JPH086620B2 - Air-fuel ratio feedback control method for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air-fuel ratio feedback control method during low load operation such as idling of an internal combustion engine.

(Prior Art and its Problems) Conventionally, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is
An exhaust gas concentration detector (eg O ₂
Sensor) output signal level to control the target air-fuel ratio (for example, stoichiometric air-fuel ratio) so that the exhaust gas characteristics and operating performance can be improved. Is known (for example, Japanese Patent Application No. 57-188743).

In such an air-fuel ratio feedback control method, the detected voltage value of the O ₂ sensor is compared with a predetermined reference voltage value, and the detected voltage value is rich side to lean side or rich side with respect to the predetermined reference voltage value. When it is determined that the air-fuel ratio has changed to the side, proportional term control (hereinafter referred to as “P term control”) that temporarily increases or decreases a constant value for the air-fuel ratio correction coefficient for controlling the air-fuel ratio of the air-fuel mixture is performed, and the detected voltage is detected. When it is determined that the value changes only on the lean side or the rich side with respect to the predetermined reference voltage value, integral term control (hereinafter referred to as “I term control”) for increasing or decreasing the correction coefficient to a constant value is performed, The air-fuel ratio is controlled so as to match the target air-fuel ratio over the entire feedback control region.

By the way, the temperature of the O ₂ sensor does not rise sufficiently at a low load such as when the engine is idle, and the responsiveness of the O ₂ sensor is lower than in other feedback control regions. Therefore, to increase or decrease correcting the air-fuel ratio correction coefficient according to the determination of whether the detected voltage of the O ₂ sensor as in the conventional method described above is in the lean side or the rich side with respect to a single reference voltage value O ₂
When the feedback control is executed when the engine is idle, the inversion cycle of the detected voltage value of the O ₂ sensor with respect to the predetermined reference voltage value becomes long, so that the responsiveness of the O ₂ sensor is further reduced, and the feedback control is performed. There is a problem that engine speed hunting occurs due to an increase in the variation range of the air-fuel ratio correction coefficient.

(Object of the Invention) The present invention has been made in order to solve such a problem, and in particular, an engine by increasing the variation range of the air-fuel ratio controlled by the air-fuel ratio feedback control during low load operation including idle time of the engine An object of the present invention is to provide an air-fuel ratio feedback control method for an internal combustion engine that prevents hunting of the rotation speed.

(Constitution of the invention) In order to achieve such an object, according to the present invention, the exhaust gas concentration detection value detected by the exhaust gas concentration detector arranged in the exhaust system of the internal combustion engine is compared with a predetermined reference value, and the engine is compared. The air-fuel ratio of the air-fuel mixture supplied to the air-fuel ratio is increased or decreased by the first correction value when the exhaust gas concentration detection value changes from the rich side to the lean side or from the lean side to the rich side with respect to the predetermined reference value. The target air-fuel ratio is adjusted by at least one of proportional control for correction and / or integral control for increasing / decreasing the air-fuel ratio by the second correction value when the exhaust concentration detection value is on the lean side or the rich side with respect to the predetermined reference value. In an air-fuel ratio feedback control method for an internal combustion engine for feedback control according to claim 1, a first reference value corresponding to an air-fuel ratio on a rich side of a theoretical air-fuel ratio as the reference value, and a theoretical air-fuel ratio. A second reference value corresponding to an air-fuel ratio on the lean side of the fuel ratio and smaller than the first reference value is set, and the exhaust gas concentration detection value is the first reference value and the second reference value. If the exhaust gas concentration detection value is greater than the first reference value, or if the exhaust gas concentration detection value is greater than the second reference value, the feedback control amount for correcting the air-fuel ratio is held. There is provided an air-fuel ratio feedback control method for an internal combustion engine, wherein the air-fuel ratio feedback control is performed by correcting the feedback control amount by at least one of the proportional control and the integral control only when it is small.

Embodiments of the Invention Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram showing a carburetor type internal combustion engine incorporating an air-fuel ratio control device for implementing the method of the present invention.

In FIG. 1, reference numeral 1 is, for example, a four-cylinder internal combustion engine, and an intake pipe 3 of the engine 1 is provided with a known carburetor 7 having an air intake 4, an air cleaner 5, and a venturi 6. A throttle valve 8 is provided downstream of the venturi 6 of the intake pipe 3.

