JPH041439A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To always maintain good air-fuel ratio feedback control without any bad influence on air-fuel ratio compensation due to existence or absence of EGR by performing the air-fuel ratio feedback control using a learn compensation value independently learned according to existence or absence of the EGR. CONSTITUTION:Existence or absence of actuation in an exhaust recirculation device is judged by a means A. A learn compensation value learned during the operation time of the exhaust recirculation device is memorized by a means B per an operation range. The learn compensation value learned during the non-operation time is memorized by a means C per an operation range. During the operation time of the exhaust recirculation device, a new learn compensation value is set based on the learn compensation value retrieved by the means B and an output of a second air-fuel ratio sensor D, and also the learn compensation value of the means B is renewed by a means E by using this learn compensation value. During the non-operation time of the exhaust recirculation device, the new learn compensation value is set based on the learn value retriexed based on an operation condition from the means C, and a newly set second air-fuel ratio compensation quantity, and the learn compensation value of the means C is renewed the learn compensation value of this means F.

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 a device for controlling the air-fuel ratio of an internal combustion engine. In preparation for this, the present invention relates to a device that performs feedback control of the air-fuel ratio with high precision based on the detected values of these two air-fuel ratio sensors.

<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 basic fuel supply amount T corresponding to the empty device sucked into the cylinder by detecting the intake air flow rate Q and rotation speed N of the engine, (=K・Q/N; K
is a constant), and the air-fuel ratio sensor (oxygen sensor) detects the air-fuel ratio of the air-fuel mixture by detecting the oxygen concentration in the exhaust gas based on the basic fuel supply amount Ta corrected by engine temperature, etc.
Feed puncture correction is performed using an air-fuel ratio feedback correction coefficient (air-fuel ratio correction amount) set by a signal from the controller, and correction based on battery voltage is also performed to finally set the fuel supply amount T.

Then, by outputting a drive pulse signal with a pulse width corresponding to the fuel supply amount T 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, I (C (hydrocarbons)) in the exhaust gas, 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 the characteristic of rapidly changing near the stoichiometric air-fuel ratio, and this output voltage
. 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, when the air-fuel ratio is lean (rich), a large proportionality constant P is increased (decreased) the first time the feed eight correction coefficient α, which is multiplied by the basic fuel supply amount TA, is changed to lean (rich). Thereafter, the air-fuel ratio is controlled to be near the stoichiometric air-fuel ratio by gradually increasing (decreasing) the fuel supply amount T 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). 6) In other words, the air-fuel ratio sensor on the downstream side has difficulty in responsiveness because it is far from the combustion chamber, but since it is downstream of the exhaust purification catalyst, it is sensitive to the effects of the exhaust component balance (CO, HC9NOX, CO2, etc.). ) is difficult to receive;
Since the amount of poisoning caused by toxic components in the exhaust is small, it is less susceptible to changes in characteristics due to poisoning (in addition, since the exhaust is in a good mixing state, it can detect the average air-fuel ratio of all cylinders, etc., making it suitable for upstream air-fuel ratio sensors. In comparison, 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 feedbank 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 the downstream air-fuel ratio sensor by correcting the control constants (proportional and integral), the comparison voltage and delay time of the output voltage of the upstream air-fuel ratio sensor, etc. This compensation is performed to perform highly accurate air-fuel ratio feedback control.

However, in the air-fuel ratio control device using two air-fuel ratio sensors as described above, the required level for air-fuel ratio correction during feedback control may be significantly different from that during non-feedback control, and especially during non-feedback control. The following problem occurs at the start of feed bank control when transitioning to feedback control.

That is, in the above case, the feedback control speed by the downstream air-fuel ratio sensor is usually set smaller than the feedback control speed by the upstream air-fuel ratio sensor, so the feedback control speed by the downstream air-fuel ratio sensor is not used. air-fuel ratio correction amount (for example, the correction amount of the proportional portion of the air-fuel ratio feedback correction coefficient by the upstream air-fuel ratio sensor)
It takes time for the air-fuel ratio to reach the required value, and in turn, it takes time to reach the target air-fuel ratio, resulting in deterioration of fuel efficiency, drivability, exhaust emissions, etc.

