JPS58107856A - Variable venturi carburetor - Google Patents

Abstract

PURPOSE:To introduce larger negative pressure to a negative pressure chamber, by communicating a Venturi part formed by a suction piston and the negative pressure chamber of said piston through a suction hole formed in the point end face of said piston gradually protruded toward the upstream side. CONSTITUTION:The captioned carburetor is operated in such a manner that a suction piston 3 is moved responsively 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 cooperatively work with a metering jet 21 to measure fuel. Here the point end face of the piston 3 is gradually protruded toward the upstream side from the needle 4 while a protrusion well 24 is formed on the internal wall face of an intake passage located at a face-to-face position to the point end face of the piston 3. Then a throttle part is formed between these protruded point end face 25 and protrusion wall 24, and the Venturi part 8 formed in the downstream of said throttle part and a negative pressure chamber 15 of the suction piston are communicated through a suction hole 18 formed to said face 25.

Description

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

In a variable venturi type carburetor, when the spring force of the compression spring that presses the suction piston is increased, the sliding hysteresis of the suction piston becomes smaller, which causes variations in the amount of fuel supplied when the lift amount of the suction piston increases and when it decreases. becomes small, and thus an appropriate amount of fuel can be constantly supplied according to the amount of intake air. If the spring force of the compression spring that presses the suction piston is strengthened, the driving force of the suction piston will increase, making it possible to move the suction piston even when a foreign object is caught in the suction piston or when the suction piston is frozen. Can be done. Therefore, in the variable Pencil type carburetor, it is preferable to strengthen the spring force of the compression spring that presses the saxilon piston. However, in conventional variable venturi type carburetors, if the spring force of the compression spring is strengthened, the suction piston will not fully open the intake passage when the amount of intake air is large, so the spring force of the compression spring cannot be strengthened.

SUMMARY OF THE INVENTION An object of the present invention is to provide a variable pliers type carburetor that allows the suction piston to fully open the intake passage when the amount of intake air is large even if the spring force of the compression spring that presses the suction piston is increased.

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 a needle attached to the tip surface of the suction piston 3. , 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 inside the carburetor float chamber, and the tip surface of the suction piston 3 and the spacer 5 are connected to each other.
In between, a penchili part 8 is created. Vaporizer body 1
A hollow cylindrical casing 9 is fixed to the casing 9, and a guide sleeve 0 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 , and 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 piston 3, and this guide rod 14 has a bearing.
2 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.

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, and a compression spring 17 is inserted into the negative pressure chamber 15 to constantly press the suction piston 3 toward the venturi section 8. . The negative pressure chamber 15 is connected to the venturi section 8 through a suction hole 18 formed in the suction piston 3, and the atmospheric pressure chamber 16 is connected to the intake air upstream of the suction piston 3 through an air hole 19 formed in the carburetor body 1. It is connected within the 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. A fuel passage 20 upstream of the metering jet 21 is connected to the float chamber 7 via a downwardly extending fuel vibe 22.
The fuel in the float chamber 7 is sent into the fuel passage 20 via this fuel pipe 22. Furthermore, the spacer 5 has a hollow cylindrical nozzle 2 disposed coaxially with the fuel passage 20.
3 is fixed. This nozzle 23 protrudes into the venturi 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.

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.

Referring to FIGS. 1 to 4, the suction piston 3
The distal end surface of the needle 4 is gradually raised upstream from the needle 4, and a groove 26 with a V-shaped cross section is formed in the center of this raised surface 25.
is formed. Therefore, the raised surface 25 has a pair of inclined wall portions 25a that are inclined toward the bottom of the groove 26, and the succilon hole 18 is formed in one of these inclined wall portions 25m.
As can be seen from the figure, the upstream end 27 of the tip surface of the suction piston has a 7-shape, and on the inner wall surface of the intake passage 2 facing this V-shaped upstream end 27, there is a horizontal direction toward the inside of the intake passage 2. A protruding raised wall 24 (FIG. 1) is formed. The upstream end 27 of the suction piston tip surface and the raised wall 24 form an intake air inflow control restrictor 9 between them. When engine operation is started, air flows downward in the intake passage 2. At this time, the airflow is restricted between the upstream end 27 of the piston tip surface and the raised wall 24, so negative pressure is generated in the venturi portion 8, and this negative pressure is applied to the suction hole 18.
It is led into the negative royal room 15 via. The suction piston 3 is arranged so that the pressure difference between the negative pressure chamber 15 and the atmospheric pressure chamber 6 becomes an almost constant pressure determined by the spring force of the compression spring 17, that is, the negative pressure inside the venturi section 8 becomes almost constant. Move to.

In this way, the suction piston 3 moves so that the negative pressure inside the venturi section 8 is constant, but the negative pressure inside the venturi section 8 is not constant over the entire area inside the venturi section 8, and there are places within the venturi area. Each one has a different size. FIG. 6 shows the magnitude of negative pressure generated within the negative chamber 15 when suction holes 8 are provided at various positions as shown in FIG. In FIG. 6, the vertical axis P indicates the negative pressure (mmAq) k in the negative pressure chamber 15, and the horizontal axis Q indicates the intake air amount (gr/see). In addition, in FIG. 6, the songs a a + b * c 1 d are at positions a in FIG. 5, respectively.

Experimental results when suction holes 18 are provided in b, c, and d are shown. Furthermore, in FIG. 6, the broken line e indicates that the suction piston 3 has a flat end surface as shown in FIG. 7 and FIG. A variable venturi type carburetor is shown. When the suction hole 18 is formed at position a in FIG. 5 as shown in FIG.
The negative pressure inside the negative pressure chamber 15 becomes considerably larger than that in the case where the negative pressure chamber 15 is formed with a break. An increase in the negative pressure in the negative pressure chamber 15 means that the spring force of the compression spring 17 can be increased accordingly.

As described above, according to the present invention, by making the shape of the suction piston tip end surface unique, it is possible to introduce a higher negative pressure into the negative pressure chamber of the suction piston than before for the same amount of intake air. In this way, the spring force of the compression spring that presses the suction piston can be strengthened. As a result, the sliding hysteresis of the suction piston is reduced, so the amount of fuel supplied becomes stable, and even if a foreign object gets caught in the suction piston or the suction piston freezes, the suction piston can be forcibly moved. . In addition, in Fig. 6, the curve a and the broken line e
When compared with tl, there is a large difference in the negative pressure P when the intake air amount Q is large, but when the intake air iQ is small, there is almost no difference in the negative pressure P. Therefore, if the spring force of the compression spring of the suction piston is set so that the suction piston fully opens the intake passage when the intake air amount Q is large, when the intake air amount Q is small, the present invention is better than the conventional variable venturi type. Compared to the carburetor, the negative pressure in the vent area is greater, and the flow rate of intake air is increased accordingly. Therefore, atomization of fuel can be promoted when the amount of intake air Q is small.

[Brief explanation of the drawing]

Fig. 1 is a side cross-sectional view of a variable venturi type carburetor according to the present invention, Fig. 2 is a front view of the front end of the piston, viewed along arrow AK in Fig. 4 is a sectional view taken along the line IV-IV in FIG. FIG. 7 is a side sectional view of a conventional suction piston, and FIG. 8 is a front view of the tip of the suction piston shown in FIG. 1... Carburetor body, 3... Suction piston, 4...
・Needle, 6-way throttle valve, 18-way spool hole,
24... Raised wall. Patent applicant Toyota Motor Corporation Aisan Industries, Ltd. Patent application agent Akira Aoki Patent attorney Kazuyuki Nishidate Patent attorney Kyosuke Nakayama Patent attorney Akira Yamaguchi

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 the variable venteri type carburetor, which is provided with a metering jet that is provided and cooperates with the needle, a raised wall projecting into the intake passage is formed on an inner wall surface of the intake passage opposite to the tip surface of the suction piston, and the suction piston The tip surface is gradually raised upstream from the needle to form an intake air inflow control throttle section between the upstream end of the raised tip surface and the raised wall, and is formed downstream of the throttle section. A variable venturi type carburetor in which a suction hole is formed on the raised tip surface of the suction piston to communicate the venturi portion and the suction piston negative pressure chamber.