JPH07305645A - Air-fuel ratio controller of engine - Google Patents

Abstract

PURPOSE:To diminish turbulance of air-fuel ratio after the valve closing operation of a purge valve means so as to prevent deterioration of exhaust emission and a torque shock by stepwise changing a feedback correction coefficient to an initial value during the valve closing operation of the purge valve means without depending on feedback control. CONSTITUTION:Basic fuel supply quantity Tp is calculated in a control unit 21 based on operation conditions detected from various sensors during the operation of an engine, and also target air-fuel ratio is set, then a feedback correction coefficient Q is calculated according to difference between air-fuel ratio detected by an O2 sensor 27 and the target air-fuel ratio. The basic fuel supply quantity Tp is corrected by the feedback correction coefficient alpha so that fuel supply quantity T is calculated and an injector 15 is drivingly controlled. Also at this time, the valve closing operation period for the purge valve 9 is detected, and the feedback correction coefficient alpha is set to an initial value alpha1 during the valve closing operation period of the purge valve 9 so that the turbulance of the air-fuel ratio after the valve closing operation of the purge valve 9 is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine air-fuel ratio controller.

[0002]

2. Description of the Related Art In automobiles and the like, in order to prevent the fuel evaporated in a fuel tank from being released into the atmosphere, the evaporated fuel is adsorbed by activated carbon in a canister when the engine is stopped, Under these operating conditions, the purge cut valve is opened to connect the canister to the intake passage, and the negative intake pressure developed during engine operation is used to separate the vaporized fuel from the activated carbon in the canister by the outside air introduced into the canister. Some include an evaporated fuel processing device that is configured to guide the fuel to the intake passage.

Further, an air-fuel ratio control device provided in a conventional engine adds or subtracts an air-fuel ratio correction control coefficient composed of a proportional control component and an integral control component to a feedback correction coefficient α based on the detected actual air-fuel ratio. To correct the fuel amount,
The air-fuel ratio is designed to be close to the target value (Japanese Patent Laid-Open No. Sho 6).
No. 4-36941, reference).

[0004]

By the way, in the case of the conventional device, the feedback control for such an air-fuel ratio is performed as shown in FIG. 21, as the response speed of the feedback correction coefficient α is changed as the purge cut valve is opened and closed. Due to the influence, there is a problem that the actual air-fuel ratio is temporarily disturbed, which causes deterioration of exhaust emission and torque shock.

For example, in the operating state in which the purge cut valve is opened and the evaporated fuel is introduced into the intake passage, the feedback correction coefficient α becomes considerably smaller than 100%, and the fuel injection amount T is corrected to be reduced. is doing. When the purge cut valve is closed from this operating state and the vaporized fuel introduced into the intake passage is shut off, the feedback correction coefficient α approaches 100% by the above feedback control, but the feedback correction coefficient It takes time to return the coefficient α to around 100%, and the actual air-fuel ratio temporarily becomes lean during this time.

Further, in the operating state in which the purge cut valve is closed and the vaporized fuel introduced into the intake passage is shut off,
The feedback correction coefficient α is maintained near a value of 100% to reduce the increase / decrease range of the fuel injection amount T. When the purge cut valve is opened from this operating state and the introduction of the evaporated fuel into the intake passage is started, the feedback correction coefficient reduces the feedback correction coefficient α from 100% by the PI control, but the feedback correction coefficient It takes time to reduce the correction coefficient α by the feedback control, and the actual air-fuel ratio becomes temporarily rich during this time.

Therefore, an object of the present invention is to suppress the disturbance of the air-fuel ratio which occurs during the opening / closing operation of the purge cut valve or the like.

[0008]

As shown in FIG. 22, an engine air-fuel ratio control apparatus according to a first aspect of the present invention includes a canister b for adsorbing fuel evaporated in a fuel tank a and an intake passage d for the canister b. A purge passage e communicating with the engine, a purge valve means f for opening and closing the purge passage e according to the operating condition of the engine c, an operating condition detecting means g for detecting the operating condition of the engine c, and a operating condition detecting means g for detecting the operating condition. And a basic fuel supply amount calculating means h for calculating the basic fuel supply amount Tp,
The target air-fuel ratio setting means i for setting the target air-fuel ratio according to the detected operating conditions, the air-fuel ratio detecting means j for detecting the air-fuel ratio of the engine c, and the difference between the detected air-fuel ratio and the target air-fuel ratio Feedback correction coefficient detection means k for calculating the feedback correction coefficient α in accordance therewith, fuel supply amount calculation means 1 for calculating the fuel supply amount T by correcting the calculated basic fuel supply amount Tp by the feedback correction coefficient α, and And a fuel supply means (m) for supplying the supplied fuel supply amount (T) to the engine.
And a feedback correction for setting the feedback correction coefficient α to an initial value α ₁ when the purge valve means f is closed. And coefficient setting means o.

As shown in FIG. 23, an engine air-fuel ratio control apparatus according to a second aspect of the present invention includes a feedback correction coefficient storage means p for storing a feedback correction coefficient αm in the open state of the purge valve means f, and the purge valve. A valve opening operation detecting means q for detecting the valve opening operation of the means f from the valve closed state to the valve opening state, and a feedback correction coefficient αm for storing the feedback correction coefficient α when the purge valve means f is opened. And a feedback correction coefficient setting means r set to.

The air-fuel ratio control apparatus for an engine according to a third aspect of the present invention, as shown in FIG. 24, detects the closing operation of the purge valve means f to detect the closing operation from the open state to the closed state. Means n, a feedback correction coefficient storage means p for storing the feedback correction coefficient αm stored in the open state of the purge valve means f, and the feedback correction coefficient α when the purge valve means f is closed. Feedback correction coefficient α stored in the valve open state of
If H is a constant based on m and the initial value α ₁ , α = α ₁
Feedback correction coefficient setting means s for setting a value calculated as + (αm−α ₁ ) H.

As shown in FIG. 25, an engine air-fuel ratio control apparatus according to a fourth aspect of the present invention includes feedback correction coefficient storage means p for storing the feedback correction coefficient αm stored when the purge valve means f is open. When the purge valve means f detects the opening operation of the purge valve means f from the closed state to the open state, the feedback correction coefficient α when the purge valve means f is opened If H is a constant based on the stored feedback correction coefficient αm and the initial value α ₁ , α = α ₁ + (αm−α ₁ ) H
Feedback correction coefficient setting means t for setting the value calculated as

[0012] As shown in Fig. 26, the air-fuel ratio control apparatus for an engine according to claim 5 is a purge actuation detecting means for detecting the start of purge or the end of purge for gradually changing the opening of the purge valve means f. x, a leak diagnosis detection means y for detecting a leak diagnosis time when the opening degree of the purge valve means f is rapidly changed, and an air-fuel ratio is feedback-controlled during the purge operation, while the purge valve means f during the leak diagnosis time.
Feedback correction coefficient correction means z for forcibly correcting the feedback correction coefficient α when the valve is operated.

[0013]

The air-fuel ratio control device for an engine according to claim 1 is
When the purge valve means f is closed, the feedback correction coefficient α is changed to the initial value α ₁ stepwise without feedback control, so that the disturbance of the air-fuel ratio that occurs after the purge valve means f is closed is suppressed to a small level. To be By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

According to another aspect of the air-fuel ratio control apparatus for an engine of the present invention, the feedback correction coefficient α is set to the memory value αm of the feedback correction coefficient stored in the open state of the purge valve means f when the purge valve means f is opened. By making a step-like change regardless of the feedback control, the disturbance of the air-fuel ratio that occurs after the opening operation of the purge valve means f can be suppressed to a small level. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

In the engine air-fuel ratio control apparatus according to the third aspect, the feedback correction coefficient α is feedback-controlled by the calculated correction amount α ₁ + (α _m −α ₁ ) H when the purge valve means f is closed. After making a step-like change, the remaining correction amount (α _m −α ₁ ) H is set by feedback control to reduce the disturbance of the air-fuel ratio caused by overshoot after the closing operation of the purge valve means f. It can be suppressed. By further suppressing the disturbance of the air-fuel ratio, the effect of suppressing exhaust emission and torque shock can be enhanced.

In the air-fuel ratio control apparatus for the engine according to the fourth aspect, the feedback correction coefficient α is feedback-controlled by the calculated correction amount α ₁ + (α _m -α ₁ ) H when the purge valve means f is opened. After making a stepwise change, the remaining correction amount (α _m −α ₁ ) H is set by feedback control to reduce the disturbance of the air-fuel ratio caused by overshoot after the opening operation of the purge valve means f. It can be suppressed. By further suppressing the disturbance of the air-fuel ratio, the effect of suppressing exhaust emission and torque shock can be enhanced.

According to a fifth aspect of the present invention, there is provided an air-fuel ratio control system for an engine according to the difference between the detected air-fuel ratio and the target air-fuel ratio at the start of purging or the end of purging for gradually changing the opening of the purge valve means f. By calculating the feedback correction coefficient α by using the feedback correction coefficient α, the actual air-fuel ratio can be made to follow the target air-fuel ratio with sufficient responsiveness, and exhaust emission can be prevented from deteriorating.

On the other hand, at the time of leak diagnosis in which the opening degree of the purge valve means f is suddenly changed, the feedback correction coefficient α is forcibly corrected when the purge valve means f is closed or opened, so that the purge valve The disturbance of the air-fuel ratio that occurs after the valve closing operation or the valve opening operation of the means f can be suppressed to a small level. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an injector 15 for injecting fuel is installed in the intake passage 8. In order to control the fuel injection amount Te from the injector 15, the control unit 21, which is a microcomputer, includes the intake air amount Q detected by the air flow meter 26 and the reference position of the crank angle detected by the engine speed sensor 25. The basic fuel injection is performed by inputting the Ref signal and the signal for each unit crank angle (every 180 ° for a 4-cylinder engine, every 120 ° for a 6-cylinder engine), the cooling water temperature TW detected by the cooling water temperature sensor 24, and the like. The amount Tp is calculated according to the operating state.

An O ₂ sensor 27 for detecting the oxygen concentration in the exhaust is installed in the exhaust passage 10. The control unit 21 inputs the output VO ₂ according to the oxygen concentration in the exhaust gas detected by the O ₂ sensor 27, and feedback-controls the fuel injection amount Te so that the air-fuel mixture has the stoichiometric air-fuel ratio, and exhausts the exhaust gas. The conversion efficiency of the three-way catalyst (not shown) installed in the middle of the passage 10 is kept to the maximum.

The air-fuel ratio control by the control unit 21 is as follows.

The fuel injector 15 is driven in synchronization with the Ref signal. For example, in the sequential injection method, once every two engine revolutions, for each cylinder Ti = 2 × Te + Ts (1) where Te: effective pulse width Ts: injection pulse given by the formula of invalid pulse width according to battery voltage Injector 15 with width Ti
Is activated. In the case of the simultaneous injection method, the engine 1
Once every rotation, all the cylinders simultaneously Ti = Te + Ts The injector 15 with the injection pulse width Ti given by the equation (2)
Is activated.

FIG. 2 is a flow chart for calculating the effective pulse width Te of the above equation (1), which is executed at a constant cycle (for example, 10 msec).

In step 1, the basic pulse width Tp is calculated from the air flow rate Q detected by the air flow meter 26 and the engine speed N detected by the crank angle sensor 27 as follows: Tp = (Q / N) × K (3) where K : Calculate with a constant formula. The air-fuel ratio determined by this Tp is called the base air-fuel ratio.

In step 2, the effective pulse width Te is calculated by using the basic pulse width Tp: Te = Tp × Co × (α + α _M -1) (4) where Co: various correction coefficients α: air-fuel ratio feedback correction coefficient [ %] Α _M : Calculated by the formula of air-fuel ratio learning value [%].

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an injector 15 for injecting fuel is installed in the intake passage 8. In order to control the fuel injection amount Te from the injector 15, the control unit 21 includes the intake air amount Q detected by the air flow meter 26 and the reference position of the crank angle detected by the engine speed sensor 25 (four-cylinder engine). Then 18
Ref every 0 °, every 120 ° for a 6 cylinder engine)
The signal, the signal for each unit crank angle, the cooling water temperature TW detected by the cooling water temperature sensor 24, etc. are input, and the basic fuel injection amount Tp is calculated according to the operating state.

An O ₂ sensor 27 for detecting the oxygen concentration in the exhaust is installed in the exhaust passage 10. The control unit 21 composed of a microcomputer outputs an output V corresponding to the oxygen concentration in the exhaust gas detected by the O ₂ sensor 27.
By inputting O ₂ and performing feedback control of the fuel injection amount Te so that the air-fuel mixture has a stoichiometric air-fuel ratio, the conversion efficiency of a three-way catalyst (not shown) installed in the middle of the exhaust passage 10 is maximized. It is supposed to do.

The air-fuel ratio control by the control unit 21 is as follows.

The fuel injector 15 is driven in synchronization with the Ref signal. For example, in the sequential injection method, once every two engine revolutions, for each cylinder Ti = 2 × Te + Ts (1) where Te: effective pulse width Ts: injection pulse given by the formula of invalid pulse width according to battery voltage Injector 15 with width Ti
Is activated. In the case of the simultaneous injection method, the engine 1
Once every rotation, all the cylinders simultaneously Ti = Te + Ts The injector 15 with the injection pulse width Ti given by the equation (2)
Is activated.

FIG. 2 is a flowchart for calculating the effective pulse width Te of the above equation (1), which is executed at a constant cycle (for example, 10 msec).

In step 1, the basic pulse width Tp is calculated from the air flow rate Q detected by the air flow meter 26 and the engine speed N detected by the crank angle sensor 27 as follows: Tp = (Q / N) × K (3) where K : Calculate with a constant formula. The air-fuel ratio determined by this Tp is called the base air-fuel ratio.