Furthermore, even during air-fuel ratio feedback control, when the operating state of the engine changes to a different region, the air-fuel ratio may deviate significantly from the target air-fuel ratio, which also causes deterioration in fuel efficiency, drivability, and exhaust emissions. .

Therefore, by sequentially calculating the average value of the second air-fuel ratio correction amount as a learning correction value and storing it for each driving region, and correcting and setting the fuel supply amount using the learning correction value, A system that allows stable air-fuel ratio control at all times has been proposed (see Japanese Patent Laid-Open No. 63-97851, etc.).
.

<Problem to be solved by the invention> By the way, in a predetermined operating range where the amount of NOx generated by the engine increases, the exhaust catalyst alone cannot sufficiently reduce NOx, so a part of the exhaust gas is recirculated into the intake air. The so-called exhaust recirculation device (
An EGR system (W) is generally provided.

When exhaust gas recirculation (EGR) is in operation, the balance of components in the exhaust gas changes significantly compared to when EGR is not in operation, and therefore the required air-fuel ratio correction amount also differs from that during EGR.
It will be significantly different from the GR time. For this reason, if the learning correction value is set regardless of the presence or absence of EGR, the accuracy of the learning correction value may deteriorate, resulting in significant deterioration of fuel efficiency, drivability, exhaust emissions, etc. For example, as shown in FIG. 5, if the air-fuel ratio is controlled using the learning correction value learned during EGR operation, the air-fuel ratio will shift to the lean side and the amount of NOx generated will increase.

The present invention has been made in view of these conventional problems, and is an internal combustion engine that solves the above problems by improving learning accuracy by learning the air-fuel ratio correction amount independently depending on the presence or absence of EGR. The purpose of the present invention is to provide an air-fuel ratio control device.

<Means for Solving the Problems> Therefore, as shown in FIG. 1, the present invention includes an exhaust gas recirculation device that recirculates part of the exhaust gas into the intake air under predetermined operating conditions, and A basic fuel supply amount setting means for setting a basic fuel supply amount to the engine corresponding to a target air-fuel ratio; First, the output value changes due to the concentration ratio of specific gas components in the exhaust gas.
and a second air-fuel ratio sensor, a first air-fuel ratio correction amount calculation means for calculating a first air-fuel ratio correction amount according to an output value of the first air-fuel ratio sensor, and the second air-fuel ratio sensor. a second air-fuel ratio correction amount calculation means for calculating a second air-fuel ratio correction amount based on the output of the controller and the learning correction value learned and stored for each operating region; the calculated basic fuel supply amount; a fuel supply amount setting means for setting a fuel supply amount based on the first and second air-fuel ratio correction amounts; a fuel supply means for supplying an amount of fuel to the engine corresponding to the set fuel supply amount; An air-fuel ratio control device for an internal combustion engine, which includes: an EGR determination means for determining whether or not the exhaust gas recirculation device is in operation; and a learning correction value learned during operation of the exhaust gas recirculation device for each operating region. EGR learned correction value storage means for storing the learned correction value learned when the exhaust gas recirculation device is not in operation; A new learning correction value is set based on the learning correction value retrieved from the learning value storage means for EGR and the output of the second air-fuel ratio sensor, and the learning correction value is used to perform the corresponding operation of the learning value storage means for EGR. EGR learning correction value updating means for updating the learning correction value of the region, and a learning value retrieved based on the operating conditions from the non-EGR learning value storage means when the exhaust gas recirculation device is not in operation, and a newly set learning value. Non-EGR learning correction that sets a new learning correction value based on the air-fuel ratio correction amount of No. 2 and updates the learning correction value of the corresponding operating region in the non-EGR learning value storage means with the learning correction value. It is configured to include a value update means, and.

