JPS62265442A - Air-fuel ratio controlling method for internal combustion engine - Google Patents

Abstract

PURPOSE:To stabilize the rotation of an engine by stopping a P-control and obtaining an air-fuel ratio controlling value only by means of an I-control when an idling condition is detected, at the time of making a PI (proportional-plus- integral) control of the secondary air feeding quantity of intake air in accordance with the detected result of air-fuel ratio. CONSTITUTION:When an engine 5 is operated, it is judged by a control circuit 20 whether an air-fuel ratio feedback control condition is satisfied or not and, when judged yes, a reference current value is retrieved in accordance with the outputs of an absolute pressure sensor 10 and a crank angle sensor 11. And, the output of an O2 sensor 14 is composed with a reference value corresponding to a target air-fuel ratio and, when it is detected that the output of the O2 sensor is changed form a larger value than its target value to a smaller value or the other way around, at least one of a P-control and an I-control is carried out. In this case, if the idling condition of an engine is detected, and air-fuel ratio controlling value is obtained only by means of the I-control, to feedback control the air-fuel ratio of a mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining the air-fuel ratio of internal combustion engines.

Before purifying the exhaust gas of an internal combustion engine and improving fuel efficiency, the oxygen concentration in the exhaust gas is detected by an oxygen Q degree sensor, and the air-fuel mixture supplied to the engine is adjusted according to the output level of this oxygen concentration sensor. An air-fuel ratio control device that performs feedback control of an air-fuel ratio is known.

As this air-fuel ratio control device, a solenoid valve is provided in the intake secondary air supply passage communicating downstream of the carburetor throttle valve, and the opening degree of the solenoid valve is adjusted according to the output level of the air temperature sensor f. Feedback system to control the intake secondary air supply ω!21
There is an air-fuel ratio II 1211 device with an intake secondary air supply system for 1 (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 depending on the determination result, It is usual to perform PI (proportional integral) control of the intake secondary air supply by determining the proportional ω and the proportional integral by δ.

By the way, when the engine is idling, the exhaust flow rate is lower than when the engine is in steady operation, so the temperature of an exhaust component temperature sensor such as an oxygen concentration sensor is lowered, and the detection sensitivity of the oxygen concentration sensor is thereby lowered. Also, since the amount of air-fuel mixture supplied to the engine from the carburetor etc. is small, the P I fil mentioned above is used to improve exhaust purification performance during idling operation.
When IIa is performed, the reversal period in which the air-fuel ratio detected by the oxygen concentration sensor is reversed from one-liter to rich or from rich to lean becomes longer. As a result, there is a problem in that the range of air-fuel ratio fluctuation becomes large, resulting in a fluctuation in engine speed Ia.

Therefore, an object of the present invention is to provide an air-fuel ratio control method that can stabilize the engine rotational speed during idling operation.

The air-fuel ratio control method of the present invention is characterized in that when the idle operating state of the engine is detected, the air-fuel ratio control value is obtained only by integral control.

Disaster-” L Once Embodiments of the present invention will be described below with reference to the drawings.

Air-fuel ratio control lI of the intake secondary air supply system of an on-vehicle internal combustion engine applying the air-fuel ratio control method of the present invention shown in FIG.
When equipped with J3, intake air is supplied to the engine 5 from an atmospheric air intake port 1 via an air cleaner 2, a carburetor 3, and an intake manifold 4.

The carburetor 3 is provided with a throttle valve 6, and a venturi 7 is formed upstream of the throttle valve 6.

The intake manifold 4 and the vicinity of the air discharge port of the air cleaner 2 are communicated through an intake secondary air supply passage 8.

A linear solenoid valve 9 is provided in the intake secondary air supply passage 8 . The degree of opening of the solenoid valve 9 changes in proportion to the direct current supplied to the solenoid 9a.

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 cold IJ water temperature sensor that generates an output at a level corresponding to the cooling water temperature of the engine 5; 14 is a cold IJ water temperature sensor that is installed in the exhaust manifold 15 of the engine 5 and outputs a voltage that corresponds to the solubility in the exhaust gas; This is an oxygen concentration sensor that generates

A catalytic converter 33 is provided in the exhaust manifold 15 downstream of the oxygen concentration sensor 14 in order to promote reduction of harmful components in the exhaust gas. Solenoid valve 9
, absolute pressure sensor 10. The crank angle sensor 11, water temperature sensor 12, and oxygen concentration sensor 14 are connected to a control circuit 20. The control circuit 20 further includes a vehicle speed sensor 16 that generates an output level that corresponds to the speed of the vehicle, and a throttle valve opening sensor 17 that is composed of a potentiometer and generates an output level that corresponds to the opening degree of the throttle valve 6. It is connected.

