JPH04124438A - Air fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To avoid any change in control performance caused by deterioration of an exhaust purifying catalyst by setting variably the updated one of a second air fuel ratio correction amount according to the control cycle of the second air fuel ratio correction amount. CONSTITUTION:For example, in the case when a first air fuel ratio correction amount is an air fuel ratio feed back correction coefficient which is set by proportional-integral control, a second air fuel ratio correction amount is an amount for correcting a proportional portion or an integral portion of the air fuel ratio feed back correction coefficient, and/or a delay time for delaying start of control in rich and lean direction of the air fuel ratio feed back correction coefficient, the updated amount in the delay time is set largely, provided that the output reversal cycle of a secondary air fuel ratio sensor 21 is long, and the updated amount is set small provided that the reversal cycle thereof is short. It is thus possible to avoid any change in control performance caused by secular change of an exhaust purifying catalyst, so as to prevent over-correction in progress of deterioration.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a device for controlling the air-fuel ratio of an internal combustion engine, and in particular, the present invention relates to an apparatus for controlling the air-fuel ratio of an internal combustion engine, and in particular, the present invention relates to an apparatus for controlling the air-fuel ratio of an internal combustion engine, and in particular, an air-fuel ratio sensor is provided on the upstream side and downstream side of an exhaust purification catalyst. The present invention relates to a device that performs feedback control of an air-fuel ratio with high accuracy based on a detected value of a fuel ratio sensor.

<Prior Art> A conventional general air-fuel ratio control device for an internal combustion engine is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-240840.

To give an overview of this, it detects the intake air flow rate Q and rotational speed N of the engine and calculates the basic fuel supply amount TP (=K・Q/N; K is a constant) corresponding to the amount of air taken into the cylinder. Then, this basic fuel supply amount T, corrected based on engine temperature, etc., is used as an air-fuel ratio feed set by a signal from an air-fuel ratio sensor (oxygen sensor) that detects the air-fuel ratio of the air-fuel mixture by detecting the oxygen concentration in the exhaust gas. ] - Feedback correction is performed using the back correction coefficient (air-fuel ratio correction amount), correction based on battery voltage, etc. are also performed, and finally the fuel supply amount T1 is set.

Then, by outputting a drive pulse signal with a pulse width corresponding to the fuel supply amount T1 thus set to the fuel injection valve at a predetermined timing, a predetermined amount of fuel is injected and supplied to the engine.

The air-fuel ratio feedback correction based on the signal from the air-fuel ratio sensor is performed to control the air-fuel ratio to around the target air-fuel ratio (stoichiometric air-fuel ratio). This is installed in the exhaust system and oxidizes Co and HC (hydrocarbons) in the exhaust, as well as NO
This is because it is set to function effectively depending on the conversion efficiency (purification efficiency) of the exhaust purification catalyst (three-way catalyst) that reduces and purifies x or the exhaust state during combustion at the stoichiometric air-fuel ratio.

As mentioned above, the electromotive force (output voltage) generated by the air-fuel ratio sensor has a characteristic that it changes suddenly near the stoichiometric air-fuel ratio, and this output voltage V
. and the reference voltage (slice level) SL corresponding to the stoichiometric air-fuel ratio.
It is determined whether the air-fuel ratio of the air-fuel mixture is rich or lean with respect to the stoichiometric air-fuel ratio. For example, in the case of a lean (rich) air-fuel ratio, the feedback correction coefficient α multiplied by the basic fuel supply amount T is increased (decreased) by a large proportionality constant P at the first time when the basic fuel supply amount T is changed to lean (rich). , the air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio by increasing (decreasing) the fuel supply amount T1 by gradually increasing (decreasing) by a predetermined integral constant ■.

By the way, in the above-mentioned normal air-fuel ratio feedback control device, one air-fuel ratio sensor is used to improve responsiveness.
It is installed in the gathering part of the exhaust manifold as close as possible to the combustion chamber, but since the exhaust temperature in this part is high, the characteristics of the air-fuel ratio sensor are likely to change due to thermal effects and deterioration.
Because the exhaust gas from each cylinder is not sufficiently mixed, it is difficult to detect the average air-fuel ratio of all cylinders, and the air-fuel ratio detection accuracy is difficult.
This in turn worsened the accuracy of air-fuel ratio control.

In view of this, it has been proposed that an air-fuel ratio sensor is also provided on the downstream side of the exhaust purification catalyst, and the air-fuel ratio is feedback-controlled using the detected values of the two air-fuel ratio sensors (Japanese Patent Laid-Open No. 58-48756). (see official bulletin).

