JPH0835448A - Membrane carburetor fuel passage structure - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent the intake negative pressure of the high-speed fuel injection hole from acting on the low-speed fuel system to prevent the fuel amount from becoming insufficient in the medium-speed operation range of the engine. A carburetor main body 15 is provided with a passageway, one end of which communicates with the constant pressure fuel chamber 25 and the other end of which opens into the intake passage 16 through the high-speed fuel injection hole 51. Constant-pressure fuel chamber 25 of high-speed fuel injection hole 51
A fixed jet 46 is provided at an upstream end portion adjacent to, and a downstream passage of the fixed jet 46 is branched into a first fuel system and a second fuel system. The first fuel system ejects a part of the fuel measured by the fixed jet 46 from the low-speed fuel injection hole 20 to the intake passage 16 via the low-speed fuel passage 36. The second fuel system injects the rest of the fuel measured by the fixed jet 46 from the high-speed fuel injection hole 51 through the throttle 43 to the bench lily portion 16a of the intake passage 16. The diaphragm 43 has substantially the same diameter as the fixed jet 46.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel passage structure of the same system of a membrane carburetor, and more particularly, to an operating range intermediate between the low speed operating range and the high speed operating range of an engine, that is, from the low speed operating range to the high speed operating range. The present invention relates to the same type fuel passage structure of a membrane carburetor, which prevents the fuel amount from becoming relatively small (thinner) in a high speed operation range.

[0002]

2. Description of the Related Art In a membrane carburetor having a low speed fuel adjusting mechanism and a high speed fuel adjusting mechanism, a passage from a constant pressure fuel chamber to a low speed fuel chamber and a passage from a constant pressure fuel chamber to a high speed fuel chamber are separately provided. Another system type fuel passage and a passage from the constant pressure fuel chamber communicate with the high speed fuel chamber through the high speed fuel adjustment mechanism, and further communicate with the low speed fuel chamber through the high speed fuel adjustment mechanism through the low speed fuel adjustment mechanism. There is a type of fuel passage, and in a two-stroke engine, a piston port type, a reed valve type, a rotary valve type, etc. are used properly according to the characteristics of the intake / fuel system.

By the way, when exhaust gas regulations are applied to portable working machines such as power saws and brush cutters,
It is difficult to comply with exhaust gas regulations for portable work machines that require readjustment of the low-speed fuel adjustment mechanism according to the driving environment such as in highlands. In the carburetor of the separate system fuel passage, the passage of the low speed fuel adjustment mechanism and the passage of the high speed fuel adjustment mechanism are independent, so that the low speed fuel adjustment mechanism is operated at a low speed from a normal adjustment position shown by a broken line in FIG. When the fuel adjustment mechanism is adjusted to increase the fuel amount, the high-speed fuel adjustment mechanism is affected, and as shown by the solid line in FIG. 4, the fuel amount during high-speed operation of the engine also increases.

On the other hand, in the carburetor of the same system type fuel passage, even if the low speed fuel adjusting mechanism is adjusted, it does not affect the fuel amount in the high speed operation of the engine, but as shown in FIG. The amount of fuel may be low in the operating range intermediate between the high speed operating range and the high speed operating range. That is, in the above-described medium speed operation range of the engine, the intake negative pressures acting on the high-speed fuel system and the low-speed fuel system start to attract each other, and the intake negative pressures cancel each other, so that the fuel amount becomes insufficient.

In the same-system fuel passage structure of the membrane carburetor according to Japanese Patent Application No. 5-24974 filed by the applicant of the present invention, a description will be given by referring to the reference numerals in the drawings of the same application. The intake negative pressure of the high-speed fuel injection hole 19 throttled by
Since it becomes stronger than that of the low-speed fuel injection hole 20, the air in the intake passage will be discharged by the low-speed fuel injection hole 2 when continuously operating at high speed.
0, the low-speed fuel chamber 21, the low-speed fuel adjusting needle valve 23, the low-speed fuel passage 36b, the high-speed fuel chamber 18 and the reverse flow into the high-speed fuel injection hole 19, and the fuel is diluted or the fuel injection becomes irregular. May result in deterioration of exhaust gas components.

The above-mentioned problem can be solved by disposing a check valve inside the low speed fuel passage 36b. However, if the check valve is provided inside the low speed fuel passage 36b where the flow of fuel is small, the check valve will be closed. Fuel vapor or air accumulates in the valve chamber, or the valve body (usually a thin rubber plate) remains attached to the valve seat, which in turn makes the low-speed fuel flow unstable. Sometimes. Further, in a small membrane vaporizer, the space for providing the check valve is limited, and the degree of freedom in design is also limited.