In step 2, the effective pulse width Te is calculated by using the basic pulse width Tp: Te = Tp × Co × (α + α _M -1) (4) where Co: various correction coefficients α: air-fuel ratio feedback correction coefficient [ %] Α _M : Calculated by the formula of air-fuel ratio learning value [%].

The various correction coefficients Co in the equation (4) are values for ensuring smooth operation under various conditions. For example, the basic pulse width Tp is corrected based on a signal from each sensor such as the water temperature sensor 15 at the time of starting, warming up, high load, and the like. At this time, the air-fuel ratio feedback correction coefficient α
The value of is clamped to 100%.

The air-fuel ratio feedback correction coefficient α in the equation (4) is a value obtained in synchronization with the Ref signal by proportional-plus-integral control (a type of feedback control) based on the output of the O ₂ sensor 27, and the value of α is 100%. Crossing over (4)
From the equation, the air-fuel ratio is returned to the rich side, and when it is less than 100%, the air-fuel ratio is returned to the lean side.

The air-fuel ratio learning value α _{M in the} equation (4) is a value for eliminating a variation caused in the injection characteristic of the injector and the flow rate characteristic of the air flow meter and a steady error due to a change with time. Will be updated based on. This value is retained so as not to disappear even after the engine is stopped.

-100 [%] in the equation (4) is a unit-matching value. This is because both the air-fuel ratio feedback correction coefficient α and the air-fuel ratio learning value α _M are values centered at 100%.

FIG. 3 is a flowchart for calculating the fuel injection pulse width Ti and executing the injection, which is executed in synchronization with the Ref signal.

Step 11 for sequential injection
Then, the fuel injection pulse width Ti of the above equation (1) is calculated, and this is transferred to the output register in step 12. With the ignition order in a four-cylinder engine set to # 1- # 3- # 4- # 2, when the Ref signal is input this time, for example, T is set to the first cylinder.
If the fuel corresponding to i is supplied, the third Ref.
When the ef signal is input, the No. 4 cylinder is supplied, and when the Ref signal is input three times after, the Ti fuel is supplied to the No. 2 cylinder.

The flow chart of FIG. 4 shows a program executed by the control unit 21 for feedback control of the air-fuel ratio, which is executed at regular intervals.

Explaining this program, first, in step S1, the engine speed N, throttle opening TVO, cooling water temperature TW, and intake air amount Q are read.

In step S2, the basic fuel injection amount Tp is calculated based on these detected values.

In step S3, it is determined whether or not the operating condition is within the preset air-fuel ratio feedback control region, and if it is outside the region, the process proceeds to step S20 to set the feedback correction coefficient α to 100%. Then, the process proceeds to step S21, the flag FlagV is reset, and the current basic fuel injection amount Tp is stored in BTp in step S11.

If it is within the air-fuel ratio feedback control region, the routine proceeds to step S4, and the purge cut valve 1 described later is executed.
The calculation for correcting the air-fuel ratio correction control coefficient is performed during the opening / closing operation of No. 4.

In step S5, the O ₂ sensor output VO ₂ is read, and in step S6 VO ₂ is compared with the predetermined value VSL to determine whether the air-fuel ratio of the exhaust gas is rich or lean.

When the lean judgment that VO ₂ is smaller than the predetermined value VSL is made, the routine proceeds to step S7, and the flag FlagVO is referred to detect the lean reversal time when the exhaust air-fuel ratio reverses from rich to lean.

During lean inversion, the routine proceeds to step S8, where the proportional control amount Pl during rich inversion is set based on a map preset according to the engine speed N and the basic fuel injection amount Tp.
Is searched and the process proceeds to step S9 to add the proportional control amount Pl to the feedback correction coefficient α.

If it is not lean inversion, step S12.
To the lean-time integral control component I of the air-fuel ratio correction control coefficient I.
1 is read, and the process proceeds to step S13 to add the integral control amount Il to the feedback correction coefficient α.

In this way, the feedback correction coefficient α
Is determined, the process proceeds to step S10, the present rich / lean determination result is stored in the flag FlagVO, and the present basic fuel injection amount Tp is stored in BTp in step S11.

On the other hand, when VO ₂ is richer than the predetermined value VSL, the routine proceeds to step S15, where the flag Flu
With reference to gVO, a rich inversion time when the exhaust air-fuel ratio is inverted from lean to rich is detected.

At the time of rich inversion, the process proceeds to step S15,
The proportional control amount P at the time of lean reversal based on a map preset according to the engine speed N and the basic fuel injection amount Tp
r is searched, and the process proceeds to step S16 to subtract the proportional control amount Pr from the feedback correction coefficient α.

If it is not during rich inversion, step S18
To the rich-time integral control component I of the air-fuel ratio correction control coefficient I.
r is read, and the process proceeds to step S19 to subtract the integral control amount Ir from the feedback correction coefficient α.

In this way, the feedback correction coefficient α
After the determination is made, the lean / rich determination result of this time is stored in the flag FlagVO in step S17, and the basic fuel injection amount Tp of this time is stored in BTp in step S11.

As shown in FIG. 4, when the air-fuel ratio is on the rich side and the output of the O ₂ sensor 27 becomes larger than the slice level corresponding to the stoichiometric air-fuel ratio, the feedback control coefficient α and the proportional control amount Pr only are increased. Step down,
Then, the air-fuel ratio is controlled to be gradually reduced by gradually lowering the slope of the integral control amount Ir. In this way, when the air-fuel ratio is on the lean side and the output of the O ₂ sensor 27 becomes smaller than the slice level, the feedback correction coefficient α is first lowered stepwise by the proportional control amount Pl, and then the integral control amount Il is tilted. The air-fuel ratio is controlled to be gradually lowered to increase the air-fuel ratio. By repeating this control, the actual air-fuel ratio can be maintained near the stoichiometric air-fuel ratio.

In FIG. 1, reference numeral 1 is a fuel tank for storing fuel, and 4 is a canister constituting an evaporated fuel processing apparatus. The fuel evaporated in the fuel tank 1 is guided to the canister 4 via the charge passage 2 and adsorbed on the activated carbon 4 a in the canister 4. A check valve 3 is interposed in the charge passage 2.

The canister 4 communicates with an intake passage 8 downstream of the intake throttle valve 7 via a purge passage 6, and a normally closed purge control valve 9 driven by a step motor is provided in the purge passage 6.

A normally closed diaphragm actuator 13 is provided in the charge passage 2 in series with the purge control valve 9. Under the condition that the purge control valve 9 is opened to introduce the purge gas, the purge cut valve 1
4 are simultaneously opened to guide the negative pressure of the intake passage downstream of the throttle valve to the negative pressure operating chamber of the diaphragm actuator 13, and the negative pressure pulls the diaphragm upward in the figure against the return spring, and the purge passage 6 is opened. . Under conditions other than the condition that the purge gas is introduced into the intake passage 8, the normally closed diaphragm actuator 13 shuts off the purge passage 6, so that the purge gas is introduced into the intake passage 8 under the condition other than the condition that the purge gas is introduced into the intake passage 8. It will not be done.

When the purge cut valve 14 is opened in response to a signal from the control unit 21 under a predetermined operating condition, the suction negative pressure generated in the downstream of the throttle valve 7 causes the lower portion of the canister 4 (in the figure, the upper portion of the canister 4 to be opened). Fresh air canister 4 from the fresh air introduction path 5 provided in (shown)
Be guided inside. The vaporized fuel separated from the activated carbon 4a by this fresh air is introduced into the intake passage 8 together with the fresh air and burned in the combustion chamber.

The flowchart of FIG. 6 shows a program executed by the control unit 21 for controlling the opening and closing of the purge cut valve 14, which is executed at regular intervals.

Explaining this program, first, at step C1, it is judged whether or not the intake throttle valve 7 is at the idle position based on a signal from an idle switch (not shown).

If it is determined that the engine is idle, step C
In step 2, it is determined based on the signal from the water temperature sensor 24 whether the engine cooling water temperature Tw is warming up, for example, 40 ° C. or lower.

When it is determined that the engine is idle during warm-up, the routine proceeds to step C3, where a flag F described later is set to 0, and then the routine proceeds to step C4 where the purge cut valve 14 is opened.

If it is determined that the operating conditions are other than after warming up or during idling, the routine proceeds to step C5, where the flag F is set to 1
After that, proceed to Step C6 and execute the purge cut valve 1
4 is closed.

FIG. 7 is a flow chart for calculating the ON duty given to the purge control valve 9 (the valve opening time ratio of a constant cycle), which is executed at a constant cycle (for example, every one second).

In step 21, it is checked whether the purge condition is satisfied. The purge condition is, for example, that the engine is in the low load region after warming up and the air-fuel ratio feedback control is being performed.

At step 22, updating of the air-fuel ratio learning value α _M is prohibited. The original purpose of the air-fuel ratio learning value α _M is to prevent the learning value α _M from being updated under the purge condition in order to eliminate the variation that occurs in the injection characteristics of the injector and the flow rate characteristics of the air flow meter and the steady-state error due to aging. However, if the learning value α _M is updated until the air-fuel ratio deviates from the stoichiometric air-fuel ratio by purging and becomes rich or lean, erroneous learning occurs.

In step 23, the purge gas concentration equivalent parameter (described later) P _EC and the intake throttle valve opening TVO are read, and the purge gas concentration equivalent parameter P _{EC is referred} to in step 24 with reference to the table having the contents of FIG. A basic purge rate PR0 is obtained by referring to a predetermined map from the correction coefficient K2, and in step 25 from the rotational speed N and the basic pulse width Tp, and in step 26, the purge rate PR is PR = PR0 × K2 (5) Calculate with the formula. According to the equation (5), the purge rate correction coefficient K2
Therefore, the basic purge rate PR0 is increased and corrected.

The basic purge rate PR0 defined by the equation: PR0 [%] = (purge volumetric flow rate / volumetric intake air amount) × 100 is basically a constant value, but near full fuel vapor is adsorbed by the canister. In this case, since the high-concentration purge gas is introduced immediately after the start, the purge rate is gradually increased from a small value immediately after the start.

As shown in FIG. 8, the value of the purge rate correction coefficient K2 is negative for the parameter P _EC (low purge gas concentration).
The time is set to be larger than when it is positive (when the purge gas concentration is high). This is because when the purge gas concentration is low,
This is because even if the purge gas flow rate is increased, the influence on the air-fuel ratio during the air-fuel ratio feedback control is small, and the large flow rate purge allows the canister 4 to be started earlier.

In step 27, the intake throttle valve opening TVO
9 is referred to, the opening area A _TH of the intake throttle valve is obtained, and in step 28, the target opening area A _P of the purge control valve is _expressed by the formula A _P = A _TH × PR (6) Calculate with. This target opening area A _P is _calculated in step 29.
With reference to the table having the contents of FIG. 10, the ON duty is converted.

Further, the drain cut valve 11 which is normally open is provided in the fresh air introduction path 5 in order to diagnose the failure of the evaporated fuel processing apparatus.
And a normally closed bypass valve 12 in parallel with the check valve 3 in the charge passage 2.
A closed space of the pipe from the intake passage 8 to the intake passage 8 is used to diagnose whether there is a pressure leak through the pressure sensor 22.

FIG. 11 and FIG. 12 are flow charts which are connected as a whole and show the leak diagnosis.
As a guideline, the frequency of diagnosis is about once per operation.

The leak diagnosis here uses the fuel vapor pressure (positive pressure) generated as the fuel temperature rises during operation. Fuel vapor is generated in the fuel tank 1 in a normal state as the fuel temperature rises after the engine is started. Vacuum cut valve 3
Has a characteristic that the positive pressure of the fuel tank 1 can be maintained at about +10 mmHg, so the positive pressure required for diagnosis can be maintained in the fuel tank 1 as long as fuel vapor is generated without a leak hole on the fuel tank 1 side. Will be done. This positive pressure is applied to the purge cut valve 14 and the drain cut valve 1
When the bypass valve 12 is opened and guided to the side of the canister 4 in a state where 1 is closed and sealed, and the bypass valve 12 is closed after a fixed time, as shown in FIG. The flow passage pressure from 12 to the purge cut valve 14 gradually decreases, but when there is a leak, the flow passage pressure sharply decreases. Therefore, the flow passage pressure after a predetermined time t2 from closing the bypass valve 12 is decreased. The presence of a leak can be determined by looking at. Of course, leak diagnosis using negative pressure may also be used.

In FIG. 11, steps 51 to 53 are portions for checking diagnostic conditions. When all the following conditions are satisfied, the process proceeds to step 54, and the purge cut valve 14 is closed to stop the purge.

<1> Diagnosis start condition (step 51). The diagnosis start condition is, for example, that the pressure sensor 22 is normal and that there is no failure in individual valves such as the drain cut valve 11 and the bypass valve 12.

<2> Positive pressure diagnostic condition (a diagnostic condition using positive pressure) (step 52). The positive pressure diagnosis condition is a condition under which it is considered that there is a positive pressure necessary for diagnosis due to the generation of fuel vapor in the fuel tank.

<3> The purge gas concentration parameter P _EC is less than the predetermined value P1 (step 53). P _EC <P
Until the value becomes 1 (that is, until the purge gas concentration decreases), the purge stop for the leak diagnosis is prohibited and the purge is executed.

In steps 55 and 56, the purge control valve 11 and the drain cut valve 11 are closed, the bypass valve 12 is opened, and it is checked in step 57 whether a predetermined time t1 (for example, several seconds) has elapsed since the bypass valve 12 was opened. Let's see.

