JP2673492B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection valve provided for each cylinder, a target air-fuel ratio switching means for setting a target air-fuel ratio based on the operating state of an internal combustion engine, and a target air-fuel ratio. A fuel injection amount control means for controlling the fuel injection amount of the fuel injection valve, and when the target air-fuel ratio setting means switches the target air-fuel ratio, the fuel injection amount control means sets a predetermined value for each fuel injection valve. The present invention relates to an air-fuel ratio control device for an internal combustion engine, which sequentially changes the fuel injection amount at time intervals .

[0002]

2. Description of the Related Art As such an air-fuel ratio control system for an internal combustion engine, the one described in Japanese Patent Application Laid-Open No. 4-295151 is known.

As shown in FIG . 7 , when the target air-fuel ratio is continuously switched from rich (point A) to lean (point B),
As shown by the solid line, there is a problem that the emission amount of NO _X sharply increases at an intermediate air-fuel ratio. On the other hand, when the target air-fuel ratio is instantaneously switched from rich (point A) to lean (point B), it is possible to avoid a sharp increase in the NO _X emission amount as shown by the chain line. However, when the target air-fuel ratio of each cylinder is instantaneously switched, the engine torque suddenly changes and a shock occurs, which causes a problem of deteriorating drivability.

Therefore, in the conventional air-fuel ratio control apparatus for an internal combustion engine, when the target air-fuel ratio is switched from rich to lean, the fuel injection amount of the fuel injection valve provided in each cylinder is an intermediate air-fuel ratio in which the emission becomes worse. The fuel ratio is successively decreased at predetermined intervals (time intervals) so as to jump over the fuel ratio. This avoids the torque shock that occurs when the fuel injection amounts of all the cylinders are reduced all at once, and improves the drivability while preventing the deterioration of emissions.

[0005]

When the conventional air-fuel ratio control system for an internal combustion engine is provided with an EGR gas recirculation device, the recirculation of EGR gas is stopped when the target air-fuel ratio is switched from rich to lean. Even the EGR in the intake system
The gas does not become zero immediately, and E
GR gas will remain. In this state, if the fuel injection amount is reduced and the air-fuel ratio is shifted to the lean side, EGR
There is a problem that the combustion state of the air-fuel mixture deteriorates due to the presence of gas, and combustion failure such as misfire occurs.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to effectively avoid defective combustion of an air-fuel mixture due to EGR gas when the air-fuel ratio is switched.

[0007]

In order to achieve the above object, the invention described in claim 1 is a fuel injection valve provided for each cylinder, and an EGR gas recirculation amount from an exhaust passage to an intake passage. For controlling the EGR gas recirculation amount, target air-fuel ratio setting means for setting a target air-fuel ratio based on the operating state of the internal combustion engine, and fuel injection for controlling the fuel injection amount of the fuel injection valve based on the target air-fuel ratio. And a quantity control means,
When the target air-fuel ratio setting means switches the target air-fuel ratio,
An air-fuel ratio control device for an internal combustion engine, wherein the fuel injection amount control means sequentially decreases the fuel injection amount for each fuel injection valve at a predetermined time interval , and the target air-fuel ratio setting means sets the target air-fuel ratio.
When switching from rich side to lean side, EGR gas
Reduction of EGR gas recirculation amount and fuel by recirculation amount control means
The injection amount control means starts decreasing the fuel injection amount and
Reduction of the residual EGR gas amount calculated by the EGR gas amount calculation means
Decrease fuel injection amount by fuel injection amount control means
It is characterized by making it.

According to a second aspect of the present invention, in addition to the structure of the first aspect, the target air-fuel ratio is in the lean limit region.
In some cases, the EGR gas recirculation amount control means returns the EGR gas
It is characterized by stopping the flow .

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

1 to 6 show an embodiment of the present invention, FIG. 1 is an overall configuration diagram of an air-fuel ratio control device for an internal combustion engine, and FIG. 2 is a block diagram showing a circuit configuration of an electronic control unit. 3 is a flowchart showing an for work, 4 KEGRN
Flow chart of calculation routine , FIG. 5 shows net EGR coefficient
Table for searching the intermediate target air-fuel ratio from
It is a timing chart to demonstrate .

