JP3972922B2 - Evaporative fuel processing device for internal combustion engine - Google Patents

Description

  The present invention relates to an evaporated fuel processing apparatus for an internal combustion engine.

  An internal combustion engine having a canister for temporarily storing evaporated fuel generated in a fuel tank and a purge control valve for controlling a purge amount of fuel vapor purged from the canister into an intake passage is adsorbed by the canister The relationship between the evaporated fuel amount and the vapor concentration in the intake passage when the purge action is performed is stored in advance, and the initial vapor concentration immediately after the start of the purge is obtained from the deviation amount of the air-fuel ratio, and the initial vapor concentration is used to determine the above-mentioned value. The initial vaporized fuel adsorption amount of the canister is obtained using the previously stored relationship, and the decrease amount of the canister vaporized fuel adsorption amount per unit time is obtained from the initial vapor concentration, and then the canister vaporized fuel adsorption amount is reduced from the reduced canister vaporized fuel adsorption amount. The vapor concentration is predicted using the stored relationship, and the unit time per unit time is again calculated from the predicted vapor concentration. The amount of decrease in the amount of adsorbed fuel vapor is calculated, and then the vapor concentration is predicted again from the decreased amount of adsorbed fuel in the canister vapor using the previously stored relationship, and the air-fuel ratio is determined based on the predicted vapor concentration. An internal combustion engine in which the amount of supplied fuel is corrected so as to satisfy is known (see Patent Document 1).

  That is, the air-fuel ratio may fluctuate during transient operation although the vapor concentration does not change. However, if the vapor concentration is calculated on the basis of the deviation amount of the air-fuel ratio, it is determined that the vapor concentration has changed even in such a case, and when the vapor concentration is updated at this time, the air-fuel ratio fluctuates conversely. Become. Therefore, in the internal combustion engine described above, it is assumed that the amount of adsorbed canister fuel gradually decreases after the purge action is started. Based on this assumption, the vapor concentration is predicted to decrease over time. Then, the fluctuation of the air-fuel ratio is suppressed by correcting the fuel injection amount based on the predicted vapor concentration.

Japanese Patent Laid-Open No. 5-248312

  However, for example, if the purge is temporarily stopped when the fuel temperature is high, a large amount of evaporated fuel is adsorbed to the canister during this period, and thus the amount of canister evaporated fuel adsorbed increases. However, in the above-described internal combustion engine, even in such a case, the canister evaporative fuel adsorption amount is gradually decreased, and the predicted value of the vapor concentration is also gradually decreased. Therefore, when the purge is resumed, the predicted value of the vapor concentration is There arises a problem that the air / fuel ratio fluctuates greatly due to a large deviation from the actual vapor concentration.

  In order to solve the above problems, in the present invention, a purge passage of a fuel vapor that connects an upper space of a fuel tank and an intake passage, a purge control valve disposed in the purge passage, and an air-fuel ratio are detected. An air-fuel ratio detection unit; a first supply fuel amount correction unit that controls the supply fuel amount so that the air-fuel ratio becomes a target air-fuel ratio based on the air-fuel ratio detected by the air-fuel ratio detection unit; A vapor concentration calculating means for calculating the vapor concentration of the fuel vapor supplied into the intake passage from the deviation amount of the fuel ratio, and a second for correcting the supplied fuel amount so that the air-fuel ratio becomes the target air-fuel ratio based on the vapor concentration. In an evaporative fuel processing apparatus for an internal combustion engine having a supply fuel amount correcting means, the purge action is stopped in the fuel tank upper space or in the purge passage from the fuel tank upper space to the purge control valve. Concentration change detecting means for detecting a change in vapor concentration of the vapor, and the second supply fuel amount correcting means is a vapor concentration calculating means so that the air-fuel ratio immediately after the resumption of purging becomes the target air-fuel ratio according to the change in vapor concentration. When the vapor concentration calculated by the equation (1) is corrected and the vapor concentration of the fuel vapor in the purge passage extending from the fuel tank upper space to the purge control valve increases when the purge action is stopped, the vapor concentration The vapor concentration calculated by the calculation means is increased.

  Further, according to the present invention, the purge passage of the fuel vapor that connects the upper space of the fuel tank and the intake passage, the purge control valve disposed in the purge passage, and the air-fuel ratio detection means for detecting the air-fuel ratio. And a first supply fuel amount correction means for controlling the supply fuel amount so that the air-fuel ratio becomes the target air-fuel ratio based on the air-fuel ratio detected by the air-fuel ratio detection means, and a deviation amount of the air-fuel ratio with respect to the target air-fuel ratio A vapor concentration calculating means for calculating the vapor concentration of the fuel vapor supplied into the intake passage from the second, and a second supplied fuel amount correction for correcting the supplied fuel amount so that the air-fuel ratio becomes the target air-fuel ratio based on the vapor concentration An evaporative fuel processing apparatus for an internal combustion engine comprising: a fuel vapor in a state where the purge action is stopped in a fuel tank upper space or a purge passage extending from the fuel tank upper space to the purge control valve. Concentration change detecting means for detecting a change in concentration is provided, and the first supplied fuel amount correcting means is configured so that the air-fuel ratio becomes the target air-fuel ratio by a feedback correction coefficient that changes according to the air-fuel ratio detected by the air-fuel ratio detecting means. The first supply fuel amount correction means controls the value of the feedback correction coefficient at the restart of the purge so that the air-fuel ratio immediately after the restart of the purge becomes the target air-fuel ratio according to the change in the vapor concentration. When the vapor concentration of the fuel vapor in the upper space of the fuel tank or in the purge passage from the upper space of the fuel tank to the purge control valve increases when the purge action is stopped, the feedback correction coefficient value is determined in advance when purging is resumed. The amount of correction is reduced by the specified amount.

  It is possible to prevent the air-fuel ratio from changing when the purge action is temporarily stopped and then the purge action is resumed.

  Referring to FIG. 1, reference numeral 1 denotes an engine body, 2 denotes an intake branch pipe, 3 denotes an exhaust manifold, and 4 denotes a fuel injection valve attached to each intake branch pipe 2. Each intake branch pipe 2 is connected to a common surge tank 5, and this surge tank 5 is connected to an air cleaner 8 via an intake duct 6 and an air flow meter 7. A throttle valve 9 is disposed in the intake duct 6. As shown in FIG. 1, the internal combustion engine includes a canister 11 in which activated carbon 10 is built. The canister 11 has a fuel vapor chamber 12 and an atmospheric chamber 13 on both sides of the activated carbon 10. The fuel vapor chamber 12 is connected on the one hand to the upper space of the fuel tank 15 via a conduit 14 and on the other hand is connected to the surge tank 5 via a conduit 16. A purge control valve 17 controlled by the output signal of the electronic control unit 20 is disposed in the conduit 16. The fuel vapor generated in the fuel tank 15 is sent into the canister 11 through the conduit 14 and adsorbed by the activated carbon 10. When the purge control valve 17 is opened, air is sent from the atmospheric chamber 13 through the activated carbon 10 into the conduit 16. When the air passes through the activated carbon 10, the fuel vapor adsorbed on the activated carbon 10 is desorbed from the activated carbon 10, and thus the air containing the fuel vapor, that is, the fuel vapor passes through the conduit 16 in the surge tank 5. Purged.

  The electronic control unit 20 comprises a digital computer and is connected to each other by a bidirectional bus 21. A ROM (read only memory) 22, a RAM (random access memory) 23, a CPU (microprocessor) 24, an input port 25 and an output port. 26. The air flow meter 7 generates an output voltage proportional to the amount of intake air, and this output voltage is input to the input port 25 via the corresponding AD converter 27. A throttle switch 28 that is turned on when the throttle valve 9 is at the idling opening is attached to the throttle valve 9, and an output signal of the throttle switch 28 is input to the input port 25. A water temperature sensor 29 that generates an output voltage proportional to the engine cooling water temperature is attached to the engine body 1, and the output voltage of the water temperature sensor 29 is input to the input port 25 via the corresponding AD converter 27. An air-fuel ratio sensor 30 is attached to the exhaust manifold 3, and an output signal of the air-fuel ratio sensor 30 is input to the input port 25 via the corresponding AD converter 27.

  The fuel vapor chamber 12 is connected to a pressure sensor 32 via a conduit 31, and the pressure in the fuel vapor chamber 12 is detected by the pressure sensor 32. The pressure sensor 32 generates an output voltage proportional to the pressure in the fuel vapor chamber 12, that is, the pressure of the conduit 16 extending from the upper space of the fuel tank 15 or the upper space of the fuel tank 15 to the purge control valve 17. Is input to the input port 25 via the corresponding AD converter 27. Further, the input port 25 is connected with a crank angle sensor 33 that generates an output pulse every time the crankshaft rotates, for example, 30 degrees. The CPU 24 calculates the engine speed based on this output pulse. On the other hand, the output port 26 is connected to the fuel injection valve 4 and the purge control valve 17 through corresponding drive circuits 34.

In the internal combustion engine shown in FIG. 1, the fuel injection time TAU is basically calculated based on the following equation.
TAU = TP / FW / (FAF + KGj-FPG)
Here, each coefficient represents the following.
TP: Basic fuel injection time FW: Correction coefficient FAF: Feedback correction coefficient KGj: Air-fuel ratio learning coefficient FPG: Purge air-fuel ratio correction coefficient (hereinafter referred to as purge A / F correction coefficient)
The basic fuel injection time TP is an injection time obtained by an experiment necessary for setting the air-fuel ratio to the target air-fuel ratio, and this basic fuel injection time TP is the engine load Q / N (intake air amount Q / engine speed N ) And a function of the engine speed N is stored in the ROM 22 in advance.

The correction coefficient FW is a summary of the warm-up increase coefficient and the acceleration increase coefficient, and FW = 1.0 when there is no need for an increase correction.
The feedback correction coefficient FAF is provided to control the air / fuel ratio to the target air / fuel ratio based on the output signal of the air / fuel ratio sensor 30.
The purge A / F correction coefficient FPG is set to FPG = 0 from the start of engine operation to the start of purge, and increases as the fuel vapor concentration increases when the purge action is started. When the purge action is temporarily stopped during engine operation, FPG = 0 is set during the purge action stop period.

As described above, the feedback correction coefficient FAF is used to control the air / fuel ratio to the target air / fuel ratio based on the output signal of the air / fuel ratio sensor 30. In this case, any air-fuel ratio may be used as the target air-fuel ratio. However, in the embodiment shown in FIG. 1, the target air-fuel ratio is the stoichiometric air-fuel ratio. Will be described. When the target air-fuel ratio is the stoichiometric air-fuel ratio, a sensor whose output voltage changes according to the oxygen concentration in the exhaust gas is used as the air-fuel ratio sensor 30. Therefore, the air-fuel ratio sensor 30 is hereinafter referred to as an O ₂ sensor. The O ₂ sensor 30 generates an output voltage of about 0.9 (V) when the air-fuel ratio is rich, that is, when it is rich, and 0.1 (V) when the air-fuel ratio is lean, that is, when it is lean. ) Generate about the output voltage.

FIG. 2 shows the relationship between the output voltage V of the O ₂ sensor 30 and the feedback correction coefficient FAF when the air-fuel ratio is maintained at the target air-fuel ratio. As shown in FIG. 2, when the output voltage V of the O ₂ sensor 30 becomes higher than a reference voltage, for example, 0.45 (V), that is, when the air-fuel ratio becomes rich, the feedback correction coefficient FAF rapidly decreases by the skip amount S. And then gradually reduced by an integral constant K. On the other hand, when the output voltage V of the O ₂ sensor 30 becomes lower than the reference voltage, that is, when the air-fuel ratio becomes lean, the feedback correction coefficient FAF is rapidly increased by the skip amount S, and then gradually with the integration constant K. Increased.

