JPS6143256A - Variable venturi type carburetor - Google Patents

Abstract

PURPOSE:To prevent the variation of engine revolution by forming a fuel passage which is branched from the upstream of the metering jet of a variable venturi type carburetor and opened to a suction passage on the upstream side of a throttle valve, and forming said opened port part into a spread form free of horizontal surface. CONSTITUTION:A needle valve 4 at the edge part of a slidable piston 14 installed onto the upstream side of a throttle valve 6 supplies the fuel corresponding to the gap between a metering jet 21 into a suction passage 5 from a nozzle 23. A fuel passage 24 branched from the upstream side of the jet 21 supplies the idle low-speed fuel into the suction passage 5 between the throttle valve 6 and a piston 14 from an opened port 25b through a vertical passage 25a. Said opened port 25b is spread towards the suction passage and formed into bugle form, and since a horizontal plane does not exist, the fuel accumulation at the opened port 25b is prevented.

Description

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

A suction piston that changes a 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 therein; Variable venturi carburetors are known which have a metering jet disposed in a fuel passage and cooperating with the needle, and a variable venturi carburetor with a pinhole passage opening from said fuel passage into an intake passage. The device is described, for example, in Japanese Patent Application Laid-Open No. 58-222956.

Problems to be Solved by the Invention The bypass fuel passage is mainly used to adjust the air-fuel ratio during idling, and is generally opened downstream of the throttle valve. If the piston fuel passage is opened upstream of the throttle valve, that is, near the bench or υ section, a constant negative pressure will always act on the variable bench or ri-type carburetor, allowing fuel to be sucked out at all times, even when not idling. will be carried out. However, when the bypass fuel passage is opened upstream of the throttle valve, fuel tends to accumulate in the horizontally extending outlet passage compared to the conventional case where the bypass fuel passage is opened directly below the throttle valve.
This dripped unsteadily into the intake passage, causing fluctuations in the idle air-fuel ratio. Furthermore, when accelerating from near idle, if the amount of fuel adhering to the wall of the intake passage is small, a transient phenomenon occurs.

Therefore, measures such as increasing the idle set rotation and increasing the discharge amount of the acceleration pump have been taken, but this leads to worsening of fuel efficiency.Means for Solving the Problems In the present invention In a variable Pencili type vaporizer,
The piston/gas fuel passage is opened in the intake passage at a position upstream of the throttle valve, and the opening is widened into a trumpet shape.

As a result, the fuel does not accumulate in the air, but actively spreads on the inner wall surface of the intake passage 9, improving idle stability and transient response.

Embodiment Referring to FIG. 1, 1 is a carburetor main body, 2 is an intake passage extending vertically downward, 3 is a piston that moves laterally in the intake passage 2, and 4 is a suction piston 3.
A needle 5 is attached to the tip surface of the piston 3, and an intake passage 2 is formed flat opposite the tip surface of the piston 3.
6 is the intake passage 2 downstream of the suction piston 3.
Throttle valves 7 provided therein indicate carburetor float chambers, and a venturi portion 8 is formed between the tip end surface of the suction piston 3 and the inner wall surface 5. The passage area of this bench 9 section 8 is defined by a bridge 9 formed integrally with the carburetor main body 1 and raised in the intake passage 2 and an upper edge of the tip surface of the suction piston 3. The bridge 9 is formed in a V-shape as shown in FIG. 4, and prevents self-excited vibration of the suction piston 3, thereby making the conventional oil stopper 4 unnecessary.

A hollow cylindrical casing 10 that encloses the rear end side of the suction piston 3 is fixed to the carburetor body 1, and a guide sleeve 11 that extends in the axial direction of the casing 10 inside the casing 10 is attached. A bearing 12 is inserted into the guide sleeve 11 , and the outer end of the guide sleeve 11 is closed by a blind cover 13 . On the other hand, a guide rod 14 is fixed to the succinct piston 3, and the guide rod 14 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 10 via the bearing 12, the suction piston 3 can move smoothly in its axial direction. The interior of the casing 10 is divided into a negative pressure chamber 15 and an atmospheric pressure chamber 16 by the suction piston 3, and within the negative pressure chamber 15 is a compression spring 1 that constantly presses the suction piston 3 toward the venturi portion 8.
7 is inserted. The negative pressure chamber 15 is connected to the pliers 8 through a suction hole 18 formed in the slit piston 3, and the atmospheric pressure chamber 16 is connected to the slit piston 3 through an air hole 19 formed in the carburetor body 1. 3 is connected to the intake passage 2 upstream.

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 jet 21 is connected to the float chamber 7 via a downwardly extending fuel pipe 22.
The fuel in the float chamber 7 is sent into the fuel passage 20 via this fuel arm hole 22. Furthermore, a hollow cylindrical nozzle 2 is disposed coaxially with the fuel passage 20 on the inner wall surface 5.
3 is fixed. This nozzle 23 protrudes from the inner wall surface 5 when the venturi is fully closed, and the upper half of the tip of the nozzle 23 is further extended from the lower half.

protrudes 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 . The needle 4 is provided with a notch for starting and increasing the amount, and when the venturi is fully closed as shown in FIG. 1, the notch and the metering jet 21 come to corresponding positions and the annular area between them increases. The metering nozzle 21 is provided with a plurality of through holes, and air is bleed from an air bleed passage (not shown) to the fuel passage 20 of the metering jet 21 section. Further, a bypass fuel passage 25 is connected to the fuel passage 20 at a position upstream of the metering jet 21, and opens into a venturi portion 8 located upstream of the throttle valve 6 in the intake passage 2. The amount of fuel from the main fuel passage 20 is about 70 inches of the total at idle, and as the load increases and the intake air flow rate increases, the proportion of fuel flow from the main fuel passage 20 increases.

An air bleed passage 26 is connected to the bypass fuel passage 25 . There is an adjuster in the bypass fuel passage 25)
! -27 is arranged so that the passage area can be adjusted.

The pinos fuel passage 25 is branched from the main fuel passage 20 and extends upward, and then horizontally extends downward into the passage 25 &
・The downward passage 25m extends vertically downward at a position slightly removed from the main fuel passage 20, and then the lateral passage 2
5b opens into the intake passage 2. Its opening position is facing the piston 3 and below the nozzle 23.

An enlarged view of the vicinity of the opening of the bypass fuel passage 25 to the intake passage 2 is shown in FIGS. 2 and 3. Lateral passage 25b
The intake passage 2 is opened into the intake passage 2 by expanding in a 4-shape shape, and has no horizontal wall. That is, the vertical downward passage 25m is uniformly inclined with respect to the horizontal until the end thereof. Therefore, unlike in conventional horizontal wall passages (in extreme cases, passages with narrowed openings), fuel does not accumulate, there is no unsteady dripping of fuel, and air-fuel ratio fluctuations are prevented. In addition, since the fuel is spread out in a trumpet shape, the fuel is washed by the airflow along the inner wall surface 5 shown by arrow F in FIG. 2 and spreads along the inner wall surface 5. Since the air flow rate in the venturi section 8 is almost constant in the 3-way type carburetor, the fuel along the inner wall surface 5 continues to wet the inner wall surface 5 almost uniformly at all times, improving transient response during acceleration.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, the present invention improves idle stability.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a variable Pencil type carburetor according to the present invention, Fig. 2 is an enlarged view of the vicinity of the opening of the pinot main fuel passage in Fig. 1, Fig. 3 is a front view of Fig. 2, and Fig. 4 is a The figure is a plan view of the intake passage viewed from above the venturi when the venturi is partially open. 3... Suction piston, 4... Needle, 5...
...Inner m surface, 6... Throttle valve, 20... Fuel passage, 25... Pie gas fuel passage, 25 &...
Lateral opening passage O

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. a variable venturi carburetor comprising a metering jet provided and cooperating with the needle; a bypass fuel passage branching from the fuel passage upstream of the metering jet and opening into the intake passage upstream of the throttle valve; A variable venturi type carburetor, characterized in that the opening of the bypass fuel passage to the intake passage is expanded into a trumpet shape.