JP2609230B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

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

BACKGROUND ART Oxygen concentration in exhaust gas is detected by an oxygen concentration sensor for purifying exhaust gas of an internal combustion engine, improving fuel efficiency, etc.
There is known an air-fuel ratio control device that performs feedback control of the air-fuel ratio of an air-fuel mixture supplied to an engine in accordance with the output level of the oxygen concentration sensor. As this air-fuel ratio control device, an electromagnetic valve is provided in an intake secondary air supply passage communicating with the carburetor throttle valve downstream, and the opening degree of the electromagnetic valve, that is, the amount of intake secondary air supply is controlled according to the output level of the oxygen concentration sensor. There is an air-fuel ratio control device of an intake secondary air supply system for feedback control (for example, Japanese Patent Publication No. 55-3533).

In such a conventional air-fuel ratio control device, 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 according to the determination result. Usually, PI (proportional integration) control of the intake secondary air supply amount by setting a proportional amount and an integral amount, or I (integral) control of the intake secondary air supply amount by setting only the integral amount.

However, when the operating state of the engine shifts from the acceleration operation to the steady operation, or shifts from the idling operation to the acceleration operation, the air-fuel ratio of the supplied air-fuel mixture may greatly deviate from the target air-fuel ratio. I
As a matter of course, the PI control operates so as to cope with the deviation of the air-fuel ratio by the integral amount, so that there is a problem that responsiveness is poor and good exhaust gas purification performance cannot be obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a PI capable of improving exhaust purification performance immediately after a change in an operating state of an engine.
An object of the present invention is to provide an air-fuel ratio control method by control, I control, or the like.

An air-fuel ratio control device of the present invention compares an exhaust component concentration detection value detected by an exhaust component concentration sensor provided in an exhaust system of an internal combustion engine with a reference value corresponding to a target air-fuel ratio, and performs the comparison every predetermined cycle. An air-fuel ratio control method that performs integral control to increase or decrease the air-fuel ratio control value by an integral amount in accordance with the comparison result and corrects the air-fuel ratio of the air-fuel mixture supplied to the engine according to the air-fuel ratio control value. A first setting step of setting an integral amount to a predetermined value when detecting that the engine is in a low load state; and setting the integral amount to be larger than a predetermined value when detecting that the engine is in a load state other than the low load state. In the second setting step, and when the amount of change in the exhaust component concentration detection value per unit time is large, the integral control increases or decreases the air-fuel ratio control value by the integration amount set in the first or second setting step. It is characterized by having a step.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In the air-fuel ratio control device of the secondary air supply system for an in-vehicle internal combustion engine to which the air-fuel ratio control method of the present invention shown in FIG. 1 is applied, intake air flows from an air intake port 1 through an air cleaner 2, a carburetor 3, Then, the air is supplied to the engine 5 through the intake manifold 4. The vaporizer 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 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 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 generates an output of a level corresponding to the absolute pressure in the intake manifold 4, and 11 generates a pulse in accordance with the rotation of a crankshaft (not shown) of the engine 5. A crank angle sensor, 12 is a cooling water temperature sensor for generating an output of a level corresponding to the cooling water temperature of the engine 5, and 14 is provided with an exhaust manifold 15 of the engine 5 and generates an output voltage corresponding to the oxygen concentration in the exhaust gas. It is an oxygen concentration sensor. Oxygen concentration sensor
A catalytic converter 33 is provided in the exhaust manifold 15 downstream of the location where the exhaust gas is disposed to promote reduction of harmful components in exhaust gas. Solenoid valve 9, absolute pressure sensor 10, crank angle sensor 11, water temperature sensor 12, and oxygen concentration sensor 14
Is connected to the control circuit 20. The control circuit 20 further includes a vehicle speed sensor 16 for generating an output of a level corresponding to the speed of the vehicle.
And a throttle valve opening sensor 17 which comprises a potentiometer and generates an output of a level corresponding to the opening of the throttle valve 6.

The control circuit 20 includes a level conversion circuit 21 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 as shown in FIG. A multiplexer 22 for selectively outputting one of the sensor outputs through a circuit 21, and a signal output from the multiplexer 22 being converted into a digital signal
An A / D converter 23, a waveform shaping circuit 24 for shaping the waveform of the output signal of the crank angle sensor 11, and a clock pulse generating circuit (not shown) for generating the TDC signal output from the waveform shaping circuit 24 as a pulse. A counter 25 that measures the number of clock pulses output from the CPU, a drive circuit 28 that drives the solenoid valve 9 to open, a CPU (central processing circuit) 29 that performs a digital operation according to a program, and various processing programs and data are stored in advance. It consists of a written ROM 30 and a RAM 31. The solenoid 9a of the solenoid valve 9 is connected in series to a drive transistor of a drive circuit 28 and a current detection resistor (both not shown), and a power supply voltage is supplied between both ends of the series circuit. Multiplexer 22, A / D converter 23, counter 2
5, drive circuit 28, CPU29, ROM30 and RAM31
Are connected to each other.

