JPH0432937B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an air-fuel ratio learning control method for an internal combustion engine. [Prior Art] Conventionally, a three-way catalyst has been used to simultaneously purify carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust gas, and in order to improve the purification rate of this three-way catalyst, O ₂ The air-fuel ratio of the intake system is estimated by detecting the residual oxygen concentration in the exhaust gas using a sensor, and the air-fuel ratio of the intake system is controlled to be close to the stoichiometric air-fuel ratio. In controlling the air-fuel ratio of the intake system to near the stoichiometric air-fuel ratio, the basic fuel injection time τP is determined by the intake pipe pressure PM and the engine speed NE.
is multiplied by the air _- fuel ratio feedback correction coefficient FAF shown in FIG. This is done by controlling the opening and closing of fuel injection valves using However, due to changes in the environment, changes in the engine over time, etc., the air-fuel ratio feedback correction coefficient FAF changes, making it impossible to control the air-fuel ratio near the stoichiometric ratio. For this reason, we introduced air-fuel ratio learning control to reduce O ₂
When the output of the sensor is reversed, the average value of the air-fuel ratio feedback correction coefficient FAF is calculated, and the air-fuel ratio learning term is calculated so that this average value falls within a predetermined range centered on the predetermined value, and the basic fuel injection amount ( The result of multiplying the air-fuel ratio feedback correction coefficient by the air-fuel ratio feedback correction coefficient is further corrected by this learning term to obtain the fuel injection amount (time), and the air-fuel ratio of the engine is controlled to be close to the stoichiometric air-fuel ratio (for example, Tokukai Akira
58-27819). As the learning control, for example, the air-fuel ratio is learned and controlled using the following formula. τ=(τp+τg)・KG・FAF・F(τ)……(1) However, τp is the basic injection time, τg is the learning term when the throttle valve is fully closed (idling), and KG is the learning term when the throttle valve is fully closed. Learning terms when there is, F
(τ) is another correction coefficient related to intake air temperature, warm-up increase, etc. In addition, the learning term KG is determined by the intake pipe pressure, for example, when the intake pipe pressure is 200 to 300.
KG ₁ when mmHg, KG ₂ when 300-400mmHg,
KG ₃ is adopted when the temperature is 400-500mmHg. These learning terms τg and KG are learned by the following method when the engine cooling water temperature exceeds a predetermined value (for example, 70° C.) during air-fuel ratio feedback control. Every time the air-fuel ratio feedback correction coefficient FAF skips, calculate the arithmetic average value FAFAV of the peak value of the correction coefficient FAF, that is, FAFAV=A+B/2, B+C/2, C+D/2, ...(2), and calculate the value for each skip. Add the following learning value to the corresponding item.

[Problem to be solved by the invention]

However, in such conventional methods, when the air-fuel ratio becomes rich for a certain period of time due to a disturbance and then returns to the lean side, the value of the learning term may be kept small. In such a case, a problem arises in that the air-fuel ratio becomes leaner, resulting in deterioration of drivability and deterioration of emission. In other words, the temporary enrichment of the air-fuel ratio due to disturbance acts to reduce the value of the learning term, and then
When the disturbance that caused the air-fuel ratio to become rich is removed and the air-fuel ratio returns to the lean side, the value of the learning term becomes too small for the air-fuel ratio that has returned to the lean side. Therefore, the value of the learning term functions to make the air-fuel ratio leaner than the stoichiometric air-fuel ratio (target air-fuel ratio), and therefore the O ₂ sensor output indicates lean, so the air-fuel ratio feedback correction coefficient FAF is increased. During the increase of this air-fuel ratio feedback correction coefficient FAF, if the enrichment by the feedback correction coefficient FAF exceeds the leanness by the value of the learning term and the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio,
At that point, the O ₂ sensor output also indicates rich (reverses from lean output to rich output), and the air-fuel ratio feedback correction coefficient FAF skips, so it is the timing for learning, the value of the learning term is also increased, and from then on, the air-fuel ratio Feedback correction factor FAF
becomes skippable, and the value of the learning term gradually increases to an appropriate value, and the value of the learning term does not remain small. However, if the value of the learning term becomes too small due to a disturbance, the enrichment caused by the feedback correction coefficient FAF cannot exceed the leanness caused by the value of the learning term during the increase in the air-fuel ratio correction coefficient FAF mentioned above.
