JP3453830B2 - Engine air-fuel ratio control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an air-fuel ratio control device for controlling the air-fuel ratio of intake air supplied to an engine.

[0002]

2. Description of the Related Art Conventionally, in order to improve the fuel efficiency of an engine, it is generally known that the fuel supply is stopped at the time of deceleration, and when the fuel supply is stopped, the intake air-fuel ratio is reduced. Becomes lean. Therefore, when the predetermined oxygen concentration in the exhaust gas is detected by the O2 sensor and the air-fuel ratio is controlled to be the air-fuel ratio corresponding to this predetermined oxygen concentration, the lean air-fuel ratio is detected to detect the air-fuel ratio. Is feedback-controlled so as to correct the value to the rich side. Then, when the fuel supply is restored after the stop, the change in the air-fuel ratio due to the returned fuel is detected by the O2 sensor, and feedback control is performed so that the air-fuel ratio becomes the target air-fuel ratio. Since there is a predetermined time delay (dead time) before the detection by the O2 sensor, the control for correcting the air-fuel ratio to the rich side is continued during that time, and as a result, the air-fuel ratio for a while immediately after the fuel supply is restored. Is erroneously corrected to the rich side.

Therefore, as disclosed in Japanese Examined Patent Publication No. 58-40009, the air-fuel ratio is largely deviated from the target air-fuel ratio until a predetermined time elapses after the fuel supply is stopped. It has been proposed to stop the feedback control and accurately control the air-fuel ratio.

[0004]

By the way, instead of using an O2 sensor for detecting a predetermined value of the oxygen concentration in exhaust gas, a linear O2 sensor in which an output signal changes according to a change in intake air-fuel ratio is used. When used, this sensor has a delay time in response to a change in the air-fuel ratio and before outputting an output signal proportional to the air-fuel ratio. Therefore, unlike the conventional example described above, only the dead time until the fuel supplied by the return of the fuel supply reaches the sensor in the exhaust passage is considered, and the delay time until the reaction of the sensor is not considered. Therefore, it is not possible to accurately detect the period during which the air-fuel ratio greatly deviates.

The present invention has been made in view of the above problems, and an object thereof is to obtain a linear O 2 when the target air-fuel ratio changes during feedback control of the air-fuel ratio.
By changing the setting condition of the period when the air-fuel ratio detected by the air-fuel ratio sensor such as a sensor largely deviates from the basic air-fuel ratio, it is possible to set the period accurately and effectively prevent erroneous correction of feedback control. is there.

[0006]

In order to achieve the above object, in the invention of claim 1, the feedback control air-fuel ratio is set based on the basic air-fuel ratio according to the operating condition of the engine, and this air-fuel ratio and While the deviation from the basic air-fuel ratio is large,
The prohibition period is set so that feedback control is not performed.

Specifically, in the present invention, as shown in FIG. 1, an air-fuel ratio detecting means 22 for detecting an air-fuel ratio of intake air supplied to the engine 1, and an air-fuel ratio detected by this air-fuel ratio detecting means 22. It is premised on an air-fuel ratio control device for an engine, which is provided with a control means 28 for performing feedback control so that the fuel consumption ratio becomes a target air-fuel ratio.

[0008] Then, the basic air-fuel ratio setting means 29 for setting a basic air-fuel ratio as the target air-fuel ratio in accordance with the operating condition of the engine 1, the basic air-fuel ratio set by the basic air-fuel ratio setting means 29, the The change in the basic air-fuel ratio is
Corrects the time until it is detected by the ratio detection means 22.
It is for the purpose of changing according to the operating state of the engine
The dead time correction coefficient and the air-fuel ratio detecting means 22 are
Delay in response from detection of change in basic air-fuel ratio to output
To correct the engine run time and to operate the engine
It can be corrected by a variable primary delay correction coefficient according to the condition.
And, feedback control air-fuel ratio setting means 30 for setting the feedback control air-fuel ratio, the basic air-fuel ratio setting means 29 and the feedback control air-fuel ratio setting means 3
The deviation detecting means 31 for obtaining the deviation between the air-fuel ratios respectively set to 0, and the controlling means 28 when the deviation obtained by the deviation detecting means 31 is a predetermined value or more.
And a feedback control prohibiting means 33 for stopping the feedback control by.