Function> The first air-fuel ratio correction amount setting means sets the first air-fuel ratio correction amount based on the detected value from the first air-fuel ratio sensor.

Further, when the exhaust gas recirculation device is activated as determined by the EGR determination means, the setting of the learning correction amount of the second air-fuel ratio correction lid is
This is set by the GR learning correction value updating means, and the learning correction value of the corresponding operating region in the EGR learning correction value storage means is updated.

On the other hand, when the exhaust gas recirculation device is not operating, the setting of the learning correction amount of the second air-fuel ratio correction amount is set by the non-EGR learning correction value updating means, and the learning correction value for non-EGR is set in the corresponding operating region of the non-EGR learning correction value storage means. The learning correction value of is updated.

The second air-fuel ratio correction amount setting means uses the EGR learning correction value updating means or the non-EGR learning correction value updating means in accordance with the detection value from the second air-fuel ratio sensor and whether the exhaust gas recirculation device is activated or not. The second learning correction value is based on the updated learning correction value.
Set the air-fuel ratio correction amount.

The fuel supply amount setting means sets the fuel supply amount based on the basic fuel supply amount set by the basic fuel supply amount setting means and the first and second air-fuel ratio correction amounts, and controls the set amount of fuel. A fuel supply means supplies the engine.

<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. In the downstream manifold portion, an N61 type fuel injection valve 15 as a fuel supply means is provided for each cylinder.

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 oxidation of Co and HC and reduction of NOx for purification, and furthermore, a second air-fuel ratio sensor having the same function as the first air-fuel ratio sensor is provided downstream of the three-way catalyst 20. An air-fuel ratio sensor 21 is provided.

Further, an EGR passage 22 is provided that connects the exhaust passage 18 and the intake passage 12, and an EGR control valve 23 is interposed in the EGR passage 22. During a predetermined operation in which the amount of NOx emissions increases, the opening degree of the EGR control valve 23 is controlled based on a control signal from the control unit 16.
EGR control is performed.

Furthermore, the distributor (not shown in FIG. 2) has a built-in crank angle sensor 24, and the crank angle signal outputted from the crank angle sensor 24 in synchronization with 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 every predetermined period (for example, 10 fflS).

In step 1 (denoted as S in the figure), the amount of intake air 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. The function of step 1 corresponds to basic fuel supply amount setting means.

TP = 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, a feed bank correction coefficient α 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
+ is calculated according to the following formula. The function of step 5 corresponds to fuel supply amount setting means.

T+ = TP XC0EFXα10T.

In step 6, 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 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 11, 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 12, the signal voltage ■ from the first air-fuel ratio sensor 19 is detected. 2 and the signal voltage "■" from the second air-fuel ratio sensor 21.2 is input.

In step 13, the signal voltage V input in step 11 is
02 and a reference value SL corresponding to the target air-fuel ratio (stoichiometric air-fuel ratio) to determine whether the air-fuel ratio is changing from lean to rich or from rich to lean.

When it is determined that the inversion is occurring, proceed to step 14 and start EGR.
Determine whether or not it is activated. That is, this step 1
The function No. 4 corresponds to the EGR determination means.

Then, when the EGR is activated, the process proceeds to step 15, where a proportional bone learning correction value PH05pi (described later) is set for each of a plurality of operating regions based on the engine rotational speed N and the basic fuel injection amount T2.
EGR map (RAM of the microcomputer in the control unit 16) that stores the learning correction value)
The learning correction value PH05ri stored in the corresponding operating region is searched from

In step 16, the signal voltage ".2" from the second air-fuel ratio sensor 21 and the reference value S corresponding to the target air-fuel ratio (theoretical air-fuel ratio)
Compare with L.

Then, when the air-fuel ratio is determined to be rich (V'0.>SL), the process proceeds to step 17, and the learning correction (1jj P HO5PE found in step 15) is
The value obtained by subtracting DPHO5 is the second air-fuel ratio correction amount P H
Set as O3 (=learning correction value).

