JPH10238411A - Carburetor with accelerator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove an inconvenience that an accelerating pump sucks air during speed reduction by providing a check valve between a throttle piece and the connecting part of an air bleed passage in a carburetor in which the throttle piece is provided in a fuel passage from a constant fuel chamber to a main nozzle and accelerating fuel is supplied from the main nozzle during acceleration. SOLUTION: When a throttle valve 4 is opened to accelerate an engine, the part of the axially peripheral surface of a cam 35 pushes a piston 36 to supply the fuel of a pump chamber 38 to a jet hole 20 as a part of a fuel passage 18 via an accelerating fuel passage 39, an annular groove 22 and a conduit hole 23. Then, this fuel passes through a check valve 25 and a needle valve 16 and is fed to an inlet passage 5 from a main nozzle 17. When the piston 36 pressed by a pressing spring 37 follows the cam 35 to increase the volume of the pump chamber 38 upon speed reduction of the engine, the valve plate 27 of the check valve 25 closes the outlet of the jet hole 20 due to the negative pressure of the pump chamber 38 so that the air of the inlet passage 5 is prevented from being sucked to the pump chamber 38 from an air bleed passage 29 and the main nozzle 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carburetor with an acceleration device suitable for a small carburetor mainly for a general-purpose two-stroke engine.

[0002]

2. Description of the Related Art It is a well-known technique to supply extra fuel, ie, accelerating fuel, to an intake passage in response to an increasing intake air amount when a throttle valve opening is increased to increase an engine rotation speed. In the carburetor which is one of the fuel supply systems, an accelerator having a piston type or diaphragm type acceleration pump interlocked with a throttle valve is provided, thereby supplying acceleration fuel.

[0003] Among the carburetors, small carburetors for supplying fuel to general-purpose two-stroke engines used as power sources for portable work machines for agriculture and forestry, and small vehicles,
In general, even in a film-type carburetor having a constant fuel chamber in which fuel supplied to an intake passage is adjusted to a substantially constant pressure by a diaphragm, an acceleration having a piston type acceleration pump and an acceleration fuel passage linked to a throttle valve is also used. The provision of a device is disclosed, for example, in JP-A-60-195365.

On the other hand, since a small vaporizer such as a membrane vaporizer has a small maximum fuel flow rate, an orifice of a jet hole is provided in a fuel passage from a constant fuel chamber to a main nozzle opened to a venturi of an intake passage. A throttle member (main jet) having an extremely small diameter is provided to regulate the fuel flow rate. In addition, it is necessary to send sufficiently atomized fuel to the engine. For this reason, the orifice has a large diameter, and bleed air is introduced into the fuel in the fuel passage to restrict the fuel flow while processing the throttle piece. It is also common practice to achieve both ease of fueling and atomization of fuel.

[0005]

In the above-described accelerator, the acceleration fuel passage into which the pump chamber of the acceleration pump sucks fuel from the constant fuel chamber when the engine decelerates and sends the fuel from the pump chamber to the intake passage during acceleration is: In a small-sized vaporizer such as a small-sized membrane vaporizer having a small space, a fuel passage and a pump chamber are simply connected as disclosed in Japanese Patent Application Laid-Open No. 60-195365. Advantageously, a single passage is used to supply the accelerating fuel from the main nozzle to the intake passage.

However, in this case, in the case where the air bleed passage is connected to the fuel passage for introducing the bleed air, the acceleration pump sucks air at the time of deceleration, and the fuel required for the next acceleration is secured. Is not possible.

Therefore, according to the present invention, a throttle member for fuel regulation is provided in a fuel passage extending from the constant fuel chamber to the main nozzle, and an air bleed passage is connected to the fuel passage. A carburetor in which the acceleration fuel is supplied from the main nozzle to the intake passage is provided with an acceleration device that does not suck air when the deceleration is performed and that can always appropriately supply the required acceleration fuel. It was invented with an object.

[0008]

That is, a check valve which closes toward the constant fuel chamber is provided at a portion between the throttle portion of the fuel passage and the connection point of the air bleed passage, and the acceleration fuel passage is throttled. The portion between the orifice and the check valve is connected to the fuel passage.

