JPS62255552A - Air-fuel ratio feedback control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent hunting of the number of revolutions due to an increase in the width of a change in an air-fuel ratio during load running, by a method wherein, only when an exhaust gas concentration detecting value exceeds a first reference value or is below a second reference value, proportional and integral control is effected. CONSTITUTION:Based on the detecting value of an O2 sensor 17 situated in an exhaust pipe 15, a control circuit 2 performs feedback control of the opening of a linear solenoid type electromagnetic valve 10 situated in a secondary air feed pipe 9 so that an air-fuel ratio is adjusted to a desired value according to an operating state. by means of the control circuit 2, a value responding to an air-fuel ratio slightly near the rich side than a theoretical air-fuel ratio is set as a first reference value and a value responding to an air-fuel ratio slightly near the lean side is set as a second reference value. Only when the detecting value of the O2 sensor 17 exceeds the first reference value or is below the second reference value, a value equivalent to a proportion or a integral amount serving as a correction factor for feedback control is computed to output it to an electromagnetic valve 10.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an air-fuel ratio feedback control method during low-load operation of an internal combustion engine, such as when idling.

(Prior Art and its Problems) Conventionally, the air-fuel ratio of the air-fuel mixture supplied to an internal combustion engine has been determined by an exhaust concentration detector (for example, Ot
An air-fuel ratio feedback control method for an internal combustion engine, which controls the air-fuel ratio to a target air-fuel ratio (for example, the stoichiometric air-fuel ratio) in immediate response to the output signal level of the internal combustion engine, thereby improving exhaust gas characteristics and driving performance. 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 0□ sensor is compared with a predetermined reference voltage value, and the detected voltage 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 voltage value. Proportional term control (hereinafter referred to as
an integral term side' that increases or decreases the correction coefficient to a constant value when it is determined that the detected voltage value is changing only on the lean side or rich side with respect to the predetermined reference voltage value; 4s (hereinafter referred to as "engineering control") to control the air-fuel ratio to match the target air-fuel ratio over the entire feedback control region.6 By the way, at low load such as when the engine is idling, the above The temperature rise of the O2 sensor is insufficient, and the responsiveness of the O2 sensor is lower than in other feedback control areas. Therefore, as in the conventional method described above, 02 feedback control is performed to increase or decrease the air-fuel ratio correction coefficient depending on whether the detected voltage value of the 02 sensor is on the lean side or rich side with respect to a single reference voltage value. If the execution is performed when the engine is idling, the reversal period of the detected voltage value of the 02 sensor with respect to the predetermined reference voltage value becomes longer, so the responsiveness of the 02 sensor further decreases, and the air-fuel ratio correction coefficient due to the feedback control increases. There was a problem that hunting in the engine speed occurred due to the increase in the variation width.

(Object of the Invention) The present invention has been made to solve the above problems, and is particularly aimed at improving the engine speed by increasing the range of change in the air-fuel ratio controlled by air-fuel ratio feedback control during low-load operation, including when the engine is idling. An object of the present invention is to provide an air-fuel ratio feedback control method for an internal combustion engine that prevents hunting in the rotational speed.

(Structure of the Invention) In order to achieve the above object, according to the present invention, an exhaust concentration detection value detected by an exhaust concentration detector disposed in the exhaust system of an internal combustion engine is compared with a predetermined reference value, and the engine When the detected exhaust gas concentration 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 air-fuel ratio of the air-fuel mixture supplied to the air-fuel mixture is adjusted by the first correction value. Proportional control that increases or decreases correction, and integral control that increases or decreases the air-fuel ratio by a second correction value when the detected exhaust gas concentration value is on the lean side or rich side with respect to the predetermined reference value. In the air-fuel ratio feedback control method for an internal combustion engine, in which a first reference value and a second reference value smaller than the first reference value are set as the reference value, When the detected exhaust gas concentration value is greater than the first reference value.

Alternatively, the air-fuel ratio feedback control for an internal combustion engine is characterized in that air-fuel ratio feedback control by at least one of the proportional control and the integral control is performed only when the detected exhaust gas concentration value is smaller than the second reference value. A method is provided.

(Example 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 carbureted 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 this engine 1 has an air intake port 4. A well-known carburetor 7 with an air cleaner 5 and a venturi 6 is provided. A throttle valve 8 is provided on the downstream side of the venturi 6 in the intake pipe 3.