  That is, when the air-fuel ratio becomes rich, the feedback correction coefficient FAF is decreased, so that the fuel injection amount is decreased. When the air-fuel ratio becomes lean, the feedback correction coefficient FAF is increased, so that the fuel injection amount is increased. Thus, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio. As shown in FIG. 2, at this time, the feedback correction coefficient FAF moves up and down around the reference value, that is, 1.0.

  In FIG. 2, FAFL indicates the value of the feedback correction coefficient FAF when the air-fuel ratio becomes rich from lean, and FAFR indicates the value of the feedback correction coefficient FAF when the air-fuel ratio changes from rich to lean. ing. In the embodiment according to the present invention, an average value of these FAFL and FAFR is used as a fluctuation average value of feedback correction coefficient FAF (hereinafter simply referred to as an average value).

  FIG. 3 shows an outline of the purge action. In FIG. 3, PGR indicates the fuel vapor purge rate. As shown in FIG. 3, in the embodiment according to the present invention, the purge rate PGR is gradually increased from zero when the purge action is started for the first time after the engine is started, and the purge rate PGR is set to a constant value, for example, 6%. After reaching, the purge rate PGR is maintained at the target purge rate.

Next, for example, when the fuel supply is stopped during the deceleration operation, the purge rate PGR is temporarily made zero as indicated by X. Next, the purge action is restarted with the purge rate PGR immediately before the purge action is stopped.
Next, a fuel vapor concentration learning method will be described with reference to FIG.
The learning of the fuel vapor concentration starts from accurately obtaining the vapor concentration per unit purge rate. The vapor concentration per unit purge rate is indicated by FGPG in FIG. The purge A / F correction coefficient FPG is obtained by multiplying FGPG by the purge rate PGR.

The vapor concentration FGPG per unit purge rate is calculated based on the following equation every time the feedback correction coefficient FAF is skipped (S in FIG. 2).
tFG = (1-FAFAV) / (PGR · a)
FGPG = FGPG + tFG
Here, tFG indicates the update amount of FGPG performed every time FAF is skipped, FAFAV indicates the average value of the feedback correction coefficient (= (FAFL + FAFR) / 2), and a is 2 in the embodiment according to the present invention. Is set to

That is, since the air-fuel ratio becomes rich when the purge is started, the feedback correction coefficient FAF becomes small so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Next, when it is determined at time t ₁ that the air-fuel ratio has been switched from rich to lean by the O ₂ sensor 31, the feedback correction coefficient FAF is increased. In this case, the change amount ΔFAF of the feedback correction coefficient FAF from the start of the purge to the time t ₁ (ΔFAF = (1.0−FAF)) represents the variation amount of the air-fuel ratio due to the purge action. The fluctuation amount ΔFAF represents the fuel vapor concentration at time t ₁ .

When the time t ₁ is reached, the air-fuel ratio is maintained at the stoichiometric air-fuel ratio, and then the vapor concentration per unit purge rate is set to return the average value FAFAV of the feedback correction coefficient to 1.0 so that the air-fuel ratio does not deviate from the stoichiometric air-fuel ratio. The FGPG is gradually updated every time the feedback correction coefficient FAF is skipped. The update amount tFG per FGPG at this time is half of the deviation amount of the average value FAFAV of the feedback correction coefficient with respect to 1.0. Therefore, the update amount tFG is tFG = (1−FAFAV) / ( PGR · 2).

  As shown in FIG. 4, when the update operation of FGPG is repeated several times, the average value FAFAV of the feedback correction coefficient returns to 1.0, and thereafter the vapor concentration FGPG per unit purge rate becomes constant. The fact that FGPG becomes constant in this way means that the FGPG at this time accurately represents the vapor concentration per unit purge rate, and thus means that learning of the vapor concentration has been completed. . On the other hand, the actual fuel vapor concentration is a value obtained by multiplying the vapor concentration FGPG per unit purge rate by the purge rate PGR. Therefore, the purge A / F correction coefficient FPG (= FGPG · PGR) representing the actual fuel vapor concentration is updated each time FGPG is updated as shown in FIG. 4, and increases as the purge rate PGR increases.

Even after learning of the vapor concentration after the start of purge is completed, if the vapor concentration changes, the feedback correction coefficient FAF deviates from 1.0, and at this time also the above-described tFG (= (1-FAFAV) / (PGR · The update amount of FGPG is calculated using a)).
Next, the purge control routine will be described with reference to FIGS. This routine is executed by interruption every predetermined time.

  5 and 6, first, at step 50, it is judged if it is time to calculate the duty ratio of the drive pulse of the purge control valve 17. In the embodiment according to the present invention, the duty ratio is calculated every 100 msec. If it is not time to calculate the duty ratio, the routine jumps to step 63 where the purge control valve 17 is driven. On the other hand, when it is time to calculate the duty ratio, the routine proceeds to step 51 where it is determined whether or not the purge condition 1 is satisfied, for example, whether or not the warm-up is completed. When the purge condition 1 is not satisfied, the routine proceeds to step 64 where initialization processing is performed, then at step 65, the duty ratio DPG and the purge rate PGR are made zero. On the other hand, when the purge condition 1 is satisfied, the routine proceeds to step 52, where it is determined whether the purge condition 2 is satisfied, for example, whether the air-fuel ratio feedback control is being performed, and the fuel supply is stopped. It is determined whether or not there is any. When the purge condition 2 is not satisfied, the process proceeds to step 65, and when the purge condition 2 is satisfied, the process proceeds to step 53.

  In step 53, a fully open purge rate PG100 (= (PGQ / QA) · 100), which is a ratio between the fully opened purge amount PGQ and the intake air amount QA, is calculated. Here, the fully open purge amount PGQ represents the purge amount when the purge control valve 17 is fully opened. The fully open purge rate PG100 is a function of, for example, the engine load Q / N (intake air amount QA / engine speed N) and the engine speed N, and is obtained in advance by experiments, and is in the form of a map as shown in the table below. It is stored in the ROM 22 in advance.

  As the engine load Q / N decreases, the fully open purge amount PGQ with respect to the intake air amount QA increases. Therefore, as shown in Table 1, the fully open purge rate PG100 increases as the engine load Q / N decreases, and the engine speed N increases. Since the fully open purge amount PGQ with respect to the intake air amount QA increases as the value decreases, the fully open purge rate PG100 increases as the engine speed N decreases as shown in Table 1.

  Next, at step 54, it is judged if the feedback correction coefficient FAF is between the upper limit value KFAF15 (= 1.15) and the lower limit value KFAF85 (= 0.85). When KFAF15> FAF> KFAF85, that is, when the air-fuel ratio is feedback controlled to the stoichiometric air-fuel ratio, the routine proceeds to step 55, where it is judged if the purge rate PGR is zero or not. Since PGR> 0 when the purge action has already been performed, the routine jumps to step 57 at this time. On the other hand, when the purge action has not been started yet, the routine proceeds to step 56, where the purge rate PGR is made the restart purge rate PGR. When the purge condition 1 and the purge condition 2 are satisfied for the first time after the operation of the engine is started, the purge rate PGRO is set to zero by the initialization process (step 64), so at this time, PGR = 0. On the other hand, when the purge action is once stopped and then purge control is resumed, the purge rate PGR0 immediately before the purge control is stopped is set to the restart purge rate PGR.

  Next, at step 57, the target purge rate tPGR (= PGR + KPGRu) is calculated by adding a constant value KPGRu to the purge rate PGR. That is, it can be seen that when KFAF15> FAF> KFAF85, the target purge rate tPGR is gradually increased every 100 msec. Note that an upper limit value P (P is, for example, 6%) is set for the target purge rate tPGR, and therefore the target purge rate tPGR can only rise to the upper limit value P. Next, the routine proceeds to step 59.

  On the other hand, when it is judged at step 54 that FAF ≧ KFAF15 or FAF ≦ KFAF85, the routine proceeds to step 58 where the target purge rate tPGR (= PGR−KGRDd) is obtained by subtracting a constant value KPGRd from the purge rate PGR. Calculated. That is, the target purge rate tPGR is reduced when the air-fuel ratio cannot be maintained at the stoichiometric air-fuel ratio due to the purge action of the fuel vapor. A lower limit value S (S = 0%) is set for the target purge rate tPGR. Next, the routine proceeds to step 59.

  In step 59, the duty ratio DPG (= (tPGR / PG100) · 100) of the drive pulse of the purge control valve 17 is calculated by dividing the target purge rate tPGR by the fully opened purge rate PG100. Therefore, the duty ratio DPG of the drive pulse of the purge control valve 17, that is, the valve opening amount of the purge control valve 17 is controlled according to the ratio of the target purge rate tPGR with respect to the fully open purge rate PG 100. As described above, when the valve opening amount of the purge control valve 17 is controlled in accordance with the ratio of the target purge rate tPGR to the fully opened purge rate PG100, the target purge rate tPGR is whatever the purge rate, regardless of the operating state of the engine. The actual purge rate is maintained at the target purge rate.

  For example, if the target purge rate tPGR is 2% and the fully open purge rate PG100 in the current operating state is 10%, the duty ratio DPG of the drive pulse is 20%, and the actual purge rate at this time is 2% It becomes. Next, if the operating state changes and the fully opened purge rate PG100 in the changed operating state becomes 5%, the duty ratio DPG of the driving pulse becomes 40%, and the actual purge rate at this time becomes 2%. That is, if the target purge rate tPGR is 2%, the actual purge rate is 2% regardless of the engine operating state, and if the target purge rate tPGR changes to 4%, regardless of the engine operating state. The actual purge rate is maintained at 4%.

  Next, at step 60, the actual purge rate PGR (= PG100 · (DPG / 100)) is calculated by multiplying the fully open purge rate PG100 by the duty ratio DPG. That is, as described above, the duty ratio DPG is represented by (tPGR / PG100) · 100. In this case, when the target purge rate tPGR is larger than the full open purge rate PG100, the duty ratio DPG becomes 100% or more. However, the duty ratio DPG cannot exceed 100%. At this time, the duty ratio DPG is set to 100%. Therefore, the actual purge rate PGR is smaller than the target purge rate tPGR. Therefore, the actual purge rate PGR is represented by PG100 · (DPG / 100) as described above.

  Next, at step 61, the duty ratio DPG is set to DPGO, and the purge rate PGR is set to PGRO. Next, at step 62, a purge execution time counter CPGR indicating the time since the purge was started is incremented by one. Next, at step 63, the purge control valve 17 is driven. This driving process is shown in FIG. 7, so the driving process shown in FIG. 7 will be described next.

  Referring to FIG. 7, first, at step 66, it is judged if it is the duty cycle output cycle, that is, if it is the rise cycle of the purge control valve 17 drive pulse. The output cycle of this duty ratio is 100 msec. When it is the duty cycle output cycle, the routine proceeds to step 67, where it is judged if the duty cycle DPG is zero or not. When DPG = 0, the routine proceeds to step 71 where the drive pulse YEVP of the purge control valve 17 is turned off. On the other hand, when DPG is not 0, the routine proceeds to step 68 where the drive pulse YEVP of the purge control valve 17 is turned on. Next, at step 69, the drive pulse OFF time TDPG (= DPG + TIMER) is calculated by adding the duty ratio DPG to the current time TIMER.

On the other hand, when it is determined in step 66 that the duty cycle is not the output cycle, the routine proceeds to step 70, where it is determined whether or not the current time TIMER is the drive pulse OFF time TDPG. When TDPG = TIMER, the routine proceeds to step 71 where the drive pulse YEVP is turned off.
Next, a routine for calculating the feedback correction coefficient FAF shown in FIG. 8 will be described. This routine is executed by interruption every predetermined time, for example.

  Referring to FIG. 8, first, at step 100, it is judged if the air-fuel ratio feedback control condition is satisfied. When the feedback control condition is not satisfied, the routine proceeds to step 113, where the feedback correction coefficient FAF is fixed at 1.0, and then at step 114, the average value FAFAV of the feedback correction coefficient is fixed at 1.0. Next, the routine proceeds to step 112. In contrast, when the feedback control condition is satisfied, the routine proceeds to step 101.

