JPH05288107A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent air-fuel ratio from being remarkably changed during detection of evaporated fuel concentration. CONSTITUTION:Evaporated fuel generated in a fuel tank 7 is adsorbed to a canister 13, and this evaporated fuel adsorbed to the canister 13 is purged to the intake side of an internal combustion engine together with air via a purge valve 16. A purge rate is changed by the purge valve 16 so that an air-fuel ratio feedback value detected by an oxygen sensor 6 may be set in a specified range. Concentration of the evaporated fuel taken into the internal combustion engine via the purge valve 16 is detected based on purge rates before and after changing this purge rate and air-fuel ratio feedback values.

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 system for an internal combustion engine for sucking vaporized fuel generated in a fuel tank to the intake side of the internal combustion engine and burning it.

[0002]

2. Description of the Related Art Conventionally, a canister purge amount is kept constant in a fuel tank in which vaporized fuel generated in a fuel tank is stored in a canister and the vaporized fuel stored in the canister is discharged together with air to the intake side of an internal combustion engine for combustion. There is a method in which only the value is changed, and the concentration of the evaporated fuel sucked from the canister to the intake side of the internal combustion engine is detected based on the amount of change in the air-fuel ratio feedback value at that time (for example, Japanese Patent Laid-Open No. HEI-2
-130240).

[0003]

However, in the above-mentioned conventional method, the evaporated fuel concentration is detected by changing the canister purge amount by a constant value, and therefore, when the adsorbed amount of evaporated fuel to the canister is large. In addition, when the concentration is detected, there is a problem that the air-fuel ratio of the mixture of fuel and air supplied to the internal combustion engine fluctuates greatly, resulting in deterioration of idle stability of the internal combustion engine and deterioration of exhaust emission.

Therefore, the present invention suppresses the fluctuation of the air-fuel ratio during the detection of the evaporated fuel concentration even when the adsorbed amount of the evaporated fuel to the canister is large, and prevents the idle stability and the exhaust emission from being deteriorated. It is intended.

[0005]

Therefore, according to the present invention, the evaporated fuel generated in the fuel tank is stored in the canister, and the evaporated fuel stored in the canister is discharged together with air to the intake side of the internal combustion engine. In the air-fuel ratio control device for an internal combustion engine, the air-fuel ratio detecting means for detecting the air-fuel ratio of the internal combustion engine, and the air-fuel ratio is supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detecting means. Air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the air-fuel mixture, and a flow rate control valve for changing the purge rate of air containing evaporated fuel released from the canister to the intake side of the internal combustion engine via the release passage, When the concentration of the evaporated fuel is detected, the purge rate is gradually changed by the flow rate control valve until the air-fuel ratio detected by the air-fuel ratio detecting means changes by a predetermined amount. An air-fuel ratio of an internal combustion engine including a concentration detecting purge rate control means, and an air-fuel ratio before and after the purge rate is changed by the purge rate control means and a concentration detecting means for detecting the concentration of evaporated fuel by the purge rate. A control device is provided.

Further, the evaporated fuel generated in the fuel tank is stored in a canister, and the evaporated fuel stored in this canister is discharged together with air to the intake side of the internal combustion engine through a discharge passage. A device, an air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine, and an air-fuel ratio of a mixture of fuel and air supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detecting means. An air-fuel ratio feedback means for feedback control, a flow control valve for changing a purge rate of air containing evaporated fuel released from the canister to the intake side of the internal combustion engine through the discharge passage, and a concentration of the evaporated fuel. Concentration detecting purge rate control means for changing the purge rate by the flow rate control valve and the purge rate by the purge rate control means After the concentration detecting means for detecting the concentration of the evaporated fuel by the air-fuel ratio and the purge rate before and after, and the concentration of the evaporated fuel is detected by the concentration detecting means, the concentration of the evaporated fuel is again detected by the concentration detecting means. In the case of detection, the air-fuel ratio of the internal combustion engine is provided with a concentration detection time fuel concentration correction means for reflecting the already detected vaporized fuel concentration amount in the fuel supply amount of the internal combustion engine according to the purge rate at the time of this concentration detection. It may be a control device.

Further, the evaporated fuel generated in the fuel tank is stored in a canister, and the evaporated fuel stored in this canister is discharged together with air to the intake side of the internal combustion engine through a discharge passage. The device is an air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine, and an air-fuel ratio feedback-controlling air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detecting means. A fuel ratio feedback means, a flow rate control valve that changes a purge rate of air containing evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage, and when updating the concentration of the evaporated fuel, Concentration updating purge rate control means for changing the purge rate by the flow rate control valve according to the already detected vaporized fuel concentration,
The air-fuel ratio control device for an internal combustion engine may include an air-fuel ratio before and after changing the purge rate by the purge rate control means and a concentration updating means for updating the concentration of the evaporated fuel by the purge rate.