When t1 has elapsed, the flow passage pressure P at that time is compared with a predetermined value p1 (for example, + several mmHg) in step 58, and if P ≧ p1, the flow passage pressure P is set to the variable DP1 in step 59. Move and determine that there is no leak on the fuel tank side.

When P <p1, it is not possible to shut off the leak using the positive pressure, so the routine returns to step 51.
It should be noted that when P <p1, it is possible to shift to leak diagnosis using negative pressure.

In step 60, the bypass valve 12 is closed and the timer is started. The timer value T2 measures the elapsed time after the bypass valve 12 is closed. The timer value T2 and the predetermined time t2 (for example, 6 seconds) are compared in step 61. When T2 ≧ t2, the flow path pressure P at that time is transferred to the variable DP2 in step 62. Figure 1
2, the leak parameter AL1 is calculated by the equation AL1 [mmHg] = DP1-DP2 (10) in step 63, and this parameter AL1 is compared with the predetermined value c1 in step 64. If AL1 <c1, it is determined in step 65 that there is no leak, and the leak diagnosis at the time of the current operation is ended. Upon completion of the leak diagnosis, the purge control is resumed (the same applies after the diagnosis when there is a leak).

When AL1 ≧ c1, the routine proceeds to step 66, where the leak diagnostic code is checked. If the leak diagnosis code is "0", it is the first time that it is determined that there is a leak, the leak diagnosis code is set to "1" in step 67, and the data is stored, and the leak diagnosis in the current operation is completed.

After completion of this diagnosis, the engine is stopped,
At the time of the next operation, AL1 ≧ c1 for the parameter AL1 obtained by entering the diagnosis using the positive pressure again, and when step 66 is reached, the leak diagnosis code at the previous operation is set to “1”. Since it has been stored, the routine proceeds to step 68, and the warning lamp provided on the operation panel in the vehicle compartment is turned on.

By the way, such feedback control for the air-fuel ratio is carried out by feedback correction according to the difference between the detected air-fuel ratio and the target air-fuel ratio at the time of the purge start or the end of the purge in which the opening of the purge control valve 9 is gradually changed. By calculating the coefficient α, the actual air-fuel ratio can be made to follow the target air-fuel ratio with sufficient responsiveness, and it is possible to prevent the exhaust emission from deteriorating. As shown in, there is a problem that the actual air-fuel ratio is temporarily disturbed due to the influence of the response speed of the feedback correction coefficient α as the purge cut valve 14 is rapidly opened and closed.

In response to this, the present invention detects the opening operation of the purge cut valve 14 and detects the purge cut valve 1
Feedback correction coefficient α is 100% when the valve is closed.
The control is performed to set the initial value α ₁ (= 1) which is the value of.
Then, the value of the feedback correction coefficient α before the purge cut valve 14 is closed is stored as a memory value αm, and the opening operation of the purge cut valve 14 is detected.
When the purge cut valve 14 is opened, the feedback correction coefficient α is set to the memory value αm.

The flowchart of FIG. 14 shows a program for controlling the air-fuel ratio when the purge cut valve 14 is opened / closed in the control unit 21, and corresponds to the subroutine executed in step S4.

Explaining this program, first, if it is determined at step A1 that the engine is rotating, the routine proceeds to step A2, where the purge cut valve 14 is open or closed based on the flag F. Whether (F = 0) is determined.

When it is judged that the purge cut valve 14 is open, the routine proceeds to step A3, where it is judged whether or not the purge cut valve 14 is in the valve closing operation in which the purge cut valve 14 is completely closed from the opened state.

If it is determined that the purge cut valve 14 is in the closing operation, the routine proceeds to step A4, where the feedback correction coefficient α before the purge cut valve 14 is closed.
The value of is stored as the memory value αm.

Then, in step A5, the feedback correction coefficient α is set to the initial value α ₁ .

On the other hand, when it is judged that the purge cut valve 14 is closed, the routine proceeds to step A6, where it is judged whether or not the purge cut valve 14 is in the valve opening operation for opening the valve from the fully closed state.

When it is determined that the purge cut valve 14 is in the valve opening operation, the routine proceeds to step A7, where the feedback correction coefficient α is set to the memory value αm.

With the above construction, as shown in FIG. 15, the purge cut valve 14 opens and the charge passage 6
In the operating state in which the evaporated fuel is introduced into the intake passage 8 from the feedback correction coefficient α is 100% of the initial value α ₁
It becomes a much smaller value, and the fuel injection amount Te is corrected to a value smaller than the basic fuel injection amount Tp. From this operating state, when the purge cut valve 14 is closed and the evaporated fuel introduced from the charge passage 6 to the intake passage 8 is shut off, feedback correction is performed in conjunction with the purge cut valve 14 being opened. By immediately setting the coefficient α to the initial value α ₁ of 100%, it is possible to prevent the air-fuel ratio from temporarily becoming lean after the purge cut valve 14 is closed.

Further, in the operating state in which the gas containing almost no evaporated fuel from the charge passage 6 is introduced into the intake passage 8, the average value αa of the feedback correction coefficient α is 100%.
Is larger than the initial value α _{1 of} the above, and the fuel injection amount Te is corrected to a value larger than the basic fuel injection amount Tp. When the purge cut valve 14 is closed from this operating state and the gas introduced from the charge passage 6 to the intake passage 8 is shut off, the feedback correction coefficient α is interlocked with the opening operation of the purge cut valve 14. Is immediately set to the initial value α ₁ , it is possible to prevent the air-fuel ratio from becoming temporarily rich after the purge cut valve 14 is closed.

On the other hand, the purge cut valve 14 is closed,
In the operating state in which the evaporated fuel introduced from the charge passage 6 to the intake passage 8 is cut off, the feedback correction coefficient α is maintained at a value near 100%. When the purge cut valve 14 is opened from this operating state and the evaporated fuel is again introduced into the intake passage 8 from the charge passage 6, the feedback correction coefficient α is immediately corrected before the purge cut valve 14 is closed. By setting the memory value αm in which the coefficient α is stored, it is possible to prevent the air-fuel ratio from becoming temporarily rich immediately after the purge cut valve 14 is opened.

When a lean gas containing almost no evaporative fuel is introduced into the intake passage 8 from the charge passage 6, the feedback cutoff coefficient α is immediately closed when the purge cut valve 14 is opened. By setting the feedback correction coefficient α before the operation to the stored memory value αm, it is possible to prevent the air-fuel ratio from temporarily becoming lean immediately after the opening of the purge cut valve 14.

As described above, as the purge cut valve 14 is opened and closed, the feedback correction coefficient α is changed stepwise to the initial value α ₁ or the memory value αm without depending on the PI control. Disturbance of the fuel ratio can be suppressed to a low level. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

By the way, in this embodiment, since the feedback correction coefficient α is set to the initial value α ₁ or the memory value αm almost at the same time when the purge cut valve 14 is opened and closed, the purge cut valve 14 is closed after the valve is closed. Before all the gas introduced from the charge passage 6 to the intake passage 8 is conveyed to the combustion chamber, the fuel injection amount from the injector 15 is increased and the air-fuel ratio becomes temporarily rich, or the purge cut valve 14 After the valve is opened, before the gas introduced from the charge passage 6 to the intake passage 8 is conveyed to the combustion chamber, the fuel injection amount from the injector 15 may be reduced and the air-fuel ratio may temporarily become lean. There is.

Therefore, as another embodiment of the present invention, when the feedback correction coefficient α at the time of the opening / closing operation of the purge cut valve 14 is H is a constant, α = α ₁ + (α _m −α ₁ ).
Control to set the value calculated as H is performed.

The flowchart of FIG. 16 shows a program for controlling the air-fuel ratio when the purge cut valve 14 is opened / closed in the control unit 21, and corresponds to the subroutine executed in step S4.

First, when it is determined in step B1 that the engine is rotating, the process proceeds to step B2, and it is determined based on the flag F whether the purge cut valve 14 is open or closed.

When it is judged that the purge cut valve 14 is open, the routine proceeds to step B3, where it is judged whether or not the purge cut valve 14 is in the valve closing operation in which the purge cut valve 14 is completely closed from the opened state.

If it is determined that the purge cut valve 14 is closed, the process proceeds to step B4, and the value of the feedback correction coefficient α before the purge cut valve 14 is closed is stored as a memory value αm.

Then, in step B5, it is determined whether the average value αa of the feedback correction coefficient α is 100% or more.

When it is determined that the average value αa is 100% or more, the process proceeds to step B6, and the feedback correction coefficient α is calculated by the following equation. However, H ₁ is a preset constant.

Α = α ₁ + (α _m −α ₁ ) H ₁ (7) As shown in FIG. 18, the purge cut valve 14 is opened and the gas containing almost no evaporative fuel is sucked from the charge passage 6. In the operating condition introduced in the passage 8, the average value αa of the feedback correction coefficient α is 100% of the initial value αa.
_The value becomes larger than ₁ , and the fuel injection amount Te is corrected to a value larger than the basic fuel injection amount Tp. When the purge cut valve 14 is closed from this operating state and the gas introduced from the charge passage 6 to the intake passage 8 is shut off, the feedback correction coefficient α is interlocked with the opening operation of the purge cut valve 14. Is immediately set to the value of α ₁ + (α _m −α ₁ ) H ₁ and then the correction component (α _m −α ₁ ) H ₁ is brought close to the initial value α ₁ of 100% by the PI control. Before the lean vaporized fuel gas introduced from 6 to the intake passage 8 is carried to the combustion chamber, the injector 15
It is possible to avoid the fuel injection amount Te from being reduced and to prevent the air-fuel ratio from overshooting to the lean side.

If it is determined that the average value αa is smaller than 100%, the process proceeds to step B7, and the feedback correction coefficient α is calculated by the following equation. However, H ₂ is a preset constant, and H ₂ is set to a value larger than H ₁ .

Α = α ₁ + (α _m −α ₁ ) H ₂ (8) As shown in FIG. 17, the purge cut valve 14 is opened and the gas containing a large amount of evaporated fuel is sucked from the charge passage 6. In the operating state introduced in the passage 8, the average value αa of the feedback correction coefficient α becomes a value smaller than the initial value α ₁ of 100%, and the fuel injection amount Te becomes the basic fuel injection amount T
It is corrected to a value smaller than p. When the purge cut valve 14 is closed from this operating state and the evaporated fuel introduced from the charge passage 6 to the intake passage 8 is shut off, feedback correction is performed in conjunction with the purge cut valve 14 being opened. The coefficient α is immediately converted to α ₁ + (α _m −
After being set to the value of α ₁ ) H ₂ , the correction component (α _m −α ₁ ) H ₂ was introduced from the charge passage 6 into the intake passage 8 by bringing the corrected amount (α _m −α ₁ ) H ₂ close to the initial value α ₁ of 100% by PI control. It is possible to prevent the fuel injection amount Te from the injector 15 from being increased before all the evaporated fuel in the gas is conveyed to the combustion chamber, and to prevent the air-fuel ratio from overshooting to the rich side.

On the other hand, when it is judged that the purge cut valve 14 is closed, the routine proceeds to step B8, where it is judged whether or not the purge cut valve 14 is in the valve opening operation for opening the valve from the fully closed state.

When it is judged that the purge cut valve 14 is in the valve opening operation, the routine proceeds to step B9, where it is judged whether the average value αa of the feedback correction coefficient α is 100% or more.

When it is determined that the average value αa is 100% or more, the process proceeds to step B10, and the feedback correction coefficient α is calculated by the above equation (7).

As shown in FIG. 18, in the operating state in which the purge cut valve 14 is closed and the gas introduced from the charge passage 6 to the intake passage 8 is shut off, the feedback correction coefficient α is close to 100%. To be kept. When the purge cut valve 14 is opened from this operating state and a lean gas containing almost no evaporated fuel is introduced into the intake passage 8 from the charge passage 6, the feedback correction coefficient α is immediately changed to α ₁ + (α _m − After setting the value of α ₁ ) H ₂ , the corrected value (α _m −α ₁ ) H ₁ is set to the initial value α ₁ of 100% by PI control.
From the charge passage 6 to the intake passage 8
It is possible to prevent the fuel injection amount Te from the injector 15 from increasing before the lean gas introduced into the fuel cell is conveyed to the combustion chamber, and to prevent the air-fuel ratio from overshooting to the rich side.

If it is determined that the average value αa is smaller than 100%, the process proceeds to step B11 to calculate the feedback correction coefficient α by the above equation (8).

As shown in FIG. 17, when the purge cut valve 14 is opened and a gas containing a large amount of evaporated fuel is introduced into the intake passage 8 from the charge passage 6, the feedback correction coefficient α is immediately changed to α ₁ +. After setting the value of (α _m −α ₁ ) H ₂ , the correction component (α _m −α ₁ ) H ₂ is set to 10 by PI control.
By approaching the initial value α ₁ of 0%, it is possible to reduce the fuel injection amount Te from the injector 15 before the evaporated fuel in the gas introduced from the charge passage 6 to the intake passage 8 is conveyed to the combustion chamber. By avoiding this, it is possible to prevent the air-fuel ratio from overshooting to the lean side.

As the purge cut valve 14 is opened and closed as described above, the feedback correction coefficient α is calculated as the correction amount α ₁ + (α _m −α ₁ ) H ₁ or the correction amount α ₁ +.
After the stepwise change to (α _m −α ₁ ) H ₂ , the remaining correction component (α _m −α ₁ ) H ₁ or the correction component (α _m −
By setting α ₁ ) H ₂ by PI control, the disturbance of the air-fuel ratio due to overshoot can be suppressed. By further suppressing the disturbance of the air-fuel ratio, the effect of suppressing the exhaust emission and the occurrence of torque shock can be enhanced.