According to a second aspect of the present invention, the engine air-fuel ratio control apparatus according to the first aspect is provided with a target air-fuel ratio change detecting means 32 for detecting a change in the target air-fuel ratio.

The feedback control prohibiting means 3 is also provided.
3 is configured to stop the feedback control by the control means 28 when the change in the target air-fuel ratio is detected by the target air-fuel ratio change detecting means 32.

According to a third aspect of the present invention, in the engine air-fuel ratio control apparatus according to the first aspect, there is provided fuel supply stopping means 34 for stopping the supply of fuel when a predetermined condition is satisfied.

Then, the feedback control prohibiting means 33
Is configured so that when the fuel supply is stopped by the fuel supply stopping means 34, the feedback control by the control means 28 is stopped until the predetermined period elapses from the time when the fuel supply is restored. And

[0013]

[0014]

[0015]

With the above construction, in the first aspect of the invention, the air-fuel ratio of the intake air supplied to the engine 1 is detected by the air-fuel ratio detecting means 22.
Is detected by the control means 28 and feedback control is performed so that the air-fuel ratio becomes the target air-fuel ratio. Also,
The basic air-fuel ratio setting means 29 sets the basic air-fuel ratio as the target air-fuel ratio according to the operating conditions of the engine 1, and the feedback control air-fuel ratio setting means 30 sets the basic air-fuel ratio to the basic air-fuel ratio. Change the air-fuel ratio
For correcting the time until the detection means 22 detects
The dead time correction coefficient and the change in the basic air-fuel ratio above are checked for air-fuel ratio.
Response delay time from detection by output means 22 to output
The feedback control air-fuel ratio is set by being corrected by the first-order lag correction coefficient for correcting the above, and the deviation between the basic air-fuel ratio and the feedback control air-fuel ratio is determined by the deviation detecting means 31, and this deviation is predetermined. When the value is not less than the value, the feedback control prohibiting means 33 stops the feedback control by the control means 28.
Thus, the basic air-fuel ratio is not only 1
The feedback control air-fuel ratio is set by being corrected by the next-delay correction coefficient, and the feedback control is stopped when the deviation from the basic air-fuel ratio is equal to or more than a predetermined value.
The period during which the air-fuel ratio detected by the air-fuel ratio detecting means 22 greatly deviates from the basic air-fuel ratio can be detected with high accuracy, and erroneous correction of the air-fuel ratio feedback control can be prevented.

In the second aspect of the invention, when the target air-fuel ratio changes, the change is detected by the target air-fuel ratio change detecting means 32, and when the change in the target air-fuel ratio is detected, the feedback control prohibiting means 33. The feedback control by the control means 28 is stopped. Therefore, when the target air-fuel ratio changes, the period during which the air-fuel ratio greatly deviates from the basic air-fuel ratio can be detected with high accuracy, and erroneous correction of the air-fuel ratio feedback control can be prevented.

According to the third aspect of the invention, the fuel supply is stopped by the fuel supply stopping means 34 when a predetermined condition is satisfied. Then, when the fuel supply is stopped by the fuel supply stopping means 34, the feedback control prohibiting means 33 stops the feedback control by the control means 28 until a predetermined period elapses after the fuel supply is restored. . Therefore, it is possible to detect with high accuracy a period during which the air-fuel ratio greatly deviates from the basic air-fuel ratio when the fuel supply is restored, and prevent erroneous correction of feedback control of the air-fuel ratio.

[0018]

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG.

(Embodiment 1) FIG. 6 shows an engine air-fuel ratio control apparatus according to Embodiment 1 of the present invention. Reference numeral 1 denotes an engine mounted on a vehicle. The engine 1 includes a cylinder block 3 having a plurality of cylinders 2, 2, ... (Only one is shown), and a cylinder head 4 mounted on the upper surface of the cylinder block 3. And a piston 5 reciprocally fitted in each cylinder 2, and a combustion chamber 6 surrounded by the piston 5 and the cylinder head 4 is formed in each cylinder 2. Reference numeral 7 is a spark plug provided in the upper part of the combustion chamber 6 in the cylinder 2,
The spark plug 7 is connected via a distributor 9 to an ignition coil 8 which receives an ignition signal from a control unit 25, which will be described later, and which generates a high voltage secondary voltage.

