JPS6053637A - Method of controlling air-fuel ratio learning for internal-combustion engine - Google Patents

Abstract

PURPOSE:To stabilize idle running by gradually increasing the value of a learning item when said value of the learning item at the time of idle running is below a certan value, with the output of an O2 sensor indicating a lean condition, while an air-fuel ratio feedback correction factor being above a certain value. CONSTITUTION:On detecting an idling condition through a throttle switch 6, a control circuit 30 which is constructed with microcomputers, judges whether an air-fuel ratio feedback correction factor FAF is above a certain value. And, only when the FAF is above a certain value, it judges whether the output of an O2 sensor 34 indicates a lean condition, i.e., an air-fuel signal is at a low level and, when a lean condition is indicated, it further judges whether the value of a learning item taug at the time of idling is below a certain value, e.g., a negative value. And, only when the value of the taug is below a certain value, this value of the taug is increased by a certain quantity X at each execution of a main routine, to correct the value so as to gradually approach a reference value. Thereby, an erroneously learned value which is learned under an unusual condition can be corrected, stabilizing the idle running.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an air-fuel ratio learning control method for an internal combustion engine, and more particularly to an air-fuel ratio learning control method for controlling an air-fuel ratio during idling by learning control.

[Prior art]

Conventionally, a three-way catalyst has been used to simultaneously purify carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust gas. The air-fuel ratio of the intake system is estimated by detecting the oxygen concentration, 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 determined by the intake pipe pressure PM and the engine speed NK is set to 0.
! The fuel injection time τ is determined by multiplying the air-fuel ratio feedback correction coefficient FAF shown in FIG. 1, which is obtained by proportionally integrating the air-fuel ratio signal obtained by processing the sensor output with a comparator. This is done by controlling the opening and closing of valves.

However, due to environmental changes, O2, sensor deterioration, etc., the air-fuel ratio feedback correction coefficient FAF changes, making it impossible to control the air-fuel ratio near the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio should be controlled by learning based on the following formula. is being carried out.

r = (r p + r g )・KG-FAF-F(
r) ”・”−・(tl However, τg is the learning term when the throttle valve is fully closed (idling), KG is the learning term when the throttle valve is open, and F(τ) is the intake temperature and This is another correction coefficient related to warm-up increase, etc. 1. The learning term KG is determined by the intake pipe pressure, for example, KG when the intake pipe pressure is 200 to 300 imHg.

KG2.400-500m when 300-400 Hg
When wHg, KG is adopted.

These learning terms τg and KG are determined when the air-fuel ratio feedback control is in progress and the engine cooling water temperature is at a predetermined value (for example, 70°C).
) is learned by the following method. Every time the air-fuel ratio feedback correction coefficient FAF skips, the arithmetic average value FAFAV of the peak value of the correction coefficient FAF, that is, the learned value shown below is added to the corresponding term for each skip.

The learning term τE, KO learned in this way is
The fuel injection amount is controlled according to the opening/closing state of the throttle valve and the magnitude of the intake pipe pressure. As a result, when the average value FAFAVf)-1.02 is exceeded, that is, when the sensor output signal is off to the one side, the value of the learning term is increased so that the average value FAFAV approaches 1 due to the value of the learning term. The air-fuel ratio is controlled toward the lean side. Also, the average value FATAV
is less than 0.98, that is, O. When the senna output signal deviates to the rich side, the value of the learning term is reduced and the average value FAFA,V is corrected to approach 1 by the value of the learning term, and the air-fuel ratio is Controlled towards the rich side.

However, in this conventional method, when racing is repeated, the air-fuel ratio becomes rich for a certain period of time, so the value of the learning term during idling is reduced by learning, and the air-fuel ratio changes to lean as shown in Figure 2. When this happens, the air-fuel ratio feedback correction coefficient FAF may reach the upper limit value and no longer skips, so learning may not be performed and the value of the learning term τg may remain at the lower limit value. In this case, 0. Even though the sensor output signal indicates lean, the value of the learning term is small, so the fuel injection time is shortened.
The fuel injection amount is reduced and the air-fuel ratio is controlled to be leaner. Therefore, there is a problem that the idle rotation cannot be maintained and the idle rotation becomes unstable.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an air-fuel ratio learning control method for an internal combustion engine that stabilizes idle rotation by correcting erroneous learning values learned in an abnormal state. shall be.

[Structure of the invention'']

To achieve the above object, the present invention provides a conventional air-fuel ratio learning control method, in which the air-fuel ratio feedback correction coefficient is equal to or greater than a predetermined value, the t-sensor output signal indicates an air-fuel ratio lean, and the When the value of the learning term is below a certain value, the value of the learning term during idling is gradually increased.