By setting H ₁ to a value smaller than H _2, the correction component (α _m −α ₁ ) H ₁ set by the PI control is set.
Becomes smaller than (α _m −α ₁ ) H ₂ and the actual air-fuel ratio can be reliably prevented from temporarily becoming lean, and sufficient operational stability can be ensured.

Further, the leak diagnosis needs to be executed after the purging is temporarily stopped, but the fuel vapor up to almost the limit is adsorbed in the canister, and the fuel temperature is high and the fuel generated in the fuel tank is generated. Even when there is a lot of steam,
When the purging is stopped, the fuel vapor may overflow from the canister. When the purging is restarted due to the end of the leak diagnosis in such a state, the air-fuel ratio largely leans to the rich side and CO and HC are discharged. The amount will increase.

To deal with this, the control unit 21 estimates the purge gas concentration and prohibits the purge stop for diagnosis until the estimated purge gas concentration becomes less than a predetermined value.

FIG. 19 is a flow chart showing the calculation of the purge gas concentration equivalent parameter. The background job is executed at regular intervals (eg, every 1 second).

From step 31 to step 35 is a part for checking whether or not the condition is for calculating the parameter. When all the following conditions are satisfied, it is judged that the condition is for calculating the parameter, and step 36 is executed. Continue below.

<1> Purging is in progress (step 3
1).

<2> The cooling water temperature Tw is within a predetermined range (for example, 80 ° C. <Tw <90 ° C.) (step 3)
2). This is the water temperature after warming up.

<3> The rotation speed N is within a predetermined range (for example, 1
000 rpm <N <3000 rpm) (step 33).

<4> The basic pulse width (engine load equivalent amount) Tp is within a predetermined range (step 34). In this load range, the suction negative pressure is -400 mmHg to -250 m.
It is a region of mHg.

<5> The air-fuel ratio feedback control is in progress (step 35). This is because the difference in purge gas concentration appears in the amount of change in the air-fuel ratio feedback correction coefficient α.

At step 36, the weighted average value α _N [%] of the air-fuel ratio feedback correction coefficient α is read.

The formula for this weighted average value is α _N = α × K3 + old α _N × (1-K3) (10) where K3: weighted average coefficient α: presently calculated α old α _N : previous α _N, which is calculated in another routine.

At step 37, the purge rate PR (= PR0
XK2) is read, and in step 38, the purge gas concentration parameter P [unknown number] is calculated by the equation P = (1−α _N ) / PR (11).

Assuming that there is no steady-state error due to variations in the injection characteristics of the injector and the flow rate characteristics of the air flow meter and changes over time, when the high-concentration purge gas is introduced during air-fuel ratio feedback control, the air-fuel ratio becomes Since it shifts to the rich side, when the air-fuel ratio shifted to the rich side is returned to the stoichiometric air-fuel ratio side, α is 100%.
If the purge gas near the air is introduced during air-fuel ratio feedback control, the air-fuel ratio will shift to the lean side, so try to return the air-fuel ratio to the rich side. And α is 100%
Get bigger. That is, 1-α _N is a value corresponding to the purge gas concentration, and when 1-α _N > 0, the larger the 1-α _N is, the higher the purge gas concentration is.
_{When N} <0, the larger the | 1-α _N | is, the lower the purge gas concentration is.

Further, the value per unit purge rate is obtained by dividing by the purge rate PR at that time as shown in the equation (11), which is 100-α which represents the deviation amount from the theoretical air-fuel ratio.
_This is because even if the value of _N is the same, if the purge rates are different, the two cannot be treated the same.

In step 39, the weighted average value P _N of the parameter P is P _N = P × K4 + old P _N × (1-K4) (12) where K4: weighted average coefficient P: current calculated parameter P _N : Count value CN for updating the number of updates by the previous P _N formula
T is incremented by 1 in step 40.

The weighted average value of the parameter P (also for α) is used to cut a value such as an abnormal value only once.

In step 41, the count value CNT is compared with a predetermined value, and if CNT <predetermined value, the process returns to the beginning of the routine.

If it has been updated a predetermined number of times continuously, the routine proceeds to step 42, where the weighted average value P _N at that time is put into the variable P _EC , and the routine is ended.

FIG. 20 shows the air-fuel ratio feedback correction coefficient α, purge rate PR, purge gas concentration equivalent in a certain test mode from cold start (this test mode is entered from the state where a considerable amount of fuel vapor is adsorbed in the canister). The change of the parameter P is shown. It should be noted that the value of α is not the value of α itself, but a mountain of traveling (in the lower part of FIG.
It is the average value for each of the above).

In this test mode, when the purge control valve is opened at the same purge ratio as that after the elapse of the predetermined time t5 from the beginning of the purge, the air-fuel ratio is largely shifted to the rich side due to the high-concentration purge gas immediately after the start of the purge. Therefore, the purge rate PR is gradually increased immediately after the start of the purge and thereafter gradually increased until the predetermined time t5 is reached. Therefore, even after the start of purging and t5, 1-
The value of α remains almost constant, and is rather small at the beginning of purging.

Thus, even when the purge rate changes, if the value itself of (1-α) (or a proportional value) is estimated to correspond to the purge gas concentration, an estimation error will occur. The actual purge gas concentration from the start of purging is
Just like the waveform shown in the middle part of FIG. 20, it is highest immediately after the start of purging, becomes smaller as the fuel vapor desorption from the canister progresses, and settles to a certain small value at the timing when the desorption is completed. This is because the value of α) does not correspond to such a change.

On the other hand, in this example, the value obtained by dividing the value of (1-α) by the purge rate PR is calculated as the purge gas concentration equivalent parameter P, so P is shown in the middle part of FIG. As shown in the figure, it is highest immediately after the start of purging, becomes smaller as the fuel vapor desorption from the canister progresses, and settles to a small value at the timing when the desorption is completed, which often affects the actual change in the purge gas concentration from the start of purging. Match.

In this way, if the purge gas concentration can be accurately estimated even immediately after the purge is started and the purge rate is changing, until the purge gas concentration parameter becomes less than the predetermined value (that is, until the purge gas concentration becomes low). When high-concentration purge gas is introduced immediately after the start of purging by prohibiting the purging stop for diagnosis and performing the purging, the purging has priority and the purging progresses to the low-concentration purging gas. The leak diagnosis is executed.

As a result, the fuel vapor up to the limit is adsorbed in the canister, and when the fuel temperature is high and the fuel vapor is likely to be generated in the fuel tank, the purge is stopped and the leak diagnosis is completed. As a result, it is possible to avoid the situation where the purging is restarted in the state where the fuel vapor overflows from the canister, and it is possible to prevent the increase of CO and HC emissions due to the enrichment of the air-fuel ratio in such a situation.

[0140]

According to the engine air-fuel ratio control apparatus of the first aspect, the feedback correction coefficient α is changed stepwise to the initial value α ₁ when the purge valve means is closed, without depending on the feedback control. It is possible to suppress the disturbance of the air-fuel ratio after the closing operation of the purge valve means. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

In the engine air-fuel ratio control apparatus according to the second aspect, the feedback correction coefficient α is feedback-controlled to the memory value αm of the feedback correction coefficient before the purge valve means is closed when the purge valve means is opened. By making the change in steps regardless of the above, it is possible to suppress the disturbance of the air-fuel ratio after the valve opening operation of the purge valve means. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

In the engine air-fuel ratio control apparatus according to the third aspect, the feedback correction coefficient α is calculated by the feedback control by the correction amount α ₁ + (α _m −α ₁ ) H calculated when the purge valve means is closed. Without changing to step shape,
By setting the remaining correction amount (α _m −α ₁ ) H by feedback control, it is possible to suppress the disturbance of the air-fuel ratio due to overshoot after the valve closing operation of the purge valve means.
By further suppressing the disturbance of the air-fuel ratio, the effect of suppressing exhaust emission and torque shock can be enhanced.

In the air-fuel ratio control apparatus for an engine according to claim 4, the feedback correction coefficient α is calculated by the feedback control by the correction amount α ₁ + (α _m −α ₁ ) H calculated when the purge valve means is opened. Without changing to step shape,
By setting the remaining correction amount (α _m −α ₁ ) H by feedback control, it is possible to suppress the disturbance of the air-fuel ratio due to overshoot after the valve opening operation of the purge valve means.
By further suppressing the disturbance of the air-fuel ratio, the effect of suppressing exhaust emission and torque shock can be enhanced.

According to a fifth aspect of the present invention, there is provided an air-fuel ratio control device for an engine according to the difference between the detected air-fuel ratio and the target air-fuel ratio at the start or end of the purge for gradually changing the opening of the purge valve means. By calculating the feedback correction coefficient α, the actual air-fuel ratio can be made to follow the target air-fuel ratio with sufficient responsiveness, and exhaust emission can be prevented from deteriorating.

On the other hand, at the time of leak diagnosis in which the opening of the purge valve means is suddenly changed, the feedback correction coefficient α is forcibly corrected when the purge valve means is closed or opened, so that the purge valve means Disturbance of the air-fuel ratio that occurs after the valve closing operation or the valve opening operation can be suppressed to a small level.
By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart for explaining calculation of an effective pulse width Te similarly.

FIG. 3 is a flowchart for explaining calculation of fuel injection pulse width Ti and execution of injection.

FIG. 4 is a flowchart showing an air-fuel ratio control program.

FIG. 5 is a timing chart showing an example of air-fuel ratio control.

FIG. 6 is a flowchart showing a control program of the purge cut valve.

[FIG. 7] Similarly, ON given to the purge control valve
The flowchart for demonstrating calculation of duty.

FIG. 8 is a characteristic diagram of a purge rate correction coefficient K2.

FIG. 9 is a characteristic diagram of the opening area A _TH of the intake throttle valve of the same.

FIG. 10 is a characteristic diagram of ON duty with respect to the target opening area A _P.

FIG. 11 is a flowchart for similarly explaining leak diagnosis.

FIG. 12 is a flowchart for explaining leak diagnosis.

FIG. 13 is a waveform diagram showing a pressure change at the time of leak diagnosis.

FIG. 14 is a flowchart showing a program for similarly correcting the feedback correction coefficient.

FIG. 15 is a timing chart showing an example of controlling the air-fuel ratio.

FIG. 16 is a flowchart showing a program for correcting a feedback correction coefficient in another embodiment.

FIG. 17 is a timing chart showing an example of controlling the air-fuel ratio.

FIG. 18 is a timing chart showing an example of controlling the air-fuel ratio.

FIG. 19 is a flowchart for explaining calculation of a purge gas concentration equivalent parameter in another embodiment.

FIG. 20 is a waveform chart for explaining the same operation.

FIG. 21 is a timing chart showing an example of air-fuel ratio control in a conventional example.

FIG. 22 is a diagram corresponding to claims of the invention according to claim 1;

FIG. 23 is a diagram corresponding to the claims of the invention according to claim 2;

FIG. 24 is a diagram corresponding to the claims of the invention according to claim 3;

FIG. 25 is a diagram corresponding to the claim of the invention according to claim 4;

FIG. 26 is a claim correspondence diagram of the invention according to claim 5;

[Explanation of symbols]

a fuel tank b canister c engine d intake passage e purge passage f purge valve means g operating condition detection means h fuel supply amount calculation means i target air-fuel ratio setting means j air-fuel ratio detection means k feedback correction coefficient detection means l fuel supply amount calculation Means m Fuel supply means n Valve closing operation detection means o Feedback correction coefficient setting means p Feedback correction coefficient storage means r Feedback correction coefficient setting means s Feedback correction coefficient setting means t Feedback correction coefficient setting means x Purge operation detection means y Leakage Diagnostic detection means z Feedback correction coefficient correction means 1 Fuel tank 2 Charge passage 4 Canister 6 Purge passage 7 Intake throttle valve 8 Intake passage 9 Purge control valve 13 Diaphragm actuator 14 Purge cut valve 15 Njekuta 21 Control unit 23 fuel temperature sensor 24 water temperature sensor 25 speed sensor 26 air flow meter 27 O ₂ sensor

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[Procedure amendment]

[Submission date] May 12, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction content]

[Document name] Statement

Title: Engine air-fuel ratio control device

[Claims]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine air-fuel ratio controller.

[0002]

2. Description of the Related Art In automobiles and the like, in order to prevent the fuel evaporated in a fuel tank from being released into the atmosphere, the evaporated fuel is adsorbed by activated carbon in a canister when the engine is stopped, Under these operating conditions, the purge cut valve is opened to connect the canister to the intake passage, and the negative intake pressure developed during engine operation is used to separate the vaporized fuel from the activated carbon in the canister by the outside air introduced into the canister. Some include an evaporated fuel processing device that is configured to guide the fuel to the intake passage.

Further, an air-fuel ratio control device provided in a conventional engine adds or subtracts an air-fuel ratio correction control coefficient composed of a proportional control component and an integral control component to a feedback correction coefficient α based on the detected actual air-fuel ratio. To correct the fuel amount,
The air-fuel ratio is designed to come close to the target value (Japanese Patent Laid-Open No. Sho 6).
No. 4-36941, reference).

[0004]

By the way, in the case of the conventional device, the feedback control for such an air-fuel ratio is performed as shown in FIG. 21, as the response speed of the feedback correction coefficient α is changed as the purge cut valve is opened and closed. Due to the influence, there is a problem that the actual air-fuel ratio is temporarily disturbed, which causes deterioration of exhaust emission and torque shock.

For example, in the operating state in which the purge cut valve is opened and the evaporated fuel is introduced into the intake passage, the feedback correction coefficient α becomes considerably smaller than 100%, and the fuel injection amount T is corrected to be reduced. is doing. When the purge cut valve is closed from this operating state and the vaporized fuel introduced into the intake passage is shut off, the feedback correction coefficient α approaches 100% by the above feedback control, but the feedback correction coefficient It takes time to return the coefficient α to around 100%, and the actual air-fuel ratio temporarily becomes lean during this time.