In step 101, it is determined whether or not the output voltage V of the O ₂ sensor 31 is higher than 0.45 (V), that is, whether or not it is rich. When V ≧ 0.45 (V), that is, when rich, the routine proceeds to step 102 where it is determined whether or not it was lean at the previous processing cycle. When the previous processing cycle is lean, that is, when the lean has changed to rich, the routine proceeds to step 103 where the feedback correction coefficient FAF is made FAFL, and the routine proceeds to step 104. In step 104, the skip value S is subtracted from the feedback correction coefficient FAF. Therefore, the feedback correction coefficient FAF is rapidly decreased by the skip value S as shown in FIG. Next, at step 105, the average value FAFAV of FAFL and FAFR is calculated. Next, at step 106, a skip flag is set. Next, the routine proceeds to step 112. On the other hand, if it is determined in step 102 that the previous processing cycle was rich, the process proceeds to step 107, where the integral value K (K << S) is subtracted from the feedback correction coefficient FAF, and then the process proceeds to 112. Therefore, as shown in FIG. 2, the feedback correction coefficient FAF is gradually decreased.

  On the other hand, when it is determined at step 101 that V <0.45 (V), that is, when the engine is lean, the routine proceeds to step 108 where it is determined whether or not the previous processing cycle was rich. When rich in the previous processing cycle, that is, when the rich has changed to lean, the routine proceeds to step 109 where the feedback correction coefficient FAF is made FAFR, and the routine proceeds to step 110. In step 110, the skip value S is added to the feedback correction coefficient FAF. Therefore, the feedback correction coefficient FAF is rapidly increased by the skip value S as shown in FIG. Next, at step 105, the average value FAFAV of FAFL and FAFR is calculated. On the other hand, if it is determined in step 108 that the current processing cycle was lean, the process proceeds to step 111 where the integral value K is added to the feedback correction coefficient FAF. Therefore, as shown in FIG. 2, the feedback correction coefficient FAF is gradually increased.

  In step 112, the feedback correction coefficient FAF is guarded by the upper limit 1.2 and the lower limit 0.8 of the allowable fluctuation range. That is, the FAF value is guarded so that the FAF does not become larger than 1.2 and does not become smaller than 0.8. As described above, when the air-fuel ratio becomes rich and the FAF becomes small, the fuel injection time TAU becomes short. When the air-fuel ratio becomes lean and the FAF becomes large, the fuel injection time TAU becomes long, so the air-fuel ratio becomes the stoichiometric air-fuel ratio. Will be maintained.

When the routine for calculating the feedback correction coefficient FAF shown in FIG. 8 is completed, the routine proceeds to the air-fuel ratio learning routine shown in FIG.
Referring to FIG. 9, first, at step 120, it is judged if the air-fuel ratio learning condition is satisfied. When the air-fuel ratio learning condition is not satisfied, the routine jumps to step 128, and when the air-fuel ratio learning condition is satisfied, the routine proceeds to step 121. In step 121, it is determined whether or not the skip flag is set. If the skip flag is not set, the process jumps to step 128. On the other hand, when the skip flag is set, the routine proceeds to step 122, where the skip flag is reset, and then proceeds to step 123. That is, the process proceeds to step 123 every time the feedback correction coefficient FAF is skipped.

  In step 123, it is determined whether or not the purge rate PGR is zero, that is, whether or not the purge action is being performed. When the purge rate PGR is not zero, that is, when the purge action is being performed, the routine proceeds to a vapor concentration learning routine shown in FIG. On the other hand, when the purge rate PGR is zero, that is, when the purge action is not performed, the routine proceeds to step 124 where the air-fuel ratio is learned.

  That is, first, at step 124, it is judged if the average value FAFAV of the feedback correction coefficient is larger than 1.02. When FAFAV ≧ 1.02, the routine proceeds to step 127, where the constant value X is added to the learning value KGj of the air-fuel ratio for the learning region j. That is, in the embodiment according to the present invention, a plurality of learning regions j are predetermined according to the engine load, and an air-fuel ratio learning value KGj is provided for each learning region j. Accordingly, at step 127, the learning value KGj of the air-fuel ratio in the learning region j corresponding to the engine load is updated. Next, the routine proceeds to step 128.

  On the other hand, when it is determined in step 124 that FAFAV <1.02, the routine proceeds to step 125, where it is determined whether or not the average value FAFAV of the feedback correction coefficient is smaller than 0.98. When FAFAV ≦ 0.98, the routine proceeds to step 126, where the constant value X is subtracted from the learning value KGj of the air-fuel ratio in the learning region j corresponding to the engine load. On the other hand, when it is determined in step 125 that FAFAV> 0.98, that is, when FAFAV is between 0.98 and 1.02, the routine jumps to step 128 without updating the learning value KGj of the air-fuel ratio. .

  In steps 128 and 129, an initialization process for learning the vapor concentration is performed. That is, at step 128, it is determined whether or not the engine is being started. When the engine is being started, the routine proceeds to step 129, where the vapor concentration FGPG per unit purge rate is made zero, and the purge execution time count value CPGR is cleared. . Next, the routine proceeds to the fuel injection time calculation routine shown in FIG. On the other hand, if it is not at the start, the routine directly proceeds to the fuel injection time calculation routine shown in FIG.

As described above, when it is determined in step 123 that the purge action is being performed, the routine proceeds to a vapor concentration learning routine shown in FIG. Next, the vapor concentration learning routine will be described.
Referring to FIG. 10, first, at step 130, it is determined whether or not the average value FAFAV of the feedback correction coefficient is within a certain range, that is, whether or not 1.02>FAFAV> 0.98. When the average value FAFAV of the feedback correction coefficient is within the set range, that is, when 1.02>FAFAV> 0.98, the routine proceeds to step 132, where the update amount tFG of the purge concentration FGPG per unit purge rate is made zero, Next, the routine proceeds to step 133. Therefore, at this time, the vapor concentration FGPG is not updated.

On the other hand, when it is determined in step 130 that the average value FAFAV of the feedback correction coefficient exceeds a certain range, that is, when FAFAV ≧ 1.02 or FAFAV ≦ 0.98, the routine proceeds to step 131, where Based on this, the update amount tFG of the vapor concentration FGPG is calculated.
tFG = (1.0−FAFAV) / PGR · a
Here, a is 2. That is, when the average value FAFAV of the feedback correction coefficient exceeds the set range (between 0.98 and 1.02), half of the FAFAV deviation with respect to 1.0 is set as the update amount tFG. Next, the routine proceeds to step 133. In step 133, the update amount tFG is added to the vapor concentration FGPG. Next, at step 134, an update number counter CFGPG indicating the number of updates of the vapor concentration FGPG is incremented by one. Next, the routine proceeds to the fuel injection time calculation routine shown in FIG.

Next, the fuel injection time calculation routine shown in FIG. 11 will be described.
Referring to FIG. 11, first, at step 140, the basic fuel injection time TP is calculated based on the engine load Q / N and the engine speed N. Next, at step 141, a correction coefficient FW for increasing the warm-up amount is calculated. Next, at step 142, the purge A / F correction coefficient FGR (= FGPG · PGR) is calculated by multiplying the vapor concentration FGPG per unit purge rate by the purge rate PGR. Next, at step 143, the fuel injection time TAU is calculated based on the following equation.

TAU = TP / FW / (FAF + KGj-FPG)
As described above, in the embodiment according to the present invention, the purge action is temporarily stopped during the purge action, and when the purge action is resumed, the purge action is resumed at the purge rate immediately before the purge action is stopped. Is done. In this case, if the vapor concentration in the intake passage immediately before the purge action is stopped is substantially the same as the vapor concentration in the intake passage when the purge is resumed, the air-fuel ratio does not fluctuate when the purge is resumed. The fuel ratio is immediately maintained at the target air / fuel ratio.

  However, if the purge action is stopped when the fuel temperature in the fuel tank 15 is high, for example, a large amount of evaporated fuel is generated in the fuel tank 15 while the purge action is stopped. Is adsorbed by the activated carbon 10 of the canister 11. In this way, when a large amount of evaporated fuel is generated in the fuel tank 15 and a large amount of evaporated fuel is adsorbed on the activated carbon 10 of the canister 11, the purge action is resumed. The concentration is considerably higher than the vapor concentration in the intake passage immediately before the purge is stopped. In this case, if the fuel supply amount is corrected on the assumption that the vapor concentration at the restart of purge is the same as the vapor concentration immediately before the purge is stopped, the air-fuel ratio becomes extremely rich.

  Therefore, in the present invention, when the purge action is stopped, the vapor concentration of the fuel vapor in the upper space of the fuel tank 15 or the purge passage from the upper space of the fuel tank 15 to the purge control valve 17 is detected, and the purge action is performed. When the vapor concentration increases while the engine is stopped, the correction value based on the vapor concentration used when calculating the fuel injection time TAU, specifically, the vapor concentration FGPG per unit purge rate is increased.

Next, a specific description will be given with reference to FIGS. In the embodiment shown in FIGS. 12 and 13, the vapor concentration FGPG is controlled based on the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32.
In FIG. 12, it is assumed that the purge action is stopped at t _{1 and the} purge action is resumed at t ₂ . Before the purge action is stopped, the pressure PT in the fuel vapor chamber 12 is negative as shown in FIG. When the fuel temperature in the fuel tank 15 is low, the amount of evaporated fuel is small, and when the purge action is stopped at this time, the pressure PT in the fuel vapor chamber 12 rises to almost atmospheric pressure as shown by the broken line in FIG. . In this case, as indicated by a broken line in FIG. 12, the value of the vapor concentration FGPG is maintained as it is without being updated.

  On the other hand, if the purge action is stopped when the fuel temperature in the fuel tank 15 is high, a large amount of evaporated fuel continues to be generated in the fuel tank 15 while the purge action is stopped. As shown by a solid line in FIG. Therefore, in the first embodiment shown in FIG. 12, when the pressure PT in the fuel vapor chamber 12 exceeds a predetermined set value KPT, the vapor concentration FGPG is gradually increased as indicated by the solid line, and the purge action is started. Sometimes, the fuel injection time TAU is corrected using the increased vapor concentration FGPG. By doing so, it is possible to prevent the air-fuel ratio from fluctuating when the purge is resumed.

FIG. 13 shows a routine for controlling the vapor concentration, and this routine is executed by interruption every predetermined time, for example, every 100 msec.
Referring to FIG. 13, first, at step 200, whether or not the purge execution time count value CPGR has exceeded a certain value K3, for example, whether or not 3 minutes have passed since the purge was first started after the engine operation was started. It is determined whether or not. When CPGR ≦ K3, the processing routine is completed. Therefore, at this time, the vapor concentration FGPG is not updated. That is, when the purge is started for the first time, the vapor concentration FGPG has not yet been learned. At this time, there is no point in updating the vapor concentration FGPG based on the pressure PT in the fuel vapor chamber 12, so at this time the vapor concentration FGPG is not used. The updating operation of the density FGPG is prohibited. On the other hand, it is considered that the learning of the vapor concentration FGPG has been completed if 3 minutes have passed since the purge was first started, and therefore the vapor concentration FGPG is updated.

  That is, when it is determined in step 200 that CPGR> K3, the routine proceeds to step 201, where it is determined whether or not the purge rate PGR is zero. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 202, where it is determined whether or not the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32 is higher than the set value KPT (FIG. 12). Determined. When PT> KPT, the routine proceeds to step 203 where the constant value ΔK is added to the vapor concentration FGPG. Therefore, at this time, the vapor concentration FGPG is gradually increased as shown in FIG.

