, and the operating region for performing the homogeneous mixture operation is first determined. If, step 40
Proceeding to 0, the homogeneous mixture operation is performed. On the other hand, when it is determined that the operation is not in the operation region where the homogeneous mixture operation is performed, the routine proceeds to step 141, and it is determined whether or not the operation is in the operation region where the strong stratification operation is performed. When the operation is in the operation region where the strong stratification operation is performed, the process proceeds to step 200, and the operation proceeds to step 300.

Next, still another embodiment will be described with reference to FIGS. Figure 20 is housed in the catalytic converter 29a as shown _the NO _x absorbent 2
Reference numeral 9 designates, for example, alumina as a carrier, on which potassium K, sodium Na, lithium Li, cesium C
alkali metals such as s, barium Ba, calcium C
at least one selected from the group consisting of alkaline earths such as a, lanthanum La, and rare earths such as yttrium Y;
A noble metal such as t is carried. Engine intake passage,
NO _x in Toko to refer to the ratio of the combustion chamber 5 and _the NO _x absorbent 29 upstream of the exhaust passage supplying air and fuel into the (hydrocarbon) and the air-fuel ratio of the exhaust gas flowing into _the NO _x absorbent 29
The absorbent 29 absorbs the NO _x when the air-fuel ratio of the inflowing exhaust gas is lean, the air-fuel ratio of the inflowing exhaust gas is performed to absorbing and releasing action of the NO _x that releases NO _x absorbed and becomes the stoichiometric air-fuel ratio or rich. Incidentally, NO _x air-fuel ratio of the absorbent 29 upstream of the exhaust passage fuel (hydrocarbons) or the inflowing exhaust gas when the air is not supplied matches the air-fuel ratio in the combustion chamber 5, therefore in this case NO _x absorbent 29 absorbs the NO _x when the air-fuel ratio is lean in the combustion chamber 5, so that the releasing NO _x the air-fuel ratio is absorbed and becomes the stoichiometric air-fuel ratio or rich in the combustion chamber 5.

[0074] While performing the absorbing and releasing action of the NO NO _x absorbent 29 when placing the _x absorbent 29 in the engine exhaust passage is actually NO _x is also not clear portion detailed mechanism of action out this absorbing . 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.

In the internal combustion engine shown in FIG. 20, combustion is performed with the air-fuel ratio in the normal combustion chamber 5 being lean.
Thus the oxygen concentration in the exhaust gas when the air-fuel ratio is performed is combusted in a lean state is high, these oxygen O ₂ as is shown in FIG. 28 (A) at this time 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. 28A while being combined with barium oxide BaO. Diffuses into agent. In this way, NO _x becomes NO
_x Absorbed in the absorbent 29. As long as the oxygen concentration in the inflowing exhaust gas is high, NO ₂ is generated on the surface of the platinum Pt, and as long as the NO _x absorption capacity of the absorbent is not saturated, NO ₂ is absorbed in the absorbent and nitrate ions NO ₃ ^- are generated. You.

On the other hand, when the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas decreases, and as a result, the amount of NO ₂ generated on the surface of the platinum Pt decreases. When the production amount of NO ₂ decreases, the reaction proceeds in the opposite direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrate ion NO ₃ ⁻ in the absorbent becomes NO ₂
Released from the absorbent in the form of At this time, NO _x absorbent 2
The NO _x released from 9 large amount of unburned HC contained in the inflowing exhaust gas as shown in FIG. 28 (B), it is caused to reduction by reaction with 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. Thus the air-fuel ratio of the inflowing exhaust gas is NO _x is released from _the NO _x absorbent 29 in a short time when it is rich, yet NO _x is discharged into the atmosphere to the released NO _x is reduced It will not be done.

In this case, the air-fuel ratio of the inflowing exhaust gas is
NO even at stoichiometric air-fuel ratio_xNO from absorbent 29_xIs released
Is done. However, the air-fuel ratio of the incoming exhaust gas is
NO if ratio_xNO from absorbent 29_xGradually
NO because only _xAbsorbed by the absorbent 29
All NO_xIt takes a little longer to release.

[0078] Incidentally, there is a limit to the absorption of NO _x capacity of the NO _x absorbent 29, it is necessary to release the NO _x from the NO _x absorbent 29 before the absorption of NO _x capacity of the NO _x absorbent 29 is saturated . Therefore, in this embodiment _the NO _x absorbent 2
Amount of NO _x absorbed in the 9 have the air-fuel ratio under uniform mixture operation by increasing the injection quantity when exceeding the allowable amount predetermined to be rich. When the fuel vapor purge operation is not performed, the injection amount QR required to set the air-fuel ratio to a predetermined rich air-fuel ratio is determined by the required load L and the engine speed N as shown in FIG. The function is stored in the ROM 42 in advance.