Further, the evaporated fuel generated in the fuel tank is stored in the canister, and the evaporated fuel stored in the canister is discharged together with air to the intake side of the internal combustion engine through the discharge passage. The device is an air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine, and an air-fuel ratio feedback-controlling air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detecting means. Fuel ratio feedback means, a flow control valve that changes a purge rate of air containing evaporated fuel that is discharged from the canister to the intake side of the internal combustion engine through the discharge passage, and detects the initial concentration of the evaporated fuel. Sometimes, the first concentration detecting par is gradually changed by the flow rate control valve until the air-fuel ratio detected by the air-fuel ratio detecting means changes by a predetermined amount. Rate control means, initial concentration detection means for detecting the initial concentration of evaporated fuel by the air-fuel ratio and purge rate before and after changing the purge rate by the purge rate control means, and when updating the concentration of the evaporated fuel , A concentration update purge rate control means for changing the purge rate by the flow rate control valve according to the already detected vapor fuel concentration, and an air-fuel ratio before and after the purge rate is changed by the purge rate control means. Also, the air-fuel ratio control device for the internal combustion engine may be provided with a concentration updating means for updating the concentration of the evaporated fuel according to the purge rate.

[0009]

Thus, when the concentration of the evaporated fuel is detected, the purge rate control means for concentration detection gradually changes the purge rate until the air-fuel ratio detected by the air-fuel ratio detection means changes by a predetermined amount. The concentration of the evaporated fuel is detected by the concentration detecting means based on the air-fuel ratio before and after the change and the purge rate.

Further, after the concentration detecting means detects the concentration of the evaporated fuel, when the concentration detecting means again detects the concentration of the evaporated fuel, the already detected amount of the evaporated fuel concentration at the time of the concentration detection is detected. It is also possible to reflect the fuel supply amount of the internal combustion engine by the fuel concentration correction means at the time of concentration detection according to the purge rate.

Further, the purge rate at the time of updating the concentration can be changed by the concentration detecting purge rate control means according to the previously detected concentration.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a vehicle is equipped with a multi-cylinder engine 1, and an intake pipe 2 and an exhaust pipe 3 are connected to the engine 1. An electromagnetic injector 4 is provided at the inner end of the intake pipe 2, and a throttle valve 5 is provided upstream of the electromagnetic injector 4. Further, the exhaust pipe 3 is provided with an oxygen sensor 6 as an air-fuel ratio detecting means, and the sensor 6 outputs a voltage signal according to the oxygen concentration in the exhaust gas.

The fuel supply system for supplying fuel to the injector 4 has a fuel tank 7, a fuel pump 8, a fuel filter 9 and a pressure regulating valve 10. Then, the fuel (gasoline) in the fuel tank 7 is pressure-fed to each injector 4 by the fuel pump 8 through the fuel filter 9.
The fuel supplied to each injector 4 is adjusted to a predetermined pressure by the pressure regulating valve 10.

A purge pipe 1 extending from the upper portion of the fuel tank 7.
1 is connected to a surge tank 12 of an intake pipe 2, and a canister 1 containing activated carbon as an adsorbent for adsorbing evaporated fuel generated in a fuel tank is provided in the purge pipe 11 in the middle thereof.
3 are provided. Further, the canister 13 is provided with an atmosphere opening hole 14 for introducing outside air. The purge pipe 11 has a discharge passage 15 on the side closer to the surge tank 12 than the canister 13, and a variable flow solenoid valve 16 (hereinafter referred to as a purge solenoid valve) is provided in the discharge passage 15. In this purge solenoid valve 16, the valve body 17 is always urged by a spring (not shown) in a direction to close the seat portion 18, but by exciting the coil 19, the valve body 17 opens the seat portion 18. Is becoming
Therefore, the discharge passage 15 is closed by demagnetizing the coil 19 of the purge solenoid valve 16, and the discharge passage 15 is opened by exciting the coil 19. The opening of the purge solenoid valve 16 is adjusted by the CPU 21, which will be described later, by the duty ratio control based on the pulse width modulation.

Therefore, the purge solenoid valve 16 has C
If a control signal is supplied from the PU 21 so that the canister 13 communicates with the intake pipe 2 of the engine 1, new air Qa is introduced from the atmosphere, which is the canister 1
3 is ventilated and sent from the intake pipe 2 of the engine 1 into the cylinder, the canister purge is performed, and the canister 1
The recovery of the adsorption function of No. 3 will be obtained. The amount of fresh air Qa introduced at this time Qp (l / _min )
Is adjusted by changing the duty of the pulse signal supplied from the CPU 21 to the purge solenoid valve 13. FIG. 2 is a characteristic diagram of the purge amount at this time, and shows the relationship between the duty of the purge solenoid valve 13 and the purge amount when the negative pressure in the intake pipe is constant.
As the purge solenoid is increased from 0%,
It can be seen that the purge amount, that is, the amount of air sucked into the engine 1 via the canister 13 increases almost directly.

The CPU 21 receives a throttle opening signal from a throttle sensor 5a for detecting the opening of the throttle valve 5, an engine rotation speed signal from a rotation speed sensor (not shown) for detecting the rotation speed of the engine 1, and a throttle valve. Intake air pressure signal from the intake pressure sensor 5b that detects the pressure of the intake air that has passed through 5, the cooling water temperature signal from the water temperature sensor 5c that detects the temperature of the engine cooling water, and the intake air temperature sensor that detects the intake air temperature ( The intake air temperature signal from (not shown) is input.

