JPH0417749A - Air-fuel ratio control system of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the shift of air-fuel ratio due to correction so as to carry out air-fuel ratio control with accuracy by providing first and second air-fuel ratio sensors on the upper and lower sides of the emission purifying catalyst of an exhaust passage, respectively, and inhibiting calculation of the amount of correction of second air-fuel ratio until the degree of the progress of learning process exceeds a predetermined level. CONSTITUTION:From a learning correction value storage means which stores the learning correction value of the amount of correction of air-fuel ratio at each driving area, a renewing means for the learning correction value retrives the learning correction value of the driving area corresponding to the storage means. Next, a new learning correction value is set in order to cause the average value of the amounts of correction of air-fuel ratio to converge to a predetermined value according to the learning correcting value and the final amount of correction of air-fuel ratio, and also the learning correction value of the driving area corresponding to the learning correction value storage means is renewed by the learning correction value.

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 feed-han 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, the intake air flow rate Q and rotational speed N of the engine are detected and the basic fuel supply amount TP (-K・Q/N, is a constant) corresponding to the amount of air taken into the cylinder is calculated. Then, this basic fuel supply amount T, corrected by engine temperature, etc., is used as air-fuel ratio feedback, which is 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 a correction coefficient (air-fuel ratio correction), and correction based on battery voltage is also performed to finally set the fuel supply amount T1.

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 the conversion efficiency (purification efficiency) of the exhaust purification catalyst (three-way catalyst) that reduces and purifies x is set to function effectively in 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
0 and the reference voltage (slice level) SL equivalent 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, when the air-fuel ratio is lean (rich), the feedback correction coefficient α multiplied by the basic fuel supply amount T is increased (decreased) by a large proportionality constant P the first time the air-fuel ratio is changed to lean (rich). Thereafter, the air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio by gradually increasing (decreasing) the fuel supply amount T1 by a predetermined integral constant (■).

In addition, in such an air-fuel ratio control device, deviations from the target value of the air-fuel ratio in a non-feedback control region of the air-fuel ratio or deviations from the stoichiometric air-fuel ratio during transient operation when the operating region moves during feedback control are controlled. In order to suppress this, it is common practice to perform learning control by setting the learning correction value to 1 so that the average value of the air-fuel ratio feedback correction coefficient α approaches the reference value under predetermined steady-state operating conditions during air-fuel ratio feed pump/puncture control. I've been doing it.

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 insufficiently mixed, it is difficult to detect the average air-fuel ratio of the gold cylinder, and the air-fuel ratio detection accuracy is difficult.
As a result, the accuracy of air-fuel ratio control was poor.

In view of this, air-fuel ratio control is also performed on the downstream side of the exhaust purification catalyst.
A system has been proposed in which the air-fuel ratio is feedback-controlled using the detected values of two air-fuel ratio sensors (see Japanese Patent Laid-Open No. 58-48756).

In other words, the air-fuel ratio sensor on the downstream side has difficulty in responsiveness because it is located far from the combustion chamber, but since it is downstream of the exhaust purification catalyst, it can eliminate variations in characteristics due to variations in exhaust components (Co, HC, NOxCo2). Because the amount of poisoning caused by toxic components in the exhaust gas is small, the characteristics are less likely to change due to poisoning. Compared to fuel ratio sensors, highly accurate and stable detection performance can be obtained.

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 use an air-fuel ratio feedback correction coefficient that is set by an upstream air-fuel ratio sensor. Variations in the output characteristics of the upstream air-fuel ratio sensor can be corrected by correcting the coefficient control constant (proportional bone or integral), comparison voltage of the output voltage of the upstream air-fuel ratio sensor, and delay time. The air-fuel ratio feedback control is performed with high accuracy.

Moreover, in this device, the above-mentioned learning of the air-fuel ratio feedback correction coefficient is also performed in an air-fuel ratio control device equipped with two air-fuel ratio sensors, for example, in Japanese Patent Laid-Open No. 62
-60965 etc.

<Problem to be Solved by the Invention> However, in the device equipped with two air-fuel ratio sensors as described above, which learns the air-fuel ratio feed bank correction coefficient as the air-fuel ratio correction amount, while such learning is not progressing,
In other words, if the average value of the air-fuel ratio feed puncture correction coefficient does not converge to a predetermined value and the air-fuel ratio correction is performed by the downstream air-fuel ratio sensor while there is a large variation in learning between operating regions and there are steps, the correction amount is a value that is significantly different from that when learning has progressed sufficiently, and the correction during this period is not reliable.

In particular, the reversal period of the downstream air-fuel ratio sensor is much slower than that of the upstream air-fuel ratio sensor, so even after learning has progressed, the air-fuel ratio correction amount by the downstream air-fuel ratio sensor remains at the predetermined value. It did not converge, and the correction actually worsened the exhaust emission characteristics.