  14 and 15 show a second embodiment. In this embodiment, the vaporized fuel amount PV per unit time in the fuel tank 15 is obtained from the pressure PT in the fuel vapor chamber 12, the cumulative value of the vaporized fuel amount PV is obtained, and this cumulative value is a predetermined set value. When KD is exceeded, the vapor concentration FGPG is gradually increased. In this case, the relationship between the pressure PT in the fuel vapor chamber 12 and the evaporated fuel amount PV per unit time is obtained in advance by experiments, and this relationship is shown in FIG.

FIG. 15 shows a routine for controlling the vapor concentration in the second embodiment. This routine is executed by interruption every predetermined time, for example, every 100 msec.
Referring to FIG. 15, first, at step 300, it is determined whether or not the update count value CFGPG is larger than a predetermined set value K20, for example, 20. When CFGPG ≦ K20, the processing cycle is completed. On the other hand, if CFGPG> K20, that is, if the number of updates of the vapor concentration FGPG is approximately 20 or more, it is determined that the learning of the vapor concentration FGPG has been completed.

  In step 301, it is determined whether or not the purge rate PGR is zero. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 302 where the evaporated fuel amount PV per unit time is calculated from the relationship shown in FIG. 14 based on the pressure PT in the fuel vapor chamber 12. Next, at step 303, the cumulative value ΣPV (= ΣPV + PV) of the evaporated fuel amount PV is calculated. Next, at step 304, it is determined whether or not the cumulative value ΣPV has become larger than a predetermined set value KD. When ΣPV ≧ KD, the routine proceeds to step 305, where the constant value ΔK is added to the vapor concentration FGPG. Accordingly, the vapor concentration FGPG is gradually increased while ΣPV ≧ KD. On the other hand, when it is judged at step 301 that the purge rate PGR> 0, the routine proceeds to step 306, where the cumulative value ΣPV is made zero.

  16 and 17 show a third embodiment. In this embodiment, the relationship between the evaporated fuel amount TV in the fuel tank 15 and the vapor concentration FGPG is obtained in advance by experiments, and the vapor concentration FGPG is obtained based on this relationship. FIG. 16 shows the relationship between the evaporated fuel amount TV in the fuel tank 15 and the vapor concentration FGPG.

  FIG. 17 shows a vapor concentration control routine for executing the third embodiment. This routine is executed by interruption every predetermined time, for example, every 100 msec. Referring to FIG. 17, first, at step 400, whether or not the purge time execution count value CPGR is larger than the set value K3, that is, whether or not 3 minutes have passed since the purge operation was started after the engine operation was started. It is determined whether or not. When CPGR ≦ K3, the processing cycle is completed. On the other hand, when CPGR> K3, the routine proceeds to step 401, where it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 402, where it is judged if the evaporated fuel amount TV1 in the fuel tank 15 immediately after the purge action is stopped is calculated. Since the evaporated fuel amount TV1 is not yet calculated immediately after the purge action is stopped, the process proceeds to step 403 at this time, and the evaporated fuel amount TV1 is calculated from the vapor concentration FGPG at that time using the relationship shown in FIG.

Next, at step 404, the evaporated fuel amount PV per unit time is calculated from the pressure PT in the fuel vapor chamber 12 using the relationship shown in FIG. 14, and then at step 405, the accumulated value ΣPV (= ΣPV + PV) of the evaporated fuel amount is calculated. Is done. In the next processing cycle, the process jumps from step 402 to step 404.
On the other hand, when it is determined in step 401 that PGR> 0, that is, when the purge action is started, the routine proceeds to step 406, where it is determined whether or not the accumulated value ΣPV of the evaporated fuel amount is larger than the set value KD. . Note that ΣPV at this time represents the amount of fuel evaporated during the period when the purge action is stopped. When ΣPV <KD, the routine jumps to step 408, where ΣPV is made zero. On the other hand, when ΣPV ≧ KD, the routine proceeds to step 407, where ΣPV is added to the evaporated fuel amount TV1 immediately after the purge stop to calculate the evaporated fuel amount PV2 in the fuel tank 15 at the time of restarting the purge (FIG. 16). The vapor concentration FGPG at the time of restarting the purge is calculated from PV2 using the relationship shown in FIG.

18 and 19 show a fourth embodiment. In this embodiment, the vapor concentration FGPG when purging is resumed is calculated based on the fuel temperature in the fuel tank 15. In this embodiment, a temperature sensor 35 for detecting the fuel temperature is attached to the fuel tank 15 as shown in FIG.
FIG. 19 shows a vapor concentration control routine for executing the fourth embodiment, and this routine is executed by interruption every predetermined time, for example, every 100 msec.

  Referring to FIG. 19, first, at step 500, whether or not the purge time execution count value CPGR is larger than the set value K3, that is, whether or not 3 minutes have passed since the purge operation was started after the engine operation was started. It is determined whether or not. When CPGR ≦ K3, the processing cycle is completed. On the other hand, when CPGR> K3, the routine proceeds to step 501, where it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 502, where the purge stop period count value COFF indicating the purge stop period is incremented by one.

  Next, at step 503, it is judged if the fuel temperature TEMP in the fuel tank 15 detected by the temperature sensor 35 is higher than a temperature K45 for generating a large amount of evaporated fuel, for example, 45 ° C. When TEMP> K45, the routine proceeds to step 504, where it is judged if the purge stop period count value COFF is larger than a certain value KC. When COFF> KC, the routine proceeds to step 505, where the constant value ΔK is added to the vapor concentration FGPG. That is, in this embodiment, when the purge stop period is short (COFF ≦ KC), the updating operation of the vapor concentration FGPG is prohibited. On the other hand, when the fuel temperature in the fuel tank 15 is 45 ° C. or higher and the purge stop period is relatively long, the vapor concentration FGPG is gradually increased. On the other hand, if it is judged at step 501 that PGR> 0, the routine proceeds to step 506, where COFF is made zero.

  20 and 21 show a fifth embodiment. In this embodiment, the relationship between the fuel temperature TEMP in the fuel tank 15 and the evaporated fuel amount PV in the fuel tank 15 per unit time is obtained in advance by experiment, and the vapor concentration FGPG at the time of restarting the purge is based on this relationship. An update action is performed. FIG. 20 shows the relationship between the fuel pressure TEMP in the fuel tank 15 and the evaporated fuel amount PV in the fuel tank 15 per unit time.

  Referring to FIG. 21, first, at step 600, whether or not the purge time execution count value CPGR is larger than the set value K3, that is, whether or not 3 minutes have passed since the purge operation was started after the engine operation was started. It is determined whether or not. When CPGR ≦ K3, the processing cycle is completed. On the other hand, when CPGR> K3, the routine proceeds to step 601, where it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 602, where the evaporated fuel amount PV per unit time is calculated from the relationship shown in FIG. 20 based on the fuel temperature TEMP in the fuel tank 15. Next, at step 603, the cumulative value ΣPV (= ΣPV + PV) of the evaporated fuel amount PV is calculated. Next, at step 604, it is determined whether or not the cumulative value ΣPV has become larger than a predetermined set value KD. When ΣPV ≧ KD, the routine proceeds to step 605, where a constant value ΔK is added to the vapor concentration FGPG. Accordingly, the vapor concentration FGPG is gradually increased while ΣPV ≧ KD. On the other hand, when it is determined in step 601 that the vapor ratio PGR> 0, the routine proceeds to step 606, where the cumulative value ΣPV is made zero.

  Next, a sixth embodiment will be described. In this embodiment, when the purge action is stopped, the vapor concentration of the fuel vapor in the upper space of the fuel tank 15 or in the purge passage from the upper space of the fuel tank 15 to the purge control valve 17 is detected. When the vapor concentration increases while the operation is stopped, the value of the feedback correction coefficient FAF when the purge is resumed is decreased. 22 and 23 specifically show the sixth embodiment.

FIG. 22 shows a case where the purge action is stopped at t ₁ and the purge action is resumed at t ₂ , as in FIG. The solid line indicates when the fuel temperature in the fuel tank 15 is high, and the broken line indicates when the fuel temperature in the fuel tank 15 is low. In the sixth embodiment, as shown in FIG. 22, when the pressure PT in the fuel vapor chamber 12 exceeds a predetermined set value KPTK during the purge stop, the value of the feedback correction coefficient FAF at the purge resumption t ₂ is used to lower by the correction amount KFAF10 predetermined for values of purge stop just before t _1. In the example shown in FIG. 22, the correction amount KFAF10 is set to 0.1.

As described above, when the pressure PT in the fuel vapor chamber 12 exceeds the set value KPTK, that is, when the vapor concentration of the purge gas at the time t ₂ when the purge is resumed is higher than the vapor concentration of the purge gas at the time t ₁ immediately before the purge stop. without the air-fuel ratio becomes rich when the value of the feedback correction coefficient FAF at restart of the purge time t ₂ is made to decrease by correcting amount KFAF10 purge resuming t _2, the air-fuel ratio from fluctuating when the purge resumed and thus Can be prevented.

  FIG. 23 shows a routine for controlling the vapor concentration for executing the sixth embodiment. This routine is executed by interruption every predetermined time, for example, every 100 msec. Referring to FIG. 23, first, at step 700, it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 701, where it is determined whether or not the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32 is higher than the set value KPTK (FIG. 22). Determined. When PT ≧ KPTK, the routine proceeds to step 702, where the correction amount KFAF of the feedback correction coefficient FAF is made KFAF10 (FIG. 22). On the other hand, when PT <KPTK, the routine proceeds to step 704, where KFAF is made zero.

  On the other hand, if it is determined in step 700 that PGR> 0, that is, if the purge action is started, the routine proceeds to step 703 where the correction amount KFAF is subtracted from the feedback correction coefficient FAF. Next, the routine proceeds to step 704. That is, if PT ≧ KPTK while the purge is stopped, the FAF at the time of restarting the purge is decreased by the correction amount KFAF.

FIG. 24 shows a seventh embodiment of the vapor concentration control routine, which is executed by interruption every predetermined time, for example, 100 msec.
This embodiment shows a case where the value of the feedback correction coefficient FAF is decreased when the purge is resumed only when the purge action has a great influence on the air-fuel ratio when the purge is resumed. For example, when the purge is started for the first time after the engine is started, the purge rate PGR is gradually increased from a small purge rate PGR. In this case, when the purge rate PGR is small, the purge is stopped, and then when the purge is resumed, if the value of the feedback correction coefficient FAF is decreased, there is a risk that the air-fuel ratio becomes significantly lean. . In order to prevent this, in the seventh embodiment, the feedback correction coefficient FAF is decreased when the purge is resumed only when the purge execution time count value CPGR exceeds a certain time KCPGR3, for example, 3 minutes.

  That is, referring to FIG. 24, first, at step 800, it is judged if the purge rate PGR is zero. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 801, where whether or not the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32 is higher than the set value KPTK (FIG. 22). Determined. When PT ≧ KPTK, the routine proceeds to step 802, where the correction amount KFAF of the feedback correction coefficient FAF is made KFAF10 (FIG. 22). On the other hand, when PT <KPTK, the routine proceeds to step 805, where KFAF is made zero.

  On the other hand, when it is determined in step 800 that PGR> 0, that is, when the purge action is started, the routine proceeds to step 803, where it is determined whether or not the purge execution time count value CPGR has become larger than the predetermined time KCPGR3. . When CPGR <KCPGR3, the routine jumps to step 805. On the other hand, when CPGR ≧ KCPGR3, the routine proceeds to step 804, where the correction amount KFAF is subtracted from the feedback correction coefficient FAF. Next, the routine proceeds to step 805. That is, if PT ≧ KPTK during the purge stop, if CPGR ≧ KCPGR3 at the time of purge restart, the FAF at the time of purge restart is decreased by the correction amount KFAK.