As shown in FIG. 1, an intake passage 1 of a four-cylinder internal combustion engine E (hereinafter simply referred to as engine E) is connected to four cylinders 3 _{1 to} 3 ₄ of # 1 to # 4 via an intake manifold 2. Connected respectively. The intake passage 1 is provided with a throttle valve 4 that is connected to an accelerator pedal (not shown) to open and close. A signal from a throttle opening sensor 5 that is connected to the throttle valve 4 and detects the throttle opening θTH is electronically transmitted. It is input to the control unit U.

The intake manifold 2 has four cylinders 3 ₁ ...
_Four fuel injection valves 8 ₁ to 8 ₄ are provided corresponding to 3 ₄ respectively. Each of the fuel injection valves 8 ₁ to 8 ₄ is connected to and controlled by the electronic control unit U.

In the intake passage 1 upstream of the throttle valve 4, an intake air amount sensor 9 composed of an air flow meter for detecting the intake air amount Q and an intake pipe absolute pressure sensor 14 for detecting the intake pipe absolute pressure P _B are provided. The signals from the intake air amount sensor 9 and the intake pipe absolute pressure sensor 14 are input to the electronic control unit U. An engine speed sensor 10 for detecting the engine speed Ne based on the rotation of a crankshaft (not shown) is provided inside the engine E. The engine speed sensor 10 is provided.
Is input to the electronic control unit U.

A three-way catalyst 11 for purifying exhaust gas is provided in an exhaust passage 7 connected to the engine E via an exhaust manifold 6. The exhaust passage 7 and the intake passage 1 are EG
The EGR valve 13 is connected by the R gas passage 12, and the EGR valve 13 provided in the EGR gas passage 12 is connected to the electronic control unit U in order to control the recirculation amount of the EGR gas.

As shown in FIG. 2, the electronic control unit U
Is the target air-fuel ratio A / F based on the operating state of the engine E.
Target air-fuel ratio setting means M1 for switching the EGR gas recirculation amount control means M2 for controlling the opening degree of the EGR valve 13 based on the target air-fuel ratio, and EGR gas residual amount in the intake system based on the operating state of the engine E. The fuel injection time of the fuel injection valves 8 ₁ to 8 ₄ is calculated based on the residual EGR gas amount calculation means M3 for calculating the operating condition of the engine E, and the outputs of the target air-fuel ratio setting means M1 and the residual EGR gas amount calculation means M3. And a fuel injection amount control means M4 for controlling

The throttle opening θTH detected by the throttle opening sensor 5 and the engine speed Ne detected by the engine speed sensor 10 are input to the target air-fuel ratio setting means M1, and the throttle opening θTH and the engine speed Ne are input. The target air-fuel ratio A / F is map-searched based on In the normal operating region of the engine E, the target air-fuel ratio is stoichiometric (rich), that is, the theoretical air-fuel ratio A / F = 14.
Set to 7. On the other hand, in a specific operating region such as when the engine E is decelerating, the target air-fuel ratio is made lean to A / F = 22 in order to improve fuel efficiency.

When the target air-fuel ratio setting means M1 switches the target air-fuel ratio from stoichiometric to lean, the EGR gas recirculation amount control means M2 restricts the opening amount of the EGR valve 13 to regulate the EGR gas recirculation amount, or Close the EGR valve 13 and E
Stop the reflux of GR gas.

The operation of the residual EGR gas amount calculation means M3 is as follows.
The details will be described later based on the flowchart of FIG.

When the target air-fuel ratio is the stoichiometric air-fuel ratio, the fuel injection quantity control means M4 uses the air intake quantity Q and the engine speed sensor 10 which are detected by the intake air quantity sensor 9 so as to obtain the stoichiometric air-fuel ratio. Detected engine speed N
The fuel injection time Ti is set according to e. On the other hand, when the target air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the fuel injection time Ti is set so that the lean target air-fuel ratio is obtained, and the fuel injection is performed when the target air-fuel ratio is switched. the change timing of the time Ti is controlled at a predetermined time interval to be described later to the cylinders 3 ₁ to 3 per _4.

Next, the operation of the embodiment of the present invention will be described with reference to the flowchart of FIG.

The destination not a, when the switching condition of the target air-fuel ratio based on the operating state of the engine E is established newly in step S11, and closes the EGR valve 13 by a command from the electronic control unit U in step S12, EGR Reduce the amount of gas recirculation. In the following step S13, since the switching flag FLGkirikae is set to "1" (switching completed) in the first loop, the process proceeds to step S14 and the switching flag FLGkirikae is set to "0" (switching not completed).