Reference numeral 9 denotes a secondary air supply passage. One end of the secondary air supply passage 9 communicates with the air cleaner 5 on the upstream side of the venturi 6 and the other end communicates with the downstream side of the throttle valve 8 of the intake pipe 3, respectively. A linear solenoid type solenoid valve 10 as a proportional control valve is provided on the way. Solenoid of solenoid valve 10
10a is connected to a control circuit (hereinafter referred to as "ECU") 2. The solenoid 10a is energized and controlled by the ECU 2, so that the solenoid valve 10 is opened with an opening area proportional to the amount of current supplied to control the amount of secondary air supply.
On the other hand, an absolute pressure (P _B ) sensor 11 is provided downstream of the throttle valve 8 of the intake pipe 3, and the absolute pressure signal P _B detected by this absolute pressure sensor 11 is sent to the ECU 2.

The engine body 1 is provided with a cooling water temperature (Tw) sensor 12. The Tw sensor 12 is composed of a thermistor or the like, is mounted inside the engine cylinder peripheral wall filled with cooling water, and supplies the detected water temperature signal Tw to the ECU 2. .

Further, an engine speed sensor (hereinafter referred to as "Ne sensor") 13 is attached around a cam shaft or a crank shaft (not shown) of the engine. The Ne sensor 13 outputs an engine speed signal, that is, a pulse signal (hereinafter, referred to as "TDC signal") generated at a predetermined crank angle position every 180 ° rotation of the crankshaft of the engine. Sent to.

A throttle opening sensor 14 is connected to the throttle valve 8 and supplies an electric signal corresponding to the opening (hereinafter referred to as “throttle opening”) θ _TH of the throttle valve 8 to the ECU 2.

A three-way catalyst 16 is arranged in the exhaust pipe 15 of the engine 1 to purify HC, CO and NOx components in the exhaust gas. An O ₂ sensor as an oxygen concentration detector is provided on the upstream side of the three-way catalyst 16.
17 is attached to the exhaust pipe 15, and this O ₂ sensor 17 detects the oxygen concentration in the exhaust and supplies the detection signal Vo ₂ to the ECU 2.

The ECU 2 determines the operating state of the engine according to the output signals from the various engine parameter sensors described above, and controls the opening area of the solenoid valve 10 according to the determined operating state.

The control of the opening area of the solenoid valve 10 is performed by calculating the energization duty ratio I _OuT of the solenoid 10a based on the following equation.

I _OuT = D _BASE × K _O2 Here, D _BASE is a reference value of the energizing duty ratio of the solenoid 10a, and is determined according to the engine speed Ne and the intake pipe absolute pressure P _B. K _O2 is the air-fuel ratio correction coefficient,
When the determined operating state is in the idle operating region, it is determined according to the output signal Vo ₂ of the O ₂ sensor 17, which will be described later.

ECU2 is the energization duty ratio I obtained as described above.
A drive signal for opening the solenoid valve 10 based on _OuT is supplied to the solenoid 10a.

FIG. 2 is a diagram showing a circuit configuration inside the ECU 2 of FIG.
The engine speed signal from the sensor 13 is a waveform shaping circuit 201.
After being waveform-shaped by, it is supplied to the Me counter 202. Me
The counter 202 counts the time interval from the input of the previous TDC signal from the Ne sensor 13 to the input of the current TDC signal, and the count value Me is proportional to the reciprocal of the engine speed Ne. The Me counter 202 supplies this count value Me to the central processing unit (hereinafter referred to as “CPU”) 203 via the data bus 210.

Absolute pressure (P _B ) sensor 11, cooling water temperature sensor 12, O ₂ sensor
Output signals from various sensors such as 17 are corrected to a predetermined voltage level by the level correction circuit 204, and then sequentially supplied to the A / D converter 206 by the multiplexer 205. The A / D converter 206 sequentially exchanges the output signals from the above-mentioned sensors into digital signals and converts the digital signals into the data bus 210.
Is supplied to the CPU 203 via.

The CPU 203 is further connected via a data bus 210 to a read only memory (hereinafter referred to as “ROM”) 207, a random access memory (hereinafter referred to as “RAM”) 208, and a drive circuit 209. The ROM 207 temporarily stores the calculation result, etc., and the ROM 207 is a reference energization duty ratio D for reading out the reference energization duty ratio D _BASE based on the control program executed by the CPU 203, the intake pipe absolute pressure P _B and the number of engine circuits Ne. I remember the _BASE map.

The CPU 203 calculates the energization duty ratio I _OuT of the solenoid 10a according to the various engine parameter signals described above in accordance with the control program stored in the ROM 207 as described above, and the calculated value is the solenoid valve via the data bus 210. To the drive circuit 209 for control. The drive circuit 209 outputs a drive signal for opening the solenoid valve 10 according to the calculated value to the solenoid 10
supply to a.

FIG. 3 is a flow chart showing a program for calculating the correction coefficient Ko ₂ in the idle operation region of the engine. The program is executed every time the pulse of the TDC signal is generated.

