JPS63253144A - Air-fuel ratio controlling method for internal combustion engine - Google Patents

Abstract

PURPOSE:To keep off any slippage of an air-fuel ratio due to a difference in a speed of response in both directions of an oxygen sensor by compensating an oxygen detecting level with the ratio of speed, having the oxygen detecting level varied in the lean direction to that varied in the rich direction. CONSTITUTION:An air flow meter 2, a suction air temperature sensor 3, an oxygen sensor 21, a water temperature sensor 22, a cylinder discriminating sensor 25, an engine speed sensor 26, a throttle sensor 29, etc., are connected to an electronic control circuit 35, and the fundamental fuel injection quantity calculated by a driving state is compensated by an oxygen detecting level of the oxygen sensor 21. The electronic control circuit 35 detects variable time per unit voltage difference at time of transition from rich to lean and vice versa on the basis of the detecting level of the oxygen sensor 21, thereby finding each speed ratio in both directions. And, it compensates the detecting level of the oxygen sensor 21 on the basis of this ratio.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention detects oxygen from the exhaust components of an internal combustion engine (hereinafter also simply referred to as the engine), and determines the air-fuel ratio of the mixture supplied to the internal combustion engine based on the oxygen detection level. The present invention relates to an air-fuel ratio control method for an internal combustion engine that performs feedback control.

[Prior Art] A technique is conventionally known in which the temperature of oxygen in exhaust gas is detected by an oxygen sensor and the air-fuel ratio is feedback-controlled by increasing or decreasing the supply of fuel to the engine. By the way, due to the characteristics of the oxygen sensor, the responsiveness when the air-fuel ratio changes from rich to lean may not match the responsiveness when the air-fuel ratio changes from lean to rich. for example,
JP-A-60-65247 discloses that oxygen is detected from exhaust components, and a high level signal is output when the air-fuel ratio is rich, which is smaller than the stoichiometric air-fuel ratio, and a low-level signal is output when the air-fuel ratio is lean, which is larger than the stoichiometric air-fuel ratio. An oxygen sensor that outputs an air-fuel ratio has been disclosed, and it has been shown that when this air-fuel ratio sensor deteriorates, the air-fuel ratio detection signal outputs a ratio verine signal for a longer time to the actual air-fuel ratio.

[Problems to be Solved by the Invention] The air-fuel ratio controlled based on such an air-fuel ratio detection signal deviates from the target stoichiometric air-fuel ratio to the rich side, making it impossible to control the air-fuel ratio with high precision. .

In other words, if the response speeds of the oxygen sensor for changes in the lean direction and rich direction differ from each other, the center value of air-fuel ratio control will shift to the lean side or rich side, causing the problem that the target air-fuel ratio cannot be controlled accurately. There is.

[Means for Solving the Problems] Therefore, the present invention is characterized in that the sensor output is corrected so that the response speeds of the oxygen sensor to the lean direction and the rich direction coincide with each other.

Specifically, the basic fuel injection port is calculated based on the operating state of the internal combustion engine (P1), and the basic fuel injection port is corrected based on the oxygen detection level of the oxygen sensor that detects oxygen from the exhaust components of the internal combustion engine (P3). ) In an air-fuel ratio control method for an internal combustion engine, a speed at which the oxygen detection level changes in a lean direction and a speed at which the oxygen detection level changes in a rich direction are detected, and the detection is performed based on the ratio of the two speeds. The gist of the internal combustion air-fuel ratio control method is that the level is corrected (P2) and used for correction of the fuel injection end (P3).

[Operation] According to the control method of the present invention, a sample fuel injection amount is calculated based on the operating state of the internal combustion engine (Pl). The speed at which the oxygen detection level of the oxygen sensor changes in the lean direction and the speed at which the oxygen detection level changes in the rich direction are respectively detected, and the ratio of the two speeds is calculated. Based on the calculated value, either the oxygen detection level that changes in a lean direction or the oxygen detection level that changes in a rich direction or the rain detection level is corrected. Based on the corrected oxygen detection level above, the basic fuel l
F3 rule 5 (time opening) is corrected (P3).

