JPS6050979B2 - Air-fuel ratio control device for variable bench lily type carburetor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable bench lily type carburetor (hereinafter referred to as an SU type carburetor) in which the opening area of a bench lily portion in an intake passage for sucking fuel is made variable by changes in the lift of a piston. In particular, the present invention relates to a device that controls the lift of the piston of the carburetor using a probe signal that senses the composition of the exhaust gas, and controls the air-fuel ratio of the air-fuel mixture supplied to the engine.

In the SU type carburetor, fuel is metered with a single needle valve over a wide operating range from no-load operation to full-load operation of the engine (see Japanese Patent Laid-Open No. 49-54730).

For this reason, during no-load operation with a small amount of intake air or at a vehicle speed of 90
During low load and medium speed operation below 9/1, the piston may not move up and down (lift change) smoothly due to the effects of friction between the piston rod and the sliding part of its guide. Therefore, the air-fuel ratio of the air-fuel mixture is disturbed in such an operating range where the amount of intake air is small, causing air pollution and deterioration of drivability. The present invention improves this problem by controlling the operating negative pressure of the piston of the SU type carburetor using a probe signal that senses the exhaust gas composition, thereby stably controlling the air-fuel ratio of the mixture supplied to the engine. Feedback control. Among these, constant feedback control of the air-fuel ratio over the entire operating range of the engine significantly deteriorates the durability of the device, complicates the structure, and increases costs. (or during high load operation), the feedback control based on the signal of the probe is stopped, and the solenoid valve that releases the piston operating negative pressure to the atmosphere is closed to reduce dilution of the piston operating negative pressure by the atmosphere. The purpose of the present invention is to obtain an air-fuel ratio control device that achieves the following. Embodiments of the present invention will be described below based on the drawings.

In Fig. 1, 1 is an SU type carburetor, 2 is an air cleaner,
3 is an engine, 4 is an intake passage, and 5 is a throttle valve.

A bench lily 6 is formed in the intake passage 4 on the upstream side of the throttle valve 5. The bench lily 6 has a fixed bench lily forming part 6a on the lower side.
1 consists of a variable bench lily forming part 6b on the upper side. A fuel jet 7 opens in the fixed bench lily forming part 6a, and the needle valve 8 of the variable bench lily forming part 6b of the jet 7 is inserted through it, and the opening area of the jet 7 is increased or decreased by its vertical movement. This jet 7 communicates with a fuel chamber (not shown) which has a constant liquid level in a known manner. The variable bench lily forming portion 6b is formed by a piston 9 that moves up and down within the piston chamber, and the up and down movement is caused by the upper piston chamber 10.
The magnitude of the bench lily negative pressure (operating negative pressure) introduced through the through hole 11 into a and the return spring 12 that pushes the piston 9 downward.
Vertical movement (lift change) due to the balance between the weight of the piston 9 and the weight of the piston 9
Then, the piston rod 13 is guided and slides inside the inner id 14. The lower piston chamber 10b communicates with the air cleaner 2 through a passage 22 and is at atmospheric pressure. The upper piston chamber 10a is openably and closably connected to an atmosphere opening 18 by a solenoid valve 17 via an atmosphere communication passage 16. The solenoid valve 17
The valve 31 made of an excitable metal is attracted by the energization and excitation, and the sealing member 32b attached to the valve 31 is separated from the atmosphere opening port 18 to open it, and conversely, when deenergized without the energization, it is returned. The valve 31 is opened by the spring force of the spring 31a.
This is a well-known solenoid type which closes the air opening 18 by pressing it onto the air opening 18. Reference numeral 19 denotes an exhaust path of the engine 3, 20 a measuring element for detecting oxygen, carbon monoxide, etc. provided in the exhaust passage 19 to detect the composition of the exhaust gas, and 21 controlling input signals from the measuring element 20 and a switch S2 to be described later. The solenoid valve 17 is operated by the output signal of the controller 21. The solenoid valve 17 controls the opening and closing of the passage of the atmosphere opening port 18 at a predetermined periodic time width to control the pressure in the upper piston chamber 10a. An orifice 23 is provided in the atmospheric communication passage 16 in order to accurately control the vent lily negative pressure in the upper piston chamber 10a. In the drawing, the solenoid valve 17 is provided with a filter 26 at the atmosphere opening 18, but the atmosphere communication passage 16 may be communicated with the cleaning side of the engine air cleaner 2 through the solenoid valve 17 with a rubber tube or the like. S1 is an ignition switch that closes during operation;
S2 is a switch (engine operating state detection means) that opens and closes by sensing the engine operating state, and its signals include vehicle speed, throttle valve opening, temperature of the thermal reactor and catalyst, engine speed,
It is possible to combine one or more of the transmission gear positions, etc., but in this case, it is closed at low output and opened at high output. Next, the operation of the present invention will be explained. When the engine 3 is operated, intake air is supplied to the engine 3 as shown by the solid line arrow in FIG.

