JP3477802B2 - 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 an internal combustion engine in which fuel is injected by an injector and vaporized fuel (hereinafter referred to as evaporative gas) generated in a fuel tank is sucked into an intake system of the internal combustion engine for combustion. The present invention relates to the air-fuel ratio control device.

[0002]

2. Description of the Related Art In an air-fuel ratio control system of this kind, a canister for adsorbing evaporative gas generated in the fuel tank is connected to a fuel tank, and an electromagnetic passage is provided in a discharge passage communicating the canister with an intake system of an internal combustion engine. An on-off valve is provided. The evaporative gas adsorbed on the canister is discharged (purged) together with air into the intake system of the internal combustion engine along with the opening / closing operation of the opening / closing valve, and is mixed with the fuel injected by the injector and burned. Further, air-fuel ratio feedback control is executed to eliminate the deviation between the air-fuel ratio detected by the air-fuel ratio sensor and the target air-fuel ratio.

Further, in such an air-fuel ratio control device,
The fuel injection amount by the injector is corrected according to the estimated concentration value of the evaporative emission gas (hereinafter referred to as the evaporative emission concentration). Therefore, in order to realize precise air-fuel ratio control according to the evaporation purge, it is necessary to accurately estimate the evaporation concentration, and various techniques have been conventionally proposed to estimate the evaporation concentration (for example, Japanese Patent Laid-Open No. 288107).

[0004]

However, in the conventional air-fuel ratio control device, the air-fuel ratio control performed using the estimated evaporation concentration becomes rough, or when the evaporation concentration changes suddenly (estimated There was a problem that it took time for the value) to match the actual density.
In particular, when the engine is started or fuel is refueled, the concentration (actual value) of the evaporative gas that is purged through the on-off valve rises sharply, so that the air-fuel ratio tends to be disturbed, and the above problems tend to become more prominent. It was

The present invention has been made in view of the above problems, and an object thereof is to always quickly and accurately estimate the concentration of evaporated fuel (evaporative gas) and to perform precise air-fuel ratio control. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can realize the above.

[0006]

In order to achieve the above object, the air-fuel ratio control device according to the first and second aspects is
As shown in FIG. 15, a canister M2 for adsorbing the evaporated fuel generated in the fuel tank M1 and the canister M2.
An on-off valve M5 that opens and closes to release the evaporated fuel adsorbed on the intake system of the internal combustion engine M4 via the release passage M3
Valve control means M6 for opening and closing the on-off valve M5 at a predetermined timing, an injector M7 for injecting and supplying fuel to the internal combustion engine M4, and fuel injection by the injector M7 according to the operating state of the internal combustion engine M4. The injection amount calculation means M8 for calculating the amount, the air-fuel ratio sensor M9 for detecting the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine M4, and the air-fuel ratio sensor M9 for opening the on-off valve M5 by the valve control means M6. If the air-fuel ratio measured by the fuel ratio sensor M9 is close to the rich side, the estimated concentration value of the evaporated fuel is increased by a predetermined updating width, and if the air-fuel ratio is lean, the estimated concentration value of the evaporated fuel is decreased by a predetermined updating width. Concentration estimating means M10
And the density estimating means M1 according to the degree of deviation between the density value estimated by the density estimating means M10 and the actual density value.
The update width setting means M11 for setting the update width of 0, the air-fuel ratio correction value based on the deviation between the air-fuel ratio and the target air-fuel ratio by the air-fuel ratio sensor M9, and the estimated concentration value of the evaporated fuel by the concentration estimating means M10. Accordingly, the injection amount calculation means M
Injection amount correction means M12 for correcting the fuel injection amount by 8
And an injector control unit M13 for driving the injector M7 based on the fuel injection amount corrected by the injection amount correction unit M12.

Further, in the invention according to claim 1, comprising a concentration change rate calculating means for calculating a change rate of the estimated density value of the evaporated fuel by the concentration estimating unit M10, the update width setting unit M11, the concentration The update width is increased as the change rate of the density calculated by the change rate calculating means increases.

Further, in the invention according to claim 2, comprising a feedback correction coefficient calculating means for calculating a feedback correction coefficient for reducing the deviation between the air-fuel ratio and the target air-fuel ratio by the air-fuel ratio sensor M9, the update The width setting means M11 is configured to set the update width according to the rate of change of the feedback correction coefficient.

[0009]

According to the structures described in claims 1 and 2 , the evaporated fuel generated in the fuel tank M1 is adsorbed to the canister M2. The valve control means M6 opens the on-off valve M5 at a predetermined timing to open the canister M2.
The vaporized fuel adsorbed by is discharged to the intake system of the internal combustion engine M4 through the discharge passage M3. The injection amount calculation means M8 calculates the fuel injection amount by the injector M7 according to the operating state of the internal combustion engine M4.

Further, when the air-fuel ratio measured by the air-fuel ratio sensor M9 is close to rich during the opening period of the on-off valve M5 by the valve control means M6, the concentration estimation means M10 increases the estimated concentration value of the evaporated fuel by a predetermined update width. If the air-fuel ratio is lean, the estimated concentration value of the evaporated fuel is reduced by a predetermined update width. The update width setting means M11 sets the update width of the density estimating means M10 in accordance with the degree of deviation between the density value estimated by the density estimating means M10 and the actual density value.
The injection amount correction means M12 is based on the injection amount calculation means M8 according to the air-fuel ratio correction value based on the deviation between the air-fuel ratio measured by the air-fuel ratio sensor M9 and the target air-fuel ratio, and the estimated concentration value of evaporated fuel by the concentration estimation means M10. Correct the fuel injection amount.
The injector control means M13 is an injection amount correction means M12.
Based on the fuel injection amount corrected by
Drive.

