JPS59138760A - Fuel control device upon choking of carburettor - Google Patents

Abstract

PURPOSE:To prevent a plug from wetting, etc. by controlling the amount of fuel supply to inhibit the pressure differential between the inside of a float chamber and a venturi section upon closing of a choke valve in a carburettor. CONSTITUTION:First and second air vent holes 54, 56 are formed upstream and downstream of a choke valve closed position 52, respectively. Further, there is provided an air vent passage 58 having these air vent holes 54, 56 as the opening end on the intake air passage side, for introducing negative pressure in an intake-air passage 42 into a float chamber 32. Upon cold starting, the negative pressure P2 of a small venturi 46 increases. Meanwhile, the negative pressure P1 downstream of the choke valve also increase, and acts the float chamber 32 through the second vent hole 56 and the air ven passage 58. With this arrangement, both negative pressures P2, P1 of the small venturi 46 and the inside of the float chamber 32 increase to restrain the increment of supply fuel.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention prevents plug bulging during cold starting by suppressing an increase in the amount of fuel supplied due to an increase in engine speed when the carburetor choke valve is closed. The present invention also relates to a fuel control device for when a carburetor is choked, which improves warm-up performance.

[Technical Background of the Invention] An internal combustion engine is equipped with a carburetor as shown in FIG. 1 in order to mix air and fuel at a ratio required by the engine, that is, at a predetermined air-fuel ratio, and supply the mixture to a combustion chamber. Fuel mixed with air in the carburetor 2 and adjusted to an appropriate air-fuel ratio is sent from a fuel tank (not shown) and enters the float chamber 4.

The fuel flowing into the float chamber 4 is maintained at a constant oil level by a needle valve 8 that is linked to the vertical movement of the float 6. When the stored fuel flows out, the flow rate is controlled by the fuel jet 10 and flows out in the direction of the nozzle 12. This fuel is sucked out from the nozzle 12 by the negative pressure of the venturi 16, and is ejected and atomized. The flow rate of this air-fuel mixture is controlled by the throttle valve 18, and the mixture is sucked into a combustion chamber (not shown) and combusted. and the intake passage 1
The upstream side of the choke valve 20 in the float chamber 4 and the inside of the float chamber 4 are communicated through an air vent tube 22 to maintain the same pressure. This prevents air suction resistance from becoming large due to air cleaner clogging, etc., and the negative pressure on the upstream side of the choke valve becoming stronger, preventing a large amount of fuel from being sucked in and ejected, resulting in an overly rich mixture.

[Problems with the Background Art] In such a carburetor, when the choke valve 20 is throttled during a cold start, the amount of air is reduced and a rich air-fuel mixture is supplied. When the engine starts rotating, the pressure P1 in the float chamber is almost constant due to the air vent tube 22 connected upstream of the choke valve, but due to the increase in the amount of intake air due to the increase in engine rotation, the pressure in the venturi 16 becomes negative. Pressure P2 increases. For this reason, the pressure difference (PI
-P2) becomes large. This increase in pressure difference results in an increase in fuel flow rate. As shown in FIG. 2, the fuel flow rate Qf is expressed as Qf=C-Af.2g (Pi-P2)/rr. Here, C: flow coefficient, Af niorifice area, g: gravitational acceleration, Pl: oil level pressure, P2: nozzle outlet pressure, γf: fuel specific gravity.

In the equation, since C, Af, g, and γf are fixed values, the flow rate Qf is Qfc)c(Pi-P2), which varies in proportion to the pressure difference.

For this reason, when the pressure difference (Pl-P2) increases as the engine speed increases, the amount of fuel sucked into the nozzle 12 side increases, making the mixture richer than necessary, resulting in poor warm-up performance such as plug fogging. There was a problem where the product was defective.

[Purpose of the Invention] This invention was made to solve the above problem, and the purpose of this invention is to prevent the pressure difference between the float chamber and the venturi from increasing when the choke valve of the carburetor is closed, thereby reducing the amount of fuel supplied. control, prevent plug fogging, etc.
It also aims to improve warm-up performance.

[Structure of the Invention] To achieve this object, the present invention provides an air vent passage that communicates the intake passage with the float chamber, and an open end of the air vent passage on the intake passage side is provided upstream of the choke valve in the closed state. The air vent hole is branched into a first air vent hole and a second air vent hole provided downstream of the choke valve in the closed state.

According to this configuration, the negative pressure generated downstream of the choke valve when the choke valve is closed acts into the float chamber through the air vent passage from the second air vent hole on the downstream side. This negative pressure increases in response to the increase in negative pressure in the venturi section as the engine speed increases, and acts on the float chamber, so the pressure difference between the venturi section and the float chamber becomes large (there is no such thing as a fuel tank). The increase in supply amount is suppressed, and the air-fuel ratio leans toward lean.

