JPH0417746A - Air-fuel ratio control system of internal combustion engine - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an internal combustion engine.
The present invention relates to an air-fuel ratio control device configured to detect air-fuel ratios on the upstream and downstream sides of a catalytic exhaust gas purification device, and perform feedback control on the air-fuel ratio of an engine intake air-fuel mixture.

<Prior art> Conventionally, in order to maintain good conversion efficiency in a three-way catalyst installed in the exhaust system for exhaust purification, feedback control of the air-fuel ratio of the engine intake air-fuel mixture to the stoichiometric air-fuel ratio has been carried out. In order to ensure responsiveness, an oxygen sensor that detects the air-fuel ratio via the oxygen concentration in the exhaust gas is installed at a gathering part of the exhaust manifold relatively close to the combustion chamber. Based on the medium oxygen concentration, the actual air-fuel ratio (rich/lean) relative to the stoichiometric air-fuel ratio is detected to perform feedbank control of the amount of fuel supplied to the engine.

However, as mentioned above, the oxygen sensor installed in the exhaust system relatively close to the combustion chamber is exposed to high-temperature exhaust gas, so its characteristics tend to change due to thermal deterioration.
Because the exhaust gas from each cylinder was not sufficiently mixed, it was difficult to detect the average air-fuel ratio for all cylinders, resulting in variations in air-fuel ratio detection accuracy, which in turn worsened air-fuel ratio control accuracy. .

In view of this, an oxygen sensor is also installed downstream of the catalyst, and two
Various methods have been proposed that feedback control the air-fuel ratio using the detected values of two oxygen sensors (Japanese Patent Laid-Open No. 58-4
(See Publication No. 8756, etc.).

In other words, the downstream oxygen sensor responds due to the 02 storage effect of the three-way catalyst (a state in which the amount of oxygen is larger when lean than the stoichiometric air-fuel ratio and smaller when it is rich continues for a certain period of time, resulting in a delay in output). Although the performance is poor, it is possible to detect the air-fuel ratio with the best conversion efficiency of Co and HCNOx for the three-way catalyst, so it is possible to obtain highly accurate and stable detection characteristics that compensate for the deterioration state of the upstream oxygen sensor.

Therefore, it is possible to perform independent air-fuel ratio feedback control based on the detected values of the two oxygen sensors, or to compensate for the characteristics of the air-fuel ratio feedback control by the upstream oxygen sensor with the downstream oxygen sensor. While ensuring responsiveness with the upstream sensor, the accuracy of the control point is compensated for on the downstream side to perform highly accurate air-fuel ratio feedback control.

As a device for compensating the characteristics of air-fuel ratio feedback control by an upstream oxygen sensor with a downstream oxygen sensor, for example, while performing air-fuel ratio feedback control based on the detection of a highly responsive upstream sensor, When the downstream sensor detects a shift in the control point and the downstream sensor detects a rich/lean condition relative to the target, the control constant of the air-fuel ratio feedback control based on the upstream sensor output is gradually adjusted in a direction that eliminates the rich/lean condition relative to the target. By changing the air-fuel ratio to the target air-fuel ratio, the air-fuel ratio detected by the downstream sensor repeats a rich/lean cycle with respect to the target, and as a result, the average of the control points of the feedback control based on the upstream sensor is controlled to be near the target air-fuel ratio. It is being done.

<Problems to be Solved by the Invention> By the way, when oxygen sensors are provided on the upstream and downstream sides of the catalytic exhaust purification device and the air-fuel ratio is feedback-controlled as described above, the output of the downstream sensor has a large response delay. Because of this, the downstream sensor is lean (rich).
is detected and the air-fuel ratio is gradually made richer (leaner).
When the downstream sensor detects a reversal of the air-fuel ratio from lean to rich (from rich to lean), the actual air-fuel ratio in the combustion chamber has already become rich (lean). There will be. For this reason, there is a problem in that when the air-fuel ratio detected by the downstream sensor is reversed from lean to lean, the amount of emissions of Co, HC, etc. increases, and conversely, when the air-fuel ratio is reversed from rich to lean, NOx increases.

The present invention was made in view of the above problems, and uses an air-fuel ratio sensor provided downstream of a catalytic exhaust purification device to compensate for deviations in air-fuel ratio feedback control accuracy caused by an air-fuel ratio sensor provided upstream. At the same time, it is an object of the present invention to provide an air-fuel ratio control device that can prevent the swing width relative to a target air-fuel ratio from becoming excessively large.