Further, the CPU 21 inputs a signal (voltage signal) from the oxygen sensor 6 and makes a rich / lean determination of the air-fuel mixture. Then, the CPU 21 changes (skips) the feedback correction coefficient stepwise in order to increase / decrease the fuel injection amount when changing from rich to lean and when changing from lean to rich, and at the time of rich or lean, the feedback correction coefficient is changed. Is gradually increased or decreased. It should be noted that this feedback control is not performed when the engine cooling water temperature is low and when the vehicle is running under high load and high rotation. Further, the CPU 21 obtains the basic injection time from the engine speed and the intake pressure, corrects the basic injection time with a feedback correction coefficient or the like to obtain the final injection time, and injects fuel at a predetermined injection timing by the injector 4. Let it be done.

The ROM 34 stores programs and maps for controlling the operation of the entire engine. RAM
Reference numeral 35 temporarily stores various data, for example, detection data such as the opening of the throttle valve 5 and the engine speed. Then, the CPU 21 controls the operation of the engine based on the program in the ROM 34.

FIG. 3 shows a full open purge rate map, which is determined by the engine speed Ne and the load (in this case, intake pipe pressure, intake air amount, throttle opening, etc.). This map shows the engine 1 through the intake pipe 2.
The ratio of the amount of air flowing through the discharge passage 15 when the duty of the purge solenoid valve 16 is 100% with respect to the total amount of air flowing in is shown in FIG.

This system uses the air-fuel ratio feedback (F
AF) control, purge rate control, initial evaporated fuel (evaporation) concentration detection, continuous evaporation concentration detection, fuel injection amount control, air-fuel ratio learning control, and purge solenoid valve control. First, in order to detect an unknown evaporation concentration level, the first evaporation concentration (FAF per unit purge rate)
Change amount) is detected. Secondly, the fuel injection amount is controlled by the detected evaporation concentration and the current purge rate. Third,
At a predetermined time interval and when the operating condition is stable, the updated evaporation concentration is detected, the evaporation concentration is updated, and the fuel injection amount is manipulated in the same manner as above. Then, the air-fuel ratio learning control is performed according to the behavior of the FAF value as a result of operating the fuel injection amount.

The operation of the embodiment will be described below for each control. Air-fuel ratio feedback control Air-fuel ratio feedback control will be described with reference to FIG. This air-fuel ratio feedback control is performed by the CPU 21 about every 4 ms.
It is executed by the base routine of.

First, in step S40, it is determined whether feedback (F / B) control is possible. The F / B condition is mainly when all the following conditions are satisfied.
(1) Not at the start. (2) Fuel is not being cut.
(3) Cooling water temperature (THW) ≧ 40 ° C. (3) TAU> T
AU _min . (4) The oxygen sensor is in an active state.

If the condition is satisfied, the routine proceeds to step S41, where it is judged whether or not the concentration has just been detected, and if not immediately after the concentration has been detected, the routine proceeds to step S42 where the oxygen sensor output and the predetermined determination level are compared, and the delay time (HI _msec ) and operate the air-fuel ratio flag XOXR. For example, when XOXR = 1, rich, and when XOXR = 0, lean. Next, in step S43, the value of FAF is manipulated based on this XOXR. That is, XOXR changes (0 → 1),
When (1 → 0), the FAF value is skipped by a predetermined amount,
While XOXR continues to be 1 or 0, integration control of the FAF value is performed. Then, the process proceeds to the next step S44 to check the upper and lower limits of the FAF value, and then proceeds to step S45 to perform smoothing processing at each skip or every predetermined time based on the determined FAF value. Calculate the averaged value FAFAV. In addition, when the F / B control is not established in step S40 and immediately after the end of the density detection in step S41 (the density detection flag to be described later is from 1 to 0).
Immediately after becoming), proceed to step S46
Is set to 1.0.

Purge Rate Control The main routine of the purge rate control is shown in FIG. This routine is also executed by the base routine of the CPU 21 about every 4 _ms .

In step S501, it is determined whether the air-fuel ratio F / B is in the same condition as in step S40 of FIG. 4, and in step S502 it is determined whether the cooling water temperature is 50 ° C. or higher. When the water temperature in B is equal to or higher than the predetermined value 50 ° C., the purge stop flag XIPGR is set to 0 in step S503 to execute the purge rate control. In the next step S504, it is determined whether or not the fuel is being cut. When the fuel is being cut, the process proceeds to step S505 to perform the fuel cut purge rate (PGR) control. When it is determined in step 504 that fuel is not being cut, the process proceeds to step S506, and it is determined by the initial concentration detection flag XFFPGPG whether the evaporative concentration from the canister has never been detected. When it has not been detected even once (first time), the process proceeds to step S507 to perform the PGR control for first time concentration detection. After the initial concentration detection,
Proceeding to step S508, the counter CPGKAN is operated, and the next step S50 is executed according to the coefficient value of this counter.
In step 9, it is determined whether or not a predetermined time (for example, 60 _sec ) has elapsed, the process proceeds to step S510 for each predetermined time, the concentration is detected, and the evaporation concentration (FGPG) is updated. In other cases, the process proceeds to step S511 and the normal purge rate control is performed. When the purge rate condition is not satisfied in steps S501 and S502, the process proceeds to step S512 to set the purge rate to 0, and then proceeds to step S513 to set the purge stop flag XIPGR to 1.