The control circuit 20 includes an absolute pressure sensor 10 as shown in FIG.
, water temperature sensor 12, oxygen concentration sensor 14, vehicle speed sensor 1
a level conversion circuit 21 that converts the respective output levels of the throttle valve opening sensor 6 and the throttle valve opening sensor 17; and a multi-break controller 2 that selectively outputs one of the outputs of each sensor that has passed through the level conversion circuit 21.
2, and an A/D converter i'! that converts the signal output from the multi-branch 22 into a digital signal. ! i23 and
The waveform shaping circuit 24 shapes the output signal of the crank angle sensor 11, and the generation interval of the TDC signal output as a pulse from the waveform shaping circuit 24 is determined by the number of clock pulses output from a clock pulse generation circuit (not shown). A counter 25 for measuring, a drive circuit 28 for controlling the solenoid valve 9, two CPUs (central processing circuits) for performing digital processing according to the program, and a ROM 30 pre-loaded with various processing programs and data. and RAM31. The solenoid 9a of the electromagnetic valve 9 is connected in series with a drive 1 transistor and a current detection resistor (both not shown) of the drive circuit 28, and a power supply voltage is supplied across the series circuit. multi breakley
22, H/'D converter 23, counter 25, drive circuit 28, CPU 29, ROM 30 and RAM 311; L
J and H are connected to the input/output bus 32.

In this configuration, the A/D converter 23 selectively transmits information on the absolute pressure in the intake manifold 4, the cooling water temperature, the oxygen concentration in the exhaust gas, the vehicle speed, and the throttle valve opening, and the counter 25 selectively transmits information on the engine rotation. Information representing the numbers is supplied to the CPU 29 via an input/output bus 32, respectively. The CPU 29 is set to a predetermined circle f91T+ (for example, 50m5ec) like a book.
), a stray signal of 1 is generated internally for every interrupt signal, and the supply current value DOUT to the solenoid 9a of the solenoid valve 9 is calculated as data, and the supply current value DOLIT that is 0 is calculated as data. The signal is supplied to the drive circuit 28. Drive circuit 2
8, the current value flowing through the solenoid 9a is the supply current value DOU
The current value flowing through the solenoid 9a is controlled in a closed loop so that the current value becomes T.

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.

First, the CPU 29 checks the driving status of the vehicle every time an interrupt signal is generated]
air-fuel ratio feedback (F,/B) control system V1. It is determined whether or not the conditions are satisfied (step 51). This determination is determined from the absolute fluid in the intake manifold, the cooling water temperature, the vehicle speed, and the engine rotation speed. For example, at low vehicle speed and low cold 7J]
．． 1, it is said that the air-fuel ratio feedback control condition is not satisfied. Here, if it is determined that the air-fuel ratio feedback control condition a'[ is not satisfied, the electromagnetic button t9 is closed and the air-fuel ratio feedback control is performed. The supply current 1i1ff D OLJ T is made equal to ◯ to stop the current (step 52). On the other hand, if it is determined that the air-fuel ratio feedback system 11 conditions are satisfied, the v quasi-current value DEIASE of the current value supplied to the solenoid valve 9 is set (step 53
), as shown in FIG. 4, the J1Z quasi-current 1-direction De ASE determined from the absolute Ff in the intake manifold, PBA, and the engine speed Ne is written in advance as a DBASE data map in the ROM 30, so the CPU 29
reads the absolute pressure PEA and engine speed Ne, and calculates the base 4L current 1st line Da A S corresponding to each read value.
Search for E from the DBAsE data map. Next, the output voltage VO2 of the oxygen concentration sensor 14 is read as an oxygen concentration sensor and it is determined whether the output voltage VO2 is smaller than the reference value VREF corresponding to the target air-fuel ratio (step 54). If VO2<VREF, the air-fuel ratio is lean, so it is determined whether the air-fuel ratio flag FAF is equal to O (step 55). If FA F-0, the air-fuel ratio continues to be in a lean state. Assuming that there is, FAF=1
If so, it is assumed that the air-fuel ratio has reversed from rich to lean. If VO2≧VREF, the air-fuel ratio is rich, so it is determined whether the air-fuel ratio flag FAF is equal to 1 (step 56). If FAF=1, it is assumed that the air-fuel ratio continues to be rich, and if FAE=O, it is not assumed that the air-fuel ratio has changed from lean to rich. When the air-fuel ratio is reversed in this way, the variable N is reset by making it equal to an integer N+ (for example, 3) (step 57), and it is determined whether or not the engine is in an idling state (step 58). The idle operating state is, for example, the throttle valve opening θth
, or when the intake manifold absolute pressure PEA is determined, and when the throttle valve opening θth is less than the predetermined opening 01, or when the intake manifold absolute sweat PBA is less than the predetermined pressure 1)I, it is determined that the engine is idling.