This correction eliminates biased deviations in the fuel injection amount, makes responsiveness uniform, and provides stable control of the fuel injection amount.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a system configuration diagram showing an embodiment of the method of the present invention. Air flow meter 2 is installed in intake passage 1 in order from upstream.
．． Intake temperature sensor 3, throttle valve 4, surge tank 5,
An intake pipe 6 is provided.

The fuel injection valve 7 is attached to the intake pipe 6 and injects fuel into the intake system. The bypass passage 8 is provided in parallel with the intake passage portion where the throttle valve 4 is provided, and is
An idle speed control valve 9 controls the flow area of the bypass passage 8. The combustion chamber 11 includes a spark plug 12, a cylinder head 13, and a cylinder block 1.
4, and a piston 15, and is supplied with air-fuel mixture via an intake valve 16. The air-fuel mixture combusted in the combustion chamber 11 is discharged to the exhaust pipe 20 via the exhaust valve 19.

A three-way catalytic converter 20a is attached to the exhaust pipe 20 for purifying exhaust gas. The oxygen sensor 21 detects the oxygen concentration in the exhaust gas, and outputs a high level signal when the air-fuel ratio is rich, which is lower than the stoichiometric air-fuel ratio, and outputs a low-level signal, when the air-fuel ratio is lean, which is higher than the stoichiometric air-fuel ratio. The water temperature sensor 22 is attached to the cylinder block 14 and detects the cooling water temperature. A cylinder discrimination sensor 25 and a rotation angle sensor 26 that also serves as a rotation speed sensor are connected to the glaze 2 of the power distributor 27.
The crank angle is detected from the rotation of 8. Cylinder discrimination sensor 2
5 and rotation angle sensor 26 each have a crank angle of 72
A pulse is generated every time the angle changes by 0° or 30'. Throttle sensor 29 detects the opening degree of throttle valve 4 .

An electronic control unit (hereinafter referred to as ECU) 35 receives input signals from the various sensors described above and controls the fuel injection valve 7 and the ISC valve 9.
and sends an output signal to the ignition device 36. The secondary ignition current of the ignition device 36 is sent to the spark plug 12 via the power distributor 27. As is well known, the air flow meter 2 measures the amount of air sucked into the intake passage 1 based on the opening indicated by the measuring plate 38.

Next, the ECU 35 will be explained.

As shown in FIG. 3, the ECU 35 includes a so-called CPU 40, R
OM41. The RAM 42 and the like are connected to each other by a bus 45 and an external input circuit 43 and an external output circuit 44 to form a logic operation circuit.

The external input circuit 43 includes the various sensors described above, the airflow meter 2. Intake temperature sensor 3. Oxygen sensor 21. Water temperature sensor 22. Cylinder discrimination sensor 25° rotation speed sensor 26
．． A throttle sensor 29 and the like are connected.

The external output circuit 44 includes the above-mentioned fuel injection valve 7°ISC.
A valve 9, an ignition device 36, etc. are connected.

With the above configuration, the ECU 35 functions to control each device connected to the external output circuit 44 based on input signals from various sensors.

Next, the air-fuel ratio control process executed by the CPU 40 will be explained based on the control program flowcharts shown in FIGS. 4 and 5. In this example, when the response speed when the detection voltage of the oxygen sensor changes from rich to lean is different from the response speed when changing from lean to ridge, the rich is adjusted to match the response speed when changing from lean to rich. The aim is to correct the response speed of the oxygen sensor, which changes from lean to lean, to prevent deviations in the center value of air-fuel ratio control. Regarding FIG. 4, first, when the process is started, in step 100, the intake air amount detected by the air flow meter 2 and the engine rotation speed data detected by the rotation speed sensor 26 are
Load it into U40 and calculate the basic fuel injection amount and step 1
Proceed to 01. In step 101, the output voltage when the oxygen sensor detects oxygen (hereinafter referred to as oxygen detection voltage) shown by the solid line in the enlarged waveform diagram of FIG. 6 (A>) changes from rich to lean. Difference VO (VO=V2-
The value of t2/ll is calculated from the change time t2 per unit voltage difference vO when the oxygen detection voltage V changes from lean to rich. tl
, t2 are values determined by the 4m5ec count routine shown in FIG. 5, which will be described later. Next, in step 102, a correction coefficient A of the oxygen detection voltage is determined using a map (Fig. 7) or a relational expression showing the relationship between the preset correction coefficient A and the above t2/ll, and the process proceeds to step 103. move on. In step 103, it is determined whether the oxygen detection voltage V exceeds the lower limit value (1) of the unit voltage difference VO. When the oxygen detection voltage V of the oxygen sensor does not exceed the lower limit value V1, the process proceeds to step 104, and the oxygen detection voltage V of the oxygen sensor is output as the corrected output voltage OX of the oxygen sensor. When the detected voltage V of the oxygen sensor exceeds the lower limit value (1), the process proceeds to step 105. In step 105,
Whether the value of the counter CLR (Fig. 6 (B)) that counts the change time t1 per unit voltage difference vO when the oxygen detection voltage ■ (described later in Fig. 5) changes from lean to rich is zero or not. be judged. If it is not zero, the process proceeds to step 104, where the same processing as described above is performed and the process ends. Above output voltage O
As shown in FIG. 6(A), when the detection voltage of the oxygen sensor is between c and d, the process including step 104 is repeatedly executed, and the waveform of X matches the waveform of the detection voltage c-d. Note that the solid line a-b-c shows the detected voltage of the oxygen sensor that has not been corrected by the method of the present invention.