FIG. 6 shows the normal purge rate control subroutine in step S511 of FIG. First, step S
FAF value (or FAF smoothed value) is 1.0 at 601
Which of the three areas (,,) with respect to the reference is detected. Here, as shown in FIG. 7A, the area is within 1.0 ± F%, and the area is 1.0 ± F% or more ±
Area is 1.0 when you are within G% (however, F <G)
Indicates the time when it is within ± G%.

If it is in the region, the process proceeds to step S602, and the purge rate (PGR) is increased by a predetermined value D%. In the case of the area, the process proceeds to step S603 and the PGR is not increased or decreased. If it is in the region, the process proceeds to step S604, where PGR is set to a predetermined value E%
Gradually decrease. Here, the predetermined values D and E are (b) in FIG.
It is preferable to change it according to the evaporation concentration (FGPG) as shown in. Then, in the next step S605, PG
Check the upper and lower limits of R. Here, the upper limit value is based on various conditions such as the purge start time shown in (c) of FIG. 7, the water temperature shown in (d) of FIG. 7, the operating condition (full open purge rate map) shown in (e) of FIG. It should be the smallest value.

FIG. 8 shows the PGR control subroutine at the time of fuel cut in step S505 of FIG. First, in step S801, PGR is set to 0 so that the evaporation from the canister 13 does not enter the engine 1. Next, in step S802, if the concentration is being detected, each flag during the concentration detection is reset to cancel the detection (for example: XPGIDL, XPGRUN, XPGNO1, X).
PGNO2 = 0).

FIG. 9 shows the PGR control subroutine for initial density detection in step S507 of FIG. This control is divided into idle control and running control. When idle, in step S901 the idle flag XIDL is 1,
When it is determined in step S902 that the vehicle speed SPD is 0 km / h, and in step S903 that the FAF value has skipped three times or more, the process proceeds to step S904, and the idling concentration detection flag XPGIDL is set to 1. Also, XPGIDL
When XIDL is 0 or SPD is greater than 0 km / h, the process proceeds to step S905, and XPGIDL is reset to 0 so as to stop the concentration detection. When traveling, the process proceeds from step S901 to step S906, where XPG
Since IDL is not 1, the process proceeds to step S907, and when the running concentration detection flag XPGRUN is 1, the process proceeds to step S908 and the learning region is the same, the FAF value is skipped three times or more, and the acceleration / deceleration is not in progress. (For example,
Change in intake pipe pressure of engine 1 DLPM <19.5 mm
If it is Hg), the routine proceeds to step S909, and the running concentration detection flag XPGRUN is set to 1. If XPPGUN is not 1 in step S907, step S907
Proceed to step 910 to determine that acceleration / deceleration is not in progress (for example, DLPM <1.
9.5 mmHg), and FAF in the same engine operating range
If the value is skipped three times or more, the process proceeds to step S911 to store the engine operating region at that time, and then the process proceeds to step S909 to further detect the concentration during running flag XPG.
Set RUN to 1. In step S908, the area / D
When the LPM deviates from the predetermined value, the process proceeds to step S912, XPGRUN is set to 0, and the concentration detection flag is canceled.

XPGIDL is 1 or XPGRUN is 1
The first way to operate the purge rate after is is to determine that the FAF value (or smoothed value) before changing the purge rate in step S913: FAF _B is determined (this F
The determination of AF _B will be described later with reference to FIG. 13), and in the next step S914, a value obtained by reducing a predetermined value A% (for example, 15%) with respect to FAF _B is obtained, and a predetermined value ± α% is obtained with respect to this value. A dead zone (for example, 2%) is provided. As a result, three areas, as shown in FIG. 10, are determined. Then, in step S915, it is determined which region the FAF value (or the smoothed value) is in. If the region, the process proceeds to step S916 to increase the purge rate PGR by a predetermined value B%. If the region, the process proceeds to step S917. There was no increase or decrease in PGR. If it is a region, the process proceeds to step S918 and PGR is decreased by a predetermined value C%. Finally, in step S819, check the upper and lower limits of PGR,
PGR is limited to the range of 0% (lower limit) to 20% (upper limit).

FIG. 11 shows the PGR control subroutine for density update in step S510 of FIG. This control is also controlled separately for idling and running. The conditions for operating the concentration detection flags (XPGNO1, XPGNO2) are the same as in the initial concentration detection routine, that is, the operation of the purge rate is idle, XIDL is 1 in step S1101, SPD is 0 km / h in step S1102, If it is determined in step S1103 that the FAF value is skipped three times or more, the process proceeds to steps S1104 and S1105, and X
FAF value (or smoothed value) when PGNO1 becomes 1
And the value of the predetermined variation F% (for example, 10%) are FAF
It is confirmed that the upper and lower limits of the value are not exceeded, this predetermined change amount F% is divided by the evaporation concentration (FGPG), and the PGR when XPGNO1 becomes 1 is added to this divided value, so that step S1106 To determine PGR.
Finally, in step S1107, the upper and lower limits of PGR are checked.