Further, when the air-fuel ratio is determined to be lean (Vo., <SL), the process proceeds to step 18, and the learning correction value PH05P□ similarly searched in the stem 15 is set to a predetermined value ΔDP)IO.
The value obtained by adding 5 is the second air-fuel ratio correction amount (-learning correction value)
P) Set as 105.

Next, in step 19, the second air-fuel ratio correction amount P
The learning correction value PHO5□ of the operating region in which the EGR map was searched by the HOS is updated.

Further, when it is determined in step 14 that EGR is not operating, the process proceeds to step 20, and the learned correction value PH0SNE (learning correction value) stored in the corresponding operating region is retrieved from the non-EGR map in which the learning correction value PH0SNE (learning correction value) is stored. After searching for PH05NE, the process proceeds to step 21, and similarly to step 16, the air-fuel ratio detected by the second air-fuel ratio sensor 21 is determined to be rich or lean. Then, when it is determined that S.7,000 is determined, the process proceeds to step 22 and a predetermined value ΔDPHO5 is determined from the learning correction value PH0SNE.
After setting the value obtained by subtracting the value as the second air-fuel ratio correction amount P)IO3, the process proceeds to step 24, where the value of the non-EGR map is updated with the second air-fuel ratio correction amount PH05. Proceed to step 23 and set the learning correction value PH05Nf
After setting the value obtained by adding the predetermined value ΔH05 to f as the second air-fuel ratio correction amount P105, the process proceeds to step 24, where the value of the non-EGR map is determined using the second air-fuel ratio correction amount PHOS. Update.

Here, the RAM that stores the learning correction value PI (O5□, PH05NE) for when EGR is activated and for when EGR is not activated corresponds to the learning correction value storage means for EGR.
The functions of step 18 and steps 20 to 24 correspond to the second air-fuel ratio correction amount setting means. Further, in this embodiment, since the learning correction value is used as it is as the second air-fuel ratio correction amount, the functions from step 15 to step 19 are the EGR learning correction value updating means, and the functions from step 20 to step 24 are disabled. This corresponds to EGR learning correction value updating means.

It will be done.

Next, the process proceeds to step 25, where the first air-fuel ratio sensor 19 makes a rich/lean judgment, and when the lean-rich state is reversed, the process proceeds to step 26, where the decreasing direction given at the time of lean reversal is used to set the air-fuel ratio feedback correction coefficient α. The proportional bone PR is changed from the reference value PIIO to the second air-fuel ratio correction amount P.
Update HOS with reduced value. Then step 27
The air-fuel ratio feedback correction coefficient α is updated to a value obtained by subtracting the proportional bone P from the current value.

Also, when the rich-lean state is reversed, the process proceeds to step 28,
The proportional bone P in the increasing direction given at the time of lean inversion for setting the air-fuel ratio feedback correction coefficient α is updated with the value obtained by adding the second air-fuel ratio correction amount P HOS to the reference value PL0. Next, in step 29, the air-fuel ratio feedback correction coefficient α is updated with a value obtained by adding the proportional bone Pt to the current value.

Furthermore, when it is determined in step 13 that the output of the first air-fuel ratio sensor 19 is not in the inversion state, the process proceeds to step 30 to perform a rich/lean determination, and if the output is rich, step 3]
The process advances to step 32, where the air-fuel ratio feedback correction coefficient α is updated with a value obtained by subtracting the integral Ill from the current value, and when lean, the process proceeds to step 32, where it is updated with a value obtained by adding the integral It.

Here, steps 25 to 32 are replaced by step 26. The function of setting the air-fuel ratio feedback correction coefficient α except for the correction in step 28 corresponds to the first air-fuel ratio correction amount setting means by the first air-fuel ratio sensor 19, and the second
The routine shown in FIG. 3 that finally sets the fuel injection amount Tr using the air-fuel ratio feedback correction coefficient α set by performing correction by the air-fuel ratio correction amount P HOS corresponds to the fuel supply amount setting means. .

