JPH07197837A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To perform high-precise control of an air-fuel ratio even when, during the starting of an engine and during fuel cut, a downstream air-fuel ratio sensor can not be used for control of an air-fuel ratio. CONSTITUTION:Outputs from upper stream air-fuel ratio sensors 13A and 13B arranged in an exhaust passage situated upper stream from catalyst converters 12A and 12B are corrected by using an integrated value of a deviation between an output from a downstream O2 sensor 17 and a reference output. An integrated value is stored at a control circuit 10, and when a downstream O2 sensor output can not be used for control of an air-fuel ratio, a downstream air-fuel ratio sensor output is corrected based on a stored integrated value to control an air-fuel ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly, to a combustion air-fuel ratio of an engine based on the outputs of air-fuel ratio sensors arranged upstream and downstream of an exhaust purification catalytic converter. The present invention relates to an air-fuel ratio control device for an internal combustion engine that controls the engine.

[0002]

2. Description of the Related Art There is known a technique in which a three-way catalytic converter is arranged in an exhaust passage of an internal combustion engine to purify three harmful components of NO _x , HC and CO in the exhaust gas at the same time. Further, the three-way catalyst can purify the above three components simultaneously only when the air-fuel ratio of the inflowing exhaust gas is in an extremely narrow range near the stoichiometric air-fuel ratio. Maintaining the vicinity is important for maintaining good exhaust properties. For this purpose, an air-fuel ratio sensor such as an O ₂ sensor is provided on the upstream side of the catalytic converter in the exhaust passage to detect the exhaust air-fuel ratio actually flowing into the catalytic converter, and the exhaust air-fuel ratio is adjusted based on the detected exhaust air-fuel ratio. Feedback control of the fuel supply amount to the engine is generally performed so as to maintain the stoichiometric air-fuel ratio. (In this specification, the ratio of the amount of air and the amount of fuel supplied to the exhaust passage on the upstream side of the catalytic converter, the engine combustion chamber, the intake passage, etc. is called the exhaust air-fuel ratio, and The air-fuel ratio of combustion is referred to as the combustion air-fuel ratio, and therefore, when fuel or secondary air is not supplied to the exhaust passage upstream of the catalytic converter, the exhaust air-fuel ratio and the combustion air-fuel ratio match. However, if the engine combustion air-fuel ratio is controlled according to the output signal of the air-fuel ratio sensor provided on the upstream side of the catalytic converter as described above, a problem may actually occur.

That is, when the above-mentioned control is performed, variations in the output characteristics of the individual air-fuel ratio sensors and changes in the output characteristics due to changes over time are directly reflected in the control.
The accuracy of the air-fuel ratio control may deteriorate. Further, the exhaust gas discharged from each cylinder is not uniformly mixed on the upstream side of the catalytic converter, and depending on the arrangement of the upstream side air-fuel ratio sensor, the sensor detects the exhaust air-fuel ratio fluctuation of a specific cylinder. As a whole, it may be difficult to accurately control the exhaust air-fuel ratio flowing into the catalytic converter to be close to the stoichiometric air-fuel ratio. Furthermore, when using a full range air-fuel ratio sensor that produces an output proportional to the air-fuel ratio over a wide range as the upstream air-fuel ratio sensor, the reference output value (output value corresponding to the theoretical air-fuel ratio) changes over time. Therefore, there arises a problem that the control center air-fuel ratio gradually deviates from the stoichiometric air-fuel ratio.

In order to solve this problem, in addition to the upstream air-fuel ratio sensor, an air-fuel ratio sensor (downstream air-fuel ratio sensor) is arranged in the exhaust passage on the downstream side of the catalytic converter, and the output of the upstream air-fuel ratio sensor is set. A so-called double sensor system has been proposed in which, in addition to signal-based air-fuel ratio control, air-fuel ratio control is performed based on the output of a downstream side air-fuel ratio sensor (see Japanese Patent Laid-Open No. 61-197738).

On the downstream side of the three-way catalyst, the exhaust gas is uniformly mixed, and the exhaust temperature is lower than that on the upstream side of the catalyst. Therefore, the downstream air-fuel ratio sensor output is more stable than the upstream air-fuel ratio sensor output. Little change in output characteristics due to aging. In the double sensor system disclosed in Japanese Patent Laid-Open No. 61-197738, the output of the downstream side air-fuel ratio sensor (in this case, the downstream O ₂ sensor) provided on the downstream side of the three-way catalyst and the reference output value (theoretical air-fuel ratio equivalent output) ), The air-fuel ratio feedback control by the upstream air-fuel ratio sensor (in this case, the upstream O ₂ sensor) is corrected, so that the air-fuel ratio variation due to the output of the upstream air-fuel ratio sensor or the output characteristic change The deviation of the fuel ratio control is corrected to perform accurate air-fuel ratio control.

In the double sensor as described above, both the upstream side air-fuel ratio sensor and the downstream side air-fuel ratio sensor must be operating normally in order to perform accurate air-fuel ratio control.
However, since the downstream side air-fuel ratio sensor is farther from the engine than the upstream side air-fuel ratio sensor, it takes time for the sensor to reach the activation temperature when the engine is cold started, for example.
There is a problem that the air-fuel ratio feedback control cannot be started until the temperature of the downstream air-fuel ratio sensor, which has a slow temperature rise, reaches the activation temperature even if the temperature of the upstream air-fuel ratio sensor has risen to the activation temperature.

In the apparatus of the above-mentioned Japanese Patent Laid-Open No. 61-197738, when the downstream side air-fuel ratio sensor is not activated, the engine air-fuel ratio is controlled by controlling only the upstream side air-fuel ratio sensor output. The engine is started early to prevent the deterioration of the exhaust property when the engine is started.

[0008]

However, when the downstream side air-fuel ratio sensor is in a non-activated state, as in the device disclosed in Japanese Patent Laid-Open No. 61-197738, the output from the downstream side air-fuel ratio sensor is used. A problem arises when the correction of the air-fuel ratio control is stopped and the engine air-fuel ratio is controlled only by the output of the upstream side air-fuel ratio sensor.