In other words, the air-fuel ratio sensor on the downstream side is far from the combustion chamber, so its response may be difficult, or because it is downstream of the exhaust purification catalyst, it is affected by the exhaust component balance (CO, HC, NOx, C).
○□, etc.), and since the amount of poisoning by toxic components in the exhaust is small, it is also less susceptible to changes in characteristics due to poisoning.Moreover, the mixture state of the exhaust is good, so it is possible to detect the average air-fuel ratio of the gold cylinder, etc. Highly accurate and stable detection performance can be obtained compared to the upstream air-fuel ratio sensor.

Therefore, it is possible to combine two air-fuel ratio feedback correction coefficients that are respectively set by calculations similar to those described above based on the detected values of the two air-fuel ratio sensors, or to combine the air-fuel ratio feedback correction coefficients that are set by the upstream air-fuel ratio sensor. Control constants (proportional and integral), comparison voltage and delay time of the output voltage of the upstream air-fuel ratio sensor (rich from output voltage reversal).

In this way, highly accurate air-fuel ratio feedback control is performed by compensating for variations in the output characteristics of the upstream air-fuel ratio sensor using the downstream air-fuel ratio sensor. There is.

<Problem to be solved by the invention> By the way, in the air-fuel ratio control device that corrects the air-fuel ratio also based on the output of the air-fuel ratio sensor downstream of the exhaust purification catalyst, the signal inversion period of the upstream air-fuel ratio sensor The average value of the air-fuel ratio feedback correction coefficient α, which fluctuates in synchronization with the air-fuel ratio sensor, is fluctuated in a large period synchronized with the signal reversal period of the air-fuel ratio sensor on the downstream side. Here, the reason why the reversal period of the air-fuel ratio sensor on the downstream side is large is because the amount of 0 that can be adsorbed and stored in the exhaust purification catalyst (hereinafter referred to as 02 storage capacity of the exhaust purification catalyst) is large. The air-fuel ratio sensor on the downstream side continues to detect the lean state until the Co and HC in the combustion exhaust gas stored in the exhaust purification catalyst during lean combustion are completely reduced in 0 minutes.

Therefore, if the update amount of the second air-fuel ratio correction amount calculated based on the output of the downstream air-fuel ratio sensor is set to a constant value as is common in the past, then The output reversal period is 02 of the exhaust purification catalyst.
Determined with storage capacity as the dominant factor.

However, since the 02 storage capacity of the exhaust purification catalyst decreases due to deterioration of the catalyst, the reversal period of the output of the downstream air-fuel ratio sensor, that is, the control period of the second air-fuel ratio correction amount period) becomes shorter as the catalyst deteriorates. In that case, if the update amount of the second air-fuel ratio correction amount per time is set small, the second air-fuel ratio correction amount when the catalyst is new
If the control cycle of the air-fuel ratio correction amount becomes too long, the response will deteriorate, and conversely, if the update amount is set too large, the air-fuel ratio will be over-corrected when the catalyst deteriorates, worsening driveability and exhaust purification performance. .

Therefore, even if the update amount is set depending on whether the catalyst is new or deteriorated, the second air-fuel ratio correction amount, specifically the control constant of the air-fuel ratio feedback correction coefficient (for example, It was inevitable that the effect would change depending on the proportion (proportional portion) and rich/lean control delay time.

The present invention has been made in view of such conventional problems, and has a configuration in which the update amount of the second air-fuel ratio correction amount is variably set according to the control cycle of the second air-fuel ratio correction amount. Accordingly, it is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that can avoid changes in control performance due to deterioration of an exhaust purification catalyst.

<Means for Solving the Problems> For this reason, the present invention provides a concentration ratio of a specific gas component in exhaust gas that is provided upstream and downstream of an exhaust purification catalyst provided in an exhaust passage of an engine, and that changes depending on the air-fuel ratio. first and second air-fuel ratio sensors whose output values change in response to; and a first air-fuel ratio correction amount that calculates a first air-fuel ratio correction amount according to the output value of the first air-fuel ratio sensor. calculation means; second air-fuel ratio correction amount calculation means for calculating a second air-fuel ratio correction amount based on the output of the second air-fuel ratio sensor; an air-fuel ratio correction amount calculation means for calculating a final air-fuel ratio correction amount based on the air-fuel ratio correction amount; a second air-fuel ratio sensor output reversal period measuring means for measuring the period at which the output value is reversed; and an update amount per time of the second air-fuel ratio correction amount updated by the second air-fuel ratio correction amount calculating means. and a second air-fuel ratio correction amount update amount setting means that sets the update amount according to the reversal period of the calculated output value of the second air-fuel ratio sensor.