At the time of running, as in the case of idling, step S1
In step S1117 via 108 to S1116, the predetermined change amount G% (for example, 7%) is divided by the evaporation concentration (FGPG), and the divided value is subtracted from the PGR when XPGNO2 becomes 1. Finally, in step S1118, the upper and lower limits of PGR are checked. The reason why the addition is performed at the time of idling and the subtraction is performed at the time of traveling is because the opening of the purge solenoid valve is small at the time of idling and is large at the time of traveling.

Evaporation Density Detection The main routine of the evaporation concentration detection executed by the base routine of the CPU 21 about every 4 _ms is shown in FIG. This routine is divided into initial density detection and density update for control. That is, in step S121, XFFGP
When G is 1 and XPGIDL is 1 or XPGRUN is 1 in step S122, the process proceeds to step S123 to detect the initial concentration of evaporation, and in step S121, XF
If FGPG is not 1, XPGNO1 is set in step S124.
Is 1 or XPGNO2 is 1, the process proceeds to step S125 to update the evaporation concentration.

FIG. 13 shows the initial density detection subroutine of step S123 of FIG. First, step S131
It is determined whether the previous concentration detection flag is 0, and if the previous concentration detection flag is 0, the purge rate control concentration detection flags (XPGIDL, XPGRUN, XP
GNO1, XPGNO2) has become 1 this time, so the routine proceeds to step S132, where PGR, F at that time
The AF value (or the smoothed value) is stored as PGR _B and FAF _B. In the next step S133, the FAF value (or the smoothed value) enters the dead zone described in the purge rate control, and if the FAF value is skipped three times or more, the process proceeds to step S134 and the PGR / FAF value (or the smoothed value) at that time. Value) to PG
R _C, stored as FAF _C. Then, in the next step S135, the difference ΔFAF between FAF _B and FAF _C is calculated as PGR.
Difference between _B and PGR _C Divided by ΔPGR Evaporation concentration FGP
Ask for G. When this density detection is completed, step S1
Flag and counter processing is performed at 36, S137, and S138 (for example, XFFPGPG is set to 1 and CPGKAN is set to 0). If the result is NO in step S133, step S1
Go to 39, FAF value becomes 3 after PGR becomes the upper limit
If skipped more than once, it is determined that the FAF value does not increase to the dead zone even if the purge amount is increased because the evaporation concentration is thin, and the process proceeds to step S134 to obtain the evaporation concentration FGPG in the same manner as described above. If the result is NO in step S139, the process returns without obtaining the evaporation concentration FGPG.

FIG. 14 shows the density update subroutine of step S125 of FIG. This density update subroutine is step S13 of the initial density detection subroutine of FIG.
1, S132, Step S similar to S134 to S138
In addition to the steps 141, S142, and S144 to S148, step S143 is performed only by determining whether the FAF value is skipped three times or more without determining the dead zone of the FAF value in step S133 of FIG. It is omitted. As a result, when updating the concentration of the detected evaporation, the PGR is changed by Δ to update the concentration.
It is executed when the FAF value is skipped three times after updating only PGR.

Fuel Injection Amount Control FIG. 15 shows the fuel injection amount control executed in the base routine of the CPU 21 about every 4 _ms .

First, in step S151, the basic fuel injection amount (TP) is obtained from the engine speed and load (for example, intake pipe pressure) based on the data stored as a map in the ROM 34, and in the next step S152. Perform various basic corrections (cooling water temperature, intake temperature after starting, etc.). Secondly, in step S153, the evaporation concentration is being detected (XPGIDL,
If XPGRUN, XPGNO1, XPGNO2 = 1), the process proceeds to step S154, and the purge correction coefficient FPG (value obtained by multiplying PGR by FGPG) when each flag becomes 1 is fixed. Otherwise, proceed to step S155 to match the PGR change,

[0038]

## EQU1 ## The FPG is calculated by FPG = (FGPG-1) .times.PGR. Finally in step S156, FA
F, FPG, the air-fuel ratio learning value (KGj) for each engine operating region,

[0039]

## EQU2 ## A correction coefficient is obtained by the calculation of 1+ (FAF-1) + (KGj-1) + FPG and is reflected in the fuel injection amount.

Purge Solenoid Valve Control FIG. 16 shows a purge solenoid valve control routine executed by the CPU 21 by interrupting every 100 _ms .
XIPGR is 1 in step S161 or step S1
If the fuel is being cut at 62, step S1
Proceeding to 63, the duty of the purge solenoid valve 16 is set to 0. Otherwise, the process proceeds to step S164, and if the drive cycle of the purge solenoid valve 16 is 100 _ms ,

[0041]

Equation 3] Duty = Request Duty of the purge solenoid valve 16 in the arithmetic expression _{(PGR / PGR fo) × (} 100 ms -P V) × P Pa + P V. Here, PGR is the purge rate obtained in FIGS. 6, 9, and 11, PGR _fo is the purge rate in each operating state when the purge solenoid valve 16 is fully open (see FIG. 3), and P _V is the battery voltage. A voltage correction value for fluctuations, P _Pa is an atmospheric pressure correction value for fluctuations in atmospheric pressure.