In short, when correcting the fuel injection amount by the injector M7 according to the estimated concentration value of the evaporated fuel, if the estimated concentration value of the evaporated fuel and the actual concentration value do not match, the correction of the fuel injection becomes insufficient. The air-fuel ratio is disturbed (rich or lean). However, in the above configuration, the estimated concentration value is increased / decreased according to the rich / lean of the air-fuel ratio, so that appropriate concentration estimation and precise air-fuel ratio control are compatible.

Further, in the above configuration, since the update width is set according to the degree of deviation between the estimated concentration value of the evaporated fuel and the actual concentration value, the actual concentration value is set, for example, when the engine is started or fuel is refueled. Even when a sudden change occurs, the density value estimated by the density estimating means M10 quickly reaches the actual density value. As a result, the temporary turbulence of the air-fuel ratio caused by the sudden change in the evaporated fuel is quickly eliminated.

[0013] According to the structure as set forth in claim 1, conc <br/> rate of change calculation means calculates the rate of change of the estimated density value of the fuel vapor by the concentration estimating unit M10. Then, the update width setting means M11 increases the update width as the density change rate by the density change rate calculating means increases. That is, a large change rate of the estimated density value indicates that the estimated density value by the density estimating means M10 is largely deviated from the actual density value. In this case, the update width is increased to quickly increase the estimated density value. The actual value will be reached.

Further, according to the configuration of claim 2, full <br/> fed back correction coefficient calculating means, a feedback correction coefficient for reducing the deviation between the air-fuel ratio and the target air-fuel ratio by the air-fuel ratio sensor M9 Is calculated. Then, the update width setting means M11 increases the update width as the rate of change of the feedback correction coefficient increases. That is, the fact that the rate of change of the feedback correction coefficient is large means that the density estimating means M1
It indicates that there is a large difference between the estimated density value and the actual density value due to 0. In this case, the estimated density value quickly reaches the actual value by increasing the update width.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the air-fuel ratio control device of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of an air-fuel ratio control system for an internal combustion engine. In FIG. 1, a multi-cylinder internal combustion engine (hereinafter referred to as an engine) 1 is mounted on a vehicle, 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.
The exhaust pipe 3 is provided with an oxygen sensor 6 as an air-fuel ratio sensor that 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 sucked up by the fuel pump 8 and is pressure-fed to each injector 4 via 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 communicates with a surge tank 12 of an intake pipe 2. A canister 13 containing activated carbon as an adsorbent for adsorbing the evaporative gas generated in the fuel tank 7 is disposed in the middle of the purge pipe 11. 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 surge tank 12 side with respect to the canister 13, and a variable flow solenoid valve (hereinafter referred to as a purge valve) 1 serving as an opening / closing valve in the middle of the discharge passage 15.
6 is provided.

In the purge valve 16, the valve body 17 is always biased by a spring (not shown) in the direction to close the seat portion 18, but by exciting the coil 19, it moves in the direction to open the seat portion 18. It has become. That is, the purge valve 16 is demagnetized by the coil 19 so that the discharge passage 1
5 is closed, and the discharge passage 15 is opened by exciting the coil 19. The opening / closing operation of the purge valve 16 is performed by the CPU 2 described later.
The duty ratio is controlled based on the pulse width modulation by 1.

Therefore, when a control signal is supplied from the CPU 21 to the purge valve 16 to connect the canister 13 and the intake pipe 2 of the engine 1, fresh air is introduced into the canister 13 through the atmosphere opening hole 14, Fresh air canister 13
Ventilate the inside. At this time, the evaporation gas is sent from the intake pipe 2 into the cylinder of the engine 1 for canister purging, and the adsorption function of the canister 13 is restored. Note that, as shown in the characteristic diagram of FIG.
It is adjusted according to the duty ratio of the pulse signal supplied to. FIG. 2 shows the characteristics when the negative pressure in the intake pipe 2 is constant. From this characteristic diagram, it can be seen that the purge air amount increases almost linearly as the duty ratio of the purge valve 16 increases from 0%.

The throttle valve 5 has a throttle sensor 22 for detecting the opening of the valve 5, and the surge tank 12 has an intake pressure sensor 23 for detecting the pressure of intake air passing through the throttle valve 5. The cylinder block is provided with a water temperature sensor 24 for detecting the temperature of the cooling water. In addition to the throttle opening signal, the intake pressure signal, and the cooling water temperature signal from each of the above-mentioned sensors, the CPU 21 has an engine speed signal from a speed sensor (not shown) and an intake temperature from an intake temperature sensor (not shown). Signal, atmospheric pressure sensor (not shown)
The atmospheric pressure signal from is input.