Reference numeral 11 denotes an intake passage for supplying intake air (air) to the combustion chamber 6 in each of the cylinders 2. The upstream end of the intake passage 11 is connected to an air cleaner (not shown), and the downstream end is provided with an intake valve 11a. And communicates with the combustion chamber 6. The intake passage 11 receives a fuel injection signal from a thermal air flow sensor 12 that detects the actual intake air amount of the engine 1, a throttle valve 13 that throttles the intake passage 11, a surge tank 14, and a control unit 25. An injector 15 for injecting and supplying fuel is arranged in order from the upstream side.

The intake passages 11, 11 on the upstream and downstream sides of the throttle valve 13 are connected by a bypass passage 17, and the bypass passage 17 is driven by an actuator 18 which operates by receiving an ISC valve drive signal from a control unit 25. ISC valve 19 (idle speed control valve) is installed.
The idle speed of the engine 1 is controlled by controlling the opening degree of the C valve 19.

On the other hand, 21 is an exhaust passage for discharging the exhaust gas in the combustion chamber 6, the upstream end of which is connected to the combustion chamber 6 via an exhaust valve 21a. In the middle of the exhaust passage 21, an air-fuel ratio sensor 22 as an air-fuel ratio detecting means for detecting the air-fuel ratio of intake air based on the oxygen concentration in the exhaust gas, and an exhaust purification device 23 for purifying the exhaust gas are provided from the upstream side. They are arranged in order. The air-fuel ratio sensor 22 is composed of a linear O2 sensor whose output signal changes in proportion to changes in the air-fuel ratio.

The injectors 15, the ignition coil 8 and the actuator 18 of the ISC valve 19 are controlled by a control unit 25 (more specifically, an engine control unit). The control unit 25 includes an intake air amount signal output from the air flow sensor 12 and a distributor 9 corresponding to a rotation angle of a crankshaft (not shown) of the engine 1 for calculating the engine speed. A crank angle signal indicating rotation, an output signal of the air-fuel ratio sensor 22,
At least the water temperature signal from the water temperature sensor 26 provided in the water jacket 3a of the cylinder block 3 of the engine 1 is input.

Now, the signal processing operation of the control unit 25 when the air-fuel ratio of intake air is controlled by the fuel injection signal to the injector 15 will be described with reference to FIG. First, the first step S1 after the start
At step S2, various signals are read and the basic air-fuel ratio A / F (o) is set. In this case, as shown in FIG. 3, the basic air-fuel ratio A / F (o) is set in advance as a map according to the engine speed and the engine load, and based on this map, the basic air-fuel ratio A / F (o) ) Is set. In the next step S3, the air flow sensor 12 is
The fuel injection signal to be output to the injector 15 should be output by dividing the intake air amount detected in step 1 by the engine speed to obtain the basic air charge amount, multiplying this by the air-fuel ratio shift coefficient according to the operating region of the engine 1. The basic pulse of is calculated. After that, in step S4, it is determined whether or not a feedback control condition for feedback controlling the air-fuel ratio is satisfied. In this determination, the operating range of the engine 1 is, for example, as shown in FIG.
It is assumed that the feedback control condition is satisfied when the area is in the hatched area. When the determination is NO,
After the feedback control of the air-fuel ratio is prohibited in step S10, the process proceeds to step S11.

On the other hand, when the determination in step S4 is YES, the process proceeds to step S5, and the feedback control air-fuel ratio A / F (i) is set. This air-fuel ratio A / F (i) is calculated by the following equation based on the previous air-fuel ratio A / F (i-1), the basic air-fuel ratio A / F (o) set in step S2 and the first-order lag coefficient α. Is calculated by

A / F (i) = α × A / F (i-1) + (1-α) × A / F (o) (i-6) ... Then, the first-order lag coefficient α is As shown in Fig. 4, the intake air basic filling amount is increased, that is, it is set to be smaller as the engine load is increased. Therefore, the air-fuel ratio A / F (i) is set so that the engine load is small and the exhaust gas The smaller the flow rate, the greater the reflection degree of the previous air-fuel ratio A / F (i-1).