The present invention has been made in view of such conventional problems, and is an air-fuel ratio control device for an internal combustion engine that is equipped with air-fuel ratio sensors upstream and downstream of an exhaust purification catalyst. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that solves the above problems by performing correction.

Means for Solving the Problems> For this reason, as shown in FIG. calculating a first air-fuel ratio correction amount according to the output value of first and second air-fuel ratio sensors whose output value changes depending on the concentration ratio of the middle specific gas component; and the first air-fuel ratio sensor. a first air-fuel ratio correction amount calculation means; a second air-fuel ratio correction amount calculation means for calculating a second air-fuel ratio correction amount according to an output value of the second air-fuel ratio sensor; an air-fuel ratio correction amount calculating means that calculates a final air-fuel ratio correction amount based on the fuel ratio correction amount and the second air-fuel ratio correction amount; and a learning correction value that stores a learning correction value of the air-fuel ratio correction amount for each driving region. storage means; a new learning correction value so as to converge the average value of the air-fuel ratio correction amount to a predetermined value based on the learning correction value retrieved from the learning correction value storage means and the final air-fuel ratio correction amount; and learning correction value updating means for updating a learning correction value of a corresponding operating region in the learning correction value storage means with the learning correction value. learning progress determining means for determining the degree of progress of learning to bring the air-fuel ratio correction amount closer to a predetermined value by the value updating means; and a second air-fuel ratio correction amount calculating means until the learning progress reaches the predetermined value. and a second air-fuel ratio correction amount calculation prohibiting means for prohibiting calculation of the second air-fuel ratio correction amount.

<Operation> The first air-fuel ratio correction amount calculation means sets 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 sets a second air-fuel ratio correction amount based on the detected value from the second air-fuel ratio sensor after the learning progress reaches a predetermined level by the learning progress determining means. do.

The air-fuel ratio correction amount calculation means calculates the final air-fuel ratio correction amount based on the first air-fuel ratio correction amount and the second air-fuel ratio correction amount.

On the other hand, the learning correction value updating means searches the learning correction value of the corresponding operating region from the learning correction value storage means storing the learning correction value of the air-fuel ratio correction amount for each operating region, and combines the learning correction value with the final learning correction value. A new learning correction value is set so that the average value of the air-fuel ratio correction amount converges to a predetermined value based on the air-fuel ratio correction amount, and the learning correction value is used to set the corresponding learning correction value storage means. Update the learning correction value of the driving area.

However, until the degree of progress of learning determined by the learning determining means reaches a predetermined level or more, the second air-fuel ratio correction amount calculation inhibiting means prohibits the second air-fuel ratio by the second air-fuel ratio correction amount calculating means. Calculation of the correction amount is prohibited.

<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 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 passagework 8 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 in the manifold gathering part, and the exhaust gas in the exhaust pipe on the downstream side thereof. A three-way catalyst 20 is provided as an exhaust purification catalyst that performs oxidation of Co and HC and reduction of NOx. Two air-fuel ratio sensors 21 are 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 us).

In step (denoted as S in the figure) 1, 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 22. The basic fuel injection amount T, which corresponds to T, is calculated using the following equation. The function of step 1 corresponds to basic fuel supply amount setting means.

T,=KxQ/N (K is a constant) In step 2, various correction coefficients C0EF are set based on the cooling water temperature Tw etc. detected by the water temperature sensor 17.

In step 3, the air-fuel ratio feedback correction coefficient α set by the air-fuel ratio feedbank correction coefficient setting routine to be described later and the learning correction coefficient to be described later are set to 2 for the engine speed N and the basic fuel injection. Based on the amount T, the corresponding operating area of the RAM is searched and 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 IC fuel supply amount) T
+ is calculated according to the following formula. The function of step 5 corresponds to fuel supply amount setting means.

T+=TF

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 T1 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 10, 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 met, this routine ends. in this case,
The feedback correction coefficient α 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 1], the signal voltage ■ from the first air-fuel ratio sensor 19 is determined. 2 and the signal voltage V'02 from the second air-fuel ratio sensor 21 are input.

In step 12, the signal voltage ■ of the first air-fuel ratio sensor 19 input in step 10 is determined. 2 and a reference value SL equivalent to the target air-fuel ratio (stoichiometric air-fuel ratio).

Then, when V oz > S L, that is, when it is determined that the engine is rich, the process further advances to step 13, and it is determined whether or not it has just been inverted from lean to rich.

At the time of reversal, the process proceeds to step 14, where the current value α of the air-fuel ratio feedback correction coefficient α is determined. and the value α-1 at the time of the previous output reversal of the first air-fuel ratio sensor 19 (value before proportional bone Pt is applied)
Calculate the average value α.