When fuel is injected with the injection amount QR calculated from the map shown in FIG. 29 during the purging operation, the air-fuel ratio becomes excessively rich. At this time, the air-fuel ratio is determined in advance. In order to obtain a rich air-fuel ratio, it is necessary to subtract the fuel vapor amount from the injection amount QR. Therefore, in this embodiment of the present invention _the NO _x absorbent 29
And using the amounts obtained by subtracting the fuel vapor quantity from the injection quantity QR calculated from the map shown in FIG. 29 as the injection quantity of when to release the NO _x from.

That is, referring to FIG. 30, first, at step 100, a purge execution judgment is made. This purge execution determination is performed by the routine shown in FIG. 8 or FIG. Next, at step 150, it is determined whether or not NO _x should be released from the NO _x absorbent 29. When it is determined that NO _x should not be released from the NO _x absorbent 29, the routine proceeds to step 152, where it is determined whether or not the operating region is for performing the stratified operation. Proceeding to step 200, a strong stratification operation is performed. On the other hand, if it is determined that the operation is not in the operation region where the strong stratification operation is performed, the process proceeds to step 153, and it is determined whether or not the operation region is the operation where the weak stratification operation is performed. If the operation range is in the weak stratification operation, step 300
Then, the operation proceeds to step 400, and when the operation is not in the operation region in which the weak stratification operation is performed, the operation proceeds to step 400, and the homogeneous mixture operation is performed.

[0081] On the other hand, NO _x releasing processing is performed proceeds to step 500 when it is determined that it should release the NO _x from the NO _x absorbent 29 at step 150. This _the NO _x releasing processing routine is shown in Figure 31. _The NO _x releasing processing as described above is carried out under uniform mixture operation. Therefore, steps A, B, D,
In E, the same control as in steps A, B, D, and E of the homogeneous mixture operation in step 400 of FIG. 7 is performed. That is,
In step A, the target opening TA of the throttle valve 17 is calculated from the map shown in FIG. 6A, and the opening of the throttle valve 17 is set to this target opening TA. Next, at step B, the target opening EG of the EGR control valve 20 is calculated from the map shown in FIG. 6B, and the opening of the EGR control valve 20 is set to this target opening EG. Next, in step D, FIG.
The ignition timing θI is determined from the map shown in FIG. 6, and then in step E, as long as the purge action is not stopped in FIG.
The duty DU of the control pulse of the purge control valve 28 is calculated from the map shown in (D).

Next, at step 501, the injection amount QR is calculated from the map shown in FIG. Then step 50
In 2, the full open purge rate PG100 is calculated from the relationship shown in FIG. Next, at step 503, the air-fuel ratio sensor 3
7, the fuel vapor concentration PV is calculated. Next, at step 504, the fuel vapor amount EVQ (g / sec) is calculated based on the following equation.

EVQ = PG100.PV.DU / 100 Next, at step 505, the fuel vapor amount EVQt (= EVQ.30 / N) supplied to each cylinder is calculated. Next, at step 506, the result of subtracting EVQt from the injection amount QR is set as the final injection amount QR0. Then amount of NO _x is absorbed in the NO _x absorbent 29 in step 507 is determined whether becomes zero, NO _x releasing processing is made to complete the routine proceeds to step 508 when it is determined that becomes zero.

[0084]

According to the present invention, it is possible to prevent the occurrence of misfire due to the purge action of the fuel vapor.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an injection amount and the like.

FIG. 3 is a side sectional view of the internal combustion engine.

FIG. 4 is a diagram showing a map of a throttle opening and the like.

FIG. 5 is a diagram showing a map of a throttle opening and the like.

FIG. 6 is a diagram showing a map of a throttle opening and the like.

FIG. 7 is a flowchart for controlling operation.

FIG. 8 is a flowchart for performing a purge execution determination.

FIG. 9 is a flowchart for performing a purge execution determination.

FIG. 10 is a flowchart showing a first example of strong stratification operation.

FIG. 11 is a flowchart showing a second example of strong stratification operation.

FIG. 12 is a flowchart showing a third example of strong stratification operation.

FIG. 13 is a flowchart illustrating a fourth example of the strong stratification operation.

FIG. 14 is a flowchart showing a first example of a weak stratification operation.

FIG. 15 is a flowchart showing a second example of the weak stratification operation.

FIG. 16 is a flowchart illustrating a third example of the weak stratification operation.

FIG. 17 is a flowchart illustrating a fourth example of the weak stratification operation.

FIG. 18 is a flowchart illustrating a first example of a homogeneous mixture operation.

FIG. 19 is a flowchart showing a second example of the homogeneous mixture operation.

FIG. 20 is an overall view showing another embodiment of the internal combustion engine.

FIG. 21 is a diagram showing a fully open purge gas amount.

FIG. 22 is a diagram showing a relationship between a purge gas flow rate and a duty ratio.

FIG. 23 is a flowchart showing a weak stratification operation.

FIG. 24 is a flowchart showing a homogeneous mixture operation.

FIG. 25 is an overall view showing still another embodiment of the internal combustion engine.

FIG. 26 is a flowchart for controlling operation.

FIG. 27 is a flowchart for controlling operation.

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

FIG. 29 is a view showing a map of an injection amount.

FIG. 30 is a flowchart for controlling operation.

FIG. 31 is a flowchart for executing a NO _x release process.

[Explanation of symbols]

 6 fuel injection valve 7 spark plug 28 purge control valve

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G022 AA00 AA07 AA09 AA10 BA01 CA00 DA02 EA01 FA08 GA00 GA01 GA05 GA07 GA08 GA11 3G301 HA01 HA04 HA13 HA14 HA16 HA18 JA23 JA28 KA00 LA00 LA03 LB00 LB04 LC01 MA01 MA11 MA18 MA19 NA06 NA08 NB06 NB11 NC02 ND02 ND41 NE00 NE01 NE06 NE11 NE13 NE14 NE15 PA00Z PA07Z PA09Z PA17Z PB00Z PB09Z PD02A PD02Z PD15Z PE01Z PE03Z PF03Z

Claims (8)

[Claims] In an internal combustion engine having an ignition plug disposed in a combustion chamber and purging fuel vapor generated in a fuel tank into an engine intake passage, an air-fuel mixture around the ignition plug is purged when the fuel vapor is purged. A control device for controlling the ignition timing or the concentration of the mixture so as to reduce the concentration of the mixture around the spark plug at the time of ignition when there is a possibility that the concentration of the mixture becomes higher than a predetermined concentration at the time of ignition. 2. A means for judging whether or not the concentration of an air-fuel mixture around an ignition plug when purging fuel vapor is equal to or higher than a predetermined limit concentration at the time of ignition, and a concentration of the air-fuel mixture around the ignition plug. And control means for controlling the ignition timing or the concentration of the air-fuel mixture so that the concentration of the air-fuel mixture around the ignition plug at the time of ignition becomes equal to or lower than the limit concentration when it is determined that the concentration becomes higher than the limit concentration at the time of ignition. 3. The control device for an internal combustion engine according to claim 1. 3. The control device according to claim 1, wherein when it is determined that the concentration of the air-fuel mixture around the ignition plug becomes equal to or higher than the limit concentration at the time of ignition, the control means stops the purging operation of the fuel vapor or reduces the purge amount of the fuel vapor. 3. The control device for an internal combustion engine according to 2. 4. The control device according to claim 2, wherein when it is determined that the concentration of the air-fuel mixture around the ignition plug becomes equal to or higher than the limit concentration at the time of ignition, the control means advances the fuel injection timing into the combustion chamber or delays the ignition timing. A control device for an internal combustion engine according to claim 1. 5. A limited area around a spark plug by injecting fuel into a combustion chamber in an engine intake passage or an intake stroke to form a homogeneous mixture, and then injecting fuel into the combustion chamber at the end of a compression stroke. When the air-fuel mixture is formed within the limited area around the spark plug and the air-fuel mixture formed in the limited area around the spark plug is ignited by the spark plug, the concentration of the air-fuel mixture around the spark plug exceeds the limit concentration at the time of ignition. 3. The control device for an internal combustion engine according to claim 2, wherein when it is determined that the internal combustion engine is to be operated, the control means reduces the amount of fuel injected into the combustion chamber during the engine intake passage or during the intake stroke. 6. In a case where a homogeneous mixture is formed by injecting fuel into a combustion chamber in an engine intake passage or during an intake stroke, and the homogeneous mixture is ignited by an ignition plug, mixing around the ignition plug is performed. 3. The internal combustion engine according to claim 2, wherein when it is determined that the concentration of air becomes equal to or higher than the limit concentration at the time of ignition, the control means reduces the injection amount of fuel injected into the combustion chamber during the engine intake passage or during the intake stroke. Control device. 7. A stratified operation in which an air-fuel mixture formed in a limited area around a spark plug is ignited by an ignition plug and a homogeneous air-fuel mixture operation in which a homogeneous air-fuel mixture is ignited by the spark plug are selectively performed. 3. The control device according to claim 2, wherein the control unit switches from the stratified operation to the homogeneous mixture operation when it is determined that the concentration of the air-fuel mixture around the ignition plug becomes higher than the limit concentration at the time of ignition during the stratified operation. Control device for internal combustion engine. 8. When the air-fuel ratio of the inflowing exhaust gas is lean.
NO contained in exhaust gas_xAbsorbs and flows in
Absorbed when the air-fuel ratio of exhaust gas becomes stoichiometric or rich
NO_xReleases NO_xAbsorbent in engine exhaust passage
Place and NO _xNO from absorbent_xWhen the fuel is released
The fuel injection amount is calculated from a predetermined fuel injection amount to a fuel vapor amount.
2. The control of an internal combustion engine according to claim 1, wherein the amount is obtained by subtracting the minute.
apparatus.