JPH0257224B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a variable bench lily type carburetor.

One way to promote atomization of fuel supplied from the nozzle of a variable bench lily type carburetor to the vent lily is to increase the negative pressure generated in the vent lily by increasing the spring force of the compression spring that presses the suction piston. There is a method of increasing the flow rate of intake air flowing inside the bench lily. However, if the spring force of the compression spring that presses the suction piston is increased in this way, the suction piston will remain closed to the intake passage when the amount of intake air is small, and the needle relative to the metering jet will remain closed even if the amount of intake air changes. There is a problem in that the required air-fuel ratio cannot be obtained because the position does not change. On the other hand, if the spring force of the compression spring that presses the suction piston is weakened to obtain the required air-fuel ratio when the amount of intake air is small, the flow rate of the air flowing inside the bench lily will slow down, resulting in fuel mist. There is a problem of insufficient compatibility.

SUMMARY OF THE INVENTION An object of the present invention is to provide a variable vent lily type carburetor that can obtain a required air-fuel ratio when the amount of intake air is low while promoting atomization of fuel.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, 1 is a carburetor main body, 2 is an intake passage extending vertically, 3 is a suction piston that moves laterally within the intake passage 2, and 4 is attached to the tip surface of the suction piston 3. 5 is a spacer fixed on the inner wall surface of the intake passage 2 facing the tip surface of the suction piston 3;
Reference numeral 6 indicates a throttle valve provided in the intake passage 2 downstream of the suction piston 3, and reference numeral 7 indicates a carburetor float chamber. A bench lily portion 8 is formed between the tip surface of the suction piston 3 and the spacer 5. .
A hollow cylindrical casing 9 is fixed to the carburetor body 1, and a guide sleeve 10 extending in the axial direction of the casing 9 inside the casing 9 is attached. A bearing 12 with a number of balls 11 is inserted into the guide sleeve 10,
Furthermore, the outer end of the guide sleeve 10 is closed by a blind cover 13. On the other hand, a guide rod 14 is fixed to the suction piston 3.
is inserted into the bearing 12 so as to be movable in the axial direction of the guide rod 14. Since the suction piston 3 is thus supported by the casing 9 via the bearing 12, the suction piston 3 can move smoothly in its axial direction. Casing 9
The interior of the is a negative pressure chamber 1 by a suction piston 3.
5 and an atmospheric pressure chamber 16, and a compression spring 17 is inserted into the negative pressure chamber 15 to constantly press the suction piston 3 toward the bench lily portion 8. The negative pressure chamber 15 is connected to the bench lily section 8 through a suction hole 18 formed in the suction piston 3, and the atmospheric pressure chamber 16 is connected to the suction piston 3 upstream through an air hole 19 formed in the carburetor body 1. The intake passage 2 is connected to the inside of the intake passage 2.

On the other hand, a fuel passage 20 extending in the axial direction of the needle 4 is formed in the carburetor body 1 so that the needle 4 can enter therein, and a metering jet 21 is provided within this fuel passage 20. The fuel passage 20 upstream of the metering jet 21 has a fuel pipe 22 extending downward.
is connected to the float chamber 7 via the float chamber 7.
The fuel inside is sent into the fuel passage 20 via this fuel pipe 22. Furthermore, a hollow cylindrical nozzle 23 arranged coaxially with the fuel passage 20 is fixed to the spacer 5 . This nozzle 23 protrudes into the bench lily portion 8 from the inner wall surface of the spacer 5, and the upper half of the tip of the nozzle 23 further protrudes from the lower half toward the suction piston 3.
Needle 4 is connected to nozzle 23 and metering jet 21
The fuel is metered by the annular gap formed between the needle 4 and the metering jet 21 and then fed into the intake passage 2 from the nozzle 23.

Referring to FIG. 1, a negative pressure port 25 is formed on the inner wall surface of the intake passage 2 near the throttle valve 6. This negative pressure port 25 opens into the intake passage 2 upstream of the throttle valve 6 when the throttle valve 6 is opened at a predetermined opening angle, for example, slightly larger than the idling opening angle. When the opening is smaller than the opening degree, it opens into the intake passage 2 downstream of the throttle valve 6. On the other hand, an air inflow port 26 is formed on the inner wall surface of the suction piston casing 9. As shown in FIGS. 1 and 3, the piston outer peripheral surface of the suction piston 3 that slides on the inner wall surface of the suction piston casing 9 is formed with a groove 27 that communicates with the atmospheric pressure chamber 16. The groove 27 and the negative pressure chamber 15 are separated by a thin wall 28. The air inflow port 26 is provided at the bottom of the inner wall surface of the suction piston casing 9 so as to be able to face this thin wall 28 . This air inflow port 26 is the first
As shown in the figure, when the intake air amount is small, it opens into the negative pressure chamber 15, and when the intake air amount increases, it opens into the atmospheric pressure chamber 16. The air inflow port 26 is always connected to the negative pressure port 25 via an air passage 29, and a throttle 30 is inserted into the air passage 29.
In addition, the suction hole 18 of the suction piston 3
A diaphragm 31 is also inserted inside.

As shown in FIG. 1, the upper end of the spacer 5 has a raised wall 2 projecting horizontally into the intake passage 2
4 is formed, and the flow rate is controlled between this raised wall 24 and the tip of the suction piston 3. When engine operation is started, air flows downward in the intake passage 2. At this time, since the airflow is restricted between the suction piston 3 and the land wall 24, negative pressure is generated in the bench lily portion 8, and this negative pressure is guided into the negative pressure chamber 15 through the suction hole 18. The suction piston 3 is arranged so that the pressure difference between the negative pressure chamber 15 and the atmospheric pressure chamber 16 becomes an almost constant pressure determined by the spring force of the compression spring 17, that is, so that the negative pressure inside the bench lily part 8 becomes almost constant. Moving.