  FIGS. 25 to 28 show modified examples of the seventh embodiment in which the value of the feedback correction coefficient FAF is decreased when the purge is resumed only when the purge action has a large influence on the air-fuel ratio when the purge is resumed. Yes. The vapor concentration control routine shown in FIGS. 25 to 28 is different from the routine shown in FIG. 24 only in step 803 in FIG. 24, and the other steps 800, 801, 802, 804, and 805 are the routine in FIG. Only the steps corresponding to step 803 in FIG. 24 will be described.

  In the routine shown in FIG. 25, it is determined in step 803a whether or not the purge rate PGR is larger than a predetermined purge rate KPGR05, for example, 0.5%, and the process proceeds to step 804 only when PGR ≧ KPRGR05. That is, when the purge rate PGR is small, the purge is resumed. At this time, if the value of the feedback correction coefficient FAF is decreased, there is a risk that the air-fuel ratio becomes excessively lean due to overcorrection. In order to prevent this, the feedback correction coefficient FAF is decreased when the purge is resumed only when the purge rate PGR exceeds a predetermined purge rate KPGR05.

  In the routine shown in FIG. 26, it is determined in step 803b whether or not the duty ratio DPG of the purge control valve 17 is larger than a predetermined duty ratio KDPG10, for example, 10%, and only in the case of DPG ≧ KDPG10, step 804 is executed. move on. That is, when the duty ratio DPG is small, the purge is resumed. At this time, if the value of the feedback correction coefficient FAF is decreased, there is a risk that the air-fuel ratio will become significantly lean due to overcorrection. In order to prevent this, the feedback correction coefficient FAF is decreased when the purge is resumed only when the duty ratio DPG is larger than the predetermined duty ratio KDPG10.

  In the routine shown in FIG. 27, it is determined in step 803c whether or not the intake air amount Ga is smaller than a predetermined intake air amount KGa, and the process proceeds to step 804 only when Ga ≦ KGa. That is, when the intake air amount is large and the fuel injection amount is large, the purge is resumed. At this time, if the value of the feedback correction coefficient FAF is decreased, there is a risk that the air-fuel ratio becomes excessively lean due to overcorrection. There is. In order to prevent this, the feedback correction coefficient FAF is decreased when the purge is resumed only when the intake air amount Ga is smaller than a predetermined intake air amount KGa.

  In the routine shown in FIG. 28, it is determined in step 803d whether or not the vapor concentration renewal count CFGPG is greater than a predetermined count KCFFGPG20, for example, 20 times, and the process proceeds to step 804 only when CFGPG ≧ KCFFGPG20. That is, when the number of updates of the vapor concentration is small, the vapor concentration often does not accurately represent the actual vapor concentration. In such a case, when the purge is resumed, the value of the feedback correction coefficient FAF is decreased. There is a risk that the air-fuel ratio fluctuates greatly due to overcorrection. In order to prevent this, the feedback correction coefficient FAF is decreased when the purge is resumed only when the vapor concentration update count CFGPG is larger than the predetermined count KCFFGPG20.

  29 and 30 show an eighth embodiment. The higher the pressure PT of the fuel vapor chamber 12 during the purge stop, the higher the vapor concentration in the purge gas when the purge is resumed. Therefore, in this embodiment, as shown in FIG. 29, the correction amount KFAF of the feedback correction coefficient FAF is increased as the pressure PT in the fuel vapor chamber 12 during the purge stop increases.

  FIG. 30 shows a vapor concentration control routine for executing the eighth embodiment, and this routine is executed by interruption every predetermined time, for example, every 100 msec. Referring to FIG. 30, first, at step 900, it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 901, where whether or not the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32 is higher than the set value KPTK (FIG. 22). Determined. When PT ≧ KPTK, the routine proceeds to step 902, where the correction amount KFAF of the feedback correction coefficient FAF is calculated based on the pressure PT from the relationship shown in FIG. On the other hand, when PT <KPTK, the routine proceeds to step 904, where KFAF is made zero.

  On the other hand, when it is determined in step 900 that PGR> 0, that is, when the purge action is started, the process proceeds to step 903 where the correction amount KFAF is subtracted from the feedback correction coefficient FAF. Next, the routine proceeds to step 904. That is, if PT ≧ KPTK while the purge is stopped, the FAF at the time of restarting the purge is decreased by the correction amount KFAF.

  31 and 32 show a ninth embodiment. The vapor concentration FGPG immediately before the stop of the purge is large even if the increase in the vapor concentration of the fuel vapor in the upper space of the fuel tank 15 during the purge stop or in the purge passage from the upper space of the fuel tank 15 to the purge control valve 17 is large. The change rate of the vapor concentration FGPG at the time of restarting the purge with respect to the vapor concentration FGPG immediately before the purge is stopped becomes smaller. Therefore, in this embodiment, the final correction amount (KFAF · KFGPG) is obtained by multiplying the correction amount KFAF by the correction coefficient KFGPG, and the correction coefficient KFGPG is made smaller as the vapor concentration FGPG increases as shown in FIG. I have to. By doing so, it is possible to prevent overcorrection of the vapor concentration FGPG when the purge is resumed.

FIG. 32 shows a vapor concentration control routine for executing the ninth embodiment, and this routine is executed by interruption every predetermined time, for example, every 100 msec.
Referring to FIG. 32, first, at step 1000, it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 1001, where it is determined whether or not the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32 is higher than the set value KPTK (FIG. 22). Determined. When PT ≧ KPTK, the routine proceeds to step 1002, where the correction amount KFAF of the feedback correction coefficient FAF is made KFAF10 (FIG. 22). On the other hand, when PT <KPTK, the routine proceeds to step 1005, where KFAF is made zero.

On the other hand, when it is determined in step 1000 that PGR> 0, that is, when the purge action is started, the process proceeds to step 1003, and the correction coefficient KFGPG is calculated based on the vapor concentration FGPG from the relationship shown in FIG. Next, at step 1004, a feedback correction coefficient FAF is calculated based on the following equation.
FAF = FAF- (KFAF ・ KFGPG)
That is, the correction amount KFAF and the correction coefficient KFGPG are subtracted from the feedback correction coefficient FAF. Next, the routine proceeds to step 1005. Therefore, in this embodiment, when PT ≧ KPTK during the purge stop, the FAF at the time of restarting the purge is decreased by KFAK · KFGPG.

  FIG. 33 shows a tenth embodiment. When the amount of increase in the vapor concentration of the fuel vapor in the upper space of the fuel tank 15 or the purge passage from the upper space of the fuel tank 15 to the purge control valve 17 during the purge stop is the same, the purge rate at the time of restarting the purge The higher the PGR, the larger the deviation amount of the air-fuel ratio when restarting the purge. Therefore, in this embodiment, the feedback correction coefficient FAF is obtained based on the following equation.

FAF = FAF- (KFAF ・ KFGPG) ・ (PGR / KPGR)
Here, KPGR is a predetermined reference purge rate. Therefore, in this embodiment, the final correction amount is calculated by multiplying the correction amount KFAF by the correction coefficient KFGPG described above and further multiplying the ratio (PGR / KPRG) of the purge rate PGR with respect to the reference purge rate KPGR.

FIG. 33 shows a vapor concentration control routine for executing the tenth embodiment, and this routine is executed by interruption every predetermined time, for example, every 100 msec.
Referring to FIG. 33, first, at step 1100, it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 1101, where it is determined whether or not the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32 is higher than the set value KPTK (FIG. 22). Determined. When PT ≧ KPTK, the routine proceeds to step 1102, where the feedback correction coefficient FAF correction amount KFAF is made KFAF10 (FIG. 22). On the other hand, when PT <KPTK, the routine proceeds to step 1105, where KFAF is made zero.

On the other hand, when it is determined in step 1101 that PGR> 0, that is, when the purge action is started, the process proceeds to step 1103, and the correction coefficient KFGPG is calculated based on the vapor concentration FGPG from the relationship shown in FIG. Next, at step 1004, a feedback correction coefficient FAF is calculated based on the following equation.
FAF = FAF- (KFAF ・ KFGPG) ・ (PGR / KPGR)
That is, the correction amount KFAF, the correction coefficient KFPGP, and the purge rate ratio (PGR / KPGR) are subtracted from the feedback correction coefficient FAF. Next, the process proceeds to step 1105. Therefore, in this embodiment, when PT ≧ KPTK while the purge is stopped, the FAF at the time of the purge restart is reduced by KFAK · KFPGP (PGR / KPGR).

34 and 35 show the eleventh embodiment. After the restart of the purge, there is a time delay until the purged fuel vapor reaches the combustion chamber and is burnt. Thus in this embodiment is to reduce the feedback correction coefficient FAF after restart of the purge time t predetermined delay time Δt ₂ has elapsed, as shown in Figure 34.

FIG. 35 shows a vapor concentration control routine for executing the eleventh embodiment, and this routine is executed by interruption every predetermined time, for example, every 100 msec.
Referring to FIG. 35, first, at step 1200, it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 1201, where the time calculation count value CFAF is made zero. Next, the routine proceeds to step 1202, where it is judged if the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32 is higher than a set value KPTK (FIG. 22). When PT ≧ KPTK, the routine proceeds to step 1203, where the correction amount KFAF of the feedback correction coefficient FAF is set to KFAF10 (FIG. 22). On the other hand, when PT <KPTK, the routine proceeds to step 1208, where KFAF is made zero.

  On the other hand, if it is determined in step 1200 that PGR> 0, that is, if the purge action is started, the routine proceeds to step 1204, where the time calculation count value CFAF is incremented by one. Next, at step 1205, it is determined whether or not the time calculation count value CFAF has reached a predetermined count value KCFAF5, that is, whether or not the delay time Δt shown in FIG. When CFAF = KCFAF5 is not satisfied, the processing cycle is completed. On the other hand, when CFAF = KCFAF5, the routine proceeds to step 1206, where the correction coefficient KFGPG is calculated based on the vapor concentration FGPG from the relationship shown in FIG. Next, at step 1207, a feedback correction coefficient FAF is calculated based on the following equation.

FAF = FAF- (KFAF ・ KFGPG) ・ (PGR / KPGR)
Next, the routine proceeds to step 1208. That is, if PT ≧ KPTK while the purge is stopped, FAF is decreased by KFAF · KFGPG · (PGR / KPGR) when a certain delay time Δt has elapsed after the purge is resumed.
36 and 37 show a twelfth embodiment. As described above, after the purge is resumed, not only is there a time lag until the purged fuel vapor reaches the combustion chamber and is burned, but the purged fuel vapor is mixed with the intake air in the surge tank 5. Since the gas is sequentially supplied to each cylinder, the vapor concentration in the intake air supplied to each cylinder increases in a stepwise manner. Therefore predetermined delay time Δt over a period of time Δt1 predetermined after a lapse reduce feedback correction coefficient FAF so little by little stepwise from the purge resumption t ₂ as shown in FIG. 36 in this embodiment I try to let them.

In this embodiment, the feedback correction coefficient FAF is calculated based on the following equation in order to decrease the feedback correction coefficient FAF step by step.
FAF = FAF− (KFAF · KFGPG) · (PGR / KPGR) / KM
Here, KM is a value of about 4 to 8. That is, in this embodiment, FAF is decreased step by step by a fraction of KFAF · KFGPG · (PGR / KPGR).

FIG. 37 shows a vapor concentration control routine for executing the twelfth embodiment. This routine is executed by interruption every predetermined time, for example, every 100 msec.
Referring to FIG. 37, first, at step 1300, it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 1301, where the time calculation count value CFAF is made zero. Next, the routine proceeds to step 1302, where it is judged if the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32 is higher than a set value KPTK (FIG. 22). When PT ≧ KPTK, the routine proceeds to step 1303, where the correction amount KFAF of the feedback correction coefficient FAF is made KFAF10 (FIG. 22). On the other hand, when PT <KPTK, the routine proceeds to step 1309, where KFAF is made zero.