With this configuration, learning is performed independently using different maps (memory means) when EGR is activated and when it is not activated, and learning correction values are set. The optimum air-fuel ratio correction is performed using the learning correction value according to each condition, and good air-fuel ratio feedback control can be maintained at all times.

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 in which the air-fuel ratio feedback correction coefficient is set by each air-fuel ratio sensor and the air-fuel ratio feedback correction coefficient obtained by combining both values is used, the application is not limited to this. The present invention can also be used to perform air-fuel ratio feedback control using the first air-fuel ratio sensor while correcting the reference value SL for rich/lean determination or the output delay time using the detection by the second air-fuel ratio sensor.

In addition, as for the learning correction value, in this embodiment, a simple control method is shown in which the second air-fuel ratio correction amount is stored as a learning correction value. Based on the second air-fuel ratio correction amount P)10
While increasing or decreasing 5, each time the second air-fuel ratio sensor is reversed, the correction amount PRO8 at the time of the reversal and the correction amount PHO8 at the previous reversal.
It may be configured such that the learning correction value is set by calculating an average value with S, and then calculating a new weighted average of the average value and a weighted average value of past average values.

<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 air-fuel ratio feedback control is performed using the learning correction value that is learned independently depending on the presence or absence of EGR, the air-fuel ratio correction is not adversely affected by the presence or absence of EGR, and the air-fuel ratio feedback control is always good. can be maintained.

[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. Similarly, FIG. 5 is a flowchart showing the air-fuel ratio feedbank correction coefficient setting routine, and is a diagram comparing the conversion efficiency of CO and NOx between the conventional EGR operation and non-operation. 11... Internal combustion engine 12... Intake passage 15.
...Fuel injection valve 16...Control unit 1
8...Exhaust passage 19...First air-fuel ratio sensor
21...Three-way catalyst 22...Second air-fuel ratio sensor Patent applicant Japan Electronics Co., Ltd. Agent Patent attorney Fujio SasashimaFigure 2Figure 5Figure 3

Claims (1)

[Claims] An exhaust gas recirculation device is provided that recirculates part of the exhaust gas into intake air under predetermined operating conditions, and a basic fuel supply amount to the engine corresponding to a target air-fuel ratio is set based on the engine operating state. A basic fuel supply amount setting means is provided on the upstream and downstream sides of an exhaust purification catalyst provided in the exhaust passage of the engine, and the output value is set in response to the concentration ratio of a specific gas component in the exhaust gas that changes depending on the air-fuel ratio. The first thing that changes
and a second air-fuel ratio sensor, a first air-fuel ratio correction amount calculation means for calculating a first air-fuel ratio correction amount according to an output value of the first air-fuel ratio sensor, and the second air-fuel ratio sensor. a second air-fuel ratio correction amount calculation means for calculating a second air-fuel ratio correction amount based on the output of the controller and the learning correction value learned and stored for each operating region; the calculated basic fuel supply amount; a fuel supply amount setting means for setting a fuel supply amount based on the first and second air-fuel ratio correction amounts; a fuel supply means for supplying an amount of fuel to the engine corresponding to the set fuel supply amount; An air-fuel ratio control device for an internal combustion engine, which includes: an EGR determination means for determining whether or not the exhaust gas recirculation device is in operation; and a learning correction value learned during operation of the exhaust gas recirculation device for each operating region. EGR learned correction value storage means for storing the learned correction value learned when the exhaust gas recirculation device is not in operation; A new learning correction value is set based on the learning correction value retrieved from the learning value storage means for EGR and the output of the second air-fuel ratio sensor, and the learning correction value is used to perform the corresponding operation of the learning value storage means for EGR. EGR learning correction value updating means for updating the learning correction value of the region; and EGR learning correction value updating means for updating the learning correction value of the region; A new learning correction value is set based on the air-fuel ratio correction amount of No. 2, and the non-EGR
1. An air-fuel ratio control device for an internal combustion engine, comprising: non-EGR learning correction value updating means for updating a learning correction value of a corresponding operating region of a learning value storage means.