At this time, a substantially constant negative pressure is generated in the bench lily 6, and the fuel is sucked out from the gap between the fuel jet 7 and the bottom of the piston 9, that is, the needle valve 8 of the variable bench lily forming part 6b, and mixed with air to form an air-fuel mixture. do. What should be noted here is that the moment M due to the negative pressure in the intake passage 4 acts on the side part 9b of the piston 9 in the direction of the dashed arrow, and the piston rod 13 closes its guide 14, so the piston moves up and down smoothly due to frictional force. This impedes the movement and causes errors in the air-fuel ratio control of the air-fuel mixture. This is because the moment M becomes large when the piston 9 has a low lift, that is, when the piston side portion 9b protrudes more than half into the intake passage 4 and has a large pressure-receiving area. Therefore, in the present invention, in a low power operation region where such air-fuel ratio control varies, the atmosphere introduced into the upper piston chamber 10a is controlled by the solenoid valve 17 to forcibly change the operating negative pressure in the upper piston chamber 10a. As a result, the piston 9 is moved, thereby changing the negative pressure in the bench lily 6, increasing or decreasing the amount of fuel supplied, and controlling the air-fuel ratio to a predetermined air-fuel ratio.

To explain this in detail, the operation of the solenoid valve 17 is caused by sensing the composition in the exhaust gas (for example, 02, C0) and sending a signal to the measuring element 20.
It is controlled by the output signal of the controller 21, which inputs the signal sent from the switch S2. The air-fuel ratio of the engine is now 90kph when the solenoid valve 17 is closed by the spring action of the return spring 31a due to de-energization, and the air intake amount is relatively small.
g/h or less, the air-fuel ratio becomes 15-16, which is leaner than the stoichiometric air-fuel ratio.
The shape of the needle valve 8 is selected and predetermined so that the air-fuel ratio is set to be richer than the stoichiometric air-fuel ratio when the intake air amount is relatively high at a vehicle speed of 90 k9/h or higher. For example, if the predetermined air-fuel ratio as the control target value is set to the stoichiometric air-fuel ratio of gasoline by the controller 21, the stoichiometric air-fuel ratio is changed from the lean side to 14.8 based on the detection signal of the measuring element 20. The solenoid valve 17 is operated until the upper piston chamber 10a is opened and closed at a predetermined period in which the proportion of time during which the atmospheric communication passage 16 is opened is increased.
Introduce the atmosphere into the As a result, the operating negative pressure in the piston chamber 10a weakens, and the piston 7 lowers, reducing the opening area of the vent lily and increasing the negative pressure for sucking out the fuel, thereby increasing the amount of fuel flowing out, thereby enriching the air-fuel ratio. The transition to the side will be controlled. On the other hand, when the engine air-fuel ratio becomes richer than 14.8, the solenoid valve 17 is activated by the detection signal of the probe 20.
In response to a signal from the controller 21, the air communication passage 16 is immediately opened and closed at a predetermined period with an increased closing time ratio, thereby increasing the negative pressure in the upper piston chamber 10a, raising the piston 9, and discharging the fuel in the vent lily 6. With a small suction, the predetermined air-fuel ratio is 14.
．． Return to 8. (Switches S1 and S2 are closed in this case because it is low-load operation.) By periodically repeating the above operations, the engine air-fuel ratio can always be maintained at a predetermined value, and the intake air amount is The air-fuel ratio can be easily controlled during relatively low-load, medium-speed operation, where fluctuations in the air-fuel ratio are likely to occur.

However, even with this air-fuel ratio control having the above-mentioned characteristics, it is difficult to constantly perform this over the entire operating range of the engine. This is undesirable because it significantly deteriorates the durability of the air-fuel ratio feedback system of the magnetic valve 17.

In particular, the probe 20 is sensitive to heat and is desirably used under conditions where the exhaust temperature is 800° C. or less. In addition, the solenoid valve 17 has a low vibration frequency of 50
To open and close as quickly as possible at ~1000Hz,
This is desired in order to ensure fine adjustment of the vertical movement of the piston 9 and stabilization of fuel supply. Moreover, the vehicle speed is 90k with a large amount of intake air.
During high output operation of 9/h or more (during high speed or high load operation), the lift amount of the piston 9 becomes 1/2 or more of the inner diameter of the intake passage 4, so the pressure receiving area becomes smaller and the negative pressure inside the intake passage 4 decreases. Since the moment M due to pressure is reduced and the piston 9 can move up and down smoothly, good exhaust gas composition and operability can be obtained without forcibly moving the piston 9 up and down. Therefore, in this embodiment, the operation of the feedback system of the air-fuel ratio control device is stopped by opening the switch S2 during high-output operation at a vehicle speed of 90 k9/h or more with a large amount of intake air.