Air-fuel ratio learning control An air-fuel ratio learning control routine is shown in FIG. During the air-fuel ratio feedback, the cooling water temperature THW is 80 ° C or higher, the increase after startup is 0, the increase in warm-up is 0, the current operation range is entered and the FAF value is skipped 5 times or more, and the battery voltage is 11.5V.
The fact that all of the above basic conditions have been met is step S17.
02 and the evaporation concentration detection flag XPGID
If all of L, XPGRUN, XPGUO1, and XPGN2 are other than 1, it is determined in step S1701 to perform learning control. Learning control is FA in step S1703.
After reading the value of FAV, it is divided into idle KG ₀ (step S1708) and traveling (step S1710) according to the determination result of whether or not the vehicle is idle in step S1705. ) Is divided into a predetermined number (for example, seven) of areas KG _{1 to} KG ₇ . When the engine speed is within the predetermined engine speed in steps S1706 and S1709 (600 at idle).
~1000 _rpm, while driving is as 1000~3200 _rpm) only, to update the learning value. Further, at the time of idling, the intake pipe pressure PM becomes 17 by step S1707.
The learning value is updated when it is 3 mmHg or more. The method of updating the learning values KG _{0 to} KG ₇ of each region is such that when the difference between the FAF smoothed value and 1.0 is larger than a predetermined value (for example, 2%),
The learning values KG _{0 to} KG ₇ of the area are set to predetermined values (K%, L
%) It is done by increasing or decreasing each. (Step S1
711-S1714). Finally, the upper and lower limits of KGj are checked (step S1715). Here, the upper limit value of KGj is set to 1.2, the lower limit value is set to 0.8, and the upper and lower limit values can be set for each engine operating region.

FIG. 18 shows the subroutine of step S44 in FIG. 4. First, in step S181, the basic upper and lower limits of FAF are set (for example, upper limit 1.2 and lower limit 0.8 are set). Next, in step S182,
If any of the evaporation concentration detection flags is 1, the process proceeds to step S183, the lower limit value of FAF is set to a value smaller than the basic lower limit value (for example, 0.6), and then the process returns. If all the evaporative concentration detecting flags are other than 1 in step S182, the process proceeds to step S184, and it is determined whether or not a predetermined time (for example, 3 seconds) has elapsed since all the evaporative concentration detecting flags became 0. When the predetermined time has not elapsed, the process proceeds to step S183, and when the predetermined time has elapsed, the process directly returns. As a result, the lower limit value of the FAF is set to a value smaller than the basic value during the evaporative concentration detection and until a predetermined time elapses after the end of the evaporative concentration detection. Prevents the concentration from being detected and updated.

A time chart of the embodiment described above is shown in FIG. (A) shows the detected evaporation concentration value FGPG, (b) shows the fuel reduction correction coefficient FPG, (c) shows the purge rate PGR, the solid line in (d) shows the FAF value, and the dashed line shows the FAF. Indicates the lower limit.

Other Embodiment A In the above-mentioned embodiment, the fuel reduction correction coefficient FP during the concentration update.
Although G is fixed to the value immediately before that, as shown in the time chart of FIG. 20, the fuel amount reduction correction coefficient FPG during the concentration update is set to the amount of the vaporized fuel concentration that has already been detected and the purge at the time of the concentration update. It is possible to make the fluctuation of the FAF value at the time of updating the density smaller by changing the FAF value according to the ratio. In this embodiment, the above-described FIGS.
Compared with the embodiment shown in FIG. 8, the fuel control of FIG. 15 is replaced with that of FIG. 21, and the concentration update subroutine of FIG. 14 is replaced with that of FIG. Here, in FIG.
5, steps S153 and S154 are omitted, and FIG.
As 145, the amount of evaporation concentration change is reflected on the previous FGPG value.

Other Embodiment B In each of the above embodiments, the intake air pressure downstream of the throttle valve 5 is detected by the intake pressure sensor 5b, and the basic fuel injection amount is determined by the engine speed and the intake pipe pressure. Although the present invention is applied to the one for calculating, the present invention is also applied to one for calculating the basic fuel injection amount from the engine speed and the intake air amount by using the intake air amount sensor that detects the intake air amount upstream of the throttle valve 5. The invention can be applied. In this way, when detecting the intake air amount upstream of the throttle valve 5,
Since the flow rate of the bypass air containing the evaporative gas introduced to the downstream side of the throttle valve 5 via the discharge passage 15 cannot be detected as the intake air amount, the basic fuel injection amount is determined by excluding the bypass air flow rate. Therefore, when the concentration of evaporative gas in the bypass air is low, the air-fuel ratio of the air-fuel mixture sucked into the combustion chamber of the internal combustion engine increases as the purge rate increases, and the purge rate increases accordingly. On the contrary, the FAF value, which should be smaller as it is increased, becomes larger, and it becomes impossible to detect the initial concentration of evaporative gas. Therefore, in this embodiment, as shown in FIG. 23, as compared with the FAF determination area shown in FIG.
A region larger than FAF _B before changing the purge rate is added, and the detection of the initial concentration is prohibited in this region. Therefore, in this embodiment, the above-described FIGS.
In the embodiment shown in FIG. 9, the initial concentration detecting purge control subroutine is shown in FIG. 24, the evaporation concentration detection in FIG. 12 is shown in FIG. 25, and the purge solenoid valve control in FIG. 16 is shown in FIG. It was replaced.