For example, in the double sensor system, even if the reference value of the upstream air-fuel ratio sensor output (theoretical air-fuel ratio equivalent output) deviates greatly from the actual theoretical air-fuel ratio due to aging, the upstream air-fuel ratio is increased. Since the air-fuel ratio control based on the sensor output is corrected by the air-fuel ratio sensor output, the engine air-fuel ratio is normally controlled accurately near the stoichiometric air-fuel ratio. However, if there is a case where the air-fuel ratio control is performed only by the upstream side air-fuel ratio sensor output without performing the correction by the downstream side air-fuel ratio sensor output as described above, the deviation of the reference value of the upstream side air-fuel ratio sensor output is the direct air-fuel ratio. Since it appears in the control, the engine air-fuel ratio is controlled with the air-fuel ratio largely deviating from the stoichiometric air-fuel ratio, which causes a problem that the exhaust property deteriorates.

In the above description, the case where the downstream side air-fuel ratio sensor is not activated has been explained. However, for example, when returning from the fuel cut during deceleration, or when the fuel amount increase for the purpose of increasing the output is completed and the normal air-fuel ratio sensor is exhausted. The same problem occurs immediately after returning to the fuel ratio control. Generally, a three-way catalyst adsorbs oxygen in the exhaust when the exhaust air-fuel ratio is larger than the theoretical air-fuel ratio (when the air-fuel ratio is lean), and when the exhaust air-fuel ratio is smaller than the theoretical air-fuel ratio (when the air-fuel ratio is rich). It has a so-called O ₂ storage function of releasing oxygen. This O
_{(2) Due to the} storage action, even if the exhaust air-fuel ratio flowing into the three-way catalytic converter deviates from the stoichiometric air-fuel ratio for a short time, the air-fuel ratio of the atmosphere of the three-way catalyst can be maintained near the stoichiometric air-fuel ratio. It is possible to maintain good exhaust purification performance, but on the other hand, the adsorption of oxygen by the three-way catalyst,
Due to the release action, the change of the exhaust air-fuel ratio on the downstream side of the catalytic converter occurs later than the change of the exhaust air-fuel ratio on the upstream side.

Therefore, immediately after the fuel cut or the fuel increase is completed, the upstream side air-fuel ratio sensor immediately produces an output corresponding to the engine air-fuel ratio, while the downstream side air-fuel ratio sensor outputs the engine air-fuel ratio. It takes some time to generate output corresponding to the above, and if the downstream side air-fuel ratio sensor output is used for air-fuel ratio control immediately after the end of fuel cut or fuel increase, the engine air-fuel ratio will deviate from the theoretical air-fuel ratio. May be corrected to.

Therefore, in the conventional double sensor system, when the downstream side air-fuel ratio sensor output is not suitable for use in the air-fuel ratio control as described above, the air amount based on only the upstream side air-fuel ratio sensor output is used. It is necessary to control the fuel ratio, and the same problem as described above occurs. On the other hand, in JP-A-64-36943, in order to solve the above problem, after the fuel cut or the fuel increase is completed and the normal air-fuel ratio control is resumed, the downstream side air-fuel ratio sensor corresponds to the engine air-fuel ratio. There is disclosed an air-fuel ratio control device in which the air-fuel ratio control is corrected using the time until the fuel cutoff or the fuel increase is started until the output of the above value is output. However, the output of the downstream side air-fuel ratio sensor immediately before the start of fuel cut or fuel increase is often affected by transient fluctuations in the operating state, and the output reference value of the upstream side air-fuel ratio sensor does not always shift. The value may not be appropriate for correction. Therefore, there is a problem that even if the value immediately before the start of the fuel cut is adopted for the air-fuel ratio control as in the above-mentioned Japanese Patent Laid-Open No. 64-36943, the accurate air-fuel ratio control cannot be guaranteed.

In view of the above problems, the present invention provides a double sensor system for performing engine air-fuel ratio control using air-fuel ratio sensors provided in the exhaust passages on the upstream side and the downstream side of the three-way catalyst, respectively. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine, which can accurately perform air-fuel ratio control of the engine even when the output is not suitable for use in air-fuel ratio control.

[0014]

According to the present invention, a three-way catalyst arranged in the exhaust passage of an internal combustion engine and an output signal corresponding to the exhaust air-fuel ratio arranged in the upstream exhaust passage of the three-way catalyst are provided. An upstream air-fuel ratio sensor that occurs, a downstream air-fuel ratio sensor that is arranged in a downstream exhaust passage of the three-way catalyst and that generates an output signal according to an exhaust air-fuel ratio, and the upstream air-fuel ratio sensor based on the output An air-fuel ratio control means for controlling the combustion air-fuel ratio of the internal combustion engine, and a parameter calculation means for calculating a parameter used for air-fuel ratio control based on the upstream side air-fuel ratio sensor output based on the downstream side air-fuel ratio sensor output, In the air-fuel ratio control device for an internal combustion engine, the parameter calculation means, the determination means for determining whether or not a condition to use the downstream side air-fuel ratio sensor output for the air-fuel ratio control, and the condition. When the above condition is satisfied, the integrated value calculation means for calculating an integrated value of a deviation between the output value of the downstream side air-fuel ratio sensor and the reference value, and a storage means for storing the calculated integrated value are provided, and the condition is When satisfied, at least the parameter used for the air-fuel ratio control is calculated based on the integrated value calculated by the integrated value calculating means, and when the condition is not satisfied, the air-fuel ratio control is performed based on the integrated value stored in the storage means. There is provided an air-fuel ratio control device for an internal combustion engine, which is characterized by calculating a parameter used for.

[0015]

The operation of the present invention will be described below with reference to FIG.
FIG. 1 shows the output fluctuation of each air-fuel ratio sensor when the engine air-fuel ratio is controlled based on both upstream and downstream air-fuel ratio sensor outputs, and FIG. 1 (A) shows the upstream air-fuel ratio sensor. Output fluctuation of the downstream side air-fuel ratio sensor, and Fig. 1 (C) shows the downstream side air-fuel ratio sensor output and reference value (theoretical air-fuel ratio equivalent output) in these cases. It shows the change over time of the integrated value of the deviation of.

When the reference output of the upstream side air-fuel ratio sensor is in agreement with the theoretical air-fuel ratio equivalent value in the section I of FIGS. 1 (A) to 1 (C), sections II and III are the upstream side air-fuel ratio sensor. Shows the case where the reference output of is deviated from the stoichiometric air-fuel ratio equivalent value to the lean side, for example. For the sake of explanation, FIG. 1 shows a case where the reference output of the upstream side air-fuel ratio sensor and the theoretical air-fuel ratio equivalent value are abruptly deviated, but actually the reference output and the theoretical air-fuel ratio are shown. The deviation from the equivalent value gradually increases due to aging, etc., and the abrupt change shown in FIG. 1 does not occur.