When the switch S2 is opened at this time, the valve 31 presses the sealing member 31b by the elasticity of the return spring 31a that is engaged with the valve 31 and closes the atmospheric communication passage 16. During high-output operation, the amount of intake air is large and the negative pressure in the bench lily 6 is greater than during low-output operation, so the upper piston chamber 1 is
The negative pressure introduced into Oa becomes large, and the amount of lift (rise) of the piston 9 becomes large. By setting the outer diameter of the needle valve 8 to a small diameter corresponding to this piston lift amount to generate a rich mixture, it is possible to improve the output, improve the durability of the feedback control means such as the solenoid valve, and so on. The separation device is simplified and costs can be prevented. Note that this switch S2 may be arranged to cut off the power supply between the electromagnetic valve 17 and the controller 21, or may be arranged in the circuit within the controller 21 as is known in the art.

Moreover, the combination of the operation switches of the air-fuel ratio control device is the second one.
As shown in the figure, a temperature switch S4 that opens when the engine temperature or intake air temperature is low, a throttle valve opening switch S3 that opens when the throttle valve opening is high, and a speed switch S2 that opens at a constant vehicle speed or engine speed are connected in series. It may be provided. The feedback operation states of the embodiment of the present invention are summarized in the following table and FIG. 3. The operation of this embodiment is as described above, but the features of other parts are listed below.

In this embodiment, since the pressure in the upper piston chamber 10a having a large volume is controlled, pressure fluctuations caused by opening and closing of the solenoid valve 17 can be reduced as much as possible, and since pressure can be applied to the entire flange 9a of the piston 9, the piston rod 13 and its guide 14, and a stable air-fuel ratio and durability can be ensured. In addition, since the orifice 23 is provided in the atmospheric communication passage 16 communicating with the upper piston chamber 10a, it is possible to accurately measure the air passing through the solenoid valve 17, and to reduce pressure fluctuations caused by opening and closing of the solenoid valve 17 as much as possible. Therefore, the vertical movement of the piston 9 can be made even smoother. As described above, according to the present invention, there is provided an engine operating state detecting means, a measuring element that senses the exhaust composition of the engine and outputs a signal, a controller that controls the detection and measurement signals and outputs an output signal, and an output thereof. A feedback system for air-fuel ratio control is configured with a solenoid valve operated by a signal, and by controlling the piston operating negative pressure of the SU type carburetor, that is, the vertical movement of the piston, the air-fuel ratio of the mixture supplied to the engine at low output can be accurately controlled. Not only can it be well controlled, but it also stops the operation of the air-fuel ratio feedback system during high-output operation.
In addition, since the solenoid valve is controlled to close, the operation of the solenoid valve is stopped during high output operation in which the air-fuel ratio is relatively easily kept constant, thereby improving the durability of the air-fuel ratio control device. Also, if you configure the solenoid valve to close at high output and enrich the air-fuel ratio,
When a three-way catalyst that purifies NOx, CO, and HC at the same time is used in the exhaust path, the durability of the catalyst can be improved because the combustion temperature and eventually the exhaust temperature decrease due to the generation of unburned components.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of essential parts of one embodiment of the present invention, FIG. 2 is a partial circuit diagram showing another embodiment of the combination of actuation switches of the air-fuel ratio control device, and FIG. 3 is the operation of the air-fuel ratio control device. It is a graph showing the area. DESCRIPTION OF SYMBOLS 1... SU type carburetor, 6... Bench lily, 6b... Variable bench lily forming part, 9... Zeston, 10a... Upper piston chamber, 11...・・・
...Through hole, 12...Return spring, 13...
Zeston rod, 14... Guide, 16... Atmospheric communication path, 17... Solenoid valve, 19...
Exhaust path, 20... Measuring head, 21... Controller, S1... Ignition switch, S2... Engine rotation speed, output sensing switch, S3... ... Throttle valve opening switch.

Claims (1)

[Claims] 1. In a variable bench lily type carburetor that forms a variable bench lily portion by changing the lift of a piston facing into the intake passage of the internal combustion engine and supplies air-fuel mixture to the internal combustion engine via the variable bench lily portion, the operating state of the engine is detected. a measuring element that detects the exhaust composition of the engine and outputs a signal; a controller that controls the signals of the detecting means and the measuring element and outputs an output signal; A solenoid valve that controls the lift of the piston by opening and closing a passage that releases the operating negative pressure to the atmosphere constitutes an air-fuel ratio feedback system, and the controller controls the air-fuel ratio of the mixture supplied to the internal combustion engine during low-output operation. The air-fuel ratio of air is feedback-controlled to a target value by opening and closing the solenoid valve according to the signal from the measuring head, and during high output operation, the operation of the feedback system is stopped and the solenoid valve is closed. This is an air-fuel ratio control device for a variable bench lily type carburetor.