After step S5, the process proceeds to step S6,
It is determined whether the target air-fuel ratio when performing the feedback control has changed from the previous air-fuel ratio. When this determination is NO, the routine proceeds to step S9, where feedback control is executed so that the air-fuel ratio detected by the air-fuel ratio sensor 22 becomes the previous target air-fuel ratio, and then the routine proceeds to step S11. When the determination in step S6 is YES, in step S7, the deviation ΔA / between the basic air-fuel ratio A / F (o) and the feedback control air-fuel ratio A / F (i) set in steps S2 and S5, respectively. Calculate F, step S
In 8, the magnitude of the deviation ΔA / F is compared with a predetermined value (the predetermined value is 0 in each of the following embodiments, but may be a value other than 0). When this determination is NO of ΔA / F> 0, the process proceeds to step S10, and the air-fuel ratio feedback control is not performed. On the other hand, if the judgment is ΔA / F ≦ 0, Y
If ES, the process proceeds to step S9, and feedback control of the air-fuel ratio is performed. In step S11 after these steps S9 and S10, various correction coefficient terms are added to the basic pulse calculated in step S3 to calculate the final pulse of the fuel injection signal, and in the next step S12, the final pulse of the final pulse is calculated. After the fuel injection signal is output to the injector 15 to execute the fuel injection, the process returns.

In this embodiment, step S of the above flow is performed.
9 constitutes a control means 28 for feedback control so that the air-fuel ratio detected by the air-fuel ratio sensor 22 becomes the target air-fuel ratio.

Further, in step S2, the basic air-fuel ratio A / F as the target air-fuel ratio is set according to the operating conditions of the engine 1.
A basic air-fuel ratio setting means 29 for setting (o) is configured.

Further, in step S5, the basic air-fuel ratio A / F set by the basic air-fuel ratio setting means 29 is set.
The feedback control air-fuel ratio setting means 30 is configured to correct (o) by the dead time correction coefficient and the first-order delay correction coefficient and set the feedback control air-fuel ratio A / F (i).

In step S7, the basic air-fuel ratio A / F set by the basic air-fuel ratio setting means 29 and the feedback control air-fuel ratio setting means 30, respectively.
Deviation detecting means 31 for obtaining the deviation ΔA / F between (o) and the feedback control air-fuel ratio A / F (i) is configured.

Further, in step S6, the target air-fuel ratio change detecting means 32 for detecting the change in the target air-fuel ratio is constructed.

Then, in steps S8 and S10, the change in the target air-fuel ratio is detected by the target air-fuel ratio change detecting means 32, and the deviation ΔA / F obtained by the deviation detecting means 31 is a predetermined value (= 0). When the above is the case, the feedback control prohibiting means 33 for stopping the feedback control by the control means 28 is configured.

Next, the operation of the above embodiment will be described. Based on the operating conditions of the engine 1, the basic air-fuel ratio of intake air A /
F (o) is set. When the air-fuel ratio feedback control condition is satisfied, the feedback control air-fuel ratio A / F is calculated based on the equation from the basic air-fuel ratio A / F (o).
When (i) is set and the target air-fuel ratio during feedback control does not change, feedback control is performed so that the air-fuel ratio detected by the air-fuel ratio sensor 22 becomes the previous target air-fuel ratio. On the other hand, as shown in FIG. 5, when the target air-fuel ratio changes, first, the basic air-fuel ratio A / F
The deviation ΔA / F between (o) and the feedback control air-fuel ratio A / F (i) is calculated, and this deviation ΔA / F is then compared with a predetermined value (= 0). When ΔA / F> 0, feedback control of the air-fuel ratio is not performed, and
When A / F ≦ 0, feedback control of the air-fuel ratio is performed.

Therefore, in this embodiment, when setting the feedback control air-fuel ratio A / F (i), the basic air-fuel ratio A / F (o) is set to 1 as well as the dead time correction coefficient.
The air-fuel ratio A / F (i) for feedback control is set by performing correction using the next delay correction coefficient as well, and the basic air-fuel ratio A / F is set.
Since the feedback control is stopped when the deviation ΔA / F from (o) is equal to or greater than a predetermined value, the air-fuel ratio detected by the air-fuel ratio sensor 22 when the target air-fuel ratio changes is the basic air-fuel ratio A /
It is possible to detect with high accuracy a period that greatly deviates from F (o) and prevent erroneous correction of feedback control of the air-fuel ratio.

(Embodiment 2) FIG. 7 shows Embodiment 2 of the present invention (note that the same parts as those in FIGS. 2 and 6 are designated by the same reference numerals and detailed description thereof will be omitted), In No. 1, when the target air-fuel ratio changes, the deviation ΔA / F between the basic air-fuel ratio A / F (o) and the feedback control air-fuel ratio A / F (i) is calculated and compared with the predetermined value. While the execution of the feedback control is determined by the above, the same operation is performed when the fuel supply is restored from the stopped state.