That's it.

Further, 9 is a secondary air supply passage, and one end of this secondary air supply passage 9 is connected to the air cleaner 5 on the upstream side of the venturi 6.
The other end communicates with the downstream side of the throttle valve 8 of the intake pipe 3, and a near solenoid type electromagnetic valve 10 is interposed therebetween as a proportional control valve. A solenoid 10a of the electromagnetic valve 10 is connected to a four-way control circuit (hereinafter referred to as rECUJ) 2. As the solenoid 10a is energized and controlled by the ECU 2, the electromagnetic valve 10 opens with an opening area proportional to the amount of current supplied to control the amount of secondary air supplied. On the other hand, an absolute pressure (Pa) sensor 11 is provided downstream of the throttle valve 8 in the intake pipe 3, and the absolute pressure signal PB detected by this absolute pressure sensor 11 is
Sent to U2.

The engine body 1 is provided with a coolant temperature (Tw) sensor 12. The Tw sensor 12 is made of a thermistor, etc., and is installed in the circumferential wall of the engine cylinder filled with coolant, and supplies the detected water temperature signal Tw to the ECU 2. .

In addition, the engine rotation speed sensor (hereinafter referred to as rNe sensor)
) 13 is attached around the camshaft or crankshaft (not shown) of the engine.

This Ne sensor 13 generates an engine rotation speed signal, that is, a pulse signal (hereinafter referred to as "TDC signal") that is generated at a predetermined crank angle position every 180@ rotations of the engine crankshaft.
This TDC signal is sent to the ECU 2.

A throttle opening sensor 14 is connected to the throttle valve 8, and an electric signal corresponding to the opening degree (hereinafter referred to as "throttle opening degree") θTH of the throttle valve 8 is sent to the ECU.
Supply to 2.

A three-way catalyst 16 is disposed in the exhaust pipe 15 of the engine 1 to purify HC, Co, and NOx components in the exhaust gas. Upstream of this three-way catalyst 16, an 02 sensor 17 as an oxygen concentration detector is attached to the exhaust pipe 15, and this 0□
The sensor 17 detects the oxygen concentration in the exhaust gas and supplies the detection signal vO□ to the ECU 2.

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

The opening area of the solenoid valve 10 is controlled by calculating the energization duty ratio Iout of the solenoid 10a based on the following equation.

IouT=DeAsHXKo.

Here, DBAs is a reference value for the energization duty ratio of the solenoid 10a, and is determined according to the engine rotational speed Ne and the intake pipe absolute pressure Pa. Ko2 is an air-fuel ratio correction coefficient, and when the determined operating state is in the idle operating region, the output signal vo of the 0□ sensor 17, which will be described later, is
2.

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

FIG. 2 is a diagram showing the circuit configuration inside the ECU 2 of FIG.
The engine rotation speed signal from the Ne sensor 13 is waveform-shaped by a waveform shaping circuit 201 and then supplied to the Me counter 202 . The Me counter 202 counts the time interval from when the previous TDC signal was input from the Ne sensor 13 to when the current TDC signal was input, and the counted value Me is proportional to the reciprocal of the engine rotation speed Ne. Me counter 20
2 supplies this count value Me to the central processing unit (hereinafter referred to as rcPUJ) 203 via the data bus 210.

Absolute pressure (Pa) sensor 11, cooling water temperature sensor 12.0□
The respective output signals from various sensors such as the sensor 17 are corrected to a predetermined voltage level by the level correction circuit 204, and then sequentially sent to the A/D converter 206 by the multiplexer 205.
is supplied to The A/D converter 206 sequentially exchanges the output signals from the aforementioned sensors into digital signals and supplies the digital signals to the CPU 203 via the data bus 210.

The CPU 203 further includes a read-only memory (hereinafter referred to as rROMJ) 207, a random access memory (hereinafter referred to as rRAMJ) 208,
and a drive circuit 209, the RAM 208 temporarily stores the calculation results etc. of the CPU 203, and the ROM
Reference numeral 207 stores a control program executed by the CPU 203, a reference energization duty ratio DBAsE map for reading the reference energization duty ratio DaAsH based on the intake pipe absolute pressure PR and the engine speed Ne, and the like.

As described above, the CPU 203 calculates the energization duty ratio Iout of the solenoid 10a according to the various engine parameter signals described above according to the control program stored in the ROM 207, and sends the calculated value to the data bus 210.
is supplied to the control drive circuit 209 of the solenoid valve. The drive circuit 209 supplies a drive signal for opening the solenoid valve 10 to the solenoid lOa in accordance with the calculated value.

FIG. 3 is a flowchart showing a program for calculating the correction coefficient KO□ in the idle operating region of the engine, and the program is executed every time a pulse of the TDC signal is generated.

First, in step 11, it is determined whether the activation of the 02 sensor 17 has been completed. That is, 0. The internal resistance detection method of the sensor 17 detects whether the output voltage of the 02 sensor 17 has reached the activation voltage value V x (for example, 0.6 V), and when it has reached Vx, it is determined that it is activated. If this determination result is negative (NO), the coefficient value K
Set O□ to 1.0 (step 12). On the other hand, if the result of determination 1 is affirmative (Yes), it is determined whether or not the engine is in the idle operation region (step 13). ID
This is done by determining whether L4 (for example, smaller than 101,000 rpm and throttle opening 6T) is smaller than a predetermined opening θIDL.

If the determination result in step 13 is negative (NO), the process proceeds to step 12, sets the value of KO2 to 1.0, and ends the program. On the other hand, the determination result is positive (Yes)
In this case, air-fuel ratio feedback control from step 14 onwards is performed.

The following is a timing chart showing the time change of the output voltage value Vo of the 0□ sensor and the time change of the correction coefficient KO□ according to the present invention in the air-fuel ratio feedback control.
This will be explained using a) and (b).

First, in step 14, the output voltage value vO2 of the 0□ sensor 17 is set to the rich side first reference value VR (for example, O,
aV). This first reference value VR is set to a value corresponding to an air-fuel ratio (for example, 14.6) that is slightly richer than the stoichiometric air-fuel ratio (=14.7).

Next, in step 15, the output voltage value Vo of the 0□ sensor 17 is set to a second reference value v on the lean side, for example, 0.
4V). This second reference value vL is set to a value corresponding to an air-fuel ratio (for example, 14.8) that is slightly leaner than the stoichiometric air-fuel ratio.

The determination results in steps 14 and 15 are both negative (NO).
In other words, when the air-fuel ratio of the air-fuel mixture is approximately equal to the stoichiometric air-fuel ratio (Fig. 4(a) to t2), the value of the correction coefficient KO□ is held in step 16 (Fig. 4(b)). )t(1~
Step 17) Set the 1 discrimination flag FP to 1 during time t2) and terminate the 1 program.

When the air-fuel ratio of the air-fuel mixture changes to the rich side from the state in which the value of the correction coefficient Ko2 is maintained in this manner, and the determination result in step 14 becomes affirmative (Yes) (time point 1 in FIG. 4(a)), Proceeding to step 18, it is determined whether the determination flag FP is 1 or not. In this case, the determination result is positive (Yes)
Then, the correction value P is added to 02 to the held correction coefficient (step 19), P-term control is performed, and the discrimination flag F is set to 0 (step 20), and the program ends.

In the next loop, the determination result in step 14 continues to be affirmative (
Yes) (Fig. 4 (a) between t* and t1), the determination result in step 18 becomes negative (NO), and the process proceeds to step 21, where the correction coefficient Ko2 set in the previous loop is used. The correction value I is added to perform one-term control, and this program ends. This correction of the correction coefficient KO2 by addition of the correction value KO2, that is, one-term control, continues while the output voltage value vo2 of the 02 sensor 17 exceeds the first reference value V (Fig. 4(b) ) between time points tz and t1).

Correction coefficient K that has been increased by P-term control and 1-term control
O □ Therefore, when the air-fuel ratio is controlled to the lean side and becomes approximately equal to the stoichiometric air-fuel ratio (Fig. 4 (a) time period t3 to t6), the determination result □ in step 14.15 is negative (NO).
Then, in step 16, the correction coefficient Ko2 is held again (1lff from ta to t8 in FIG. 4(b)), and the discrimination flag F is set to 1 (step 17).

On the other hand, when the air-fuel ratio changes to the lean side while the value of the correction coefficient Ko is maintained, and the determination result in step 15 becomes affirmative (Yes) (Fig. 4 (a) at time ts)
, the process proceeds to step 22 and the determination flag F is set.

is 1 or not. In this case, the 1 determination result is affirmative (Yes), and the correction coefficient Ko2 that was held
Subtract the correction value P from (Step 23) to perform P-term control, and set the discrimination flag F to 0.Step 24) 1
Exit this program.

In the next loop, the determination result in step 15 continues to be positive (
If Yes) (Fig. 4(a) ts to 1F, time interval), the determination result in step 22 becomes negative (No), and the process proceeds to step 25, where the correction coefficient Ko set in the previous loop is Perform one-term control by subtracting the correction value I from
Exit this program.

Correction of the correction coefficient Ko2 by subtracting this correction value Ko2, that is, 1
The term control is the output voltage value Vo of the 02 sensor 17.

continues while V is below the second reference value v (
FIG. 4(b) between time points ts and t6).

Correction coefficient K corrected to decrease by P-term control and 1-term control
When the air-fuel ratio is controlled to the rich side by O2 and becomes approximately equal to the stoichiometric air-fuel ratio (Fig. 4 (a) time period ts to t1),
The determination results in steps 14 and 15 are both negative (NO).
Then, in step 16, the correction coefficient KO
is set to 1 (step 17).

Therefore, as mentioned above, the output voltage value v of the O2 sensor 17
When O□ is higher than the first reference value Ve.

When the output voltage value vO is lower than the second reference value vL, responsive air-fuel ratio feedback control is performed by either P-term control or 1-term control, while the output voltage value vO□
is between the first reference value v2 and the second reference value VL, the value of the correction coefficient KO□ is held at the value set at the previous loop.

As a result, the range of change in the correction coefficient KO□ is reduced compared to the conventional method (Fig. 4 (C)) in which the output voltage value Vo is compared with a single reference value V ref (=0.6). .

(Effects of the Invention) As detailed above, according to the present invention, the first reference value and the first A second reference value smaller than the reference value is set, and the mixing is performed only when the detected exhaust gas concentration value is larger than the first reference value or when the detected exhaust gas concentration value is smaller than the second reference value. Since either the proportional control that increases or decreases the air-fuel ratio by the first correction value or the integral control that increases or decreases the air-fuel ratio by the second correction value is performed, hunting of the engine speed due to the air-fuel ratio feedback control is performed. This will help prevent this.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of an air-fuel ratio control device that implements 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 block diagram showing the control method of the present invention. A program flowchart showing the procedure of FIG. 4(a),
(b) and (c) are timing charts showing, respectively, changes over time in the output voltage value vO2 of the O2 sensor, changes over time in the correction coefficient Ko according to the present invention, and changes over time in the correction coefficient Ko according to the conventional method. . 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... 02 sensor.

Claims (1)

[Claims] 1. Compare the detected exhaust concentration value detected by the exhaust concentration detector disposed in the exhaust system of the internal combustion engine with a predetermined reference value, and determine the air-fuel ratio of the air-fuel mixture supplied to the engine. When the detected exhaust gas concentration value changes from a rich side to a lean side or from a lean side to a rich side with respect to the predetermined reference value, proportional control is performed to increase or decrease the air-fuel ratio by a first correction value, and the detected exhaust concentration value is changed from a rich side to a lean side or from a lean side to a rich side. Air-fuel ratio feedback control for an internal combustion engine that performs feedback control to a target air-fuel ratio by at least one of integral control that increases or decreases the air-fuel ratio by respectively increasing or decreasing the air-fuel ratio by a second correction value when the air-fuel ratio is on the lean side or rich side with respect to the predetermined reference value. In the method, a first reference value and a second reference value smaller than the first reference value are set as the reference value, and when the detected exhaust gas concentration value is larger than the first reference value, or An air-fuel ratio feedback control method for an internal combustion engine, characterized in that air-fuel ratio feedback control by at least one of the proportional control and the integral control is performed only when the detected exhaust gas concentration value is smaller than the second reference value. 2. The detected exhaust gas concentration value is different from the first reference value and the second reference value.
2. The air-fuel ratio feedback control method for an internal combustion engine according to claim 1, wherein the feedback control amount for correcting the air-fuel ratio is held when the air-fuel ratio is between the reference value.