JPS6228306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an automobile carburetor, and particularly to an improvement of a main fuel control device.

Figure 1 is a system diagram for explaining the configuration of a carburetor air-fuel ratio control device that employs a method of correcting the air-fuel ratio by controlling fuel passing through a fuel jet, as disclosed in Japanese Patent Application Laid-Open No. 51-54131. It is. The air-fuel mixture supplied from the carburetor 2 is combusted by the engine 1, and its exhaust gas is discharged from the exhaust pipe 3. In exhaust pipe 3
An O ₂ sensor 4 is installed to detect components in the exhaust from the engine 1 and transmit the signal to the control unit 8. Control unit 8
determines whether the air-fuel ratio of the air-fuel mixture supplied to the engine 1 from the carburetor 2 is appropriate based on the signal from the O ₂ sensor 4, and controls the amount of fuel supplied to the intake path of the carburetor 2 using the slow actuator 6 and the main The air-fuel mixture is adjusted by an actuator 7 to supply a mixture with a suitable air-fuel ratio to the engine 1.

A three-way catalyst pipe 5 is provided at the tip of the exhaust pipe 3, and the three-way catalyst filled in this pipe oxidizes or reduces harmful components in the exhaust gas to convert them into harmless gases. Figure 2 is a diagram showing the relationship between the output voltage of the O ₂ sensor and the air-fuel ratio of the air-fuel mixture supplied to the engine, where the vertical axis shows the output voltage and the horizontal axis shows the air-fuel ratio (A/F) of the air-fuel mixture. It shows. If the air-fuel ratio of the air-fuel mixture supplied to the engine is high, it means that the air-fuel mixture has become lean, and in this case O ₂ in the exhaust gas is
The amount increases and the output voltage of the _O2 sensor decreases. Conversely, when the air-fuel mixture becomes rich, the output voltage increases. Curve S shows this situation, and the output of the O ₂ sensor changes rapidly in a narrow air-fuel ratio range including the optimum air-fuel ratio T, which is called the ternary point. This three-way point T is an air-fuel ratio that maximizes the efficiency of the engine and the exhaust purification efficiency of the three-way catalyst. At the three-dimensional point T
If the output voltage of the O ₂ sensor is V _Sl , the air-fuel ratio control device shown in FIG. 1 is a device that controls the output of the O ₂ sensor so that it shows V _Sl .

Fig. 3 is a diagram explaining the operation of the actuator shown in Fig. 1, in which the vertical axis shows the air-fuel ratio A/F of the air-fuel mixture, and the horizontal axis shows the valve opening time ratio of the solenoid valve that constitutes the actuator. ing. The P _S line in the figure shows the operation of the slow actuator 6 in Figure 1, and when the air-fuel ratio (A/F) increases and the mixture becomes lean, the opening time ratio of the solenoid valve is decreased. This reduces the amount of air introduced into the slow fuel flow path and increases the amount of slow fuel supplied to the intake path. On the other hand, the Pm line shows the operation of the main actuator 7 in Figure 1. When the air-fuel ratio (A/F) increases and the mixture becomes lean, the opening time ratio of the solenoid valve is increased. , the amount of main fuel supplied from the main nozzle is increased. That is, the slow actuator 6 adjusts the opening time of the bleed air passage introduced into the slow fuel flow path, and the main actuator 7 adjusts the opening time of the main fuel passage to adjust the amount of each fuel. .

FIG. 4 is a sectional view of a conventional air-fuel ratio control device for a carburetor, in which the same parts as in FIG. 1 are given the same reference numerals. The main nozzle 9 is located in the bench lily of the carburetor 2.
is open, and a slow fuel passage bypass 16 and slow port 17 are open near a throttle valve installed downstream thereof.

The main nozzle 9 has a main air bleed 1 at the upper end.
0 into the float chamber 1 through the gas-liquid mixing pipe 11 opened.
It communicates with the main jet 12 provided at 8.
It also communicates with a correction fuel passage 13 branched from the main fuel passage that communicates the gas-liquid mixing pipe 11 and the main jet 12. This correction fuel passage 13
communicates with the float chamber 18 via a correction nozzle 20 and a correction needle 21, and also with a fuel reservoir 23 having a communication hole 22. The main actuator 7, which is a solenoid valve for moving the correction needle 21 up and down, is composed of an electromagnetic coil 25 and a core 24, and when the electromagnetic coil 25 is energized, the correction needle 21 is pulled up and opened.

The bypass 16 and slow port 17, which are the ends of the slow fuel passage, include a second slow air bleed 26 that is opened and closed by a solenoid valve of the slow actuator 6, and a slow jet 14 provided in a fuel passage branched from the main fuel passage. The passage downstream of this slow jet 14 is connected to the first
It communicates with the slow air bleed 15.

The operation of the conventional air-fuel ratio control device configured as described above will be briefly described. When the engine is rotating at low speed, a relatively large negative pressure is generated in the bypass 16 and slow port 17, so the slow jet 1
4, the fuel is mixed with the intake air of the carburetor 2, which sucks air from the slow air bleed 15 and supplies it to the intake passage, and is introduced into the engine. At this time, the solenoid valve of the slow actuator 6 changes the opening time ratio of the second slow air bleed 26 in accordance with the command from the control unit 8 shown in FIG. 1 to perform more precise air-fuel ratio control.

As the engine speed increases, the amount of intake air passing through the bench lily increases, so the main nozzle 9
A large negative pressure is generated in the main air bleed 10.
Air is taken in through the main jet 12, and fuel is taken in through the gas-liquid mixing pipe 11 and then discharged from the main nozzle 9. As mentioned above, since the correction fuel passage 13 is connected to the fuel passage communicating between the main jet 12 and the gas-liquid mixing pipe 11, negative pressure also acts on this correction fuel passage 13, causing the correction needle 21 to open. When the main fuel amount is increased. Since the valve opening time ratio of the correction needle 21 is changed in accordance with a command from the control unit 8 shown in FIG. 1, it is possible to supply an air-fuel mixture with a suitable air-fuel ratio even when the engine is rotating at high speed.

However, when the conventional air-fuel ratio control device is actually operated, the result is that the exhaust composition is intermittently deteriorated. FIG. 5 is a diagram showing changes in exhaust gas composition due to the air-fuel ratio control device shown in FIG. 4, where the vertical axis shows the CO content in the exhaust gas and the horizontal axis shows time. When CO in the exhaust gas is continuously measured, the content rate is below the regulation value as shown by line b, but intermittently the measured value a is abnormally high, and the overall exhaust composition is deteriorating.

After examining the cause of this, we found that the fuel reservoir 23
It turned out to be the cause. This fuel reservoir 2
3 is provided to surround the correction needle 21 in order to improve the responsiveness of fuel supply when the correction needle 21 opens, but during high-speed operation, this part near the carburetor 2 also rises in temperature. ,
The temperature rise due to the energization of the electromagnetic coil 25 also directly affects the fuel in the fuel reservoir 23, causing bubbles to be generated. These bubbles remain under pressure in the upper part of the sealed fuel reservoir 23, so when the correction needle 21 opens, either the fuel in the fuel reservoir 23 is expelled or the bubbles themselves come out. The amount of corrected fuel was increased intermittently. Such disturbances cannot be controlled by an air-fuel ratio control device. That is, since the control unit 8 that controls the air-fuel ratio at the three-point point receives the signal from the O ₂ sensor 4 caused by the above-mentioned disturbance as a control signal, the position of the control signal to be output is shifted and correct control cannot be performed. The disadvantage was that it was impossible.

The purpose of the present invention is to provide a highly accurate and stable air-fuel ratio control device for a carburetor, and its features are that a vent hole is provided in the core at the top of the fuel reservoir, and the vent hole and the upper part of the float chamber are This is because the space is communicated with a vent pipe to allow air bubbles generated in the fuel reservoir to escape.

FIG. 6 is a sectional view of a main part of an air-fuel ratio control device according to an embodiment of the present invention, and the same parts as in FIG. 4 are given the same reference numerals. The difference from Figure 4 is core 2.
A ventilation hole 31 is provided in the center of the float chamber 18, and the ventilation hole 31 is connected to the upper space of the float chamber 18 and the ventilation pipe 3.
This is because the connection was made with 0. By making such a simple modification, even if the fuel contained in the fuel reservoir 23 and the vent hole 31 is heated and generates bubbles, it easily flows into the space of the float chamber 18. Therefore, the liquid levels in the float chamber 18 and the vent hole 31 are always equal, and the correction needle 2
The corrected fuel amount supplied when valve 1 opens is exactly proportional to the valve opening time ratio.

Continuous measurement of the exhaust gas composition using this air-fuel ratio control device showed stable records as shown by line b in FIG. 5, and it was found that the drawbacks of the conventional device were completely eliminated.

As described above, the air-fuel ratio control device of this embodiment is capable of accurately correcting the main fuel amount and supplying the mixture to the engine by providing an air passage that allows air bubbles generated from the fuel in the fuel reservoir to escape into the space of the float chamber. This has the effect of improving the accuracy of air-fuel ratio control. Therefore, there are also the advantages of fuel savings and improved exhaust purification.

In the above embodiment, the fuel reservoir 23 and the float chamber 18
Although the vent pipe 30 is provided to communicate with the space, the same effect can be obtained even if the fuel reservoir 23 is opened to the atmosphere through the vent hole 31 without providing the vent pipe 30. However, in this case, fuel vapor is released into the outside air, which is not preferable.

The air-fuel ratio control device for a carburetor of the present invention has the effect of being able to control the main fuel amount with high precision.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing the configuration of the air-fuel ratio control device for the carburetor, Figure 2 is a diagram showing the relationship between the output voltage of the O ₂ sensor and the air-fuel ratio of the mixture, and Figure 3 is the same as Figure 1. A line diagram showing the operation of the actuator, Fig. 4 is a cross-sectional view of a conventional air-fuel ratio control device for a carburetor, Fig. 5 is a line diagram showing changes in exhaust composition due to the air-fuel ratio control device of Fig. 4, and Fig. 6 1 is a sectional view of a main part of an air-fuel ratio control device that is an embodiment of the present invention. 2... Carburetor, 7... Main actuator (electromagnetic valve), 9... Main nozzle, 12... Main jet, 13... Correction fuel passage, 18... Float chamber, 20... Correction nozzle, 21... Correction needle, 23... Fuel reservoir, 24... Core, 30...
...Vent pipe, 31...Vent hole.

Claims (1)

[Claims] 1. A fuel reservoir that communicates with the bottom of the float chamber and is located below the liquid level, a solenoid valve that has a correction needle that can move up and down within this fuel reservoir, and energized this solenoid valve to pull up the correction needle. In the fuel correction type air-fuel ratio control device for a carburetor, which includes a correction nozzle through which fuel sometimes passes, and a correction fuel passage communicating the correction nozzle with a main fuel passage, the solenoid valve located above the correction needle. 1. A fuel correction type air-fuel ratio control device, characterized in that a vent hole is provided in the core of the float chamber, and the vent hole is communicated with the upper space of the float chamber through a vent pipe.