[Effects of the Invention] As described above, according to the present invention, even if the negative pressure increases due to the increase in engine speed when the choke valve is closed, it is possible to limit the amount of fuel supplied and prevent the mixture from becoming too rich. can. Therefore, problems such as plug fogging do not occur, and appropriate warm-up performance can be obtained. Furthermore, since the restrictive conditions are reduced, it is easy to adapt the system to a vaporizer.

[Embodiments of the invention] Next, embodiments of the present invention will be described based on the drawings.

The figures are cross-sectional views of a carburetor showing an embodiment of the present invention, FIG. 3 is a cross-sectional view in the direction of intake air flow, and FIG. 4 is a cross-sectional view in a direction perpendicular to the direction of air flow. Float chamber 3 of vaporizer 30
The amount of fuel flowing into the float chamber 32 is controlled by a fuel valve 36 which is controlled by a float 34, and a fixed amount of fuel is stored in the float chamber 32. The outflow of fuel within the float chamber 32 is controlled by a fuel jet 38 and is ejected from a nozzle 40 . The fuel is sucked in and ejected by the negative pressure generated by the large bench lily 44 and the small vent lily 46 in the intake passage 42, and becomes an air-fuel mixture with a predetermined air-fuel ratio. The nozzle 40 is arranged approximately at the center of the small bench lily 46. The flow rate of the air-fuel mixture having a predetermined air-fuel ratio is controlled by the throttle valve 48, and the mixture is sucked into the combustion chamber. A choke valve 50 disposed upstream of the small bench lily 46 rotates toward a closed position 52 during a cold start to throttle the amount of intake air and enrich the air-fuel ratio.

A first air vent hole 54 is provided upstream of this choke valve closed position 52, and a second air vent hole 56 is provided downstream thereof. These first and second air vent holes 54, ≦6 are defined as opening ends on the intake passage side, and the intake passage 4
An air vent passage 58 for introducing negative pressure of 2 into the float chamber 32 is provided.

Next, this invention will be explained in detail. When the choke valve 50 is open, the negative pressure in the first air vent hole 54 and the second air vent hole 56 is the same, and the negative pressure is the same in the float chamber 32.
This prevents the air-fuel mixture from becoming too rich due to increased negative pressure due to a clogged air cleaner, etc.

When starting in cold weather, choke valve 5o is closed to position 5.
When it is rotated to 2, the amount of intake air is throttled and the air-fuel ratio becomes lynch, improving ignition performance and improving engine startability. When the engine starts and the rotation gradually increases, the negative pressure P2 in the small bench lily 46 increases due to the increase in the amount of intake air. On the other hand, the pressure does not change upstream of the choke valve closed position 52, but
On the downstream side, the amount of intake air is restricted by closing the choke valve, so the negative pressure P1 becomes stronger. This negative pressure P1 acts on the float chamber 32 from the second air vent hole 56 through the air vent passage 58. Therefore, both the negative pressure P2 in the small bench lily portion 46 and the negative pressure P1 in the float chamber 32 become stronger. There is no problem that the pressure difference (P 1 - P 2) becomes large. Therefore, since the increase in the amount of fuel supplied is suppressed, the amount of fuel does not increase much as shown in FIG. 5, even though the amount of intake air increases due to the increase in engine speed, and the air-fuel ratio becomes lean.

Therefore, even if the negative pressure increases as the engine speed increases when the choke valve is closed, the mixture will not become too rich, and the plug will not fog up, allowing for proper warm-up operation. Moreover, since the structure is simple, manufacturing and processing are easy, and installation in the vaporizer is also easy.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a conventional carburetor equipped with an air vent passage, and FIG. 2 is a sectional view showing the principle of fuel supply. 3 to 5 show embodiments of the present invention, FIG. 3 is a sectional view of the carburetor in the intake air flow direction, FIG. 4 is a sectional view in a direction perpendicular to the intake air flow direction, and FIG. 5 is the invention. Fuel flow rate Q
It is a figure which shows the graph of the relationship between f and the number of times C Ne. In the figure, 32 is a float chamber, 40 is a nozzle,
46 is a small bench lily, 50 is a choke valve, 52 is a choke valve in a closed position, 54 is a first air vent hole, 56
58 is a second air vent hole, and 58 is an air vent passage. Agent Patent Attorney Yoshimi Saigo

Claims (1)

[Claims] An air vent passage communicating between the intake passage and the float chamber is provided, an open end of the air vent passage on the intake passage side is provided upstream of the choke valve in the closed state, and a first air vent hole is provided downstream of the choke valve in the closed state. 1. A fuel control device when a carburetor is choked, characterized by having two air vent holes.