JP2000274294A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deviation of an air-fuel ratio from a target air-fuel ratio due to a purge gas sucked into an engine after a purge stop. SOLUTION: In this controller, deviation between an air-fuel ratio in a purging state and an air-fuel ratio in a purge stop state is calculated as a purge amount in the purging state (S6). When the purge is stopped, a base model stored with a purge gas amount sucked into an engine after a purge stop according to a lapsed time from the purge stop is corrected on the basis of a purge gas amount during purging and an engine operation state to estimate the purge gas amount sucked into the engine at that time (S7). Fuel injection amount is corrected (S8), based on the estimated purge gas amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly, to a technique for improving the air-fuel ratio control accuracy when purging is stopped in an internal combustion engine provided with an evaporative fuel processing apparatus. About.

[0002]

2. Description of the Related Art Conventionally, a canister provided with an adsorbent such as activated carbon for adsorbing and trapping evaporated fuel generated in a fuel tank of a vehicle, and a fuel purged from the canister using negative suction pressure of an engine. And a purge control valve interposed in the purge passage to control the purge from the canister. The purge control valve is provided in accordance with the operating state of the engine. 2. Description of the Related Art There is known an evaporative fuel processing apparatus configured to control the purge control valve to adjust the amount of purge gas (the amount of desorbed fuel) supplied to an engine.

[0003]

When the purge gas (desorbed fuel) from the canister is supplied to the engine, extra fuel is supplied to the fresh air amount, and the air-fuel ratio shifts richly. Because it will be
Conventionally, during a purge, a correction for suppressing a rich shift due to supply of a purge gas is added to a fuel injection amount, and the correction is canceled with a stop of the purge (close control of a purge control valve) (or a purge stop). (Switching to a correction value corresponding to the state).

However, even when the purge control valve is closed, the supply of the purge gas to the engine is not interrupted immediately. Even after the purge control valve is closed, the purge gas is supplied to the engine while reducing the amount (see FIG. 5). ). For this reason, conventionally, immediately after the purge control valve is closed, even if the air-fuel ratio feedback control is being performed, the air-fuel ratio may fluctuate greatly and transiently, causing a torque step or deteriorating the emission. there were.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an air-fuel ratio control device capable of suppressing the occurrence of transient air-fuel ratio fluctuations when purging is stopped. .

[0006]

An air-fuel ratio control apparatus for an internal combustion engine according to the first aspect of the present invention is configured as shown in FIG.

In FIG. 1, an evaporative fuel processing apparatus includes a canister for adsorbing and collecting evaporative fuel generated in a fuel tank, a purge passage for supplying fuel purged from the canister to an intake system of the engine, and A purge control valve interposed in the purge passage to control purge.

Here, the purge gas amount estimating means estimates the amount of purge gas supplied to the engine after closing the purge control valve to stop purging from the state where the purge control valve is opened and purging is performed. The fuel amount correcting means corrects the fuel amount supplied to the engine according to the estimated purge gas amount.

With this configuration, after the purge is stopped, the amount of purge gas (desorbed fuel) supplied to the engine is estimated while decreasing the amount, and the fuel amount is corrected based on the estimation result. Thus, the fuel amount is corrected according to the dynamic change.

[0010] In the second aspect of the present invention, the purge gas amount estimating means estimates a change in a purge gas amount supplied to the engine in accordance with an elapsed time after the purge control valve is closed to stop purging. The configuration was adopted.

[0011] With this configuration, the amount of purge gas supplied to the engine decreases and changes with the lapse of time after the purge control valve is closed. The purge gas amount supplied to the engine at that time is estimated.

According to the third aspect of the present invention, the purge gas amount estimating means pre-stores a basic model of a change in purge gas amount according to an elapsed time after the purge control valve is closed to stop purging, and the purging process is performed during purging. The change in the actual purge gas amount is estimated based on the purge gas amount obtained in (1) and the basic model.

With this configuration, a basic model indicating a change in the amount of purge gas (desorbed fuel) sucked into the engine is stored in advance in accordance with the elapsed time since the purge was stopped. Because of the variation, the actual purge gas amount during the purge is determined, for example, from the result of the air-fuel ratio feedback control (that is, the air-fuel ratio), and the basic model is corrected based on the purge gas amount during the purge. The change in the purge gas amount is estimated.