Further, in the operating state in which the purge cut valve is closed and the vaporized fuel introduced into the intake passage is shut off,
The feedback correction coefficient α is maintained near a value of 100% to reduce the increase / decrease range of the fuel injection amount T. When the purge cut valve is opened from this operating state and the introduction of the evaporated fuel into the intake passage is started, the feedback correction coefficient reduces the feedback correction coefficient α from 100% by the PI control, but the feedback correction coefficient It takes time to reduce the correction coefficient α by the feedback control, and the actual air-fuel ratio becomes temporarily rich during this time.

Therefore, an object of the present invention is to suppress the disturbance of the air-fuel ratio which occurs during the opening / closing operation of the purge cut valve or the like.

[0008]

As shown in FIG. 22, an engine air-fuel ratio control apparatus according to a first aspect of the present invention includes a canister b for adsorbing fuel evaporated in a fuel tank a and an intake passage d for the canister b. A purge passage e communicating with the engine, a purge valve means f for opening and closing the purge passage e according to the operating condition of the engine c, an operating condition detecting means g for detecting the operating condition of the engine c, and a operating condition detecting means g for detecting the operating condition. And a basic fuel supply amount calculating means h for calculating the basic fuel supply amount Tp,
The target air-fuel ratio setting means i for setting the target air-fuel ratio according to the detected operating conditions, the air-fuel ratio detecting means j for detecting the air-fuel ratio of the engine c, and the difference between the detected air-fuel ratio and the target air-fuel ratio Feedback correction coefficient detection means k for calculating the feedback correction coefficient α in accordance therewith, fuel supply amount calculation means 1 for calculating the fuel supply amount T by correcting the calculated basic fuel supply amount Tp with the feedback correction coefficient α, and And a fuel supply means (m) for supplying the supplied fuel supply amount (T) to the engine.
Valve closing operation detection means n for detecting the valve closing operation from the valve opening state to the valve closing state, and the feedback correction for setting the feedback correction coefficient α to the initial value α ₁ when the purge valve means f is closed. And coefficient setting means o.

As shown in FIG. 23, an engine air-fuel ratio control apparatus according to a second aspect of the present invention includes a feedback correction coefficient storage means p for storing a feedback correction coefficient αm in the open state of the purge valve means f, and the purge valve. A valve opening operation detecting means q for detecting the valve opening operation of the means f from the valve closed state to the valve opening state, and a feedback correction coefficient αm for storing the feedback correction coefficient α when the purge valve means f is opened. And a feedback correction coefficient setting means r set to.

The air-fuel ratio control apparatus for an engine according to a third aspect of the present invention, as shown in FIG. 24, detects the closing operation of the purge valve means f to detect the closing operation from the open state to the closed state. Means n, a feedback correction coefficient storage means p for storing the feedback correction coefficient αm stored in the open state of the purge valve means f, and the feedback correction coefficient α when the purge valve means f is closed. Feedback correction coefficient α stored in the valve open state of
If H is a constant based on m and the initial value α ₁ , α = α
Feedback correction coefficient setting means s for setting a value calculated as ₁ + (αm−α ₁ ) H.

As shown in FIG. 25, an engine air-fuel ratio control apparatus according to a fourth aspect of the present invention includes feedback correction coefficient storage means p for storing the feedback correction coefficient αm stored when the purge valve means f is open. When the purge valve means f detects the valve opening operation from the closed state to the valve open state, the valve opening operation detecting means q and the purge correction coefficient f when the purge valve means f operates in the valve opening state. If H is a constant based on the stored feedback correction coefficient αm and the initial value α ₁ , α = α ₁ + (αm−α ₁ )
Feedback correction coefficient setting means t for setting the value calculated as H.

As shown in FIG. 26, the air-fuel ratio control apparatus for an engine according to claim 5 is a purging operation detecting means for detecting a barge start time or a purge end time when the opening degree of the purge valve means f is gradually changed. x, a leak diagnosis detection means y for detecting a leak diagnosis time when the opening degree of the purge valve means f is rapidly changed, and an air-fuel ratio is feedback-controlled during the purge operation, while the purge valve means f during the leak diagnosis time.
Feedback correction coefficient correction means z for forcibly correcting the feedback correction coefficient α when the valve is operated.

[0013]

The air-fuel ratio control device for an engine according to claim 1 is
When the purge valve means f is closed, the feedback correction coefficient α is changed to the initial value α ₁ stepwise without feedback control, so that the disturbance of the air-fuel ratio that occurs after the purge valve means f is closed is suppressed to a small level. To be By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

According to another aspect of the air-fuel ratio control apparatus for an engine of the present invention, the feedback correction coefficient α is set to the memory value αm of the feedback correction coefficient stored in the open state of the purge valve means f when the purge valve means f is opened. By making a step-like change regardless of the feedback control, the disturbance of the air-fuel ratio that occurs after the opening operation of the purge valve means f can be suppressed to a small level. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

In the engine air-fuel ratio control device according to the third aspect, the feedback correction coefficient α is feedback-controlled by the calculated correction amount α ₁ + (α _m -α ₁ ) H when the purge valve means f is closed. After making a stepwise change, the remaining correction amount (α _m −α ₁ ) H is set by feedback control to reduce the disturbance of the air-fuel ratio caused by overshoot after the closing operation of the purge valve means f. It can be suppressed. By further suppressing the disturbance of the air-fuel ratio, the effect of suppressing exhaust emission and torque shock can be enhanced.

In the engine air-fuel ratio control device according to the fourth aspect, the feedback correction coefficient α is feedback-controlled by the calculated correction amount α ₁ + (α _m −α ₁ ) H when the purge valve means f is opened. After making a stepwise change, the remaining correction amount (α _m −α ₁ ) H is set by feedback control, so that the disturbance of the air-fuel ratio caused by overshoot after the valve opening operation of the purge valve means f is reduced. It can be suppressed. By further suppressing the disturbance of the air-fuel ratio, the effect of suppressing exhaust emission and torque shock can be enhanced.

According to a fifth aspect of the present invention, there is provided an air-fuel ratio control system for an engine according to the difference between the detected air-fuel ratio and the target air-fuel ratio at the start of purging or the end of purging for gradually changing the opening of the purge valve means f. By calculating the feedback correction coefficient α by using the feedback correction coefficient α, the actual air-fuel ratio can be made to follow the target air-fuel ratio with sufficient responsiveness, and exhaust emission can be prevented from deteriorating.

On the other hand, at the time of leak diagnosis in which the opening degree of the purge valve means f is suddenly changed, the feedback correction coefficient α is forcibly corrected when the purge valve means f is closed or opened, so that the purge valve The disturbance of the air-fuel ratio that occurs after the valve closing operation or the valve opening operation of the means f can be suppressed to a small level. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, an injector 15 for injecting fuel is installed in the intake passage 8. In order to control the fuel injection amount Te from the injector 15, the control unit 21 includes the intake air amount Q detected by the air flow meter 26 and the reference position of the crank angle detected by the engine speed sensor 25 (four-cylinder engine). Then 18
Ref every 0 °, every 120 ° for a 6 cylinder engine)
The signal, the signal for each unit crank angle, the cooling water temperature TW detected by the cooling water temperature sensor 24, etc. are input, and the basic fuel injection amount Tp is calculated according to the operating state.

An O ₂ sensor 27 for detecting the oxygen concentration in the exhaust gas is installed in the exhaust passage 10. The control unit 21 composed of a microcomputer outputs an output V according to the oxygen concentration in the exhaust gas detected by the O ₂ sensor 27.
O ₂ is input and the fuel injection amount Te is feedback-controlled so that the mixture air-fuel ratio becomes the stoichiometric air-fuel ratio, and the conversion efficiency of a three-way catalyst (not shown) installed in the middle of the exhaust passage 10 is maintained to the maximum. It is like this.

The air-fuel ratio control by the control unit 21 is as follows.

The fuel injector 15 is driven in synchronization with the Ref signal. For example, in the sequential injection method, once for every two engine revolutions, for each cylinder Ti = 2 × Te + TS (1) where Te: effective pulse width Ts: injection pulse given by the formula of invalid pulse width according to battery voltage Injector 15 with width Ti
Is activated. In the case of the simultaneous injection method, the engine 1
Once every rotation, all the cylinders simultaneously Ti = Te + Ts The injector 15 with the injection pulse width Ti given by the equation (2)
Is activated.

FIG. 2 is a flow chart for calculating the effective pulse width Te of the above equation (1), which is executed at a constant cycle (for example, 10 msec).

In step 1, the basic pulse width Tp is calculated from the air flow rate Q detected by the air flow meter 26 and the engine speed N detected by the crank angle sensor 27 as follows: Tp = (Q / N) × K (3) where K : Calculate with a constant formula. The air-fuel ratio determined by this Tp is called the base air-fuel ratio.

In step 2, the effective pulse width Te is calculated by using the basic pulse width Tp as follows: Te = Tp × Co × (α + α _M -1) (4) where Co: various correction coefficients α: air-fuel ratio feedback correction coefficient [ %] Α _M : Air-fuel ratio learning value [%] is calculated by the formula.

The various correction coefficients Co in the equation (4) are values for ensuring smooth operation under various conditions. For example, the basic pulse width Tp is corrected based on a signal from each sensor such as the water temperature sensor 15 at the time of starting, warming up, high load, and the like. At this time, the air-fuel ratio feedback correction coefficient α
The value of is clamped to 100%.

The air-fuel ratio feedback correction coefficient α in the equation (4) is a value obtained in synchronization with the Ref signal by proportional-plus-integral control (a kind of feedback control) based on the output of the O ₂ sensor 27, and the value of α is 100%. Crossing over (4)
From the equation, the air-fuel ratio is returned to the rich side, and when it is less than 100%, the air-fuel ratio is returned to the lean side.

The air-fuel ratio learning value α _{M in the} equation (4) is a value for eliminating a variation which occurs in the injection characteristic of the injector and the flow rate characteristic of the air flow meter and a steady-state error due to a change with time. Will be updated based on. This value is retained so as not to disappear even after the engine is stopped.

-100 [%] in the equation (4) is a unit-matching value. This is because both the air-fuel ratio feedback correction coefficient α and the air-fuel ratio learning value α _M are values centered on 100%.

FIG. 3 is a flowchart for calculating the fuel injection pulse width Ti and executing the injection, which is executed in synchronization with the Ref signal.

Step 11 for sequential injection
Then, the fuel injection pulse width Ti of the above equation (1) is calculated, and this is transferred to the output register in step 12. With the ignition order in a four-cylinder engine set to # 1- # 3- # 4- # 2, when the Ref signal is input this time, for example, T is set to the first cylinder.
If the fuel corresponding to i is supplied, the third Ref.
When the ef signal is input, the No. 4 cylinder is supplied, and when the Ref signal is input three times after, the Ti fuel is supplied to the No. 2 cylinder.

The flow chart of FIG. 4 shows a program executed by the control unit 21 for feedback control of the air-fuel ratio, which is executed at regular intervals.

Explaining this program, first, in step S1, the engine speed N, throttle opening TVO, cooling water temperature TW, and intake air amount Q are read.

In step S2, the basic fuel injection amount Tp is calculated based on these detected values.

In step S3, it is determined whether or not the operating condition is within the preset air-fuel ratio feedback control region, and if it is outside the region, the process proceeds to step S20 to set the feedback correction coefficient α to 100%. Then, the process proceeds to step S21, the flag FlagV is reset, and the current basic fuel injection amount Tp is stored in BTp in step S11.

If it is within the air-fuel ratio feedback control region, the routine proceeds to step S4, and the purge cut valve 1 described later is executed.
The calculation for correcting the air-fuel ratio correction control coefficient is performed during the opening / closing operation of No. 4.

In step S5, the O ₂ sensor output VO ₂ is read, and in step S6 VO ₂ is compared with a predetermined value VSL to determine whether the air-fuel ratio of the exhaust gas is rich or lean.

When the lean judgment that VO ₂ is smaller than the predetermined value VSL is made, the routine proceeds to step S7, and the flag FlagVO is referred to detect the lean reversal time when the exhaust air-fuel ratio reverses from rich to lean.

During lean reversal, the routine proceeds to step S8, where the proportional control amount Pl during rich reversal is set based on a map preset according to the engine speed N and the basic fuel injection amount Tp.
Is searched and the process proceeds to step S9 to add the proportional control amount Pl to the feedback correction coefficient α.

If it is not lean inversion, step S12.
To the lean-time integral control component I of the air-fuel ratio correction control coefficient I.
1 is read, and the process proceeds to step S13 to add the feedback correction coefficient and this integral control amount Il.

In this way, the feedback correction coefficient α
Is determined, the process proceeds to step S10, the present rich / lean determination result is stored in the flag FlagVO, and the present basic fuel injection amount Tp is stored in BTp in step S11.

On the other hand, when VO ₂ is richer than the predetermined value VSL, the routine proceeds to step S15, where the flag Flu is detected.
With reference to gVO, a rich inversion time when the exhaust air-fuel ratio is inverted from lean to rich is detected.

At the time of rich inversion, the process proceeds to step S15,
The proportional control amount P at the time of lean reversal based on a map preset according to the engine speed N and the basic fuel injection amount Tp
r is searched, and the process proceeds to step S16 to subtract the proportional control amount Pr from the feedback correction coefficient α.

When it is not the time of rich inversion, step S18
To the rich-time integral control component I of the air-fuel ratio correction control coefficient I.
r is read, and the process proceeds to step S19 to subtract the integral control amount Ir from the feedback correction coefficient α.

