JPS58107852A - Variable venturi carburetor - Google Patents

Abstract

PURPOSE:To prevent a drop of fuel dripping from a needle while to prevent the fuel from accumulating in the end face of a piston, by constituting the suction piston such that a guide rod slidably guiding the piston is formed hollow and the needle is fitted to the end of the rod. CONSTITUTION:The captioned carburetor is operated such that a suction piston 3 is responsively moved to an intake air quantity to change area of a Venturi part 8 while a needle 4 connected to said piston 3 is intruded into a fuel passage 20 to measure fuel cooperatively with a metering jet 21. Here a guide rod 14 slidably guiding the piston 13 is formed of a hollow pipe and a root part of the needle 4 is fitted to one end of said rod 14 while said needle 4 is fixed by mounting a screw 34 to a threaded hole 32 formed to the end part of the piston 3. Then an open end of the hole 32 is closed by a seal member 37 while the other open end part of the rod 14 is closed by a seal member 38.

Description

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

A suction piston that changes the venturi area in response to the amount of intake air, a needle connected to the suction piston, a fuel passage extending in the axial direction of the needle so that the needle can enter, and a needle provided in the fuel passage. In a variable venturi type carburetor equipped with a metering jet that cooperates with the needle, when the opening amount of the suction piston is small, such as during idling operation or light load operation, the fuel metered by the needle and metering jet flows through the needle. It is transmitted and flows to the suction piston side. As this fuel travels over the needle, if it becomes large droplets, the balance with the surface tension cannot be maintained and they fall. However, when fuel droplets fall when the amount of supplied fuel is small, such as during idling or light load operation, the fuel efficiency of these fuel droplets occupies a large proportion compared to the amount of supplied fuel, so the reason for the droplets to fall is the engine. The air-fuel mixture supplied into the cylinder becomes too rich. In addition, the fuel that reaches the tip of the suction piston without falling from the needle flows down the tip of the suction piston, but the flow path is extremely unstable, and especially during idling, the fuel mixture supplied into the engine cylinder The air-fuel ratio changes periodically. As a result, the engine speed fluctuates accordingly, resulting in a problem that the eye P ring becomes unstable. Furthermore, as mentioned above, if fuel adheres to the tip surface of the suction piston, the air-fuel mixture supplied to the engine cylinder will become 1.
Occasionally, the concentration becomes too high, resulting in a problem of worsening exhaust emissions.

The present invention prevents fuel droplets from falling from the needle, prevents fuel from accumulating on the tip surface of the suction piston, and further allows the fuel adhering to the tip surface of the suction piston to flow down continuously and stably. To provide a pendant type carburetor which secures stable idling operation during idling operation or engine light load operation.

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

Referring to Figure 1, 1 is the 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. needle, 5 is suction piston 3
A spacer 6 is fixed on the inner wall surface of the intake passage 2 facing the tip surface of the intake passage 2 downstream of the suction piston 3.
Throttle valves 7 are provided within the carburetor float chamber, and a spacer 5 on the tip surface of the suction piston 3
A venturi portion 8 is formed between them. 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 sloped. A bearing 12 with a number of balls 11 is inserted into the guide sleeve 10, and the outer end of the guide sleeve 10 is closed by a lid 13. On the other hand, a guide rod 14 is fixed to the piston 3, and the guide rod 14 is inserted into a bearing 12 so as to be movable in the axial direction of the guide rod 14.

In this way, the suction piston 3 is 111III receiver 12
Since the suction piston 3 is supported by the casing 9 via the casing 9, the suction piston 3 can move smoothly in its axial direction. The interior of the casing 9 is divided by the suction piston 3 into a negative pressure chamber 15 and an atmospheric pressure chamber 16.
A royal spring 17 that constantly presses the suction piston 3 toward the venturi portion 8 is inserted into the suction piston 5 . Negative pressure chamber 15
is the suction hole 18 formed in the suction piston 3
The atmospheric pressure 16 is connected to the intake passage 2 upstream of the suction piston 3 through an air hole 19 formed in the carburetor body 1 .