In such a configuration, the 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 can be alternatively selected from the A / D converter 23, and the engine rotation can be determined from the counter 25. Information representing the numbers is supplied to the CPU 29 via the input / output bus 32, respectively. CPU29 predetermined period T ₁ as mentioned below (e.g., 50 m sec) are adapted to generate an internal interrupt signal each time, the supply current value D _OUT to the solenoid 9a of the solenoid valve 9 in response to an interrupt signal Calculated as data,
The calculated supply current value D _OUT is supplied to the drive circuit 28.
In the drive circuit 28, the current value flowing through the solenoid 9a is the supply current value.
Closed-loop control of the current flowing through the solenoid 9a so that the D _OUT.

Next, the procedure of the air-fuel ratio control method according to the present invention will be described in detail with reference to the operation flowchart of the CPU 29 shown in FIG.

First, the CPU 29 determines whether or not the operating state of the vehicle (including the operating state of the engine) satisfies the air-fuel ratio feedback (F / B) control condition every time the interrupt signal is generated (step 51). This determination is determined from the absolute pressure in the intake manifold, the cooling water temperature, the vehicle speed, and the engine speed. For example, it is determined that the air-fuel ratio feedback control condition is not satisfied at a low vehicle speed and a low cooling water temperature. Here, if it is determined that the air-fuel ratio feedback control condition is not satisfied, the supply current value D _OUT is made equal to 0 to close the solenoid valve 9 and stop the air-fuel ratio feedback control (step 52). On the other hand, if it is determined that the air-fuel ratio feedback control condition is satisfied, a reference current value D _BASE of a current value supplied to the solenoid valve 9 is set (step 53). As shown in FIG. 4, a reference current value D _BASE determined from the intake manifold absolute pressure P _BA and the engine speed Ne is written in the ROM 30 in advance as a D _BASE data map.
_BA and the engine speed Ne are read, and a reference current value D _BASE corresponding to each read value is searched from the D _BASE data map. Next, the output voltage _VO2 of the oxygen concentration sensor 14 is read as an oxygen concentration detection value, and it is determined whether or not the output voltage _VO2 is smaller than a reference value _VREF corresponding to the target air-fuel ratio (step 54). If V _O2 <V _REF , the air-fuel ratio is lean, so it is determined whether the air-fuel ratio flag F _AF is equal to 0 (step 55). If F _AF = 0, it is considered that the air-fuel ratio is continuing the lean state, and if F _AF = 1, it is considered that the air-fuel ratio has reversed from rich to lean. V _O2 > V _REF
In the case of, since the air-fuel ratio is rich, the air-fuel ratio flag F
_It is determined whether or not _AF is equal to 1 (step 56). F _AF
If = 1, it is assumed that the air-fuel ratio continues to be rich, and if F _AF = 0, it is assumed that the air-fuel ratio has reversed from lean to rich. Thus integer N ₁ to the variable N when the air-fuel ratio is inverted (e.g., 3) a reset (step 57) by equal, determines whether or not the idling operation state (step 58). Idling, for example, to determine the throttle valve opening [theta] th, or the intake manifold absolute pressure P _BA, when the throttle valve opening [theta] th is a predetermined opening theta ₁ below, or in the intake manifold absolute pressure P _BA is a predetermined pressure it is determined that the idling time of the P ₁ below. If it is not in the idling operation state, it is determined whether or not the output voltage _VO2 of the oxygen concentration sensor 14 is smaller than the reference value _VREF corresponding to the target air-fuel ratio (step 59). If V _O2 <V _REF , the air-fuel ratio is leaner than the target air-fuel ratio, so the air-fuel ratio flag F _AF is made equal to 0 (step 60), and a predetermined proportional amount P is subtracted from the air-fuel ratio feedback correction coefficient K _O2. New calculated coefficient K
_O2 is set (step 61). If V _O2 ≧ V _REF , the air-fuel ratio is richer than the target air-fuel ratio, so the air-fuel ratio flag F _{AF is set} to 1
(Step 62), a predetermined proportional amount P is added from the air-fuel ratio feedback correction coefficient K _O2, and the calculated value is newly set as a correction coefficient K _O2 (Step 63). After calculating the correction coefficient K _O2 in step 61 or 63, the reference current value D _BASE set in step 53 is multiplied by the correction coefficient K _O2 and the multiplication result is set as a supply current value D _OUT (step 64).
_OUT is output to the drive circuit 28 (step 65). If it is determined in step 58 that the vehicle is in the idle operation state, step 64 is immediately executed to supply the supply current value D _OUT
Is calculated.