The CPU 21 calculates the intake pressure PM, the cooling water temperature THW, the engine speed NE, the intake temperature THA, the atmospheric pressure PA, etc. on the basis of the respective detection signals, and uses these data as RA.
It is temporarily stored in M26. A backup RAM that stores and retains data even when the power is cut off in a part of the RAM 26
(Not shown) is configured. Note that, for example, instead of the intake pressure signal from the intake pressure sensor 23, the intake air amount signal from the intake air amount sensor is input to the CPU 21, or the intake pressure signal before engine start is used as the atmospheric pressure signal.
You can also enter in 21.

Further, the ROM 25 stores arithmetic programs and various maps for controlling the operation of the entire engine. Then, the CPU 21 executes the air-fuel ratio control based on the calculation program and the map in the ROM 25.
That is, the CPU 21 inputs the voltage signal from the oxygen sensor 6 and performs rich / lean determination of the air-fuel mixture. Then, the CPU 21 changes (skips) the feedback correction coefficient FAF stepwise in order to increase or decrease the fuel injection amount when changing from rich to lean and when changing from lean to rich, and when it is rich or lean, the feedback correction coefficient FAF is changed. FAF (reference value of feedback correction coefficient FAF = 1.0) is gradually increased or decreased.

Further, the CPU 21 obtains the basic injection time Tp from the engine speed NE and the intake pressure PM. And
Feedback correction coefficient FAF for basic injection time Tp
The final injection time τ is obtained by performing the correction by the above, and the fuel injection by the injector 4 is performed at a predetermined injection timing. In the present embodiment, the CPU 21 constitutes the valve control means, the injection amount calculation means, the concentration estimation means, the update width setting means, the injection amount correction means, the injector control means, the concentration change rate calculation means, and the feedback correction coefficient calculation means. ing.

The operation of the air-fuel ratio control device configured as described above will be described below with reference to FIGS. 4 to 13.
In the flowchart used in the present embodiment, FIG. 4 shows an air-fuel ratio learning control routine as a base routine by the CPU 21, and FIGS. 5 and 6 show a purge rate calculation routine and an evaporation concentration calculation routine as subroutines of FIG. Show. Further, FIG. 7 shows a density update width setting routine, and FIG.
Is an air-fuel ratio feedback control routine, FIG. 9 is a fuel injection control routine, and FIG. 10 is a purge valve control routine.
The routines shown in FIGS. 7 to 10 are executed at a predetermined interrupt timing by the CPU 21.

First, the overall control operation by the routines of FIGS. 4 to 10 will be briefly described. In the routine of FIG. 4, after the power is turned on, initial learning is first performed (step 1
02, 103), and then purge control (step 104
To 108) and regular learning (steps 111 and 112) are repeatedly executed. At this time, in the learning period, the air-fuel ratio deviation amount for each operating state of the engine 1 is obtained, and the learning correction value FLRN for correcting the deviation amount is the RAM2.
6 stored in the backup RAM.

Further, during the purge control period shown in FIG. 4, the routines shown in FIGS. 5 and 6 are executed to calculate the purge rate RPRG and the evaporation concentration FLPRG (estimated concentration value) according to the air-fuel ratio. Here, the purge rate RPRG (%) indicates the ratio of the purge flow rate GPRG of the evaporative gas to the intake air amount GA in the intake pipe 2 (RPRG = GPRG / G
A) and evaporation concentration FLPRG (%) indicate the ratio of the fuel contained in the evaporation gas per 1% of the purge rate. It should be noted that in the evaporation concentration calculation according to FIG. 6, the evaporation concentration FLPRG is increased / decreased by the predetermined concentration update width α according to the rich / lean of the air-fuel ratio.
Is set in the routine of FIG.

Further, during the purge control period, the purge valve 16 is driven at a predetermined duty ratio by the routine shown in FIG. Further, in the routine of FIG. 8, the feedback correction coefficient FAF is calculated. In the routine of FIG. 9, the basic injection time Tp is calculated, and the final injection time τ by the injector 4 is calculated by performing feedback correction, air-fuel ratio learning correction, etc. on the basic injection time Tp.

The following conditions (1) to (6) are mainly set as the execution conditions (feedback conditions) of the air-fuel ratio feedback in the following routines. Suppose the conditions are met. (1) Do not start. (2) The fuel is not being cut. (3) Cooling water temperature THW ≧ 40 ° C.
To be. (4) τ> τ _min (however, τ
_min is the minimum injection time of the injector 4). (5) The oxygen sensor 6 is in an active state. (6) Not under high load and high rotation.

Further, in the following routine, the feedback correction coefficient FAF is smoothed (averaged) every skip or every predetermined time, and the value is used as the smoothed value FAFAV. The absolute value of the difference between the smoothed value FAFAV and the reference value (= 1) of the feedback correction coefficient FAF is used as the deviation ΔFAF of the feedback correction coefficient FAF (ΔFAF = | FAFAV-1 |).

Specific processing contents of each routine will be described below in order from the air-fuel ratio learning control routine of FIG. Now, when the routine shown in FIG. 4 is started when the power to the CPU 21 is turned on, the CPU 21 first executes step 10
At 1, the air-fuel ratio learning condition is determined. This air-fuel ratio learning condition includes the above-mentioned feedback condition and water temperature condition (THW
> 80 ° C.) and the like. Then, if the learning condition is satisfied, the CPU 21 executes the initial air-fuel ratio learning in steps 102 and 103. That is, the CPU 21 executes air-fuel ratio learning (update of the learning correction value FLRN) in step 102. When the deviation ΔFAF (= | FAFAV-1 |) of the feedback correction coefficient FAF is stable within 2% (the smoothed value FAFAV is stable with respect to the reference value), the feedback correction coefficient FAF is set to 1
When the two skips are completed, that is, when step 103 is satisfied, the CPU 21 determines that the initial learning is completed and proceeds to step 104.