In the present invention, the air-fuel ratio control means controls the engine air-fuel ratio to the target air-fuel ratio (theoretical air-fuel ratio) based on the output of the upstream side air-fuel ratio sensor. In addition, the parameter calculation means normally uses at least a parameter used for air-fuel ratio control based on the integrated value of the deviation between the downstream air-fuel ratio sensor output and the theoretical air-fuel ratio equivalent output (for example, correction of the upstream air-fuel ratio sensor output. Amount) is calculated.

Therefore, when there is no deviation in the reference output of the upstream side air-fuel ratio sensor as shown in section I in FIG. 1, the engine air-fuel ratio is accurately controlled to the stoichiometric air-fuel ratio and the upstream side air-fuel ratio sensor output. (Fig. 1 (A)) and the downstream side air-fuel ratio sensor output (Fig. 1 (B)) are both in a narrow range near the stoichiometric air-fuel ratio, and the deviation between the downstream side air-fuel ratio sensor output and the stoichiometric air-fuel ratio equivalent output is zero. Therefore, the integrated value of this deviation (Fig. 1 (C))
Also becomes almost zero.

In this state, when the reference output (theoretical air-fuel ratio equivalent output) of the upstream side air-fuel ratio sensor suddenly changes to the lean side as shown in section II of FIG. 1 (A), the engine air-fuel ratio remains unchanged. Since it is controlled based on the reference output, the engine air-fuel ratio is controlled to be richer than the theoretical air-fuel ratio, and is controlled to a value that deviates significantly from the theoretical air-fuel ratio (that is, the downstream side air-fuel ratio sensor output Since the integrated deviation value of is not corrected, the upstream air-fuel ratio sensor output is not corrected, and the change in the reference output of the upstream air-fuel ratio sensor appears directly in the air-fuel ratio control).

However, this increases the deviation between the output of the downstream side air-fuel ratio sensor and the theoretical air-fuel ratio equivalent value (FIG. 1 (B)), so that the deviation integrated value (FIG. 1 (C)) also gradually increases. Since the air-fuel ratio is increased and the air-fuel ratio control is corrected based on this deviation integral value, the engine air-fuel ratio gradually converges to the theoretical air-fuel ratio despite the change in the reference output of the upstream side air-fuel ratio sensor (section III). In this state, the engine air-fuel ratio is controlled near the stoichiometric air-fuel ratio, so the deviation between the downstream side air-fuel ratio sensor output and the stoichiometric air-fuel ratio equivalent value becomes approximately zero (Fig. 1 (B)). Therefore, the integrated value of the deviation (FIG. 1 (C)) does not increase or decrease, but converges to a substantially constant value.

That is, when a certain period of time elapses after the reference output of the upstream side air-fuel ratio sensor has changed, the engine air-fuel ratio is again controlled to the stoichiometric air-fuel ratio, and the deviation of the downstream side air-fuel ratio sensor is integrated. The value converges to a substantially constant value. The value of the deviation integrated value at this time (shown as SUMΔV _O2 in FIG. 1 (C)) is
The amount of change in the reference output of the upstream side air-fuel ratio sensor (Δ in Fig. 1 (A))
(I amount). In other words, in other words
By deviation integral amount increases to SUMderutaV _O2, and the correction amount of the air-fuel ratio control is increased, it become possible to change the amount ΔI of the reference output of the upstream air-fuel ratio sensor is canceled.

Therefore, the above-mentioned Japanese Patent Laid-Open No. 61-19773.
When it is not appropriate to use the downstream side air-fuel ratio sensor output for the air-fuel ratio control like the device of Japanese Patent No. 8 publication, if the air-fuel ratio control is performed only by the upstream side air-fuel ratio sensor output, the reference of the upstream side air-fuel ratio sensor is obtained. Since the output deviation is not corrected, the engine air-fuel ratio is controlled so as to largely deviate from the stoichiometric air-fuel ratio in the same manner as shown in the section II in FIG. 1 described above.

In the present invention, the deviation integral value of the output of the downstream side air-fuel ratio sensor is stored, and the output of the downstream side air-fuel ratio sensor is used as the output of the downstream side air-fuel ratio sensor, for example, during cold start of the engine, fuel cut, or a predetermined period after increasing the amount. If it is not suitable for control,
This problem is solved by correcting the air-fuel ratio control based on the upstream side air-fuel ratio sensor output using the stored deviation integral value.

In the above description, the case where the reference output change of the upstream side air-fuel ratio sensor suddenly occurs is dealt with, but in reality, the reference output change gradually occurs over time, and therefore the downstream side air-fuel ratio sensor changes. The output deviation integrated value of the fuel ratio sensor also hardly changes in a short time. Therefore, the deviation integral value is stored when the correction of the air-fuel ratio control based on the downstream side air-fuel ratio sensor output is performed, and this storage is performed when the downstream side air-fuel ratio sensor output cannot be used for the air-fuel ratio control. By correcting the air-fuel ratio control based on the output of the upstream side air-fuel ratio sensor using the value obtained, even if the air-fuel ratio is controlled only based on the output of the upstream side air-fuel ratio sensor, the deviation of the reference output is appropriately corrected, The engine air-fuel ratio can be accurately controlled to the stoichiometric air-fuel ratio.

[0025]

FIG. 2 shows a V-type 6 air-fuel ratio control device according to the present invention.
It is the whole schematic diagram showing the example when applied to a cylinder engine. It goes without saying that the present invention is naturally applicable to in-line cylinder engines other than V-type engines. In FIG. 2, reference numeral 1 denotes a main body of a V-type 6-cylinder engine in which three cylinders are arranged in two rows in a V-shape. Engine body 1
An air flow meter 3 is provided in the intake passage 2. The air flow meter 3 is a device for directly measuring the intake air amount. For example, a movable vane type air flow meter having a built-in potentiometer is used, and an output signal of an analog voltage proportional to the intake air amount is generated. This output signal is input to the A / D converter 101 with a built-in multiplexer of the control circuit 10. In Distributor 4,
For example, a crank angle sensor 5 whose axis generates a reference position detection pulse signal every 720 ° converted into a crank angle, and a crank angle sensor which generates each crank detection pulse signal every 30 ° converted into a crank angle Each sensor 6 is provided. The pulse signals of the crank angle sensors 5 and 6 are input / output interface 1 of the control circuit 10.
02, of which the output of the crank angle sensor 6 is supplied to the interrupt terminal of the CPU 103.

