JPS6054500B2 - Variable stage vaporizer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable stage carburetor for an internal combustion engine, and more particularly to a variable stage carburetor equipped with a device for quickly disposing of air bubbles remaining in the fuel passage of the carburetor. .

Recently, in order to meet the demand for smaller and lower profile carburetors, the fuel passage from the float chamber of the carburetor to the fuel nozzle has become complex in shape, making it easier for bubbles generated within the passage to remain. If bubbles remain in the fuel passage, they will grow and temporarily block the fuel flow when large bubbles pass through the fuel metering jet, causing problems such as irregular engine operation and misfires. Ta.

In particular, in a downdraft type variable stage carburetor as disclosed in Japanese Patent Application Laid-Open No. 50-53733, the needle provided at the tip of the vane is arranged diagonally upward.
A downward fuel passage is inevitably formed. When the fuel passage is inclined downward, the generated air bubbles do not flow together with the fuel, so that the bubbles grow significantly due to the accumulation of air bubbles, and the above-mentioned problems are likely to occur. An object of the present invention is to quickly cause bubbles generated in the downward fuel passage to flow downstream of the fuel metering jet before they grow, thereby preventing the bubbles from temporarily blocking the metering jet.

A feature of the present invention is that a bubble removal passage is provided in parallel with the fuel passage, which communicates the top of the downward fuel passage with a constriction portion provided upstream of the fuel metering jet and close to the jet.

The embodiments shown in the drawings will be described below.

The variable stage carburetor has a vane 2 installed in the intake cylinder 1 and a throttle valve 3 linked together by a link 4, and the vane 3 changes the cross-sectional area of the vent lily to always generate an appropriate negative pressure in the vent lily. Interlocking jet needle 5
The fuel is metered by a fuel metering jet 7 composed of a fixed orifice 6, and is injected into the bench lily section by the negative pressure of the bench lily, thereby supplying an appropriate air-fuel mixture to the engine.

Therefore, in the variable stage type carburetor, it is advantageous to install the vane shaft 9 as far away from the throttle valve shaft 10 as possible in terms of the accuracy of the interlocking between the throttle valve 3 and the vane 2, and the jet needle 5 is attached to the tip of the vane. This is advantageous in terms of fuel metering accuracy and space, so when this carburetor is used as a downward ventilation type, the configuration shown in the drawing is advantageous, and the tip of the jet needle 5 faces upward, making it easier to measure fuel. The jet 7 and the upstream fuel passage 11 face downward. Therefore, there is a drawback that air bubbles accumulate at the upper end 15 of the downward fuel passage 11, grow, and reach the vicinity of the fuel metering jet 7, causing irregular fluctuations in the fuel flow rate. Therefore, on the upstream side of the fuel metering jet 7, there is a fuel passage 11 located close to the jet 7 and having a slightly larger diameter than the jet 7.
A constricted portion 12 smaller than the diameter of the constricted portion 12 is formed.
and the upper end 15 of the fuel passage 11.
3 will be provided. The passage 13 requires consideration so that minute air bubbles accumulated on the soil edge 15 do not grow large when passing through the passage 13.

According to the test results conducted by the present inventors, it has been found that when the cross-sectional area of the passage 13 becomes large, the flow velocity in this passage decreases, and the movement of bubbles is not performed satisfactorily. Therefore, good results were obtained when the cross-sectional area of the passage 13 was less than half the cross-sectional area of the passage 11, preferably about 1 B. The bubble removal passage 13 is
It is preferable to provide it parallel to the downward fuel passage 11 and above the passage 11.

In a carburetor having such a configuration, minute bubbles are generated in the fuel due to heat from the engine during engine operation, and accumulate at the upper end 15 of the downward fuel passage 11.

Since the upper end 15 and the throttle part 12 are communicated with each other through the air bubble removal passage 13, a fuel flow is generated in the passage 13 from the upper end 15 toward the throttle part during operation of the engine. This fuel flow is
2, this occurs because the pressure drop due to the increase in fuel flow rate in this portion exceeds the water head difference between the constricted portion 12 and the upper end 15. Therefore, the minute bubbles reach the constriction part 12 together with the fuel flowing through the passage 13, and because the fuel flow rate is high in this part, they do not rise in the passage 11 but are sucked into the intake cylinder 1 through the metering jet 7. be done.

The bubbles generated in the fuel passage 11 quickly flow into the passage 13 when they reach the upper end 15, so the bubbles do not grow and pass through the metering jet 7 in a minute state, so that the fuel is temporarily absorbed. There is no stagnation, and fluctuations in fuel flow rate are also reduced.

The smaller the inner diameter of the throttle part 12 is set, the narrower the passage 13 becomes.
However, if the throttle portion 12 is made smaller, there is a risk that the resistance of the fuel will increase during high-speed operation.

Therefore, the diameter of the constricted part 12 is determined by taking into account the water head difference between the constricted part 12 and the upper end 15, the amount of bubbles generated, and the like.

Under normal operating conditions of the engine, the fuel passing through the passage 13 is also metered by the metering jet 7, so the provision of the bubble removal passage does not reduce the accuracy of fuel metering.

As described above, according to the present invention, it is possible to reduce irregular fluctuations in fuel flow rate caused by grown bubbles passing through a metering jet.

[Brief explanation of the drawing]

The figure is a sectional view of a variable stage carburetor embodying the present invention. 1... Intake cylinder, 2... Vane, 3...
... Throttle valve, 5 ... Needle, 7 ...
・Fuel metering jet, 8... Bench lily part, 1
1... Downward fuel passage, 12... Throttle part,
13...Bubble removal passage, 15...Top end.

Claims (1)

[Claims] 1. An intake passage that allows intake air to flow in a substantially vertical direction, a throttle valve that controls the amount of intake air flowing through the intake passage, and a vane that forms a variable bench lily between the intake passage wall and the intake passage upstream of the throttle valve. a link mechanism that communicates the vane and the throttle valve; a fuel nozzle that opens in the variable bench lily; and a fuel nozzle that extends from the fuel nozzle and partially allows fuel to flow obliquely downward toward the intake flow that flows through the intake passage. A fuel passage forming a passage portion and leading to a float chamber, a metering jet provided in the obliquely downward passage portion, and a needle attached to the vane for cooperating with the metering jet to meter the fuel. In the variable stage carburetor, a constriction part is formed upstream of the metering jet and close to the metering jet and has a larger diameter than the metering jet and a smaller diameter than the diagonally downward passage section, and the slanted downward passage section A variable stage type vaporizer, characterized in that a bubble removal passage is provided in parallel with the throttle part and the vicinity of the highest point of the obliquely downward passage part on the upstream side of the metering jet.