After that, the CPU 21 calculates the purge rate RPRG in step 104, and also executes step 105.
Then, the evaporation concentration FLPRG is calculated. Here, step 104 is the same as the purge rate calculation routine of FIG.
5 corresponds to the evaporative concentration calculation routine of FIG. 6, and details thereof will be described later.

Next, the CPU 21 executes steps 106-1.
The purge continuation condition shown in 08 is determined. Specifically, C
The PU 21 determines in step 106 whether the intake air temperature THA is higher than 50 ° C. At this time, if THA> 50 ° C., the CPU 21 determines that the amount of heat received in the fuel tank 7 increases and the amount of evaporative gas generation increases, and step 104
Return to and continue the purge control. Further, the CPU 21 determines in step 107 whether the evaporation concentration FLPRG is a value larger than 1%. At this time, FLPRG> 1%
If so, the CPU 21 determines that the amount of evaporation gas adsorbed by the canister 13 is large, and returns to step 104 to continue the purge control. Further, the CPU 21 executes step 1
At 08, it is determined whether the elapsed time from the start of purging is within 120 seconds, and if it is within 120 seconds, step 104
Return to and continue the purge control. That is, step 106
If any of the determinations to 108 is affirmatively determined, it is considered that the purging is necessary, and the purging is preferentially performed rather than the air-fuel ratio learning.

If all of the conditions in steps 106 to 108 are negatively determined, the CPU 21 determines that the purge is not necessary and proceeds to step 109 to execute the purge execution flag XP.
Reset RG to "0" and follow step 1
At 10, the purge rate RPRG is reset to 0%. Here, the purge execution flag XPRG determines whether or not the evaporation purge by the purge valve 16 is executed, and X
If PRG = “0”, purging is not executed.

After that, the CPU 21 executes regular learning of the air-fuel ratio in steps 111 and 112. That is, CPU2
1 is the air-fuel ratio learning (learning correction value FLR in step 111).
Update N). Then, when the deviation ΔFAF is stable within 2%, the feedback correction coefficient F
When 6 skips of AF are completed, that is, step 11
When 2 is satisfied, the CPU 21 returns to step 104 as the regular learning is completed. After that, the CPU 21 repeatedly executes steps 104 to 112 described above.

Next, the purge rate calculation routine of FIG. 5 will be described. In FIG. 5, the CPU 21 determines in step 201 whether the above-mentioned feedback condition is satisfied, and also determines in step 202 whether the cooling water temperature THW> 80 ° C. When either of the steps 201 and 202 is negatively determined, the CPU 21 proceeds to step 20.
In step 3, the purge execution flag XPRG is reset to "0", and this routine ends.

If both steps 201 and 202 are affirmatively determined, the CPU 21 sets the purge execution flag XPRG to "1" in step 204, and then executes step 2
The purge rate RPRG is calculated from 05 to 209. Specifically, the CPU 21 determines the deviation ΔFAF> 5% in step 205.
Is determined, and the deviation ΔFAF is determined in step 206.
It is determined whether or not> 10%. And ΔFAF ≦
If it is 5%, the CPU 21 proceeds to step 207 and increases the value of the purge rate RPRG by 0.05%. 5% <Δ
If FAF ≦ 10%, the CPU 21 proceeds to step 208.
Then, the purge rate RPRG is held at the value at that time. If ΔFAF> 10%, the CPU 21 proceeds to step 209 to decrease the value of the purge rate RPRG by 0.05%.

Finally, in step 210, the CPU 21 checks whether or not the purge rate RPRG is within the upper limit set in FIG. 3, and if the value exceeds the upper limit value, holds it at the upper limit value. Note that FIG. 3 is a full-open purge ratio map determined by the engine speed NE and the engine load (in this embodiment, the intake pressure PM, but other intake air amount or throttle opening may be used). The maximum purge rate when the duty ratio of the valve 16 = 100% is shown.

On the other hand, in the evaporative concentration calculation routine of FIG. 6, the CPU 21 determines in step 301 the purge execution flag X.
It is determined whether or not PRG = “1”. And XP
If RG = “0”, the CPU 21 ends the routine as it is. If XPRG = "1", CPU2
In step 302, 1 is the feedback correction coefficient FAF from the smoothed value FAFAV of the feedback correction coefficient FAF.
A value (= FAFAV-1) is obtained by subtracting the reference value (= 1) of the above, and then, in steps 303 to 307, the evaporation concentration F
Calculation of LPRG (estimation of evaporation concentration FLPRG) is performed.