In this way, the feedback correction coefficient α
After the determination is made, the lean / rich determination result of this time is stored in the flag FlagVO in step S17, and the basic fuel injection amount Tp of this time is stored in BTp in step S11.

As shown in FIG. 4, when the output of the O ₂ sensor 27 becomes larger than the slice level corresponding to the stoichiometric air-fuel ratio when the air-fuel ratio is on the rich side, the feedback correction coefficient α and the proportional control amount Pr only are added. Step down,
Then, the air-fuel ratio is controlled to be gradually reduced by gradually lowering the slope of the integral control amount Ir. In this way, when the air-fuel ratio is on the lean side and the output of the O ₂ sensor 27 becomes smaller than the slice level, the feedback correction coefficient α is first lowered stepwise by the proportional control amount Pl, and then the slope of the integral control amount Il is used. The air-fuel ratio is controlled to be gradually lowered to increase the air-fuel ratio. By repeating this control, the actual air-fuel ratio can be maintained near the stoichiometric air-fuel ratio.

In FIG. 1, 1 is a fuel tank for storing fuel, and 4 is a canister which constitutes an evaporated fuel processing apparatus. The fuel evaporated in the fuel tank 1 is guided to the canister 4 via the charge passage 2 and adsorbed on the activated carbon 4 a in the canister 4. A check valve 3 is interposed in the charge passage 2.

The canister 4 communicates with an intake passage 8 downstream of the intake throttle valve 7 via a purge passage 6, and a normally closed purge control valve 9 driven by a step motor is provided in the purge passage 6.

A normally closed diaphragm actuator 13 is provided in the charge passage 2 in series with the purge control valve 9. Under the condition that the purge control valve 9 is opened to introduce the purge gas, the purge cut valve 1
4 are simultaneously opened to guide the negative pressure of the intake passage downstream of the throttle valve to the negative pressure operating chamber of the diaphragm actuator 13, and the negative pressure pulls the diaphragm upward in the figure against the return spring, and the purge passage 6 is opened. . Under conditions other than the condition that the purge gas is introduced into the intake passage 8, the normally closed diaphragm actuator 13 shuts off the purge passage 6, so that the purge gas is introduced into the intake passage 8 under the condition other than the condition that the purge gas is introduced into the intake passage 8. It will not be done.

When the purge cut valve 14 is opened in response to a signal from the control unit 21 under a predetermined operating condition, the suction negative pressure generated downstream of the throttle valve 7 causes the lower part of the canister 4 (in the figure, the upper part of the canister 4 to be opened). Fresh air canister 4 from the fresh air introduction path 5 provided in (shown)
Be guided inside. The vaporized fuel separated from the activated carbon 4a by this fresh air is introduced into the intake passage 8 together with the fresh air and burned in the combustion chamber.

The flowchart of FIG. 6 shows a program executed by the control unit 21 for controlling the opening and closing of the purge cut valve 14, which is executed at regular intervals.

Explaining this program, first, at step C1, it is judged based on a signal from an idle switch (not shown) whether or not the intake throttle valve 7 is at the idle position.

If it is determined that the engine is idle, step C
In step 2, it is determined based on the signal from the water temperature sensor 24 whether the engine cooling water temperature Tw is warming up, for example, 40 ° C. or lower.

When it is determined that the engine is idle during warm-up, the routine proceeds to step C3, where a flag F described later is set to 0, and then the routine proceeds to step C4 where the purge cut valve 14 is opened.

If it is determined that the operating conditions are other than after warming up or during idling, the routine proceeds to step C5, where the flag F is set to 1
After that, proceed to Step C6 and execute the purge cut valve 1
4 is closed.

FIG. 7 is a flow chart for calculating the ON duty given to the purge control valve 9 (that is, the valve opening time ratio of a constant cycle), which is executed at a constant cycle (for example, every 1 second).

In step 21, it is checked whether the purge condition is satisfied. The purge condition is, for example, that the engine is in the low load region after warming up and the air-fuel ratio feedback control is being performed.

In step 22, updating of the air-fuel ratio learning value α _M is prohibited. The original purpose of the air-fuel ratio learning value α _M is to prohibit the update of the learning value α _{M under} the purge condition in order to eliminate the steady-state error due to variations and changes over time in the injection characteristics of the injector and the flow characteristics of the air flow meter. Even though
This is because if the learning value α _M is updated until the air-fuel ratio deviates from the stoichiometric air-fuel ratio due to purging and becomes rich or lean, erroneous learning occurs.

In step 23, the purge gas concentration equivalent parameter (described later) P _EC and the intake throttle valve opening TVO are read, and the purge gas concentration equivalent parameter P _{EC is referred} to in step 24 from the table having the contents shown in FIG. A basic purge rate PR0 is obtained by referring to a predetermined map from the correction coefficient K2, and in step 25 from the rotational speed N and the basic pulse width Tp, and in step 26, the purge rate PR is PR = PR0 × K2 (5) Calculate with the formula. According to the equation (5), the purge rate correction coefficient K2
Therefore, the basic purge rate PR0 is increased and corrected.

The basic purge rate PR0 defined by the equation PR0 [%] = (purge volumetric flow rate / volumetric intake air amount) × 100 is basically a constant value, but near full fuel vapor is adsorbed by the canister. In this case, since the high-concentration purge gas is introduced immediately after the start, the purge rate is gradually increased from a small value immediately after the start.

As shown in FIG. 8, the value of the purge rate correction coefficient K2 is larger when the parameter P _EC is negative (the purge gas concentration is low) than when it is positive (the purge gas concentration is high). This is because when the purge gas concentration is low, even if the flow rate of the purge gas is increased, the influence on the air-fuel ratio during the air-fuel ratio feedback control is small, and the canister 4 can be activated earlier by the large flow rate purge.

In step 27, the intake throttle valve opening TVO
9 is referred to, the opening area A _TH of the intake throttle valve is obtained, and in step 28, the target opening area A _p of the purge control valve is expressed as A _p = A _TH × PR (6) Calculate with. This target opening area A _p is _calculated in step 29.
With reference to the table having the contents of FIG. 10, the ON duty is converted.

Further, in order to diagnose the failure of the evaporated fuel processing apparatus, the drain cut valve 11 which is normally open in the fresh air introduction path 5 is used.
And a normally closed bypass valve 12 in parallel with the check valve 3 in the charge passage 2.
A closed space of the pipe from the intake passage 8 to the intake passage 8 is used to diagnose whether there is a pressure leak through the pressure sensor 22.

FIG. 11 and FIG. 12 are flow charts which are connected as a whole and show the leak diagnosis.
As a guideline, the frequency of diagnosis is about once per operation.

The leak diagnosis here uses the fuel vapor pressure (positive pressure) generated as the fuel temperature rises during operation. Fuel vapor is generated in the fuel tank 1 in a normal state as the fuel temperature rises after the engine is started. Vacuum cut valve 3
Has a characteristic that the positive pressure of the fuel tank 1 can be maintained at about +10 mmHg, so the positive pressure required for diagnosis can be maintained in the fuel tank 1 as long as fuel vapor is generated without a leak hole on the fuel tank 1 side. Will be done. This positive pressure is applied to the purge cut valve 14 and the drain cut valve 1
When the bypass valve 12 is opened and guided to the side of the canister 4 in a state where 1 is closed and sealed, and the bypass valve 12 is closed after a fixed time, as shown in FIG. The flow passage pressure from 12 to the purge cut valve 14 gradually decreases, but when there is a leak, the flow passage pressure sharply decreases. Therefore, the flow passage pressure after a predetermined time t2 from closing the bypass valve 12 is decreased. The presence of a leak can be determined by looking at. Of course, leak diagnosis using negative pressure may also be used.

In FIG. 11, steps 51 to 53 are portions for checking the diagnostic conditions. When all the following conditions are satisfied, the process proceeds to step 54, and the purge cut valve 14 is closed to stop the purge.

<1> Diagnosis start condition (step 51). The diagnosis start condition is, for example, that the pressure sensor 22 is normal and that there is no failure in individual valves such as the drain cut valve 11 and the bypass valve 12.

<2> Positive pressure diagnostic condition (a diagnostic condition using positive pressure) (step 52). The positive pressure diagnosis condition is a condition under which it is considered that there is a positive pressure necessary for diagnosis due to the generation of fuel vapor in the fuel tank.

<3> Purge gas concentration parameter P _EC
Is less than the predetermined value P1 (step 53). P _EC
Until <P1 (that is, until the purge gas concentration decreases), the purge stop for the leak diagnosis is prohibited and the purge is executed.

In steps 55 and 56, the purge control valve 11 and the drain cut valve 11 are closed, the bypass valve 12 is opened, and it is checked in step 57 whether a predetermined time t1 (for example, several seconds) has elapsed since the bypass valve 12 was opened. Let's see.

When t1 has elapsed, in step 58, the flow passage pressure P at that time is compared with a predetermined value p1 (for example, + several mmHg), and if P ≧ p1, the flow passage pressure P is set to a variable DP1 in step 59. Move and determine that there is no leak on the fuel tank side.

When P <p1, it is not possible to shut off the leak using the positive pressure, so the process returns to step 51.
It should be noted that when P <p1, it is possible to shift to leak diagnosis using negative pressure.

In step 60, the bypass valve 12 is closed and the timer is started. The timer value T2 measures the elapsed time after the bypass valve 12 is closed. The timer value T2 and the predetermined time t2 (for example, 6 seconds) are compared in step 61. When T2 ≧ t2, the flow path pressure P at that time is transferred to the variable DP2 in step 62. Figure 1
2, the leak parameter AL1 is calculated by the equation AL1 [mmHg] = DP1-DP2 (10) in step 63, and this parameter AL1 is compared with the predetermined value c1 in step 64. If AL1 <c1, it is determined in step 65 that there is no leak, and the leak diagnosis at the time of the current operation is ended. Upon completion of the leak diagnosis, the purge control is resumed (the same applies after the diagnosis when there is a leak).

When AL1 ≧ c1, the routine proceeds to step 66, where the leak diagnostic code is checked. If the leak diagnosis code is "0", it is the first time that it is determined that there is a leak, the leak diagnosis code is set to "1" in step 67, and the data is stored, and the leak diagnosis in the current operation is completed.

After the end of this diagnosis, the engine is stopped,
At the time of the next operation, AL1 ≧ c1 for the parameter AL1 obtained by entering the diagnosis using the positive pressure again, and when step 66 is reached, the leak diagnosis code at the previous operation is set to “1”. Since it has been stored, the routine proceeds to step 68, and the warning lamp provided on the operation panel in the vehicle compartment is turned on.

By the way, such feedback control for the air-fuel ratio is performed by feedback correction according to the difference between the detected air-fuel ratio and the target air-fuel ratio at the time of starting the purge or ending the purge in which the opening of the purge control valve 9 is gradually changed. By calculating the coefficient α, the actual air-fuel ratio can be made to follow the target air-fuel ratio with sufficient responsiveness, and it is possible to prevent the exhaust emission from deteriorating. As shown in, there is a problem that the actual air-fuel ratio is temporarily disturbed due to the influence of the response speed of the feedback correction coefficient α as the purge cut valve 14 is rapidly opened and closed.

In response to this, the present invention detects the opening operation of the purge cut valve 14 to detect the purge cut valve 1
Feedback correction coefficient α is 100% when the valve is closed.
The control is performed to set the initial value α ₁ (= 1) which is the value of
Then, the value of the feedback correction coefficient α before the purge cut valve 14 is closed is stored as a memory value αm, and the opening operation of the purge cut valve 14 is detected.
When the purge cut valve 14 is opened, the feedback correction coefficient α is set to the memory value αm.

The flowchart of FIG. 14 shows a program for controlling the air-fuel ratio when the purge cut valve 14 is opened / closed in the control unit 21, and corresponds to the subroutine executed in step S4.

Explaining this program, first, when it is judged at step A1 that the engine is rotating, the routine proceeds to step A2, where the purge cut valve 14 is opened or closed based on the flag F. Whether (F = 0) is determined.

When it is determined that the purge cut valve 14 is open, the routine proceeds to step A3, where it is determined whether or not the purge cut valve 14 is in the valve closing operation in which the purge cut valve 14 is fully closed from the open state.

When it is determined that the purge cut valve 14 is in the closing operation, the process advances to step A4, and the feedback correction coefficient α before the purge cut valve 14 is closed.
The value of is stored as the memory value αm.

Then, in step A5, the feedback correction coefficient α is set to the initial value α ₁ .

On the other hand, when it is judged that the purge cut valve 14 is closed, the routine proceeds to step A6, where it is judged whether or not the purge cut valve 14 is in the valve opening operation for opening the valve from the fully closed state.

When it is judged that the purge cut valve 14 is in the valve opening operation, the routine proceeds to step A7, where the feedback correction coefficient α is set to the memory value αm.

With the above construction, as shown in FIG. 15, the purge cut valve 14 opens and the charge passage 6
In the operating state in which the evaporated fuel is introduced into the intake passage 8 from the above, the feedback correction coefficient α has an initial value α ₁ of 100%.
It becomes a much smaller value, and the fuel injection amount Te is corrected to a value smaller than the basic fuel injection amount Tp. From this operating state, when the purge cut valve 14 is closed and the evaporated fuel introduced from the charge passage 6 to the intake passage 8 is shut off, feedback correction is performed in conjunction with the purge cut valve 14 being opened. By immediately setting the coefficient α to the initial value α ₁ of 100%, it is possible to prevent the air-fuel ratio from temporarily becoming lean after the purge cut valve 14 is closed.

Further, in the operating state in which the gas containing almost no evaporated fuel from the charge passage 6 is introduced into the intake passage 8, the average value αa of the feedback correction coefficient α is 100%.
Becomes larger than the initial value α _{1 of} the above, and the fuel injection amount Te is corrected to a value larger than the basic fuel injection amount Tp. When the purge cut valve 14 is closed from this operating state and the gas introduced from the charge passage 6 to the intake passage 8 is shut off, the feedback correction coefficient α is interlocked with the opening operation of the purge cut valve 14. Immediately after setting the initial value α ₁ to α ₁ , it is possible to prevent the air-fuel ratio from becoming temporarily rich after the purge cut valve 14 is closed.

On the other hand, the purge cut valve 14 is closed,
In the operating state in which the evaporated fuel introduced from the charge passage 6 to the intake passage 8 is cut off, the feedback correction coefficient α is maintained at a value near 100%. When the purge cut valve 14 is opened from this operating state and the evaporated fuel is again introduced into the intake passage 8 from the charge passage 6, the feedback correction coefficient α is immediately corrected before the purge cut valve 14 is closed. By setting the memory value αm in which the coefficient α is stored, it is possible to prevent the air-fuel ratio from becoming temporarily rich immediately after the purge cut valve 14 is opened.

When a lean gas containing almost no evaporative fuel is introduced into the intake passage 8 from the charge passage 6, the purge cut valve 14 immediately closes the feedback correction coefficient α when the purge cut valve 14 is opened. By setting the feedback correction coefficient α before the operation to the stored memory value αm, it is possible to prevent the air-fuel ratio from temporarily becoming lean immediately after the opening of the purge cut valve 14.

As described above, as the purge cut valve 14 is opened and closed, the feedback correction coefficient α is changed to the initial value α ₁ or the memory value αm stepwise without depending on the PI control. Disturbance of the fuel ratio can be suppressed to a low level. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

In this embodiment, since the feedback correction coefficient α is set to the initial value α ₁ or the memory value αm almost at the same time when the purge cut valve 14 is opened and closed, the purge cut valve 14 is closed after the valve is closed. Before all the gas introduced from the charge passage 6 to the intake passage 8 is conveyed to the combustion chamber, the fuel injection amount from the injector 15 is increased and the air-fuel ratio becomes temporarily rich, or the purge cut valve 14 After the valve is opened, before the gas introduced from the charge passage 6 to the intake passage 8 is conveyed to the combustion chamber, the fuel injection amount from the injector 15 may be reduced and the air-fuel ratio may temporarily become lean. There is.

Therefore, as another embodiment of the present invention, when the feedback correction coefficient α at the time of the opening / closing operation of the purge cut valve 14 is H is a constant, α = α ₁ + (α _m −
Control is performed to set the value calculated as α ₁ ) H.

The flowchart of FIG. 16 shows a program for controlling the air-fuel ratio when the purge cut valve 14 is opened / closed in the control unit 21, and corresponds to the subroutine executed in step S4.

First, when it is determined in step B1 that the engine is rotating, the process proceeds to step B2, and it is determined based on the flag F whether the purge cut valve 14 is open or closed.

When it is judged that the purge cut valve 14 is open, the routine proceeds to step B3, where it is judged whether or not the purge cut valve 14 is in the valve closing operation in which the purge cut valve 14 is completely closed from the opened state.

If it is determined that the purge cut valve 14 is in the closing operation, the process proceeds to step B4, and the value of the feedback correction coefficient α before the purge cut valve 14 is closed is stored as the memory value αm.

Then, the process proceeds to step B5, where it is determined whether the average value αa of the feedback correction coefficient α is 100% or more.

When it is determined that the average value αa is 100% or more, the process proceeds to step B6, and the feedback correction coefficient α is calculated by the following equation. However, H ₁ is a preset constant. As shown in _{α = α 1 + (α m} -α 1) H 1 ... (7) Fig. 18, and opening the purge cut valve 14, a gas containing little fuel vapor from the charge passage 6 to the intake passage 8 In the introduced operation state, the average value αa of the feedback correction coefficient α is 100% of the initial value αa.
_The value becomes larger than ₁ and the fuel injection amount Te is corrected to a value larger than the basic fuel injection amount Tp. When the purge cut valve 14 is closed from this operating state and the gas introduced from the charge passage 6 to the intake passage 8 is shut off, the feedback correction coefficient α is interlocked with the opening operation of the purge cut valve 14. To α ₁ + (α _m −α ₁ ) H immediately
After setting the value to ₁ , the correction component (α _m −α ₁ ) H _{1 is set} to PI.
By approaching the initial value α ₁ of 100% by the control, the fuel injection amount Te from the injector 15 is changed before all the lean gas of the evaporated fuel introduced from the charge passage 6 to the intake passage 8 is carried to the combustion chamber. It is possible to prevent the air-fuel ratio from being reduced and prevent the air-fuel ratio from overshooting to the lean side.

If it is determined that the average value αa is smaller than 100%, the process proceeds to step B7, and the feedback correction coefficient α is calculated by the following equation. However, H ₂ is a preset constant, and H ₂ is set to a value larger than H ₁ . As shown in _{α = α 1 + (α m} -α 1) H 2 ... (8) 17, opens the purge cut valve 14, it contains large amounts gas fuel vapor from the charge passage 6 to the intake passage 8 In the introduced operating state, the average value αa of the feedback correction coefficient α becomes a value smaller than the initial value α ₁ of 100%, and the fuel injection amount Te is changed to the basic fuel injection amount T.
It is corrected to a value smaller than p. When the purge cut valve 14 is closed from this operating state and the evaporated fuel introduced from the charge passage 6 to the intake passage 8 is shut off, feedback correction is performed in conjunction with the purge cut valve 14 being opened. The coefficient α is immediately converted to α ₁ + (α _m −α
₁₎ After setting the value of the _{H 2,} the correction amount (α _m -α _{1) H 2}
Is brought close to the initial value α ₁ of 100% by PI control, so that the fuel injection amount Te from the injector 15 is delivered before all the evaporated fuel in the gas introduced from the charge passage 6 to the intake passage 8 is carried to the combustion chamber. It is possible to prevent the air-fuel ratio from increasing and to prevent the air-fuel ratio from overshooting to the rich side.

On the other hand, when it is judged that the purge cut valve 14 is closed, the routine proceeds to step B8, where it is judged whether or not the purge cut valve 14 is in the valve opening operation for opening the valve from the fully closed state.

When it is judged that the purge cut valve 14 is in the valve opening operation, the routine proceeds to step B9, where it is judged whether the average value αa of the feedback correction coefficient α is 100% or more.

When it is determined that the average value αa is 100% or more, the process proceeds to step B10, and the feedback correction coefficient α is calculated by the above equation (7).

As shown in FIG. 18, in the operating state in which the purge cut valve 14 is closed and the gas introduced from the charge passage 6 to the intake passage 8 is shut off, the feedback correction coefficient α becomes a value near 100%. To be kept. When the purge cut valve 14 is opened from this operating state and a lean gas containing almost no evaporative fuel is introduced from the charge passage 6 into the intake passage 8, the feedback correction coefficient α is immediately changed to α ₁ + (α _m − After being set to the value of α ₁ ) H ₂ , the correction component (α _m −α ₁ ) H ₁ was introduced from the charge passage 6 to the intake passage 8 by bringing the corrected value (α _m −α ₁ ) H ₁ close to the initial value α ₁ of 100% by PI control. It is possible to prevent the fuel injection amount Te from the injector 15 from being increased before the lean gas is conveyed to the combustion chamber, and to suppress the air-fuel ratio from overshooting to the rich side.

If it is determined that the average value αa is smaller than 100%, the process proceeds to step B11 to calculate the feedback correction coefficient α by the above equation (8).

As shown in FIG. 17, when the purge cut valve 14 is opened and a gas containing a large amount of evaporated fuel is introduced from the charge passage 6 into the intake passage 8, the feedback correction coefficient α is immediately changed to α ₁ +. After the value of (α _m −α ₁ ) H ₂ is set, the correction amount (α _m −α ₁ ) H ₂ is brought closer to the initial value α ₁ of 100% by PI control, so that the charge passage 6 is changed to the intake passage 8. It is possible to prevent the fuel injection amount Te from the injector 15 from being reduced before the evaporated fuel in the gas introduced into the fuel cell is conveyed to the combustion chamber, and to suppress the air-fuel ratio from overshooting to the lean side.

As the purge cut valve 14 is opened and closed in this way, the feedback correction coefficient α is calculated as the correction amount α ₁ + (α _m −α ₁ ) H ₁ or the correction amount α.
₁ + After (α _m -α ₁₎ stepwise changing to _{H 2,} remaining correction amount (α _m -α _{1) H 1} or correction amount (α _m -α _{1) H 2} PI control By setting by, the disturbance of the air-fuel ratio due to overshoot can be suppressed. By further suppressing the disturbance of the air-fuel ratio, the effect of suppressing the exhaust emission and the occurrence of torque shock can be enhanced.

By setting H ₁ to a value smaller than H _2, the correction amount (α _m −α ₁ ) set by PI control is set.
H ₁ becomes smaller than (α _m −α ₁ ) H ₂ , and it is possible to reliably prevent the actual air-fuel ratio from temporarily becoming lean, and it is possible to sufficiently secure operational stability.

Further, the leak diagnosis needs to be executed after the purging is temporarily stopped, but the fuel vapor up to almost the limit is adsorbed in the canister, and the fuel temperature is high and the fuel generated in the fuel tank is generated. Even when there is a lot of steam,
When the purging is stopped, the fuel vapor may overflow from the canister. When the purging is restarted due to the end of the leak diagnosis in such a state, the air-fuel ratio largely leans to the rich side and CO and HC are discharged. The amount will increase.

To deal with this, the control unit 21 estimates the purge gas concentration and prohibits the purge stop for the diagnosis until the estimated purge gas concentration becomes less than the predetermined value.

FIG. 19 is a flow chart showing the calculation of the purge gas concentration equivalent parameter. The background job is executed at regular intervals (eg, every 1 second).

From step 31 to step 35 is a part for checking whether or not the condition is for calculating the parameter. When all the following conditions are satisfied, it is judged that the condition is for calculating the parameter, and step 36 is executed. Continue below.

<1> Purging is in progress (step 3
1).

<2> Cooling water temperature Tw is within a predetermined range (for example, 80 ° C. <Tw <90 ° C.) (step 3)
2). This is the water temperature after warming up.

<3> The rotation speed N is within a predetermined range (for example, 1
000 rpm <N <3000 rpm) (step 33).

<4> The basic pulse width (engine load equivalent amount) Tp is within a predetermined range (step 34). In this load range, the suction negative pressure is -400 mmHg to -250 m.
It is a region of mHg.

<5> The air-fuel ratio feedback control is in progress (step 35). This is because the difference in purge gas concentration appears in the amount of change in the air-fuel ratio feedback correction coefficient α.

At step 36, the weighted average value α _N [%] of the air-fuel ratio feedback correction coefficient α is read.

The formula of this weighted average value is α _N = α × K3 + old α _N × (1−K3) (10) where K3: weighted average coefficient α: calculated α old α _N : previous α _N, which is calculated in another routine.

At step 37, the purge rate PR (= PR0
XK2) is read, and in step 38, the purge gas concentration parameter P [unknown number] is calculated by the equation P = (1−α _N ) / PR (11).

Assuming that there is no steady-state error due to variations in the injection characteristics of the injector and the flow characteristics of the air flow meter and changes over time, when the high-concentration purge gas is introduced during air-fuel ratio feedback control, the air-fuel ratio becomes Since it shifts to the rich side, when the air-fuel ratio shifted to the rich side is returned to the stoichiometric air-fuel ratio side, α is 100%.
If the purge gas near the air is introduced during air-fuel ratio feedback control, the air-fuel ratio will shift to the lean side, so try to return the air-fuel ratio to the rich side. And α is 100%
Get bigger. That is, 1-α _N is a value corresponding to the purge gas concentration, and when 1-α _N > 0, the larger the 1-α _N is, the higher the purge gas concentration is.
When α _N <0, it means that the purge gas concentration is lower as | 1-α _N | increases.

Further, the value per unit purge rate is obtained by dividing by the purge rate PR at that time as in the equation (11), and the value which is the deviation from the theoretical air-fuel ratio is 100-α.
_This is because, even if the value of _N is the same, if the purge rates are different, the two cannot be treated the same.

In step 39, the weighted average value P _N of the parameter P is P _N = P × K4 + old P _N × (1-K4) (12) where K4: weighted average coefficient P: current calculated parameter P _N : Count value CN for updating the number of updates by the previous P _N formula
T is incremented by 1 in step 40.

The weighted average value for the parameter P (also for α) is used to cut a value such as an abnormal value only once.

At step 41, the count value CNT is compared with a predetermined value, and if CNT <predetermined value, the process returns to the beginning of the routine.

If it has been updated a predetermined number of times continuously, the routine proceeds to step 42, where the weighted average value P _N at that time is set to the variable P _EC.
To end the routine.

FIG. 20 shows the air-fuel ratio feedback correction coefficient α, purge rate PR, purge gas concentration equivalent in a certain test mode from cold start (this test mode is entered from the state where a considerable amount of fuel vapor is adsorbed in the canister). The change of the parameter P is shown. It should be noted that the value of α is not the value of α itself, but a mountain of traveling (in the lower part of FIG.
It is the average value for each of the above).

In this test mode, when the purge control valve is opened at the same purge rate as that after the elapse of the predetermined time t5 from the beginning of the purge, the air-fuel ratio is largely shifted to the rich side due to the high concentration of purge gas immediately after the start of the purge. Therefore, the purge rate PR is gradually increased immediately after the start of the purge and thereafter gradually increased until the predetermined time t5 is reached. Therefore, even after the start of purging and t5, 1-
The value of α remains almost constant, and is rather small at the beginning of purging.

As described above, even when the purge rate changes, if the value itself of (1-α) (or a proportional value) is estimated to correspond to the purge gas concentration, an estimation error occurs. The actual purge gas concentration from the start of purging is
Just like the waveform shown in the middle part of FIG. 20, it is highest immediately after the start of purging, becomes smaller as the fuel vapor desorption from the canister progresses, and settles to a certain small value at the timing when the desorption is completed. This is because the value of α) does not correspond to such a change.

On the other hand, in this example, the value obtained by dividing the value of (1-α) by the purge rate PR is calculated as the purge gas concentration equivalent parameter P, so P is shown in the middle part of FIG. As shown in the figure, it is highest immediately after the start of purging, becomes smaller as the fuel vapor desorption from the canister progresses, and settles to a small value at the timing when the desorption is completed, which often affects the actual change in the purge gas concentration from the start of purging. Match.

In this way, if the purge gas concentration can be accurately estimated even immediately after the purge is started and the purge rate is changing, until the purge gas concentration parameter becomes less than the predetermined value (that is, until the purge gas concentration becomes low). When high-concentration purge gas is introduced immediately after the start of purging by prohibiting the purge stop for diagnosis and performing the purge, the priority is given to the purge, and the purge progresses to a low-concentration purge gas The leak diagnosis is executed.

As a result, the fuel vapor up to almost the limit is adsorbed in the canister, and when the fuel temperature is high and the amount of fuel vapor generated in the fuel tank is likely to increase, the purge is stopped and the leak diagnosis ends. As a result, it is possible to avoid the situation where the purging is restarted in the state where the fuel vapor overflows from the canister, and it is possible to prevent the increase of CO and HC emissions due to the enrichment of the air-fuel ratio in such a situation.

[0131]

According to the air-fuel ratio control apparatus for an engine of the first aspect, the feedback correction coefficient α is changed stepwise to the initial value α ₁ during the closing operation of the purge valve means without depending on the feedback control. It is possible to suppress the disturbance of the air-fuel ratio after the closing operation of the purge valve means. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

In the engine air-fuel ratio control apparatus according to the second aspect, the feedback correction coefficient α is feedback-controlled to the memory value αm of the feedback correction coefficient before the purge valve means is closed when the purge valve means is opened. By making the change in steps regardless of the above, it is possible to suppress the disturbance of the air-fuel ratio after the valve opening operation of the purge valve means. By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

In the air-fuel ratio control apparatus for an engine according to the third aspect, the feedback correction coefficient α is calculated by the feedback control by the correction amount α ₁ + (α _m −α ₁ ) H calculated when the purge valve means is closed. After the stepwise change, the remaining correction amount (α _m −α ₁ ) H is set by the feedback control, so that the disturbance of the air-fuel ratio due to the overshoot after the valve closing operation of the purge valve means can be suppressed to be small. By further suppressing the disturbance of the air-fuel ratio,
Exhaust emission is deteriorated, and the effect of suppressing torque shock can be enhanced.

In the air-fuel ratio control apparatus for an engine according to the fourth aspect, the feedback correction coefficient α is calculated by the feedback control by the correction amount α ₁ + (α _m −α ₁ ) H calculated when the purge valve means is opened. After the stepwise change, the remaining correction amount (α _m −α ₁ ) H is set by feedback control, so that the disturbance of the air-fuel ratio due to overshoot after the valve opening operation of the purge valve means can be suppressed to be small. By further suppressing the disturbance of the air-fuel ratio,
Exhaust emission is deteriorated, and the effect of suppressing torque shock can be enhanced.

According to a fifth aspect of the present invention, there is provided an air-fuel ratio control device for an engine according to the difference between the detected air-fuel ratio and the target air-fuel ratio at the start of purging or the end of purging for gradually changing the opening of the purge valve means. By calculating the feedback correction coefficient α, the actual air-fuel ratio can be made to follow the target air-fuel ratio with sufficient responsiveness, and exhaust emission can be prevented from deteriorating.

On the other hand, at the time of leak diagnosis in which the opening of the purge valve means is suddenly changed, the feedback correction coefficient α is forcibly corrected when the purge valve means is closed or opened, so that the purge valve means Disturbance of the air-fuel ratio that occurs after the valve closing operation or the valve opening operation can be suppressed to a small level.
By suppressing the turbulence of the air-fuel ratio to be small, it is possible to prevent deterioration of exhaust emission and torque shock.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart for explaining calculation of an effective pulse width Te similarly.

FIG. 3 is a flowchart for explaining calculation of fuel injection pulse width Ti and execution of injection.

FIG. 4 is a flowchart showing an air-fuel ratio control program.

FIG. 5 is a timing chart showing an example of air-fuel ratio control.

FIG. 6 is a flowchart showing a control program of the purge cut valve.

[FIG. 7] Similarly, ON given to the purge control valve
The flowchart for demonstrating calculation of duty.

FIG. 8 is a characteristic diagram of a purge rate correction coefficient K2.

FIG. 9 is a characteristic diagram of the opening area A _TH of the intake throttle valve of the same.

FIG. 10 is a characteristic diagram of ON duty with respect to the target opening area A _P.

FIG. 11 is a flowchart for similarly explaining leak diagnosis.

FIG. 12 is a flowchart for explaining leak diagnosis.

FIG. 13 is a waveform diagram showing a pressure change at the time of leak diagnosis.

FIG. 14 is a flowchart showing a program for similarly correcting the feedback correction coefficient.

FIG. 15 is a timing chart showing an example of controlling the air-fuel ratio.

FIG. 16 is a flowchart showing a program for correcting a feedback correction coefficient in another embodiment.

FIG. 17 is a timing chart showing an example of controlling the air-fuel ratio.

FIG. 18 is a timing chart showing an example of controlling the air-fuel ratio.

FIG. 19 is a flowchart for explaining calculation of a purge gas concentration equivalent parameter in another embodiment.

FIG. 20 is a waveform chart for explaining the same operation.

FIG. 21 is a timing chart showing an example of air-fuel ratio control in a conventional example.

FIG. 22 is a diagram corresponding to claims of the invention according to claim 1;

FIG. 23 is a diagram corresponding to the claims of the invention according to claim 2;

FIG. 24 is a diagram corresponding to the claims of the invention according to claim 3;

FIG. 25 is a diagram corresponding to the claim of the invention according to claim 4;

FIG. 26 is a claim correspondence diagram of the invention according to claim 5;

[Explanation of reference symbols] a fuel tank b canister c engine d intake passage e purge passage f purge valve means g operating condition detecting means h fuel supply amount calculating means i target air-fuel ratio setting means j air-fuel ratio detecting means k feedback correction coefficient detecting means l fuel supply amount calculation means m fuel supply means n valve closing operation detection means o feedback correction coefficient setting means p feedback correction coefficient storage means r feedback correction coefficient setting means s feedback correction coefficient setting means t feedback correction coefficient setting means x purge operation Time detection means y Leak diagnosis time detection means z Feedback correction coefficient correction means 1 Fuel tank 2 Charge passage 4 Canister 6 Purge passage 7 Intake throttle valve 8 Intake passage 9 Purge control valve 13 Diaphragm actuator 14 Purge cap Tobarubu 15 injector 21 control unit 23 fuel temperature sensor 24 water temperature sensor 25 speed sensor 26 air flow meter 27 O ₂ sensor

Claims (5)

[Claims] 1. A canister for adsorbing fuel evaporated in a fuel tank, a purge passage for connecting the canister to an intake passage, a purge valve means for opening and closing the purge passage according to operating conditions of the engine, and operating conditions of the engine. Operating condition detection means for detecting the basic fuel supply amount Tp for calculating the basic fuel supply amount Tp according to the detected operating condition, and a target air-fuel ratio for setting the target air-fuel ratio according to the detected operating condition Setting means, air-fuel ratio detecting means for detecting the air-fuel ratio of the engine, feedback correction coefficient detecting means for calculating a feedback correction coefficient α according to the difference between the detected air-fuel ratio and the target air-fuel ratio, and the calculated basic A fuel supply amount calculation means for calculating the fuel supply amount T by correcting the fuel supply amount Tp with the feedback correction coefficient α, and the calculated fuel supply amount T An engine including fuel supply means for supplying the engine to the engine, and a closing operation detecting means for detecting a closing operation time of the purge valve means from an open state to a closed state, and a closing operation of the purge valve means. An air-fuel ratio control device for an engine, comprising: a feedback correction coefficient setting means for sometimes setting the feedback correction coefficient α to an initial value α ₁ . 2. A canister for adsorbing fuel evaporated in a fuel tank, a purge passage for connecting the canister to an intake passage, purge valve means for opening and closing the purge passage according to operating conditions of the engine, and operating conditions of the engine. Operating condition detection means for detecting the basic fuel supply amount Tp for calculating the basic fuel supply amount Tp according to the detected operating condition, and a target air-fuel ratio for setting the target air-fuel ratio according to the detected operating condition Setting means, air-fuel ratio detecting means for detecting the air-fuel ratio of the engine, feedback correction coefficient detecting means for calculating a feedback correction coefficient α according to the difference between the detected air-fuel ratio and the target air-fuel ratio, and the calculated basic A fuel supply amount calculation means for calculating the fuel supply amount T by correcting the fuel supply amount Tp with the feedback correction coefficient α, and the calculated fuel supply amount T An engine including fuel supply means for supplying fuel to the engine, feedback correction coefficient storage means for storing a feedback correction coefficient αm in the open state of the purge valve means, and the closed state of the purge valve means from the closed state to the open state. And a feedback correction coefficient setting means for setting the feedback correction coefficient α to a stored feedback correction coefficient αm when the purge valve means is opened. An air-fuel ratio control device for an engine. 3. A canister for adsorbing fuel evaporated in a fuel tank, a purge passage for connecting the canister to an intake passage, a purge valve means for opening and closing the purge passage according to operating conditions of the engine, and operating conditions of the engine. Operating condition detection means for detecting the basic fuel supply amount Tp for calculating the basic fuel supply amount Tp according to the detected operating condition, and a target air-fuel ratio for setting the target air-fuel ratio according to the detected operating condition Setting means, air-fuel ratio detecting means for detecting the air-fuel ratio of the engine, feedback correction coefficient detecting means for calculating a feedback correction coefficient α according to the difference between the detected air-fuel ratio and the target air-fuel ratio, and the calculated basic A fuel supply amount calculation means for calculating the fuel supply amount T by correcting the fuel supply amount Tp with the feedback correction coefficient α, and the calculated fuel supply amount T An engine including fuel supply means for supplying the engine to the engine, and a closing operation detection means for detecting a closing operation time of the purge valve means from an open state to a closed state, and an open state of the purge valve means. Feedback correction coefficient αm for storing the feedback correction coefficient αm, and the feedback correction coefficient α when the purge valve means is closed and the feedback correction coefficient αm and the initial value α ₁ stored when the purge valve means is open. Based on H
Is a constant, feedback correction coefficient setting means for setting a value calculated as α = α ₁ + (αm−α ₁ ) H, and an air-fuel ratio control device for an engine, comprising: 4. A canister for adsorbing fuel evaporated in a fuel tank, a purge passage for connecting the canister to an intake passage, purge valve means for opening and closing the purge passage according to operating conditions of the engine, and operating conditions of the engine. Operating condition detection means for detecting the basic fuel supply amount Tp for calculating the basic fuel supply amount Tp according to the detected operating condition, and a target air-fuel ratio for setting the target air-fuel ratio according to the detected operating condition Setting means, air-fuel ratio detecting means for detecting the air-fuel ratio of the engine, feedback correction coefficient detecting means for calculating a feedback correction coefficient α according to the difference between the detected air-fuel ratio and the target air-fuel ratio, and the calculated basic A fuel supply amount calculation means for calculating the fuel supply amount T by correcting the fuel supply amount Tp with the feedback correction coefficient α, and the calculated fuel supply amount T In an engine including fuel supply means for supplying fuel to the engine, feedback correction coefficient storage means for storing the feedback correction coefficient αm in the open state of the purge valve means, and opening of the purge valve means from the closed state to the open state. Based on the feedback correction coefficient αm and the initial value α ₁ stored in the valve closed state, the feedback correction coefficient α when the valve opening operation is detected for detecting the valve operation time and the purge valve means when the purge valve means is opened. Is a constant, feedback correction coefficient setting means for setting a value calculated as α = α ₁ + (αm−α ₁ ) H, and an air-fuel ratio control device for an engine, comprising: 5. A canister for adsorbing fuel evaporated in a fuel tank, a purge passage for connecting the canister to an intake passage, purge valve means for opening and closing the purge passage according to operating conditions of the engine, and operating conditions of the engine. Operating condition detection means for detecting the basic fuel supply amount Tp for calculating the basic fuel supply amount Tp according to the detected operating condition, and a target air-fuel ratio for setting the target air-fuel ratio according to the detected operating condition Setting means, air-fuel ratio detecting means for detecting the air-fuel ratio of the engine, feedback correction coefficient detecting means for calculating a feedback correction coefficient α according to the difference between the detected air-fuel ratio and the target air-fuel ratio, and the calculated basic A fuel supply amount calculation means for calculating the fuel supply amount T by correcting the fuel supply amount Tp with the feedback correction coefficient α, and the calculated fuel supply amount T In an engine equipped with fuel supply means for supplying fuel to the engine, a purge operation detection means for gradually detecting the start or end of purge for gradually changing the opening degree of the purge valve means, and the opening degree of the purge valve means Leak diagnosis detection means that detects when the leak diagnosis is changed to, and while feedback control of the air-fuel ratio during purge operation,
An air-fuel ratio control apparatus for an engine, comprising: a feedback correction coefficient correction means for forcibly correcting the feedback correction coefficient α when the purge valve means f is operated during a leak diagnosis.