Further, for example, the first air-fuel ratio correction amount is an air-fuel ratio feedback correction coefficient set by proportional-integral planning, and the second air-fuel ratio correction amount is a proportional or integral amount of the air-fuel ratio feedback correction coefficient. It may also be an amount that corrects the amount.

Further, for example, the first air-fuel ratio correction amount is an air-fuel ratio feedback correction coefficient set by proportional-integral control, and the second air-fuel ratio correction amount is a rich or lean direction of the air-fuel ratio feedback correction coefficient. It may also be a delay time that delays the start of control.

<Operation> The first air-fuel ratio correction amount calculation means calculates the first air-fuel ratio correction amount based on the detected value from the first air-fuel ratio sensor,
The second air-fuel ratio correction amount calculation means calculates a second air-fuel ratio correction amount based on the detected value from the second air-fuel ratio sensor.

On the other hand, the second air-fuel ratio sensor output reversal period measuring means measures the period at which the output of the second air-fuel ratio sensor is reversed.

Then, the second air-fuel ratio correction amount update amount calculation means sets the update amount of the second air-fuel ratio correction amount based on the measured period.

For example, the first air-fuel ratio correction amount is an air-fuel ratio feedback correction coefficient set by proportional-integral control, and the second air-fuel ratio correction amount corrects the proportional or integral part of the air-fuel ratio feedback correction coefficient. If the output reversal period of the second air-fuel ratio sensor is long, the update amount is set to be large, and when the reversal period is short, the update amount is set to be small.

Similarly, the first air-fuel ratio correction amount is the air-fuel ratio feedback correction coefficient set by proportional-integral control, and the second air-fuel ratio correction amount is the start of control in the rich or lean direction of the air-fuel ratio feedback correction coefficient. If the delay time is such that the output reversal period of the second air-fuel ratio sensor is long, the update amount of the delay time is set to be large, and when the reversal period is short, the update amount is set to be small.

<Example> Embodiments of the present invention will be described below based on the drawings.

In FIG. 2 showing the configuration of one embodiment, an air flow meter 13 for detecting an intake air flow rate Q and a throttle valve 14 for controlling the intake air flow rate Q in conjunction with an accelerator pedal are provided in an intake passage 12 of an engine 11. An electromagnetic fuel injection valve 15 serving as a fuel supply means is provided for each cylinder in the downstream manifold portion.

The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 having a built-in microcomputer, and injects fuel that is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator. Further, a water temperature sensor 17 is provided to detect the temperature Tw of cooling water in the cooling jacket of the engine 11.

On the other hand, the exhaust passage 18 is provided with a first air-fuel ratio sensor 19 that detects the air-fuel ratio of the intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas at the manifold gathering part, and the exhaust gas A three-way catalyst 20 is provided as an exhaust purification catalyst that performs purification by oxidizing CO and HC and reducing NOx, and further has the same function as the first air-fuel ratio sensor 19 on the downstream side of the three-way catalyst 20. A second air-fuel ratio sensor 2I is provided.

Further, the distributor (not shown in FIG. 2) has a built-in crank angle sensor 22, and a crank angle signal outputted from the crank angle sensor 22 in synchronization with the engine rotation is counted for a certain period of time, or The engine rotation speed N is detected by measuring the period of the crank reference angle signal.

Next, the air-fuel ratio control routine by the control unit 16 will be explained according to the flowcharts of FIGS. 3 and 4. FIG. 3 shows a fuel injection amount setting routine, and this routine is performed at predetermined intervals (for example, every 10 m5).

In step (denoted as S in the figure) l, the intake air amount per unit rotation is determined based on the intake air flow rate Q detected by the air flow meter 13 and the engine rotation speed N calculated based on the signal from the crank angle sensor 24. The basic fuel injection amount T, which corresponds to T, is calculated using the following equation.

T,=KxQ/N (K is a constant) In step 2, various correction coefficients C0FF are set based on the cooling water temperature Tw etc. detected by the water temperature sensor 17.

In step 3, an air-fuel ratio feedback correction coefficient ALPP set by a feedback correction coefficient setting routine to be described later is read.