The air-fuel ratio remains leaner than the stoichiometric air-fuel ratio and the air-fuel ratio feedback correction coefficient FAF is the upper limit value (guard value)
(Figure 2). As mentioned above, if there is a skip in FAF (if the output of the O ₂ sensor is reversed), the value of the learning term is updated according to the average value of the feedback correction value at that time, but the value of the learning term is updated according to the average value of the feedback correction value at that time. After FAF reaches the upper limit value, FAF continues to maintain the same upper limit value, so the air-fuel ratio cannot change and the air-fuel ratio continues to be lean, and the O ₂ sensor output does not change from lean to rich, so there is no skipping of FAF. Therefore, the value of the learning term remains small. Therefore, the lean state continues after that and the above-mentioned problem occurs. To give a specific example, when racing is repeated, the center of the air-fuel ratio may temporarily shift to a rich degree for a certain period of time. This deviation is first reflected in the air-fuel ratio feedback correction coefficient FAF, so the arithmetic average value FAFAV for each skip of FAF is
is a value (a small value) that reduces the amount of fuel by the amount that the center of the air-fuel ratio shifts toward richness, and therefore, the value of the learning term (learning value) is changed to a smaller value. When racing is stopped after such a situation is repeated, after a while the enrichment of the air-fuel ratio due to racing will be removed and the center of the air-fuel ratio will no longer be rich, but by this time the learned value has already become quite large. The value is on the side of small reduction. Therefore, the air-fuel ratio shifts to lean depending on the learned value,
Since the air-fuel ratio signal based on the O ₂ sensor output indicates lean, the air-fuel ratio feedback correction coefficient FAF gradually increases as shown in FIG. At this time, if the learning value becomes very small, FAF
will reach its upper limit. Note that during this period, the FAF increases monotonically and there is no skipping, so the learned value remains at the previous small value. Here, even if FAF reaches the upper limit value, the learned value is small, so if the air-fuel ratio is leaner than the stoichiometric air-fuel ratio (that is, it cannot be made richer), the air-fuel ratio signal will not change to rich even after that, so FAF is not skipped, so the learned value is not updated and the air-fuel ratio remains lean. As a result, drivability and emission deteriorate. An object of the present invention is to provide an air-fuel ratio learning control method for an internal combustion engine that can correct an erroneous learning value learned in an abnormal state. [Means for Solving the Problems] In order to achieve the above object, the present invention provides a basic fuel injection amount determined based on the engine load and engine speed, and an air-fuel ratio feedback correction coefficient determined by calculation. An air-fuel learning control method for an internal combustion engine, which determines the fuel injection amount based on the air-fuel ratio learning term and controls the air-fuel ratio of the air-fuel mixture supplied to the engine to be a target air-fuel ratio, the method comprising: The system detects whether the engine's air-fuel ratio is richer or leaner than the target air-fuel ratio from the output signal of the oxygen concentration sensor that detects oxygen concentration, and changes the air-fuel ratio to the richer side when the detected air-fuel ratio is lean. In order to change the air-fuel ratio, the air-fuel ratio feedback correction coefficient is increased within a range that does not exceed a predetermined upper limit value, and when the detected air-fuel ratio is rich, the air-fuel ratio feedback correction coefficient is increased in order to change the air-fuel ratio to a leaner side. decreasing the detected air-fuel ratio from rich to lean;