Here, in FIG. 24, an area larger than FAF _B is added as the area confirmation step S915 to that of FIG. 9, and when it is determined that this area is reached, the process proceeds to step S920 to set the purge rate to 0. After that, the process proceeds to step S921, and the area 4 flag XRYU4
It is designed to return after setting 1 to 1. Further, in FIG. 25, step S
Insert the region 4 confirmation step S126 before 121,
When it is determined in step S126 that the area 4 flag XRYU4 is not 1, the process proceeds to step S121, and the same operation as that shown in FIG. 12 is performed thereafter. After the evaporative concentration is set to 1.0, the process returns. Further, in FIG. 26, the area 4 confirmation step S165 is inserted before the step S161 for the step shown in FIG.
If it is determined at 65 that the region 4 flag XRYU4 is not 1, the process proceeds to step S161 and the same operation as that shown in FIG. 16 is performed thereafter. If it is determined at step S165 that the region 4 flag XRYU4 is 1, the process proceeds to step S163. It was done.

[0048]

As described above, in the present invention, the purge rate and the fuel amount during evaporative fuel concentration detection or renewal are controlled in consideration of the air-fuel ratio and the evaporative fuel concentration, so that the evaporative fuel to the canister is controlled. Even when the adsorbed amount is large, there is an excellent effect that the fluctuation of the air-fuel ratio during the evaporative fuel concentration detection or renewal can be suppressed, and the idling stability and the exhaust emission can be prevented from deteriorating.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.

FIG. 2 is a characteristic diagram of the purge solenoid valve in the above embodiment.

FIG. 3 is a full open purge rate map in the above embodiment.

FIG. 4 is a flowchart of air-fuel ratio feedback control in the above embodiment.

FIG. 5 is a flowchart of purge rate control in the above embodiment.

FIG. 6 is a flowchart of a normal purge rate control subroutine in the above embodiment.

7 (a) to 7 (e) are various characteristic diagrams used in the normal purge rate control subroutine in the above embodiment.

FIG. 8 is a flowchart of a fuel cut purge rate control subroutine in the above embodiment.

FIG. 9 is a flowchart of an initial concentration detecting purge rate control subroutine in the above embodiment.

FIG. 10 is a region determination characteristic diagram used in a purge ratio control subroutine for initial concentration detection in the above embodiment.

FIG. 11 is a flowchart of a concentration update purge rate control subroutine in the above embodiment.

FIG. 12 is a flow chart of evaporation concentration detection in the above embodiment.

FIG. 13 is a flowchart of an initial concentration detection subroutine in the above embodiment.

FIG. 14 is a flowchart of a density update subroutine in the above embodiment.

FIG. 15 is a flowchart of fuel injection amount control in the above embodiment.

FIG. 16 is a flowchart of purge solenoid valve control in the above embodiment.

FIG. 17 is a flowchart of air-fuel ratio learning control in the above embodiment.

FIG. 18 is a flowchart of an air-fuel ratio feedback control upper / lower limit check subroutine in the above embodiment.

FIG. 19 is a time chart showing waveforms at various points in the above embodiment.

FIG. 20 is a time chart showing waveforms at various points in another embodiment A of the device of the present invention.

FIG. 21 is a flow chart of fuel injection amount control in the other embodiment A.

FIG. 22 is a flowchart of a density update subroutine in the other embodiment A.

FIG. 23 is a region determination characteristic diagram used in an initial concentration detection purge rate control subroutine in another embodiment B of the device of the present invention.

FIG. 24 is a flowchart of an initial concentration detecting purge rate control subroutine in the other embodiment B.

FIG. 25 is a flow chart of evaporation concentration detection in the other embodiment B.

FIG. 26 is a flowchart of purge solenoid valve control in Embodiment B described above.