In step 4, a voltage correction numerator is set based on the battery voltage value. This is to correct changes in the injection flow rate of the fuel injection valve 15 due to battery voltage fluctuations.

In step 5, the final fuel injection amount (fuel supply amount) T
1 is calculated according to the following formula.

T,=Tp xCOEFxALPP+TIlStep 6
Now, the calculated fuel injection valve T1 is set in the output register.

As a result, at a predetermined fuel injection timing synchronized with the engine rotation, a drive pulse signal having a pulse width of the calculated fuel injection amount TI is applied to the fuel injection valve 15 to perform fuel injection.

Next, the air-fuel ratio feedback correction coefficient setting routine will be explained with reference to FIG. This routine is executed in synchronization with engine rotation.

In step II, it is determined whether the operating conditions are such that feedback control of the air-fuel ratio is performed. If the operating conditions are not satisfied, this routine is terminated. In this case, the air-fuel ratio feedback correction coefficient ALPP is clamped to the value at the end of the previous feedback control or a constant reference value, and the feedback control is stopped.

In step I2, the signal voltage V from the first air-fuel ratio sensor 19 is determined. 2 and the signal voltage v' from the second air-fuel ratio sensor 21. Enter 2.

In step 13, the signal voltage V'02 from the second air-fuel ratio sensor 21 is compared with a reference value SL corresponding to the target air-fuel ratio (theoretical air-fuel ratio).

Then, when the air-fuel ratio is determined to be rich (V'.2>SL), the process proceeds to step 14, where the previous proportional correction amount PH03-+ (or divided by the engine speed N, basic fuel injection amount T1, etc.) is determined. The proportional correction amount is stored as it is or by learning weighted average etc. for each driving region, and the set value DPH is calculated from the value obtained by searching from the corresponding driving region.
After the value obtained by subtracting O3 is updated and set as a new proportional correction amount PH03, the process proceeds to step 16.

Further, when the air-fuel ratio is determined to be lean (V'02<SL), the process proceeds to step 15, and the value obtained by adding the set value DPHO3 to the proportional correction amount PH03-, obtained in the same manner, is set as the new proportional correction amount. After setting the update as P HO3,
Proceed to step 16.

In step 16, the input signal voltage V of the first air-fuel ratio sensor 19 is determined. , and a reference value SL corresponding to the target air-fuel ratio (stoichiometric air-fuel ratio).

Then, when it is determined that the air-fuel ratio is rich (VO2>SL), the process proceeds to step 17, and it is determined whether or not the air-fuel ratio is being reversed from 1/2 to rich.

When it is determined that the inversion is occurring, the process proceeds to step 18, where the proportional amount P in the decreasing direction given at the time of rich inversion for setting the air-fuel ratio feedback correction coefficient ALPP is set to a value obtained by subtracting the proportional correction amount PHO3 from the reference value P1°. Update with.

Next, in step 19, the air-fuel ratio feedback correction coefficient ALPP is updated with a value obtained by subtracting the proportional amount PR from the current value.

If it is determined in step 17 that it is not the time of reversal from lean to rich, the process proceeds to step 20, and the air-fuel ratio feedback correction coefficient ALPP is calculated by the integral I from the current value.
, is updated with the subtracted value.

On the other hand, in step 16, the air-fuel ratio is lean (VO2<SL)
When it is determined that this is the case, the process proceeds to step 21, and it is determined whether or not the air-fuel ratio is being reversed from rich to lean.

When it is determined that it is the time of reversal, the process proceeds to step 22, and the proportional amount PL in the increasing direction given at the time of reversal is updated with the value obtained by adding the proportional amount correction amount PH03 to the reference value PL0. do. Then,
In step 23, the air-fuel ratio feedback correction coefficient ALPP is
is updated with a value obtained by adding the proportional amount PL from the current value.

Further, when it is determined in step 21 that it is not the time of reversal from rich to lean, the process proceeds to step 24, and the air-fuel ratio feedback correction coefficient ALPP is changed to the current value by the integral IL.
Update with the added value.

Next, in step 25, it is determined whether the output of the second air-fuel ratio sensor 21 has just changed from rich to lean or from lean to rich.

If it is determined that it is immediately after the reversal, the process proceeds to step 26, and the elapsed time from the previous reversal to the present time, that is, the second
The reversal period of the output of the air-fuel ratio sensor 21 is read from the count value C of the timer.