[0007]

SUMMARY OF THE INVENTION In view of the above problems, the object of the present invention is to reduce the influence of the intake negative pressure of the high-speed fuel injection hole on the low-speed fuel system, so that the fuel amount in the medium-speed operation range of the engine is reduced. It is an object of the present invention to provide a systematic fuel passage structure for a membrane carburetor, which prevents shortage of fuel.

[0008]

In order to achieve the above object, the structure of the present invention comprises a high speed fuel passage, one end of which communicates with the constant pressure fuel chamber and the other end of which opens into the intake passage through the high speed fuel injection hole. In the same type fuel passage structure of the membrane carburetor, a fixed jet is provided at the upstream end adjacent to the constant pressure fuel chamber of the high-speed fuel injection hole, and the downstream passage of the fixed jet is used as the first and second fuel systems. The first fuel system branches and a part of the fuel measured by the fixed jet is ejected from the low speed fuel injection hole to the intake passage through the low speed fuel passage, and the second fuel system is divided into the fixed fuel measured by the fixed jet. The remaining portion is jetted from the high-speed fuel injection hole to the bench lily portion of the intake passage through the throttle, and the throttle has approximately the same diameter as the fixed jet.

[0009]

By arranging a throttle adjacent to the high-speed fuel injection hole and upstream of the high-speed fuel injection hole, the intake negative pressure acting on the low-speed fuel system from the high-speed fuel injection hole is weakened, and the fuel of the low-speed fuel system is reduced. Prevent it from running low.

Since the fuel passage structure is of the same system, even if the fuel amount of the low speed fuel system is adjusted, it does not affect the fuel amount in the high speed operation of the engine (the throttle valve is fully open), and the exhaust gas component is deteriorated. It can be prevented.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a side sectional view of a membrane type carburetor equipped with the same type fuel passage structure according to the present invention. Main body of vaporizer 1
5 includes an intake passage 16 having a bench lily portion 16a. An upstream end wall 15a of the intake passage 16 is connected to an air purifier and a downstream end wall 15b is connected to an intake port of the engine. The chuck yoke valve 5 is disposed on the upstream side of the intake passage 16 by the shaft 4 and the throttle valve 17 is rotatable on the downstream side by the shaft 17a. The upper wall portion of the main body 15 is partitioned by the membrane 10, and the pulsating pressure chamber 8 and the pump chamber 9, and the check valve 1
A fuel pump 11 including 2 and 7 is configured. When the pulsating pressure in the crank chamber of the two-stroke engine is introduced into the pulsating pressure chamber 8 from the passage 14, fuel in a fuel tank (not shown) is passed through the passage 13,
The check valve 7 is sucked into the pump chamber 9 through the check valve 12,
Through the strainer 6, the passage 3 and the inflow valve 2, the constant pressure fuel chamber 25
Is exhaled to.

The constant-pressure fuel chamber 25 is defined on the lower wall of the main body 15 and above the membrane 29 joined together with the cover 31.
The lower side is an atmosphere chamber 30. Support shaft 2 in constant pressure fuel chamber 25
The lever 28 rotatably supported by 7 has its left end engaged with the inflow valve 2 and its right end engaged with the membrane 29. Lever 2
8 is urged to rotate in the clockwise direction by the force of the spring 24 to close the inflow valve 2. When the amount of fuel in the constant pressure fuel chamber 25 is low, the membrane 29 that receives the atmospheric pressure is pushed up, the lever 28 rotates counterclockwise against the force of the spring 24, and the inflow valve 2 opens. The constant pressure fuel chamber 25 is replenished with fuel from the fuel pump 11.

