JPS58204947A - Feedback control method for air-fuel ratio - Google Patents

Abstract

PURPOSE:To realize air-fuel ratio correction on a high ground by controlling air-fuel ratio on the basis of oxygen concentration sensor provided in an exhaust system. CONSTITUTION:Through reading an output signal from an atmospheric pressure sensor 3 first, and reading an output signal from a rotational speed sensor 4 subsequently, the integral constant is determined from an output signal level of the atmospheric pressure sensor 3 and an output signal level of the rotational speed sensor 4. The lower the atmospheric pressure is, the larger the integral constant is, while the lower the engine rotational speed is, the smaller the set value of the integral constant is. Subsequently, the output signal from an oxygen concentration sensor 1 is read, and judgement is made from the output signal level if air-fuel ratio of the mixed gas is rich or lean, air-fuel ratio being feedback-controlled state.

Description

[Detailed description of the invention] The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine.

In internal combustion engines, air-fuel ratio feedback control calculates a control amount through integral processing etc. based on the output of an oxygen concentration sensor installed in the exhaust system, and controls the air-fuel ratio of the mixture to an appropriate value according to the control amount. Equipment may be provided.

When a vehicle equipped with an engine drives at high altitudes, the atmospheric pressure is lower than on flat ground, so even if the throttle valve opening is the same, the amount of intake air M is smaller than on flat ground, and the air-fuel ratio of the mixture becomes richer. It becomes. Decrease in intake air suspension causes a decrease in engine output, so in order to drive in the same way as on flat ground, the opening of the throttle valve must be larger than that on flat ground, and the range of variation in the opening of the throttle valve used It gets bigger in the highlands. For this reason, in order to increase the opening degree of the carburetor and the throttle valve, we decided to operate in a region where fuel r1 is supplied from the main side of the Bricoli system and further from the secondary system.
The air-fuel mixture is supplied with a richer air-fuel ratio than the air-fuel ratio found on flat ground. Therefore, when driving on flat ground, the deviation of the air-fuel ratio from the stoichiometric air-fuel ratio becomes much more concentrated on the rich side, and the fluctuation range of the air-fuel ratio is also larger than on flat ground, so the amount of adjustment of the air-fuel ratio per unit time that was set in advance is In this case, the time required to supply the air-fuel mixture with the richer air-fuel ratio becomes longer, resulting in a delay in feedback control to bring the air-fuel ratio to the feedback target value. Therefore, in order to correct the air-fuel ratio to the target value, it is necessary to speed up the air-fuel ratio correction at high altitudes.

Furthermore, the air-fuel ratio of the mixer supplied from the fuel supply means such as the carburetor is determined based on the output signal of the oxygen concentration sensor through the intake pipe, combustion chamber, and exhaust pipe depending on the engine operating state, for example, changes in engine load or engine speed. Since the response time required for this change varies, it is desirable to prevent response delays during high loads or high rotations.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an air-fuel ratio feedback control method that speeds up air-fuel ratio correction at high altitudes. Another object of the present invention is to provide an air-fuel ratio feedback control method in which the speed of air-fuel ratio correction is appropriately set depending on the operating state of the engine.

In the air-fuel ratio feedback control method according to the present invention, the integral constant of the integral process is changed according to the magnitude of atmospheric pressure to 1:1.'::
.

It is designed to make it easier to understand. Furthermore, the integral constant is changed depending on the operating state of the engine.

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

In Fig. 1, an oxygen concentration sensor 1 is installed in the 1-gas system of an internal combustion engine (not shown) and uses the oxygen temperature in the exhaust gas. A control circuit 2 is connected to the output terminal of the control circuit jf1.
Reference numeral 2 is a micro-coater which generates a control signal representing a control period based on the output signal of the oxygen concentration sensor 1. Also connected to the control circuit 2 are an atmospheric pressure sensor 3 for high altitude correction and an engine rotation speed sensor 4 for correction of engine operating conditions. The air-fuel ratio adjusting device 6 provided in the fuel supply means is connected to the output end of the control circuit 2 via the drive circuit 5, and the air-fuel ratio adjusting device 6 receives the control signal. Accordingly, for example, the air-fuel ratio of the air-fuel mixture is adjusted by driving a needle valve that controls the opening area number of the air bleed of the carburetor.

Next, the operation of the control circuit 2 will be explained using the operation flow diagram of FIG.

When the control circuit 2 starts operating, first, the atmospheric pressure sensor 3
Read the output signal of (step 1).

Next, the output signal of the rotation speed sensor 4 is read (step 2), and an integral constant is determined from the output signal level of the atmospheric pressure sensor 3 and the output signal level of the rotation speed sensor 4 (step 3). This integral constant may be stored in a memory such as a ROM in advance, and may be calculated after being looked up in a table according to the output signal level of the atmospheric pressure sensor 3 and the output signal level of the rotational speed sensor 4, or even both of them. It may be read out from a map or calculated and determined according to the output signal level of the map. This integral constant becomes a larger value as the atmospheric pressure decreases, and is set to a smaller value as the engine speed decreases. Next, the output signal of the oxygen concentration sensor 1 is read (step 4). Then, it is determined from the output signal level of the oxygen concentration sensor 1 whether the air-fuel ratio of the air-fuel mixture supplied to the engine is rich or lean (Stella 5-B 5). A control signal that should control the air-fuel ratio in a lean direction if the air-fuel ratio is rich, and in a rich direction if it is lean, is determined based on the division-within-one constant (step 6.7).
. Then, in response to this signal, a drive signal is generated to be applied to a needle valve drive device, for example, a pulse motor (step 8).

