JPS62139943A - Air-fuel ratio control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To correct the tolerance of a lean sensor properly by changing an air-fuel ratio to a theoretical air-fuel ratio for keeping engine output unchanged in a steady running condition wherein said ratio is feedback controlled to a target ratio at lean side, and using the deviation of an operated ratio on the basis of a value obtainable therefrom. CONSTITUTION:An electronic control circuit 44 is inputted with values detected by an air flow meter 2, a rotary angle sensor 47, an O2 sensor 30, a lean sensor 52 and the like. The electronic control circuit 44, when an engine has been judged to be in a steady running condition, turns an air-fuel ratio from lean side to rich side, and keeps engine output at a constant level, delaying ignition timing. Also, said circuit 44 judges that the air-fuel ratio has reached a theoretical value, according to output from the O2 sensor and operates the ratio at the lean side of a predetermined value on the basis of a ratio then available, thereby controlling the ratio at a level so operated. And according to the deviation of output of the lean sensor 52 from the operated air-fuel ratio, correction is made on said sensor 52 for the air-fuel ratio feedback control.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an air-fuel ratio control method for an internal combustion engine, and in particular to an air-fuel ratio control method using a lean sensor that outputs an air-fuel ratio signal proportional to the residual oxygen concentration in exhaust gas. The present invention relates to an air-fuel ratio control method for an internal combustion engine that controls the air-fuel ratio to a target air-fuel ratio that is leaner than the stoichiometric air-fuel ratio.

[Prior Art] Conventionally, in order to simultaneously purify HC, CO, and NOx in exhaust gas, basic fuel injection has been performed depending on the engine load (for example, the amount of intake air per engine revolution or the intake pipe pressure) and the engine speed. Determine H1 and detect the residual oxygen concentration in exhaust gas02
Feedback control of the air-fuel ratio to the stoichiometric air-fuel ratio is carried out by correcting the main fuel injection ratio based on the sensor output. Since the signal is inverted at the boundary, the air-fuel ratio can be accurately controlled to the stoichiometric air-fuel ratio.

On the other hand, recently, as well as reducing fuel consumption costs, H
In order to reduce C and Co emissions, a lean sensor is used to make the air-fuel ratio leaner than the stoichiometric air-fuel ratio based on the lean sensor output under steady-state operating conditions where the emissions of harmful components in exhaust gas are relatively low. Feedback control is performed on the side air-fuel ratio. Since this lean sensor outputs a signal proportional to the residual oxygen concentration in the exhaust gas in an air-fuel ratio range on the leaner side than the stoichiometric air-fuel ratio, the air-fuel ratio can be controlled to be leaner than the stoichiometric air-fuel ratio. However, this lean sensor's output becomes unstable near the stoichiometric air-fuel ratio, and although it outputs a stable signal at a sufficiently lean side of the stoichiometric air-fuel ratio, it is difficult to manufacture with high precision.
It was difficult to accurately control the air-fuel ratio to the target air-fuel ratio.

For this reason, conventionally, as shown in Japanese Unexamined Patent Publication No. 198752/1983, the air-fuel ratio is controlled by determining the calibration amount of the lean sensor from the lean sensor output when the air-fuel ratio is controlled to the stoichiometric air-fuel ratio. [Problem to be solved by the invention] However, as mentioned above, the lean sensor output becomes unstable near the stoichiometric air-fuel ratio, so the calibration amount is determined based on the output signal at the stoichiometric air-fuel ratio. However, there was a problem in that it was not possible to perform accurate calibration.

The present invention has been made to solve the above problems, and by determining the calibration M) based on the output signal when the lean sensor is stable, the air-fuel ratio can be accurately controlled to the leaner side than the stoichiometric air-fuel ratio. An object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine.