According to a fourth aspect of the present invention, the purge gas amount estimating means estimates an actual change in the purge gas amount based on the purge gas amount obtained during the purge, the basic model, and operating conditions of the engine. did.

According to this configuration, the time lag until all the purge gas remaining in the intake system of the engine when the purge is stopped is sucked into the engine varies depending on the operating conditions (rotational speed, intake air amount, etc.) of the engine. Correspondingly, the amount of purge gas (desorbed fuel) sucked into the engine after the purge is stopped is estimated.

According to a fifth aspect of the present invention, there is provided a configuration in which basic model correction means for correcting the basic model based on the air-fuel ratio when the fuel amount is corrected by the fuel amount correction means is provided.

According to this configuration, the deviation of the air-fuel ratio when the fuel amount is corrected by the fuel amount correcting means can be considered to be due to the correction error. Modify the model.

[0018]

According to the first aspect of the present invention, since the purge gas amount (desorbed fuel amount) supplied to the engine after the purge is stopped is corrected to correct the fuel supply amount, the purge is stopped. Immediately after this, the accuracy of the air-fuel ratio control is improved, and it is possible to prevent the occurrence of a large torque step when the purge is stopped and the deterioration of the emission.

According to the second aspect of the present invention, in response to the purge gas amount (desorbed fuel amount) supplied to the engine decreasing according to the elapsed time after the purge is stopped,
There is an effect that the amount of purge gas can be accurately estimated.

According to the third aspect of the invention, there is an effect that the fuel amount can be appropriately corrected without being affected by the purge concentration. According to the invention described in claim 4, there is an effect that the purge gas amount can be accurately estimated in accordance with the difference in the purge gas suction speed depending on the engine operating conditions.

According to the fifth aspect of the present invention, the basic model can be corrected to an appropriate characteristic for each applicable engine, and the fuel supply amount can be corrected with high accuracy even if there is a variation in parts or a change with time. There is an effect that can be made.

[0022]

Embodiments of the present invention will be described below. FIG. 2 is a system configuration diagram of the internal combustion engine according to the embodiment.

In FIG. 2, air is introduced into each cylinder of a combustion chamber of an internal combustion engine 1 mounted on a vehicle under the control of an electronically controlled throttle valve 4 through an intake passage 3 from an air cleaner 2. Is done.

An electromagnetic fuel injection valve 5 is provided to inject fuel (gasoline) directly into the combustion chamber of each cylinder. The fuel injection valve 5 is energized by a solenoid in response to an injection pulse signal output in an intake stroke or a compression stroke from the control unit 20 in synchronization with engine rotation, opens the valve, and injects fuel adjusted to a predetermined pressure. It has become. The injected fuel diffuses into the combustion chamber in the case of the intake stroke injection to form a homogeneous mixture, and in the case of the compression stroke injection, forms a layered mixture intensively around the spark plug 6. Based on an ignition signal from the control unit 20, the ignition plug 6 ignites the fuel and performs combustion (homogeneous combustion or stratified combustion).

The combustion method is a combination of air-fuel ratio control and homogeneous stoichiometric combustion, homogeneous lean combustion (air-fuel ratio of 20 to
30) and stratified lean combustion (air-fuel ratio of about 40) according to operating conditions.

However, the internal combustion engine 1 is not limited to the direct injection gasoline engine described above, but may be an engine configured to inject fuel into the intake port. Exhaust gas from the engine 1 is exhausted from an exhaust passage 7, and an exhaust purification catalyst 8 is interposed in the exhaust passage 7.

Further, a canister 10 constituting an evaporative fuel processing device is provided to process the evaporative fuel generated from the fuel tank 9. The canister 10 is a sealed container filled with an adsorbent 11 such as activated carbon, and is connected to an evaporative fuel introduction pipe 12 from the fuel tank 9. Therefore, the evaporated fuel generated in the fuel tank 9 while the engine 1 is stopped or the like passes through the evaporated fuel introduction pipe 12 and passes through the canister 1.
It is guided to 0 and is adsorbed and collected here.

The canister 10 has a fresh air inlet 1.
3, and a purge passage 14 is led out. The control unit 2 is connected to the purge passage 14.
A purge control valve 15 whose opening and closing are controlled by a control signal from 0 is interposed.

In the above configuration, when the purge control valve 15 is controlled to open, the suction negative pressure of the engine 1 acts on the canister 10, so that the air introduced from the fresh air inlet 13 causes the adsorbent 11 of the canister 10 to act on the adsorbent 11 of the canister 10. The adsorbed evaporative fuel is desorbed (purged), and the desorbed evaporative fuel (purge gas) is sucked into the intake passage 3 downstream of the throttle valve 4 through the purge passage 14, and thereafter, in the combustion chamber of the engine 1. Combustion treatment.

The control unit 20 includes a CPU, an R
A microcomputer including an OM, a RAM, an A / D converter, an input / output interface, and the like is provided. The microcomputer receives input signals from various sensors, performs arithmetic processing based on the input signals, And the operation of the purge control valve 15 and the like.

The various sensors include a crank angle sensor 21 for detecting rotation of a crankshaft or a camshaft of the engine 1,
22 are provided. These crank angle sensors 2
1, 22 are 720 ° crank angle, where n is the number of cylinders.
/ N, outputs a reference pulse signal REF at a predetermined crank angle position (for example, 110 ° before compression top dead center) and outputs a unit pulse signal POS every 1 to 2 °. From the REF cycle etc., the engine speed N
e can be calculated.

In addition, an air flow meter 23 for detecting an intake air flow rate Qa upstream of the throttle valve 4 in the intake passage 3,
An accelerator sensor 24 for detecting an accelerator pedal depression amount (accelerator opening) APS, an opening TV of the throttle valve 4
O, a water temperature sensor 26 for detecting the cooling water temperature Tw of the engine 1, an air-fuel ratio sensor 27 for outputting a signal corresponding to the exhaust air-fuel ratio in the exhaust passage 7, and a vehicle speed V.
A vehicle speed sensor 28 for detecting SP is provided.

The air-fuel ratio feedback control for setting the air-fuel ratio feedback coefficient for correcting the fuel injection amount so that the exhaust air-fuel ratio detected by the air-fuel ratio sensor 27 matches the target air-fuel ratio is performed at a predetermined air-fuel ratio. The canister 1 is operated under feedback conditions.
The purge of the fuel vapor from zero is executed on condition that the air-fuel ratio feedback control is being performed.

Next, the state of the purge control by the control unit 20, that is, the control unit 20
The function as the purge gas amount estimating means and the fuel amount correcting means will be described with reference to the flowchart of FIG.

In the flowchart of FIG. 3, in step S1, the target purge amount is calculated, and in step S2, the purge control valve 15 is controlled according to the target purge amount. Note that the calculation of the target purge amount includes the determination of the purge condition. When the purge condition is not satisfied, the target purge amount is set to 0 and the purge is stopped.

In S3, it is determined whether or not the purging is completed. If not, the process proceeds to S4. still,
The end of the purge indicates a period from the stop of the purge to the end of fuel correction described later.

In S4, it is determined whether or not the purging is being performed. If the purging is not being performed, the process proceeds to S5, in which the air-fuel ratio feedback correction coefficient at that time is divided into a plurality of operating regions according to the load and rotation of the engine. The learning is performed as the air-fuel ratio learning value corresponding to the corresponding area of the divided map.

On the other hand, if it is determined in step S4 that the purging is being performed, the process proceeds to step S6, in which the deviation between the air-fuel ratio learning value of the corresponding region learned during the purge stop and the air-fuel ratio feedback correction coefficient at that time. Is calculated as a value indicating the purge gas amount (desorbed fuel amount) at that time.

When the purge is stopped by closing the purge control valve 15 from the state where the purge is being performed while obtaining the purge gas amount (desorbed fuel amount) as described above, the process proceeds from S3 to S7, The amount of purge gas (the amount of desorbed fuel) drawn into the engine after stopping the operation is estimated.

More specifically, a basic model indicating a change in the amount of purge gas sucked into the engine according to the elapsed time after stopping the purge is stored in advance.
It is assumed that the amount of purge gas sucked into the engine gradually decreases according to the characteristics of the basic model.

However, since the purge concentration varies, the purge gas amount with respect to the elapsed time in the basic model is shifted by the purge gas amount obtained during the purge. Further, even when the amount of the purge gas remaining in the intake system of the engine is the same when the purge is stopped, the speed at which the purge gas (desorbed fuel) is sucked into the engine varies depending on the operating conditions of the engine, resulting in high rotation and high load. Since the remaining purge gas is processed earlier, the time in the basic model is corrected to decrease as the rotation speed and the load are increased, and the purge gas amount is corrected to decrease more rapidly as the rotation speed and the load are increased.