Further, the intake passage 2 is provided with fuel injection valves 7A and 7B for supplying the pressurized fuel from the fuel supply system to the intake port for each cylinder. The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 generates an electric signal of analog voltage according to the temperature of the cooling water. This output is also the A / D converter 101.
Is being supplied to.

In the exhaust system downstream of the exhaust manifolds 11A and 11B of the right bank (hereinafter referred to as A bank) and the left bank (hereinafter referred to as B bank) of the engine 1, three harmful components HC and CO in the exhaust gas are respectively provided. , A catalytic converter 12A containing a three-way catalyst for purifying NO _x at the same time,
12B is provided. The catalytic converters (start catalysts) 12A and 12B have a relatively small capacity and are installed in the engine room so that the catalyst can be warmed up when the engine is started.

In the exhaust manifold 11A of the A bank,
That is, the exhaust pipe 14A on the upstream side of the catalytic converter 12A
Is provided with a first air-fuel ratio sensor (upstream air-fuel ratio sensor) 13A for the A bank, and the exhaust manifold 11B of the B bank, that is, the exhaust pipe 14B on the upstream side of the catalytic converter 12B, is the same. Is provided with a first air-fuel ratio sensor (upstream air-fuel ratio sensor) 13B for the B bank.

Further, the two exhaust pipes 14A and 14B are joined together in the collecting portion 15a at the downstream thereof, and the exhaust pipe downstream of the collecting portion 15a has a catalytic converter (main catalyst) 16 for accommodating a three-way catalyst. Are arranged. The catalytic converter 16 has a relatively large capacity and is installed under the floor of the vehicle body. Catalytic converter 16
A second air-fuel ratio sensor (downstream air-fuel ratio sensor) 17 is provided in the collective exhaust pipe 15 on the downstream side of the.

In this embodiment, the upstream air-fuel ratio sensor 13
As A and 13B, there is a one-to-one correspondence with the oxygen component concentration in the exhaust gas over a wide air-fuel ratio range, that is, an all-area air-fuel ratio sensor (A /
F sensor) is used. As an A / F sensor,
There are several types. FIG. 8 schematically shows the structure of a general A / F sensor. The A / F sensor 210 is
A solid electrolyte 213 such as zirconia is arranged between the platinum electrodes 211 and 212, and a diffusion resistance layer formed of a ceramic coating layer on the surface of the cathode (exhaust side electrode) 212 that restricts oxygen molecules in the exhaust gas from reaching the cathode. The structure is provided with 214. In the A / F sensor of FIG. 8, the cathode 2
12 is placed in contact with exhaust gas, the anode 211 is placed in contact with the atmosphere, and a voltage is applied between the electrodes 211 and 212 at a certain temperature or higher, the cathode 21
On the 2nd side, oxygen molecules in the exhaust gas are ionized, and the ionized oxygen molecules move in the solid electrolyte 213 toward the anode 211, so that the anode 211 has an oxygen pumping action to become oxygen molecules again. By this oxygen pump action, the electrode 21
An electric current proportional to the amount of oxygen molecules moved per unit time flows between Nos. 1 and 212. However, since the diffusion resistance layer 214 restricts oxygen molecules from reaching the cathode, the output current saturates at a certain constant value, and the current does not increase even if the voltage is increased. The value of this saturation current is approximately proportional to the oxygen concentration in the exhaust gas. Therefore, by appropriately setting the applied voltage, it is possible to obtain an output current approximately proportional to the oxygen concentration. In this embodiment, this output current is converted into a voltage signal and supplied to the A / D converter 101 of the control circuit 10.
Since the oxygen concentration in the exhaust gas and the air-fuel ratio have a one-to-one correlation, the output voltage has a one-to-one correlation with the exhaust air-fuel ratio,
The exhaust air-fuel ratio can be known from the output current. FIG. 9 shows the output characteristics of the A / F sensors 13A and 13B used in this embodiment.

On the other hand, in this embodiment, the downstream air-fuel ratio sensor 1
As 7, a so-called O ₂ sensor is used, which outputs a voltage signal according to the oxygen concentration in the exhaust gas as in the A / F sensor, but the output voltage changes relatively rapidly around the theoretical air-fuel ratio. . The O ₂ sensor has substantially the same structure as the A / F sensor shown in FIG. 8, but the diffusion resistance layer 214 of FIG. 8 is not provided, and the O ₂ sensor is used with the electrodes 211 and 212 open. In this state, when the solid electrolyte 213 is exposed to exhaust gas and its temperature rises, the atmosphere side (high oxygen concentration side) electrode 211 to the exhaust side (low oxygen concentration side) electrode 212.
Since the movement of oxygen ions toward the electrode 211,
A voltage corresponding to the difference in oxygen concentration between the atmosphere side and the exhaust side is generated between 212. Also, the oxygen concentration in the exhaust gas changes rapidly between the rich side and the lean side at the boundary of the stoichiometric air-fuel ratio,
As shown in FIG. 10, the output of the O ₂ sensor exhibits a so-called Z characteristic that changes relatively rapidly near the stoichiometric air-fuel ratio.

In the present embodiment, the control of correcting the output of the upstream side air-fuel ratio sensor using the output of the downstream side air-fuel ratio sensor is performed, and the problem of time delay due to the O ₂ storage effect of the catalyst described above is solved. Relatedly, it is desirable that the response speed of the downstream air-fuel ratio sensor be as fast as possible.
As the downstream side air-fuel ratio sensor 17, an O ₂ sensor, which has less aging change of the reference output voltage (theoretical air-fuel ratio equivalent output voltage) than the A / F sensor and has good response, is used. In the following description, the upstream air-fuel ratio sensor will be referred to as the A / F sensor 13.
The A, 13B and downstream side air-fuel ratio sensors will be referred to as O ₂ sensors 17 to distinguish them.

In the present embodiment, the control circuit 10 is configured as, for example, a microcomputer, and the A / D converter 1 is used.
01, input / output interface 102, CPU 103, ROM 104, RAM 105, backup RA
An M106, a clock generation circuit 107, etc. are provided. In the present embodiment, the control circuit 10 performs basic control such as fuel injection control and ignition timing control of the engine 1, as well as parameter calculation means, determination means, and the like described in claim 1 as described later.
It functions as an integral value calculation means and a storage means, and controls the air-fuel ratio of the engine 1.

Further, the throttle valve 18 in the intake passage 2 is provided with an idle switch 19 for generating a signal indicating whether or not the throttle valve 18 is fully closed, that is, an LL signal. The idle state output signal LL is supplied to the input / output interface 102 of the control circuit 10. Further, 20A and 20B are secondary air introduction intake valves for supplying secondary air from an air source such as an air pump (not shown) to the exhaust manifolds 11A and 11B during deceleration or idle to reduce HC and CO emissions. belongs to.

Further, in the control circuit 10, the down counter 108A, the flip-flop 109A, and the drive circuit 110A are for controlling the fuel injection valve 7A of the A bank, and the down counter 108B, the flip-flop 109B, and the drive circuit 110B. Is for controlling the fuel injection valve 7B of the B bank. That is, in the routine described later, the fuel injection amount (injection time) fi
_{When (A)} (fi _(B) ) is calculated, the injection time fi
_(A) (fi _(B) ) is the down counter 108A (108
B) preset and flip-flop 109
A (109B) is also set. As a result, the drive circuit 1
10A (110B) starts energizing the fuel injection valve 7A (7B). On the other hand, down counter 108A (108B)
Counts a clock signal (not shown), and when its output terminal finally becomes "1" level, the flip-flop 109A (109B) is set and the drive circuit 110A
(110B) stops energizing the fuel injection valve 7A (7B). That is, the above-mentioned fuel injection time fi _(A) (fi _(B) )
Only the fuel injection valve 7A (7B) is energized for a time fi _(A)
The amount of fuel corresponding to (fi _(B) ) is A bank (B
Bank) will be sent to the combustion chamber.

Incidentally, the interrupt generation of the CPU 103 is A /
For example, when the input / output interface 102 receives the pulse signal of the crank angle sensor 6 after the A / D conversion of the D converter 101 is completed. The intake air amount data and the cooling water temperature data of the air flow meter 3 are fetched by an A / D conversion routine executed at a predetermined time or at a predetermined crank angle and stored in a predetermined area of the RAM 105. That is,
The intake air amount data and the cooling water temperature data in the RAM 105 are updated every predetermined time. Further, the rotation speed data is calculated by interruption of the crank angle sensor 6 for each 30 ° CA (crank angle) and stored in a predetermined area of the RAM 105.

In the embodiment according to the present invention, the control circuit 10 calculates the integrated value of the deviation between the output of the downstream O ₂ sensor 17 and the reference value (the output equivalent to the theoretical air-fuel ratio), and based on this integrated value the upstream side. The air-fuel ratio control by the A / F sensor is corrected.
Below, the output of the upstream A / F sensor and the downstream A of this embodiment
The air-fuel ratio control based on the / F sensor output will be described.

In this embodiment, the correction amount ΔV _{A / F} of the upstream A / F sensor output is used as the parameter used for the air-fuel ratio control based on the output of the upstream A / F sensor, and this correction amount is used as the downstream O ₂ Calculate based on sensor output. That is, when it is determined that it is appropriate to use the output of the downstream side O ₂ sensor for air-fuel ratio control (for example, the downstream side O ₂ sensor is activated, and after a predetermined amount of fuel cut or fuel increase is completed, When the time elapses), the deviation between the downstream O ₂ sensor output and the reference output (theoretical air-fuel ratio equivalent output) is used to correct the upstream side A / F sensor output V _{A / F} correction amount ΔV _{A / F} Is calculated as follows.

ΔV _{A / F} = KP · ΔV _O2 + KI · (SUMΔV _O2 ) + KD · (dΔV _O2 ) where ΔV _O2 is the deviation between the downstream O ₂ sensor output V _O2 and the reference output V _O2 s. ΔV _O2 = V _O2 −V _O2 s), and
KP represents a constant coefficient (proportional coefficient). In addition, SUMΔ
V _O2 is an integrated value of the deviation ΔV _O2 (SUMΔV _O2 = ΣΔV _O2 ) obtained by the method described later, and KI is a constant coefficient (integral coefficient). Furthermore, dΔV _O2 represents the rate of change (differential value) of ΔV _O2 , and KD is a constant coefficient (differential coefficient).

That is, the upstream A / F sensor output V _{A / F}
The correction amount ΔV _{A / F} is determined by PID (proportional, integral, differential) processing based on the deviation ΔV _O2 of the downstream O ₂ sensor output V _{O2 from} the reference output. Where KP, KI, KD
Is a feedback gain constant, which is determined by experiments or the like. Here, the proportional term KP · [Delta] V _O2, and differential term KD · (dΔV _O2) is for correcting the transient variations of the upstream A / F sensor output shown in ΔPD in FIG 1 (A) And the integral term KI · (SUMΔV _O2 ) is shown in Fig. 1 (A).
Steady deviation of upstream A / F sensor output indicated by ΔI (for example, steady deviation caused by secular change of reference output)
It is for correcting.

Further, the control circuit 10 controls the correction amount ΔV _{A / F.}
The upstream side A / F sensor correction output * V _{A / F} is calculated using * V _{A / F} = V _{A / F} + ΔV _{A / F} , and the corrected output * V _{A / F} will be used later. The fuel injection amount fi of the engine is calculated by the method described above.

On the other hand, when the downstream O ₂ sensor is not activated, when a predetermined time has not passed after the fuel cut or the fuel increase is completed, the downstream O ₂ sensor output should be used for the air-fuel ratio control. correction amount [Delta] V a _{/ F} of the case is not appropriate, the control circuit 10 upstream a / F sensor output V _{a / F}
Is calculated as ΔV _{A / F} = KI · * SUM using the smoothed value * SUM of the integral term SUMΔV _O2 , and similarly the correction output * V _{A / F} = V _{A / F} + ΔV
_The fuel injection amount fi is calculated using _{A / F.} Here, the use of the smoothed value * SUM of the integrated value is because the integrated value SUMΔ
Since the influence of the variation indicated by ΔPD in FIG. 1 is added to the value of V _O2 itself, these influences are eliminated and the upstream side A
This is because it is more appropriate to use the smoothed value to represent only the deviation of the / F sensor output (ΔI in FIG. 1A).