As described above, by providing the check valve at a portion between the connection point of the air bleed passage and the acceleration fuel passage to the fuel passage, the air of the intake passage is decelerated at the time of deceleration. It will not be sucked into the pump chamber through the passage.

Here, if the check valve is provided at a position for opening and closing the jet hole outlet of the throttle member and the acceleration fuel is connected to the jet hole downstream of the orifice, the check valve can be easily installed. There is an advantage that the structure can be simplified.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. A fuel pump is provided on an outer surface of a carburetor body 1 with an intake passage 5 having a choke valve 2, a venturi and a throttle valve 4 interposed therebetween. 6 and a constant fuel chamber 7 are provided.

The fuel pump 6 is a well-known diaphragm type fuel pump, which operates a diaphragm by pressure pulsation generated in a crankcase of an engine.
The fuel in a fuel tank (not shown) is suctioned and pressurized to
To send to.

The constant fuel chamber 7 is separated from the atmosphere chamber 10 in the diaphragm cover 9 by a diaphragm 8 and a fuel valve 13 engaged with a lever 12 brought into contact with the center of the diaphragm 8 by the force of a spring 11. Is diaphragm 8
By controlling the fuel sent from the fuel pump 6 in accordance with the displacement of the fuel, a predetermined amount of fuel is held at a constant pressure.

The fuel in the constant fuel chamber 7 is supplied to the throttle piece 15.
The flow rate is regulated by the main jet, and the flow rate is further adjusted by the manual needle valve 16, and is sucked into the intake passage 5 from the main nozzle 17 opened at the narrowest part of the venturi 3. The fuel that has passed through the throttle piece 15 is also drawn into the intake passage 5 from an idle port and a slow port (not shown) opened to the side of the throttle valve 4.

The structure of the fuel pump 6, the diaphragm-type constant fuel chamber 7, and the fuel passage are the same as those of a conventional membrane carburetor.

A throttle piece 15 provided in a fuel passage 18 extending from the constant fuel chamber 7 to the main nozzle 17 is opened to a wall face of the constant fuel chamber 7 facing the diaphragm 8 and is mounted on the carburetor body 1. It is fitted and fixed in the hole 19,
A check valve 25 in which a flat valve plate 27 is inserted is used as a valve chamber 26 with a space on the bottom side of the mounting hole 19 as a valve chamber 26, and the check valve 25 is arranged side by side with the throttle piece 15.

As described above, when the check valve 25 is provided in the mounting hole 19 of the throttle piece 15, the check valve 25 can be easily installed and the structure of the fuel passage 18 can be simplified. There are advantages.

The throttle piece 15 is provided with an orifice 21 for regulating the maximum flow rate of the fuel near the inlet of the jet hole 20 penetrating forward and backward, an annular groove 22 on the outer peripheral surface and the orifice 21 of the jet hole 20. Downstream part and annular groove 2
2 is provided, and the valve plate 27 of the check valve 25 opens and closes the outlet of the jet hole 20.

Further, the check valve 25 and the needle valve 1 of the fuel passage 18 are provided.
6 is connected to an air bleed passage 29 opened at the inlet of the venturi 3 of the intake passage 5.
When bleed air is introduced into the fuel sucked into the intake passage 5 from the main nozzle 17, the atomization of the fuel is improved, and the orifice 21 can be formed to have a large diameter because the fuel flow rate is reduced by air mixing. Therefore, the throttle piece 1
Processing of No. 5 becomes easy.

On the other hand, when the opening degree of the throttle valve 4 is increased, the accelerator 31 for supplying the fuel for acceleration to the intake passage 5 in response to the increase in the intake air amount is provided by a piston type acceleration linked to the throttle valve 4. It has a pump 32 and a single accelerating fuel passage 39 for sucking and delivering fuel to the pump chamber 38.

A piston 36 of the acceleration pump 32 is fitted into a cylinder chamber 33 formed inside the carburetor body 1 and has a cam formed by a cutout surface provided on a throttle valve shaft 34 and a substantially semicircular shaft peripheral surface. 35 is constantly brought into contact with the force of the pressing spring 37. A space on the opposite side of the cylinder 35 from the cam 35 with respect to the piston 36 is a pump chamber 38, and a pressing spring 37.
And the annular groove 22 of the throttle piece 15
And an acceleration fuel passage 39.

When the engine is idling, the piston 3
Numeral 6 contacts the notched surface of the cam 35 to maximize the volume of the pump 38. When the throttle valve 4 for accelerating operation is opened, the portion of the shaft peripheral surface of the cam 35 presses the piston 36 to transfer the fuel in the pump chamber 38 through the accelerating fuel passage 39, the annular groove 22 which is a part thereof, and the conduction hole 23. The fuel is fed into a jet hole 20 which is a part of the fuel passage 18. This fuel is a check valve 2
5. The air is sent from the main nozzle 17 to the intake passage 5 through the needle valve 16.

When the engine is decelerated, the piston 36 pressed by the pressing spring 37 follows the cam 35 to increase the volume of the pump chamber 38. At this time, the valve plate 27 of the check valve 25 closes the outlet of the jet hole 20 due to the negative pressure in the pump chamber 38, and the air bleed passage 29 and the main nozzle 1
The phenomenon that the air in the intake passage 5 is sucked into the pump chamber 38 from 7 is prevented. Therefore, only the fuel from the constant fuel chamber 7 is introduced into the pump chamber 38, and the fuel required for the next acceleration can be secured.

The check valve 25 also has a function of preventing the air in the intake passage 5 from flowing into the constant fuel chamber 7 at the time of deceleration, so that it is not necessary to provide the main nozzle 17 with a check valve.

In the present invention, the constant fuel chamber 7 is of a floating type,
The present invention can be applied to a fuel tank having no manual needle valve 16 in the fuel passage 18. In addition, the check valve 25 is
The accelerating fuel passage 39 can be connected to an appropriate portion between the orifice 21 of the throttle piece 15 and the check valve 25.

Further, the illustrated embodiment in which the acceleration pump 32 is operated by the cam 35 formed on the throttle valve shaft 34 can be implemented without increasing the size of the entire carburetor and has a simple structure. Alternatively, if there is enough space for the carburetor, an acceleration pump 32 may be provided outside the carburetor main body 1 and linked with the throttle valve shaft 34 by a link mechanism.

[0027]

As described above, the carburetor has a simplified passage structure in which the fuel for acceleration delivered from the accelerator is supplied from the main nozzle to the intake passage, and the fuel passage is used as a part of the acceleration fuel passage. In this case, it is possible to avoid a disadvantage that the acceleration pump and the constant fuel chamber draw in air at the time of deceleration with a simple configuration in which one check valve is provided.

Therefore, the required acceleration fuel is appropriately supplied without deteriorating the acceleration performance, and the constant fuel chamber holds a predetermined amount of fuel so as not to affect the operation of the engine.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention.

[Explanation of symbols]

1 carburetor body, 4 throttle valve, 5 intake passage, 7 constant fuel chamber, 15 throttle piece, 17 main nozzle, 18 fuel passage,
20 jet holes, 21 orifices, 22 annular grooves,
23 communication hole, 25 check valve, 29 air bleed passage, 31 accelerator, 32 acceleration pump, 34 throttle valve shaft, 36 piston, 38 pump chamber, 39 acceleration fuel passage,

Claims (2)

[Claims] 1. A fuel passage from a constant fuel chamber to a main nozzle is provided with a throttle member for regulating fuel and is connected to an air bleed passage. A carburetor having an accelerating device having a single accelerating fuel passage for sucking and delivering fuel; and an accelerating device for delivering accelerating fuel from the main nozzle to the intake passage; the throttle portion of the fuel passage and an air bleed passage A check valve that closes toward the constant fuel chamber is provided at a portion between the connection point and the constant fuel chamber, and the acceleration fuel passage is connected to the fuel passage at a portion between the orifice of the throttle piece and the check valve. A vaporizer with an accelerator. 2. The acceleration according to claim 1, wherein the check valve is provided at a position for opening and closing a jet hole outlet of the throttle piece, and the acceleration fuel passage is connected to a downstream side of the orifice of the jet hole. Vaporizer with device.