JPH0417750A - Air-fuel ratio control system of internal combustion engine - Google Patents

Abstract

PURPOSE:To enable control in which steps are eliminated as many as possible while maintaining the accuracy of learning by performing learning when shifting a driving area whose learning correction value is renewed, with the average value of the renewed value and retrieved value of a learning correction value before and after the shift as an initial value. CONSTITUTION:A learning correction value is normally renewed according to another learning correction value retrieved by a learning correction value renewing means from the corresponding driving area of a learning correction value storage means and an output value from a second air-fuel ratio sensor. If in this case the driving area of the previous renewal is different from that of the retrieved learning correction value, learning correction is renewed while the average value of a learning correction value retrieved by the learning correction value initial setting means and the learning correction value of the initial renewal is used as an initial value. Fluctuation of air-fuel ratio can thus be restrained by reducing the number of steps between driving areas while maintaining the accuracy of learning.

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 high-precision feed control of an air-fuel ratio 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 (L=K・Q/N; K is a constant) corresponding to the amount of air taken into the cylinder is calculated. This basic fuel supply amount T is calculated and corrected based on engine temperature, etc., and then the air-fuel ratio 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 coefficient (air-fuel ratio correction amount) is used to perform fuel charge correction, 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 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 NOx.
This is because the conversion efficiency (purification efficiency) of the exhaust purification catalyst (three-way catalyst) that reduces and purifies the exhaust gas is set so that it functions 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), 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). By gradually increasing (decreasing $i) the fuel supply amount T1 by a predetermined integral constant I, the air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio.

By the way, in the above-mentioned normal air-fuel ratio feed hack control device, in order to improve the responsiveness of one air-fuel ratio sensor,
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 has difficulty in responsiveness because it is far from the combustion chamber, but since it is downstream of the exhaust purification catalyst, it is affected by the exhaust component balance (COHC, NOX, Co
t, etc.), and because the amount of poisoning by toxic components in the exhaust is small, it is also less susceptible to changes in characteristics due to poisoning (in addition, because the exhaust is in a good mixing state, the average air-fuel ratio of all cylinders can be detected. Highly accurate and stable detection performance can be obtained compared to air-fuel ratio sensors located on the same upstream side.

Therefore, it is possible to combine two air-fuel ratio feedbank correction coefficients that are respectively set by calculations similar to those described above based on the detection values of 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 the downstream air-fuel ratio sensor by correcting the control constants (proportional and integral), 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-feedbank control, especially in non-feedhack control. The following problem occurs at the start of feedback control when transitioning from time 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 proportional correction amount 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 range, the air-fuel ratio may deviate significantly from the target air-fuel ratio, which also causes deterioration of 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 Application Laid-Open No. 63-97851, etc.).
.

<Problems to be Solved by the Invention> However, since the second air-fuel ratio correction amount corrects the deviation of the first air-fuel ratio correction amount over a long period of time, the control period is longer than the first air-fuel ratio correction amount. It is very long compared to the control cycle, and therefore the operating range in which the learning correction value is stored cannot be made finer. That is, if the operating ranges are made smaller, the time spent in each range becomes shorter and learning does not progress, and the required value of the learning correction value differs depending on the presence or absence of EGR, intake air flow rate, and exhaust temperature conditions.

In this way, if the operating range is large, there will be a large step difference between the regions, but since the required value of the learning correction value does not have a large step difference before and after switching between regions, a step difference will occur in the air-fuel ratio.
This sometimes resulted in deterioration of exhaust emission performance.

The present invention has been made in view of these conventional problems.The present invention solves the above-mentioned problems by eliminating as much as possible the difference in learning correction values while maintaining learning accuracy before and after switching the driving range in which learning correction values are stored. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that solves the problem.