On the other hand, if it is determined in steps 53 or 56 that the air-fuel ratio has not been reversed, the absolute pressure in the intake manifold is determined.
P _BA reading the absolute pressure P _BA is determined whether or not greater than 410MmHg (step 66). If P _BA ≤410mmHg,
Since a low load and reset by equalizing the variable N to an integer N ₁ (step 67), also equal to the unit integration quantity I _n to an initial value I ₁ (step 68), if P _BA> 410mmHg,
Since the load is not low, it is determined whether or not the variable N is equal to 0 (step 69). If N ≠ 0, then it subtracts 1 from the variable N and the calculated value as a new variable N (step 70), equal to the unit integration quantity I _n to an initial value I ₁ (step 68). N = 0
If the unit integration quantity I _n the previous and I the unit integration quantity read as _n-1 I _n-1 to the coefficient K ₁ (for example 1.1) by multiplying the calculated value unit integration quantity of current to the I _n ( step 71), the unit integration quantity I _n this time it is determined whether or not more than the guard value I _G (step 72). If I _n ≧ I _G, equal the current unit integration quantity I _n the guard value I _G (step 73), if I _n ≦ I _G, holding the unit integration quantity I _n calculated in step 71 .

When the unit integration quantity I _n are determined, the output voltage V _O2 of the oxygen concentration sensor 14 it is determined whether or not smaller than the reference value V _REF corresponding to the target air-fuel ratio (step 74). If V _O2 <V _REF ,
Since the air-fuel ratio is leaner than the target air-fuel ratio, the air-fuel ratio flag
_Set F _AF equal to 0 (step 75), and set the previous output voltage V _O2
the amount of change between _n-1 and the present output voltage _{V O2 ΔV O2 (= V O2} -V O2
_n-1 ) is determined to be smaller than a predetermined value ΔV _O2H (negative value) (step 76). If ΔV _O2 <ΔV _O2H, since lean air-fuel ratio continues to subtract the unit integration quantity I _n from the correction coefficient K _O2 is the calculated value with the current correction coefficient K _O2 (step 77). If ΔV ₀₂ ≧ V _O2H, equally so lean degree of the air-fuel ratio is lowered the unit integration quantity I _n order to prevent an increase in the unit integration quantity I _n to an initial value I ₁ (step 7
8), and by the execution of step 77 by subtracting the unit integration quantity I _n from the correction coefficient K _O2 is the calculated value with the current correction coefficient K _O2. If V _O2 ≧ V _REF in step 74, the air-fuel ratio is richer than the target air-fuel ratio, and the air-fuel ratio flag F _{AF is set} to 1
Equal to (step 79), the variation between the previous output voltage V _{O2 n-1} and the present output voltage _{V O2 ΔV O2 (= V O2} -V O2 n-1)
Is larger than a predetermined value ΔV _O2L (positive value) (step 80). Delta _O2> if [Delta] V _O2L, since enrichment of the air-fuel ratio continues by adding the unit integration quantity I _n the correction coefficient K _O2 is the calculated value with the current correction coefficient K _O2 (step 81). If ΔV _O2 ≦ ΔV _O2L, equal to the unit integration quantity I _n for enrichment degree of the air-fuel ratio is to prevent an increase in the unit integration quantity I _n so dropped to the initial value I ₁ (step 82), and step 81 units integrated amount I _n the correction coefficient K _O2 by the execution of
And the calculated value is used as the current correction coefficient K _O2 .

Thus, in step 77 or 81, the correction coefficient K _O2
Is determined, the supply current value is obtained by performing steps 64 and 65.
And D _OUT, supplies a supply current value D _OUT to the drive circuit 28.

The drive circuit 28 detects the value of the current flowing through the solenoid 9a of the solenoid valve 9 with a current detection resistor, compares the detected current value with the supply current value D _OUT, and turns on and off the drive transistor according to the comparison result. A current is supplied to the solenoid 9a. Therefore, a current having a supply current value D _OUT flows through the solenoid 9a, and the amount of intake secondary air proportional to the value of the current flowing through the solenoid 9a is supplied into the intake manifold 4. When the supply current value _DOUT is 0, the solenoid valve 9 closes and the supply of the intake secondary air is stopped.

In the apparatus to which the air-fuel ratio control method of the present invention is applied, if the air-fuel ratio detected from the oxygen concentration is not in the idling state when the air-fuel ratio is inverted with respect to the target air-fuel ratio, first, the proportional amount of the correction coefficient K _O2 is calculated. PI (proportional integration) control is performed in which the air-fuel ratio is changed in the direction opposite to the reverse direction, and subsequently, the integration amount of the correction coefficient K _O2 is gradually changed. This PI
If the rich or lean state continues during the control and the load is not low, the integral amount per unit as shown in FIG. 5 is used to improve the response to the change in the air-fuel ratio of the supplied air-fuel mixture after the air-fuel ratio inversion. There is increased as time elapses, then the change per unit of the air-fuel ratio time becomes gentle until the air-fuel ratio inversion integral quantity in order to prevent an overshoot after inversion is fixed to the initial value I _1. Therefore, when the air-fuel ratio of the supplied air-fuel mixture is substantially stable at the target air-fuel ratio, the reversal period of the air-fuel ratio is shortened, and the integral amount per unit is not increased. On the other hand, during idle operation, I control is performed to gradually change only the integral amount of the correction coefficient K _{O2 in} order to prevent fluctuations in the engine speed due to air-fuel ratio control.

In the embodiment of the present invention described above, the step
Integration per unit by the operation of the _{I n = K 1 · I n} -1 in 71 is adapted to change, but the invention is not limited thereto, I _n = K ₁
² · I _n-1 of as changing the amount of integration per unit and is also good.

In the above-described embodiment of the present invention, the air-fuel ratio control device including the linear solenoid valve has been described.
An electromagnetic on-off valve is provided in the air secondary air supply passage, and the valve opening time T _OUT of the electromagnetic on-off valve (= reference valve opening time T _BASE × correction coefficient K _O2 ) is calculated for each predetermined cycle, and the electromagnetic valve is opened only for the valve opening time T _OUT. The present invention can also be applied to an air-fuel ratio control device that opens an on-off valve.

Further, in the above-described embodiment of the present invention, the air-fuel ratio control method of the present invention is applied to the air-fuel ratio control device of the intake secondary air supply system, but the method of controlling the injection amount by injecting and supplying the fuel by the injector. The present invention can also be applied to the above device.

Effect of the Invention As described above, in the air-fuel ratio control method of the present invention, the amount of increase / decrease at every predetermined cycle in the integral control, that is, the integral amount is increased in accordance with the amount of change in the detected value of the exhaust gas component concentration per unit time. Better response than before even if the air-fuel ratio of the supplied air-fuel mixture greatly deviates from the target air-fuel ratio when the operating state of the vehicle shifts from acceleration operation to steady operation or from idle operation to acceleration operation Property can be obtained, and the exhaust purification performance can be improved. Further, when the low load state of the engine is detected, the amount of increase / decrease at each predetermined cycle in the integral control is fixed to a predetermined value, so that hunting of the air-fuel ratio can be suppressed, and a decrease in exhaust purification performance can be prevented. .

[Brief description of the drawings]

FIG. 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, FIG. 2 is a block diagram showing a specific configuration of a control circuit in the device shown in FIG. 1, and FIG. flow diagram illustrating the operation of FIG. 4 is a view showing a data map that is written in the ROM, FIG. 5 is a graph showing a change characteristic of the unit integration quantity I _n. Description of Signs of Main Parts 2 Air Cleaner 3 Vaporizer 4 Intake Manifold 6 Throttle Valve 7 Venturi 8 Intake Secondary Air Supply Channel 9 Linear Electromagnetic 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

Continuation of the front page (56) References JP-A-55-112838 (JP, A) JP-A-58-204947 (JP, A) JP-A-59-87242 (JP, A) JP-A-58-152147 (JP) , A) JP-A-58-152148 (JP, A) JP-A-58-143145 (JP, A)

Claims (2)

(57) [Claims] An exhaust gas component concentration sensor provided in an exhaust system of an internal combustion engine compares a detected value of an exhaust gas component concentration with a reference value corresponding to a target air-fuel ratio. An air-fuel ratio control method for performing an integral control for increasing or decreasing the air-fuel ratio control value by an integral amount in accordance with the air-fuel ratio, and correcting the air-fuel ratio of the air-fuel mixture supplied to the engine according to the air-fuel ratio control value. A first setting step of setting the integral amount to a predetermined value when detecting that the engine is in a state, and increasing the integral amount from the predetermined value when detecting that the engine is in a load state other than a low load state. A second setting step of setting the air-fuel ratio control value in the first or second setting step in the integration control when the amount of change in the exhaust component concentration detection value per unit time is large. Air-fuel ratio control method characterized by having an integrating step of the increased or decreased by the integral amount. 2. When the air-fuel ratio continues to be detected to be leaner than the target air-fuel ratio from the result of the comparison, if the amount of change in the detected concentration of the exhaust gas component per unit time is smaller than a first predetermined negative value. If the change amount of the exhaust component concentration detection value per unit time is larger than a second predetermined positive value when it is continuously detected that the air-fuel ratio is richer than the target air-fuel ratio from the comparison result, 2. The air-fuel ratio control method according to claim 1, wherein the integral amount in the integral control is increased.