<Means for Solving the Problems> Therefore, in the present invention, as shown in FIG. first and second air-fuel ratio sensors whose output value changes in response to the concentration of a specific component in the exhaust gas that changes depending on the air-fuel ratio of the air; and engine intake air-fuel mixture based on the output value of the first air-fuel ratio sensor. an air-fuel ratio feedback control means for feedback controlling the air-fuel ratio of the second air-fuel ratio to a target air-fuel ratio; A control operation amount setting means for setting an increase/decrease, a rich/lean time measuring means for respectively measuring a rich detection time and a lean detection time with respect to a target air-fuel ratio based on an output value of a second air-fuel ratio sensor, and a rich-lean time measuring means for measuring the rich/lean time. an increase/decrease degree control means for changing the degree of increase/decrease in the control operation amount by the control operation amount setting means based on the rich detection time and the lean detection time measured by the means. I made it.

<Operation> According to this configuration, the air-fuel ratio feedback control means adjusts the air-fuel ratio of the engine intake air-fuel mixture to the target air-fuel ratio based on the output value of the first air-fuel ratio sensor provided on the upstream side of the catalytic exhaust purification device. feedback control. The air-fuel ratio as a result of the feedback control is detected by a second air-fuel ratio sensor provided downstream of the catalytic exhaust purification device, and the control operation amount setting means detects the output of the second air-fuel ratio sensor. The control operation amount in the air-fuel ratio feedback control means is set to increase or decrease based on the rich/lean detection with respect to the target air-fuel ratio by the value, and the control point of the feedback control by the first air-fuel ratio sensor becomes the target air-fuel ratio by increasing or decreasing the control operation amount. Try to get it close to the fuel ratio.

Here, the rich/lean time measuring means measures the rich detection time and the lean detection time respectively with respect to the target air-fuel ratio based on the output value of the second air-fuel ratio sensor, and the increase/decrease degree control means performs control based on the measured time. The degree of increase/decrease in the control operation amount by the operation amount setting means is changed.

That is, when the second air-fuel ratio sensor detects a rich (lean) state with respect to the target air-fuel ratio, the control point of the air-fuel ratio feedback control based on the first air-fuel ratio sensor is corrected in the lean (rich) direction. The amount of control operation is controlled to increase or decrease, but the degree of increase or decrease in this increase/decrease control is not constant, but changes according to the rich (lean) detection time, and the amount of control operation corresponds to the rich/lean detection time. Because it can be increased or decreased with arbitrary change characteristics,
When a delay in detection response by the second air-fuel ratio sensor is expected, it is possible to suppress overshoot by reducing the degree of increase/decrease.

<Example> The present invention will be explained in detail below.

In FIG. 2 showing one embodiment, an engine 1 has an air cleaner 2 to an intake duct 3. Air is taken in via the throttle valve 4 and the intake manifold 5. A fuel injection valve 6 is provided in a branch portion of the intake manifold 5 for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that opens when the solenoid is energized and closes when the energization is stopped. Fuel that is pressure-fed from a fuel pump that does not operate and is adjusted to a predetermined pressure by a pressure regulator is injected and supplied into the intake manifold 5.

In this embodiment, a multi-point injection system (MPr method) is used as described above, but a single-point injection system (SP1
A spark plug 7 is provided in each of the combustion chambers of the engine Ml, which may be of the type (type), and ignites a spark to ignite and burn the air-fuel mixture.

From engine 1, exhaust manifold 8° exhaust duct 9. Exhaust gas is discharged via the three-way catalyst 1o and the muffler 11. The three-way catalyst 1o eliminates Co and H in the exhaust components.
This is a catalytic exhaust purification device that oxidizes C and reduces NOx to convert it into other harmless substances.The best conversion efficiency is achieved when the engine intake air-fuel mixture is combusted at the stoichiometric air-fuel ratio. (See Figure 4).

Control o - Roux 2 - Knit 12 is CPU, ROM
.

Equipped with a microcomputer that includes a RAM, an A/D converter, and an input/output interface, it inputs detection signals from various sensors, processes them as described later, and controls the operation of the fuel injection valve 6. Control.

As the various sensors, an air flow meter 13 such as a hot wire type or a flap type is provided in the intake duct 3, and outputs a voltage signal according to the intake air flow rate Q of the engine 1.

Further, a crank angle sensor 14 is provided, and in the case of a four-cylinder engine, outputs a reference signal for every 180 degrees of crank angle and a unit signal for every 1 degree or 2 degrees of crank angle. Here, the engine rotational speed N can be calculated by measuring the cycle of the reference signal or the number of occurrences of the unit signal within a predetermined time.

Further, a water temperature sensor 15 is provided to detect the cooling water temperature Tw of the water jacket of the engine 1.

Furthermore, an exhaust manifold 8 is provided on the upstream side of the three-way catalyst 10.
A first oxygen sensor 16 as a first air-fuel ratio sensor is provided at the collecting part of An oxygen sensor 17 is provided.

The first oxygen sensor 16 and the second oxygen sensor 17 are known sensors whose output values change in response to the concentration of oxygen as a specific component in the exhaust gas, and the oxygen concentration in the exhaust gas changes at the stoichiometric air-fuel ratio. Taking advantage of the sudden change in the air-fuel ratio, the voltage is set at around 1■ when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, depending on the difference in oxygen concentration between the atmosphere as a reference gas and the exhaust gas. At some times, a voltage near O is output (see Fig. 4).

Here, the CPU of the microcomputer built into the control unit 12 performs arithmetic processing according to the program on the ROM shown in the flowchart of FIG. 3, and controls the amount of fuel supplied to the engine 1.

The functions of the air-fuel ratio feedback control means, the control operation amount setting means, the increase/decrease degree control means, and the rich/lean time measuring means are provided in the control unit 12 in the form of software, as shown in the flowchart of FIG. .

Next, the state of arithmetic processing by the microcomputer in the control unit 12 will be explained with reference to the flowchart in FIG.

The flowchart in FIG.
m5), and the air-fuel ratio feedback correction coefficient α
This is a program that sets the fuel injection amount Ti by setting the basic fuel injection amount TP by proportional-integral control based on the air-fuel ratio feedbank correction coefficient α, and sets the fuel injection amount Ti. A drive pulse signal corresponding to the fuel injection valve 6 is outputted at a predetermined timing to cause the fuel injection valve 6 to perform fuel injection.

First, step 1 (indicated as Sl in the figure).

(Similarly below), the output value (voltage value) of the second oxygen sensor 17 provided downstream of the three-way catalyst 10 is set to RVO□.

In the next step 2, the RVOt for which the latest output value was set in step 1 is compared with a predetermined voltage (for example, 500av) corresponding to the stoichiometric air-fuel ratio, which is the target air-fuel ratio, and the air-fuel ratio of the engine intake air-fuel mixture is determined. Determine whether the air-fuel ratio is rich or lean relative to the stoichiometric air-fuel ratio.

Then, the second oxygen sensor 17 detects the stoichiometric air-fuel ratio by 7.
If it is determined that the flag FRR is the same, the process advances to step 3 and the flag FRR is determined.

As described later, the flag FRR is set to 1 at the first lean detection and remains at 1 in the lean state, so if the flag FRR is determined to be 1 in step 3, the lean state is This is the first reversal from to rich.

When it is determined that this is the first reversal from lean to rich, the process proceeds to step 4, where the flag FRR is set to zero so that it can be determined next time that lynch has been detected, and in the next step 5, lean is detected. T measured time
Set the value of L to MTL as a fixed value. The lean detection time TL is determined by the second oxygen sensor 17 as described later.
When the lean state relative to the stoichiometric air-fuel ratio is measured by is set in TL.

In the next step 6, the TL is reset to zero in order to measure time anew the next time the air-fuel ratio detected by the second oxygen sensor 17 becomes lean.

Then, in step 7, the newly set lean detection time and the weighted average of the lean detection time up to the previous time 1
MTLaν and the result is newly calculated as MTLa.
The weighted average value of the lean detection time is updated and set as v.

On the other hand, in the continuous rich air-fuel ratio state where FRR is determined to be 1 in step 3, the process proceeds to step 8. In step 8, proportional control of the air-fuel ratio feedback correction coefficient α is performed based on the ratio of the rich detection time TR to the rich detection average time MTRav calculated in the same manner as the lean detection average time MTLav in step 7. The correction coefficient γ, which determines the degree of change of the coefficient Sr for correcting the constant P, is set by referring to the map.

The rich detection time TR is incremented by 1 in step 9 every time this program is executed in the rich detection state by the second oxygen sensor 17, and is reset to zero when lean is detected, so it is inverted from lean to rich. It shows the elapsed time since then. Here, as shown in the figure, when TR/M T Raν is near zero, the correction coefficient T is set to approximately 1, but as the rich detection time TR becomes longer and approaches the average time MTRav, the correction coefficient T is set to approximately 1. It is preset to decrease.

When the second oxygen sensor 17 determines that the air-fuel ratio is rich, this indicates that the control point of the air-fuel ratio feedback control by the first oxygen sensor 16, which will be described later, has shifted toward the rich direction. , it is necessary to correct the characteristics of the air-fuel ratio feedback control in the lean direction, and in this embodiment, as will be described later, the characteristics of the feedback control are corrected by increasing or decreasing the proportional control constant P as the control operation amount by the correction coefficient Sr. is changed to correct the deviation of the control point.

Since the second oxygen sensor 17 is provided downstream of the three-way catalyst 10 as described above, it is exposed to relatively low-temperature exhaust gas, and harmful substances such as lead and sulfur are exposed to the three-way catalyst 10. 10 and avoids poisoning, the condition is less likely to deteriorate, and the exhaust gas from each cylinder is sufficiently mixed, making it possible to detect an approximately balanced oxygen concentration. Therefore, the detection reliability of the second oxygen sensor 17 is higher than that of the first oxygen sensor 16;
6, the control center of the air-fuel ratio that repeats rich and lean can be detected.
Even if feedback control is performed to the stoichiometric air-fuel ratio based on the output of the oxygen sensor 16, the second oxygen sensor 17 can accurately detect that the control point of the first oxygen sensor 16 has shifted.

Therefore, when the second oxygen sensor 17 detects that the air-fuel ratio becomes rich, it is assumed that the control point has shifted in the rich direction.
This is an attempt to return the control point to the stoichiometric air-fuel ratio by changing the feedback control characteristics, and in step 10,
A value obtained by multiplying a basic amount (for example, 0.001%) by the correction coefficient T is subtracted from the correction coefficient Sr for correcting the proportional control constant P (Sr-5r-T×basic amount).

As described later, as the correction coefficient Sr (%) increases, the proportional control amount in the rich direction (fuel increase direction) is increased and the proportional control amount in the lean direction (fuel decrease direction) is decreased. , 7 control points are shifted in the rich direction, so the second air-fuel ratio sensor 1
7, when a rich air-fuel ratio is detected, it is necessary to conversely decrease the correction coefficient Sr and shift the control point of the air-fuel ratio feedback control in the lean direction,
As described above, the correction coefficient Sr is set to decrease by the Tx basic amount.

Here, the correction coefficient Sr is set to decrease each time this program is executed in the rich detection state, and the control point of the air-fuel ratio feedback control gradually shifts in the lean direction as the correction coefficient Sr decreases. However, as mentioned above, the correction coefficient γ, which is multiplied by the basic quantity, decreases with the rich detection time TR and changes the degree of decrease, so at the beginning of the reversal from lean to rich, it is determined approximately at the basic quantity. However, as the rich detection time TR becomes longer, the amount by which the correction coefficient Sr is reduced becomes smaller, and the shift of the control point in the lean direction becomes slower.

Since the second oxygen sensor 17 is provided on the downstream side of the three-way catalyst 10 far from the combustion chamber as described above, the air-fuel ratio detection response is poor, and the feedback control characteristics are determined based on the rich detection by the sensor 17. Even if the combustion chamber air-fuel ratio is reversed to lean as a result of the change in the lean direction, there is a delay time until it is detected by the second oxygen sensor 17.

Therefore, when attempting to return the control point to the stoichiometric air-fuel ratio by correcting the proportional control constant P as described above, control is performed to further reduce the correction coefficient Sr even though the rich air-fuel ratio state has actually been resolved. If you do so, an overshoot error will occur.

However, as mentioned above, the average time of rich detection M
If the degree of decrease in the correction coefficient Sr is gradually attenuated based on the ratio of the actual elapsed time TR to TRav, it is possible to avoid excessively decreasing the correction coefficient Sr during the response delay time. Therefore, it is possible to prevent the control point from overshooting in the lean direction, and since the correction coefficient Sr can be changed at a relatively large rate at the early stage of rich detection, control responsiveness can also be ensured. It is. As a result, the first oxygen sensor 1
It is possible to compensate for the shift in the control point due to the deterioration of the three-way catalyst 10, suppress the swing of the air-fuel ratio around the stoichiometric air-fuel ratio due to air-fuel ratio feedback control, and maintain the conversion efficiency in the three-way catalyst 10 at a good level. .