As a result, even if it is not appropriate to use the output of the downstream O ₂ sensor for air-fuel ratio control, the upstream side A /
The steady deviation of the output of the F sensor (ΔI in FIG. 1 (A)) is corrected, and the engine air-fuel ratio is controlled to be near the stoichiometric air-fuel ratio. FIG. 3 is a flowchart showing an example of the fuel injection control operation described above. This routine is executed by the control circuit 10 every constant rotation of the crankshaft (for example, every 360 degrees).

When the routine starts in FIG. 3,
In steps 301 to 305, the operation of changing the value of the flag i from the value at the time of executing the previous routine is performed. Here, the value of the flag i represents the cylinder bank from which the fuel injection amount is to be calculated, i = 0 represents the A bank, and i = 1 represents the B bank. When the value of the flag i is set in steps 301 to 305, the address of the RAM 105 is set according to the value of the set flag i in the following calculation, and the calculation is performed using the parameter according to each bank. Be done. That is, when i = 0, the address of the RAM 105 is set for the A bank, and the fuel injection amount is calculated using the parameters for the A bank (in this case, the parameters are added to the parameters in the following calculation). The subscript “(i)” shall mean “A”). When i = 1, the address of the RAM 105 is similarly set for the B bank, and the fuel injection amount is calculated using the B bank parameter (in this case, the subscript "A" attached to the parameter). (i) "means" B ").

As a result, the fuel injection valves of the A bank and the B bank are alternately calculated once during one cycle of the engine (rotation of crankshaft 720 degrees). Next, at step 307, it is judged if the condition for correcting the air-fuel ratio control by the output of the downstream O ₂ sensor is satisfied. Here, the above conditions are, for example, that the cooling water temperature is equal to or higher than a predetermined value, that the engine has been started, the amount of fuel after starting, the amount of warming up, the amount of power increasing, the amount of OTP increasing for preventing catalyst overheating, etc. The amount of fuel is not being increased, and the specified amount of time has passed since the amount was increased, the fuel cut is not being executed, and the specified amount of time has elapsed after the fuel cut was completed. The output of the side O ₂ sensor 17 is inverted at least once (change from lean output to rich output, or vice versa,
That is, it is determined that the downstream O ₂ sensor has been activated, etc., and steps 307 to 315 are executed only when all of these conditions are satisfied.

[0046] When the condition in step 307 is satisfied, the deviation from the reference output V _O2 s the downstream O ₂ sensor output V _O2 proceeds to step 309, [Delta] V _O2 is calculated as ΔV _O2 = V _O2 -V _O2 s It The downstream O ₂ sensor output V _O2 and the upstream A / F sensor outputs V _{A / F (i) of} both A and B banks
Is read by AD conversion by a routine (not shown) separately executed by the control circuit 10 at regular time intervals (for example, every 8 ms), and the latest data is always stored in the RAM 105.

[0047] Next, at step 311, using the value of the [Delta] V _O2, the integral value SUMderutaV _O2 and its smoothed value of [Delta] V _O2 * SUM is calculated. FIG. 4 is a flowchart showing an example of a subroutine for calculating SUMΔV _O2 and * SUM executed in step 311. When the subroutine is started in FIG. 4, in step 401, using the deviation [Delta] V _O2 determined by the integral value of the deviation (accumulated value) SUMΔV _O2 is calculated. In addition, step 403
From 409 to 409, the maximum value MAX and the minimum value MIN which the integrated value SUMΔV _O2 has taken in the past are updated as necessary.

Further, at step 411, the maximum value MAX and the minimum value MIN are weighted and averaged by using the coefficient β, and the smoothed value * SUM of the integrated value becomes * SUM = β · MAX + (1-β ) · Calculated as MIN (β is a constant smaller than 1). As a result, for example, even when the value of SUMΔV _O2 was temporarily increased at the time of the previous routine execution due to the variation ΔPD shown in FIG. 1 (A), the smoothed value * SUM does not change significantly. , The influence of the temporary variation ΔPD is reduced. After the operation ends, step 413, and the above _{calculation, SUMΔV O2, MAX, MIN,} * SUM values are stored in the backup RAM 106, the subroutine is terminated.

After the execution of the above subroutine, the routine is as shown in FIG.
Proceeding to step 313, ΔV from when the previous routine was executed
Variation of _O2, i.e., the differential value DiderutaV _O2 of [Delta] V _O2, is calculated as _{dΔV O2 = ΔV O2 -ΔV O2 (} K-1). Here, ΔV _{O2 (K-1)} is the value of ΔV _O2 at the time of executing the previous routine.

[0050] In step 315, [Delta] V _O2 were calculated by the above, SUMderutaV _O2, using the value of DiderutaV _O2,
The correction amount ΔV _{A / F (i) of the} upstream side A / F sensor output V _{A / F (i)} is ΔV _{A / F (i)} = KP · ΔV _O2 + KI · (SUMΔV _O2 ) + KD · (dΔV _O2 ). Calculated.

Meanwhile, in FIG. 3 step 307, the downstream O ₂
If any one or more of the conditions for using the sensor output to correct the air-fuel ratio control are not satisfied, the routine proceeds to step 317, is calculated when the routine is executed up to the previous time, and is stored in the backup RAM 106. The correction amount ΔV _{A / F} is calculated as ΔV _{A / F (i)} = KI · * SUM using the value of the smoothing value * SUM.

After the correction amount ΔV _{A / F (i)} is calculated in any of steps 315 and 317, the routine proceeds to step 31.
Proceed to step 9 and correct the upstream A / F sensor output value * V _{A / F (i)}
Is calculated as * V _{A / F (i)} = V _{A / F (i)} + ΔV _{A / F (i)} , and in step 321, this * V _{A / F (i)} is calculated.
Fuel injection amount fi _{(i) of the} corresponding bank based on _{A / F (i)}
Is calculated and a down-counter 108 (i) of the control circuit 10 is executed by a fuel injection routine (not shown) separately executed.
Is set to the time fi _(i) . As a result, the drive circuit 110 (i) injects an amount of fuel corresponding to fi _(i) from the fuel injection valve 7 (i).

