JPH0338417B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application of the Invention) The present invention relates to an air-fuel ratio control device that performs feedback control to maintain the air-fuel ratio at a predetermined value based on a signal from an exhaust sensor that detects the concentration of exhaust gas components of an engine. In particular, this invention relates to control of an engine such as a V-type engine in which the exhaust system is divided into two systems.

(Prior Art) FIG. 1 is an example diagram showing a fuel control system of a conventional V-type engine.

In Figure 1, 1 is an air cleaner, 2 is an air flow meter that measures the amount of intake air, 3 is a throttle valve, 4 is a right bank intake port, 5 is a left bank intake port, 6 is a right bank injection valve, 7 is a left bank Injection valve, 8 is right bank cylinder, 9 is left bank cylinder,
10 is the right bank exhaust pipe, 11 is the left bank exhaust pipe,
12 is a right bank exhaust sensor provided on the right bank exhaust pipe 12; 13 is a left bank exhaust sensor provided on the left bank exhaust pipe 11; 14 and 15 are catalytic converters that purify exhaust gas; 16 is a muffler;
7 is a rotation sensor that detects the rotational speed of the engine (for example, a sensor that outputs a pulse signal every time the crankshaft 20 rotates by a predetermined angle), 18 is a temperature sensor that detects the engine cooling water temperature, and 19 is a control device (details will be described later). ) 20 is the crankshaft of the engine.

Further, 21 is an exhaust gas recirculation control valve, which is a device that controls the amount of exhaust gas recirculated, that is, the amount of exhaust gas recirculated to the intake system.

Further, reference numeral 22 denotes an auxiliary air valve, which is used for the purpose of controlling the idle speed and the like by controlling the amount of air that bypasses the throttle valve 3.

The control device 19 includes, for example, CPU.I/O.RAM.
It consists of a microcomputer consisting of a ROM, etc., and a drive circuit that amplifies the output of the microcomputer and uses it as a drive pulse to drive the injection valve. Then, the basic fuel injection amount is calculated based on various engine operating variables, such as the engine rotational speed given from the rotation sensor 17 and the intake air amount given from the air flow meter 2, and a variable related to the engine temperature given from the temperature sensor 18. The actual fuel supply amount is calculated by adding correction based on information regarding the exhaust gas component concentration (for example, oxygen concentration) given from the exhaust gas sensors 12 and 13, and the injection valves 6 and 7 are adjusted according to the result.
control and supply fuel.

Although Fig. 1 shows only one cylinder in each of the right and left banks, in reality, for example, in the case of a V-type 8-cylinder engine, each bank has four cylinders. ing.

There are many known air-fuel ratio control devices that perform feedback control based on signals from exhaust sensors, such as those disclosed in Japanese Patent Publication No. 91425/1971.

In the conventional air-fuel ratio control device for a V-type engine, one is known that has a well-known feedback control system in the left and right banks, such as the previous model, and performs independent control of the two systems (for example, the Nissan Motor Service Circular Bulletin No. 476).

FIG. 2 is a diagram showing an example of signals in the conventional air-fuel ratio control device as described above.

In FIG. 2, when the air-fuel ratio changes as shown in c, the output of the exhaust sensor changes as shown in b. In a general feedback control system, it is normal to perform integral proportional control that has integral characteristics and proportional characteristics, so in that case, the fuel supply amount changes as shown in a, and the air-fuel ratio changes. λ=1
(a value close to the stoichiometric air-fuel ratio).

However, in such an air-fuel ratio control device, there is a delay time between when the exhaust sensor detects a change in the air-fuel ratio and the fuel supply amount changes accordingly until the result is detected again by the exhaust sensor. That is, Td shown in FIG. 2 exists.

Therefore, the air-fuel ratio fluctuates between rich and lean around λ=1.
In other words, a hunting phenomenon occurs.

On the other hand, the output torque of the engine varies depending on the air-fuel ratio, as shown in FIG. 3, and reaches its maximum when λ is slightly richer than 1.

Therefore, when the air-fuel ratio is hunted between rich and lean due to feedback control, the output torque also fluctuates accordingly.