As described above, when the purge gas amount (desorbed fuel amount) sucked into the engine after purging is completed, the fuel injection amount is determined in S8 according to the estimated purge gas amount at that time. To correct. Specifically, the purge gas amount is converted into a correction amount by multiplying the purge gas amount by a predetermined coefficient, and the correction amount is subtracted from the basic fuel injection amount. Try to reduce the amount of fuel used.

By the way, if the correction of the fuel amount in S8 is properly performed, the air-fuel ratio should be stabilized near the target air-fuel ratio even immediately after the purge is stopped.
The accuracy of estimating the purge gas amount deteriorates due to variations in the engine or changes with time, and the air-fuel ratio may deviate from the target air-fuel ratio even if the fuel injection amount is corrected based on the estimated purge gas amount.

Therefore, as shown in the flowchart of FIG. 4, it is preferable to modify the basic model according to the deviation of the air-fuel ratio. In the flowchart of FIG. 4, in S11, it is determined whether or not the fuel injection amount is being corrected based on the estimated purge gas amount.
Proceed to 2.

At S12, the deviation of the actual air-fuel ratio from the target air-fuel ratio when the fuel injection amount is corrected based on the estimated purge gas amount is monitored. Then, in the next S13,
The purge gas amount stored in the basic model corresponding to the time when the air-fuel ratio shift occurs is corrected and rewritten in a direction in which the air-fuel ratio shift is suppressed (basic model correcting means). The purge gas amount is estimated according to the basic model.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of the invention according to claim 1;

FIG. 2 is a diagram showing a system configuration of an internal combustion engine in the embodiment.

FIG. 3 is a flowchart showing an estimation of a purge gas amount when the purge is stopped and a control for correcting a fuel injection amount based on the estimation result.

FIG. 4 is a flowchart showing correction control of a basic model.

FIG. 5 is a time chart showing a change in an engine suction purge gas amount after the purge is stopped.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Intake passage 4 ... Throttle valve 5 ... Fuel injection valve 6 ... Spark plug 9 ... Fuel tank 10 ... Canister 14 ... Purge passage 15 ... Purge control valve 20 ... Control unit 27 ... Air-fuel ratio sensor

Continued on the front page F term (reference) 3G301 HA01 HA04 HA14 HA16 JA04 JA21 LA00 LB04 MA01 NB02 NC01 ND01 ND25 ND33 ND45 NE23 PA01Z PA11Z PD03A PD03Z PE01Z PE03Z PE08Z PF01Z PF03Z

Claims (5)

[Claims] 1. A canister for adsorbing and collecting fuel vapor generated in a fuel tank, a purge passage for supplying fuel purged from the canister to an intake system of an engine, and a purge passage interposed in the purge passage. An internal combustion engine provided with an evaporative fuel treatment device comprising: a purge control valve for controlling purge by performing a purge by closing the purge control valve from a state where the purge is performed by opening the purge control valve to stop purging. Purge gas amount estimating means for estimating the amount of purge gas supplied to the engine after having been made; fuel amount correcting means for correcting the fuel amount supplied to the engine according to the purge gas amount estimated by the purge gas amount estimating means; An air-fuel ratio control device for an internal combustion engine, comprising: 2. The system according to claim 1, wherein said purge gas amount estimating means estimates a change in a purge gas amount supplied to the engine according to an elapsed time since the purge control valve is closed to stop purging. Item 2. An air-fuel ratio control device for an internal combustion engine according to Item 1. 3. The purging gas amount estimating means stores in advance a basic model of a purging gas amount change according to an elapsed time after the purging is stopped by closing the purging control valve. 3. The air-fuel ratio control device for an internal combustion engine according to claim 2, wherein an actual change in the purge gas amount is estimated based on the basic model. 4. The purge gas amount estimating means estimates an actual change in purge gas amount based on the purge gas amount obtained during the purge, the basic model, and operating conditions of the engine. An air-fuel ratio control device for an internal combustion engine according to the above. 5. A basic model correcting means for correcting the basic model based on an air-fuel ratio when the fuel amount is corrected by the fuel amount correcting means. Air-fuel ratio control device for an internal combustion engine.