That is, the CPU 21 determines (F
It is determined whether or not AFAV-1)> 2%, and it is determined at step 304 whether or not (FAFAV-1) <-2%. If (FAFAV-1)> 2%, that is, if the air-fuel ratio is lean, the CPU 21 determines that the actual concentration FLPRG is lighter than the current evaporation concentration FLPRG, and the value of the evaporation concentration FLPRG is determined in step 305. Is reduced by the density update width α. (FAFAV-1) <
-2%, that is, if the air-fuel ratio is near the rich side, CP
U21 determines that the actual concentration FLPRG is higher than the current evaporation concentration FLPRG, and increases the value of the evaporation concentration FLPRG by the concentration update width α in step 306. or,
-2% ≤ (FAFAV-1) ≤ 2%, CPU2
1 judges that the current evaporation concentration FLPRG is substantially the actual value, and holds the evaporation concentration FLPRG at the value at that time in step 307.

After the estimation of the evaporation concentration FLPRG, the CPU 2
In step 308, it is checked whether the evaporation concentration FLPRG is within 0 to 25% which is the upper and lower limit value, and the routine ends.

Next, the density update width setting routine of FIG. 7 will be described. This routine is 4 msec by the CPU 21
It is executed by interruption every time. In FIG. 7, CP
First, in step 401, the U21 determines whether or not a predetermined time (3 seconds in the present embodiment) has elapsed since the last time the density update width α was determined, and if 3 seconds has not elapsed, the routine ends as it is. . If 3 seconds have elapsed, the CPU 21 proceeds to step 402 and the evaporative emission concentration FLPRG _i at that time.
(The subscript i indicates that it is the current value). Then, in the subsequent step 403, the CPU 21 calculates the amount of change in the evaporation concentration FLPRG per unit time (hereinafter referred to as the change rate β) from the current evaporation concentration FLPRG _i and the previous evaporation concentration FLPRG _i-1 ( β = | F
LPRG _i- FLPRG _i-1 | / 3 sec).

After that, the CPU 21 executes steps 404-4.
At 08, the density update width α (%) corresponding to the value of the change rate β is obtained. Specifically, the CPU 21 determines β> 1.
It is determined whether or not 0%, and β> 0.
It is determined whether it is 2%. If β> 1.0%, the CPU 21 proceeds to step 406 and α = 0.0.
5%. If 0.2% <β ≤ 1.0%, CPU
In step 21, the flow advances to step 407 to set α = 0.03%. β
If ≦ 0.2%, the CPU 21 proceeds to step 408 and sets α = 0.01%. That is, the evaporation concentration FLPRG
The larger the change rate β of is, the larger the density update width α is set. If the density update width α is too large, it may cause an overshoot when the density value converges. Therefore, it is preferable to set the maximum value of the density update width α to a value at which overshoot does not occur.

Thereafter, the CPU 21 at step 409 sets the current evaporation concentration FLPRG _i to the previous evaporation concentration FL.
The data is stored in the RAM 26 as PRG _i-1 , and the routine ends.

Next, the air-fuel ratio feedback control routine of FIG. 8 will be described. This routine is executed by the CPU 21 by interrupting every 4 msec. In FIG. 8, the CPU 21 first determines in step 501 whether the above-mentioned feedback condition is satisfied. If the feedback condition is not satisfied, the CPU 21 proceeds to step 502 and returns the feedback correction coefficient FAF = 1.
Set to 0. When the feedback condition is satisfied, C
The PU 21 proceeds to step 503 to compare the oxygen sensor output with the predetermined determination level and delay time H, I (ms) respectively.
ec) to operate the air-fuel ratio flag XOXR. For example, if the output of the oxygen sensor 6 is on the rich side, XOXR =
If it is "1" and the lean side, XOXR = "0".

Next, the CPU 21 proceeds to step 504 to operate the value of the feedback correction coefficient FAF based on the air-fuel ratio flag XOXR. That is, the air-fuel ratio flag X
When the OXR changes from "0" to "1" or from "1" to "0", the value of the feedback correction coefficient FAF is skipped by a predetermined amount, and the air-fuel ratio flag XOXR continues to "1" or "0". At this time, integral control of the feedback correction coefficient FAF is performed. Then, the CPU 21 proceeds to the next step 505 to check the upper and lower limits of the value of the feedback correction coefficient FAF, and thereafter ends this routine.

Next, the fuel injection control routine of FIG. 9 will be described. This routine is executed by the CPU 21 by interrupting every 4 msec. In FIG. 9, the CPU
21. In step 601, the basic injection time Tp corresponding to the engine speed NE and the intake pressure PM is calculated based on the data stored as a map in the ROM 25 in step 601. next,
In step 602, the CPU 21 corrects the correction coefficient related to the operating state of the engine 1 (cooling water temperature, increase after starting, intake air temperature, etc.)
, Feedback correction coefficient FAF, and learning correction value FL
A basic correction coefficient Fc corresponding to RN is calculated. Also, C
In the next step 603, the PU 21 calculates the purge correction coefficient FPRG by multiplying the evaporation concentration FLPRG calculated in the routine of FIG. 6 and the purge rate RPRG calculated in the routine of FIG. 5 (FPRG = FLPRG · RPR
G).

Thereafter, in step 604, the CPU 21 calculates the final injection time τ based on the basic injection time Tp, the basic correction coefficient Fc, the purge correction coefficient FPRG, and the invalid injection time Tv (τ = Tp · (Fc− FPRG) + T
v). Then, the CPU 21 carries out fuel injection by the injector 4 at a predetermined fuel injection timing based on the final injection time τ.