The number of drive pulses per unit time to a pulse motor whose rotation angle per drive pulse is constant varies depending on the magnitude of the drive signal, in other words, the integral constant.

As a result, as the atmospheric pressure decreases and the engine speed increases, the integral processing speed increases, and the amount of change in the control signal per unit time due to the integral process becomes large. The amount of change in air/fuel per unit 11 can also be increased. Therefore, rapid air-fuel ratio correction is possible when the atmospheric pressure is low or when the engine speed is high.

FIG. 3 shows another embodiment of the invention. In FIG. 3, the portion surrounded by a broken line corresponds to the control circuit 2 in FIG. Atmospheric pressure sensor 3's 6- output terminal is connected to V-F (voltage-frequency) via buffer 7.
A converter 8 is connected. Further, a buffer 9 is connected to the output end of the rotation speed sensor 4 which detects the engine operating state. On the other hand, a comparison circuit 11 for determining the air-fuel ratio is connected to the output end of the oxygen concentration sensor via a buffer 'IO. The comparison circuit 11 is supplied with a reference tp-voltage Vr for determination, and for example, when the output voltage of the buffer 10 is smaller than the M quasi-voltage Vr, the comparison circuit 11 determines that the air-fuel ratio is lean and changes the output to a low level or a high level. When the air-fuel ratio is rich, the output is set to a high level.

The output terminal of the comparator circuit 11 has a drive pulse generator and a circuit 12.
is connected, and the drive pulse generation circuit 12 generates drive pulses per unit time in accordance with the output signal of the V-F converter 8 and the output signal of the buffer 9, which are supplied separately from the output signal of the comparator circuit 11, in accordance with the above-mentioned method. The number of generated pulses, that is, the integral constant, is determined and a driving pulse corresponding to the number of pulses generated is generated. The drive pulse is sent to the pulse motor via the drive circuit 13.
It is designed to be supplied to 4 pulses, and the pulse
/I l;L It rotates by a predetermined angle every time a drive pulse is supplied, and the direction of rotation is determined by the output signal of the comparator circuit 11.

A rotation shaft (not shown) of the pulse motor 14 is provided with a motion converter 15 formed of a gear Ill structure, such as a trapezoidal screw, for converting rotational motion into vertical motion in the direction of the rotation shaft. A needle valve 17 provided in a correction air passage 16 of the carburetor is connected to the conversion output end of the motion converter 15, and the opening area of the correction air passage 16 is changed by the sub valve 17. Note that 1/I to 17 correspond to the air-fuel ratio adjusting device 6 in FIG.

In this configuration, the drive pulse generation circuit 12 determines the generation order of the drive pulses generated according to the output signal of the comparison circuit 11, that is, the control direction of the air-fuel ratio, and determines the output pulse of the V-Fla exchanger 8 and the output pulse of the buffer 9. The number of drive pulses generated per unit time, that is, the integral constant, is determined according to the output signal. The V-F converter 8 has the characteristic shown in FIG. The number of shots will also increase. Therefore, when the output signal of the comparator circuit 11 has a waveform as shown in FIG. 5 (ω), the movement of the needle valve 17 due to the rotation of the pulse motor 14 is as shown in FIG. As shown in (C), as the atmospheric pressure decreases, the number of drive pulses generated per unit time increases and the interval between drive pulses is shortened, so that the movement range of the needle valve 17 per unit time becomes larger.

Therefore, the amount of correction of the air-fuel ratio per intermediate time changes depending on the magnitude of the atmospheric pressure.

As described above, according to the air-fuel ratio feedback control method according to the present invention, the integral constant of the integral process is changed according to the magnitude of atmospheric pressure, so it is possible to speed up the air-fuel ratio correction at high altitudes. . Furthermore, depending on the engine operating condition,
In other words, since the integral constant is made large even under high loads and high engine speeds, delays in control response of the feedback system can be avoided.

[Brief explanation of drawings]

9- Fig. 1 is a block diagram of a control device using the air-fuel ratio feedback control method according to the present invention, Fig. 2 is an operational diagram of the control circuit of Fig. 1, and Fig. 413 is another embodiment of the present invention. 4 is a conversion characteristic diagram of the V-F converter of FIG. 3, and FIG. 5 is an operation waveform diagram of each part of the circuit of FIG. 3. Explanation of symbols of main parts 1...Oxygen level 2...Control circuit 3...Atmospheric pressure sensor 4...Rotational speed sensor 6 ... Air-fuel ratio adjustment device 14 ... Pulse motor 15 ... Motion converter 16 ... Correction air path 17 ... Needle valve applicant Hon. Mouth] Giken Kogyo Co., Ltd. Agent Patent Attorney Motohiko Fujimura 10- Machine-Y-4-hi 8 people 8 +/+J

Claims (2)

[Claims] (1) An air-fuel ratio feedback control method that generates a control signal through integral processing based on the output signal of an oxygen concentration sensor installed in the exhaust system of an internal combustion engine, and adjusts the air-fuel ratio of the air-fuel mixture according to the control signal. An air-fuel ratio feedback control method, characterized in that an integral constant of the integral process is increased in accordance with a decrease in atmospheric pressure. (2) The air-fuel ratio feedback control method according to claim 1, characterized in that the integral constant of the integral process is further changed depending on the operating state of the engine.