Therefore, when the engine is operating at a constant low rotational speed, such as when idling or idling, the engine rotational speed may fluctuate periodically, causing discomfort to the driver. .

Furthermore, since the conversion efficiency of the catalytic converter is at its best when λ=1 as shown in FIG. 4, if the air-fuel ratio hunts between rich and lean, the catalytic conversion efficiency may also decrease.

(Object of the Invention) The present invention has been made to solve the problems of the prior art as described above. By controlling the fluctuations in the fuel ratio so that they are in opposite phases, that is, symmetrical around a predetermined value, it is possible to equalize the output torque of the engine, enable smooth operation, and improve catalyst conversion efficiency. It is also an object of the present invention to provide an air-fuel ratio control device that can also correct an overall deviation in air-fuel ratio.

(Configuration of the Invention) FIG. 5 is a block diagram showing the configuration of the present invention.

First, in FIG. 5, 31 is a first exhaust detection means.

The first exhaust detection means 31 is an exhaust sensor provided in the exhaust pipe of the first system (for example, the right bank in FIG. 1), and outputs a signal corresponding to the concentration of exhaust gas components in the first system.

Further, 36 is a second exhaust detection means.

This second exhaust detection means 36 is an exhaust sensor provided in the exhaust pipe of the second system (for example, the left bank in FIG. 1).

Note that a zirconia oxygen meter that detects the oxygen concentration in exhaust gas is often used as an exhaust sensor.

Next, the first calculation means 32 performs the first exhaust detection means 3
Based on the detection result of No. 1, the first control signal S1 is calculated and outputted for correcting and controlling the air-fuel ratio of the air-fuel mixture supplied to the first system so as to maintain it at a predetermined value (details will be described later).

The first air-fuel mixture adjusting means 33 adjusts the air-fuel mixture to be supplied to the first system in accordance with the first control signal S1, and is, for example, a fuel injection device, a carburetor, or a fuel injection device. A device that corrects the air-fuel mixture basically metered by a carburetor or a carburetor in accordance with the first control signal S1, for example, a bypass air passage that bypasses the upstream and downstream parts of the throttle valve, and the bypass air passage that flows through the bypass air passage. A device consisting of a bypass control valve regulating the amount of auxiliary air can be used.

Next, the second calculation means 37 corrects and controls the deviation of the air-fuel ratio in the second system from the predetermined value so as to be symmetrical with the deviation in the first system about the predetermined value, and a second control signal S that corrects and controls the overall level of the air-fuel ratio of the air-fuel ratio based on the correlation between the detection result of the first exhaust detection means 31 and the detection result of the second exhaust detection means 36;
2 is calculated and output.

Further, the second air-fuel mixture adjusting means 35 measures the air-fuel mixture to be supplied to the second system in accordance with the second control signal S2, and the specific content is the same as that of the first air-fuel mixture adjusting means 33. It is.

Next, the configuration shown in FIG. 5 will be explained in more detail.

(a) First, when both the first mixture adjusting means 33 and the second mixture adjusting means 35 are fuel injection devices,
In other words, as shown in Figure 1, the first system and the second system
A case will be described in which the system is provided with fuel injection valves 6 and 7, respectively, and the air-fuel ratio of the air-fuel mixture is controlled by controlling the respective fuel injection amounts.

In this case, the first calculation means 32 adds the first calculation means 32 to the separately calculated basic fuel supply amount (details will be described later).
By multiplying or adding a first correction signal based on the deviation between the detection result of the exhaust detection means 31 and a predetermined value (for example, a signal obtained by adding a value obtained by integrating the above deviation and a value proportional to the deviation), The first air-fuel mixture adjusting means 33 is a device for calculating a first control signal, and the first air-fuel mixture adjusting means 33 is a fuel injection device (a device consisting of a drive circuit and a fuel injection valve) that injects fuel into a first system according to the first control signal. ).

Further, the second calculation means 37 generates a correction signal that is symmetrical about a predetermined value with respect to the first correction signal.
A signal for correcting the overall level of the air-fuel ratio of the second system based on the correlation between the detection result of the first exhaust detection means 31 and the detection result of the second exhaust detection means 36, that is, increases the fuel supply amount. Alternatively, a second correction signal is calculated by adding a signal for decreasing the amount of fuel, and the second control signal S2 is calculated by multiplying or adding the second correction signal to the basic fuel supply amount. The second air-fuel mixture metering means 35 is a fuel injection device that injects fuel into the second system according to the second control signal.

Note that the basic fuel supply amount is a value calculated from various operating variables of the engine, such as rotational speed N and intake air amount Q, using TP=K・Q/N (K is a constant).
It is calculated by adding corrections based on engine temperature, etc. to TP.

(b) Next, in the case where the first mixture adjusting means 33 and the second mixture adjusting means 35 are a bypass air passage and a bypass control valve provided in the first system and the second system, respectively, that is, A case will be described in which a valve similar to the auxiliary air valve 22 shown in FIG. 1 is provided for each system.

In this case, the basic mixture is supplied by the fuel injection valve or the carburetor, and the first mixture adjusting means 33 and the second mixture adjusting means 35 only supply the corrected air amount. It will be controlled.

Therefore, the first calculation means 32 and the second calculation means 37 output only the correction amount mentioned in (a) above as the first control signal S1 and the second control signal S2.

In this case, the fuel injection valves and carburetors may be provided for each system, or may be common to both systems. In this case, the fuel injection valve injects the basic fuel supply amount described above.

(C) Next, if both the first air-fuel mixture metering means 33 and the second air-fuel mixture metering means 35 are carburetors, in other words, the air-fuel mixture is supplied to the first system and the second system from separate vaporizers. The case where is supplied will be explained.

In this case, basic fuel is supplied from the carburetor according to the suction negative pressure for each system, but the air-fuel ratio can be controlled, for example, by controlling the air bleed of the carburetor. .

This technology is known, for example, from the published patent publication published in 1975.
As disclosed in numerous publications such as No. 132326, this is a commonly used technology as an air-fuel ratio control device.

Therefore, in this case, the first calculation means 32 and the second calculation means 37 calculate only the correction amount and output them as the first control signal and the second control signal,
These control signals may be used to control the solenoid valves that control the air bleed of the vaporizers in each system.

As mentioned above, in the configuration shown in FIG. 5A, the air-fuel ratio of the air-fuel mixture supplied to the cylinders in the first system (for example, the right bank) and the air-fuel ratio Hunting with the air-fuel ratio varies symmetrically (hereinafter referred to as anti-phase) around a predetermined value. Therefore, the output torque appearing on the output shaft of the engine is averaged as a whole, so fluctuations are extremely small.

Furthermore, since the exhaust gas is also mixed with anti-phase hunting, the value as a whole is always close to λ=1, and the catalytic converter can be operated near the highest conversion efficiency of the catalyst.

Furthermore, in addition to correcting the opposite phase between the first system and the second system as described above, correction is performed in accordance with the detection results of the first exhaust detection means and the detection results of the second exhaust detection means. Therefore, the first system and the second system
It is possible to correct the overall air-fuel ratio deviation with the system.

That is, due to variations in the dimensions and characteristics of engine component parts, the air-fuel ratio may deviate as a whole between the first system and the second system.

In such a case, if correction is performed based on the correlation between the signal of the first exhaust detection means and the signal of the second exhaust detection means as described above, the overall deviation in the air-fuel ratio can be corrected. I can do it.

For example, if the detection result of the second exhaust detection means is lean when the detection result of the first exhaust detection means changes from rich to lean, this indicates that the air-fuel mixture in the second system is lean as a whole. As shown, it is sufficient to perform a correction such as increasing the fuel supply amount of the second system by a predetermined amount (or decreasing the auxiliary air amount).

Moreover, contrary to the above, if the detection result of the second exhaust detection means is rich when the detection result of the first exhaust detection means changes from lean to rich, the second exhaust detection means
Since this indicates that the air-fuel mixture in the system as a whole is biased toward richness, it is sufficient to perform a correction to reduce the fuel supply amount to the second system by a predetermined amount (or increase the amount of auxiliary air).

