JPH0776539B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an air-fuel ratio control method for an internal combustion engine.

BACKGROUND ART For the purpose of purifying exhaust gas from internal combustion engines and improving fuel efficiency, the oxygen concentration in the exhaust gas is detected by an oxygen concentration sensor, and the air-fuel ratio of the air-fuel mixture supplied to the engine is set as a target value according to the output level of the oxygen concentration sensor. An air-fuel ratio control device that performs feedback control on the fuel ratio is known (for example, Japanese Examined Patent Publication 55
-3533 publication).

In such an air-fuel ratio control device, a reference value for air-fuel ratio control is set according to a plurality of engine operating parameters related to engine load, and the output value of an exhaust gas component concentration sensor such as an oxygen concentration sensor and a target air-fuel ratio are set at predetermined intervals. The output value is determined by comparing the target value corresponding to the fuel ratio and correcting the reference value according to the comparison result, and the opening of the air-fuel ratio adjusting solenoid valve is controlled according to the output value. Has become.

By the way, the base air-fuel ratio of the carburetor deviates from a predetermined value due to the aging of the carburetor or deterioration, so that the set reference value does not correspond to the target air-fuel ratio and an error is usually generated. is there. Therefore, when the error of the reference value becomes larger than the predetermined value, it becomes impossible to control the air-fuel ratio of the air-fuel mixture supplied to the engine to the target air-fuel ratio with high accuracy by the air-fuel ratio feedback control, and good exhaust gas purification performance is obtained. There was a problem that it could not be obtained.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an air-fuel ratio control method capable of obtaining a good exhaust gas purification performance even if the error in the reference value exceeds a predetermined value.

The air-fuel ratio control method of the present invention is characterized in that a correction value representing an error of the reference value is calculated, and the target value to be compared with the output value of the exhaust gas component concentration sensor is corrected according to the magnitude of the calculated correction value. .

Embodiments 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 a vehicle-mounted internal combustion engine to which the air-fuel ratio control method of the present invention shown in FIG. It is supplied to the engine 5 via the intake manifold 4. A throttle valve 6 is provided in the vaporizer 3, and a venturi 7 is formed upstream of the throttle valve 6.

The intake manifold 4 and the vicinity of the air outlet of the air cleaner 2 are connected by an intake secondary air supply passage 8.
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.

On the other hand, 10 is an absolute pressure sensor which is provided in the intake manifold 4 and which produces an output at a level according to the absolute pressure in the intake manifold 4, and 11 produces a pulse in response to rotation of a crankshaft (not shown) of the engine 5. Crank angle sensor, 12 is a cooling water temperature sensor that produces an output at a level according to the cooling water temperature of the engine 5, and 14 is oxygen that is provided in the exhaust manifold 15 of the engine 5 and that produces an output according to the oxygen concentration in the exhaust gas. It is a density sensor. A catalytic converter 33 is provided in the exhaust manifold 15 downstream of the position where the oxygen concentration sensor 14 is arranged in order to promote reduction of harmful components in the exhaust gas.
Is provided. Linear solenoid valve 9, absolute pressure sensor
The crank angle sensor 11, the water temperature sensor 12, and the oxygen concentration sensor 14 are connected to the control circuit 20. The control circuit 20 is further connected to a vehicle speed sensor 16 which produces an output of a level according to the speed of the vehicle and a throttle valve opening sensor 17 which is composed of a potentiometer and produces an output of a level according to the opening of the throttle valve 6. Has been done.

As shown in FIG. 2, the control circuit 20 is a level conversion circuit for converting the output levels of the absolute pressure sensor 10, the water temperature sensor 12, the oxygen concentration sensor 14, the vehicle speed sensor 16 and the throttle valve opening sensor 17.
21, a multiplexer 22 that selectively outputs one of the sensor outputs that have passed through the level conversion circuit 21, and an A / D that converts the signal output from this multiplexer 22 into a digital signal.
The D converter 23, the waveform shaping circuit 24 that 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 are output from a clock pulse generation circuit (not shown). A counter 25 for measuring the number of clock pulses generated, a drive circuit 28 for driving the solenoid valve 9, and a digital operation according to a program
It comprises a CPU (central processing unit) 29, a ROM 30 in which various processing programs and data are written in advance, and a RAM 31. The solenoid 9a of the solenoid valve 9 is connected in series with a drive transistor of the drive circuit 28 and a current detection resistor (both not shown), and a power supply voltage is supplied across the series circuit. The multiplexer 22, the A / D converter 23, the counter 25, the drive circuit 28, the CPU 29, the ROM 30 and the RAM 31 are connected to each other by the input / output bus 32.