Next, the purge valve control routine of FIG. 10 will be described. This routine is 100ms by CPU21
It is executed by a time interrupt every ec. In FIG. 10, the CPU 21 determines in step 701 the purge execution flag X.
It is determined whether PRG is "1". And XP
If RG = “1”, the intake pressure PM is read in step 702, and the engine speed N is read in step 703.
Read E. Then, the CPU 21 continues to step 70.
4, the predetermined coefficient Ka, the engine speed NE, and the intake pressure P
The intake air amount GA is calculated by multiplying by M (GA = Ka
・ NE ・ PM).

After that, the CPU 21 proceeds to step 705 to calculate the purge flow rate GPRG by multiplying the intake air amount GA by the purge rate RPRG obtained by the routine of FIG. 5 (GPRG = GA.RPRG). Then, the CPU 21
Is based on the two parameters of the purge flow rate GPRG and the pressure difference between the atmospheric pressure PA and the intake pressure PM (hereinafter, this pressure difference is referred to as a gauge pressure) in step 706, using the duty ratio map of FIG. A duty ratio for driving 16 is obtained. When the value of each parameter takes an intermediate value of map values, the duty ratio is obtained by interpolation.

Thereafter, the CPU 21 proceeds to step 708 to
The purge valve 16 is driven at the above duty ratio. On the other hand, if XPRG = "0" in step 701,
The CPU 21 executes the process of step 708 after setting the duty ratio = 0 in step 707.

Next, the CP according to the above flow chart
The operation of U21 will be described with reference to the time charts of FIGS. In FIG. 12, time t1 is the timing when the air-fuel ratio feedback condition is first satisfied after the power is turned on, time t2 is the timing when the water temperature condition (THW> 80 ° C.) is satisfied, and time t2 to t3 and time From t4 to t5, the period during which the air-fuel ratio learning is performed by the routine of FIG. 4 is shown.

FIG. 12 will be described over time. First, when the air-fuel ratio feedback condition is satisfied at time t1, the feedback correction coefficient FAF is set to the reference value (= 1).
Begins to change. When the water temperature condition is satisfied at time t2, the air-fuel ratio learning is started and the feedback correction coefficient F
The AF changes to converge to the reference value (= 1). And
During the initial learning period of time t2 to t3, 12 times of skips are performed in a state where the feedback correction coefficient FAF (moderate value FAFAV) is stable within 2% of the reference value.

At time t3, the purge execution flag XP
RG is set to "1" and the purge valve 16 is opened at a predetermined duty ratio. Then, the adsorbed fuel in the canister 13 is purged, then the evaporation concentration FLPRG becomes thin (FLPRG ≦ 1%), and the purge duration time 1
Purge control is executed until 20 seconds have elapsed (time t
Period of 3 to t4).

At time t4, the air-fuel ratio learning is restarted and the feedback correction coefficient FAF (the smoothed value FAFA
V) is stable within 2% of the reference value, and the air-fuel ratio learning is carried out until the six skips are completed (periodic learning period from time t4 to t5). After that, the purge control and the regular learning are alternately repeated.

On the other hand, the time chart of FIG. 13 shows in detail how the evaporation concentration FLPRG changes. Figure 1
3, the concentration update width α = 0.01% at the time t11 when the evaporation concentration FLPRG started to change (same as time t3 in FIG. 12), and after time t11, the amount of change in the evaporation concentration FLPRG was changed. Thus, the density update width α is changed. In the figure, α = 0.03% at time t12, time t1
In 3, α = 0.05%. Then, at time t14 when the evaporation concentration FLPRG (estimated concentration value) reaches the actual concentration value, the concentration update width α returns to 0.01%. afterwards,
Since the change in the evaporation concentration FLPRG is relatively small, the density update width α is held at 0.01%, and when the density change occurs, the density update width α corresponding to the change amount is set.

Further, the smoothed value FAFAV of the feedback correction coefficient FAF temporarily shifts to the rich side after time t11, but converges to the reference value (= 1.0) as the evaporation concentration FLPRG reaches the actual value. There is.

As described above in detail, in the air-fuel ratio control system of this embodiment, the fuel injection amount by the injector 4 is calculated based on the feedback correction coefficient FAF, the learning correction value FLRN, and the purge correction coefficient FPRG (= FLPRG · RPRG). It was corrected (steps 602-604 in FIG. 9).
Further, the opening period of the purge valve 16 (purge execution flag XPR
In the period of G = “1”), if the air-fuel ratio is close to the rich side, the evaporation concentration FLPRG is increased by the concentration update width α, and if the air-fuel ratio is close to the lean side, the evaporation concentration FLPRG is increased.
Is reduced by the density update width α (steps 303 to 307 in FIG. 6). Further, the density update width α is set to a larger value as the rate of change β of the evaporation density FLPRG is larger (steps 404 to 40 of FIG. 7).
8).

That is, when the fuel injection amount is corrected according to the evaporation concentration FLPRG, if the evaporation concentration FLPRG (estimated concentration value) and the actual concentration value do not match, the correction of the fuel injection becomes insufficient and the air-fuel ratio Disturbance occurs. But,
In the above-described configuration, by appropriately increasing / decreasing the evaporation concentration FLPRG according to the rich / lean air-fuel ratio, it is possible to achieve both appropriate concentration estimation and precise air-fuel ratio control.