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. A fuel passage 20 upstream of the metering unit 21 is connected to the float chamber 7 via a fuel pipe 22 extending downward.
The fuel in the float chamber 7 is sent into the fuel passage 20 via this fuel outlet 22. Furthermore, a hollow cylindrical nozzle 23 arranged coaxially with the fuel passage 20 is fixed to the spacer 5 . This nozzle 23 protrudes from the inner wall surface of the spacer 5 into the venturi portion 8, and further protrudes from the upper half of the tip of the nozzle 23 toward the piston 3. The needle 4 extends through the nozzle 23 as well as the metering jet 21 , and the fuel is metered by the annular gap formed between the needle 4 and the metering jet 21 before being fed from the nozzle 23 into the intake passage 2 . As shown in FIG. 1, the fuel passage 20 upstream of the metering jet 21 and the fuel passage 20 downstream of the metering jet 21 are connected to
1 passage 24 interconnects each other.

The fuel bypass passage 24 includes an intermediate portion 24m extending in a substantially horizontal direction, and a metering jet 24 extending from one end of the intermediate portion 24m.
an inflow passage portion 24b extending into the fuel passage 20 one upstream;
The outlet passage ff624c extends from the other end of the intermediate part 24m into the fuel passage 20 downstream of the violet jet 21, and the jet 25 is inserted into the intermediate part 24&. Furthermore, the lower end of the outflow passage 24c is connected to the fuel passage 20 via a jet 26 formed on the upper wall surface of the nozzle 23, while the upper end of the outflow passage 24c is connected to an air bleed passage 27 and an air bleed jet 28. It is connected to the intake passage 2 upstream of the suction piston 3 via the suction piston 3 .

As shown in FIGS. 1 and 2, the guide rod 14 fixed to the succinct piston 3 is formed of a hollow tube with both ends open, and a needle 4 is attached to one open end of the guide rod 14. A supporting needle holder 31 is fitted. A threaded hole 32 is threaded above the needle holder 31 and extends upward from the outer peripheral wall of the needle holder 31 through the guide rod 14 and the suction piston 3, and a small diameter protrusion 33 is integrally formed within this threaded hole 32. Tanesh 4 is screwed on. The needle holster 31 is fixed to the suction piston 3 with a screw 34 so that its distal end surface 35 protrudes from the distal end surface 36 of the suction piston 3.

The open end of the threaded hole 32 of this screw 34 is filled with a sealing member 37 for preventing air leakage.
4 and the tapped hole 2 are formed to prevent air from leaking into the venturi portion 8 through the space between the outer peripheral surface of the needle holder 31 and the guide rod 14. On the other hand, a seal member 38 for preventing air leakage is packed in the open end of the guide rod 14 on the opposite side to the needle holder 31, so that the seal member 38 passes between the blind lid 13 and the guide sleeve 10 and connects to the outer peripheral surface of the needle holder 31. , air is prevented from leaking into the venturi section 8 between the guide rods 14. The four tip surfaces of the suction piston 3 below the needle holder 31 are downwardly inclined surfaces 39.
As shown in FIGS. 2 and 3, a guide groove 40 extending straight downward from the needle holder 31 is formed on this inclined surface 39. On the other hand, a fuel suction tube 41 is arranged near the lower end of this guide groove 40, and this tube 41 is connected to an opening 43 via a fuel passage 42 formed in the carburetor main body 1. As shown in FIG. 2, this opening 43 opens into the intake passage 2 downstream of the throttle valve 6 when the throttle valve 6 is idling, and when the throttle valve 6 opens, the opening 43 opens into the intake passage 2 upstream of the throttle valve 6. Open inward.

As shown in FIG. 1, an intake passage 2 is provided at the upper end of the spacer 5.
A raised wall 30 is formed that projects inward in the horizontal direction,
Flow rate control is performed between this raised wall 30 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 air flow is restricted between the suction piston 3 and the raised wall 30, negative pressure is generated in the venturi portion 8, and this negative pressure is guided into the negative pressure chamber 15 through the suction hole 18. The suction piston 3 moves so that the pressure difference between the negative pressure chamber 15 and the atmospheric pressure chamber 16 becomes a substantially constant value determined by the spring force of the compression spring 17, that is, the negative pressure within the venturi portion 8 becomes substantially constant. do.

During engine idling operation, since the area of the annular gap formed between the needle 4 and the metering jet 21 is small, part of the fuel is fed into the nozzle 23 through this annular gap, and the remaining fuel is transferred to the fuel pipe 4. It is fed into the nozzle 23 from a jet 26 via a passage 24 . There is an air bleed passage 27 in the fuel flowing in the fuel pipe/gas passage 24.
Air is bled out, and fuel containing bubbles is thus supplied from the jet 26 into the nozzle 23. Nozzle 23 via an annular gap between needle 4 and metering jet 21
The fuel fed into the nozzle 23 travels along the bottom wall surface of the nozzle 23 and is atomized at the tip of the nozzle 23 by being subjected to shearing force by the air flow.