[Means for Solving the Problems] In order to achieve the above object, the present invention outputs a first signal proportional to the residual oxygen concentration in the exhaust gas at a leaner side than the stoichiometric air-fuel ratio, and outputs the first signal proportional to the residual oxygen concentration in the exhaust gas at a leaner side than the stoichiometric air-fuel ratio. In the air-fuel ratio control method for an internal combustion engine, which outputs an inverted second signal and controls the air-fuel ratio to a target air-fuel ratio on the lean side of the stoichiometric air-fuel ratio based on the first signal under steady-state operating conditions. Under such conditions, the air-fuel ratio is changed while keeping the engine output unchanged so that the second signal is output, and the air-fuel ratio is set to a predetermined value on the lean side based on the air-fuel ratio when the second signal is output. Calculating the air-fuel ratio and measuring the actual air-fuel ratio when controlling the air-fuel ratio to the calculated air-fuel ratio based on the first signal, and calculating the difference between the calculated air-fuel ratio and the measured air-fuel ratio. The air-fuel ratio is controlled to the target air-fuel ratio based on the first signal.

[Operation] According to the present invention, under steady operating conditions, that is, when the air-fuel ratio is controlled to a target air-fuel ratio on the leaner side than the stoichiometric air-fuel ratio,
A second signal that is inverted from the stoichiometric air-fuel ratio is output while changing the air-fuel ratio and keeping the engine output constant. This second signal is obtained by using, for example, an 02 sensor, and can be output in accordance with the stoichiometric air-fuel ratio.The second signal is based on the air-fuel ratio at the time the second signal is output. An air-fuel ratio on the lean side by a predetermined value is calculated, and the air-fuel ratio is controlled to this calculated air-fuel ratio. Subsequently, the air-fuel ratio is measured based on a first signal proportional to the residual oxygen concentration in the exhaust gas output at this time, such as the output signal from the air sensor. This first signal is stable because the air-fuel ratio is output at a sufficiently lean side than the stoichiometric air-fuel ratio. Then, a deviation between the air-fuel ratio calculated as described above and the measured air-fuel ratio is calculated, and the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio based on this deviation and the first signal. Since the above deviation corresponds to the tolerance of the lean sensor, the air-fuel ratio can be accurately controlled to the target air-fuel ratio.

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

FIG. 2 schematically shows an internal combustion engine to which the present invention can be applied.

This engine is controlled by an electronic control circuit such as a microcomputer, and is equipped with an x7 flow meter 2 downstream of an air cleaner (not shown) for detecting intake air 1j2. The air flow meter 2 includes a damping motion plate 2A rotatably provided in the damping chamber 4, a measuring plate 2B connected to the compensation plate 2A, and a potentiometer 4 that detects the opening degree of the measuring plate 2B. It is equipped with Therefore, the intake air amount is determined from the intake air amount signal output from the potentiometer as a voltage value.

A throttle valve 8 is arranged downstream of the air flow meter 2, and the throttle valve 8 is in a fully closed state (
An idle switch 10 that is turned on at idle position) is attached, and a surge tank 12 is provided downstream of the throttle valve 8. Further, a bypass passage 14 is provided so as to bypass the throttle valve 8 and communicate the upstream side of the throttle valve with the surge tank 12 on the downstream side of the throttle valve. An idle speed control (ISO) valve 16B whose opening degree is adjusted by a pulse motor 16A equipped with a four-pole stator is attached to this bypass path 14. The surge tank 12 communicates with the combustion chamber of the engine 20 via an intake manifold 18 and an intake port 22. A fuel injection valve 24 is attached to each cylinder or cylinder group so as to protrude into the intake manifold 18.

The combustion chamber of the engine 20 is communicated via an exhaust boat 26 and an exhaust manifold 28 to a catalytic converter (not shown) filled with a three-way catalyst. The extreme manifold 28 includes an 02 sensor 30 that outputs a signal inverted from the stoichiometric air-fuel ratio, and a lean sensor 30 that outputs an air-fuel ratio signal as a current proportional to the residual oxygen concentration in the exhaust gas in a region leaner than the stoichiometric air-fuel ratio. A sensor 52 is attached. A cooling water temperature sensor 34 is attached to the engine block 32 so as to penetrate through the block 32 and protrude into the water jacket. This cooling water temperature sensor 3
4 detects the engine cooling water temperature and outputs a water temperature signal.