Next, the process proceeds to step 27, where the update amount DPIO3 of the proportional correction amount PH03 corresponding to the count value C is read from the map table stored in the ROM. Here, the update amount DPHO3 is set to a smaller value as the count value C (cycle) is larger as shown in the figure.

In step 28, the count value C is cleared.

As a result, the count value C read at the next time of reversal of the second air-fuel ratio output represents the period until the next time of reversal.

In this way, when the three-way catalyst 20 is new, the 02 storage capacity is large, and the output reversal period of the second air-fuel ratio sensor 21 is large, the update amount DPIO3 of the proportional correction amount PHO3 is set to be large. By doing so, good control responsiveness can be ensured. Further, as the three-way catalyst 20 deteriorates and the output reversal period is shortened due to a decrease in the 02 storage capacity, the update amount DPHOS is made smaller, thereby making it possible to prevent over-correction by the proportional correction amount PHO8.

In addition, in this embodiment, the second air-fuel ratio correction amount is a proportional correction amount PHO3 that corrects the proportional portion P of the air-fuel ratio feedback correction coefficient ALPP. The same method can be used for correcting.

Here, steps 16 to 24 are replaced by step 18. The function of calculating the air-fuel ratio feedback correction coefficient ALPP excluding the correction in step 22 is similar to the first air-fuel ratio correction amount calculating means of the first air-fuel ratio sensor]9, and the part of steps 13 to 15 is 2, steps 16 to 24 including step 18 and step 22 correspond to the air-fuel ratio correction amount calculation means, and steps 25, 26, and 28 and the function of the counter correspond to the air-fuel ratio correction amount calculation means. This corresponds to the second air-fuel ratio sensor output reversal period measuring means, and the part of step 27 corresponds to the second air-fuel ratio correction amount update amount setting means. FIG. 5 shows a control routine of an embodiment that corrects the delay time from when the output of the first air-fuel ratio sensor 19 is reversed to when the control direction of the air-fuel ratio feedback correction coefficient ALPP is reversed as the second air-fuel ratio correction amount. It is something that FIG. 6 shows changes in the state of each part in the method of this embodiment.

Steps 31 to 33 are steps 11 in FIG.
- Same as step 13.

When the air-fuel ratio is determined to be rich in step 33, the process proceeds to step 34, where the output of the first air-fuel ratio sensor 19 is reversed from lean to rich until the air-fuel ratio feedback correction coefficient ALPP is controlled in the lean direction. delay time (
(hereinafter referred to as rich delay time) TDR is updated with a value obtained by adding a set amount DTD.

Further, when the air-fuel ratio is determined to be lean in step 33, the process proceeds to step 35, and after the output of the first air-fuel ratio sensor I9 is reversed from rich to lean, the air-fuel ratio feedback correction coefficient ALPP is controlled in the rich direction. The delay time until TDL (hereinafter referred to as lean delay time) is the set amount D
Update with the value obtained by subtracting TD.

In step 36, it is determined whether the output of the first air-fuel ratio sensor 19 is rich or lean, and if it is determined to be rich, the process proceeds to step 37, where the delay counter CDLY is decremented. Next, in step 38, the delay counter CDLYO value is compared with the rich delay time TDR, and if CDLY<TDR, then in step 39, the CDLYO value is compared with the rich delay time TDR.
= After holding at TDR, proceed to step 43.

On the other hand, when it is determined in step 36 that the lean state is reached, the process proceeds to step 40, where the delay counter CDLY is incremented, and in step 41, the value of the delay counter CDLY is compared with the lean delay time TDL, and CDLY>T
If it is DL, step 42 holds CDLY=TDL, and then the process advances to step 43.

In step 43, it is determined whether the sign of the value of the delay counter CDLY has been inverted.

When it is determined that it is the time of reversal, the process proceeds to step 44, where it is determined whether the delay counter CDLY is positive or negative, that is, whether the simulated air-fuel ratio is rich or lean, and when it is positive, step 45
Step 46 updates the air-fuel ratio feedback correction coefficient ALPP with the value obtained by subtracting the proportional portion P from the current value, and when it is negative, proceeds to step 46 and updates the air-fuel ratio feedback correction coefficient ALPP with the current value and the proportional portion PL. Update with the added value.

