JPS63113147A - Air-fuel ratio controlling method for internal combustion engine - Google Patents

Abstract

PURPOSE:To aim at improvement air-fuel ratio control accuracy just after a drive range variation, by varying a reference correction value, controlling the reference value of air-fuel ratio control, gradually from value just before a variation to that just after the variation at a time when a drive range is varied. CONSTITUTION:A control circuit 20 reads the reference value of air-fuel ratio control to be outputted to a linear type solenoid valve 9, on the basis of each detected value out of a suction absolute pressure sensor 10 and a crank angle sensor 11, and it determines an air-fuel ratio correction value on the basis of the detected value of the oxygen sensor 14 when an air-fuel ratio feedback condition is effected. And, when the detected value of the oxygen sensor 14 is reversed, it calculates a reference for compensating an error in the reference value corresponding to a drive range and renews it. And, when this drive range is varied, it sets the value between the adjacent reference correction value and the newset reference correction value in the adjacent drive range as the reference correction value, thereby determining the air-fuel ratio control output value.

Description

[Detailed description of the invention] 1 hill and 1 The present invention relates to an air-fuel ratio control method for an internal combustion engine.

1.5I In order to purify the exhaust gas of an internal combustion engine and improve fuel efficiency, the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the air-fuel ratio of the mixture supplied to the engine is determined according to the output level of this oxygen concentration sensor. Feedback control of air-fuel ratio 1I
Jtll devices are known.

This air fuel ratio is 11JI! As a device, a solenoid valve is provided in the intake secondary air supply passage that communicates with the downstream side of the vaporizer throttle valve, and is used for feedback control to control the opening degree of the solenoid valve, that is, the intake secondary air supply rate, according to the output level of the oxygen concentration sensor. There is an air-fuel ratio control device that uses an intake secondary air supply force (for example, Japanese Patent Publication No. 55-3533).

In such conventional air-fuel ratio control devices, it is determined from the output level of the oxygen concentration sensor whether the air-fuel ratio of the supplied air-fuel mixture is lean or rich with respect to the target air-fuel ratio, and the control is performed according to the determination result. PI (proportional integral) control is normally performed in which the air-fuel ratio correction value is increased or decreased by a proportional wall or an integral amount at predetermined intervals, and the intake secondary air supply member is corrected and controlled in accordance with the air-fuel ratio correction value.

By the way, it is common for the base air-fuel ratio of the carburetor to deviate from a predetermined value due to aging or deterioration of the carburetor, causing the set reference value to no longer correspond to the target air-fuel ratio and resulting in an error. It is. Therefore, there are systems that perform learning control in which a reference correction value for correcting the error in the reference value is calculated for each operating region and a new reference correction value is stored, thereby improving the accuracy of air-fuel ratio control.

However, if there is a large difference between the reference correction values stored for each operating region due to learning control, when the operating region changes, the reference correction value will fluctuate greatly from the value immediately before the change, and the reference value and PI sub-control Even when the change in the air-fuel ratio correction value is small, the air-fuel ratio control value changes due to fluctuations in the reference correction value, so the air-fuel ratio control accuracy may deteriorate.

11 Summer and I Therefore, an object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine that can improve the accuracy of air-fuel ratio control immediately after the operating range for setting a reference correction value changes. be.

In the air-fuel ratio control method for an internal combustion engine of the present invention, at least immediately after the operating range changes, the value between the reference correction value used for determining the previous control output value and the latest reference correction value in the current operating range is set. is set as the reference correction value for determining the current control output value.

叉-1Jl Embodiments of the present invention will be described below with reference to the drawings.

In the air-fuel ratio control device of the intake secondary air supply system for an on-vehicle internal combustion engine to which the air-fuel ratio control method of the present invention is applied, as shown in FIG. The vicinity of the air outlet is the intake 2
The air supply passages 8 communicate with each other. A linear solenoid valve 9 is provided in the intake secondary air supply passage 8 . The opening degree of the solenoid valve 9 changes in proportion to the current value supplied to the solenoid 9a.

A negative pressure detection boat 6 is provided on the inner wall surface of the carburetor 1 near the throttle valve 3. The negative pressure detection boat 6 is located upstream of the throttle valve 3 when the opening of the throttle valve 3 is less than a predetermined opening, and is located downstream of the throttle valve 3 when the opening of the throttle valve 3 is greater than the predetermined opening. The negative pressure in the negative pressure detection boat 6 is supplied to the negative pressure switch 7 via the negative pressure passage 6a. The negative pressure switch 7 is provided to detect the closed state of the throttle valve 3, and is turned on when the negative pressure in the negative pressure detection boat 6 is, for example, 30 mmt1g or less.