<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 values change in response to 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 based on the output of the second air-fuel ratio sensor and the learning correction value; learning correction value storage means for storing a learning correction value of a second air-fuel ratio correction amount for each driving region; and learning correction value storage means for storing a learning correction value of a second air-fuel ratio correction amount; learning correction value updating means for setting a learning correction value and updating the learning correction value of the corresponding operating region in the learning value storage means with the learning correction value; the first air-fuel ratio correction amount; 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; If the state does not belong to the operating region in which the learning correction value was updated last time, calculate the average value of the learning correction value at the time of the previous update and the learning correction value searched this time,
Learning correction value initial setting means for updating the learning correction value using the average value as the initial value of the learning correction value.

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, normally, the learning correction value is updated by the learning correction value updating means based on the learning correction value retrieved from the corresponding operating region in the learning correction value storage means and the output value from the second air-fuel ratio sensor. At that time, if the operating area at the time of the previous update and the operating area of the searched learning correction value are different, the learning correction value searched by the learning correction value initial setting means and the learning at the time of the previous update are different. The learning correction value is updated by using the average value of the learning correction value as the initial value of the learning correction value.

Thereby, while maintaining learning accuracy, it is possible to reduce the difference in level between operating regions and suppress fluctuations in the air-fuel ratio.

<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 at 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 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, 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 every predetermined period (for example, 10 is).

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.

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, 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
1 is calculated according to the following formula. The function of step 5 corresponds to fuel supply amount setting means.

T+=TpXCOEFXα+T.

In step 6, the calculated fuel injection valve T 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 of the calculated fuel injection amount T1 is applied to the fuel injection valve 15, and fuel injection is performed.

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 VOR from the first air-fuel ratio sensor 19 and the signal voltage V' from the second air-fuel ratio sensor 21 are determined. Enter 2.

In step 13, the signal voltage V input in step 11 is
OZ is compared with a reference value SL corresponding to the target air-fuel ratio (stoichiometric air-fuel ratio), and it is determined whether the air-fuel ratio is inverted from lean to rich or from rich to lean.

When it is determined that it is the time of reversal, the process proceeds to step 14, where a map (control unit The learning correction value PH03t stored in the corresponding operating region is retrieved from the memory stored in the RAM of the built-in microcomputer in the sixth step. The map is divided into two parts depending on the engine rotational speed N and the basic fuel injection IiT P into a total of four operating ranges, and the RAM in which this map is written corresponds to the learning correction value storage means.

In step 15, it is determined whether the current driving state (the driving state at the time of the learning correction value search) belongs to the driving region of the map at the time of the previous learning correction value P)10SL update.

If it is determined that it belongs, the process directly proceeds to step 17, but if it is determined that it does not belong, the process proceeds to step 16, and the operation area that is different from the previous learning correction value PH05LO searched in step 14 is The average value with the updated learning correction value PH05L-1 is the learning correction value P
After setting as the initial value of H0SL, the process advances to step 17. In other words, the functions of step 15 and step A correspond to learning correction value initial setting means.

In step 17, the signal voltage v' 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).

When the air-fuel ratio is determined to be rich (V'oz>SL), the process proceeds to step 18, and the learning correction value PH0 searched in step 14 or initialized in step 16 is
The value obtained by subtracting the predetermined value HO5 from SL is set as the second air-fuel ratio correction amount PHOS.

Furthermore, when the air-fuel ratio is determined to be lean (■".2<SL), the process proceeds to step 19, and the value obtained by adding the predetermined value DPHO5 to the similarly searched or initialized learning correction value PH0SL is added to the second air-fuel ratio. Set as fuel ratio correction amount PHOS.

That is, the functions of steps 14, 17, 18, and 19 correspond to the second learning correction value calculation means.

Next, in step 20, the learning correction value PH0SL of the corresponding operating region of the map is set as the second air-fuel ratio correction amount P).
Rewrite and update using IOS.

In this way, in this embodiment, the second air-fuel ratio correction amount is stored and updated as a learned correction value, so step 14.1
The functions of 7.18.19.20 correspond to learning correction value updating means.

Next, the process proceeds to step 21, 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 22, where the decreasing direction given at the time of rich reversal is used to set the air-fuel ratio feedback correction coefficient α. The proportional bones P, l are calculated from the reference value Pro by the second air-fuel ratio correction amount P.
Update HOS with reduced value. Then step 23
Then, the air-fuel ratio feed bank 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 24,
The proportional bone PL in the increasing direction given at the time of lean inversion for setting the air-fuel ratio feed bank correction coefficient α is updated with the value obtained by adding the second air-fuel ratio correction amount P HOS to the reference value PLO. Next, in step 25, the air-fuel ratio fee lower hack correction coefficient α is updated with a value obtained by adding the proportional bone PL to the current value.

Further, 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 26 to perform a lynch/lean determination, and if the output is rich, step 27
The process proceeds to step 28, where the air-fuel ratio feedback correction coefficient α is updated with a value obtained by subtracting the integral 3 from the current value, and when the process is lean, the process proceeds to step 28, where the air-fuel ratio feedback correction coefficient α is updated with a value obtained by adding the integral It.

Here, steps 21 to 28 are replaced by step 22. The function of setting the air-fuel ratio feedback correction coefficient α, excluding the correction in step 24, corresponds to the first air-fuel ratio correction amount setting means by the first air-fuel ratio sensor 19, and step 22. Steps 21 to 28 including step 24 correspond to air-fuel ratio correction amount setting means.

With such a configuration, the difference in the learning correction value PH03 when the operating range in which the learning correction value PH05L is updated is changed to half that of the conventional one, and air-fuel ratio correction is performed that balances learning accuracy and reduction in difference. , the exhaust emission performance can be improved. FIG. 5 shows changes in the learning correction value PH05L when the operating state shifts from region A to region B, where the dotted line shows the conventional example and the solid line shows the state of the present invention.

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 applied to a system in which the air-fuel ratio feedback control is performed 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.

Furthermore, 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. , the second air-fuel ratio correction amount P HO based on lean
While increasing or decreasing S, each time the second air-fuel ratio sensor is reversed, the correction amount PH08 at the time of the reversal and the correction amount PHO at the previous reversal are calculated.
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. When the operating region where the learning correction value is updated changes, the learning is performed using the average value of the updated learning correction value before and after the change and the search value as the initial value, so the accuracy of learning can be maintained. , it is possible to perform air-fuel ratio feed-hack control with as little difference as possible, and it is possible to improve exhaust emission performance, etc.

[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, the fifth flowchart is a flowchart showing the air-fuel ratio foot correction coefficient setting routine. 11... Internal combustion engine 12... Intake passage 15.
...Fuel injection valve 16...Control unit 1
9... First air-fuel ratio sensor 20... Three-way catalyst
21...Second Air-Fuel Ratio Sensor Patent Applicant Japan Electronics Co., Ltd. Agent Patent Attorney Fujio SasashimaFigure 1Figure 5Figure 2

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 based on the output of the fuel ratio sensor and the learning correction value; learning correction value storage means to store the learning correction value retrieved from the learning correction value storage means and a second learning correction value;
learning correction value updating means for setting a new learning correction value based on the output of the air-fuel ratio sensor, and updating the learning correction value of the corresponding operating region in the learning value storage means with the learning correction value; an air-fuel ratio correction amount calculation means for calculating a final air-fuel ratio correction amount based on the first air-fuel ratio correction amount and the second air-fuel ratio correction amount; In the control device, if the operating state at the time of the learning correction value search does not belong to the operating region in which the learning correction value was updated last time, the average value of the learning correction value at the previous update and the learning correction value searched this time is used. calculate,
An air-fuel ratio control device for an internal combustion engine, comprising: learning correction value initial setting means for updating a learning correction value using the average value as an initial value of the learning correction value.