Further, when it is determined in step 43 that there is no inversion, the process proceeds to step 47 to determine whether the delay counter CDLY is positive or negative in the same manner as in step 44, and when it is positive, the process proceeds to step 48 to calculate the air-fuel ratio feedback correction coefficient ALPP.
is updated with a value obtained by subtracting the integral part (1) from the current value, and when it is negative, the process proceeds to step 49, where the air-fuel ratio feedback correction coefficient ALPP is updated with a value obtained by adding the integral part IL to the current value.

Next, in step 50, it is determined whether or not the output of the second air-fuel ratio sensor 21 has just been reversed. If it is determined that the output has just been reversed, the process proceeds to step 51, where a timer is set to determine the reversal period of the second air-fuel ratio sensor output. After reading the count value (:), the process proceeds to step 52, where the update amount DT of the rich delay time TDR and lean delay time TDL according to the count value C is
D is read from the map table stored in the ROM.

Here, the update amount DTD is the count value C as shown in the figure.
The larger the (period) is, the smaller the value is set.

In step 53, the count value C is cleared.

Here, the portion from step 36 to step 49 excluding step 37 to step 44 and step 47 corresponds to the first air-fuel ratio correction amount calculation means, and the portion from step 33 to step 35 corresponds to the second air-fuel ratio correction amount calculation means. Corresponds to correction amount calculation means, all of steps 36 to 49 corresponds to air-fuel ratio correction amount calculation means, steps 5051 and 53 and the counter function correspond to second air-fuel ratio sensor output reversal period measurement means, The part of step 52 corresponds to the second air-fuel ratio correction amount update amount setting means.

In this embodiment as well, control responsiveness when the exhaust catalyst is new is ensured as in the first embodiment by setting the delay time update amount DPHOS to be larger when the reversal period of the second air-fuel ratio sensor output is long. It is possible to achieve both this and prevention of over-correction at the time of deterioration.

<Effects of the Invention> As explained above, according to the present invention, 1 of the second air-fuel ratio correction amount for correcting the proportional component or integral component of the air-fuel ratio feedback correction coefficient, or the delay time of starting rich or lean control, etc.
By configuring the opening update amount to be variably set according to the control cycle of the air-fuel ratio correction amount of the ring 2, changes in control performance due to changes in the exhaust purification catalyst over time can be avoided,
It is possible to prevent over-correction when deterioration progresses while ensuring control responsiveness when new.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, FIG. 3 is a flowchart showing the fuel injection amount setting routine of the same embodiment, and FIG. Similarly, a flowchart showing an air-fuel ratio feedback correction coefficient setting routine, FIG. 5 is a flowchart showing an air-fuel ratio feedback correction coefficient setting routine of another embodiment,
FIG. 6 is a diagram showing the state of each part of the same embodiment. 11... Internal combustion engine 12... Intake passage 15.
...Fuel injection valve 16...Control unit
19...First air-fuel ratio sensor 20...Three-way catalyst 21...Second air-fuel ratio sensor Patent applicant Japan Electronics Co., Ltd. Representative Patent attorney Fujio Sasashima Figure 3

Claims (3)

[Claims] (1) The first and second catalysts are provided upstream and downstream of the exhaust purification catalyst provided in the exhaust passage of the engine, and whose output value changes in response to the concentration ratio of a specific gas component in the exhaust gas, which changes depending on the air-fuel ratio. a second air-fuel ratio sensor; a first air-fuel ratio correction amount calculating means for calculating a first air-fuel ratio correction amount according to an output value of the first air-fuel ratio sensor; a second air-fuel ratio correction amount calculating means for calculating a second air-fuel ratio correction amount based on the output; and a final air-fuel ratio correction amount based on the first air-fuel ratio correction amount and the second air-fuel ratio correction amount. an air-fuel ratio correction amount calculating means for calculating an air-fuel ratio correction amount; A fuel ratio sensor output reversal period measuring means and an update amount of the second air-fuel ratio correction amount updated by the second air-fuel ratio correction amount calculation means are calculated by the calculated second air-fuel ratio sensor. An air-fuel ratio control device for an internal combustion engine, comprising: second air-fuel ratio correction amount update amount setting means that is set in accordance with a reversal period of an output value. (2) The first air-fuel ratio correction amount is an air-fuel ratio feedback correction coefficient set by proportional-integral control;
2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio correction amount is an amount that corrects a proportional component or an integral component of the air-fuel ratio feedback correction coefficient. (3) The first air-fuel ratio correction amount is an air-fuel ratio feedback correction coefficient set by proportional-integral control;
2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio correction amount is a delay time for delaying the start of control of the air-fuel ratio feedback correction coefficient in a rich or lean direction.