Further, in the above configuration, the evaporation concentration FLPRG
The rate of deviation β between the evaporation concentration FLPRG and the actual concentration value can be inferred from the rate β of change. By setting the concentration update width α in accordance with the rate of change β, the evaporative concentration FLPRG can quickly reach the actual concentration value even when the evaporative gas concentration suddenly changes, for example, at the time of engine start or fuel refueling. Evaporative concentration FLPRG
The estimation accuracy of is improved. At this time, even when the evaporative purge from the breakthrough state of the canister 13 (the state in which the adsorption of the evaporative gas is saturated) is performed, the evaporative concentration F is promptly and accurately determined.
The LPRG can be estimated. Further, by improving the accuracy of the evaporation concentration FLPRG, it is possible to quickly eliminate the temporary disturbance of the air-fuel ratio that occurs due to the sudden change in the evaporation gas.

Next, another embodiment in which a part of the above embodiment is modified will be described with reference to the flowchart of FIG. FIG. 14 is a routine corresponding to the density update width setting routine of FIG. In FIG. 14, the CPU 21
In step 801, it is determined whether or not a predetermined time (3 seconds in the present embodiment) has elapsed since the last time the density update width α was determined, and if 3 seconds have not elapsed, the routine ends. If 3 seconds have passed, the CPU 21 proceeds to step 8
In step 02, the smoothed value FAFAV _i of the feedback correction coefficient FAF at that time is fetched. And the CPU 21
Then, in step 803, the averaged value FAFAV _i and the previous averaged value FAFAV _i-1 are used to determine the averaged value FAF.
The change rate γ of AV is calculated (γ = | FAFAV _i −FA
FAV _i-1 | / 3 sec).

Thereafter, the CPU 21 executes steps 804-8.
At 08, the density update width α (%) corresponding to the value of the change rate γ is obtained. That is, if γ> 1.0%, the CPU 21 sets α = 0.05% in step 806. 0.2% <γ ≦
If 1.0%, the CPU 21 makes α = α in step 807.
It is set to 0.03%. If γ ≦ 0.2%, the CPU 21
Is set to α = 0.01% in step 808. That is, as the rate of change γ of the smoothed value FAFAV is larger, the CPU 21 considers that the degree of deviation between the evaporation concentration FLPRG (estimated concentration value) and the actual concentration value is larger, and sets the concentration update width α to a larger value. After that, the CPU 21 sets the current smoothed value FAFAV _i to the previous smoothed value FAFA in step 809.
It is stored in the RAM 26 as V _i−1 and the routine is finished.

That is, according to the routine of FIG. 14, similarly to the first embodiment, even when the evaporation concentration FLPRG suddenly changes at the time of engine start or fuel refueling, for example, the concentration update width according to the situation. α is set. As a result, the evaporation concentration FLPRG (estimated concentration value) can be quickly converged to the actual concentration value, the accuracy of the evaporation concentration FLPRG can be improved, and precise air-fuel ratio control can be realized.

The present invention is not limited to the above embodiments, but can be embodied in the following modes. In the routines of FIGS. 7 and 14 of each of the above-described embodiments, the change amounts of the evaporation concentration FLPRG and the smoothed value FAFAV are obtained at 3-second intervals, and then the change rates β, γ and the concentration update width α are calculated. However, if the interval for obtaining the change amount is shortened, the accuracy of the evaporation concentration FLPRG can be improved (the concentration update width α can be set for each change amount for each routine).

In each of the above embodiments, the evaporation concentration FLPR
G, the density update width α in three steps is set according to the change rates β, γ of the smoothed value FAFAV, but it is also possible to set the density update width α in four or more steps. Also, for example, the expression α
= Kb · β (Kb is a coefficient) can be used to set the density update width α steplessly. In this case, if the upper and lower limits are set for the density update width α, the occurrence of overshoot can be avoided.

[0066]

Effects of the Invention According to the invention described in the claims, together with an estimate of the concentration of fuel vapor (evaporative gas) always quickly and accurately, an excellent effect that it is possible to realize precise air-fuel ratio control Demonstrate.

[0067] According to the invention described in claims 1 and 2, the degree of deviation of the density value of the evaporated fuel can be easily identified, it is possible to perform quick and accurate concentration estimation.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an air-fuel ratio control device in an embodiment.

FIG. 2 is a diagram showing a characteristic of a purge air amount with respect to a duty ratio.

FIG. 3 is a map showing the upper limit of the purge rate when the purge valve is fully opened.

FIG. 4 is a flowchart showing an air-fuel ratio learning control routine executed by a CPU.

FIG. 5 is a flowchart showing a purge rate calculation routine executed by a CPU.

FIG. 6 is a flowchart showing an evaporation concentration calculation routine executed by a CPU.

FIG. 7 is a flowchart showing a density update width setting routine executed by a CPU.

FIG. 8 is a flowchart showing an air-fuel ratio feedback control routine executed by a CPU.

FIG. 9 is a flowchart showing a fuel injection control routine executed by a CPU.

FIG. 10 is a flowchart showing a purge valve control routine executed by a CPU.

FIG. 11 is a map for obtaining a duty ratio.

FIG. 12 is a time chart for explaining the operation of the embodiment.

FIG. 13 is a time chart for explaining the operation of the embodiment.

FIG. 14 is a flowchart showing a density update width setting routine in another embodiment.

FIG. 15 is a block diagram corresponding to a claim.