When not in idle operation (Oxygen concentration cent ±1
4 output voltage VO2 corresponds to the target air-fuel ratio.
RE r: Determine whether there is a smaller one (step 5
). If Vo2<VnEp, the air-fuel ratio is leaner than the target air-fuel ratio, so the air-fuel ratio flag FA+: is set to 01. : Equally (step 60), the predetermined ratio +x+ :n p is subtracted by 0 from the air-fuel ratio feedback correction coefficient KO2, and the calculated value is newly set as the i1j positive coefficient KQ2 (step 61).
. VO2≧VRar/; Since the air-fuel ratio is richer than the target air-fuel ratio, the air-fuel ratio flag FAF is set equal to 1 (Step 62), the air-fuel ratio feedback correction coefficient KO
Add a predetermined proportion ff1P to 2 and use the calculated field as a new correction coefficient K.

2 and T (step 63), J to step 61 or 63
3 and after the correction system FJ K 02 () appears, step 53
The correction coefficient Ko2 is applied to the reference current supply DeASE set in Step 64), and the critical state result is set as the supply current value DOUT.
8 (step 65). Also step 5
If it is determined in step 8 that the engine is in an idling state, step 64 is immediately executed and the supply current value D o u
r @calculate.

On the other hand, in steps 53 to 56, the air-fuel ratio is reversed to 1.
When it is determined that there is no air pressure, the absolute pressure PBA in the intake manifold is read and the absolute pressure PB△ is 410 mm.
Determine whether it is greater than 11g (step 66)
, P8A≦410 mm11g, the load is low, so reset the variable N by making it equal to the integer N1 (step 67), and set the unit product numerator lJi I n equal to the initial field 11 (step 68), Pa A>
If 410II 1ml 1g, 4rX negative? m te tx
Ino so weird v! Determine whether IN is O(,:'yr) (step 69). If N≠0, subtract 1 from variable N and set its → output value as new variable N (step 7o),
Unit integral Φ1. is equal to the initial value It (step 6
8). If N=O, the previous intermediate integral mln is ■. -1
Read its unit product numerator fi-1 as the coefficient +
(For example, 1.1) is multiplied by ('I) and the p output value is set as the current intermediate product numerator filn (step 71), and it is determined whether or not the current unit integral integral In is greater than or equal to the guard lfl I c. (Step 72). If In≧tc, the current single (
Q integral quantity I. is equal to the guard value 1c (step 73
), if In < Ic, the intermediate integral In I n calculated in step 71 is retained.

When the unit integral φ]n is determined, the output type I'1Fvo2 of the oxygen temperature sensor 14 becomes the reference value VRE corresponding to the target empty ratio.
It is determined whether or not it is smaller than F (step 74).

If VO2<VREF, the air-fuel ratio is leaner than the target air-fuel ratio, so set the air-fuel ratio flag FAF to Ol, :=
Step 75), the amount of change ΔVO2 (=VO2Vo2n) between the previous output voltage ■02n-1 and the current output voltage VO2
-+) is smaller than a predetermined value Δ■02H (negative value) (step 76). ΔVO2<Δ■o2H
Then, since the air-fuel ratio continues to lean, the m-order product numerator fi I n is subtracted from 02 to the correction coefficient, and its ejection 1
KO2 is set as the current correction coefficient KO2 (step 77). Δ
If VO2≧ΔV02H, the leanness of the air-fuel ratio has decreased, so add unit integral I. To prevent an increase in the unit product fil. is equal to the initial value 11 in step 78.
), and by executing step 77, the unit product numerator fiIn is subtracted from the correction coefficient KO2, and the calculated first shift is set as the current correction coefficient KO2. In step 74, VO2≧V
If RE F, the air-fuel ratio is richer than the target air-fuel ratio, so the air-fuel ratio flag FA is set equal to 1 and step 79 is executed.
), previous output voltage V O2n-+ and current output voltage V
Change with O2 h1△Vo 2 (=Vo 2 - VO2
It is determined whether n-+) is greater than a predetermined value Δ■02 (positive value) (step 80). ΔVO2>ΔVO
If it is 2L, the enrichment of the air-fuel ratio continues, so the unit integral amount In is added to the correction coefficient KO2, and the resulting value is set as the current correction coefficient KO2 (step 81).

If ΔV○2≦ΔV02, the degree of enrichment of the air-fuel ratio has decreased, so in order to prevent the middle integral from increasing by 11°, i
The 11th-order product numerator fl + n is set to the initial value 11 (step 82), and by executing step 81, the unit integral m I n is added to the correction coefficient KO2, and the output value is set as the current correction coefficient KO2.

In this way, in step 77 or 81, J5 corrects (f
After determining the + number KO2, the supply current value Douv is set by executing steps 64 and 65, and the supply current 1i11Dou
v is supplied to the drive circuit 28.

The drive J 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 supplied current value DOUT, and turns on and off the drive transistor according to the comparison result. Solenoid 9
Supply current to a.

Therefore, a current having the supply current value DOLJT flows through the solenoid 9a, and an amount of secondary intake air proportional to the current value flowing through the solenoid 9a is supplied into the intake manifold 4. In addition, when the supply current 1-direction DouT is O, M
[Valve a 9 closes to valve 111, and intake secondary air is supplied.

In an apparatus to which the air-fuel ratio i, 111211 method of the present invention is applied, if the air-fuel ratio detected from the oxygen concentration is reversed with respect to the target air-fuel ratio and is not in an idling operating state, first, the proportional amount of the correction coefficient KO2 is PI (proportional-integral) control is performed in which the air-fuel ratio is changed in the air-fuel ratio direction opposite to the reversal direction, and then the integral m of the correction coefficient KO2 is gradually changed. During this PI sub-control, if the rich or lean state continues and the load is not low, after the air-fuel ratio is reversed, the air-fuel ratio per unit is increased as shown in Figure 5 in order to improve the responsiveness to changes in the air-fuel ratio of the supplied mixture. The integral amount is increased as time passes, and thereafter, when the change in the air-fuel ratio per unit time becomes gradual, the integral amount is fixed at the initial value 11 until the air-fuel ratio is reversed to prevent overshoot after the reversal. Therefore, as long as the air-fuel ratio of the supplied air-fuel mixture is approximately stable at the target air-fuel ratio, the inversion period of the air-fuel ratio becomes intermediate, so that the integral a per unit is not increased. On the other hand, during idling, I control is performed in which only the integral amount of correction coefficient KO2 is gradually changed in order to prevent fluctuations in engine speed due to air-fuel ratio control.

Note that in the embodiment of the present invention described above, step 7
The integral per unit (d is designed to change depending on the operation of In = + ・11-1 in 1, but it is not limited to this). It is also possible to change Ia every minute.

Furthermore, in the above-described embodiments of the present invention, an air-fuel ratio control device equipped with a linear solenoid valve has been described. TouT between valve opening surfaces (=standard valve opening time TOA
SEX correction staff HKo2) and its amount valve time TO
The present invention can also be applied to an air-fuel ratio control device in which only UT has 611 electromagnetic on-off valves.

Further, in the embodiment of the present invention described above, the air-fuel ratio control method of the present invention is applied to the air-fuel ratio control g head of the intake secondary air supply system, but the fuel is injected and supplied by the injector and the injection speed is controlled. The present invention can also be applied to devices of this type.

As described above, in the air-fuel ratio control method of the present invention, when the idle operating state of the engine is detected, the P control is stopped and the air-fuel ratio control is obtained and supplied only by the I1tlJ control. Since the air-fuel ratio of the air-fuel mixture is gradually changed, fluctuations in the air-fuel ratio are smaller than in the case of PI control, and the engine speed can be stabilized.

4. Explanation of how to hit the target Figure 1 is a schematic diagram showing an air-fuel ratio control device to which the air-fuel ratio control method of the present invention is applied, and Figure 2 shows the specific configuration of the control circuit in the device shown in Figure 1. 3 is a flowchart showing the operation of the CPU, FIG. 4 is a diagram showing a data map written in the ROM, and FIG. 5 is a diagram showing the change characteristics of the unit integral amount In.

Explanation of symbols of main parts 2...Air cleaner 3... vaporizer 4...Intake manifold 6... Throttle valve 7...Venturi 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 17... Throttle valve opening sensor 33...Catalytic converter Applicant: Honda Motor Co., Ltd. Agent: Patent Attorney: Motohiko Fujitoshi Figure 4 r, p, m Figure 5

Claims (1)

[Claims] The exhaust component concentration detection value detected by the exhaust component concentration sensor provided in the exhaust system of the internal combustion engine is compared with a reference value corresponding to the target air-fuel ratio, and from the comparison result, the exhaust component concentration detection value is lower than the target value. Proportional control that changes the air-fuel ratio control value when detecting a reversal from large to small or from small to large, and Integral control that increases or decreases the air-fuel ratio control value at predetermined intervals according to the comparison result. The air-fuel ratio control method corrects the air-fuel ratio of the air-fuel mixture supplied to the engine according to the air-fuel ratio control value by performing at least one of the following: An air-fuel ratio control method characterized by obtaining an air-fuel ratio control value.