〔Effect of the invention〕

According to the above configuration of the present invention, when the value of the learning term during idling is incorrectly learned to a small value, the value of the learning term is corrected to be large, so that the idling rotation can be stabilized. You can get this effect.

[Embodiments of the invention]

An example of an internal combustion engine to which the present invention is applied will be explained in detail based on FIG. 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 arranged downstream of the intake air temperature sensor 2, and a throttle switch 6 is attached which is interlocked with the throttle valve 4 and turns off when the throttle valve is on when the throttle valve is fully closed and the throttle valve is opened. 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 communicated with a combustion chamber 14 of the °C engine via an intake manifold 12. 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 is, for example, 7
A cylinder discrimination signal is outputted to the control circuit 30 made up of a microcomputer or the like every 20°C, and the engine rotation speed sensor 28 outputs an engine rotational speed signal to the control circuit 30, for example, every 30°C. And distributor 24
is connected to the igniter 32. Note that 34 is an O sensor that detects the residual acidity in the exhaust gas and outputs an air-fuel ratio signal.

As shown in FIG. 10, the control circuit 30 includes a central processing unit (C
PU) 36, read-only memory (ROM) 38, random access memory (RAM) 40, backup RAM (Bu-RAM) 42, input/output board (engineering 10) 4
4, an analog-to-digital converter (ADC) 46 and paths 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/044, and a fuel signal that controls the opening/closing time of the fuel injection valve 16 via the drive circuit is input. An ignition signal that controls the injection signal and the on/off time of the igniter 32 is output.

Further, an intake pipe pressure signal, an intake air temperature signal, and a water temperature signal are input to the ADC 4fi and converted into digital signals.

This routine is executed in the mail routine, and first, in step 50, it is determined whether or not the engine is in an idle link state based on the throttle signal.

Only in the idle link state, it is determined in step 52 whether the 1 air-fuel ratio feedback correction coefficient PAF is greater than or equal to a predetermined value, and only when it is greater than or equal to the predetermined value, it is determined to be 0. It is determined whether the sensor output signal is at a low level, that is, whether the air-fuel ratio signal output from the comparator that compares the sensor output with a reference value is at a low level. 0. When the sensor output indicates a lean air-fuel ratio, it is determined in step 56 whether the value of the learning term τg during idle link is less than or equal to a certain value (for example, a negative value). Then, in step 58, the value of the learning term τg is increased by a predetermined amount X only when the value of the learning term τg is less than a certain value.

As a result of the above, when all the conditions of idle link state, FAF≧predetermined value, air-fuel ratio lean, and τg≦constant value are satisfied, the value of learning term τg increases by a predetermined amount X each time the main routine is executed. The value of the learning term τg is corrected by 1ω 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.

Although the above description has been given of an engine in which the basic fuel injection time is determined based on the intake pipe pressure and the engine speed, the present invention is not limited to this, and the basic fuel injection time is determined based on the intake pipe pressure and the engine speed. It can also be applied to engines where 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.

[Brief explanation of drawings]

Figure 1 is a line diagram showing changes in the conventional air-fuel ratio signal and air-fuel ratio feedback correction coefficient, Figure 2 is a line diagram showing changes in the conventional air-fuel ratio signal, air-fuel ratio feedback correction coefficient, and learning term value. 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, and FIG. 5 is a flowchart showing a processing routine in an embodiment of the present invention. , FIG. 6 is a diagram showing changes in the values of learning terms in this embodiment. 6-゛Throttle switch, 10...Pressure sensor, 16...Fuel injection valve. Agent Tatsuyuki Unuma (and 1 other person) Figure 5 Figure 6 Figure 9-ke

Claims (1)

[Claims] (1) The sum of the basic fuel injection time determined by the engine load and engine speed and the value of the learning term during idle link, 0 that detects the residual oxygen concentration in the exhaust gas, and the air-fuel ratio feedback obtained from the sensor output signal. The fuel injection time is determined based on the value multiplied by a correction coefficient, and when the average value of the air-fuel ratio feedback correction coefficient becomes a value outside a predetermined range centered on a predetermined value, the average value of the air-fuel ratio feedback correction coefficient is determined. In an air-fuel ratio learning control method for an internal combustion engine, the method includes controlling the air-fuel ratio of the air-fuel mixture to a target air-fuel ratio by changing the value of the learning term during idle link so as to approach the predetermined value,
When the air-fuel ratio feedback correction coefficient is greater than or equal to a predetermined value, the 02 sensor output signal indicates a lean air-fuel ratio, and the value of the learning term during idle linking is below a certain value, the learning term during idle linking is An air-fuel ratio learning control method for an internal combustion engine characterized by gradually increasing a value.