[Explanation of symbols]

1 ... Engine (multi-cylinder internal combustion engine), 4 ... Injector,
6 ... Oxygen sensor as air-fuel ratio sensor, 7 ... Fuel tank, 13 ... Canister, 15 ... Release passage, 16 ... Purge valve (variable flow solenoid valve) as open / close valve, 21 ... Valve control means, injection amount calculation means, Density estimation means, update width setting means,
C as an injection amount correction means, an injector control means, a concentration change rate calculation means, and a feedback correction coefficient calculation means
PU.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 5-288107 (JP, A) JP 5-33733 (JP, A) JP 2-248638 (JP, A) JP 5- 223021 (JP, A) JP-A-63-186955 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 41/00-41/40 F02D 45/00 F02M 25/08

Claims (3)

(57) [Claims] 1. A canister for adsorbing vaporized fuel generated in a fuel tank; an on-off valve for opening and closing to release vaporized fuel adsorbed by the canister to an intake system of an internal combustion engine through a release passage; Valve control means for opening and closing the on-off valve at a predetermined timing, an injector for injecting fuel into the internal combustion engine, and an injection amount calculation for calculating the fuel injection amount by the injector according to the operating state of the internal combustion engine. Means, an air-fuel ratio sensor for detecting the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine, and during the opening period of the on-off valve by the valve control means, if the air-fuel ratio by the air-fuel ratio sensor is close to evaporation Concentration estimating means for increasing the estimated concentration value of fuel by a predetermined update width, and decreasing the estimated concentration value of evaporated fuel by a predetermined update width if the air-fuel ratio is leaner. , The rate of change of the estimated concentration value of the evaporated fuel by the concentration estimating means
A density change rate calculation means for calculating the density change rate calculation means, an update width setting means for setting an update width of the density estimation means in accordance with the degree of deviation between the density value estimated by the density estimation means and the actual density value, Injection amount correction for correcting the fuel injection amount by the injection amount calculation means in accordance with the air-fuel ratio correction value based on the deviation between the air-fuel ratio by the fuel ratio sensor and the target air-fuel ratio, and the estimated concentration value of evaporated fuel by the concentration estimation means Means and injector control means for driving the injector based on the fuel injection amount corrected by the injection amount correction means , and the update width setting means is based on the concentration change rate calculation means.
An air-fuel ratio control device for an internal combustion engine , wherein the update width is increased as the rate of change of the concentration is increased . 2. Adsorption of vaporized fuel generated in a fuel tank
Canister and the vaporized fuel adsorbed on the canister.
Open to release the fuel to the intake system of the internal combustion engine through the discharge passage.
An on-off valve that closes and a valve control that opens the on-off valve at a predetermined timing
Control means, an injector for injecting and supplying fuel to the internal combustion engine, and the injector according to the operating state of the internal combustion engine.
And an air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine.
The difference between the fuel ratio sensor and the air-fuel ratio measured by the air-fuel ratio sensor and the target air-fuel ratio
Calculates the feedback correction coefficient to reduce
The feedback correction coefficient calculation means and the opening / closing valve opening period by the valve control means,
If the air-fuel ratio measured by the air-fuel ratio sensor is close to rich, evaporative combustion
The estimated concentration value of the fuel is increased by a specified update width to
Is lean, the estimated concentration value of evaporated fuel is
The density estimation means for reducing the new width and the estimated density value by the density estimation means and the actual density value
Set the update width of the density estimation means according to the degree of deviation
The update width setting means for adjusting the difference between the air-fuel ratio measured by the air-fuel ratio sensor and the target air-fuel ratio
Air-fuel ratio correction value based on evaporation and evaporation by the concentration estimating means
According to the estimated concentration value of fuel, the injection amount calculation means
An injection amount correction means for correcting the fuel injection amount, and based on the fuel injection amount corrected by the injection amount correction means
Injector control means for driving the injector
And the update width setting means sets the feedback correction coefficient
The larger the change rate, the larger the update width.
Air-fuel ratio control device for internal combustion engine. 3. Adsorption of vaporized fuel generated in a fuel tank
And the vaporized fuel adsorbed in the canister through the discharge passage.
Valve that opens and closes to be released to the intake system of the internal combustion engine
And a valve control for opening and closing the on-off valve at a predetermined timing.
Control means, an injector for injecting and supplying fuel to the internal combustion engine, and the injector according to the operating state of the internal combustion engine.
And an air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine.
During the opening period of the fuel ratio sensor and the on- off valve by the valve control means,
If the air-fuel ratio measured by the air-fuel ratio sensor is close to rich, evaporative combustion
The estimated concentration value of the fuel is increased by a specified update width to
Is lean, the estimated concentration value of evaporated fuel is
Depending on the density estimation means for reducing the new width and the rate of change of the density value estimated by the density estimation means,
Update width setting means for setting the update width of the density estimating means
And the difference between the air-fuel ratio measured by the air-fuel ratio sensor and the target air-fuel ratio
Air-fuel ratio correction value based on evaporation and evaporation by the concentration estimating means
According to the estimated concentration value of fuel, the injection amount calculation means
An injection amount correction means for correcting the fuel injection amount, and based on the fuel injection amount corrected by the injection amount correction means
Injector control means for driving the injector
An air-fuel ratio control device for an internal combustion engine, comprising: