JPH11270381A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enrich an air-fuel ratio favorably in responsiveness at the time of temporarily changing the air-fuel ratio over to rich while lean-driving a cylinder injection engine. SOLUTION: This control device restrain a change of an air system such as intake air quantity, swirl current strength, EGR quantity, etc., by fixing throttle opening, swirl control valve opening, EGR valve opening by a current control value or controlling them to the closing side only by fine quantity α0-α2. Thereafter, fuel injection quantity is increased by changing fuel injection timing from a compression process (stratified charge combustion) over to an air intake process (homogeneous combustion) where a corrective range of ignition timing is extensive. Consequently, an air-fuel ratio of air-fuel mixture speedily changes in accordance with a change of the fuel injection quantity, and the air-fuel ratio is enriched favorably in responsiveness for a demand for enrichment. Additionally, at the time of changing it over to enrichment, it is possible to improve drivability by delaying the ignition timing and restraining a torque change in accordance with a change of the air-fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-cylinder injection type internal combustion engine in which fuel is directly injected into a cylinder, and an improved control system for temporarily switching the air-fuel ratio from lean to rich. The present invention relates to a fuel ratio control device.

[0002]

2. Description of the Related Art In recent years, the demand for an in-cylinder injection engine having features of low fuel consumption, low exhaust emission, and high output has been rapidly increasing. This in-cylinder injection engine makes the air-fuel ratio lean and burns fuel in an excess oxygen state, so that the NOx amount (nitrogen oxide amount) in the exhaust gas increases. As a countermeasure, in a direct injection engine, a NOx storage type lean NOx catalyst is often installed in an exhaust pipe. This lean NO
The x catalyst adsorbs NOx in the exhaust during lean operation in which the oxygen concentration in the exhaust gas is high, and reduces and purifies the adsorbed NOx when the air-fuel ratio is switched to rich and the oxygen concentration in the exhaust gas drops. discharge. Therefore, the N of the lean NOx catalyst
In order to maintain the Ox purification performance, it is necessary to switch to the rich operation from time to time during the lean operation.

A brake booster for increasing the braking force of the brake is operated by the negative pressure of the intake pipe. However, during lean operation, the negative pressure of the intake pipe is small, and the braking booster effect of the brake booster is reduced. During the lean operation, it is necessary to switch to the rich operation from time to time to increase the negative pressure in the intake pipe to secure the negative pressure in the brake booster.

[0004]

However, lean NO
If the x catalyst has deteriorated or the amount of NOx emission is very large, it is necessary to quickly make the air-fuel ratio rich and repeat the lean / rich switching in a short time. Furthermore, when the driver operates the brake during enrichment to ensure the negative pressure of the brake booster, there is a possibility that a sufficient braking booster effect may not be obtained because the negative pressure of the brake booster is insufficient. From this point, it is necessary to quickly enrich the air-fuel ratio.

In the conventional air-fuel ratio control, when enriching the air-fuel ratio, the air-fuel ratio is enriched by controlling the throttle valve or the like to the closed side to reduce the amount of air charged in the cylinder. Since there is a delay in switching the air system, there is a disadvantage that the air-fuel ratio cannot be enriched with good responsiveness to the enrichment request.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and accordingly, an object thereof is to enable switching from lean to rich with good responsiveness, and to improve NOx purification performance and braking performance of a lean NOx catalyst. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can improve the air-fuel ratio.

[0007]

In order to achieve the above object, according to the air-fuel ratio control apparatus for an internal combustion engine of the first aspect of the present invention, the air-fuel ratio control means requests the enrichment from the enrichment requesting means. Is output, the fuel injection timing is switched to the intake stroke and the fuel injection amount is increased while the opening of the air system control valve such as the throttle valve is maintained or slightly closed, and the air-fuel ratio is changed from lean to lean. Switch to rich. here,
The term "rich" means that the air-fuel mixture is richer than in the lean operation.Therefore, when switching to rich, the air-fuel ratio near the stoichiometric air-fuel ratio, or the air-fuel ratio slightly lower than that, or the air-fuel ratio richer than the stoichiometric air-fuel ratio You can switch to any of the fuel ratios.
What is necessary is just to switch to an air-fuel ratio that is richer than during the lean operation.

In the present invention, when switching the air-fuel ratio from lean to rich, the air-fuel ratio is switched to rich by fixing the air system with a delay or minimizing the change amount thereof and increasing the fuel injection amount. Unlike the switching of the air system, the increase of the fuel injection amount can be performed without a response delay, so that the switching from lean to rich can be performed quickly, and the NOx purification performance and the brake performance of the lean NOx catalyst are improved. be able to. Further, in the present invention, when switching to rich, the fuel injection timing is switched to the intake stroke, so that the combustion state is switched from stratified combustion to homogeneous combustion. In homogeneous combustion, the state of the mixture is more stable than in stratified combustion,
The range of adjustment of the ignition timing can be expanded and the range of adjustment of the opening / closing timing and opening / closing time of the intake / exhaust valves can also be expanded. be able to.

By the way, when the switching to the rich state is performed abruptly, the output torque of the internal combustion engine changes abruptly, causing a torque shock and reducing drivability. As a countermeasure against this, as shown in Japanese Patent Application Laid-Open No. Hei 7-166913, the air-fuel ratio is gradually enriched, or
As disclosed in Japanese Patent Publication No. 05-2005, it has been proposed to delay the fuel injection timing in accordance with the delay in the change of the air system. However, any of these known techniques requires a relatively long time to switch to rich, so that the air-fuel ratio cannot be quickly enriched.

Therefore, in a system according to a second aspect of the present invention, there is provided a system including engine control means for controlling at least one of the opening / closing timing, opening / closing time, and ignition timing of an ignition plug of at least one of an intake valve and an exhaust valve. After ensuring the responsiveness of the enrichment as described in the item 1, when the enrichment requesting unit issues a request for enrichment, the torque correction unit operates the engine control unit in the torque decreasing direction to enrich the enrichment. May be suppressed.
As described above, when switching to rich, the fuel injection timing is switched to the intake stroke to switch to homogeneous combustion, whereby the adjustment range of the ignition timing, the opening and closing timing of the intake and exhaust valves, and the adjusting range of the opening and closing time can be expanded. Therefore, a wide range of torque correction can be performed with respect to a change in torque due to enrichment.

In this case, the change in torque due to enrichment is
Since the larger the increase in the fuel injection amount, the larger the increase, the torque correction amount is preferably set according to the increase in the fuel injection amount. By doing so, it is possible to accurately set an appropriate amount of torque correction that suppresses a change in torque due to enrichment.

Further, there is a slight time delay from when the fuel injection amount is increased to when it actually appears as a torque change. Considering this point, as in claim 4,
It is preferable that the start time and the end time of the torque correction are delayed for a predetermined period from the start time and the end time of the increase in the fuel injection amount due to the enrichment request. By doing so, more accurate torque correction can be performed in consideration of the delay in torque change.

[0013]

[Embodiment (1)] An embodiment (1) of the present invention will be described below with reference to FIGS.
First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of an intake pipe 12 of a direct injection engine 11 which is a direct injection internal combustion engine, and a throttle valve whose opening is adjusted by a step motor 14 is provided downstream of the air cleaner 13. 15 (pneumatic control valve) is provided. The step motor 14 is connected to an engine electronic control circuit (hereinafter referred to as “ECU”).
The throttle valve 15 is controlled based on the output signal from the throttle valve 16 (throttle opening), and the amount of intake air to each cylinder is adjusted according to the throttle opening. You. A throttle sensor 17 for detecting a throttle opening is provided near the throttle valve 15.

A surge tank 19 is provided downstream of the throttle valve 15, and an intake manifold 20 for introducing air into each cylinder of the engine 11 is connected to the surge tank 19. Intake manifold 20 for each cylinder
A first intake path 21 and a second intake path 22 are respectively formed in the inside of the first intake path 21 and the second intake path 22.
Are connected to two intake ports 23 formed in each cylinder of the engine 11, respectively. A swirl control valve 24 (pneumatic control valve) is arranged in the second intake passage 22 of each cylinder. The swirl control valve 24 of each cylinder is connected to a step motor 26 via a common shaft 25. This step motor 26 is EC
By driving based on the output signal from U16, the opening of the swirl control valve 24 is controlled, and the swirl flow intensity in each cylinder is adjusted according to the opening. A swirl control valve sensor 27 for detecting the opening of the swirl control valve 24 is attached to the step motor 26.