[Explanation of symbols]

 1 Multi-cylinder engine 2 Intake pipe 5 Throttle valve 5a Throttle sensor 5b Intake pressure sensor 6 Oxygen sensor 7 Fuel tank 13 Canister 15 Release passage 16 Purge solenoid valve 21 CPU

Claims (6)

[Claims] 1. An air-fuel ratio control of an internal combustion engine, wherein evaporated fuel generated in a fuel tank is stored in a canister, and the evaporated fuel stored in the canister is discharged together with air to an intake side of the internal combustion engine through a discharge passage. An air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine, and an air-fuel ratio feedback controlling air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detecting means. A fuel ratio feedback means, a flow rate control valve for changing a purge rate of air containing evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage, and the flow control valve for detecting a concentration of the evaporated fuel. Concentration detection purge rate control means for gradually changing the purge rate by the flow rate control valve until the air-fuel ratio detected by the air-fuel ratio detection means changes by a predetermined amount. Air-fuel ratio control apparatus for an internal combustion engine and a concentration detection means for detecting the concentration of fuel vapor by the air-fuel ratio and the purge rate before and after changing the purge rate by the purge rate control means. 2. An air-fuel ratio control of an internal combustion engine, wherein evaporated fuel generated in a fuel tank is stored in a canister, and the evaporated fuel stored in the canister is discharged together with air to an intake side of the internal combustion engine through a discharge passage. In the device, an air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine, and an air-fuel ratio of a mixture of fuel and air supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detecting means. An air-fuel ratio feedback means for feedback control of the air-fuel ratio, a flow rate control valve for changing a purge rate of air containing evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage, and a concentration of the evaporated fuel. Before the purge rate is changed by the purge rate control means for concentration detection, which changes the purge rate by the flow rate control valve when detecting the A concentration detecting means for detecting the concentration of the evaporated fuel based on the air-fuel ratio and the purge rate, and a concentration detecting means for detecting the concentration of the evaporated fuel, and then detecting the concentration of the evaporated fuel again by the concentration detecting means. In this case, the air-fuel ratio control of the internal combustion engine is provided with a fuel concentration correction means at the time of concentration detection for reflecting the already-evaporated fuel concentration amount on the fuel supply amount of the internal combustion engine according to the purge rate at the time of the concentration detection. apparatus. 3. An air-fuel ratio control of an internal combustion engine, wherein evaporated fuel generated in a fuel tank is stored in a canister, and the evaporated fuel stored in this canister is discharged together with air to an intake side of the internal combustion engine through a discharge passage. An air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine, and an air-fuel ratio feedback controlling air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detecting means. A fuel ratio feedback means, a flow rate control valve that changes a purge rate of air containing evaporated fuel released from the canister to the intake side of the internal combustion engine through the discharge passage, and a concentration of the evaporated fuel is updated, Concentration updating purge rate control means for changing the purge rate by the flow rate control valve according to the already detected vaporized fuel concentration, and the purge rate control means. Air-fuel ratio control apparatus for an internal combustion engine and a concentration updating means for updating the density of the evaporated fuel by the air-fuel ratio and the purge rate before and after changing the purge rate by. 4. An air-fuel ratio control of an internal combustion engine, wherein evaporated fuel generated in a fuel tank is stored in a canister, and the evaporated fuel stored in this canister is discharged together with air to an intake side of the internal combustion engine through a discharge passage. An air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine, and an air-fuel ratio feedback controlling air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detecting means. A fuel ratio feedback means, a flow rate control valve for changing a purge rate of air containing evaporated fuel released from the canister to the intake side of the internal combustion engine via the discharge passage, and a first concentration of the evaporated fuel is detected. Purge for initial concentration detection, in which the purge rate is gradually changed by the flow rate control valve until the air-fuel ratio detected by the air-fuel ratio detecting means changes by a predetermined amount. Control means, an initial concentration detection means for detecting the initial concentration of the evaporated fuel by the air-fuel ratio and the purge rate before and after changing the purge rate by the purge rate control means, and when updating the concentration of the evaporated fuel, Concentration updating purge rate control means for changing the purge rate by the flow rate control valve in accordance with the already detected vaporized fuel concentration, and air-fuel ratios before and after changing the purge rate by this purge rate control means, and An air-fuel ratio control device for an internal combustion engine, comprising: a concentration updating means for updating the concentration of evaporated fuel according to a purge rate. 5. The air-fuel ratio of an internal combustion engine according to claim 1, wherein the air-fuel ratio used by the concentration detecting means for concentration detection is an air-fuel ratio feedback value of the air-fuel ratio feedback means. Control device. 6. An air-fuel ratio control of an internal combustion engine, wherein vaporized fuel generated in a fuel tank is stored in a canister, and the vaporized fuel stored in this canister is discharged together with air to an intake side of the internal combustion engine through a discharge passage. In the device, an air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine, and an air-fuel ratio of a mixture of fuel and air supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detecting means. An air-fuel ratio feedback means for feedback control of the air-fuel ratio, a flow rate control valve for changing a purge rate of air containing evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage, and a concentration of the evaporated fuel. Before the purge rate is changed by the purge rate control means for concentration detection, which changes the purge rate by the flow rate control valve when detecting the Concentration detecting means for detecting the concentration of the evaporated fuel by the air-fuel ratio feedback value of the air-fuel ratio feedback means and the purge rate, and the air-fuel ratio feedback means when the concentration of the evaporated fuel is detected by the concentration detecting means An air-fuel ratio control device for an internal combustion engine, comprising: concentration-detecting lower limit guard changing means for expanding the lower limit guard of the air-fuel ratio feedback value.