  On the other hand, if it is determined in step 1300 that PGR> 0, that is, if the purge action is started, the routine proceeds to step 1304, where the time calculation count value CFAF is incremented by one. Next, in step 1305, it is determined whether or not the time calculation count value CFAF exceeds a predetermined count value KCFAF5, that is, whether or not the delay time Δt shown in FIG. When CFAF <KCFAF5, the processing cycle is completed. On the other hand, when CFAF ≧ KCFAF5, the routine proceeds to step 1306, where the correction coefficient KFGPG is calculated based on the vapor concentration FGPG from the relationship shown in FIG. Next, at step 1307, a feedback correction coefficient FAF is calculated based on the following equation.

FAF = FAF− (KFAF · KFGPG) · (PGR / KPGR) / KM
Next, at step 1308, it is determined whether or not the time calculation count value CFAF exceeds a predetermined count value KCFAF15, that is, whether or not the time range Δt1 of FIG. When CFAF <KCFAF15, the processing cycle is completed. On the other hand, when CFAF ≧ KCFAF15, the routine proceeds to step 1309. That is, when PT ≧ KPTK while the purge is stopped, the constant periods Δt1 and FAF are decreased step by step by KFAF · KFGPG · (PGR / KPGR) / KM after a certain delay time Δt has elapsed after the purge is resumed.

38 and 39 show a thirteenth embodiment. In this embodiment, as shown in FIG. 38, the feedback correction coefficient FAF is decreased stepwise until the air-fuel ratio becomes lean after restarting the purge. In this way, overcorrection of FAF can be prevented.
FIG. 39 shows a vapor concentration control routine for executing the thirteenth embodiment. This routine is executed by interruption every predetermined time, for example, every 100 msec.

  Referring to FIG. 39, first, at step 1400, it is judged if the purge rate PGR is zero or not. When PGR = 0, that is, when the purge action is stopped, the routine proceeds to step 1401, where the time calculation count value CFAF is made zero. Next, the routine proceeds to step 1402, where it is judged if the pressure PT in the fuel vapor chamber 12 detected by the pressure sensor 32 is higher than a set value KPTK (FIG. 22). When PT ≧ KPTK, the routine proceeds to step 1403, where the correction amount KFAF of the feedback correction coefficient FAF is made KFAF10 (FIG. 22). On the other hand, when PT <KPTK, the routine proceeds to step 1409, where KFAF is made zero.

  On the other hand, if it is determined in step 1400 that PGR> 0, that is, if the purge action is started, the routine proceeds to step 1404, where the time calculation count value CFAF is incremented by one. Next, at step 1405, it is determined whether or not the time calculation count value CFAF exceeds a predetermined count value KCFAF5, that is, whether or not the delay time Δt shown in FIG. When CFAF <KCFAF5, the processing cycle is completed. On the other hand, when CFAF ≧ KCFAF5, the routine proceeds to step 1406, where a correction coefficient KFGPG is calculated based on the vapor concentration FGPG from the relationship shown in FIG. Next, at step 1407, a feedback correction coefficient FAF is calculated based on the following equation.

FAF = FAF− (KFAF · KFGPG) · (PGR / KPGR) / KM
Next, at step 1408, it is judged from the output signal of the O ₂ sensor 30 whether or not the air-fuel ratio has become lean. When the air-fuel ratio is not lean, the processing cycle is completed. When the air-fuel ratio becomes lean, the process proceeds to step 1409. That is, if PT ≧ KPTK during purge stop, after a certain delay time Δt has elapsed after resuming purge, FAF is gradually decreased by KFAF · KFGPG · (PGR / KPGR) / KM until the air-fuel ratio becomes lean. It is done.

A fourteenth embodiment is shown in FIGS. First, FIG. 40 will be described. FIG. 40 shows a first purge stop action I and a second purge stop action II. t ₁ and t ₂ indicate the purge stop timing and purge restart timing in the first purge stop action I, respectively, and t ₃ and t ₄ indicate the purge stop timing and purge restart timing in the second purge action II, respectively. Each shows.

In this embodiment, whether or not the vapor concentration of the fuel vapor in the upper space of the fuel tank 15 or the purge passage extending from the upper space of the fuel tank 15 to the purge control valve 17 during the purge stop is increased after the purge is started. This is determined from the change in the correction coefficient FAF. For example, in FIG. 40, if the vapor concentration of the fuel vapor in the upper space of the fuel tank 15 or the purge passage from the upper space of the fuel tank 15 to the purge control valve 17 increases during the first purge stop period I, the purge is resumed. Immediately after (t _{2 in} FIG. 40), the feedback correction coefficient FAF becomes small. In the example shown in FIG. 40, when the feedback correction coefficient FAF becomes smaller than a predetermined set value KFAF09, for example, 0.9, for example, in the upper space of the fuel tank 15 or the upper portion of the fuel tank 15 during the purge stop. It is determined that the vapor concentration of the fuel vapor in the purge passage extending from the space to the purge control valve 17 has increased, and at this time, the vapor concentration increase flag XVAPOR indicating that the vapor concentration has increased is set.

Each time the vapor concentration increase flag XVAPOR once set is the subsequent purge is stopped and then the purge is restarted, the vapor concentration in the second purge stop period II after restart of the purge time t ₄ in the example shown in FIG. 40 FGPG Is increased by a predetermined correction amount KFGPG. As described above, when the vapor concentration FGPG is increased at the restart of the purge, the feedback correction coefficient FAF is maintained at the reference value (= 1.0) at the restart of the purge, and the air-fuel ratio A / F is maintained at the stoichiometric air-fuel ratio.

41 and 42 show a vapor concentration control routine for executing the fourteenth embodiment. This routine is executed by interruption every predetermined time, for example, every 100 msec.
41 and 42, first, at step 1500, it is determined whether or not the purge time execution count value CPGR is larger than the set value KCPGR3, for example, 3 minutes after the purge operation is started after the engine is started. It is determined whether or not it has elapsed. When CPGR <KCPGR3, the routine proceeds to step 1508, where the vapor concentration increase flag XVAPOR is reset. Next, at step 1509, it is judged if the purge rate PGR0 at the previous processing cycle was zero. When PGRO = 0, the routine proceeds to step 1510, where the purge stop time count value CPGROF representing the purge stop time is incremented by 1, and then proceeds to step 1512. On the other hand, when PGRO = 0 is not established, the routine proceeds to step 1511 where the purge stop time count value CPGROF is made zero, and then the routine proceeds to step 1512. In step 1512, the purge time count value CPGRON indicating the purge duration time is set to zero, and then the processing cycle is completed.

  On the other hand, when it is determined at step 1500 that CPGR ≧ KCPGR3, the routine proceeds to step 1501, where it is determined whether or not the purge rate PGR is zero. When PGR = 0, the process proceeds to step 1509. On the other hand, when PGR> 0, that is, when the purge is started, the routine proceeds to step 1502, where it is determined whether or not the purge stop time count value CPGOF is larger than the set value KCUT. When CPGROF ≧ KCUT, the routine proceeds to step 1503.

  In step 1503, it is determined whether or not the vapor concentration increase flag XVAPOR is set. When XVAPOR = 0, that is, when the vapor concentration increase flag XVAPOR is reset, the routine proceeds to step 1504, where it is determined whether or not the number of skips SSKIP of the feedback correction coefficient FAF after starting purge is smaller than three. . When CSKIP ≦ 3, the routine proceeds to step 1505, where it is judged if the feedback correction coefficient FAF has become smaller than the set value KFAF09 (FIG. 40). When FAF ≦ KFAF09, the routine proceeds to step 1506, where the vapor concentration increase flag XVAPOR is set. That is, when CSKIP ≦ 3 and FAF ≦ KFAF09, the vapor concentration increase flag XVAPOR is set. Next, at step 1507, the purge time count value CPGRON is set to 1.

  When the vapor concentration increase flag XVAPOR is set, in the next processing cycle, the routine proceeds from step 1503 to step 1513, and the purge time count value CPGRON is incremented by one. Next, at step 1514, it is judged if the vapor concentration increase flag XVAPOR is set and the purge time count value CPGRON is 1. At this time, since XVAPOR = 1 but CPGRON = 2, the processing cycle is completed. At this time, the vapor concentration FGPG is not corrected.

  If purging is stopped again and then purging is resumed, the vapor concentration increase flag XVAPOR is already set at this time, so the routine proceeds from step 1503 to step 1513. At this time, the purge time count value CPGRON is 1. Accordingly, in the next step 1514, it is determined that XVAPOR = 1 and CPGRON = 1, so that the process proceeds to step 1515, and a predetermined correction amount KFGPG is added to the vapor concentration FGPG. Therefore, as described above with reference to FIG. 40, it is possible to prevent the air-fuel ratio A / F from changing when the purge is resumed.

  43 to 45 show the fifteenth embodiment. In this embodiment, when the vapor concentration FGPG at the time of resuming the purge increases by a certain value or more, the fuel vapor in the purge passage extending from the upper space of the fuel tank 15 or from the upper space of the fuel tank 15 to the purge control valve 17 during the purge stop. It is determined that the vapor concentration of That is, in FIG. 43, when the vapor concentration FGPG becomes larger than the set value KFG compared to the vapor concentration FGPGOF just before the purge stop when the purge is restarted after the first purge stop period I, that is, when FGPG ≧ FGPGOF + KFG. When the concentration increase flag XVAPOR is set, and then purge is stopped and then purge is restarted, the vapor concentration FGPG is increased by a predetermined correction amount KFGPG.

44 and 45 show a vapor concentration control routine for executing the fifteenth embodiment. This routine is executed by interruption every predetermined time, for example, every 100 msec.
44 and 45, first, at step 1600, it is determined whether or not the purge time execution count value CPGR is larger than the set value KCPGR3, for example, 3 minutes after the purge operation is started after the engine is started. It is determined whether or not it has elapsed. When CPGR <KCPGR3, the routine proceeds to step 1608, where the vapor concentration increase flag XVAPOR is reset. Next, at step 1609, it is judged if the purge rate PGR0 at the previous processing cycle was zero. When PGRO = 0, the routine proceeds to step 1610, where the purge stop time count value CPGROF indicating the purge stop time is incremented by 1, and then proceeds to step 1612. On the other hand, when PGR0 is not 0, the routine proceeds to step 1611 where the purge stop time count value CPGROF is set to zero, and then the routine proceeds to step 1612. In step 1612, the vapor concentration FGPG is set to FGPGOF. Next, at step 1613, the purge time count value CPGRON representing the purge duration time is set to zero, and then the processing cycle is completed.

  On the other hand, when it is determined at step 1600 that CPGR ≧ KCPGR3, the routine proceeds to step 1601, where it is determined whether or not the purge rate PGR is zero. When PGR = 0, the process proceeds to step 1609. On the other hand, when PGR> 0, that is, when the purge is started, the routine proceeds to step 1602, where it is determined whether or not the purge stop time count value CPGOF is larger than the set value KCUT. When CPGROF ≧ KCUT, the routine proceeds to step 1603.

  In step 1603, it is determined whether or not the vapor concentration increase flag XVAPOR is set. When XVAPOR = 0, that is, when the vapor concentration increase flag XVAPOR is reset, the routine proceeds to step 1604, where it is judged if the number of skips CSKIP of the feedback correction coefficient FAF after starting purge is smaller than 6. . When CSKIP ≦ 6, the routine proceeds to step 1605, where it is judged if the vapor concentration FGPG is larger than the sum (FGPGOF + KFG) of the vapor concentration FGPGOF just before the purge stop and the set value KFG. When FGPG ≧ FGPGOF + KFG, the routine proceeds to step 1606, where the vapor concentration increase flag XVAPOR is set. That is, when CSKIP ≦ 6, if FGPG ≧ FGPGOF + KFG, the vapor concentration increase flag XVAPOR is set. Next, at step 1607, the purge time count value CPGRON is set to 1.