The upper part of each cylinder of the engine 11
A fuel injection valve 28 for directly injecting fuel into the cylinder is provided. From a fuel tank (not shown) to a fuel pipe 45
The fuel sent to the fuel delivery pipe 29 through the is injected into the combustion chamber from the fuel injection valve 28 of each cylinder,
The mixture with the intake air introduced from the intake port 23 forms an air-fuel mixture. A fuel pressure sensor 30 for detecting the pressure of the fuel is attached to the fuel delivery pipe 29.

Further, an ignition plug (not shown) is attached to the cylinder head of the engine 11 for each cylinder, and each ignition plug ignites to ignite an air-fuel mixture in the combustion chamber. The cylinder discrimination sensor 32 generates an output pulse when a specific cylinder (for example, the first cylinder) reaches the intake top dead center. The crank angle sensor 33 detects that the crankshaft of the engine 11 has a constant crank angle (for example, 30 ° C.). A)
An output pulse is generated each time the motor rotates. From these output pulses, the crank angle and the engine speed NE are detected, and cylinder discrimination is performed.

On the other hand, an exhaust pipe 37 is connected to an exhaust port 35 of the engine 11 via an exhaust manifold 36. The exhaust pipe 37 has a three-way catalyst 38 for purifying exhaust gas near a stoichiometric air-fuel ratio and a NOx storage type lean NOx.
The catalyst 39 is arranged in series. This lean NOx
During the lean operation in which the oxygen concentration in the exhaust gas is high, the catalyst 39
When the NOx in the exhaust gas is adsorbed and the air-fuel ratio is switched to rich and the oxygen concentration in the exhaust gas drops, the adsorbed NOx
Is reduced and purified. On the downstream side of the lean NOx catalyst 39, a NOx concentration sensor (not shown) for detecting the concentration of NOx in the exhaust gas flowing out of the lean NOx catalyst 39
Is installed, and lean N estimated from NOx concentration in exhaust gas
When the NOx adsorption amount of the Ox catalyst 39 becomes larger than a predetermined value, the air-fuel ratio is temporarily switched from lean to rich as described later.

An EGR pipe 40 for recirculating a part of the exhaust gas is connected between the upstream side of the three-way catalyst 38 in the exhaust pipe 37 and the surge tank 19.
EGR controlling the EGR amount (exhaust gas recirculation amount) in the middle of 0
A valve 41 (pneumatic control valve) is provided. Further, the accelerator pedal 18 is provided with an accelerator sensor 42 for detecting an accelerator opening. In the surge tank 19,
A brake booster (not shown) is connected, and the intake pipe negative pressure is introduced into the brake booster.
A negative pressure sensor (not shown) for detecting an internal negative pressure is attached to the brake booster, and when the negative pressure of the brake booster falls below a predetermined value, the air-fuel ratio temporarily decreases as described later. Is switched to rich.

The output signals of the various sensors described above are supplied to the ECU
16 is input. The ECU 16 is mainly composed of a microcomputer, and controls the aforementioned step motors 14, 26, E based on various sensor outputs in accordance with a control program stored in a built-in ROM (storage medium).
The operation of the GR valve 41, the fuel injection valve 28, and the spark plug is controlled. For example, during low / medium load operation, a small amount of fuel is injected in the compression stroke so that the air-fuel ratio becomes lean, a partially rich mixture is formed around the ignition plug, and stratified combustion is performed. The air-fuel ratio as a whole is made lean (lean operation). During high load operation, the fuel injection amount is increased so as to be near or slightly richer than the stoichiometric air-fuel ratio, and fuel is injected in the intake stroke to perform homogeneous combustion (rich operation).

The ECU 16 executes an air-fuel ratio control routine shown in FIGS. 2 and 3 to determine whether there is a request for enrichment of the air-fuel ratio during engine operation.
If there is a request for enrichment, the air-fuel ratio is temporarily enriched. Hereinafter, the processing contents of each program will be described.

The air-fuel ratio control routine shown in FIG. 2 is repeatedly executed at every predetermined crank angle, every predetermined time, or every ignition (each injection). When this routine is started, first, at step 100, it is determined whether or not there is a request for enrichment. The determination of the enrichment request is performed in accordance with the enrichment request determination routine shown in FIG. Specifically, in step 200, it is determined whether or not the NOx adsorption amount of the lean NOx catalyst 39 is larger than a predetermined value L. If the NOx adsorption amount is larger than the predetermined value L, the process proceeds to step 203, where the enrichment is performed. It is determined that there is a request. Here, the predetermined value L is the lean N
The NOx adsorption amount at which the NOx concentration in the exhaust gas passing through the Ox catalyst 39 becomes higher than a predetermined value is set. The NOx adsorption amount is estimated from a detection value of a NOx concentration sensor (not shown) provided on the downstream side of the lean NOx catalyst 39, or
It may be estimated from operating conditions such as the lean operating time and the catalyst temperature (exhaust gas temperature) of the lean NOx catalyst 39.

On the other hand, in step 200, the lean NO
When it is determined that the NOx adsorption amount of the x catalyst 39 is equal to or less than the predetermined value L, the process proceeds to step 201, and it is determined whether the negative pressure in the brake booster (not shown) has dropped below the predetermined value M. If the negative pressure is lower than the predetermined value M, the routine proceeds to step 203, where it is determined that there is a request for enrichment. Here, the predetermined value M is set to a negative pressure at which a sufficient boosting effect of the brake booster cannot be obtained. The negative pressure in the brake booster may be directly detected by a negative pressure sensor (not shown) provided in the brake booster, or may be estimated from the number of times of operation of the brake or the driving state.

If the determinations in steps 200 and 201 are both "No", it is not necessary to enrich the air-fuel ratio, so the process proceeds to step 202, where it is determined that there is no enrichment request. The enrichment request determination routine described above plays a role as an enrichment request means referred to in the claims.

As a result of executing the enrichment request determination routine, if it is determined that there is no enrichment request, the process proceeds from step 100 to step 104 in FIG. 2 to switch the fuel injection timing of the fuel injection valve 28 to the compression stroke. (Or continue in the compression stroke). Thereafter, step 105
The throttle opening TA, the swirl control valve opening SCV, the EGR valve opening EGR, and the purge valve opening PRG
Is set in accordance with the engine speed NE, the engine load, the combustion method (stratified combustion or homogeneous combustion), and the like, and this routine ends.

On the other hand, if it is determined in step 100 that there is a request for enrichment, the process proceeds to step 101, where the throttle opening TA, swirl control valve opening SCV, EGR are set to maintain the air system as it is. The valve opening EGR and the purge valve opening PRG are fixed as shown in the following equation. TA (i) = TA (i-1) SCV (i) = SCV (i-1) EGR (i) = EGR (i-1) PRG (i) = PRG (i-1) where (i) Is the current value and (i-1) is the previous value. As a result, the amount of air charged into the cylinder, the swirl flow intensity of the air-fuel mixture in the cylinder, the EGR amount, and the purge flow rate are fixed.

Then, in the next step 102, the fuel injection timing of the fuel injection valve 28 is switched from the compression stroke to the intake stroke. In step 103, the fuel injection amount is increased and the air-fuel ratio is switched to rich, and End the routine. Here, the term "rich" means that the air-fuel mixture is richer than in the lean operation. Therefore, when switching to rich, the air-fuel ratio near the stoichiometric air-fuel ratio, or the air-fuel ratio slightly lower than that, or the stoichiometric air-fuel ratio The air-fuel ratio may be switched to any of the richer air-fuel ratios. In short, the air-fuel ratio may be switched to a richer air-fuel ratio than during the lean operation. Incidentally, the processing of steps 100 to 103 plays a role as an air-fuel ratio control means referred to in the claims.

According to the embodiment (1) described above, it is noted that the fuel injection amount can be increased without a response delay unlike the air system switching, and the air-fuel ratio is increased in response to the enrichment request. When switching from lean to rich, the air system with a delay is fixed and the fuel injection amount is increased to switch to rich, so that switching from lean to rich can be performed with good responsiveness, The NOx purification performance of the lean NOx catalyst 39 and the braking booster effect of the brake booster can be improved.

It should be noted that instead of the processing of step 101 in FIG. 2, as shown in step 101a in parentheses in FIG.
Throttle opening TA, swirl control valve opening SC
V, the EGR valve opening EGR and the purge valve opening PRG may be controlled to be closed by a very small amount (α0 to α3), respectively (see the broken line in FIG. 7). Even in this case, the change in the air system can be suppressed to a very small value, and the air-fuel ratio can be switched richly with good responsiveness.

Further, in the above embodiment (1), the air-fuel ratio is required to be enriched in order to secure the NOx purification performance and the braking boosting effect of the brake booster.
In addition to this, for example, in order to quickly warm up the catalyst and improve the air-conditioner / heater capacity, the air-fuel ratio may be required to be enriched.

[Embodiment (2)] By the way, when the air-fuel ratio is rapidly switched from lean to rich, the engine torque changes abruptly, causing a torque shock and reducing drivability. Therefore, in the embodiment (2) of the present invention, the ECU 16 executes the air-fuel ratio control routine shown in FIG. 4 for each ignition so as to perform the torque correction when switching to rich as follows.

In the air-fuel ratio control routine shown in FIG. 4, when it is determined in step 300 that there is a request for enrichment, the air system is maintained and the fuel injection timing is changed to the intake stroke as in steps 101 to 103 in FIG. (Steps 301 to 303). Thereafter, in order to suppress an increase in torque due to enrichment (increase in fuel injection amount), the process proceeds to step 304, where torque correction is performed. In this torque correction, the ignition timing is retarded to suppress an increase in torque. At this time, the ignition timing retard amount is set according to the current fuel injection amount increase by searching a map using the increase amount of the fuel injection amount shown in FIG. 5 as a parameter. The timing chart of the ignition timing indicated by the broken line A in FIG. 7 shows an example in which the ignition timing is retarded in accordance with the increase in the fuel injection amount.

In general, as the amount of increase in the fuel injection amount increases, the torque increase amount increases, and as the ignition timing retard amount increases, the torque suppressing effect increases. The characteristics of the map of the amount are set such that the greater the increase in the fuel injection amount, the greater the retard amount of the ignition timing. The map of the retard amount of the ignition timing is set in advance by experimental data and theoretical formulas, and is stored in the ROM of the ECU 16. The processing of step 304 functions as a torque correction unit referred to in the claims. Further, the function of retarding the ignition timing by the ECU 16 corresponds to the engine control means in the claims.

Thereafter, when there is no longer any request for enrichment, the process proceeds to steps 305 and 306, and step 10 in FIG.
In the same manner as in steps 4 and 105, the process returns to the compression stroke injection, returns to normal control of the air system according to the engine operating condition, and further returns to normal ignition timing control in step 307 to cancel the torque correction. To end.

In the above-described embodiment (2), similar to the above-described embodiment (1), the response of the enrichment is ensured, and when the enrichment request is issued, the increase in the fuel injection amount is performed. Since the ignition timing is retarded accordingly, a change in torque due to enrichment can be suppressed, and drivability can be improved. In the compression stroke injection (stratified combustion), the flammable air-fuel mixture needs to be ignited in a short period in which it is unevenly distributed around the spark plug. Therefore, the correctable range of the ignition timing is extremely narrow. Then, after switching to the intake stroke injection (homogeneous combustion), the ignition timing is retarded, so that the range of possible correction of the ignition timing is widened and the correction width of the torque correction can be expanded. Thus, a wide range of torque correction can be performed.

In the above-mentioned embodiment (2), when the switching is made rich, the ignition timing is retarded to suppress the torque change. However, the variable timing for changing the opening / closing timing of at least one of the intake valve and the exhaust valve. When the present invention is applied to a system equipped with a valve timing mechanism, at the time of rich switching, the opening / closing timing and / or opening / closing time (operating angle) of at least one of the intake valve and the exhaust valve is set to the increased amount of the fuel injection amount. By making corrections accordingly, the change in torque due to enrichment may be suppressed (in this case, the variable valve timing mechanism serves as engine control means described in the claims). Of course, the opening and closing timing of the intake and exhaust valves and / or
Alternatively, the change in torque due to enrichment may be suppressed by combining the correction of the opening and closing time and the correction of the retardation of the ignition timing. Further, step 301 in FIG. 4 may be changed to 101a in FIG.

[Embodiment (3)] By the way, there is a slight time delay from when the fuel injection amount is increased to when it actually appears as a torque change. In consideration of this point, in the embodiment (3) of the present invention, the ECU 16 executes the air-fuel ratio control routine shown in FIG. The injection amount increase start time and the increase end time are delayed by a predetermined period.

In the air-fuel ratio control routine shown in FIG. 6, first, at step 400, when it is determined that there is a request for enrichment, at step 401, the count value of the counter CINJ after the increase is canceled is reset to zero. After this increase is released, the counter CIN
J is a counter that counts the number of ignitions after the increase in the fuel injection amount is canceled, and is incremented for each ignition. Then, the process proceeds to steps 402 to 404, similarly to steps 101 to 103 in FIG. 2 described above, while maintaining the air system, switching the fuel injection timing to the intake stroke, switching to homogeneous combustion, and increasing the fuel injection amount, thereby increasing the rich fuel injection amount. Switch to.

Thereafter, at step 405, it is determined whether or not the count value of the counter CSA after the start of the increase is larger than the predetermined number of ignitions KCSA in order to determine whether or not the timing is appropriate for starting the torque correction. Is determined. Here, the counter CSA after the start of the increase is a counter that counts the number of ignitions after the increase of the fuel injection amount is started, and is incremented for each ignition. Predetermined ignition count KC
SA is set in consideration of the time required from the start of increasing the fuel injection amount to the actual change in torque.

If the count value of the counter CSA is equal to or less than KCSA after the start of the increase and it is not yet a proper timing to start the torque correction, the torque correction is not started.
This routine ends. Then, the counter C after the increase is started
When the SA count value exceeds KCSA, it is determined that it is the appropriate timing to start torque correction, and step 406 is performed.
Then, the ignition timing is retarded in the same manner as in step 304 of FIG. 4 to execute the torque correction.

Thereafter, when this routine is started, if it is determined in step 400 that there is no enrichment request, the process proceeds to step 407, where the count value of the counter CSA after the increase is started is reset to 0, and steps 408, 409 so,
As in steps 104 and 105 in FIG. 2, the control returns to the compression stroke injection and returns to the normal control of the air system according to the engine operating state. Thereafter, in step 410, it is determined whether or not the count value of the post-increase release counter CINJ is greater than a predetermined ignition count KCSA in order to determine whether or not the timing is appropriate to release the torque correction. .

When the count value of the counter CINJ is equal to or less than KCSA and the timing is not appropriate for releasing the torque correction, the torque correction is not released.
Continue the torque correction as it is. Then, when the count value of the counter CINJ exceeds KCSA after the cancellation of the increase,
It is determined that it is the appropriate timing for canceling the torque correction, and the process proceeds to step 411 to return to the normal ignition timing control, cancel the torque correction, and end this routine. Step 402 in FIG. 6 may be changed to 101a in FIG.

An example in which the above-described air-fuel ratio control routine is executed will be described with reference to FIG. When a request for enrichment occurs during the operation of the engine, the throttle opening, swirl control valve opening, EGR valve opening, and purge valve opening are fixed, and the state of the air system is maintained. Then, the fuel injection timing is switched from the compression stroke (stratified combustion) to the intake stroke (homogeneous combustion) to increase the fuel injection amount. As a result, the air-fuel ratio of the air-fuel mixture changes quickly in accordance with the change in the fuel injection amount, and the air-fuel ratio is enriched with good responsiveness to a request for enrichment. Thereafter, when the count value of the counter CSA exceeds KCSA after the start of the increase, the ignition timing is retarded as indicated by a dashed line B. In this manner, the torque correction is started at the timing when the torque change due to the increase in the fuel injection amount actually occurs, and the torque change due to the switching to the rich state is suppressed.

