JPS60216057A - Variable venturi carburetor - Google Patents

Abstract

PURPOSE:To suck fuel smoothly by employing a linear tube between the float chamber and the variable throttle section of variable Venturi carburetor while atomizing the vapor bubble at the variable throttle. CONSTITUTION:A tapered needle 16 fixed to the end of a laterally slidable suction piston 15 will adjust the throttle area through the gap against the restricting section 13 thus to control the amount of fuel. The fuel path 20 of float chamber 17 will open to said section 13 but a linear tube is amployed for the fuel path to eliminate storage of steam. When fuel is sucked from the float chamber 17 into the restricting section 13 by the negative pressure at the Venturi section, bubbles to be produced in the fuel under high temperature of float chamber will pass through the linear tube 20 and arrive to the restricting section 13 then ejected together with the air fed through an air-bleed path 21 with high speed thus to never impede ejection of atomized fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a variable venturi type carburetor, and more particularly to a carburetor that suppresses coalescence and growth of vapor bubbles generated in fuel in a fuel passage. .

(Prior Art) A variable venturi type carburetor, for example, a horizontal needle type variable venturi type carburetor, has a constriction part in a part of a fuel suction hole 2 whose one end opens into a venturi part 1, as shown in FIG. 3, and a venturi part 1 facing the fuel suction hole 2.
A suction piston 4, which is provided so as to be movable back and forth, is provided with a tapered needle 5 that penetrates the inside of the constriction part 3.
The amount of sucked fuel is measured by the effective cross-sectional area of the gap formed between the constriction part 3 and the constriction part 3. Here, the suction piston 4 moves according to the amount of intake air in the intake system, and serves to keep the venturi negative pressure C constant.

(Problems to be Solved by the Invention) Incidentally, in a conventional carburetor of this kind, the upper end of the fuel passage 7 whose lower end opens into the float chamber 6 is connected to the fuel suction hole 2 upstream of the throttle part 3. Since the opening is made inward, when the fuel is kept idling due to high temperature, vapor bubbles 8 generated in the fuel stay in the fuel suction hole 2, coalesce and grow, and block the throttle part 3. A phenomenon occurred in which the air-fuel mixture gradually became thinner. Further, when the vapor bubbles 8 pass through the throttle section 3, the air-fuel mixture becomes thinner rapidly, sometimes causing hunting in the air-fuel ratio as shown in the characteristic curve A in FIG.

As a result of these phenomena, the stability of the engine during idling deteriorates, and in some cases, the engine stalls.

(Means for Solving the Problems) In order to solve the problems of the conventional art described in L, the present invention forms a constriction part in a part of the fuel suction hole whose one end opens to the venturi part. A suction piston that is opened 1-1 so as to be able to move forward and backward into the venturi section is provided with a tapered needle that passes through the throttle section, and one end of which is open to the float chamber and is made of a thin tube with a uniform C cross section. The gist is that the other end of the fuel passage is opened to the inner wall of the throttle part, and furthermore, the air bleed passage is opened directly upstream of the throttle part, so that it has a shape of φ.

(Function) In the variable venturi type carburetor configured as described above, the other end of the fuel passage is opened in the constriction part which has the smallest flow passage area and the highest fuel flow rate among the fuel suction holes, so that the above-mentioned It is possible to prevent the accumulation of bubbles and to prevent their coalescence and growth. Moreover, since the air bleed passage is opened upstream of the constriction, by introducing bleed air into the constriction, the fuel flow velocity in the constriction can be further increased, and the effect of sucking out vapor bubbles can be further enhanced.

(Example) An example in which the present invention is applied to a horizontal needle variable venturi type carburetor will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which lO
1 is a carburetor main body, 11 is a venturi portion, 12 is a fuel suction hole whose one end opens into the venturi portion ll, and 13 is a constriction portion provided in a part of the fuel suction hole 12. This aperture part 1
3 is formed on a cylindrical member 14 inserted into the main body IO. 14a is an O-ring, and 14b is a suppression spring.

A suction piston 15 is provided facing the fuel suction hole 12 and movable back and forth within the venturi portion 11. The suction piston 15 has its base located within a suction chamber (not shown) provided outside the main body 10. The venturi portion 11 is normally biased by a spring in a direction to narrow down the effective cross-sectional area of the venturi portion 11. The suction piston 15 moves forward and backward depending on the amount of intake air to keep the venturi negative pressure almost constant.

1B is a tapered needle fixed to the suction piston 15, which faces the inside of the constriction part 13, and measures the fuel by displacing within the constriction part 13 in conjunction with the suction piston 15.

A float chamber 17 is provided in the main body lO below the fuel suction hole 12. 20 is a vertical fuel passage for guiding the fuel in the float chamber 17 into the fuel suction hole 12;
The lower end 20A of the float chamber 17 opens near the bottom of the float chamber 17, and the upper end 20b penetrates the main body 10 and the side wall of the cylindrical member 14 and opens into the throttle section 13. This passage 20 is preferably a thin tube with a uniform C cross section.

On the other hand, one end of an air bleed passage 21 is opened in the fuel suction hole 12 on the upstream side of the throttle part 13. The other end of the air bleed passage faces the outside of the main body 1O, from which bleed air is supplied.

With this configuration, the fuel in the float chamber 17 rises in the fuel passage 20 due to venturi negative pressure, and the fuel in the fuel suction hole 1
The liquid is sucked into the constriction part 13 in the needle 16 and the constriction part 13, is metered in the annular gap formed between the needle 16 and the constriction part 13, and is injected into the venturi part 11. Since the annular gap has a very small area, the fuel flow rate is high. Therefore, small bubbles of fuel vapor generated in the fuel passage 20 at high temperatures are sucked out from the passage 20 into the annular gap. In addition, since there is no enlarged diameter portion (dead space) between the fuel passage 20 and the annular gap, air bubbles do not accumulate in the middle, so the bubbles pass through the annular gap without coalescing and growing. and is sucked out to the venturi section.

However, at this time, bleed air is introduced into the fuel suction hole 12 from the air bleed passage 21, the fuel flow rate within the constriction part 13 is further accelerated, and the bubble suction effect is enhanced.

As a result, the air-fuel ratio of the mixture supplied to the engine is 5th.
As shown by characteristic surface 1iB in the figure, C is kept constant without any hunting phenomenon or attenuation, and the stability of the engine during idling is ensured.

As shown in FIG. 2, the present invention provides two annular grooves 22 and 23 on the outside of the constricted part 13 of the cylindrical member 14, and a plurality of small annular grooves 22 and 23 each opening into the constricted part 13. The fuel passage 20 and the air bleed passage 21 may be opened into the throttle portion 13 through the holes 24 and 25, respectively.

In the case of this example, since fuel and bleed air are introduced into the throttle part 13 through the plurality of small holes 24 and 25, the degree of mixing between the fuel and bleed air is increased, a uniform emulsion flow is formed, and the fuel and bleed air are The vapor bubbles inside are smoothly sucked out, and the same effect as in the above embodiment is achieved.

Furthermore, as shown in FIG.
A plurality of small holes 24' opening into the throttle portion 13 are provided at 2' at intervals in one circumferential direction, and the fuel passage 2 is opened through the plurality of small holes 24'.
0 and the air bleed passage 21 may be opened in the throttle part 13.

In this example, the small steam bubbles generated in the passage 20 are removed from the annular groove 2.
It is separated from the fuel in 2' and flows into the throttle part 1 along with the bleed air.
3, and is rapidly discharged from there, producing the same effects as in the above two embodiments.

Although each embodiment has been described above, it goes without saying that the present invention can also be applied to a ti (variable venturi type carburetor) other than the horizontal needle type, that is, a carburetor in which the intake passage is arranged horizontally.

(Effects of the invention) As explained above, the present invention provides a variable venturi type carburetor in which one end of the fuel passage is made of a thin tube with a uniform cross section and which opens into the float chamber. Since the opening is made directly in the constriction part, which has the smallest flow path area and the highest fuel flow velocity, it is possible to prevent the coalescence and growth of vapor bubbles that occur in the fuel in the fuel passage under high temperatures. Since the air bleed passage is opened on the upstream side, the introduction of bleed air further accelerates the fuel flow velocity within the constriction, making it extremely easy to discharge vapor bubbles.
As a result, the thinning of the air-fuel ratio and the hunting phenomenon caused by the combined growth of vapor bubbles were prevented, and the stability of the engine during idling was improved.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a horizontal needle variable venturi type carburetor showing one embodiment of the present invention, and FIGS. 2 and 3 are longitudinal cross-sectional views of essential parts showing other embodiments of the present invention, respectively. FIG. 4 is a longitudinal sectional view showing a conventional horizontal needle variable venturi type carburetor, and FIG. 5 is a diagram showing the air-fuel ratio and time characteristics during fitting of the conventional device and the device of the present invention. 11 ... Venturi section 12 ... Fuel suction hole 13 ... Throttle section 15 ... Suction piston 16 ... Needle 17 ... Float chamber 20 ... Fuel passage 21 ... Air bleed passage No. 1 Figure 2 t”1 ′!;'= 3 Whistle 4 Figure 5

Claims (1)

[Claims] (1) A constriction part is formed in a part of the fuel suction hole whose one end opens in the venturi part, and the suction piston, which is opened in the fuel suction hole and is provided so as to be movable in and out of the venturi part, penetrates the inside of the constriction part. A tapered needle is provided,
The other end of the fuel passage, which is made of a thin tube with a uniform cross section of C and whose one end opens into the float chamber, is opened directly to the inner wall of the throttle part, and furthermore, an air bleed passage is opened upstream of the throttle part. if) a modified venturi type vaporizer.