JPH0874684A - Evaporated fuel treatment device - Google Patents

Abstract

PURPOSE: To prevent the turbulence of an engine air-fuel ratio from being increased by purge gas from an evaporated fuel canister. CONSTITUTION: A control circuit 20, which performs feedback control of an engine air-fuel ratio according to outputs of an O2 sensor 31 provided in the exhaust line 3 of an engine 1, is provided. The control circuit 20 adjusts the opening of a purge control valve 15 controlling the flow rate of purge gas from a gaseous fuel canister 10, controls the purge rate of the purge gas based on the average value FAFAV of air-fuel ratio correction factors used in the air-fuel ratio feedback control, and inhibits the change of the purge rate if the difference between the air-fuel ratio correction factor average value FAFAV and the newest air-fuel ratio correction factor FAF is equal to or greater than a predetermined value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporated fuel processing apparatus for controlling the supply of purge gas from a canister that adsorbs evaporated fuel to an engine intake passage.

[0002]

2. Description of the Related Art In order to prevent vaporized fuel from a fuel tank of an internal combustion engine from being released into the atmosphere, the vaporized fuel is adsorbed to a canister, and purge air is passed through the canister during engine operation to be adsorbed from the canister. There is known an evaporative fuel treatment device that releases the above-mentioned fuel and supplies a mixture gas (purge gas) of purge air and the released fuel to an engine intake passage for combustion in the engine.

An example of this type of evaporated fuel processing device is disclosed in Japanese Patent Laid-Open No. 6-2591.
The apparatus of the publication is provided with a purge solenoid valve for controlling a purge rate (a ratio of a purge gas flow rate Q _PG and an engine intake air amount Q, Q _PG / Q) of a purge gas supplied from a canister to an engine intake passage. The opening degree (duty ratio) of the solenoid valve is controlled based on the average value of the feedback control values in the air-fuel ratio feedback control.

That is, in the device of the above publication, the engine air-fuel ratio is feedback-controlled to the target air-fuel ratio based on the output of the air-fuel ratio sensor arranged in the exhaust passage, and this feedback control value (FAF) increases in a skip manner or Each time it decreases, the average value of the FAF value immediately before the previous skip and the FAF value immediately before the current skip is calculated. Further, the purge rate is increased or decreased according to the magnitude of this FAF average value.

When the purge gas is introduced into the intake passage of the engine, the total amount of fuel supplied to the engine is increased by the evaporated fuel in the purge gas, so the engine air-fuel ratio shifts to the rich side by the supply of the purge gas. However, since the engine air-fuel ratio is controlled to the target air-fuel ratio by the feedback control, the air-fuel ratio shifted to the rich side comes to converge to the target air-fuel ratio by the feedback control. In this case, if the engine air-fuel ratio at the time of introducing the purge gas greatly deviates from the target air-fuel ratio, the deviation of the engine air-fuel ratio from the target air-fuel ratio further increases due to the introduction of the purge gas, and the time until it converges to the target air-fuel ratio becomes longer. There are cases.

The apparatus disclosed in the above publication judges the deviation of the engine air-fuel ratio from the target air-fuel ratio based on the FAF average value, and when this deviation is large, the purge rate is set small and the engine air-fuel ratio is affected by the purge gas. The deviation from the target air-fuel ratio is prevented from becoming large.

[0007]

However, if the purge rate is controlled on the basis of the FAF average value calculated for each FAF skip change as in the apparatus disclosed in Japanese Unexamined Patent Publication No. 6-2591, the reverse is true. The air-fuel ratio may be greatly disturbed. That is, in the device of the above publication, the engine air-fuel ratio is feedback-controlled with the theoretical air-fuel ratio as the target value.
FAF is increased or decreased in a skip manner when the engine reverses from the rich air-fuel ratio to the lean air-fuel ratio or from the lean air-fuel ratio to the rich air-fuel ratio. Therefore, when the engine air-fuel ratio periodically fluctuates between the rich air-fuel ratio and the lean air-fuel ratio, the average value of FAF is calculated and updated at an appropriate time interval, and the average value of FAF of the engine is calculated. The value corresponds to the air-fuel ratio.