When the value of the counter CLR is zero in step 105, the process proceeds to step 106, where it is determined whether the detected voltage V of the oxygen sensor is less than the upper limit value v2 of the unit voltage difference 2O. When the detected voltage (2) of the oxygen sensor is not less than the upper limit value v2 of the unit voltage difference vO, the process proceeds to step 104, where the same process as described above is performed and the process ends. Above output voltage O
The waveform of X matches the waveform of the detected voltage def when the detected voltage of the oxygen sensor is between def and the process including step 104 is repeatedly executed. When the detection voltage V of the oxygen sensor is less than the upper limit value v2 of the unit voltage difference VO, the process proceeds to step 107, where the upper limit value v2 of the unit voltage difference O and the detection voltage V of the oxygen sensor are calculated based on equation (1). The value of the difference is determined, and the value DOx is determined by correcting the above-mentioned difference value using the correction coefficient A of the oxygen detection voltage determined in step 102 (FIG. 6(A)).

DOX=(V2-V)*A・(1) Next, the process proceeds to step 108, and the value obtained by subtracting the above value DOX from the voltage V of the oxygen sensor based on equation (2) is determined as the corrected output voltage OX of the oxygen sensor. do.

0X=V-DOX=-(2) Next, the process proceeds to step 109, where it is determined whether the corrected output voltage OX is less than or equal to the lower limit value v1.

When the corrected output voltage OX is not below the lower limit value V1, the corrected output voltage OX is output. The waveform of the output voltage OX becomes a broken line f-g' when the detection voltage (2) of the oxygen sensor is between f-9 as a result of repeated execution of the process including steps 107, 108, and 109. Next, when the output voltage OX is less than the lower limit value (1), the process proceeds to step 110, where the lower limit value V1 is outputted as the corrected output voltage OX of the oxygen sensor. The waveform of the output voltage OX becomes a broken line g'-h when the detection voltage V of the oxygen sensor is between Q-h as the process including step 110 is repeatedly executed. Note that when the detection voltage V of the oxygen sensor is h-i-j-, which is less than the lower limit value v1, the waveform of the output voltage OX matches the detection voltage h-i-j-k of the oxygen sensor. . When the detection voltage V of the oxygen sensor changes from lean to rich, the above output voltage OX becomes j-to-' instead of j-Ω-Ω', and the corrected output level becomes between f-g-h. Since it has been corrected, responsiveness will be improved.

As a result, step 10 is performed based on the detected voltage of the oxygen sensor.
The processes from step 0 to step 110 are repeatedly executed.

Next, FIG. 5 is a flowchart for calculating the values of counters CLR and CRL that perform counting processing every 4 m5 ec. It is determined whether or not the detected voltage V of the oxygen sensor is larger than the detected voltage V DLD of the oxygen sensor 4 m5 ec ago (step 111), and if the detected voltage V is not larger than the voltage V OLD 4 m5 ec ago. Then, the process proceeds to step 112, where a counter CLR that counts the change time ↑1 per unit voltage VO when the oxygen detection voltage V changes from lean to rich is cleared, and the process proceeds to step 117. In step 111, the detected voltage V is 4m5ec.
If it is larger than the previous detected voltage V DLD, it is determined whether the detected voltage V is larger than the lower limit v1 of the unit voltage difference VO (step 113).

If the detected voltage V is not larger than the upper limit value v2 of the unit voltage difference vO, the process proceeds to step 112 and the same process as the previous step is performed.
Step 114). When the detected voltage V is larger than the upper limit value V2, the process proceeds to step 115, where the value of the counter CLR is entered into the change time t1, and step 112
Proceed to. Step 112 performs the same processing as described above and proceeds to step 117. If the detected voltage V is not larger than the upper limit value ■2 in step 114, 1 is added to the counter CLR (step 116), and step 11
Proceed to step 7. In step 117, the detection voltage V is 4m5.
It is determined whether or not the detection voltage V before ec is greater than the detection voltage VOLD before ec, and the detection voltage V before 4m5ec is determined.
If the value is greater than the mouth, the process proceeds to step 118, where a counter CR counts the change time t2 per unit voltage VO when the oxygen detection voltage changes from rich to lean.
Clear L and exit. In step 117, if the detected voltage V is not larger than the detected voltage VOLD 4 m5ec ago, the process proceeds to step 119, where it is determined whether the detected voltage V is larger than the upper limit value 2, and if it is, step 118 Proceed to perform the above-mentioned processing and end.

If the detected voltage ■ is not larger than the upper limit value V2 in step 119, the process proceeds to step 121. Step 1
21, the detection voltage V is the lower limit value v1 of the unit voltage difference ■O
If not, the value of the counter CRI- is determined based on the change time t2 per unit voltage difference VO when the oxygen detection voltage changes from rich to lean.
Then, the process proceeds to step 118, where the above-mentioned processing is performed and the process ends. Step 12], it is determined whether the detected voltage V is larger than the lower limit value v1 of the unit voltage difference VO, and if it is, 1 is added to the counter CRL (Step 1
22) Finish. Steps 111 to 12 above
Repeat step 2. Thereby, the speed at which the detection voltage of the oxygen sensor changes from rich to lean and the speed at which it changes from lean to rich can be measured. In addition, this embodiment corrects the speed change from rich to lean in accordance with the speed change from lean to rich in the detection voltage of the oxygen sensor, so that the change from lean to rich and from rich to lean is corrected. Consistency can be maintained. As a result, a balanced gas mixture can be supplied.

In the above embodiment, a case has been described in which the oxygen sensor outputs a signal that inverts from stoichiometric to richer, but the present invention outputs a linear signal according to the air-fuel ratio. It can also be applied to oxygen sensors.

[Effects of the Invention] As explained above, according to the air-fuel ratio control method of the present invention,
The sensor output is corrected so that the response speed of the oxygen sensor's change in lean direction and rich direction match each other.
The air-fuel ratio can be accurately controlled to the target value by preventing the central value of the air-fuel ratio control from shifting toward the one-in side or the rich side.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of the present invention, Fig. 2 is a schematic configuration diagram of an engine and its peripheral equipment to which the method of the present invention is applied, Fig. 3 is a block diagram of an electronic control circuit, and Figs. 4 and 5. is a flowchart showing a control program of an embodiment of the method of the present invention,
Figure 6 is a detection signal wave diagram and a shaping waveform diagram of the air-fuel ratio sensor,
FIG. 7 shows a diagram of the relationship between the air-fuel ratio correction coefficient and the speed ratio according to the embodiment of the present invention. 2...Air flow meter 7...Fuel injection valve 11...
・Combustion chamber 20a...Three-way catalytic converter 21・
...Oxygen sensor 26...Rotation angle sensor 35...
Electronic control unit (ECU) 40...CPU

Claims (1)

[Scope of Claims] An internal combustion engine that calculates the basic fuel injection amount based on the operating state of the internal combustion engine and corrects the basic fuel injection amount based on the oxygen detection level of an oxygen sensor that detects oxygen from exhaust components of the internal combustion engine. In the air-fuel ratio control method, a speed at which the oxygen detection level changes in a lean direction and a speed at which the oxygen detection level changes in a rich direction are detected, and the detection level is determined based on the ratio of the two speeds. An air-fuel ratio control method for an internal combustion engine, characterized in that the air-fuel ratio is corrected and used for correcting a fuel injection amount.