  When the vapor concentration increase flag XVAPOR is set, the process proceeds from step 1603 to step 1614 in the next processing cycle, and the purge time count value CPGRON is incremented by one. Next, at step 1615, it is judged if the vapor concentration increase flag XVAPOR is set and the purge time count value CPGRON is 1. At this time, since XVAPOR = 1 but CPGRON = 2, the processing cycle is completed. At this time, the vapor concentration FGPG is not corrected.

  If purging is stopped again and then purging is resumed, the vapor concentration increase flag XVAPOR is already set at this time, so the routine proceeds from step 1603 to step 1614. At this time, the purge time count value CPGRON is 1. Accordingly, in the next step 1615, it is determined that XVAPOR = 1 and CPGRON = 1, so the process proceeds to step 1616, and a predetermined correction amount KFGPG is added to the vapor concentration FGPG. Therefore, it is possible to prevent the air-fuel ratio A / F from fluctuating when the purge is resumed.

A sixteenth embodiment is shown in FIGS. In this embodiment, as shown in FIG. 46, almost the entire amount KFGPG of the increase in the vapor concentration FGPG after the first purge stop period I is the correction amount KFGPG of the purge concentration when the purge is restarted after the second purge stop period II. It is said.
47 and 48 show a vapor concentration control routine for executing the sixteenth embodiment, and this routine is executed by interruption every predetermined time, for example, every 100 msec. 47 are the same as steps 1600 to 1613 in FIG. 44, and are different from the routines shown in FIGS. 44 and 45 after step 1714 in FIG. 48. Steps after step 1714 will be described.

  After the start of purging, FGPG ≧ FGPGOF + KFG, and when the vapor concentration increase flag XVAPOR is set, the process proceeds from step 1703 to step 1714 in the next processing cycle. In step 1714, it is determined whether the vapor concentration increase flag XVAPOR is set, the skip count CSKIP is 6 or less, and the purge time count value CPGRON is 1 or more. At this time, since XVAPOR = 1 and CPGRON ≧ 1, if CSKIP ≦ 6, the process proceeds to step 1715, and the difference (FGPG−FGPGOF) obtained by subtracting the vapor concentration FGPGOF just before the purge stop from the current vapor concentration FGPG is corrected. KFGPG.

  Next, at step 1716, the purge time count value CPGRON is incremented by one. Next, at step 1717, it is judged if the vapor concentration increase flag XVAPOR is set and the purge time count value CPGRON is 1. At this time, since XVAPOR = 1 but CPGRON = 2, the processing cycle is completed. At this time, the vapor concentration FGPG is not corrected.

In the next processing cycle, as long as SKIP ≦ 6, the routine proceeds from step 1714 to step 1715, where the correction amount KFGPG is updated. When SKIP = 6, the learning of the vapor concentration FGPG is almost completed, and therefore the correction amount KFGPG substantially coincides with the increase amount of the vapor concentration FGPG.
If purging is stopped again and purging is resumed, the vapor concentration increase flag XVAPOR is already set at this time, so the routine proceeds from step 1703 to step 1714. At this time, since the purge time count value CPGRON is zero, the routine jumps from step 1714 to step 1716. In step 1716, the purge time count value CPGRON becomes 1. Accordingly, in the next step 1717, it is determined that XVAPOR = 1 and CPGRON = 1, so that the process proceeds to step 1718, and the already calculated correction amount KFGPG is added to the vapor concentration FGPG. Therefore, it is possible to prevent the air-fuel ratio A / F from fluctuating when the purge is resumed.

In the next processing cycle, if CSKIP ≦ 6, the routine proceeds to step 1715 where the correction amount KFGPG is updated again.
49 and 50 show a seventeenth embodiment. In this embodiment, a correction amount ΔFGPG per unit purge stop time is obtained, and a final correction amount KFGPG proportional to the purge stop time is obtained from the correction amount ΔFGPG. Specifically, the final correction amount KFGPG is calculated based on the following equation.

ΔFGPG = (FGPG−FGPGOF) · KCPPGOF / CPGROF (1)
KFGPG = ΔFGPG · (CPGROF / KCPGROF) (2)
Here, KCPGROF is a reference purge stop time, for example, 10 sec.
Referring to FIG. 46, CPGROF in the equation (1) represents the first purge stop period I. Therefore, the correction amount ΔFGPG per 10 seconds of the purge stop time is obtained from the equation (1).

On the other hand, CPGROF in the equation (2) represents the second purge stop period II. Therefore, the final correction amount KFGPG is increased as the purge stop time becomes longer.
49 and 50 show a routine for controlling the vapor concentration, and this routine is executed by interruption every predetermined time, for example, every 100 msec. Note that steps 1800 to 1813 in FIG. 49 are the same as steps 1600 to 1613 in FIG. 44, and are different from the routines shown in FIGS. 44 and 45 after step 1814 in FIG. Step 1814 and subsequent steps will be described.

  After the start of purging, FGPG ≧ FGPGOF + KFG, and when the vapor concentration increase flag XVAPOR is set, the process proceeds from step 1803 to step 1814 in the next processing cycle. In step 1814, it is determined whether the vapor concentration increase flag XVAPOR is set, the skip count CSKIP is 6 or less, and the purge time count value CPGRON is 1 or more. At this time, since XVAPOR = 1 and CPGRON ≧ 1, if CSKIP ≦ 6, the routine proceeds to step 1815 and represents the current vapor concentration FGPG, the vapor concentration FGPGOF just before the purge stop, the reference purge stop time KCPGROF and the purge stop time. The correction amount ΔFGPG per unit purge stop time is calculated based on the following equation using the purge stop time count value CPGROF.

ΔFGPG = (FGPG−FGPGOF) · KCPPGROF / CPGROF
Next, at step 1816, the purge time count value CPGRON is incremented by one. Next, at step 1817, it is judged if the vapor concentration increase flag XVAPOR is set and the purge time count value CPGRON is 1. At this time, since XVAPOR = 1 but CPGRON = 2, the processing cycle is completed. At this time, the vapor concentration FGPG is not corrected.

In the next processing cycle, as long as SKIP ≦ 6, the routine proceeds from step 1814 to step 1815, where ΔFGPG is updated.
If purging is stopped again and then purging is resumed, the vapor concentration increase flag XVAPOR is already set at this time, so the routine proceeds from step 1803 to step 1814. At this time, since the purge time count value CPGRON is zero, the routine jumps from step 1814 to step 1816. In step 1816, the purge time count value CPGRON becomes 1. Accordingly, in the next step 1817, it is determined that XVAPOR = 1 and CPGRON = 1, so the process proceeds to step 1818, and the final correction amount KFGPG is calculated based on the following equation.

KFGPG = ΔFGPG · (CPGROF / KCPPGOF)
Next, at step 1819, the correction amount KFGPG is added to the purge concentration FGPG. In the next processing cycle, if CSKIP ≦ 6, the process proceeds to step 1815, and ΔFGPG is updated again.
51 and 52 show an eighteenth embodiment. In this embodiment, the purge time count value CPGRON is set to a constant value KCPG in consideration of the delay time from when the purge is resumed until the purged fuel vapor reaches the combustion chamber. It is delayed by a certain time until it becomes.

  51 and 52 show a routine for controlling the vapor concentration, and this routine is executed by interruption every certain time, for example, every 100 msec. 51 are the same as steps 1600 to 1613 in FIG. 44, and are different from the routines shown in FIGS. 44 and 45 after step 1914 in FIG. 52. Step 1914 and subsequent steps will be described.

  After the start of purging, FGPG ≧ FGPGOF + KFG, and when the vapor concentration increase flag XVAPOR is set, the process proceeds from step 1903 to step 1914 in the next processing cycle. In step 1914, it is determined whether the vapor concentration increase flag XVAPOR is set, the skip count CSKIP is 6 or less, and the purge time count value CPGRON is KCPG or more. At this time, since XVAPOR = 1 but CPGRON is 1, the process jumps to step 1916.

  In step 1916, the purge time count value CPGRON is incremented by one. Next, at step 1917, it is judged if the vapor concentration increase flag XVAPOR is set and the purge time count value CPGRON is KCPG. At this time, since XVAPOR = 1 but CPGRON = 2 (<KCPG), the processing cycle is completed. At this time, the vapor concentration FGPG is not corrected.

  Next, when CPGRON becomes KCPG in step 1916, the process proceeds to step 1918. When the operation proceeds to step 1918 for the first time after the engine is started, ΔFGPG is not yet calculated and ΔFGPG is zero, so the correction amount KFGPG is zero, so that the vapor concentration FGPG is also corrected at this time. There is no effect.

  On the other hand, when CPGRON becomes KCPG, if CSKIP ≦ 6 in the next processing cycle, the process proceeds from step 1914 to step 1915, and the current vapor concentration FGPG, the vapor concentration FGPGOF just before the purge stop, the reference purge stop time KCPPROF, and the purge stop time are set. A correction amount ΔFGPG per unit purge stop time is calculated based on the following equation using the purge stop time count value CPGROF expressed.

ΔFGPG = (FGPG−FGPGOF) · KCPPGROF / CPGROF
Next, in step 1916, CPGRON becomes KCPG + 1, so that the processing cycle is completed through step 1917.
In the next processing cycle, as long as SKIP ≦ 6, the routine proceeds from step 1914 to step 1915, where ΔFGPG is updated.

If purging is then stopped again and purging is resumed, the vapor concentration increase flag XVAPOR is already set at this time, so the routine proceeds from step 1903 to step 1914. At this time, since the purge time count value CPGRON is zero, the routine jumps from step 1914 to step 1916.
Next, when CPGRON becomes KCPG in step 1916, the process proceeds from step 1917 to step 1918, and a final correction amount KFGPG is calculated based on the following equation.

KFGPG = ΔFGPG · (CPGROF / KCPPGOF)
Next, at step 1919, the correction amount KFGPG is added to the purge concentration FGPG. That is, when the purge is resumed, the vapor concentration FGPG is corrected when CPGRON becomes KCPG after the purge is resumed, that is, after a certain time delay after the purge is resumed. In the next processing cycle, if CSKIP ≦ 6, the routine proceeds to step 1915, where ΔFGPG is updated again.

Next, a description will be given of a case where the vapor concentration increase flag XVAPOR is reset when the correction is overcorrected when the vapor concentration FGPG is corrected at the time of restarting the purge. Figure 53 is the vapor concentration is corrected in the purge resuming t _4, shows a case where this correction is overcorrection. As described above, when the correction is overcorrected, the feedback correction coefficient FAF increases as shown in FIG. 53, and the vapor concentration FGPG decreases rapidly.

  Therefore, in the control routine of the vapor concentration increase flag XVAPOR shown in FIG. 54, as shown in FIG. 53, when the feedback correction coefficient FAF exceeds a predetermined value KFAF11, for example, 1.1 within a certain period after restarting the purge, the vapor concentration is increased. It is determined whether or not the vapor concentration of the fuel vapor in the upper space of the fuel tank 15 or the purge passage extending from the upper space of the fuel tank 15 to the purge control valve 17 is increased while the purge is stopped again by resetting the increase flag XVAPOR. In the control routine of the vapor concentration increase flag XVAPOR shown in FIG. 55, as shown in FIG. 53, the vapor concentration FGPG has fallen below a predetermined value FGPGOF + α (α ≧ 0) within a certain period after restarting the purge. Sometimes the vapor concentration increase flag XVAPOR is reset and purge is stopped again. During stopping, it is determined whether or not the vapor concentration of the fuel vapor in the upper space of the fuel tank 15 or the purge passage from the upper space of the fuel tank 15 to the purge control 17 has increased.

  Referring to FIG. 54, first, at step 2000, it is judged if the purge stop time count value CPGROF is larger than the predetermined time KCUT. When CPGROF ≧ KCUT, the routine proceeds to step 2001, where it is judged if the purge time count value CPGRON is larger than the predetermined time KCPG. When CPGRON ≧ KCPG, the routine proceeds to step 2002, where it is judged if the vapor concentration increase flag XVAPOR is set.