On the other hand, 10 is an absolute pressure sensor installed in the intake manifold 4 and generates an output at a level corresponding to the absolute pressure inside the intake manifold 4, and 11 generates a pulse in accordance with the rotation of the crankshaft (not shown) of the engine 5. 12 is a cooling water temperature sensor that generates an output at a level corresponding to the cooling water temperature of the engine 5; 13 is an intake temperature sensor that detects the intake air temperature; 14 is an exhaust manifold 1 of the engine 5;
The exhaust manifold 15 downstream of the installation position of the a oxygen concentration sensor 14, which is an oxygen concentration sensor installed in the exhaust gas and generates an output voltage according to the oxygen concentration in the exhaust gas, is equipped with an exhaust manifold 15 that promotes the reduction of harmful components in the exhaust gas. A catalytic converter 33 is provided for this purpose.

The negative pressure switch 7 , solenoid valve 9 , absolute pressure sensor 101 , crank angle sensor 11 , water temperature sensor 12 , intake temperature sensor 13 , and oxygen concentration sensor 14 are connected to a control circuit 20 . The negative pressure switch 7 generates a low level output when turned off, and generates a high level output when turned on.

The control circuit 20 includes an absolute pressure sensor 10, as shown in FIG.
Water temperature sensor 12, intake temperature sensor 13, oxygen S degree sensor 1
4, a multiplexer 22 that selectively outputs one of the sensor outputs that have passed through the level conversion circuit 21;
A/2 converts the signal output from 2 into a digital signal.
A D converter 23, a waveform shaping circuit 24 that shapes the output signal of the crank angle sensor 11, and a clock pulse generation circuit (not shown) that outputs the generation interval of the TDC signal output as a pulse from the waveform shaping circuit 24. A counter 25 that measures the number of clock pulses, a level conversion circuit 26 that converts the output level of the negative pressure switch 7, a digital input camosulator 27 that converts the converted output into digital data, and a solenoid valve 9 that is driven to open. Drive circuit 2
8, and a CP that performs digital operations according to the program.
U (central processing circuit) 29, ROM 30 in which various processing programs and data are written in advance, and RAM 31
It consists of The solenoid 9a of the electromagnetic valve 9 is connected in series with a drive transistor and a current detection resistor (both not shown) of a drive circuit 28, and a power supply voltage is supplied across the series circuit. Multiplexer 22, A/D converter 23, counter 25, digital input camosulator 2
7. Drive circuit 28, CPtJ29, ROM30 and RA
M31 are connected to each other by an input/output bus 32.

In such a configuration, the information on the absolute pressure in the intake manifold 4, the cold W*fan, the intake temperature, and the oxygen concentration in the exhaust gas is alternatively transmitted from the A/D converter 23, and the engine speed is determined from the counter 25. The information displayed is also the on/off of the negative pressure switch 7 from the digital input camosulator 27.
29 via an input/output bus 32. C.P.L.
I29 has a predetermined period T+ (for example, 50 m
By executing the processing program every 5 ec), an air-fuel ratio control output value DOUT representing the value of current supplied to the solenoid 9a of the solenoid valve 9 is calculated as data, and the calculated output value DOUT is supplied to the drive circuit 28.

The drive circuit 28 performs closed loop control on the current value flowing through the solenoid 9a so that the current value flowing through the solenoid 9a becomes the output value DOUT.

Next, the steps of the air-fuel ratio control method according to the present invention will be described in the third step.
A detailed explanation will be given according to the operation flow diagram of the CPU 29 shown in the figure.

As shown in FIG. 3, the CPU 29 first calculates the intake absolute pressure P.
s A 1 Cooling water temperature Tw 1 Intake temperature TA, engine speed Ne, and oxygen concentration 02 are each read (step 51)
, it is determined whether the intake air temperature TA is higher than a predetermined temperature T1 (for example, 25° C.) (step 52). TA>T
If it is I, it is determined whether the cooling water m T w is higher than a predetermined temperature T2 (for example, 80° C.) (step 53). If TA≦T+ or TW≦T2, the air-fuel ratio feed □ back control condition is not satisfied, so the output value DOLJT is made equal to O (step 54), and the air-fuel ratio feedback coefficient Koz is made equal to 1 (step 55). If T W > T 2, it is assumed that the air-fuel ratio feedback control conditions are satisfied, and a reference 1iflDeASE representing a reference current value to be supplied to the electromagnetic valve 9 is searched (step 56). As shown in FIG. 4, the reference value D8ASε determined from the absolute pressure PBA and the engine speed Ne is pre-written in the ROM 30 as a DOA SE data map, so the CPU 29 uses the read absolute pressure PBA and the engine speed Ne. Reference value D corresponding to
Search for 8A s E from the DBASE data map.

After searching for the reference value D8ASE, it is determined whether the oxygen concentration is leaner than the reference temperature corresponding to the target air-fuel ratio, that is, the output voltage VO2 of the oxygen concentration sensor 14 is determined as the reference value v'rer.
It is determined whether it is smaller than (, 0, 5 (V)) (step 57). If VO2<Vref, the air-fuel ratio is leaner than the target air-fuel ratio, so it is determined whether the air-fuel ratio flag FAF representing the determination result of the previous step 57 is 1 (step 58).

If FAF=O, the previous air-fuel ratio was determined to be rich and changed from rich to lean, so the air-fuel ratio correction coefficient K
Subtract the proportional control amount PL from O2 (air-fuel ratio correction value) and set the calculated value as 02 as the current correction coefficient (step 59),
Set the air-fuel ratio flag FAF equal to 1 (step 6
0). If FA F -1, it was determined that the air-fuel ratio was lean last time as well, so the integral control portion IL is subtracted from the air-fuel ratio correction coefficient KO2, and the calculated value is set as the current correction coefficient KO2 (step 61). On the other hand, in step 57, the VO
If 2≧V ref, the air-fuel ratio is richer than the target air-fuel ratio, so it is determined whether the air-fuel ratio flag FAF is 0 (step 62). If FA r--1, the previous air-fuel ratio was determined to be lean and reversed from lean to rich, so add the proportional control amount PR to the air-fuel ratio correction coefficient KO2 and set the calculated value as the current correction coefficient KO2. Step 63) and setting the air-fuel ratio flag FAF equal to O (Step 64). If it is FA F-0, the air-fuel ratio was determined to be rich last time, so the integral control amount IR is added to the air-fuel ratio correction coefficient KO2, and the calculated value is used as the current correction coefficient Koz.
(Step 65). After execution of step 60 or 64, intake manifold absolute pressure PBA and engine speed N
The correction coefficient Krer (reference correction value) corresponding to e is K r
Search from the ef data map (step 66). Kr
The er data map is formed in the RAM 31, and
As shown in the figure, the correction coefficient K ref is enriched for each of a plurality of operating regions determined according to the intake manifold absolute pressure PBA and the engine rotation speed Ne. Each of these correction coefficients Kre
f is initialized when power is turned on to the control circuit 20, and its initial value is 1.0. When the correction coefficient K rer is searched, the correction coefficient K is calculated using the following formula using the correction coefficient Kref.
ref is calculated (step 67).

Here, crer is a constant, 10000+ is 1 in hexadecimal
0000, and Douvn→ is the previous step 73
This is the output value DOLIT calculated in .

After calculating the correction coefficient Kref, the calculated correction coefficient Kref is written in the area of the Kref data map corresponding to the absolute pressure PBA and the engine speed Ne (step 68), and it is determined whether or not it is in the idle operating range. . (
Step 69). Furthermore, if the integral control is performed in step 61 or 65, the correction coefficient Kref corresponding to the intake manifold absolute pressure PEA and the engine speed Ne is set to K.
The engine is searched from the ref data map (step 70), and in step 69 it is determined whether or not the engine is in the idle operating range.

If it is in the idle operating range, the correction coefficient KAVε is the correction coefficient Kref read or calculated at that time.

In other words, if the value is equal to Krefo (step 71), and if it is not in the idle operating range, the correction coefficient KA V is calculated by the following formula using the read or calculated correction coefficient Krer.
E j! r is calculated (step 72).

...(2) Here, α and β are weighted average calculation rate change coefficients, KA
v i:n-+ is the correction coefficient KAVε determined during the previous execution of this routine, and once the correction coefficient KAVε is determined in step 71 or 72, it is held until the next execution of step 71 or 72. When the correction coefficient KAVE is determined in this way, the output is 1! by multiplying the reference value DBASε, the correction coefficient KAVE, and the air-fuel ratio correction coefficient KO2. Calculate ID0LJT Step 7
3) The calculated output value Dour is output to the drive circuit 28 (step 74).

The drive circuit 28 detects the current value flowing through the solenoid 9a of the solenoid valve 9 using a current detection resistor, compares the detected current value with the output value DOUT, and turns on and off the drive transistor according to the comparison result to control the solenoid 9a. supply current to. Therefore, the solenoid 9a has an output 1iI.
A current having a magnitude represented by Do u y flows, and an amount of secondary intake air proportional to the value of the current flowing through the solenoid 9a is supplied into the intake manifold 4. Also, the output value D
When OUT is 0, the solenoid valve 9 is closed and the supply of intake secondary air is stopped.

Note that the idle operating range is determined as follows, for example.

As shown in FIG. 6, the CPU 29 first determines whether the negative pressure switch 7 is on (step 81). When the negative pressure switch 7 is on, the absolute pressure PBA in the intake manifold 4 reaches a predetermined value PeArof (for example, 460 to 4
80a+11g) (step 82). If P8^<PaAref, it is assumed that a large negative pressure exists in the intake manifold 4 and the throttle valve 3 is fully closed, and the engine speed Ne is the predetermined value Ne! It is determined whether the value is smaller than (for example, 900 to 1000r, p, m) (step 83). If Ne<NeTDL, it is determined that the engine is in the idle operating range.

As shown in JJ and 1 Ri, in the air-fuel ratio control method of the present invention, when the operating region for learning control of the reference correction value changes, the reference correction value used for determining the air-fuel ratio control output value Douy immediately before the change is changed. Since the reference correction value KAVε for determining the air-fuel ratio control output value is set so that the reference correction value gradually changes from Immediately after the change, the air-fuel ratio control output value is prevented from being significantly different from the value immediately before the change. Therefore,
This makes it possible to improve the accuracy of air-fuel ratio control immediately after a change in the operating range, and to obtain good exhaust purification performance.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an apparatus to which the air-fuel ratio control method of the present invention is applied, FIG. 2 is a block diagram showing a specific configuration of a control circuit in the apparatus of FIG. 1, and FIGS. 3 and 6 are FIG. 4 is a flowchart showing the operation of the CPU, FIG. 4 is a diagram showing a DBASε data map, and FIG. 5 is a diagram showing a Kraf data map. Explanation of symbols for main parts 1... Carburetor 2... Air cleaner 3... Throttle valve 4... Intake manifold 7... Negative pressure Switch 8...Intake secondary air supply passage 9...Linear type solenoid valve 10...Absolute pressure sensor 11...Crank angle sensor 12... ... Cooling water temperature sensor 14 ... Oxygen concentration sensor 15 ... Exhaust manifold 33 ... Catalytic converter Applicant Honda Motor Co., Ltd. Agent Patent attorney Motohiko Fujimura Procedural Amendment Form Showa January 27, 63

Claims (1)

[Claims] In internal combustion engines equipped with an exhaust component concentration sensor in the exhaust system that generates an output according to the concentration of exhaust components in exhaust gas, air-fuel ratio control reference values are set in advance according to multiple operating parameters related to engine load, and air-fuel ratio feedback is performed. When the control conditions are satisfied, the output value of the exhaust component concentration sensor is compared with a target value at predetermined intervals, and an air-fuel ratio correction value is set according to the comparison result, so that at least the output value of the exhaust component concentration sensor is When a reversal with respect to the target value is detected, a reference correction value for correcting an error in the air-fuel ratio control reference value corresponding to the detected value of the plurality of operating parameters at that time is calculated, and based on the plurality of operating parameters. The air-fuel ratio control reference value corresponding to the detected values of the plurality of operating parameters is corrected according to the air-fuel ratio correction value and the reference correction value to adjust the air-fuel ratio to the target air-fuel ratio. An air-fuel ratio control method that determines a fuel ratio control output value and adjusts the air-fuel ratio of the air-fuel mixture supplied to the engine according to the control output value, and at least immediately after the operating region changes, the previous control output is used. A value between the reference correction value used for value determination and the latest reference correction value in the operating region at that time is set as the reference correction value for determining the current control output value. air-fuel ratio control method.