Alternatively, if the detection result of the first exhaust detection means is rich and the detection result of the second exhaust detection means is also rich, it can be determined that the air-fuel mixture in the second system is biased towards rich as a whole. Because it shows
A correction is made to reduce the fuel supply amount of the second system by a predetermined amount, and if the detection result of the second exhaust detection means is also lean when the detection result of the first exhaust detection means is lean, the second exhaust system Since this indicates that the air-fuel mixture as a whole is biased toward lean, a correction may be made to increase the amount of fuel supplied to the second system by a predetermined amount.

(Examples of the Invention) The present invention will be described in detail below based on Examples.

The hardware configuration of the present invention is the same as that shown in FIG. 1, except that the calculations within the control device 19 are different.

6 and 7 are flowcharts showing an example of the calculation process within the control device 19. FIG. 6 shows the air-fuel ratio control, and FIG. 7 shows the calculation of the fuel injection amount.

Further, FIG. 8 is a diagram showing changes in control signals in the air-fuel ratio control of FIG. 6.

First, FIG. 6 is a flowchart showing calculations when only the right bank exhaust sensor (12 in FIG. 1) is used as a preliminary stage of the present invention.

In FIG. 6, first at 101, it is determined from the signal of the right bank exhaust sensor 12 whether the right bank is rich or lean.

If it is rich in step 101, the process goes to step 102, where it is determined whether the previous calculation was rich or lean.

If the previous time was also rich, the process goes to 104 and the value obtained by subtracting the predetermined value ΔI from the correction coefficient α1 is set as a new α1 (integral operation).

On the other hand, if it was lean last time at 102,
In this calculation, it is shown that there is a change from lean to rich for the first time, so go to step 105 and set the value obtained by subtracting ΔP from the correction coefficient α1 as the new α1 (proportional operation).

Also, if it is lean in the above 101, 1
03, it is determined whether the air-fuel ratio in the previous calculation was rich or lean.

If it was rich last time, it means that it has changed from lean to rich in the current calculation, so it is 1.
06, the value obtained by adding the predetermined value ΔP to the correction coefficient α1 is set as a new α1 (proportional operation).

On the other hand, if it is lean at 103, the process goes to 107, and the value obtained by adding a predetermined value ΔI to the correction coefficient α1 is set as a new α1 (integral operation).

Next, in step 108, a value obtained by subtracting α1 obtained as described above from 1 is set as a correction coefficient α2.

Next, in FIG. 7, first in step 111, the basic fuel supply amount TP is calculated.

For example, the basic fuel supply amount TP is calculated from the rotational speed N and the intake air amount Q, which have been separately determined, according to the formula: basic fuel supply amount TP=K·Q/N.

Next, in 112, the above basic fuel supply amount TP
The actual fuel supply amount F1 for the right bank is calculated by multiplying by the correction coefficient α1 for the right bank, and
The actual fuel supply amount F2 of the left bank is calculated by multiplying the basic fuel supply amount TP by the correction coefficient α2 of the left bank.
Calculate.

Next, at 113, the above F1 (corresponding to the first control signal) is output to the right bank drive circuit, and F2
(corresponding to the second control signal) is output to the left bank drive circuit.

As mentioned above, the correction coefficient α1 of the right bank and the correction coefficient α2 of the left bank are multiplication correction coefficients with 1 as the median value, and by setting α2 = 1 - α1, the correction coefficient α1 of the right bank and the correction coefficient α2 of the left bank are Correction can be performed in opposite phase.

Fluctuations in the air-fuel ratio in the above control will be explained using FIG. 8.

In FIG. 8, a is the right bank exhaust sensor 12
The output signal b is a control signal for the fuel supply amount of the right bank.

Further, d is an output signal of the left bank exhaust sensor 13, and c is a control signal for the fuel supply amount of the left bank.

In the calculation shown in FIG. 6, the fuel supply amount of the right bank shown in b and the fuel supply amount of the left bank shown in c are controlled to have opposite phases in accordance with the signal of the right bank exhaust sensor 12 shown in a. , if there is no overall difference in air-fuel ratio between the right bank and the left bank, then section A
As shown in the part, the right bank and left bank are λ
They are controlled to have opposite phases with respect to 1 as the center.

Therefore, the air-fuel ratio fluctuations and output torque fluctuations between the right bank and the left bank are in opposite phases, so
It is possible to achieve smooth control with no fluctuations in the output torque, which is averaged as a whole, and the catalytic converter can also be operated at the point where the conversion efficiency is highest.

In FIG. 8, Td indicates the delay time from when the fuel supply amount changes until it is detected by the exhaust sensor.

Next, if the air-fuel ratios of the left and right banks deviate overall due to variations in engine components or characteristics, the air-fuel ratios of the left and right banks will simply differ, as shown in section B in Figure 8. It is not possible to achieve the initial objective simply by controlling the phase to the opposite phase.

That is, in section B, the right bank is controlled to decrease the fuel supply amount because the exhaust sensor output indicates rich, and the left bank is controlled to increase the fuel supply amount in the opposite phase. ing.

Then, at time T0, the exhaust sensor of the right bank detects that the air-fuel ratio of the right bank has changed from rich to lean, and accordingly, the fuel supply amount of the right bank changes from decreasing to increasing.

According to this, in the left bank, the time point
Control switches to reducing fuel from T0.

By the way, if the air-fuel ratios of the right bank and left bank do not deviate as a whole, the left bank should change from lean to rich when the right bank changes from rich to lean, but as can be seen from c and d. In addition, the left bank as a whole has shifted toward the lean side, so even when the right bank changes from rich to lean at time T0, the left bank continues to be lean.

In this way, if the air-fuel ratio of one bank switches from rich to lean and the air-fuel ratio of the other bank remains lean, the air-fuel ratio of the latter bank is determined to be lean overall. Ru.

In such a case, a correction is made to increase the fuel supply amount by a predetermined amount S at time T1, and the air-fuel ratio of the left bank is moved to the rich side as a whole.

In the example shown in Fig. 8, even after one correction operation at time T1, the left bank still remains in a lean state, so the same correction is repeated once again at time T2, and as a result, the left and right banks are changed as shown in section A. are always controlled to have opposite phases.

Note that the above example illustrates a case where the left bank is biased towards the lean side as a whole, but if it is biased towards the rich side, a correction is made to reduce the fuel supply amount by a predetermined amount S, contrary to the above. Just go.

A flowchart of calculations for performing the above correction is shown in FIG.

In FIG. 9, 101 to 107 are the same as in FIG. 6 above.

Next, in step 121, it is determined whether the air-fuel ratio of the left bank is rich or lean in accordance with the signal from the left bank exhaust sensor.

If 121 is rich, the left bank remains rich when the right bank changes from lean to rich, indicating that the air-fuel ratio of the left bank is biased toward the rich side. The value obtained by subtracting the value S is set as a new Δα.

Further, at step 122, it is determined whether the left bank is rich or lean.

In the case of lean at 122, the left bank remains lean when the right bank changes from rich to lean, indicating that the left bank as a whole is biased towards lean, so at 124 the coefficient Δα
The value obtained by adding a predetermined value S to Δα is set as a new Δα.

Next, in step 125, the value obtained by adding Δα to 1−α1 is set as α2.

Note that when 121 is lean and 122 is rich, the left and right banks are controlled to have opposite phases, which is a normal state, so Δα is left as is.

Further, when there is no variation in air-fuel ratio between the left and right banks, Δα is 0.

By controlling as described above, even if the air-fuel ratios of the left and right banks deviate as a whole, the deviation can be corrected and the air-fuel ratios of both banks can be controlled to have opposite phases.

Next, FIG. 10 is a flowchart of an embodiment showing another operation of the present invention.

In FIG. 10, at 101, it is determined whether the right bank is rich or lean.

If it is rich in step 101, the process goes to step 132, where it is determined whether the left bank is rich or lean.

If 132 is rich, it indicates that the left bank as a whole is rich, so go to 134,
The value obtained by subtracting the predetermined value M from the coefficient Δα is set as a new Δα.

If the signal is lean at 132, this indicates that the opposite phase control is being performed normally.

On the other hand, if it is lean in 101, the process goes to 133, where it is also determined whether the left bank is rich or lean.

If it is lean at 133, it indicates that the left bank is lean as a whole, so go to 135,
The value obtained by adding the predetermined value M to the coefficient Δα is set as a new Δα.

If 133 is rich, it indicates that normal anti-phase control is being performed.

Thereafter, in steps 102 to 107, integral proportional operations similar to those shown in FIG. 6 are performed.

Next, at 142, the value obtained by adding Δα to 1−α1 is α2
shall be.

FIG. 11 shows control waveforms in the above calculation. In FIG. 11, a is an output signal of the right bank exhaust sensor 12, b is a control signal for the fuel supply amount of the right bank, c is a control signal for the fuel supply amount of the left bank,
d indicates the value of the coefficient Δα for correcting the left bank.

Further, e indicates the output signal of the left bank exhaust sensor 13.

In section B of FIG. 11, the exhaust sensor signals for the right bank and the left bank are in opposite phase, so no correction is performed.

In section A, when the right bank exhaust sensor indicates lean, the left bank exhaust sensor also indicates lean, so the left bank as a whole is biased toward the lean side, as shown in d. The coefficient Δα is gradually added and increased, and the fuel supply amount of the left bank shown in c gradually increases, and finally a normal control state is reached in which the right bank and the left bank are in opposite phases.

In addition, in the embodiment described above, the case of multiplicative correction in which the basic fuel supply amount TP is multiplied by the correction coefficients α1 and α2 was illustrated, but the same control can be performed in the case of additive correction in which the correction values are added or subtracted. can.

Further, in the above embodiment, only the case where a fuel injection valve is used as the air-fuel mixture adjusting means is illustrated, but as detailed in (a) to (c) in the explanation of FIG. The present invention can be similarly applied even when a bypass control valve is used.

Further, in FIG. 1, a case has been described in which the present invention is applied to a V-type engine, but similar control can be performed also in a horizontal engine.

(Effects of the Invention) As explained above, in the present invention, in an engine in which a plurality of cylinders are divided into two systems, the deviation of the air-fuel ratio from a predetermined value in the cylinders belonging to the first system and the cylinders belonging to the second system As a result, torque fluctuations caused by air-fuel ratio hunting caused by feedback control can be suppressed and smooth output characteristics can be achieved. = 1, the catalytic converter can be operated at the point where the conversion efficiency is highest, and the exhaust purification performance can also be improved.

In addition, even if the air-fuel ratio of the first system and the second system differs as a whole, the difference can be corrected, and the air-fuel ratio difference due to variations in engine mechanical parts can also be corrected. There is.

[Brief explanation of drawings]

Figure 1 is an example of a conventional air-fuel ratio control device;
The figure is a control signal waveform diagram of a conventional device, Figure 3 is a characteristic diagram of air-fuel ratio and output torque, Figure 4 is a characteristic diagram of air-fuel ratio and catalyst conversion efficiency, and Figure 5 is a block diagram showing the configuration of the present invention. , FIG. 6 and FIG. 7 are flowcharts of an embodiment showing the calculations of the present invention, FIG. 8 is a control signal waveform diagram in the calculation of FIG. 6, and FIGS. 9 and 1.
0 is a flowchart of another embodiment of the present invention, and FIG. 11 is a control signal waveform diagram in the calculation of the embodiment of FIG. Explanation of symbols, 1...Air cleaner, 2...Air flow meter, 3...Throttle valve, 4...Right bank intake port, 5...Left bank intake port, 6
...Right bank injection valve, 7...Left bank injection valve, 8
...Right bank cylinder, 9 ...Left bank cylinder, 10...
...Right bank exhaust pipe, 11...Left bank exhaust pipe, 1
2... Right bank exhaust sensor, 13... Left bank exhaust sensor, 14, 15... Catalytic converter, 16
... Muffler, 17 ... Rotation sensor, 18 ... Temperature sensor, 19 ... Control device, 20 ... Crankshaft, 21 ... Exhaust recirculation control valve, 22 ... Auxiliary air valve, 31 ... First exhaust detection means, 32...first calculation means, 33...first air-fuel mixture metering means, 34...
Second calculation means, 35...Second air mixture metering means, 3
6...Second exhaust detection means, 37...Second calculation means.