Next, the air-fuel ratio control based on the corrected output * _{VA / F (i)} of the upstream side A / F sensor 13 (i) will be described. There are various methods of controlling the air-fuel ratio based on the output signal of the upstream side A / F sensor, but here, in order to make the most of the O ₂ storage action of the three-way catalyst, adsorption ( An example of an air-fuel ratio control method based on modern control that allows the engine combustion air-fuel ratio to converge to the stoichiometric air-fuel ratio with high accuracy and in a short time while keeping the stored amount of oxygen at a predetermined amount. I will explain. The applicant of the present application has already proposed this air-fuel ratio control method in Japanese Patent Application No. 5-68391.

In this air-fuel ratio control method, the amount of air sucked into the cylinder per one engine revolution (the amount of air in the cylinder) mc from the output of the air flow meter 3 and the engine speed.
And the corrected output * V of the upstream A / F sensor 13
_The combustion air-fuel ratio α _(i) is obtained from _{A / F (i),} and the fuel amount fc _(i) actually supplied into the cylinder is calculated from these as fc _(i) = mc
Calculate as / α _(i) . Similarly, the theoretical air-fuel ratio αr
The target fuel amount fcr _(i) required to make the combustion air-fuel ratio the stoichiometric air-fuel ratio is calculated as fcr _(i) = mc / αr, and the difference fc _(i) -fcr _(i) and, the fuel injection amount fi _(i) is determined so as to zero the time integral value x1 _{(i) is} at the same time.

Further, since a part of the fuel injected from the fuel injection valve 7 adheres to the wall surface of the intake port, the injection amount from the fuel injection valve 7 and the fuel amount supplied to the cylinder do not always match, This fuel adhesion is taken into consideration when determining the fuel injection amount fi _(i) . As described above, the target value fcr
By controlling the fuel injection amount fi _(i) so that the deviation of the actual fuel supply amount from _(i) and its time integrated value are simultaneously made zero, the three-way catalyst is always supplied with a predetermined amount of oxygen. While being stored, the responsiveness of air-fuel ratio control can be improved.

When the routine starts in FIG. 5,
In step 501, the air-fuel ratio α _(i) is calculated from the output characteristic of FIG. 7 using the output * V _{A / F (i)} of the upstream side A / F sensor 13 corrected by the routine of FIG. Next, at steps 502 and 503, the air-fuel ratio α obtained above is calculated.
_{Based on (i)} , the intake air amount mc per engine revolution obtained from the output of the air flow meter 3 and the engine speed, and the theoretical air-fuel ratio αr (constant), the fuel amount fc ₍ actually supplied to the cylinder _i) and the target fuel amount fcr _(i) are calculated. Further, in step 504, the above fc _(i) and fc
The deviation δfc _{(i) from} r _(i) is δfc _(i) = fc _(i) −
It is calculated as fcr _(i) .

In step 505, the fuel injection amount fi _(i)
The nominal value fim _(i) of fim _{(k) (i)} = {fcr _{(k) (i)} -(1-P) fwm
It is calculated as _{(k) (i)} } / (1-R). In this embodiment, the fuel injection amount f
i _(i) , the amount of fuel in the injected fuel that adheres to the wall surface of the intake port, etc. fw _(i) , the amount of fuel that is supplied into the cylinder fc
_(i) are nominal values fim _(i) , fwm _(i) , and
fcm _(i) and deviations δfi _(i) , δfw _(i) , δfc _(i)
It is expressed as the sum of and.

Fi _(i) = fim _(i) + δfi _(i) fw _(i) = fwm _(i) + δfw _(i) fc _(i) = fcm _(i) + δfc _(i) It is assumed that the model formula of is satisfied. fw _{(k + 1) (i)} = Pfw _{(k) (i)} + Rfi _{(k) (i)} fc _{(k) (i)} = (1-P) fw _{(k) (i)} + (1-R) fi _{(k) (i)} fwm _{(k + 1) (i)} = Pfwm _{(k) (i)} + Rfim _{(k) (i)} fcm _{(k) (i)} = (1-P) fwm _{(k) (i )} + (1-R) fim _{(k) (i)} fcm _{(k) (i)} = fcr _{(k) (i)} where the subscript k is the value at the time of execution of this routine, (k-
1) indicates the value at the time of executing the previous routine. Further, in this embodiment, P and R are constants. By modifying the above model equation, in step 505, the nominal value fim _(i) is obtained in the above form.

Next, at step 506, the time integral value x1 _{(i) of} δfc _(i) is set as x1 _{(k) (i)} = x1 _{(k-1) (i)} + δfc _{(k) (i)} , and In step 507, the time integral value x2 _{(i) of} x1 _(i) is further _obtained as x2 _{(k) (i)} = x2 _{(k-1) (i)} + x1 _{(k) (i)} . Further, in step 508, the deviation δfi _(i) is calculated as δfi _{(k) (i)} using the values of fi _(i) , δfc _(i) , x1 _(i) , x2 _(i) obtained up to the previous time. = F1 · δfi _{(k-1) (i)} + f2 · δfc _{(k-1) (i)} + f3 · x1 _{(k) (i)} + f4 · x1 _{(k-1) (i)} + f5 · x1 _{(k-2 ) (i)} + f6 * x2 _{(k-1) (i)} + f7 * x2 _{(k-2) (i)} . Here, f1 to f7 are constants.

In step 509, the fuel injection amount fi _(i) is fi _{(k) (i)} = fim ₍ using the nominal value fim _{(i) of} the fuel injection amount and the deviation δfi _(i) obtained as described above. _{k) (i)} + δfi _{(k) (i)} . Further, in step 510, in preparation for the next routine execution, the nominal value of the amount of fuel adhered to the wall surface is calculated by using the values of fwm _(i) and Rfim _(i) at the time of execution of this routine, and fwm _(i) = Pfwm _{( k) (i)} + Rfim _{(k) (i)} , and in steps 511 to 516, δfi _(k-1) , δfc _{(k-1) (i)} , in preparation for the next routine execution.
x1 _{(k-1) (i)} , x1 _{(k-2) (i)} , x2 _{(k-1) (i)} , x2
The values of _{(k-2) (i)} are updated using the values at the time of execution of this routine.

As described above, the fuel injection amount fi _(i) obtained as described above is calculated by the control circuit 10 in step 323 of FIG.
Is set in the corresponding down counter 108 _(i) , and fuel injection is performed. As a result, highly accurate air-fuel ratio control becomes possible. Next, another embodiment of the calculation of the smoothed value * SUM of the integrated value SUMΔV _O2 will be described with reference to FIG.

In the above-mentioned embodiment, the weighted average of the maximum value and the minimum value of the integrated value SUMΔV _O2 of the deviation of the output of the downstream O ₂ sensor is calculated and used as the smoothed value * SUM. In the example, the integrated value SUMΔV _O2 calculated this time and the smoothed value * SUM up to the previous time are used, and * SUM = 1 / n {(n−1) · * SUM + n · S
UMΔV _O2 ). That is, the point is different from the above-described embodiment in that a value obtained by weighting and averaging the previously calculated * SUM and the currently calculated SUMΔV _O2 using the coefficient n is adopted as the * SUM at the time of execution of the current routine. By adopting the above-mentioned smoothed value, similar to the above-mentioned embodiment, the temporary air-fuel ratio fluctuation with respect to the smoothed value * SUM (Fig. 1 (A) ΔP
It is possible to correct the deviation of the reference value of the output of the upstream A / F sensor by reducing the influence of D).

When the subroutine starts in FIG. 6, in step 601, the deviation ΔV _{O2 of the} output of the downstream O ₂ sensor, which is obtained in step 309 of FIG. 3, from the reference value.
Is used to calculate the integrated value SUMΔV _{O2 of the} deviation, and then, in step 601, the smoothed value * SUM at the time of execution of this routine is calculated by the above equation using the smoothed value calculated last time. Further, SUMΔV _O2 and * SUM calculated as described above are stored in the backup RAM 106 in step 613 and prepared for the next calculation, as in the above-described embodiment.

Further, n used for the weighted average of the above smoothed values
The value of is, for example, about n = 8. In addition, the above-described embodiment applies the present invention to the start catalyst (FIG. 2, 12).
A, 12B) and a main catalyst (FIGS. 2 and 16) are applied to a V-type 6-cylinder engine, but the present invention can be applied to engines having other configurations.

FIG. 7 shows another example of the structure of an engine to which the present invention can be applied. For example, FIG. 7A shows a configuration in which the present invention is applied to a V-type engine that does not have a start catalyst, in which the exhaust manifolds of each bank are provided with upstream A / F sensors 13A and 13B, respectively. This is a configuration in which a downstream O ₂ sensor 17 is provided in the collective exhaust pipe on the downstream side of the wrist 16.

Further, FIG. 7B shows an example in which the catalytic converter is not provided in the collective exhaust pipe, and the exhaust gas is purified only by the catalytic converters 12A and 12B provided in the exhaust pipe of each bank. In FIG. 7 (A), upstream A / F sensors 13 are provided on the upstream side and the downstream side of the catalytic converters 12A and 12B, respectively.
An example in which A, 13B and downstream O ₂ sensors 17A, 17B are arranged is shown. In this case, the downstream O ₂ sensor may not be provided downstream of each of the catalytic converters 12A and 12B, but only one may be provided in the collective exhaust pipe.

Further, FIG. 7 (C) shows a configuration in which the present invention is applied to an in-line cylinder type engine. As described above, the present invention can be applied to engines having various configurations.

[0068]

According to the present invention, as described above, the parameter used for the air-fuel ratio control by the upstream side air-fuel ratio sensor output is normally used by using the integrated value of the deviation between the downstream side air-fuel ratio sensor output and the reference output. When it is not appropriate to calculate and use the downstream side air-fuel ratio sensor output for air-fuel ratio control, by calculating the parameter used for air-fuel ratio control using the integral value of the deviation stored in advance, The air-fuel ratio can be accurately controlled even when the engine is started, the amount of fuel is increased or immediately after the fuel is cut, and the deterioration of the exhaust property can be prevented.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an operation of the present invention.

FIG. 2 is an embodiment showing a case where the present invention is applied to a V-6 cylinder engine.

FIG. 3 is an example of a flowchart showing air-fuel ratio control of the present invention.

FIG. 4 is a flowchart showing an example of a deviation integral value calculation subroutine for a downstream O ₂ sensor output.

FIG. 5 is a flowchart showing an example of a fuel injection amount calculation subroutine.

FIG. 6 is a flowchart showing another example of a deviation integrated value calculation subroutine for the downstream O ₂ sensor output.

FIG. 7 is a diagram showing a case where the present invention is applied to an engine having a configuration different from that of FIG.

FIG. 8 is a diagram for explaining a general structure of an A / F sensor.

FIG. 9 is a diagram showing an example of output characteristics of an upstream A / F sensor.

FIG. 10 is a diagram showing an example of output characteristics of a downstream O ₂ sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine main body 2 ... Intake passage 3 ... Air flow meter 7A, 7B ... Fuel injection valve 10 ... Control circuit, 12A, 12B ... Catalytic converter 13A, 13B ... Upstream air-fuel ratio sensor 17 ... Downstream air-fuel ratio sensor

Claims (1)

[Claims] 1. A three-way catalyst arranged in an exhaust passage of an internal combustion engine, and an upstream air-fuel ratio sensor arranged in an upstream exhaust passage of the three-way catalyst for generating an output signal according to an exhaust air-fuel ratio,
A downstream side air-fuel ratio sensor that is arranged in a downstream side exhaust passage of the three-way catalyst and generates an output signal according to an exhaust air-fuel ratio, and controls a combustion air-fuel ratio of the internal combustion engine based on the upstream side air-fuel ratio sensor output. In an air-fuel ratio control device for an internal combustion engine, comprising air-fuel ratio control means and parameter calculation means for calculating a parameter used for air-fuel ratio control based on the upstream side air-fuel ratio sensor output based on the downstream side air-fuel ratio sensor output The parameter calculating means determines whether or not a condition for using the downstream side air-fuel ratio sensor output for the air-fuel ratio control is satisfied, and when the condition is satisfied, the downstream side air-fuel ratio sensor An integrated value calculating means for calculating an integrated value of a deviation between the output value and the reference value, and a storage means for storing the calculated integrated value are provided, and when the condition is satisfied, A parameter used for the air-fuel ratio control is calculated based on at least the integrated value calculated by the integrated value calculation means, and the parameter used for the air-fuel ratio control based on the integrated value stored in the storage means when the condition is not satisfied. An air-fuel ratio control device for an internal combustion engine, wherein: