JPH0229862B2 - - Google Patents

Description

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

a suction piston that changes a bench lily 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 therein;
In a variable bench lily type carburetor equipped with a metering jet installed in the fuel passage and cooperating with a needle, metering is performed by the needle and metering jet when the opening amount of the suction piston is small, such as during idling or light load operation. The fuel travels through the needle and reaches the tip of the suction piston. The fuel that has reached the tip of the suction piston then flows down the tip of the suction piston, but the flow path is extremely unstable, and especially during idling, the air-fuel ratio of the mixture supplied into the engine cylinders is cyclic. fluctuates. the result,
As a result, the engine speed fluctuates, resulting in unstable idling. In addition, as mentioned above, if fuel adheres to the tip surface of the suction piston, the adhering fuel will be supplied into the engine cylinder when the engine is accelerating, causing the air-fuel mixture supplied to the engine cylinder to become temporarily enriched. , thus giving rise to the problem of deterioration of exhaust emissions. Furthermore, if the fuel adhering to the tip of the suction piston becomes large fuel 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 amount of fuel in these fuel droplets occupies a large proportion compared to the amount of supplied fuel, so each time the fuel droplets fall, the engine The air-fuel mixture supplied into the cylinder becomes too rich. As a result, the problem arises that idling becomes unstable due to fluctuations in engine speed.

The present invention prevents fuel droplets from falling from the suction piston tip surface and allows the fuel adhering to the suction piston tip surface to flow down continuously and stably, thereby providing stability during engine idling operation or engine light load operation. To provide a variable bench lily type carburetor which ensures a stable idling operation.

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. As shown in FIG. 1, a fuel passage 20 upstream of the metering jet 21 and a fuel passage 20 downstream of the metering jet 21 are interconnected by a fuel bypass passage 24. This fuel bypass passage 24 includes an intermediate portion 24a extending in a substantially horizontal direction, and a fuel passage 20 upstream of the metering jet 21 from one end of the intermediate portion 24a.
An inflow passage portion 24b extending inward, and a fuel passage 20 downstream of the metering jet 21 from the other end of the intermediate portion 24a.
an outflow passage portion 24c extending inward;
A jet 25 is inserted into the intermediate portion 24a.
Further, 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 the air bleed passage 27 and the air bleed jet. It is connected to the intake passage 2 upstream of the suction piston 3 via 28.

As shown in FIGS. 1 and 2, the guide rod 14 fixed to the suction piston 3 is formed from a hollow tube with both ends open.
A needle holder 31 carrying a needle 4 is fitted into one open end of the needle holder 31 . Needle holder 3
A threaded hole 32 is threaded above the needle holder 31 and extends upward from the outer circumferential wall of the needle holder 31 through the guide rod 14 and the suction piston 3. 34 is screwed on. The needle holder 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. A sealing member 37 for preventing air leakage is packed into the open end of the screw hole 32 of this screw 34, so that the seal member 37 passes between the screw 34 and the screw hole 32 and connects the outer peripheral surface of the needle holder 31 and the guide rod 14. Air is prevented from leaking through the bench lily portion 8 into the bench lily portion 8. On the other hand, the open end of the guide rod 14 on the opposite side to the needle holder 31 is filled with a sealing member 38 for preventing air leakage, so that the seal member 38 passes between the blind cover 13 and the guide sleeve 10 and the outer peripheral surface of the needle holder 31 Air is prevented from leaking into the bench lily portion 8 between the guide rod 14 and the guide rod 14. The distal end surface of the suction piston 3 below the needle holder 31 is formed with a downwardly inclined surface 39, and as shown in FIGS. 2 and 3, the needle holder 3
A guide groove 40 is formed that extends directly downward from 1. 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 a fuel passage 4 formed in the carburetor main body 1.
2 to the aperture 43. This opening 43
As shown in FIG. 2, when the throttle valve 6 is idling open, it opens into the intake passage 2 downstream of the throttle valve 6, and when the throttle valve 6 opens, it opens into the intake passage 2 upstream of the throttle valve 6. .

As shown in FIG. 1, the upper end of the spacer 5 has a raised wall 3 that projects horizontally into the intake passage 2.
0 is formed, and the flow rate is controlled 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 airflow is restricted between the suction piston 3 and the raised wall 30, 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 is a substantially constant value determined by the spring force of the compression spring 17, that is, the negative pressure inside the bench lily portion 8 is substantially constant. Moving.

When the engine is idling, 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 flows through the fuel bypass passage 24. from jet 26 to nozzle 2 through
Supplied within 3 days. Air is bleed from the air bleed passage 27 into the fuel flowing through the fuel bypass passage 24, and thus fuel containing air bubbles is supplied from the jet 26 into the nozzle 23. The fuel fed into the nozzle 23 through the annular gap between the needle 4 and the metering jet 21 travels along the bottom wall surface of the nozzle 23, and is atomized by the shear force exerted by the air flow at the tip of the nozzle 23. . On the other hand, the fuel flowing out from the jet 26 is sucked by the negative pressure generated in the bench lily portion 8 and advances along the upper wall surface of the nozzle 23, 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 without accumulating and flows into the guide groove 40. sent to. Further, at this time, since air does not leak from between the outer peripheral surface of the needle holder 31 and the guide rod 14, the fuel sent onto the needle holder 31 is not blown away by the leaked air, and thus this fuel is guided. It will flow down towards the groove 40. The leaked air also prevents the movement of the fuel flow over the needle 4, causing the fuel to accumulate on the needle 4, thereby preventing the formation of droplets on the needle 4. . The fuel that has flown down from the tip end surface 35 of the needle holder 31 into the guide groove 40 continuously flows within the guide groove 40 . It can thus be seen that this guide groove 40 constitutes a guide for guiding the flow of liquid fuel. Next, the fuel that has reached the lower end of the guide groove 40 is sucked by the tube 41 and sent into the intake passage 2 downstream of the throttle valve 6. Therefore, the fuel does not accumulate on the lower edge of the tip surface of the suction piston 3 and fuel droplets are not formed, and thus it is possible to prevent the occurrence of fluctuations in the air-fuel ratio due to periodic falling of these fuel droplets. can. In this way, the guide groove 40 is formed on the tip inclined surface 39 of the suction piston 3.
By capturing the liquid fuel flowing down from the guide groove 40 with the tube 41, the flow of fuel becomes continuous and stable during engine idling operation or light load operation, and thus the air-fuel ratio changes. Since fluctuations are eliminated, stable idling operation can be ensured. When the throttle valve 6 opens 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 sent into the nozzle 23 through this annular gap without bypassing the fuel bypass passage 24.

As described above, according to the present invention, it is possible to prevent fuel droplets from forming on the lower edge of the suction piston tip surface, to prevent fuel from staying on the suction piston tip surface, and to prevent fuel droplets from forming on the suction piston tip surface. The fuel adhering to the tip surface is allowed to flow down continuously and stably. As a result, when the engine is idling,
Alternatively, since the air-fuel ratio does not fluctuate during engine light load operation, stable idling operation can be ensured, and the air-fuel mixture supplied into the engine cylinders can be prevented from becoming temporarily overrich during engine acceleration operation. Since this can be prevented, good exhaust emissions can be maintained.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of a variable bench lily type carburetor according to the present invention, FIG. 2 is an enlarged view of a part of FIG. 1,
FIG. 3 is a front view of the front end of the suction piston taken along arrow A in FIG. 2. 1... Carburetor body, 3... Suction piston, 4... Needle, 6... Throttle valve, 14
...Guidance rod, 21...Measuring jet, 32...
...Threaded hole, 34...Screw, 37, 38...Seal member, 40...Guide groove.

Claims (1)

[Claims] 1. A suction piston that changes the area of the bench lily 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 the fuel In a downdraft type variable bench lily type carburetor equipped with a metering jet disposed in a passage and cooperating with the needle, a suction piston is inserted from near the root of the needle onto the tip surface of the suction piston below the root of the needle. A fuel suction tube that forms a liquid fuel distribution guide that extends to the lower end edge of the tip surface, and captures liquid fuel flowing down along the guide below the guide and sends it into the intake passage downstream of the throttle valve. Variable bench lily type vaporizer with