In this embodiment, the basic structure is the same as that of the first embodiment.
(See FIG. 6), and the control unit 25
In the above, only the signal processing operation when controlling the intake air-fuel ratio by the fuel injection signal to the injector 15 is different.
That is, as shown in FIG. 7, steps T1 to T3 are the same as steps S1 to S3 of the first embodiment, respectively. After step T3, in step T4, it is determined whether or not the condition of fuel supply stop (fuel cut) is satisfied. judge.
This condition is satisfied when the engine 1 is in a decelerated state in a predetermined operating range, or when the torque of the engine 1 is reduced to prevent a shift shock of the automatic transmission. If this determination is YES, the fuel supply is stopped in step T5.

On the other hand, when the determination in step T4 is NO, the process proceeds to step T6, and it is determined whether or not the feedback control condition for feedback controlling the air-fuel ratio is satisfied. If this determination is NO, step T1
After prohibiting the air-fuel ratio feedback control in 2,
Go to step T13.

On the other hand, when the determination in step T6 is YES, the feedback control air-fuel ratio A / F (i) is set in step T7 (see the equation). After that, the routine proceeds to Step T8, where it is determined whether or not a predetermined period has elapsed from the point of time when the fuel supply was stopped. If this determination is NO, the routine proceeds to Step T11, where the air detected by the air-fuel ratio sensor 22 is detected. After performing the feedback control so that the fuel ratio becomes the target air-fuel ratio, the process proceeds to step T13. Also,
When the determination in step T8 is YES, step T9
In step A2, the basic air-fuel ratio A / F (o) and the feedback control air-fuel ratio A set in steps T2 and T7 are set.
Deviation ΔA / F from / F (i) is calculated, and step T10
In, the magnitude of this deviation ΔA / F with respect to a predetermined value (= 0) is determined. When this determination is NO when ΔA / F> 0, the routine proceeds to step T12, where the air-fuel ratio feedback control is not performed, but when the determination is YES when ΔA / F ≦ 0, the routine proceeds to step T11, where the air-fuel ratio feedback control is performed. I do. In step T13 after these steps T11 and T12, the final pulse of the fuel injection signal is calculated, and in the next step T14, the fuel injection signal of the final pulse is output to the injector 15 to execute fuel injection,
To return.

In this embodiment, step T of the above flow is performed.
11. The control means 28 is constituted by 11, the basic air-fuel ratio setting means 29 is constituted by step T2, the feedback control air-fuel ratio setting means 30 is constituted by step T7, and the deviation detecting means 31 is constituted by step T9.

The steps T4 and T5 constitute the fuel supply stopping means 34 for stopping the fuel supply when the predetermined fuel supply stop condition is satisfied.

Further, in steps T8, T10 and T12, the fuel supply is stopped by the fuel supply stopping means 34, and the deviation detecting means 31 continues until a predetermined period elapses after the fuel supply is restored. Calculated deviation ΔA
If / F is equal to or greater than the predetermined value (= 0), the feedback control prohibiting means 33 that stops the feedback control by the control means 28 is configured.

Therefore, in this embodiment, the intake basic air-fuel ratio A / F (o) is determined based on the operating conditions of the engine 1.
Is set. Further, when the condition for stopping the fuel supply is satisfied, the fuel supply is stopped, and when the fuel supply is restored thereafter, from the time of the restoration until a predetermined period elapses,
The feedback control air-fuel ratio A / F (i) is set based on the basic air-fuel ratio A / F (o), and the basic air-fuel ratio A / F (o) and the feedback control air-fuel ratio A / F ( i) deviation ΔA / F is calculated, and this deviation Δ
The A / F is compared with a predetermined value (= 0). And ΔA /
If F> 0, the air-fuel ratio feedback control is not performed, but if ΔA / F ≦ 0, the air-fuel ratio feedback control is performed.

Therefore, in this embodiment, the period during which the air-fuel ratio detected by the air-fuel ratio sensor 22 when returning from the stopped state of the fuel supply greatly deviates from the basic air-fuel ratio A / F (o) can be detected with high accuracy, It is possible to prevent erroneous correction of feedback control of the air-fuel ratio.