In step 15, the average value α8 and the predetermined value α.

The absolute value of the deviation Δα from the positive reference value Δα. Compare with.

Here, the predetermined value α. is a value at which the air-fuel ratio feedback correction coefficient α converges when learning of the air-fuel ratio feedback correction coefficient α, which will be described later, has progressed sufficiently; in other words, the air-fuel ratio feedback correction coefficient α is set to this value α. The target air-fuel ratio (stoichiometric air-fuel ratio) is set to a value that can be obtained when the air-fuel ratio is clamped.

and 1Δα]≦Δα. When it is determined that the learning has progressed sufficiently, the process proceeds to step 16, where the signal voltage v'o2 from the second air-fuel ratio sensor 21 and the target air-fuel ratio (
Compare with the standard value SL corresponding to the stoichiometric air-fuel ratio.

When the air-fuel ratio is determined to be rich (V″oz>SL), the process proceeds to step 17, where a second air-fuel ratio correction amount P is determined to correct the proportional bone P given at the time of reversal for setting the air-fuel ratio feedback correction coefficient α. HOS to current value P) IO5
After updating the value by subtracting the predetermined amount ΔKo HOS from -, the process proceeds to step 18, and the second
After updating the air-fuel ratio correction amount PHOS with a decreased value, the process proceeds to step 21.

Further, when it is determined that the air-fuel ratio is lean (V".2<SL,), the process proceeds to step 19 and the second air-fuel ratio correction amount P is determined.
After updating HOS with a value obtained by adding a predetermined amount ΔKo HO5 to the current value PH05-, proceed to step 2o, and update with a value obtained by increasing the second air-fuel ratio correction amount P HOS to the reference value pto of the proportional bone P. Then proceed to step 21.

On the other hand, in step 15, 1Δα1>Δα. When it is determined that the learning of the air-fuel ratio feedback correction coefficient α has not progressed sufficiently, the second air-fuel ratio correction amount P H
The process proceeds to step 21 without correcting the proportional bones P and l by the OS.

In step 21, the air-fuel ratio feedbank correction coefficient α is updated to a value obtained by subtracting the proportional bone PR from the current value.

After setting the air-fuel ratio feedback correction coefficient α in this way, the process proceeds to step 22, and the learning correction coefficient of the air-fuel ratio feedback correction coefficient α is set and updated to 2 in the following manner. First, the learning correction coefficient (learning correction value of the air-fuel ratio correction amount) Kf of the corresponding operating region stored in the map of the RAM is searched from the engine speed N and the basic fuel injection amount T.
A new learning correction coefficient Kl is calculated by adding a predetermined proportion of the deviation Δα to the current learning correction coefficient Kf retrieved according to the following formula, and becomes the learning correction coefficient for the same area! Correct and rewrite the data. That is, the learning correction coefficient Kff
The RAM that stores i corresponds to learning correction value storage means, and the function of step 22 corresponds to learning correction value updating means.

K! ← to! -Δα/M (M is a constant, M>1) Also, when it is determined in step 13 that the condition is rich but not immediately after the inversion, the process proceeds to step 23, and the air-fuel ratio foot hack correction coefficient α is calculated by integrating I from the current value. Update with the deleted value.

Meanwhile, ■ in step 12. When it is determined that 2<SL,
That is, when it is determined that the lean state is determined, the process proceeds to step 24, and it is determined whether or not the lynch lean has just been reversed, and when it is reversed, the process proceeds to step 25, where the average value αi is calculated in the same manner as in step 14, and step 26 As in step 15, the absolute value of the deviation Δα is set to a positive reference value Δα. Compare with.

Similarly, jΔα; ≦Δα. When it is determined that the learning has progressed sufficiently, the process proceeds to step 27, and the second
The signal voltage voltage V° of the air-fuel ratio sensor 21. 2 and standard value S
When it is determined to be rich, the process proceeds to step 28 and updates the second air-fuel ratio correction amount PHOS with a value obtained by decrementing the predetermined amount ΔDPHO5, and then proceeds to step 29 to change the proportional bone P8 from the reference value PRO. Update the second air-fuel ratio correction amount P)105 with a decreased value, and when determining lean, proceed to step 30 and set the second air-fuel ratio correction amount PHOS to a predetermined amount 〇PH05
After updating with the added value, proceed to step 31 and calculate the proportional bone P.
After updating L to the reference value Pto by increasing the second air-fuel ratio correction amount PHOS, the process proceeds to step 32.

In step 32, the air-fuel ratio feedback correction coefficient α is updated to the current value, and the proportional bone P is updated with the increased value, and then the process proceeds to step 22 to update the learning correction coefficient! Update settings.