In the following step S15, the net EGR of this time is performed.
It is determined whether the coefficient KEGRN is less than or equal to a predetermined value. Said positive
The taste EGR coefficient KEGRN is the residual EG remaining in the intake system.
It corresponds to the amount of R gas, and the specific content of the calculation
Will be described with reference to the flowchart of FIG. First, in step S31, on the basis of the intake pipe absolute pressure P _B detected by the engine speed Ne and the intake pipe absolute pressure sensor 14 detected by the engine speed sensor 10, Ne-P _B map EGR direct supply ratio E _A and from Search EGR take-away rate E _B. Then, in step S32, the EGR gas amount Gt that has passed through the EGR valve 13 is calculated by Gt = TiM (τ) * (1-KEGR (τ)). Here, TiM (τ) is the fuel injection time Ti before τTDC, and KEGR (τ) is the EGR coefficient before τTDC.

Next, in step S32, the EGR gas amount Gin drawn into the cylinder is calculated by Gin = E _A * Gt + E _B * Gc. Here, Gc is the amount of EGR gas staying in the intake passage 1 calculated in step S35 described later.

Next, at step S34, the net EGR coefficient K
EGRN is calculated by KEGRN = (1-Gin / TiM). Here, TiM is the current fuel injection time Ti
It is.

[0025] Finally, the Gc is EGR gas amount staying in the intake passage 1 at step S35, is calculated by _{Gc = (1-E A)} * Gt + (1-E B) * Gc.

Then , in step S15, E
In the first loop immediately after the reduction of the GR gas recirculation amount, the net EG
Since the R coefficient KEGRN is not less than the predetermined value, step S
The process proceeds to step 16 and searches the KEGRN to KBS ₁ table shown in FIG . That is, the target air-fuel ratio KBS ₁ is searched according to the net EGR coefficient KEGRN, and in the subsequent step S17, the target air-fuel ratio KBS ₁ is set as the intermediate target air-fuel ratio. The intermediate target air-fuel ratio shifts to the lean side as the net EGR coefficient KEGRN decreases.

When the intermediate target air-fuel ratio is set in this manner, the air-fuel ratio of each cylinder is made lean so that the intermediate target air-fuel ratio can be obtained in step S18. Leaning of the air-fuel ratio, # 1 cylinder 3 ₁ 6, # 3 cylinder ₃ 3, between the # 4 cylinder 3 _4, # 2 cylinder 3 ₂ order at predetermined time
It takes place at intervals . Then, until the air-fuel ratio switching is finally ended in step S19, the leaning of the air-fuel ratio of each of the cylinders 3 _{1 to} 3 ₄ is repeated in accordance with the change of the intermediate target air-fuel ratio. When EGR coefficient KEGRN is below a predetermined value, the target air-fuel ratio KBS _LL when satisfied changeover condition to the final target air-fuel ratio in step S20, the final target air-fuel ratio cylinders 3 ₁ to 3 ₄ as obtained in step S18 The air-fuel ratio of.

When the switching of the air-fuel ratio is finally completed in step S19, the process proceeds to step S21 and the switching flag FLGkirikae is set to "1" (completion of switching).

The target air-fuel ratio KBS _LL when the switching condition is satisfied
Is close to the lean limit, the EGR gas recirculation amount is cut to 0 in step S12 of the flowchart of FIG. 3 , and the target air-fuel ratio KBS _LL is set in step S20 when the net EGR coefficient KEGRN becomes 0 in step S15. It can be the final target air-fuel ratio. If you do this,
Even when the target air-fuel ratio KBS _LL is close to the lean limit, it is possible to reliably prevent the occurrence of combustion failure and misfire.

As described above, since the air-fuel ratio is switched to the lean side in accordance with the net EGR coefficient, even if the state of the intermediate air-fuel ratio occurs, the deterioration of the emission is prevented by the presence of the residual EGR gas corresponding to it. It Moreover, when the air-fuel ratio is switched from stoichiometric to lean, the air-fuel ratio is gradually switched to the lean side according to the decrease of the net EGR coefficient at the same time when the air-fuel ratio switching condition is satisfied, so the timing of leaning the air-fuel ratio Does not deteriorate the fuel consumption rate, and the EGR gas recirculation amount does not decrease and the emission does not deteriorate while the air-fuel ratio remains stoichiometric.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various design changes can be made.

[0032]

As it is evident from the foregoing description, according to the invention described in claim 1, provided with a residual EGR gas quantity calculating means for calculating a residual EGR gas quantity in the air intake system, the target is the target air-fuel ratio setting means When the air-fuel ratio is switched from the rich side to the lean side, the reduction of the EGR gas recirculation amount by the EGR gas recirculation amount control means and the reduction of the fuel injection amount by the fuel injection amount control means are started, and the residual EGR gas amount calculation means is started. Calculated residual E
Since the fuel injection amount by the fuel injection amount control means is decreased in accordance with the decrease in the GR gas amount, even if the state of the intermediate air-fuel ratio occurs, the amount of residual EGR gas commensurate with it reduces deterioration of emission. Further, since the air-fuel ratio is gradually switched to the lean side at the same time when the air-fuel ratio switching condition is satisfied, there is no delay in the timing of making the air-fuel ratio lean and the fuel consumption rate does not deteriorate, and the air-fuel ratio remains stoichiometric. The EGR gas recirculation amount does not decrease and the emission does not deteriorate.

According to the invention described in or claim 2,
Than the EGR gas reflux quantity control means when the target air-fuel ratio is lean limit area stops reflux the EGR gas,
Even if the target air-fuel ratio is in the lean limit region, it is possible to reliably prevent the occurrence of combustion failure or misfire.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an air-fuel ratio control device for an internal combustion engine.

FIG. 2 is a block diagram showing a circuit configuration of an electronic control unit.

FIG. 3 is a flowchart for explaining the operation for

FIG. 4 is a flowchart of a KEGRN calculation routine .

FIG. 5: Retrieving an intermediate target air-fuel ratio from a net EGR coefficient
table

FIG. 6 is a timing chart illustrating the operation .

FIG. 7 is a graph showing the relationship between air-fuel ratio and NO _X emission amount.

[Explanation of symbols]

1 intake passage 3 _{1 to} 3 ₄ cylinder 7 exhaust passage 8 ₁ to 8 ₄ fuel injection valve E internal combustion engine M1 target air-fuel ratio setting means M2 EGR gas recirculation amount control means M3 residual EGR gas amount calculation means M4 fuel injection amount control means

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location F02D 45/00 301 F02D 45/00 301G F02M 25/07 550 F02M 25/07 550R (72) Inventor Eisuke Kimura 1-4-1, Chuo, Wako-shi, Saitama Inside Honda R & D Co., Ltd. (56) References JP-A-6-66183 (JP, A) JP-A-4-295151 (JP, A) JP-A-6 -264786 (JP, A) JP-A-53-88414 (JP, A)

Claims (2)

(57) [Claims] 1. A fuel injection valve (8 ₁ to 8 ₄ ) provided for each cylinder (3 _{1 to} 3 ₄ ) and an EGR gas recirculation amount from an exhaust passage (7) to an intake passage (1) are controlled. EGR gas recirculation amount control means (M2) and target air-fuel ratio setting means (M) that sets a target air-fuel ratio based on the operating state of the internal combustion engine (E).
1), the fuel injection valve based on the target air-fuel ratio (8 ₁ -
8 ₄₎ fuel injection quantity control means for controlling the fuel injection amount (M
4), and when the target air-fuel ratio setting means (M1) switches the target air-fuel ratio, the fuel injection amount control means (M
4) is a air-fuel ratio control apparatus for each fuel injection valve (8 _{1-8 4)} internal combustion engine for sequentially reducing the fuel injection quantity at a predetermined time interval <br/> every residual EGR gas in the intake system Residual EGR gas for calculating amount
An amount calculation means (M3) is provided, and a target air-fuel ratio setting means (M
1) switched the target air-fuel ratio from rich side to lean side
Sometimes, the EG by the EGR gas recirculation amount control means (M2)
Reduction of R gas recirculation amount and fuel injection amount control means (M4)
Start decreasing the fuel injection amount by calculating the residual EGR gas amount
According to the decrease of the residual EGR gas amount calculated by the means (M3)
Decrease the fuel injection amount by the fuel injection amount control means (M4)
Characterized in that makes the air-fuel ratio control apparatus for an internal combustion engine. 2. The target air-fuel ratio is in the lean limit region.
In this case, the EGR gas recirculation amount control means (M2)
The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the recirculation of the air is stopped .