Thereafter, when the request for enrichment of the air-fuel ratio is eliminated, the fuel injection timing is switched to the intake stroke, the fuel injection amount is reduced to return the air-fuel ratio to lean, and the throttle opening, swirl control valve opening, The control of the EGR valve opening and the purge valve opening is returned to the normal control. Thereafter, when the count value of the counter CINJ exceeds the KCSA after the release of the increase, the control of the ignition timing is returned to the normal control as shown by the dashed line B, and the timing at which the torque change due to the decrease of the fuel injection amount actually occurs is performed. Cancels torque correction and suppresses torque change due to switching to lean.

As described above, by starting and canceling the torque correction at an appropriate timing when a torque change actually occurs, accurate torque correction can be realized, and the torque change can be suppressed to a very small value. Becomes

In the above embodiment (3), the start timing and the end timing of the torque correction accompanying the enrichment are set by the number of ignitions, but may be set by any one of the crank angle, the time and the number of injections. May be.

In each of the above embodiments (1) to (3), when the air conditioner is switched to the rich mode, all the air system control valves (throttle valve 15, swirl control valve 24, EGR
The opening degree of the valve 41 and the purge valve) is maintained or controlled to be slightly closed. However, the opening degree is not necessarily maintained for some air-based control valves having little effect on the combustion state and the air-fuel ratio. Alternatively, it is not necessary to slightly control the closing side.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an entire engine control system according to an embodiment (1) of the present invention.

FIG. 2 is a flowchart showing a flow of processing of an air-fuel ratio control routine according to the embodiment (1).

FIG. 3 is a flowchart showing the flow of processing of a routine for determining a rich request in the embodiment (1).

FIG. 4 is a flowchart showing a flow of processing of an air-fuel ratio control routine according to the embodiment (2) of the present invention.

FIG. 5 is a diagram showing a map that defines a relationship between a fuel injection amount increase and an ignition timing retard amount;

FIG. 6 is a flowchart showing a flow of processing of an air-fuel ratio control routine according to the embodiment (3) of the present invention.

FIG. 7 is a time chart showing an example when the air-fuel ratio control routine according to the embodiments (2) and (3) is executed;

[Explanation of symbols]

11: engine (internal combustion engine), 12: intake pipe, 15: throttle valve (air system control valve), 16: ECU (air-fuel ratio control means, enrichment request means, torque correction means, engine control means), 24: swirl Control valve (pneumatic control valve), 28: fuel injection valve, 37: exhaust pipe, 39: lean NOx catalyst, 41: EGR valve (pneumatic control valve).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/34 F02D 41/34 E 43/00 301 43/00 301A 301E 301Z F02P 5/15 F02P 5/15 B

Claims (4)

[Claims] An air-fuel ratio control device for an in-cylinder injection type internal combustion engine for directly injecting fuel into a cylinder and burning a lean mixture, wherein a throttle valve or the like for controlling an air system for introducing air into the cylinder is provided. An air system control valve, enrichment requesting means for requesting that the air-fuel ratio be temporarily switched from lean to rich during engine operation, and the air system control when the enrichment request is issued from the enrichment requesting means. Air-fuel ratio control means for switching the fuel injection timing to the intake stroke and increasing the fuel injection amount while maintaining or slightly controlling the opening of the valve to the closed side. apparatus. 2. An engine control means for controlling at least one of opening / closing timing, opening / closing time, and ignition timing of a spark plug of at least one of an intake valve and an exhaust valve; and a request for enrichment is issued from the enrichment requesting means. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising: a torque correcting unit that operates the engine control unit in a torque decreasing direction to suppress a torque fluctuation due to enrichment. 3. The air-fuel ratio control device for an internal combustion engine according to claim 2, wherein the torque correction means sets the torque correction amount in accordance with an increase in the fuel injection amount due to the enrichment request. 4. The method according to claim 2, wherein the torque correction means delays the start time and the end time of the torque correction by a predetermined period from the start time and the end time of increasing the fuel injection amount in response to the enrichment request. An air-fuel ratio control device for an internal combustion engine according to the above.