Further, when it is determined in step 24 that it is not immediately after reversal, the process proceeds to step 33, and the air-fuel ratio feed bank correction coefficient α
is updated to the current value by increasing the integral I.

With such a configuration, the air-fuel ratio feedback correction coefficient α
While learning has not progressed sufficiently, the correction calculation of the proportional bones PR and PL using the second air-fuel ratio correction amount PHOS is prohibited, which prevents air-fuel ratio deviations due to incorrect correction and maintains a good air-fuel ratio. Feedhack control can be maintained.

In this embodiment, while air-fuel ratio feedback control is based on the detected value of the first air-fuel ratio sensor 19, the proportionality of the air-fuel ratio feedback correction coefficient is corrected based on the detected value of the second air-fuel ratio sensor. Although we have shown an example that is applicable to those that use the air-fuel ratio sensor, the present invention is not limited to this. The present invention can also be applied to a system in which the reference value SL for rich/lean determination and the output delay time are corrected by detection by the second air-fuel ratio sensor while performing air-fuel ratio feedback control by the first air-fuel ratio sensor.

In addition, the second air-fuel ratio correction amount P HOS is also stored for each operating region divided by engine speed N, basic fuel injection amount T1, etc. (Since the reversal period is long, the air-fuel ratio feedback correction coefficient α is stored. A learning function may be provided to update the stored value as an initial value when the area (which is more roughly divided than the area) changes. Saramuko, 2nd
Instead of using the air-fuel ratio correction amount P HOS as it is, each time the second air-fuel ratio sensor is reversed, the average value of the correction amount P HOS at the time of the reversal and the correction amount P HOS at the previous time of reversal is calculated, and the average value is calculated. The learning correction value may be set by newly calculating a weighted average of the value and a weighted average value of past average values. In such a device that performs learning of the second air-fuel ratio correction amount, learning of the second air-fuel ratio correction amount naturally also stops until learning of the air-fuel ratio feedback correction coefficient α is not progressed.

In addition, P HO at step 17.19.28.30
The calculation of S corresponds to the second air-fuel ratio correction amount calculating means, which calculates the air-fuel ratio feedback correction coefficient α in steps 21, 23, 32, and 33 except for the proportional bone correction in steps 18, 20, and 29.31. The function corresponds to the first air-fuel ratio correction amount calculating means, and the comparison function in step 15.26 corresponds to the learning means determining means.

Furthermore, the method of determining the learning progress level is not limited to the method of this embodiment.
For example, a method may be adopted in which the determination is made based on the number of times of learning, the number of regions in which learning has been performed, or the like.

<Effects of the Invention> As explained above, according to the present invention, air-fuel ratio sensors are provided on the upstream and downstream sides of the exhaust purification catalyst, and air-fuel ratio feedback control is performed based on the detected values of these rain air-fuel ratio sensors. Since the calculation of the second air-fuel ratio correction amount is prohibited while the learning of the air-fuel ratio correction amount has not progressed sufficiently, it is possible to prevent deviations in the air-fuel ratio due to incorrect correction. By performing the correction using the fuel ratio correction amount, it is possible to execute air-fuel ratio control with as high precision as possible.

[Brief explanation of the drawing]

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. It is a flowchart similarly showing an air-fuel ratio feedbank correction coefficient setting routine. 11... Internal combustion engine 12... Intake passage 15 Fuel injection valve 16... Control unit 18.
...Exhaust passage medium 19...First air-fuel ratio sensor 20...Three-way contact 21...Second air-fuel ratio sensor

Claims (1)

[Claims] The catalyst is provided on the upstream and downstream sides of an exhaust purification catalyst provided in the exhaust passage of an engine, and its 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. first and second air-fuel ratio sensors; first air-fuel ratio correction amount calculation means for calculating a first air-fuel ratio correction amount according to the output value of the first air-fuel ratio sensor; a second air-fuel ratio correction amount calculation means for calculating a second air-fuel ratio correction amount according to the output value of the fuel ratio sensor; an air-fuel ratio correction amount calculation means for calculating an air-fuel ratio correction amount; a learning correction value storage means for storing a learning correction value of the air-fuel ratio correction amount for each driving region; and a learning correction value retrieved from the learning correction value storage means. and the final air-fuel ratio correction amount, a new learning correction value is set so that the average value of the air-fuel ratio correction amount converges to a predetermined value, and the learning correction value storage means uses the learning correction value. learning correction value updating means for updating a learning correction value of a corresponding operating region; and a second air-fuel ratio correction amount calculation means for prohibiting the second air-fuel ratio correction amount calculation means from calculating the second air-fuel ratio correction amount until the learning progress rate reaches a predetermined level or more. An air-fuel ratio control device for an internal combustion engine, comprising: means for inhibiting fuel ratio correction amount calculation.