Alternatively, the average value of the air-fuel ratio feedback correction coefficient is determined when the air-fuel ratio changes from rich to lean, and when the average value is larger than the first reference value at the time of the air-fuel ratio reversal, the air-fuel ratio is adjusted by an air-fuel ratio learning term. In order to correct it to the rich side, the air-fuel ratio learning term is increased, and when the average value is smaller than a second reference value that is smaller than the first reference value at the time of the air-fuel ratio reversal,
In order to correct the air-fuel ratio to the lean side using the air-fuel ratio learning term, the air-fuel ratio learning term is decreased, so that the average value is a value within a predetermined range determined by the first reference value and the second reference value. In the air-fuel ratio learning control method for an internal combustion engine, when the air-fuel ratio feedback correction coefficient is above a predetermined value, the detected air-fuel ratio is lean, and the air-fuel ratio learning term is below a certain value, Control is performed to gradually increase the air-fuel ratio learning term. [Operation] When controlling the air-fuel ratio of the air-fuel mixture, it is determined whether erroneous learning has occurred according to the air-fuel ratio feedback coefficient, the output signal of the oxygen concentration sensor, and the air-fuel ratio learning term, and the air-fuel ratio feedback correction coefficient is set to a predetermined value. In the above, when the output signal of the oxygen concentration sensor indicates a lean air-fuel ratio and the air-fuel ratio learning term is below a certain value, it is assumed that erroneous learning has occurred, and the air-fuel ratio learning term is forcibly corrected to gradually increase. Therefore, it is possible to prevent the air-fuel ratio from becoming lean. [Embodiment] Hereinafter, as an embodiment of the present invention, an air-fuel ratio learning control method during idling will be described with reference to FIGS. 3 to 6. An intake temperature sensor 2 is installed downstream of an air cleaner (not shown) to detect the temperature of intake air and output an intake temperature signal. A throttle valve 4 is disposed downstream of the intake temperature sensor 2, and a throttle switch 6 is attached which is interlocked with the throttle valve 4 and turns off when the on-throttle valve opens when the throttle valve is fully closed. A surge tank 8 is provided downstream of the throttle valve 4, and a pressure sensor 10 is attached to the surge tank 8 for detecting the intake pipe pressure downstream of the throttle valve and outputting an intake pipe pressure signal.
The surge tank 8 is connected to the intake manifold 12
The combustion chamber 14 of the engine is communicated with the engine through the combustion chamber 14 of the engine. A fuel injection valve 16 is attached to the intake manifold 12 for each cylinder. The combustion chamber 14 of the engine is communicated via an exhaust manifold with a catalytic converter (not shown) filled with a three-way catalyst. Further, a water temperature sensor 20 is attached to the engine block to detect the engine cooling water temperature and output a water temperature signal.
The tip of a spark plug 22 projects into the combustion chamber 14 of the engine, and the spark plug 22 is connected to a distributor 24. The distributor 24 is provided with a cylinder discrimination sensor 26 and an engine rotation speed sensor 28, each of which includes a pickup fixed to the distributor housing and a signal rotor fixed to the distributor shaft. The cylinder discrimination sensor 26 outputs a cylinder discrimination signal, for example, every 720°C to a control circuit 30 composed of a microcomputer or the like.
The engine rotation speed sensor 28 outputs an engine rotation speed signal to the control circuit 30, for example, every 30°C. Then, the distributor 24 is connected to the igniter 32.
It is connected to the. Note that 34 is an O ₂ sensor that detects residual acidity in exhaust gas and outputs an air-fuel ratio signal. As shown in FIG. 4, the control circuit 30 includes a central processing unit (CPU) 36, a read-only memory (ROM) 38, a random access memory (RAM) 40, and a backup RAM (Bu-RAM).
42, an input/output port (I/O) 44, an analog-to-digital converter (ADC) 46, and buses such as a data bus and a control bus that connect these. A cylinder discrimination signal, an engine speed signal, an air-fuel ratio signal, and a throttle signal output from the throttle switch 6 are input to the I/O 44, and the opening/closing time of the fuel injection valve 16 is controlled via the drive circuit. A fuel injection signal and an ignition signal that controls the on/off time of the igniter 32 are output. Further, an intake pipe pressure signal, an intake air temperature signal, and a water temperature signal are inputted to the ADC 46 and converted into digital signals. Next, a processing routine of an embodiment in which the present invention is applied to the engine as described above will be explained based on FIG. This routine is executed in the main routine, and first, in step 50, it is determined whether or not the engine is in an idling state based on the throttle signal. Step only when idling
Air-fuel ratio feedback correction coefficient FAF at 52
is greater than a predetermined value, and only when it is greater than a predetermined value, in step 54 is the O ₂ sensor output signal indicating lean, that is, the O ₂ sensor output is compared with the reference value. Determine whether the fuel ratio signal is at a low level. When the _O2 sensor output indicates a lean air-fuel ratio, the value of the learning term τg during idling is set to a constant value (for example,
(negative value) or less. Then, only when the value of the learning term τg is less than a certain value, the value of the learning term τg is increased by a predetermined amount X in step 58. As a result of the above, when all the conditions of idling, FAF≧predetermined value, lean air-fuel ratio, and τg≦constant value are satisfied, the value of learning term τg is increased by a predetermined amount X each time the main routine is executed. ,
The value of the learning term τg is corrected so that it gradually approaches the reference value. FIG. 6 shows changes in the air-fuel ratio feedback correction coefficient FAF, the value of the learning term τg, and the air-fuel ratio signal when controlled as described above. In addition, although the engine in which the basic fuel injection time is determined by the intake pipe pressure and the engine rotation speed has been described above, the present invention is not limited to this, and the engine rotation speed is determined by the intake air amount per engine rotation and the engine rotation speed. It can also be applied to an engine in which the basic fuel injection time is determined by In this case, an air flow meter is provided upstream of the throttle valve, and the amount of intake air is detected by this air flow meter. [Effects of the Invention] As explained above, according to the present invention, it is determined whether the air-fuel ratio learning term has been erroneously learned, and when the learning term has been erroneously learned, correction is performed to gradually increase the learning term. This makes it possible to prevent the air-fuel ratio from becoming leaner, thereby contributing to improving drivability and reducing emissions.

[Brief explanation of drawings]

FIG. 1 is a diagram showing changes in the conventional air-fuel ratio signal and air-fuel ratio feedback correction coefficient; FIG. 2 is a diagram showing changes in the conventional air-fuel ratio signal, air-fuel ratio feedback correction coefficient, and learning term values; FIG. 3 is a schematic diagram showing an example of an engine to which the present invention is applied;
FIG. 4 is a block diagram showing an example of the control circuit of FIG. 3, FIG. 5 is a flowchart showing a processing routine in an embodiment of the present invention, and FIG. 6 shows changes in the values of learning terms, etc. in this embodiment. FIG. 6...Throttle switch, 10...Pressure sensor, 16...Fuel injection valve.

Claims (1)

[Scope of Claims] 1. Fuel injection based on the basic fuel injection amount determined based on the engine load and engine speed, and the air-fuel ratio feedback correction coefficient and air-fuel ratio learning term determined by calculation. An air-fuel ratio learning control method for an internal combustion engine in which the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to a target air-fuel ratio by determining the amount of air-fuel From the signal, it is detected whether the air-fuel ratio of the engine is richer or leaner than the target air-fuel ratio, and when the detected air-fuel ratio is lean, the air-fuel ratio is set to a predetermined upper limit value in order to change the air-fuel ratio to the richer side. The air-fuel ratio feedback correction coefficient is increased within a range that does not exceed 100%, and when the detected air-fuel ratio is rich, the air-fuel ratio feedback correction coefficient is decreased in order to change the air-fuel ratio to a leaner side, and when the detected air-fuel ratio is From rich to lean,
Alternatively, when the air-fuel ratio is reversed from rich to lean, the average value of the air-fuel ratio feedback correction coefficient is determined, and when the average value is larger than the first reference value during the air-fuel ratio reversal, the air-fuel ratio is enriched by an air-fuel ratio learning term. In order to correct the air-fuel ratio to the side, the air-fuel ratio learning term is increased, and when the average value is smaller than a second reference value that is smaller than the first reference value at the time of the air-fuel ratio reversal,
In order to correct the air-fuel ratio to the lean side using the air-fuel ratio learning term, the air-fuel ratio learning term is decreased, so that the average value is a value within a predetermined range determined by the first reference value and the second reference value. In the air-fuel ratio learning control method for an internal combustion engine, when the air-fuel ratio feedback correction coefficient is above a predetermined value, the detected air-fuel ratio is lean, and the air-fuel ratio learning term is below a certain value, An air-fuel ratio learning control method for an internal combustion engine, characterized in that the air-fuel ratio learning term is gradually increased.