According to the present invention, the assembly A is fitted in the cylindrical portion 47 connecting the constant pressure fuel chamber 25 and the bench lily portion 16a. As shown in FIG. 2, the assembly A has a cylindrical main body 50.
A cylindrical high-speed fuel injection hole 51, a valve chamber 52, a throttle 43, a passage 54, and a cylindrical portion 55 are sequentially formed from the top. The high-speed fuel injection hole 51 is projected to the bench lily portion 16a. When the check valve 42 made of a rubber valve plate is housed in the valve chamber 52 and the pressure of the throttle 43 becomes low, the check valve 42 is adsorbed to the valve seat 53 and closes the throttle 43, but the high speed fuel injection hole 51 When the negative pressure of intake air acting on the cylinder becomes strong, it is sucked up, and the high-speed fuel injection hole 5
The plurality of leg pieces 41a that curve downward and project from the seat plate 41 fitted to the first portion 41 maintain the communication between the valve chamber 52 and the intake passage 16. The fixed jet 46 having the passage 46a is fitted into the cylindrical portion 55. The passage 54 is the radial passage 45.
Through the annular groove 44 formed on the outer peripheral surface of the main body 50.

As shown in FIG. 1, the annular groove 44 passes through the low-speed fuel passage 36, the low-speed fuel adjusting needle valve 23, and the low-speed fuel chamber 2.
It is connected to 1. The low-speed fuel chamber 21 is arranged near the closed position of the throttle valve 17, and the low-speed fuel chamber 21 enters the intake passage 16,
A plurality of low speed fuel injection holes 20 are provided along the axial direction of the intake passage 16.
Is opened.

The passage area of the fixed jet 46 is substantially equal to the passage area of the throttle 43, and is set to a value that provides a fuel amount that does not exceed the exhaust gas regulation value at high speed operation of the engine. The inner diameter of the fixed jet 46 varies depending on the output of the engine and the portable working machine on which the engine is mounted, but it is 1 mm or less for a two-stroke engine with a displacement of about 20 cc.

Next, the operation of the same type fuel passage of the membrane vaporizer according to the present invention will be described. During idle or low speed operation of the engine, the low speed fuel injection hole 2 adjacent to the throttle valve 17
Since a strong intake negative pressure acts on 0, the fuel in the constant pressure fuel chamber 25 receives the fixed jet 46, the passage 45, the annular groove 44, the low speed fuel passage 36, the low speed fuel adjusting needle valve 23, the low speed fuel chamber 21,
It is supplied to the intake passage 16 through the low-speed fuel injection hole 20. At this time, the intake negative pressure acting from the bench lily portion 16a to the high-speed fuel injection hole 51 is weak, the check valve 42 adheres to the valve seat 53 due to the viscosity of the fuel, and the high-speed fuel injection hole 51 causes the valve chamber 52, the throttle 43, Passage 45, annular groove 44, low speed fuel passage 36, low speed fuel adjusting needle valve 23, low speed fuel chamber 21, low speed fuel injection hole 20
Block the flow of air to.

In the high speed operation of the engine, the bench lily portion 16a
The intake negative pressure acting on the high-speed fuel injection hole 51 becomes strong, the check valve 42 is sucked up, and the fuel in the constant-pressure fuel chamber 25 is fixed jet 46, passage 54, throttle 43, valve chamber 52, high-speed fuel injection hole 51. And is supplied to the intake passage 16.

During high-speed operation of the engine with the throttle valve 17 fully opened, the negative suction pressure acting on the high-speed fuel injection hole 51 of the bench lily portion 16a becomes stronger than the negative suction pressure acting on the low-speed fuel injection hole 20. The air in the passage 16 is the low-speed fuel injection hole 20,
Low speed fuel chamber 21, low speed fuel adjusting needle valve 23, low speed fuel passage 36, annular groove 44, passages 45 and 54, throttle 43, valve chamber 5
Attempt to flow into the high-speed fuel injection hole 51 via 2. But,
The passage from the high speed fuel injection hole 51 to the low speed fuel injection hole 20 is
Since the throttle 43 and the low-speed fuel adjustment valve 23 restrict the pressure in two stages, the amount of fuel supplied from the high-speed fuel injection hole 51 to the intake passage 16 is not adversely affected.

In the medium speed operation range of the engine, the high speed fuel injection holes 51
And the intake negative pressure acting on the low-speed fuel injection hole 20 become substantially equal, but the amount of fuel supplied from both fuel injection holes 51, 20 to the intake passage 16 is defined by the fixed jet 46 and the high-speed fuel injection hole 51. The low-speed fuel injection hole 20 and the throttle 43
And the low-speed fuel adjusting needle valve 23, the intake negative pressure in both fuel injection holes 51, 20 is suppressed, and the fuel flows from both fuel injection holes 51, 20 into the intake passage. 16 is smoothly supplied.

When the opening degree of the low speed fuel adjusting needle valve 23 is small, the fuel amount increases in accordance with the engine speed as shown by the broken line in FIG. On the other hand, when the opening degree of the low speed fuel adjusting needle valve 23 is increased, the amount of fuel supplied from both fuel injection holes 51, 20 to the intake passage 16 as shown by the solid line in FIG. It will not increase and fuel shortage will not occur in the medium speed operation range of the engine. That is, even if the fuel amount in the low speed operation range of the engine is adjusted by adjusting the low speed fuel adjustment needle valve 23, both fuel injection holes 5 are
The amount of fuel supplied to the intake passage 16 from 1, 20 does not change and is maintained at a predetermined value, so that it does not adversely affect the exhaust gas regulation.

[0021]

As described above, according to the present invention, the same type fuel of the membrane type carburetor having the high speed fuel passage having one end communicating with the constant pressure fuel chamber and the other end opening to the intake passage through the high speed fuel injection hole is provided. In the passage structure, a fixed jet is provided at the upstream end adjacent to the constant-pressure fuel chamber of the high-speed fuel injection hole, and the downstream passage of the fixed jet is branched into the first and second fuel systems. A part of the fuel measured by the fixed jet is ejected from the low speed fuel injection hole to the intake passage through the low speed fuel passage, and the second fuel system is the high speed fuel injection hole after the rest of the fuel measured by the fixed jet is throttled. Spouts from the intake passage to the bench lily part of the intake passage,
Since the diameter of the throttle is approximately the same as that of the fixed jet, it does not increase the number of parts or change the passage, is easy to process, and can be configured in a limited space.

By disposing a throttle adjacent to the high-speed fuel injection hole and upstream of the high-speed fuel injection hole, the intake negative pressure acting on the low-speed fuel system from the high-speed fuel injection hole is weakened, and the fuel amount of the low-speed fuel system is reduced. Can be prevented from decreasing.

Since the passage connecting the high-speed fuel injection hole and the low-speed fuel injection hole is throttled in two stages by the throttle and the low-speed fuel adjusting needle valve, the intake negative pressure of the high-speed fuel injection hole in the medium and high-speed operation region of the engine. Influence on the low-speed fuel injection hole is weakened, and backflow of air from the low-speed fuel injection hole to the high-speed fuel injection hole can be prevented.

Due to the systematic fuel passage structure, even if the fuel amount of the low speed fuel system is adjusted, it does not affect the fuel amount during high speed operation of the engine (throttle valve is fully open), and deterioration of exhaust gas components can be prevented. .

[Brief description of drawings]

FIG. 1 is a side cross-sectional view of a membrane type carburetor equipped with the same type fuel passage structure according to the present invention.

FIG. 2 is a side cross-sectional view showing an enlarged main part of the same-system fuel passage structure according to the present invention.

FIG. 3 is a characteristic diagram of a membrane vaporizer provided with the same-system fuel passage structure according to the present invention.

FIG. 4 is a characteristic diagram of a membrane vaporizer having a separate system fuel passage structure.

FIG. 5 is a characteristic diagram of a conventional membrane carburetor having the same system fuel passage structure.

[Explanation of symbols]

15: Vaporizer main body 16: Intake passage 16a: Bench lily part 20: Low speed fuel injection hole 21: Low speed fuel chamber 23:
Low speed fuel adjusting needle valve 25: Constant pressure fuel chamber 36: Low speed fuel passage 43: Throttling 46: Fixed jet 51: High speed fuel injection hole 54: Passage

Claims (2)

[Claims] 1. A high-speed fuel injection hole in a system fuel passage structure of a membrane carburetor having a high-speed fuel passage, one end of which communicates with a constant-pressure fuel chamber and the other end of which opens through a high-speed fuel injection hole into an intake passage. A fixed jet is provided at the upstream end adjacent to the constant pressure fuel chamber, and the downstream passage of the fixed jet is branched into the first and second fuel systems, and the first fuel system is provided with the fuel measured by the fixed jet. Part of the fuel is ejected from the low-speed fuel injection hole to the intake passage through the low-speed fuel passage, and the second fuel system is ejected from the high-speed fuel injection hole to the bench lily portion of the intake passage through the rest of the fuel measured by the fixed jet. The diaphragm has the same diameter as that of the fixed jet, and the same-system fuel passage structure of the membrane carburetor is characterized. 2. The same-system fuel passage structure for a membrane carburetor according to claim 1, wherein a low-speed fuel adjusting needle valve is arranged in the low-speed fuel passage.