However, when the engine air-fuel ratio is deviated to one of the lean side and the rich side, the FAF value is not updated because the inversion of the air-fuel ratio does not occur and it is calculated before the air-fuel ratio deviates. The average value will be retained. For example, when the engine is in the steady operation state and the throttle valve is fully closed to decelerate suddenly, the engine air-fuel ratio is greatly deviated from the stoichiometric air-fuel ratio to the rich side due to the rapid decrease in the engine intake air amount. . In such a state, the air-fuel ratio does not reverse, so the purge rate is calculated by FA calculated before the start of deceleration.
It will be controlled based on the average value of F. Therefore,
The purge rate may be increased depending on the FAF average value calculated before the start of deceleration, and the air-fuel ratio that has become rich due to deceleration may shift to the rich side, causing a problem that the disturbance of the air-fuel ratio increases.

In view of the above problems, the present invention has
An object of the present invention is to provide an evaporated fuel processing device capable of preventing an increase in the disturbance of the air-fuel ratio due to purge gas when the engine is operated in a state where the air-fuel ratio is deviated to the rich or lean side.

[0010]

According to the present invention, an air-fuel ratio sensor arranged in an exhaust passage of an internal combustion engine, and a correction coefficient calculation means for calculating an air-fuel ratio correction coefficient based on the output of the air-fuel ratio sensor, Means for controlling the amount of fuel supplied to the engine based on the air-fuel ratio correction coefficient, and the air-fuel ratio correction coefficient of the air-fuel ratio correction coefficient calculated by the correction coefficient calculation means each time the maximum value or the minimum value is reached. An average value calculating means for calculating an average value, a canister for adsorbing the evaporated fuel from the engine fuel tank, and an average value of the air-fuel ratio correction coefficient calculated by the average value calculating means from the canister to the engine intake passage Purge control means for controlling the purge rate of the supplied purge gas, the latest value of the air-fuel ratio correction coefficient calculated by the correction coefficient calculation means, and the average value calculation means The difference between the average value of the air-fuel ratio correction coefficient which is the inhibiting means for inhibiting the change of the purge rate by the purge control means when a predetermined value or more, the evaporated fuel processing apparatus having a city is provided.

[0011]

The average value calculating means reverses every time the air-fuel ratio correction coefficient reaches the maximum value or the minimum value, that is, the engine air-fuel ratio is reversed between the rich air-fuel ratio side and the lean air-fuel ratio side with respect to the target air-fuel ratio. Each time, the average value of the air-fuel ratio correction coefficient is calculated. Therefore, if the engine air-fuel ratio continues to deviate from the target air-fuel ratio to the rich air-fuel ratio side or lean air-fuel ratio side and the air-fuel ratio correction coefficient continues to increase or decrease, the value of the air-fuel ratio correction coefficient is updated. Instead, the average value calculated before the air-fuel ratio shift occurs is held as it is. Therefore, the difference between the held average value and the latest value of the air-fuel ratio correction coefficient gradually increases.

The prohibiting means sets the predetermined value based on the current engine air-fuel ratio when the difference between the average value and the latest value of the air-fuel ratio correction coefficient exceeds a predetermined value. When the state is out of the range, changing the purge rate of the canister is prohibited.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall view showing the configuration when the evaporated fuel processing device of the present invention is applied to a vehicle internal combustion engine. In FIG. 1, 1 is an internal combustion engine body, 2 is an intake passage, and 3 is an exhaust passage.

The intake passage 2 is provided with, for example, a vane type air flow meter 4 for directly measuring the intake air amount. The air flow meter 4 has a built-in potentiometer, for example, and generates an analog voltage output signal proportional to the intake air amount. In addition, 6 is shown in FIG.
A throttle valve provided in the intake passage, which opens and closes in response to the driver's operation of the accelerator pedal to control the intake air amount of the engine 1.

Further, in this embodiment, the throttle valve 6 is provided with an idle switch 8 which outputs an idle signal (LL signal) when the throttle valve is fully closed. The LL signal from the idle switch 8 is supplied to the input port of the control circuit 20 described later. Reference numeral 10 in FIG. 1 is a canister for adsorbing the evaporated fuel from the fuel tank 11 of the engine. The canister 10 is connected to the upper space of the fuel tank 11 via a passage 12, and the evaporated fuel in the tank is adsorbent 13 such as activated carbon in the canister 10.
Adsorb to. The canister 10 is connected to a portion of the intake passage 2 downstream of the throttle valve 6 by a purge passage 14 having a purge control valve 15. Purge control valve 15
Is opened during engine operation, and the evaporated fuel adsorbed by the adsorbent of the canister 10 is purged into the intake passage 2. That is, when the purge control valve 15 is opened, negative pressure on the downstream side of the throttle valve 6 in the intake passage 2 acts in the canister 10, so that the purge air inlet 16 provided in the canister 10 is provided.
Air flows into the canister. The purge air removes the evaporated fuel adsorbed by the adsorbent 13, becomes a purge gas containing the evaporated fuel, flows into the engine intake passage 2 from the purge passage 14, and burns in the engine combustion chamber. This prevents the adsorbent 13 from being saturated with the evaporated fuel.

The purge control valve 15 is an electromagnetic valve having a solenoid actuator, and the engine control circuit 2 described later is used.
By controlling the duty ratio of the drive pulse of the solenoid (the ratio of the ON / OFF total time of the drive current to the ON time of the drive current) by 0, the amount of the purge gas passing through the purge control valve 15 is adjusted. In the present embodiment, as will be described later, the control circuit 20 sets the purge gas rate, that is, the ratio of the purge gas flow rate Q _PG and the engine intake air amount Q (Q _PG / Q) according to the engine air-fuel ratio, and the air flow is set. From the value of the engine intake air amount Q detected by the meter 4, the opening degree of the purge control valve 15 (driving pulse duty ratio) required to obtain the purge rate is set.

As a result, even if the engine intake air amount fluctuates, the ratio of the purge gas flow rate Q _PG to the engine intake air amount Q is kept constant, so that the engine air-fuel ratio is prevented from largely fluctuating due to the purge gas. The purge control valve 1
5 is not limited to the solenoid valve, but any type that can control the flow rate of the purge gas according to the control signal of the control circuit 20 can be used in the present invention.

1 is a fuel injection valve for injecting pressurized fuel from an engine fuel pump (not shown) into the intake port of each cylinder of the engine 1. The fuel injection valve 7 opens in response to a control signal from the engine control circuit 20, and supplies fuel in an amount proportional to the valve opening time to the engine intake port.
Further, the engine exhaust passage 3 is provided with an O ₂ sensor 31 and a catalytic converter 35 downstream thereof. Catalytic converter 35 has a built-in three-way catalyst, has an exhaust air-fuel ratio NO _X in the exhaust gas in the case of near stoichiometric air-fuel ratio, HC, the ability to simultaneously purify three components of CO. Further, the O ₂ sensor 31 detects the oxygen concentration in the exhaust gas and generates an output voltage according to whether the exhaust air-fuel ratio is greater than the theoretical air-fuel ratio (lean side) or smaller (rich side). . In this embodiment,
The output of the O ₂ sensor 31 is supplied to the engine control circuit,
The air-fuel ratio of the engine is feedback-controlled to the stoichiometric air-fuel ratio based on the output of the O ₂ sensor 31.

Reference numeral 32 in FIG. 1 denotes a rotation speed sensor provided in the distributor of the engine 1. The rotation speed sensor 32 generates a pulse signal having a frequency according to the engine crankshaft rotation speed. An engine control circuit 20 shown in FIG. 1 includes a ROM (read only memory) 22, a RAM (random access memory) 23, a CPU (microprocessor) which are interconnected by a bidirectional bus 21.
24, an input port 25, and an output port 26.

The control circuit 20 performs basic control such as fuel injection control and engine speed control of the engine, and in the present embodiment, the purge ratio is adjusted by adjusting the duty ratio of the drive pulse of the purge control valve 15 as described later. Purge control for controlling For controlling these, the input port 2 of the control circuit 20
5, the outputs of the air flow meter 4 and the O ₂ sensor 31 are input via an AD converter 27 with a built-in multiplexer, and a signal representing the engine cooling water temperature or the like is input from a sensor (not shown) via the AD converter 27. Has been entered. Further, the rotation speed pulse of the rotation speed sensor 32 is input to the input port 25 of the control circuit 20 in order to calculate the engine rotation speed.

The output port of the control circuit 20 has a fuel injection valve 7 and a purge control valve 1 via a drive circuit (not shown).
5 and the fuel injection amount and the purge control valve 1 respectively.
The opening degree of 5 is controlled. Next, the engine air-fuel ratio control, which is the premise of the purge control of this embodiment, will be described with reference to FIGS. 2 and 3. In this embodiment, the fuel injection valve 7 of FIG.
The fuel injection amount TAU from is set by the control circuit 20 as follows.

That is, the control circuit 20 calculates the fuel injection amount TAU by the following equation using the intake air amount Q and the engine speed NE at a constant crank rotation angle (for example, every one rotation of the crankshaft). TAU = {α × (Q / NE) × β} × FAF + γ where Q / NE is the intake air amount per engine revolution. α is a predetermined constant and α × (Q / N
E) represents the fuel injection amount required to obtain the stoichiometric air-fuel ratio. Further, β and γ are correction coefficients set according to the engine operating state, and FAF is an air-fuel ratio correction coefficient set according to the output of the O ₂ sensor 31 in the exhaust passage, as described later. When the fuel injection amount TAU is calculated as described above, the control circuit 20 drives the fuel injection valve 7 to open for a time corresponding to TAU through a drive circuit (not shown), and
Is injected into the intake port of each cylinder. That is, if the operating conditions are the same, the fuel supply amount (air-fuel ratio) of the engine changes according to the value of the air-fuel ratio correction coefficient FAF.

2 and 3 are flowcharts showing a routine for calculating the air-fuel ratio correction coefficient FAF. In this routine, the air-fuel ratio correction coefficient FAF is determined so that the engine air-fuel ratio is feedback-controlled to the target value (theoretical air-fuel ratio) based on the output of the O ₂ sensor 31. This routine is executed by the control circuit 20 at regular intervals (for example, every 4 ms).

When the routine starts in FIG. 2,
In step 201, it is judged whether or not the closed loop (feedback) condition of the air-fuel ratio by the O ₂ sensor 31 is satisfied. For example, when the cooling water temperature is below a predetermined value,
The closed loop condition is not satisfied during engine startup, and the closed loop condition is satisfied in other cases. When the closed loop condition is not established, the value of the air-fuel ratio correction coefficient FAF is set to 1.0 in step 230 of FIG. 3 and the routine is ended as it is. When the closed loop condition is satisfied in step 201, the process proceeds to step 202.

In step 202, the output V ₁ of the O ₂ sensor 31 is A / D converted and taken in, and then in step 2
In 03, it is determined whether or not V ₁ is less than or equal to the comparison voltage V _R1 , for example, 0.45 V or less, that is, whether or not the air-fuel ratio is lean. If the air-fuel ratio is lean (V ₁ ≦ V _R1 ), the routine proceeds to step 204, where it is judged if the delay counter CDLY is negative. If CDLY> 0, then at step 205, CDLY is set to 0, and then at step 206 Proceed to. In step 206, the delay counter CDLY is decremented by 1, and in steps 207 and 208, the delay counter CDLY is guarded by the minimum value TDL. in this case,
When the delay counter CDLY reaches the minimum value TDL, the air-fuel ratio flag F1 is set to "0" (lean) in step 209. The minimum value TDL is a negative value.

On the other hand, if rich (V ₁ > V _R1 ), in step 210 the delay counter CDLY
Is determined to be positive. If CDLY <0, then in step 211 CDLY is set to 0, and then step 212
Proceed to. In step 212, the delay counter CDLY
Is incremented by 1, and the delay counter CDLY is guarded by the maximum value TDR in steps 213 and 214. In this case, when the delay counter CDLY reaches the maximum value TDR, the air-fuel ratio flag F is determined in step 215.
1 is set to "1" (rich). The maximum value TDR is a positive value.

Next, at step 216 in FIG. 3, the air-fuel ratio flag F1 is inverted ("0" → "1" or "1" →
It is determined whether or not it has changed to "0". When the air-fuel ratio flag F1 is inverted, it is determined in step 217 whether the air-fuel ratio is changed from rich to lean or lean to rich, depending on the value of the air-fuel ratio flag F1. If it is the inversion from rich to lean, in step 218 the current FAF value is changed to the FAF value immediately before the rich skip (FAFS).
After being stored in the RAM 23 as R), the current FAF value is skippedly increased to FAF + RSR in step 220. On the contrary, if it is the reverse from lean to rich, the current FAF value is stored in the RAM 23 as the FAF value (FAFSL) immediately before the lean skip in step 219, and then the current FAF value is FAF-.
RSL and skip decrease.

That is, in steps 220 and 221, skip processing of the air-fuel ratio correction coefficient is performed. In addition, each time any skip processing is executed by executing steps 218 and 219, the FAF value immediately before the skip processing is stored as FAFSR and FAFSL. As will be described later, the values of FAFSR and FAFSL represent the minimum value and the maximum value of the periodic fluctuation of FAF, respectively.

When the skip processing in either of steps 220 and 221 is performed, in step 222, F
The average value FAFV of AF is calculated as the arithmetic mean (FAFSR + FAFSL) / 2 of FAFSR and FAFSL, and stored in the RAM 23. That is, step 22
In 2, the average value FAFAV of the latest minimum value and maximum value of the air-fuel ratio correction coefficient FAF is calculated every time the skip processing of steps 220 and 221 is executed.

When the sign of the air-fuel ratio club F1 is not reversed in step 816, steps 223 and 22 are executed.
In 4, 225, integration processing is performed. Step 22
In 3, it is determined whether or not F1 = "0", and F1 =
If “0” (lean), FA is executed in step 224.
If F is set to FAF + KIR and F1 = "1" (rich), FAF is FAF-KIL in step 225.
It is said. Here, the integration constants KIR and KIL are set sufficiently smaller than the skip amounts RSR and RSL.

Steps 220, 221, 224, 225
The air-fuel ratio correction coefficient FAF calculated in
26,227 are guarded at a minimum value, eg 0.8, and at steps 228,229 are guarded at a maximum value, eg 1.2. This prevents the air-fuel ratio correction coefficient FAF from becoming too large or too small for some reason.

In the above air-fuel ratio control, the delay time TD
L and TDR are provided to prevent the air-fuel ratio correction coefficient FAF from being corrected by a temporary fluctuation of the O ₂ sensor output 31 for a short time, and are empty only when the lean state or the rich state continues for a predetermined time. Reverse the fuel ratio flag F1 (0 →
1 or change from 1 to 0). That is, the air-fuel ratio state (rich / lean) represented by the air-fuel ratio flag F1 is stable with respect to short-term fluctuations in the output of the O ₂ sensor 31.

Further, as described above, the air-fuel ratio correction coefficient FAF
Is decreased when the air-fuel ratio flag F1 is in the rich state and is increased when the air-fuel ratio is in the lean state, and the fuel injection amount is increased or decreased so that the engine air-fuel ratio approaches the stoichiometric air-fuel ratio. FIG.
Is the engine air-fuel ratio when the above control is executed (Fig. 4 (A)
), Air-fuel ratio flag F1 (FIG. 4 (B)), air-fuel ratio correction coefficient FAF (solid line in FIG. 4 (C)) and average value FAFV (FIG. 4 (C)).
It is a figure explaining the change in a steady operation of a dotted line. As shown in FIG. 4, the air-fuel ratio flag F1 (FIG. 4 (B)) indicates that the engine air-fuel ratio (FIG. 4 (A)) has changed from lean air-fuel ratio to rich air-fuel ratio or from rich air-fuel ratio to lean air-fuel ratio. After a lapse of a predetermined time (TDR, TDL), it changes from 0 to 1 or from 1 to 0, and the air-fuel ratio correction coefficient FAF (solid line in FIG. 4 (C)) changes the air-fuel ratio flag F1 from 0 to 1 or from 1 to 0. It is increased / decreased in a skip manner for each time. That is, the FAF value immediately before each skip (FIG. 4 (C), FAFSR, FAF
SL) represents the maximum value and the minimum value, respectively, during the fluctuation cycle of FAF.

Further, as shown by the dotted line in FIG. 4 (C), the average value FAFAV of the air-fuel ratio correction coefficient is the FAF value (FA
FSL or FAFSR) and F just before executing this time skip
Calculated as the arithmetic mean of the AF values (FAFSR or FAFSL). Therefore, after the skip processing is executed, FAFAV is executed until the next skip processing is executed.
The value of is not updated.

As shown in FIG. 4, when the engine is operating in a stable steady state, the engine air-fuel ratio is relatively short with respect to the stoichiometric air-fuel ratio on the lean side and the rich side (for example, 1 Air-fuel ratio correction factor FA
The value of F fluctuates, and the average value FAFAV of the air-fuel ratio correction coefficient becomes close to 1.0. In such cases, FAFA
Since the value of V becomes a value corresponding to the average air-fuel ratio of the engine, by adjusting the purge rate of the purge gas according to the value of FAFV as described later, the engine air-fuel ratio becomes larger than the theoretical air-fuel ratio due to the influence of the purge gas. It is prevented from coming off.

However, the air-fuel ratio correction coefficient average value FAFAV may not always be a value corresponding to the average air-fuel ratio of the engine except in steady operation of the engine. For example, when the engine started to decelerate from steady operation, or after racing (idling) during idle operation, a sudden decrease in intake air amount and adhesion to the intake port wall surface due to intake negative pressure increase The engine air-fuel ratio shifts to the rich side from the theoretical air-fuel ratio due to fuel vaporization and the like. Even in such a case, FIG. 2 and FIG.
By the air-fuel ratio feedback control of No. 3, the engine air-fuel ratio is corrected to near the stoichiometric air-fuel ratio after a certain amount of time, and the inversion is repeated cyclically between the rich air-fuel ratio and the lean air-fuel ratio. However, the average value FAFAV of the air-fuel ratio correction coefficient is not updated until the engine air-fuel ratio is corrected to near the stoichiometric air-fuel ratio and the inversion of the air-fuel ratio occurs, and before the engine air-fuel ratio shifts to the rich air-fuel ratio. The calculated value will be retained as it is.

FIG. 5 shows the engine air-fuel ratio (FIG. 5A) when the engine air-fuel ratio deviates to the rich side as described above, and the air-fuel ratio flag F.
5 is a view similar to FIG. 4, showing changes in 1 (FIG. 5 (B)), air-fuel ratio correction coefficient FAF (solid line in FIG. 5 (C)), and average value FAFAV (dotted line in FIG. 5 (D)). As shown in FIGS. 5 (A) and 5 (B),
When the engine air-fuel ratio shifts to the rich side and the value of F1 remains unchanged at 1, the value of the air-fuel ratio correction coefficient FAF becomes as shown in the solid line in FIG.
The guard value (0.
Continue to decrease until reaching 8).

On the other hand, since the value of the flag F1 is not inverted,
During this period, the average value FAFAV of the air-fuel ratio correction coefficient is not updated, and the value FAFAV before the air-fuel ratio shifts to the rich side is retained as it is. For this reason, FAFA
The value of V no longer corresponds to the air-fuel ratio of the engine, and if the purge rate is controlled based on this FAFAV value,
Although the engine air-fuel ratio is significantly rich, the purge rate is increased and the deviation of the engine air-fuel ratio from the theoretical air-fuel ratio becomes large. As described above, if the operation continues in a state where the engine air-fuel ratio greatly deviates from the stoichiometric air-fuel ratio, the catalytic converter 35 has a problem that the exhaust gas purification capability is reduced, and particularly emissions of HC, CO and the like increase.

In this embodiment, the control circuit 20 has a configuration shown in FIGS.
The latest value of the air-fuel ratio correction coefficient FAF calculated by the routine is compared with the average value FAFAV, and if the difference between these two values exceeds a predetermined value, FAFAV becomes the engine air-fuel ratio. When it is judged that it is no longer compatible, it is prohibited to change the purge rate of the purge gas. As a result, the purge rate is controlled to be increased or decreased based on the value of FAFAV that does not correspond to the actual engine air-fuel ratio, which prevents the disturbance of the air-fuel ratio from increasing.

FIG. 6 is a flow chart for explaining the purge control operation of this embodiment. This routine is executed by the control circuit 20 at regular time intervals (for example, every 4 ms).
When the routine starts in FIG. 6, step 60
At 1, the values of the air-fuel ratio correction coefficient FAF and the average value FAFAV stored in the RAM 23 are read. Since this routine is executed at the same time intervals (4 ms in this embodiment) as the routines of FIGS. 2 and 3, the FAF value read in step 601 is calculated by the routines of FIGS. 2 and 3. The FAFAV value is the latest value when the skip processing was executed last time.

Next, at step 603, it is determined whether the engine is in the idle state (the throttle valve 6 is fully closed) based on whether the output signal (LL signal) of the idle switch 8 is on. If the engine is not in the idle state, the average value FAFA of the air-fuel ratio correction coefficient is calculated in step 607.
It is determined whether V is in the range of 0.95 to 1.1, and if FAFAV is in this range, step 60
In 9, the purge rate PGR is the value PGR at the time of the previous routine execution.
_{From i-1} to a predetermined value ΔPGR (for example, ΔPGR = 0.005)
%). After the step 609 is completed, the purge rate PGR is set to the maximum value PG in steps 611 and 613.
R _MAX guards to prevent unlimited purging rate. In this embodiment, the maximum purge rate PGR _MAX
Is about 5%.

If FAFAV is not within the above range in step 607, the purge rate PGR is not changed and the routine is ended. In this embodiment, the purge rate is changed only when the average value FAFAV of the air-fuel ratio correction coefficient is within the range of 0.95 ≦ FAFAV ≦ 1.1. Value (0.8 ≦ FAF ≦ 1.
2) is provided and the speed of correction of the engine air-fuel ratio to the stoichiometric air-fuel ratio by execution of the air-fuel ratio control routine of FIGS. 2 and 3 is limited, so purging is performed when the FAFAV value is outside the above range. This is because if the ratio is increased, it may not be possible to correct the effect of introducing the purge gas by the air-fuel ratio control routine.

On the other hand, if it is determined at step 603 that the engine is not in the idle state, then the routine proceeds to step 605, at which the air-fuel ratio correction coefficient average value FAFAV calculated at the previous skip processing and the latest FAF are calculated. It is determined whether or not the absolute value of the difference from the value is less than or equal to a predetermined value (0.1 in this embodiment). If this difference is greater than or equal to a predetermined value, the average value FAF
Since it is considered that the value of AV does not correspond to the air-fuel ratio of the engine, the purge rate PGR is not updated and the routine is ended as it is. If the difference between FAFAV and FAF is within the predetermined range, step 607 and thereafter are executed to change the purge rate PGR based on the value of FAFAV.

In this embodiment, whether or not the purge rate can be changed is determined based on the difference between FAFAV and FAF only when the engine is in the idle state (steps 601 and 605).
When decelerating with the throttle valve fully closed, the engine air-fuel ratio may shift to the rich side as described above, and with the throttle valve fully closed, the engine air-fuel ratio fluctuation cycle (skip processing This is because the FAFAV update interval becomes longer and the FAFAV may not correspond to the engine air-fuel ratio in some cases. Needless to say, the determination in step 605 may be performed to determine whether the purge rate can be updated regardless of whether the engine is in the idle state.

According to this embodiment, as described above, FAFA
When the value of V no longer corresponds to the actual engine air-fuel ratio, updating of the purge ratio is prohibited, so that, for example, during engine deceleration, during idle operation after racing, idle operation and running are frequently repeated. It is possible to prevent the air-fuel ratio from being greatly disturbed by the purge gas during a traffic jam or the like.

[0046]

According to the present invention, the difference between the value of the air-fuel ratio correction coefficient average value FAFAV and the latest value of the air-fuel ratio correction coefficient FAF becomes larger than a predetermined value, and the average value FAFAV becomes the actual air-fuel ratio of the engine. When the fuel ratio is no longer reflected, the update of the purge rate is prohibited, so that the disturbance of the air-fuel ratio due to the influence of the purge gas is prevented from increasing.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of an internal combustion engine for a vehicle to which an evaporated fuel processing device of the present invention is applied.

2 is a part of a flowchart illustrating an air-fuel ratio control operation of the internal combustion engine of FIG.

FIG. 3 is a part of a flowchart illustrating an air-fuel ratio control operation of the internal combustion engine of FIG.

FIG. 4 is a timing diagram that supplementarily describes the air-fuel ratio control of FIGS. 2 and 3.

FIG. 5 is a timing diagram for supplementarily explaining the air-fuel ratio control of FIGS. 2 and 3.

6 is a flow chart illustrating a purge control operation of the embodiment of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine body 2 ... Intake passage 7 ... Fuel injection valve 10 ... Canister 11 ... Fuel tank 15 ... Purge control valve 20 ... Control circuit 31 ... O ₂ sensor 31

Claims (1)

[Claims] 1. An air-fuel ratio sensor arranged in an exhaust passage of an internal combustion engine, a correction coefficient calculating means for calculating an air-fuel ratio correction coefficient based on the output of the air-fuel ratio sensor, and an engine based on the air-fuel ratio correction coefficient. Means for controlling the amount of fuel to be supplied, and an average value calculating means for calculating an average value of the air-fuel ratio correction coefficient each time the air-fuel ratio correction coefficient calculated by the correction coefficient calculation means reaches a maximum value or a minimum value. Controlling the purge rate of the purge gas supplied from the canister to the engine intake passage based on the canister that adsorbs the evaporated fuel from the engine fuel tank and the average value of the air-fuel ratio correction coefficient calculated by the average value calculating means. Purge control means, the latest value of the air-fuel ratio correction coefficient calculated by the correction coefficient calculation means, and the average of the air-fuel ratio correction coefficient calculated by the average value calculation means And a prohibition means for prohibiting the purge rate from being changed by the purge control means when the difference from the value is a predetermined value or more.