  When the vapor concentration increase flag XVAPOR is set, the routine proceeds to step 2003, where it is determined whether or not the skip count CSKIP of the feedback correction coefficient FAF is 3 or less. When CSKIP ≧ 3, the routine proceeds to step 2004, where it is judged if the feedback correction coefficient FAF has become larger than a predetermined value KFAF11. When FAF ≧ KFAF11, the routine proceeds to step 2005, where the vapor concentration increase flag XVAPOR is reset.

  Next, referring to FIG. 55 showing another embodiment, first, at step 2100, it is judged if the purge stop time count value CPGROF is larger than the predetermined time KCUT. When CPGROF ≧ KCUT, the routine proceeds to step 2101 where it is judged if the purge time count value CPGRON is larger than the predetermined time KCPG. When CPGRON ≧ KCPG, the routine proceeds to step 2102, where it is judged if the vapor concentration increase flag XVAPOR is set.

  When the vapor concentration increase flag XVAPOR is set, the routine proceeds to step 2103, where it is judged if the skip count CSKIP of the feedback correction coefficient FAF is 6 or less. When CSKIP ≦ 6, the routine proceeds to step 2104, where it is judged if the vapor concentration FGPG has become smaller than a predetermined value FGPGOF + α. When FGPG ≦ FGPGOF + α, the routine proceeds to step 2105, where the vapor concentration increase flag XVAPOR is reset.

1 is an overall view of an internal combustion engine. It is a figure which shows the change of the feedback correction coefficient FAF. It is a figure which shows the change of the purge rate PGR. It is a figure which shows changes, such as a feedback correction coefficient FAF at the time of purge action | operation start. It is a flowchart for performing purge control. It is a flowchart for performing purge control. It is a flowchart for a purge control valve drive process. It is a flowchart for calculating a feedback correction coefficient FAF. It is a flowchart for performing learning of an air fuel ratio. It is a flowchart for performing the learning of vapor concentration. It is a flowchart for calculating fuel injection time. It is a figure which shows changes, such as vapor concentration FGPG. 5 is a flowchart for controlling the vapor concentration in the first embodiment. It is a figure which shows the relationship between the pressure PT in a fuel vapor chamber, and the amount of fuel vapor PV. It is a flowchart for controlling a vapor | steam density | concentration in 2nd Example. It is a figure which shows the relationship between vapor concentration FGPG and vapor fuel amount TV. It is a flowchart for controlling a vapor | steam density | concentration in 3rd Example. 1 is an overall view of an internal combustion engine. It is a flowchart for controlling vapor concentration in 4th Example. It is a figure which shows the relationship between the fuel temperature TEMP in a fuel tank, and evaporated fuel amount PV. It is a flowchart for controlling the vapor concentration in the fifth embodiment. It is a figure which shows changes, such as feedback. It is a flowchart for controlling a vapor | steam density | concentration in 6th Example. It is a flowchart of 7th Example for controlling vapor concentration. It is a flowchart for controlling the vapor | steam density | concentration which shows the modification of 7th Example. It is a flowchart for controlling the vapor | steam density | concentration which shows the modification of 7th Example. It is a flowchart for controlling the vapor | steam density | concentration which shows the modification of 7th Example. It is a flowchart for controlling the vapor | steam density | concentration which shows the modification of 7th Example. It is a figure which shows the relationship between the pressure PT in a fuel vapor chamber, and the correction amount KFAF. It is a flowchart for controlling the vapor concentration in the eighth embodiment. It is a figure which shows the relationship between vapor concentration FGPG and the correction coefficient KFGPG. It is a flowchart for controlling the vapor concentration in the ninth embodiment. It is a flowchart which shows 10th Example for controlling vapor concentration. It is a figure which shows changes, such as a feedback correction coefficient FAF. It is a flowchart for controlling the vapor concentration in the eleventh embodiment. It is a figure which shows changes, such as a feedback correction coefficient FAF. It is a flowchart for controlling the vapor concentration in the twelfth embodiment. It is a figure which shows changes, such as a feedback correction coefficient FAF. It is a flowchart for controlling a vapor | steam density | concentration in 13th Example. It is a figure which shows feedback correction coefficient FAF, vapor concentration FGPG, air fuel ratio A / F, etc. It is a flowchart for controlling vapor concentration in 14th Example. It is a flowchart for controlling vapor concentration in 14th Example. It is a figure which shows feedback correction coefficient FAF, vapor concentration FGPG, air fuel ratio A / F, etc. It is a flowchart for controlling vapor concentration in 15th Example. It is a flowchart for controlling vapor concentration in 15th Example. It is a figure which shows feedback correction coefficient FAF, vapor concentration FGPG, air fuel ratio A / F, etc. It is a flowchart for controlling the vapor concentration in the sixteenth embodiment. It is a flowchart for controlling the vapor concentration in the sixteenth embodiment. It is a flowchart of the 17th Example for controlling vapor concentration. It is a flowchart of the 17th Example for controlling vapor concentration. It is a flowchart of 18th Example for controlling a vapor | steam density | concentration. It is a flowchart of 18th Example for controlling a vapor | steam density | concentration. It is a figure which shows feedback correction coefficient FAF, vapor concentration FGPG, air fuel ratio A / F, etc. 6 is a flowchart for controlling a vapor concentration increase flag XVAPOR. It is a flowchart of another Example for controlling the vapor concentration increase flag XVAPOR.

Explanation of symbols

4 ... Fuel injection valve 5 ... Surge tank 11 ... Canister 17 ... Purge control valve 30 ... Air-fuel ratio sensor

Claims (14)

  A fuel vapor purge passage connecting the upper space of the fuel tank and the intake passage, a purge control valve disposed in the purge passage, an air-fuel ratio detection means for detecting the air-fuel ratio, and the air-fuel ratio detection means First supply fuel amount correction means for controlling the supply fuel amount so that the air-fuel ratio becomes the target air-fuel ratio based on the detected air-fuel ratio, and the amount of deviation of the air-fuel ratio with respect to the target air-fuel ratio is supplied into the intake passage. An internal combustion engine comprising vapor concentration calculation means for calculating the vapor concentration of the fuel vapor and second supply fuel amount correction means for correcting the supply fuel amount so that the air-fuel ratio becomes the target air-fuel ratio based on the vapor concentration In a fuel vapor processing apparatus for an engine, a change in fuel vapor vapor concentration is detected while the purge action is stopped in a fuel tank upper space or a purge passage extending from the fuel tank upper space to a purge control valve. Concentration change detection means is provided, and the second supply fuel amount correction means is a vapor concentration calculated by the vapor concentration calculation means so that the air-fuel ratio immediately after restarting the purge becomes the target air-fuel ratio according to the vapor concentration change. Is corrected by the vapor concentration calculating means when the vapor concentration of the fuel vapor in the upper space of the fuel tank or in the purge passage from the upper space of the fuel tank to the purge control valve increases when the purge action is stopped. A fuel vapor processing apparatus for an internal combustion engine that increases the vapor concentration.   2. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1, wherein the concentration change detecting means detects a vapor concentration change from a pressure in a purge passage extending from the fuel tank upper space or the fuel tank upper space to the purge control valve.   2. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1, wherein the concentration change detecting means detects a change in vapor concentration from the temperature in the fuel tank.   When the purge operation is started for the first time after the engine is started and then the purge action is stopped, the change in the vapor concentration is detected, and the vapor concentration calculated by the vapor concentration calculation means is corrected according to the change in the vapor concentration. The evaporative fuel processing apparatus of the internal combustion engine according to claim 1.   2. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1, wherein when the purge operation stop period is shorter than a predetermined period, correction of the vapor concentration by the second fuel supply amount correction means is prohibited.   A fuel vapor purge passage connecting the upper space of the fuel tank and the intake passage, a purge control valve disposed in the purge passage, an air-fuel ratio detection means for detecting the air-fuel ratio, and the air-fuel ratio detection means First supply fuel amount correction means for controlling the supply fuel amount so that the air-fuel ratio becomes the target air-fuel ratio based on the detected air-fuel ratio, and the amount of deviation of the air-fuel ratio with respect to the target air-fuel ratio is supplied into the intake passage. An internal combustion engine comprising vapor concentration calculation means for calculating the vapor concentration of the fuel vapor and second supply fuel amount correction means for correcting the supply fuel amount so that the air-fuel ratio becomes the target air-fuel ratio based on the vapor concentration In a fuel vapor processing apparatus for an engine, a change in fuel vapor vapor concentration is detected while the purge action is stopped in a fuel tank upper space or a purge passage extending from the fuel tank upper space to a purge control valve. Concentration change detection means is provided, and the first supply fuel amount correction means supplies fuel so that the air-fuel ratio becomes the target air-fuel ratio by a feedback correction coefficient that changes according to the air-fuel ratio detected by the air-fuel ratio detection means. The first supply fuel amount correction means controls the feedback correction coefficient value at the restart of purge so that the air-fuel ratio immediately after the restart of the purge becomes the target air-fuel ratio according to the change in the vapor concentration, When the vapor concentration of the fuel vapor in the upper space of the fuel tank or in the purge passage extending from the upper space of the fuel tank to the purge control valve increases when the purge action is stopped, the value of the feedback correction coefficient is determined in advance when purging is resumed. An evaporative fuel processing apparatus for an internal combustion engine that reduces the correction amount by a specified amount.   7. The evaporative fuel processing apparatus for an internal combustion engine according to claim 6, wherein the concentration change detecting means detects the vapor concentration change from the pressure in the purge passage extending from the fuel tank upper space or the fuel tank upper space to the purge control valve.   7. The evaporative fuel processing apparatus for an internal combustion engine according to claim 6, wherein the correction amount is increased as the pressure in the purge passage extending from the fuel tank upper space or the fuel tank upper space to the purge control valve when the purge is stopped.   The evaporated fuel processing apparatus for an internal combustion engine according to claim 6, wherein the correction amount is decreased as the vapor concentration calculated by the vapor concentration calculating means is higher.   The evaporated fuel processing apparatus for an internal combustion engine according to claim 6, wherein the correction amount is made smaller as the purge rate of the fuel vapor is smaller.   When the vapor concentration of the fuel vapor in the upper space of the fuel tank or in the purge passage extending from the upper space of the fuel tank to the purge control valve when the purge action is stopped, the value of the feedback correction coefficient is determined in advance when the purge is resumed. The evaporative fuel processing apparatus for an internal combustion engine according to claim 6, wherein the correction amount is decreased stepwise by a plurality of correction amounts.   When the purge action is stopped, when the vapor concentration of the fuel vapor in the upper space of the fuel tank or in the purge passage from the upper space of the fuel tank to the purge control valve increases, the above feedback is made until the air-fuel ratio becomes lean when the purge is resumed. The evaporated fuel processing device for an internal combustion engine according to claim 6, wherein the correction coefficient value is decreased stepwise by a predetermined correction amount a plurality of times.   When the vapor concentration of the fuel vapor in the fuel tank upper space or the purge passage from the fuel tank upper space to the purge control valve increases when the purge action is stopped, the purge execution time after the start of engine operation is predetermined. The purge rate of the fuel vapor is higher than a predetermined purge rate, or the opening of the purge control valve is larger than the predetermined opening, or the intake air amount is 7. The value of the feedback correction coefficient is decreased by a predetermined correction amount at the time of restarting the purge only when the amount is less than the predetermined amount or when the vapor concentration is updated more than the predetermined number. The evaporative fuel processing apparatus of the internal combustion engine described in 1.   When the purge action is stopped, when the vapor concentration of the fuel vapor in the fuel tank upper space or in the purge passage from the fuel tank upper space to the purge control valve increases, after the purge is restarted, the feedback correction is performed after a certain period of time. The evaporated fuel processing device for an internal combustion engine according to claim 6, wherein the coefficient value is decreased by a predetermined correction amount.

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