On the other hand, the fuel flowing out from the jet 26 is transferred to the venturi section 8.
The needle moves forward along the upper wall surface of the nozzle 23 by being sucked by the negative pressure generated, and then travels through the needle 4 and reaches the tip surface 35 of the needle holder 31.

As mentioned above, since the tip surface 35 of the needle holder 31 protrudes from the tip surface 36 of the suction piston 3, the fuel that has reached the tip surface 35 of the needle holder 31 flows down into the guide groove 40 without being accumulated. sent. Also, at this time, the outer peripheral surface of the needle holder 31 and the guide rod 3
Since air does not leak from between 1 and 1, the fuel sent onto the needle holder 31 is not blown away by this leaked air, and the movement of the fuel flow above the needle 4 is still blocked by this leaked air, causing the fuel to flow onto the needle 4. is delayed
d, thereby preventing droplets from forming on the needle 4.

The fuel that has flowed down into the guide groove 40 from the tip surface 35 of the needle holder 31 flows continuously within the guide groove 40, and then the fuel that has reached the lower end of the guide groove 40 is sucked by the tube 41 and flows downstream of the throttle valve 6. It is sent into the intake passage 2. In this way, air leakage from between the outer peripheral surface of the needle holder 31 and the guide rod 31 is prevented, and the needle holder 3
1 protrudes from the distal end surface 36 of the suction piston 3, and the distal end surface 35 of the suction piston 3 protrudes from the distal end surface 36 of the suction piston 3.
By forming the guide groove 40 on the engine 9, the flow of fuel becomes continuous and stable during engine idling operation or light load operation, thus eliminating fluctuations in the air-fuel ratio and ensuring stable idling operation. can do. When the throttle valve 6 is opened and the amount of intake air increases, the suction piston 3 moves toward the negative pressure chamber 15, so that the area of the annular gap formed between the needle 4 and the metering jet 21 increases. At this time, most of the fuel is fuel pie A? It is fed into the nozzle 23 through this annular gap without bypassing the passage 24.

As described above, according to the present invention, fuel droplets are prevented from forming on the needle, fuel is prevented from staying on the tip surface of the suction piston, and fuel attached to the tip surface of the suction piston is continuously prevented. The water flows down accurately and stably. As a result, the air-fuel ratio does not fluctuate during engine idling or engine light load operation, ensuring stable idling. Furthermore, when the engine is accelerating, the air-fuel mixture supplied into the engine cylinders is Since it is possible to prevent the exhaust gas from becoming excessively concentrated from time to time, it is possible to maintain good exhaust emissions.

[Brief explanation of the drawing]

Fig. 1 is a side sectional view of a variable venturi type carburetor according to the present invention, Fig. 2 is an enlarged view of a part of Fig. 1, and Fig. 3 is a sectional view of a portion of Fig. 1.
FIG. 3 is a front view of the front end surface of the suction piston as seen along arrow A in the figure. 1... Carburetor body, 3... Suction piston, 4
... Needle, 6... Throttle valve, 14... Guide rod, 21... Metering jet, 32... Threaded hole, 34... Screw, 37.38... Seal member, 40
...Guide groove. Patent Applicant Toyota Motor Corporation Patent Application Agent Patent Attorney Akira Aoki Patent Attorney Kazuyuki Nishidate Patent Attorney Kyosuke Nakayama Patent Attorney Akira Yamaguchi Figure 1

Claims (1)

[Claims] A suction piston that changes the venturi area in response to the amount of intake air, a needle connected to the suction piston, a fuel passage extending in the axial direction of the needle so that the needle can enter, and a fuel passage inside the fuel passage. In a variable venturi type carburetor provided with a metering jet cooperating with the needle, a suction piston guide rod slidably held by the suction piston casing is formed from a hollow tube open at both ends; A root portion of the needle is fitted into one open end of the guide rod, and a screw hole is bored in the suction piston, the threaded hole extending from the outer peripheral wall of the root portion of the guide rod in a direction transverse to the longitudinal direction of the guide rod. A variable venturi type carburetor, wherein a needle fixing screw is screwed into the screw hole, an open end of the screw hole is closed by a sealing member, and the other open end of the guide rod is closed by a sealing member.