First, it is determined whether the activation step 11 0 ₂ sensor 17 is complete. That is, 0 ₂ output voltage activation voltage value Vx of 0 ₂ sensor 17 by the internal resistance detecting method of the sensor 17
(For example, 0.6 V) is detected, and when it reaches Vx, it is determined that it is activated. If the determination result is negative (No), the coefficient value Ko ₂ is set to 1.0 (step 12). On the other hand, if the determination result is affirmative (Yes),
It is determined whether the engine is in the idle operation range (step 13). This determination is performed by determining whether the engine speed Ne is lower than a predetermined speed Ne _IDL (for example, 1000 rpm) and the throttle opening θ _TH is smaller than a predetermined opening θ _IDL .

If the determination result in step 13 is negative (No), the process proceeds to step 12, the value of Ko ₂ is set to 1.0, and this program ends. On the other hand, when the determination result is affirmative (Yes), the air-fuel ratio feedback control after step 14 is performed.

FIG. 4 (a) is a timing chart showing the time variation of the output voltage value Vo ₂ of the 0 ₂ sensor and the time variation of the correction coefficient Ko ₂ according to the present invention.
An explanation will be given using (b).

First, in step 14, the output voltage value Vo ₂ of the 0 ₂ sensor 17
Is larger than the first reference value V _R on the rich side (for example, 0.8 V). This first reference value V _R is an air-fuel ratio (eg, 1) slightly on the rich side of the theoretical air-fuel ratio (= 14.7).
It is set to the value corresponding to 4.6).

Next, at step 15, the output voltage value Vo of the O ₂ sensor 17
_It is determined whether or not ₂ is smaller than the second reference value V _L on the lean side (for example, 0.4 V). The second reference value V _L is set to a value slightly corresponding to the air-fuel ratio on the lean side of the stoichiometric air-fuel ratio (for example, 14.8).

When the determination results of steps 14 and 15 are both negative (No), that is, when the air-fuel ratio of the air-fuel mixture is substantially equal to the stoichiometric air-fuel ratio (FIG. 4 (a) t _{0 to} t ₂ time point), step 16 is performed. Correction factor Ko
The value of ₂ is held (between t _{0 and} t _{2 in} FIG. 4 (b)), the discrimination flag F _P is set to 1 (step 17), and the main body program is terminated.

When the value of the correction coefficient Ko ₂ is changed from the state where it is held to the air-fuel ratio rich side of the air-fuel mixture and the determination result of step 14 becomes affirmative (Yes) (time t _{2 in} FIG. 4 (a)), In step 18, it is determined whether or not the determination flag F _P is 1. In this case, the determination result is affirmative (Yes), the correction value P is added to the held correction coefficient Ko ₂ (step 19), the P term control is performed, and the determination flag F _P is set to 0 (step 19). 20), end this program.

In the next loop, if the determination result of step 14 is still affirmative (Yes) (between t _{2 and} t _{3 in} FIG. 4), the determination result of step 18 is negative (No),
Go to step 21 and set the correction coefficient Ko set in the previous loop.
_The correction value I is added to ₂ to perform the I term control, and this program ends. The correction of the correction coefficient Ko ₂ by adding the correction value I, that is, the I term control is continued while the output voltage value Vo ₂ of the O ₂ sensor 17 exceeds the first reference value V _R (fourth). (B) Between t _{2 and} t ₃ time points).

Correction coefficient increased and corrected by P term control and I term control
By ko _2, when the air-fuel ratio becomes substantially equal to the stoichiometric air-fuel ratio is controlled to the lean side (FIG. 4 (a) t ₃ between ~t ₅ point), the result of the determination at step 14 and 15 are both negative (No) Then, in step 16, the correction coefficient Ko ₂ is held again (Fig. 4 (b) t
_The determination flag F _P is set to 1 (between _{3 and} t ₅ ) (step 17).

On the other hand, when the value of the correction coefficient Ko ₂ is changed from the state where it is held to the lean side of the air-fuel ratio and the determination result of step 15 becomes affirmative (Yes) (at time t _{5 in} FIG. 4A), Proceeding to 22, it is determined whether or not the discrimination flag F _P is 1.
In this case, the determination result is affirmative (Yes), and the correction value P is subtracted from the held correction coefficient Ko ₂ (step 2
3) The P term control is performed, the discrimination flag F _P is set to 0 (step 24), and this program ends.

If the determination result of the continuing step 15 in the next loop is affirmative (Yes) (FIG. 4 (a) t ₅ ~t between ₆ point), the determination result is negative at step 22 (No), and the
Go to step 25 and set the correction coefficient Ko set in the previous loop.
_The correction value I is subtracted from _2, the I term control is performed, and this program ends. Correction coefficient Ko ₂ by subtraction of this correction value I
The correction of I, that is, the I term control is continued while the output voltage value Vo ₂ of the O ₂ sensor 17 is below the second reference value V _L (fourth).
Figure (b) t ₅ ~t between ₆ point).

Correction coefficient reduced and corrected by P term control and I term control
By ko _2, when substantially equal to the stoichiometric air-fuel ratio is controlled to an air-fuel ratio rich side (FIG. 4 (a) t ₆ ~t between ₈ point), the result of the determination step 14 and 15 becomes both negative (No) , And the correction coefficient Ko ₂ is held again in step 16 (FIG. 4 (b) t ₆
The determination flag F _P is set to 1 from the time point between t _{8 and} t ₈ (step 17).

Therefore, as described above, the output voltage value Vo ₂ of the O ₂ sensor 17
Is higher than the first reference value V _R and lower than the second reference value V _L, air-fuel ratio feedback control with good responsiveness is performed by one of the P term control and the I term control, Meanwhile, the output voltage value Vo ₂ is the first reference value V _R
And the second reference value V _L , the correction coefficient Ko
The value of ₂ is retained at the setting value of the previous loop.

As a result, the variation range of the correction coefficient Ko ₂ is smaller than that in the conventional method (FIG. 4 (c)) in which the output voltage value Vo ₂ is compared with the single reference value Vref (= 0.6).

(Effects of the Invention) As described in detail above, according to the present invention, the air-fuel ratio on the rich side of the theoretical air-fuel ratio is set as the reference value to be compared with the exhaust gas concentration detection value during low load operation such as idling of the internal combustion engine. A corresponding first reference value and a second reference value corresponding to an air-fuel ratio leaner than the stoichiometric air-fuel ratio and smaller than the first reference value are set, and the exhaust gas concentration detection value is set to the first reference value. When it is between the reference value and the second reference value, the feedback control amount for correcting the air-fuel ratio is held, and when the exhaust gas concentration detection value is larger than the first reference value, or the exhaust gas concentration Only when the detected value is smaller than the second reference value, one of proportional control for increasing / decreasing the air-fuel ratio of the air-fuel mixture by the first correction value and integral control for increasing / decreasing the air-fuel ratio by the second correction value are performed. To compensate the feedback control amount. Since the air-fuel ratio feedback control is performed by correcting this, the engine speed hunting occurs due to an increase in the range of change in the air-fuel ratio controlled by the air-fuel ratio feedback control, especially during low load operation including engine idle time. Can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall configuration of an air-fuel ratio control apparatus for carrying out the method of the present invention, FIG. 2 is a block diagram showing the internal configuration of the control circuit of FIG. 1, and FIG. 3 is a control method of the present invention. flowchart program showing the procedure Figure 4 the relationship temporal change of the O ₂ sensor output voltage value Vo _2, temporal change of the correction coefficient Ko ₂ according to the present invention, the time variation of the correction coefficient Ko ₂ by the conventional method 2 is a timing chart showing 1 ... Internal combustion engine, 2 ... Control circuit (ECU), 3 ...
Intake pipe, 7 ... Carburetor, 9 ... Secondary air supply passage,
10 …… solenoid valve, 10a …… solenoid, 15 …… exhaust pipe, 17
…… O ₂ sensor.

Claims (1)

[Claims] 1. An exhaust gas concentration detection value detected by an exhaust gas concentration detector arranged in an exhaust system of an internal combustion engine is compared with a predetermined reference value to detect an air-fuel ratio of an air-fuel mixture supplied to the engine. When the value changes from the rich side to the lean side or from the lean side to the rich side with respect to the predetermined reference value,
Proportional control for increasing / decreasing the air-fuel ratio by the first correction value, and when the exhaust concentration detection value is on the lean side or the rich side with respect to the predetermined reference value, the air-fuel ratio is increased / decreased by the second correction value, respectively. In an air-fuel ratio feedback control method of an internal combustion engine for performing feedback control to a target air-fuel ratio by at least one of integral control, a first reference value corresponding to an air-fuel ratio richer than a theoretical air-fuel ratio as the reference value, and a theoretical value. A second reference value corresponding to an air-fuel ratio leaner than the air-fuel ratio and smaller than the first reference value is set, and the exhaust concentration detection value is the first reference value and the second reference value. And the feedback control amount for correcting the air-fuel ratio is held, and the exhaust gas concentration detection value is larger than the first reference value, or the exhaust gas concentration detection value is the second exhaust gas concentration value. The proportional control and the air-fuel ratio feedback control method for an internal combustion engine and performs air-fuel ratio feedback control by correcting the feedback control amount by at least one of the integral control only when smaller than the reference value.