In addition, in step 8, TR/MTRav of the correction coefficient T
The change characteristics for can be arbitrarily set based on empirical rules confirmed through experiments and the like.

Substantially the same control as the control at the time of rich detection shown above is performed also at the time of lean detection by the second oxygen sensor 17.

That is, in the first lean detection when the flag FRR is zero, the flag FRR is set to 1 (step 12), and the weighted average value MTRav of the rich detection time is updated based on the time TR measured in the previous rich detection state (step 12).
Step 13.14.15).

When lean detection continues, lean detection time TL
is increased by 1 each time this program is executed (step 17)
, the coefficient γ is searched from the map and set based on the ratio of the lean detection time TL to the weighted average time MTLaν (step 16).

Coefficient 1 variably set based on the lean detection time TL
is multiplied by the basic quantity in step 18, and the multiplication result is added to the correction coefficient Sr (step 18).
).

When the second oxygen sensor 17 detects lean, it is necessary to correct the control point of the air-fuel ratio feedback control in the rich direction, so by gradually increasing the correction coefficient Sr, the air-fuel ratio feedback correction coefficient α is proportionally controlled to increase. This makes the constant larger, and in this case,
Since the degree of increase in the correction coefficient Sr gradually decreases as the lean detection time TL increases, overshooting in the rich direction can be suppressed.

After setting the coefficient Sr for correcting the proportional control constant P based on the rich/lean relative to the stoichiometric air-fuel ratio detected by the second oxygen sensor 17 and the rich/lean detection time as described above, the next step 19 Thereafter, proportional-integral control of the air-fuel ratio feedbank correction coefficient α based on the output value of the first oxygen sensor 16 is executed.

In step 19, the output value of the first oxygen sensor 16 (FO
Set to 2.

In the next step 20, the output value (voltage value) set in the FVO7 in step 1 is combined with a predetermined iff pressure (for example, 50
0 mV), the first oxygen sensor 1
It is determined whether the air-fuel ratio of the engine intake air-fuel mixture detected in step 6 is rich or lean with respect to the stoichiometric air-fuel ratio (fifth step).
(see figure).

If it is determined in step 20 that FV○z > 500 mv, and the air-fuel ratio is richer than the stoichiometric air-fuel ratio, the process proceeds to step 21, where the flag FR is determined.

The flag FR is rich like the flag FRR.
This is to determine whether or not it is the first time of lean detection, and when it is determined in step 21 that the flag FR is zero, it is the first time of reversal to rich, and in this case, the process advances to step 22, which will be described later. The air-fuel ratio feedback correction coefficient α (reference value=1) multiplied by the basic fuel injection amount Tp is set to be decreased by proportional control in accordance with the following equation.

α←α−PX (1-3R) In the above formula, P is a proportional control constant as a preset control operation amount, and the correction coefficient S is set as described above.
Since the value obtained by subtracting r from 1 is multiplied, the correction coefficient Sr
(%), the smaller the reduction correction amount by the proportional control of the air-fuel ratio feedback correction coefficient α becomes, and the control point shifts in the rich direction.

In the next step 23, the flag FR is set to I. As a result, the next time the rich determination is made in step 20, the process will proceed from step 21 to step 24, and in step 24, the air-fuel ratio feed hack correction coefficient α is gradually decreased by integral control. Specifically, a preset integral control constant 1 is multiplied by a fuel injection amount Ti representing the engine load, and the result is subtracted from the air-fuel ratio feedback correction coefficient α.

On the other hand, when it is determined in step 20 that the detection result by the first oxygen sensor 16 is lean, the flag FR is first determined in step 25 in the same manner as in the case of rich detection.

When it is determined that the flag FR is 1 and this is the first time of reversal to lean, the process proceeds to step 26, where the air-fuel ratio feedback correction coefficient α is increased by proportional control. Here, a value obtained by multiplying the proportional control constant P by the correction coefficient Sr is added to the correction coefficient α,
As a result, when the correction coefficient Sr increases, the correction coefficient α
The increased control amount due to the proportional control becomes larger, and the control point shifts in the rich direction.

In the next step 27, the flag FR is set to zero.

Furthermore, in the lean continuation state in which the flag FR is determined to be zero in step 25, the process proceeds to step 28, where the correction coefficient α is gradually increased by integral control. The integral control is performed by adjusting the fuel injection amount Ti to a predetermined integral control constant I.
This is done by adding the value obtained by multiplying by the previous correction coefficient α.

In this way, if the correction coefficient Sr is increased, the air-fuel ratio control point by the air-fuel ratio feedback correction coefficient α is shifted toward the rich direction, and when the correction coefficient Sr is decreased, the control point is shifted toward the lean direction. When the second oxygen sensor 17 detects that the control point deviates in the rich direction, the correction coefficient Sr is decreased (see step 10), and when it is detected that the control point deviates in the lean direction, the correction coefficient Sr By increasing Sr (see step 18), the control point can be shifted in a direction closer to the stoichiometric air-fuel ratio, and this control for setting the correction coefficient Sr is performed in steps 1 to 18 above. .

When the air-fuel ratio feedback correction coefficient α is increased or decreased by the proportional-integral control as described above, in step 29, which is processed every time this program is executed, the fuel injection amount Ti is adjusted using the correction coefficient α. Settings are made.

In step 29, first, from the intake air flow rate Q detected by the air flow meter 13 and the engine rotation speed N calculated based on the detection signal from the crank angle sensor 14,
While calculating the basic fuel injection amount Tp (=KxQ/N; is a constant), the cooling water temperature T detected by the water temperature sensor 15
Various correction coefficients C0EF based on engine operating conditions, mainly w
In addition, a correction numerator s for correcting the change in the effective valve opening time of the fuel injection valve 6 due to the battery voltage is set, and the basic fuel injection is performed using these correction values and the air-fuel ratio feedback correction coefficient α. The final fuel injection amount Ti (←2TpXα×COEF+Ts) is set by correcting fTp.

When the predetermined fuel injection timing comes, the control unit 12 reads the latest value of the fuel injection amount Ti that is updated every time this program is executed in step 21, and sets the pulse width corresponding to the fuel injection amount Ti. The amount of fuel injected by the fuel injection valve 6 is controlled by outputting the drive pulse signal to the fuel injection valve 6.

<Effects of the Invention> As explained above, according to the present invention, in air-fuel ratio feedback control performed by providing air-fuel ratio sensors on the upstream and downstream sides of a catalytic exhaust purification device, the air-fuel ratio sensor provided on the downstream side This makes it possible to avoid control overshoot caused by sensor response delays, and thereby compensates the feedbank control point to the target air-fuel ratio while suppressing the swing range of the air-fuel ratio. ,
This has the effect of maintaining good conversion efficiency in the catalyst and improving exhaust characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a system schematic diagram showing an embodiment of the present invention, FIG. 3 is a flowchart showing air-fuel ratio feedback control in the above embodiment, and FIG. 4 5 is a diagram showing the relationship between the conversion efficiency of the three-way catalyst and the air-fuel ratio, and FIG. 5 is a time chart showing the change characteristics of the air-fuel ratio feed bank correction coefficient α in the same embodiment. 1... Engine hold unit sensor) 6... Fuel injection valve 8... Exhaust manifold 10... Three-way catalyst 12... Control 16... First oxygen sensor (first air-fuel ratio 17...Second oxygen sensor (second
Air-fuel ratio patent applicant Japan Electronics Co., Ltd. Patent attorney Fujio Sasashima

Claims (1)

[Scope of Claims] The device is provided on the upstream and downstream sides of a catalytic exhaust purification device installed in the exhaust system of an internal combustion engine, and is sensitive to the concentration of a specific component in the exhaust gas that changes depending on the air-fuel ratio of the engine intake air-fuel mixture. first and second air-fuel ratio sensors whose output values change based on the output value of the first air-fuel ratio sensor; and air-fuel ratio feedback control which feedback controls the air-fuel ratio of the engine intake air-fuel mixture to a target air-fuel ratio based on the output value of the first air-fuel ratio sensor. and control operation amount setting means for increasing or decreasing the control operation amount in the air-fuel ratio feedback control means based on rich/lean detection with respect to the target air-fuel ratio based on the output value of the second air-fuel ratio sensor; A rich/lean time measuring means for respectively measuring a rich detection time and a lean detection time with respect to a target air-fuel ratio based on an output value of an air-fuel ratio sensor; An air-fuel ratio control device for an internal combustion engine, comprising: an increase/decrease degree control means for changing the degree of increase/decrease in the control operation amount by the control operation amount setting means based on the control operation amount setting means.