In such a configuration, from the A / D converter 23, the absolute pressure in the intake manifold 4, the cooling water temperature, the oxygen concentration in the exhaust gas,
Information on vehicle speed and throttle valve opening is selected alternatively, and counter 25
The information indicating the engine speed is sent to the CPU 29 from the input / output bus 3
Each is supplied via 2. CPU 29 has a predetermined cycle as described later
An internal interrupt signal is generated every T ₁ (for example, 5 msec), and the solenoid of the solenoid valve 9 is responsive to the interrupt signal.
The output value T _OUT representing the value of the current supplied to 9a is calculated as data, and the calculated output value T _OUT is supplied to the drive circuit 28. The output value of the drive circuit 28 is the current value flowing through the solenoid 9a.
The value of the current flowing through the solenoid 9a is closed-loop controlled so that it has a value according to T _OUT .

Next, the operation of such an air-fuel ratio control device is shown in the CP shown in FIG.
A detailed description will be given according to the operation flow chart of U29.

As shown in FIG. 3, the CPU 29 first sets a reference value D _BASE representing the reference current value supplied to the solenoid valve 9 each time an interrupt signal is generated (step 51). Since the ROM30 are written in advance reference value D _BASE determined from within the intake manifold absolute pressure P _BA and the engine speed Ne as shown in FIG. 4 is a D _BASE data map, the CPU29 absolute pressure P _BA and engine The rotation speed Ne and are read, and the reference value D _BASE corresponding to each read value is searched from the D _BASE data map. After setting the reference value D _BASE , the operating status of the vehicle (including the operating status of the engine) is the air-fuel ratio feedback (F / B).
It is determined whether the control conditions are satisfied (step 5).
2). This determination is determined from the absolute pressure P _BA in the intake manifold, the cooling water temperature Tw, the vehicle speed V, and the engine speed Ne. For example, it is assumed that the air-fuel ratio feedback control condition is not satisfied at the low vehicle speed and the low cooling water temperature. If it is determined that the air-fuel ratio feedback control condition is not satisfied, the reference value D _BASE is multiplied by the correction value Kref and the calculated value is used as the output value T _OUT (step 53). Since the RAM31 correction value Kref for each area corresponding to the inside of the intake manifold absolute pressure P _BA and the engine speed Ne as shown in FIG. 5 it is written as Kref data map, CPU 29 is an absolute pressure P _BA The correction value Kref corresponding to the engine speed Ne is retrieved from the Kref data map and used to calculate the output value T _OUT .

On the other hand, if it is determined that the air-fuel ratio feedback control condition is satisfied, it is determined whether or not the counting time of the internal timer counter A (not shown) of the CPU 29 has passed a predetermined time Δt ₁ (step 56). . The predetermined time output Δt ₁ corresponds to the response delay time from the supply of the secondary intake air until the result is detected by the oxygen concentration sensor 14 as a change in the oxygen concentration in the exhaust gas. When the predetermined time Δt ₁ has elapsed from the time when the time counter A was reset and started counting, the time counter A is reset and counting is started from the initial value (step 57). That is, it is determined in step 56 whether or not the predetermined time Δt ₁ has elapsed after the time counter A started counting from the initial value by executing step 57. When the counting of the predetermined time Δt ₁ by the time counter A is started in this way, the output value L _{O2 of the} oxygen concentration sensor 14 is determined from the oxygen concentration information.
Is larger than the target value Lref corresponding to the target air-fuel ratio (step 58). That is, it is determined whether the air-fuel ratio of the air-fuel mixture supplied to the engine 5 is leaner than the target air-fuel ratio. If L _O2 > Lref, the air-fuel ratio is leaner than the target air-fuel ratio, so it is determined whether or not the air-fuel ratio flag F _AF indicating the determination result of the previous step 58 is "1" (step 59). If F _AF = 0, it is determined that the previous air-fuel ratio is rich, and since it has been inverted from rich to lean, the proportional subtraction value P _L is calculated (step 60). Subtracted value P _L
Is obtained by multiplying (K ₁ · I _L ) by a constant K ₁ (> 1) and an integral subtraction value I _L described later. After calculating the subtraction value P _L , the correction value I _OUT already calculated by executing this A / F routine is read from the storage position a _{1 of the} RAM 31, and the subtraction value P _L is subtracted from the read air-fuel ratio correction value I _OUT to calculate it. The value is set as a new correction value I _OUT and is written in the storage position a _{1 of the} RAM 31 (step 61). If F _AF = 1, it is determined that the air-fuel ratio was lean last time, so the integral subtraction value I _L is calculated (step 62). The subtracted value I _L is a constant K ₂ , the engine speed Ne
And the absolute pressure P _BA are multiplied by each other (K ₂ · Ne · P _BA ) and are dependent on the intake air amount of the engine 5. After the subtraction value I _L is calculated, the correction value I _OUT already calculated by executing this A / F routine is stored in the RAM 31 at the storage position a.
Read from ₁ , subtract the subtraction value I _L from the read correction value I _OUT, and use the calculated value as the new correction value I _OUT.
To the memory location a ₁ of (step 63). After the correction value I _OUT is calculated in step 61 or 63, “1” is set to the flag F _AF to indicate that the air-fuel ratio is lean (step 64), and the reference value D _BASE set in step 51 is set.
The correction value I _OUT is added to and the addition result is used as the output value T _OUT (step 65). On the other hand, in step 58, L _O2 ≦ Lre
If f, the air-fuel ratio is richer than the target air-fuel ratio, so it is determined whether or not the air-fuel ratio flag F _AF is "O" (step 66). If F _AF = 1, it is determined that the previous air-fuel ratio is lean, and since lean was reversed to rich, the proportional addition value P _R
Is calculated (step 67). The added value P _R is a constant K ₃ (> 1)
And the integrated addition value I _R described later are multiplied by each other (K ₃ · I _R ). After calculating the added value P _R, the correction value I _OUT already calculated by executing this A / F routine is stored in RAM 31.
Reading from the storage position a _1, adds the read correction value I _OUT and additional value P _R, and writes the calculated value in the storage position a ₁ of the new correction value I _OUT Toshikatsu RAM 31 (step 68). If F _AF = 0 in step 66, it is determined that the air-fuel ratio was rich in the previous time, so the integral addition value I _R is calculated (step 69). The added value I _R is a constant K ₄ (≠ K ₂ ), engine speed
It is obtained by multiplying Ne and the absolute pressure P _BA by each other (K ₄ · Ne · P _BA ) and depends on the intake air amount of the engine 5. After the addition value I _R is calculated, the correction value I _OUT already calculated by executing the A / F routine is stored in the RAM 31 at the storage position a ₁
Read from the read correction value by adding the addition value I _R in I _OUT writes the calculated value in the storage position a ₁ of the new correction value I _OUT Toshikatsu RAM 31 (step 70). After the correction value I _OUT is calculated in step 68 or 70, “0” is set to the flag F _AF to indicate that the air-fuel ratio is rich (step 7
1) Calculate the correction value Kref (step 72). Correction value Kref
Is calculated from the equation Kref = α · I _OUT + (1−α) · Kref _n-1 . Here, α is a constant, and Kref _n−1 is a correction value Kref obtained by executing the previous step 72. The calculated correction value Kref is stored in the Kref data map position of the RAM 31 corresponding to the intake manifold absolute pressure P _BA and the engine speed Ne at this time. The calculated correction value Kref is 0.
It is determined whether it is greater than 9 and less than 1.1 (step 73). If 0.9 <Kref <1.1, the output value T _OUT is immediately calculated by executing step 65. Kref ≦ 0.9 or Kre
If f ≧ 1.1, it is considered that the correction value Kref is large due to the deviation of the base air-fuel ratio of the carburetor, and the target value Lref corresponding to the target air-fuel ratio is corrected (step 74). The output value T _OUT is calculated by execution. For example, the sixth
Target value Lref corresponding to correction value Kref with the characteristics shown in the figure
Is previously stored in the ROM 30 as an Lref data map, and if Kref ≦ 0.9 or Kref ≧ 1.1, the target value Lref corresponding to the correction value Lref is searched from the Lref data map. When the correction value Kref is 1.1 or more, the target value Lref is reduced because the base air-fuel ratio of the carburetor is shifted to the rich side,
When the correction value Kref is 0.9 or less, the target value Lref is increased because the base air-fuel ratio of the carburetor is shifted to the lean side. After calculating the output value T _OUT in step 53 or 65, and outputs the output value T _OUT with respect to the drive circuit 28 (step 75).

In addition, as shown in FIG. 6, the target value for the correction value Kref
The target value Lref may be continuously determined with respect to the correction value Kref instead of being determined stepwise. Also RA
M31 is a non-volatile memory content that does not volatilize even when the operation of the engine 5 is stopped, and each Kref in the Kref data map is initially set to 1 before the use of this device.

The drive circuit 28 detects the current value flowing through the solenoid 9a of the solenoid valve 9 by the current detection resistor, compares the detected current value with the output value T _OUT, and turns on / off the drive transistor according to the comparison result, thereby turning on / off the solenoid 9a. Supply current to the. Therefore, the current represented by the output value T _OUT flows through the solenoid 9a, and the intake secondary air in an amount proportional to the value of the current flowing through the solenoid 9a of the solenoid valve 9 is supplied into the intake manifold 4.

After the time counter A is reset in step 57 and counting from the initial value is started, a predetermined time Δt ₁
If it is determined in step 56 that has not elapsed, step 65 is immediately executed, and in this case, the correction value I _OUT obtained by the previous execution of the A / F routine is read.

Further, in the above-described embodiment of the present invention, the air-fuel ratio control device provided with the linear type electromagnetic valve has been described. However, the electromagnetic on-off valve is provided in the intake secondary air supply passage, and the electromagnetic valve is provided at predetermined intervals. Open / close valve opening time T _OUT (= reference valve opening time T
_The present invention can also be applied to an air-fuel ratio control device that calculates _BASE + correction value I _OUT ) and opens the solenoid on-off valve for the valve opening time T _OUT .

As described above, in the air-fuel ratio control method of the present invention, the correction value representing the error of the reference value is calculated, and the target value corresponding to the target air-fuel ratio to be compared with the output value of the exhaust gas component concentration sensor is calculated. Since it is changed according to the magnitude of the correction value, the air-fuel ratio can be controlled to the target air-fuel ratio with high accuracy even if the deviation of the base air-fuel ratio of the carburetor becomes large, and the exhaust purification performance can be improved. Of.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an apparatus to which the air-fuel ratio control method of the present invention is applied, FIG. 2 is a block diagram showing a concrete configuration of a control circuit in the apparatus of FIG. 1, and FIG. FIG. 4 is a flow chart showing the D _BASE data map written in the ROM, FIG. 5 is a diagram showing the Kref data map written in the RAM, and FIG. 6 shows the correction value Kref-target value Lref characteristics. FIG. 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 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

Claims (1)

[Claims] 1. An internal combustion engine having an exhaust component concentration sensor for producing an output according to an exhaust component concentration in exhaust gas in an exhaust system, wherein a reference value for air-fuel ratio control is set in accordance with a plurality of engine operating parameters related to engine load. Set, compare the output value of the exhaust gas component concentration sensor and the target value for each predetermined cycle, determine the output value for the target air-fuel ratio by correcting the set reference value according to the comparison result and the reference value Is an air-fuel ratio control method for calculating a correction value representing the error, wherein the target value is corrected according to the magnitude of the correction value when the correction value is calculated.