A spark plug 38 is attached to each cylinder so as to penetrate the cylinder head 36 of the engine 20 and protrude into the combustion chamber. The spark plug 38 is connected to a distributor 40, an igniter 42, and an electronic control circuit 44 comprised of a microcomputer and the like.

A cylinder discrimination sensor 46 and a rotation angle sensor 48 are installed inside the distributor 40, each of which is composed of a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing. In the case of a six-cylinder engine, the cylinder discrimination sensor 46 outputs a cylinder discrimination signal, for example, every 720'CA, and the rotation angle sensor 48 outputs an engine rotation speed signal, for example, every 30'CA.

The electronic control circuit 44, as shown in FIG.
i! t (MPU) 60, read-only memory (ROM) 62, lambdam access memory (RA)
M)64. Backup RAM (BU-RAM) 66, input/output capotro 8. Input port door 0° output port) 72,7
4.76 and a bus 78 such as a data bus or a control bus that connects them. The input/output capotro 8 includes an analog-digital (A/D) converter 78 . The air flow meter 2 and water temperature sensor 34 are connected via a multiplexer 80 and buffers 82, 84. The 02 sensor 32 is connected to the input capo 70 via a comparator 88 and a buffer 86, and the cylinder discrimination sensor 46 and rotation angle sensor 48 are also connected via a waveform shaping circuit 90.
A lean sensor 52 is connected via a current-voltage converter 53 that converts a current value into a voltage value and an A/D converter 55 that converts the output of the current-voltage converter 53 into a digital signal. Output port door 2 is drive circuit 9
2 to the igniter 42, and the output port door 4
is connected to the fuel injection valve 24 via a drive circuit 94, and the output port door 6 is connected to the ISO valve pulse motor 16A via a drive circuit 96. In addition, 98
is a clock, and 100 is a timer. The ROM 62 stores in advance a control routine program, etc., which will be explained below.

Next, a control routine of an embodiment in which the present invention is applied to the above engine will be explained. FIG. 1 shows the air-fuel ratio feed pack correction coefficient FAF calculation routine.
0, it is determined whether a predetermined time has elapsed since the previous lean sensor output was calibrated, and if the predetermined time has elapsed, a steady running state is established by detecting a change in the amount of intake air per engine rotation in step 122. Determine whether or not. When it is determined that the vehicle is in a steady running state, that is, when the air-fuel ratio is currently controlled to be leaner than the stoichiometric air-fuel ratio based on the lean sensor output, the fuel injection valve and igniter are controlled in steps 124 to 128. O2 sensor 30 while keeping the engine output constant
Control the output to be inverted. That is, in step 124, the fuel injection amount τ is increased by a predetermined amount Δτ, and in step 126, the ignition timing is retarded so that the engine output does not change due to the increase in the fuel injection amount, and in step 128
It is determined whether the 02 sensor output is inverted or not, and steps 124 to 1 are performed until the 02 sensor output is inverted.
Repeat step 28. If the air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio, reduce the fuel injection amount and advance the ignition timing so that the signal from the 02 sensor is reversed. to control.

In the next step 130, the fuel injection amount τ when the 02 sensor output is reversed is set to a predetermined value lK (for example, 30%).
The reduced calibration fuel injection amount is calculated, and an amount of fuel corresponding to this calibration fuel injection amount τ is injected, and in step 132, the ignition timing is returned so that the engine output does not change due to the change in the fuel injection amount. . In the next step 134,
The air-fuel ratio is measured based on the output of the lean sensor 52, and the air-fuel ratio corresponding to the calibration fuel injection amount τ calculated as described above is calculated, and the measured air-fuel ratio, EtA/ Calculate the deviation e by subtracting F. and,
In step 136, it is determined whether or not it is in a steady running state. If it is in a steady running state, in step 138, the deviation e is
It is stored in a predetermined area of RAM.