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

As described above, according to the invention of claim 1, in the case where feedback control is performed so that the air-fuel ratio of the intake air supplied to the engine becomes the target air-fuel ratio,
Set the basic air-fuel ratio as the target air-fuel ratio according to the operating conditions of the engine , and change this basic air-fuel ratio
Correction of the time until is detected by the air-fuel ratio detection means
Of the basic air-fuel ratio as well as the dead time correction coefficient for
The response from when the change is detected by the air-fuel ratio detection means until it is output.
By the primary delay correction coefficient for correcting the answer delay time
Corrected, the feedback control air-fuel ratio is set, and the feedback control is stopped when the deviation between the basic air-fuel ratio and the feedback control air-fuel ratio is equal to or more than a predetermined value. The period during which the detected air-fuel ratio greatly deviates from the basic air-fuel ratio can be detected with high accuracy, and erroneous correction of feedback control of the air-fuel ratio can be prevented.

According to the second aspect of the present invention, the feedback control is stopped when the target air-fuel ratio changes, so that the period during which the air-fuel ratio deviates from the basic air-fuel ratio when the target air-fuel ratio changes can be accurately determined. It can be detected well and erroneous correction of feedback control of the air-fuel ratio can be prevented.

According to the third aspect of the invention, after the fuel supply is stopped, the feedback control is stopped from the time when the fuel supply is returned until a predetermined period elapses, so that the fuel supply is returned. At times, it is possible to detect with high accuracy a period during which the air-fuel ratio greatly deviates from the basic air-fuel ratio, and prevent erroneous correction of the air-fuel ratio feedback control.

[0055]

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of the present invention.

FIG. 2 is a flowchart showing a signal processing operation performed by the control unit according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram for setting a basic air-fuel ratio according to engine operating conditions.

FIG. 4 is a characteristic diagram for setting a first-order lag coefficient for a basic intake charge amount.

FIG. 5 is a time chart diagram showing changes in the feedback control air-fuel ratio when the target air-fuel ratio changes.

FIG. 6 is an overall configuration diagram of the first embodiment.

FIG. 7 is a view corresponding to FIG. 2 showing a second embodiment.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-136446 (JP, A) JP-A-62-240446 (JP, A) JP-A-5-141294 (JP, A) Actual flat 4- 69658 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) F02D 41/00-45/00

Claims (3)

(57) [Claims] 1. An air-fuel ratio detecting means for detecting an air-fuel ratio of intake air supplied to an engine, and a control means for performing feedback control so that the air-fuel ratio detected by the air-fuel ratio detecting means becomes a target air-fuel ratio. In the engine air-fuel ratio control device, a basic air-fuel ratio setting means for setting a basic air-fuel ratio as the target air-fuel ratio according to the engine operating conditions, and a basic air-fuel ratio set by the basic air-fuel ratio setting means, For correcting the time until the change in the basic air-fuel ratio is detected by the air-fuel ratio detecting means, and a variable dead time correction coefficient according to the operating state of the engine,
The air-fuel ratio detecting means is for correcting the response delay time from the detection of the change in the basic air-fuel ratio to the output thereof, and is based on a primary delay correction coefficient which is variable according to the operating state of the engine. Deviation detection for obtaining a deviation between the air-fuel ratios set by the feedback-control air-fuel ratio setting means for setting the feedback-control air-fuel ratio and the basic air-fuel ratio setting means and the feedback control air-fuel ratio setting means by correcting An air-fuel ratio control apparatus for an engine, comprising: a means and a feedback control prohibiting means for stopping the feedback control by the control means when the deviation obtained by the deviation detecting means is equal to or more than a predetermined value. 2. The air-fuel ratio control device for an engine according to claim 1, further comprising a target air-fuel ratio change detecting means for detecting that the target air-fuel ratio has changed, and the feedback control prohibiting means comprises the target air-fuel ratio change detecting means. When the change in the target air-fuel ratio is detected by the, the air-fuel ratio control device for the engine is configured to stop the feedback control by the control means. 3. The engine air-fuel ratio control device according to claim 1, further comprising fuel supply stopping means for stopping the supply of fuel when a predetermined condition is satisfied, and the feedback control prohibiting means is the fuel supply stopping means. When the supply of the fuel is stopped by the fuel cell, the feedback control by the control means is stopped until the predetermined period elapses from the time when the fuel supply is returned to the air-fuel ratio control of the engine. apparatus.