As shown by the broken line in FIG. 1, if the throttle valve 6 is below the set opening, the negative pressure port 25
opens into the intake passage 2 downstream of the throttle valve 6. At this time, the negative pressure applied to the negative pressure port 25 is much larger than the negative pressure in the negative pressure chamber 15, so the air in the negative pressure chamber 15 flows into the intake passage 2 via the air passage 29, and thus As a result, the negative pressure inside the negative pressure chamber 15 increases. As a result, the lift of the suction piston 3 is increased. Next, throttle valve 6
When the opening degree is slightly larger than the set opening degree, a slightly smaller negative pressure acts on the negative pressure port 25 than in the bench lily part 8, so the negative pressure in the negative pressure chamber 15 becomes the negative pressure in the bench lily part 8. approximately equal to . Next, when the throttle valve 6 is further opened and the amount of intake air is increased, the lift of the suction piston 3 becomes larger, so that the air inflow port 26 opens into the atmospheric pressure chamber 16. At this time, the negative pressure port 25
Negative pressure is acting on the inside of the atmospheric pressure chamber 16, and the inside of the atmospheric pressure chamber 16 is at approximately atmospheric pressure, but since the negative pressure applied to the negative pressure port 25 is small, the inside of the atmospheric pressure chamber 16 is maintained at approximately atmospheric pressure. Therefore, the lift of the suction piston 3 is as shown in FIG. In FIG. 2, the vertical axis L shows the lift of the suction piston 3, and the horizontal axis Q shows the amount of intake air. As can be seen from Fig. 2, even when the amount of intake air is small, the suction piston 3 is moved according to the amount of intake air, so the required air-fuel ratio can be obtained; when the amount of intake air is large, the suction piston 3 moves according to the amount of intake air. Since the lift of No. 3 is reduced and the flow velocity of the intake air is increased, atomization of the fuel can be promoted.

FIG. 4 shows another embodiment. In this embodiment, the negative pressure port 25 is always open into the intake passage 2 downstream of the throttle valve 6. Therefore, in this embodiment, when the amount of intake air exceeds a certain amount, that is, when the lift of the suction piston 3 exceeds a certain level, the speed of the intake air flow is increased. In the embodiment shown in FIGS. 1 and 4, the air inflow port 26 is connected to the suction piston casing 9.
Since the fuel accumulated in the suction piston casing 9 is discharged into the intake passage 2 through the air passage 29, the suction piston 3 caused by the fuel accumulation is removed. This has the advantage that poor sliding can be prevented.

As described above, according to the present invention, even when the amount of intake air is small or the throttle valve opening is small, the lift of the suction piston is changed according to the amount of intake air, so the amount of intake air or A mixture with an air-fuel ratio corresponding to the throttle valve opening can be formed, and when the amount of intake air is large or the throttle valve opening is large, the lift amount of the suction piston is reduced and the flow velocity of the intake air is increased. Since the speed is increased, atomization of the fuel can be promoted. Furthermore, since the fuel accumulated in the suction piston casing is sucked out into the intake passage, fuel does not accumulate in the suction piston casing, thus preventing sliding failure of the suction piston caused by fuel accumulation. be able to.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of the variable bench lily type carburetor according to the present invention, FIG. 2 is a diagram showing the relationship between the lift L of the suction piston and the intake air amount Q, and FIG. 3 is a diagram showing the suction piston of FIG. 1. FIG. 4 is a side sectional view of another embodiment. 3... Suction piston, 4... Needle,
6... Throttle valve, 18... Suction hole, 2
3... Nozzle, 25... Negative pressure port, 26... Air inflow port, 29... Air passage.

Claims (1)

[Scope of Claims] 1. A suction piston slidably inserted into a casing in order to change the bench lily area in response to the amount of intake air, a needle connected to the suction piston, and a needle connected to the suction piston. In a downdraft variable bench valve carburetor having a fuel passage penetably extending in the axial direction of the needle and a metering jet disposed within the fuel passage and cooperating with the needle, the carburetor throttle A negative pressure port is provided that opens into the intake passage downstream of the throttle valve when the opening of the valve is below a predetermined opening, and opens into the intake passage upstream of the throttle valve when the opening of the throttle valve exceeds the set opening. Further, when the suction piston rises above a predetermined set lift, it opens into the atmospheric pressure chamber of the suction piston, and when the suction piston falls below the set lift, it opens into the negative pressure chamber of the suction piston. A variable bench lily type carburetor, wherein an air inflow port is formed on the bottom of the inner wall surface of the casing, and the air inflow port is always connected to a negative pressure port. 2. A suction piston slidably inserted into the casing in order to change the bench lily area in response to the amount of intake air, a needle connected to the suction piston, and a needle connected to the suction piston so that the needle can enter. A downdraft variable bench lily carburetor having a fuel passage extending in the axial direction of the needle and a metering jet disposed in the fuel passage and cooperating with the needle, wherein the suction piston is predetermined. An air inflow port is provided on the bottom of the inner wall surface of the casing, which opens into the atmospheric pressure chamber of the suction piston when the lift rises above the set lift and opens into the negative pressure chamber of the suction piston when the suction piston falls below the set lift. A variable vent lily type carburetor, in which the air inflow port is always connected to an intake passage downstream of a carburetor throttle valve.