Claims (1)

[Scope of Claims] 1 Feedback control of the fuel supply amount so as to maintain the air-fuel ratio at a predetermined value based on the signal of the means for detecting the concentration of exhaust gas components of the engine, and the exhaust systems of the plurality of cylinders are controlled by the first and second cylinders. In a second engine divided into two systems, a first exhaust detection means detects the concentration of exhaust gas components in the exhaust system of the first system, and a basic fuel supply amount calculated separately according to various operating variables of the engine. A correction control is performed to maintain the air-fuel ratio of the air-fuel mixture supplied to the first system at a predetermined value by multiplying the first correction signal based on the deviation between the detection result of the first exhaust detection means and the predetermined value. a first calculation means for calculating a first control signal; a first mixture adjusting means for supplying the mixture corrected according to the first control signal to the first system; and exhaust gas components in the exhaust system of the second system. a second exhaust gas detection means for detecting the concentration; and a correction signal that is symmetrical about a predetermined value with the first correction signal, from a state in which the detection result of the first exhaust gas detection means indicates that the mixture is rich. When the state changes to indicate a lean mixture, if the detection result of the second exhaust detection means is lean, a signal is added to increase the fuel supply amount by a predetermined amount, and the first exhaust detection means When the detection result of the second exhaust gas detection means changes from lean to rich, if the detection result of the second exhaust detection means is rich, a second correction signal is generated by adding a signal that reduces the fuel supply amount by a predetermined amount. a second calculation means for calculating a second control signal by multiplying the basic fuel supply amount by the second correction signal; and a second air-fuel mixture adjusting means for supplying the air-fuel ratio to the cylinders belonging to the first system and the cylinders belonging to the second system so that deviations from a predetermined value of the air-fuel ratio in the cylinders belonging to the first system and the cylinders belonging to the second system are symmetrical about the predetermined value. An air-fuel ratio control device characterized in that the air-fuel ratio control device corrects an overall deviation in air-fuel ratio between the first system and the second system. 2 The first mixture adjusting means is a fuel injection device that supplies fuel to the first system according to the first control signal, and the second mixture adjusting means corresponds to the second control signal. 2. The air-fuel ratio control device according to claim 1, wherein the air-fuel ratio control device is a fuel injection device that supplies fuel to a second system. 3 Feedback control of the fuel supply amount to maintain the air-fuel ratio at a predetermined value based on a signal from a means for detecting the concentration of exhaust gas components of the engine, and connect the exhaust systems of the plurality of cylinders to two systems, the first and second systems. In the separated engine, the first exhaust detection means detects the concentration of exhaust gas components in the exhaust system of the first system, and the first exhaust detection means detects the basic fuel supply amount separately calculated according to various operating variables of the engine. By multiplying the first correction signal based on the deviation between the detection result and the predetermined value, a first control signal for correcting and controlling the air-fuel ratio of the air-fuel mixture supplied to the first system to be maintained at a predetermined value is calculated. a first calculation means; a first air-fuel mixture adjusting means for supplying the air-fuel mixture corrected according to the first control signal to the first system; an exhaust detection means; and a correction signal that is symmetrical with the first correction signal about a predetermined value, such that when the detection result of the first exhaust detection means is rich, the detection result of the second exhaust detection means is rich. If the detection result of the first exhaust detection means is lean and the detection result of the second exhaust detection means is lean, a signal is added to reduce the fuel supply amount by a predetermined amount. a second calculation means that calculates a second correction signal by adding a signal that increases the amount by a fixed amount, and calculates the second control signal by multiplying the basic fuel supply amount by the second correction signal; and a second air-fuel mixture adjusting means for supplying the air-fuel mixture corrected according to the second control signal to the second system, the air-fuel ratio being adjusted between the cylinders belonging to the first system and the cylinders belonging to the second system. An air-fuel ratio control device, characterized in that the deviation from a predetermined value is controlled to be symmetrical about the predetermined value, and the overall deviation in air-fuel ratio between a first system and a second system is corrected.