By controlling as described above, the 02 sensor output is reversed at the accurate stoichiometric air-fuel ratio, so the lean side air-fuel ratio calculated based on the accurate stoichiometric air-fuel ratio and the amount of fuel corresponding to this calculated air-fuel ratio are The deviation e from the air-fuel ratio measured from the lean sensor output after injection is stored.

In step 140, the target air-fuel ratio A/F is compared with the calibrated air-fuel ratio obtained by correcting the measured air-fuel ratio A/F by the deviation e, and if the target air-fuel ratio is equal to or higher than the calibrated air-fuel ratio, air-fuel ratio feedback correction is performed in step 142. The coefficient FAF is reduced by a predetermined value α, and if the target air-fuel ratio is less than the calibrated air-fuel ratio, step 144
As a result of increasing the air-fuel ratio feedback correction coefficient FAF by a predetermined value α, the air-fuel ratio feedback correction coefficient F
AF changes as shown in FIG.

FIG. 4 shows the main routine of an unimplemented example. In step 150, the basic fuel injection amount τB is calculated based on the intake air amount per unit time and the engine rotational speed.
By multiplying the basic fuel injection amount τB by the air-fuel ratio feedback correction coefficient FAF in step 152,
The fuel injection amount for controlling the air-fuel ratio to a target air-fuel ratio on the leaner side than the stoichiometric air-fuel ratio is calculated, the ignition timing is calculated in step 154, and the fuel injection valve and igniter are controlled based on these values.

Left, above we explained an example of controlling the air-fuel ratio to calibrate the lean sensor output by controlling the fuel injection amount, but it is also possible to calibrate the lean sensor output by controlling the ISO valve and controlling the intake air amount. The air-fuel ratio may be controlled. Further, although the above description has been made regarding an engine in which the basic fuel injection amount is determined based on the intake air amount and the engine speed, the present invention can also be applied to an engine in which the basic fuel injection amount is determined based on the intake pipe pressure and the engine speed. It is possible. Furthermore, in the above, an example was explained in which two sensors, the 02 sensor and the lean sensor, are used. However, by applying a voltage to the oxygen concentration sensor, it can be used as a lean sensor, and by stopping the application of voltage, it can be used as an 02 sensor. For example, it may be one sensor.

[Effects of the Invention] As explained above, according to the present invention, accurate calibration can be performed even when the tolerance of the lean sensor is large.
It is possible to perform air-fuel ratio feedback control in the lean range with very high accuracy, and there is no need to manufacture the lean sensor with high precision, resulting in the effect that costs can be reduced.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an air-fuel ratio feedback correction coefficient FAF calculation routine according to an embodiment of the present invention, Fig. 2 is a schematic diagram showing an engine to which the present invention is applicable, and Fig. 3 is a control circuit of Fig. 2. FIG. 4 is a flowchart showing part of the main routine of the above embodiment, and FIG. 5 is a diagram showing changes in the air-fuel ratio feedback correction coefficient FAF. 24...Conflict...Fuel injection valve, 3011/02 sensor. 52...Lean sensor. Figure 4 Figure 5

Claims (1)

[Claims] (1) A first signal proportional to the residual oxygen concentration in the exhaust gas is output at a leaner side than the stoichiometric air-fuel ratio, and a second signal inverted at the stoichiometric air-fuel ratio is output, and the signal is output under normal operating conditions. In an air-fuel ratio control method for an internal combustion engine, which controls the air-fuel ratio to a target air-fuel ratio on the leaner side than the stoichiometric air-fuel ratio based on the signal No. 1, the air-fuel ratio is changed while the engine output does not change under steady operating conditions. When the second signal is outputted, an air-fuel ratio on the lean side by a predetermined value is calculated based on the air-fuel ratio when the second signal is output, and the air-fuel ratio is controlled to the calculated air-fuel ratio. the actual air-fuel ratio of the air-fuel ratio is measured based on the first signal, and the air-fuel ratio is controlled to the target air-fuel ratio based on the difference between the calculated air-fuel ratio and the measured air-fuel ratio and the first signal. An air-fuel ratio control method for an internal combustion engine, characterized in that: