JPH094516A - Fuel adjusting needle of diaphragm type carburetor - Google Patents

Abstract

PURPOSE: To prevent the shifting of the flow rate of a main jet just after adjusting this fuel adjusting needle from a regular flow rate and facilitate the adjustment of a fuel adjusting needle and also reduce an adjusting time, in a carburetor in which the throttle diameter of a main jet is adjusted by the fuel adjusting needle. CONSTITUTION: A passage communicating the large diameter room of a screw hole for storing the head part of a fuel adjusting needle with a fuel supply passage 6 on the upperstream side of a main jet 31 is provided. The pressure in the large diameter room is always same as that of the fuel supply passage 6 on the upperstream side of the main jet 31 and the pressure in the large diameter room is not changed at the turning time of the fuel adjust needle 30. Therefore, the fuel flow rate flowing in the main jet 31 can be stabilized just after adjusting and the fuel adjusting needle 30 can be adjusted in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diaphragm type carburetor used in a portable general-purpose engine mounted as a drive source for a brush cutter, a chain saw, and the like.

[0002]

2. Description of the Related Art Conventionally, in a diaphragm type carburetor 1 shown in FIG. 9, a fuel adjusting needle 3 is provided midway along a fuel supply passage 6 from a diaphragm chamber 7 to a fuel nozzle 5 of an intake passage 3.
A main jet 31 whose aperture diameter is adjusted by 0 is formed. The fuel adjustment needle 30 is substantially orthogonal to the fuel nozzle 5 and is located in the back.
The main jet 31 is screwed into a screw hole 32 in which the main jet 31 is formed, and a needle portion 33 provided at the tip of the fuel adjusting needle 30 is inserted into the main jet 31. By rotating the fuel adjusting needle 30, the fuel adjusting needle 30 is advanced and retracted to adjust the main jet diameter 31. A large-diameter chamber 40 for accommodating the head portion 39 of the fuel adjusting needle 30 is formed on the outer side of the screw hole 32, and a seal for sealing the screw hole 32 is formed in the head portion 39 of the fuel adjusting needle 30. Material 41 is provided. (See Japanese Utility Model Publication No. 2-14451)

[0003]

2. Description of the Related Art When the fuel adjusting needle 30 is adjusted, the pressure within the large diameter chamber 40 sealed by the head portion 39 changes due to the forward and backward movement of the needle 30, and this pressure is due to the threaded portion of the needle 30. Since it acts on the main jet 31 through the passage, the negative pressure applied to the main jet 31 shifts immediately after the adjustment, and even if the fuel flow rate is adjusted in this state, the large chamber 40
The internal pressure disappears with time, and the main jet 31
There is a problem that the fuel flow rate deviates from the adjustment value when the pressure applied to the fuel cell stabilizes.

For example, when the fuel adjusting needle 30 is tightened and the adjusting needle 30 is moved in a direction to decrease the diameter of the main jet 31, the large diameter chamber 40 is compressed and the pressure in the large diameter chamber 40 rises. Immediately after the adjustment of the fuel adjusting needle 30, this pressure passes through the threaded portion of the needle 30 and pressurizes the main jet 31. Therefore, the flow rate of the fuel flowing through the main jet 31 increases. In the adjustment in this state, the area of the main jet 31 is adjusted to be smaller than appropriate. When the pressure in the large diameter chamber 40 disappears with the passage of time, the flow rate of the fuel flowing through the main jet 31 becomes smaller than that at the time of adjustment.

When the fuel adjusting needle is returned and the fuel adjusting needle 30 is moved in the direction to increase the diameter of the main jet 31, the volume of the large diameter chamber 40 increases and the inside of the large diameter chamber 40 becomes negative pressure. Become. This negative pressure is applied to the needle 3
When it acts on the main jet 31 through the screwing portion of 0, the negative pressure of the main jet 31 portion becomes small and the flow rate of fuel flowing through the main jet 31 decreases. Therefore, in this state, the diameter of the main jet 31 is adjusted to be larger than that in the normal state. When the negative pressure in the large-diameter chamber 40 disappears with the passage of time, the flow rate of fuel flowing through the main jet 31 increases more than during adjustment.

Therefore, when the fuel adjusting needle 30 is adjusted, it is necessary to wait until the flow rate of the main jet 31 after the adjustment becomes stable and then confirm it.
There is a problem that it takes a lot of time to adjust the flow rate.

An object of the present invention is to prevent pressure fluctuations in the large-diameter chamber during adjustment of the fuel adjusting needle, to obtain a stable fuel flow rate immediately after the adjustment, and to shorten the adjusting time.

[0008]

The present invention is characterized in that a passage is provided which connects the large-diameter chamber for accommodating the head of the fuel adjusting needle and the fuel feed passage on the upstream side of the main jet. .

[0009]

Since the large-diameter chamber is connected to the fuel supply passage upstream of the main jet by the passage, the large-diameter chamber always has the same pressure as the fuel supply passage upstream of the main jet, and the fuel adjusting needle is provided. The pressure fluctuation in the large chamber that occurs during the rotation of is quickly eliminated. Therefore, the flow rate of the fuel flowing through the main jet is stable immediately after the adjustment, and the adjustment of the fuel adjustment needle can be performed in a short time.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings, in which the same parts as in the conventional example are designated by the same reference numerals. 1 is a vertical sectional view showing a diaphragm type vaporizer of the present invention, FIG. 2 is an enlarged view of a main part of the present invention, and FIG. 3 is a sectional view taken along the line AA of FIG.

Reference numeral 1 denotes a diaphragm type carburetor, which is provided with an intake passage 3 penetrating through the body 2.
The upstream side is connected to an air cleaner (not shown), and the downstream side is connected to an intake port of the engine (not shown).
Further, a throttle valve 4 for varying the effective diameter of the intake passage 3 is arranged in the intake passage 3. A fuel nozzle 5 is opened in the intake passage wall below the throttle valve 4, and the other of the fuel nozzles 5 is connected to a diaphragm chamber 7 by a fuel supply passage 6. An atmosphere chamber 15 is formed on the back surface of the diaphragm 19 forming the diaphragm chamber 7.

A fuel pump 10 driven by the operating pressure of the engine is connected to a fuel inlet 8 of the diaphragm chamber 7 through a fuel supply passage 9. The fuel pump 10 includes a pump diaphragm 11 and a pair of check valves 1.
It is a conventionally well-known diaphragm pump composed of 2 and 13, and a working pressure of an engine, for example, a crank chamber pressure in a two-cycle engine is applied to a pressure chamber 14 formed on one side of the pump diaphragm 11.
The pump diaphragm 11 is vibrated, and fuel is sucked from a fuel tank (not shown) through one check valve 12 into a pump chamber 17 formed on the other side of the pump diaphragm 11, and the fuel is supplied from the other check valve 13 to the fuel supply passage 9 It is pressure-fed to the diaphragm chamber 7 via.

The inlet 8 of the diaphragm chamber 7 is provided with a fuel valve 20 which operates in association with the diaphragm 19 to open and close the inlet 8, that is, to connect and disconnect the fuel pump 10 and the diaphragm chamber 7. Has been. A shaft 21 is provided between the fuel valve 20 and the diaphragm 19.
A lever 22 having one side connected to the fuel valve 20 and the other side connected to the diaphragm 19 is arranged. The lever is biased by a spring 23 in a direction to normally close the needle valve 20. Therefore, when an intake negative pressure acts on the inside of the diaphragm chamber 6 through the fuel nozzle 5, the diaphragm 19 causes the fuel valve 2 to pass through the lever 22 to introduce fuel into the diaphragm chamber 6.
0 is held in the open position of the fuel inlet 8. The fuel valve 2
0 changes the opening area of the fuel inlet 8 according to the displacement amount of the diaphragm, that is, the magnitude of the intake negative pressure,
The inside of the diaphragm chamber 7 is always adjusted to a constant pressure.

A suction passage 27 of the starting pump 25 is connected to the diaphragm chamber 7. This pump 2
By operating 5 repeatedly, a negative pressure is exerted in the diaphragm chamber 7 and the fuel in the fuel tank 15 is sucked into the chamber 7 via the fuel pump 10. The fuel that has flowed into the diaphragm chamber 7 is returned to the fuel tank 7 through the discharge passage 28 in accordance with the subsequent operation of the starting pump 25. Reference numeral 26 is a combination valve in which an umbrella-type check valve 26a is integrally formed with a suction valve and a duckbill-type check valve 26b is integrally formed with a discharge valve.

In the middle of the fuel feed passage 6, the main jet 3 whose throttle diameter is adjusted by a fuel adjusting needle 30.
1 is formed. The fuel adjusting needle 30 is substantially orthogonal to the fuel nozzle 5 and is screwed into a screw hole 32 in which the main jet 31 communicating with the fuel nozzle 5 is formed at the back, and the fuel adjusting needle 30 has a tip end. The needle part 33 provided is connected to the main jet 31.
Has been inserted. Therefore, by rotating the fuel adjusting needle 30, the fuel adjusting needle 30 is advanced and retracted to adjust the throttle diameter of the main jet 31.

The fuel feed passage 6 connected from the diaphragm chamber 7 to the main jet 31 is provided with a check valve 34 which allows only the flow from the diaphragm chamber 7 to the fuel nozzle 5 in the middle, and the main jet 31 The side is connected to a needle chamber 38 formed between the tip of the screw portion 35 of the fuel adjusting needle 30 and the inner wall of the screw hole 32.
The needle chamber 38 substantially forms a part of the fuel delivery passage 6. A large diameter chamber 4 for accommodating the head portion 39 of the fuel adjusting needle 30 is provided on the outer opening side of the screw hole 32.
0 is formed, and the head 39 of the fuel adjusting needle is provided with a sealing material 41 for sealing the screw hole 32. A compression spring 43 is arranged between the shoulder portion 42 formed at the back of the large diameter chamber 40 and the head portion 39 of the fuel adjusting needle to prevent the needle 30 from loosening.

The thread portion 35 of the fuel adjusting needle 30 is provided with a groove 44 extending in the direction of the central axis from the large diameter chamber 40 to the needle chamber 38. By this groove 44, the large diameter chamber 40 and the needle chamber upstream of the main jet 31 are provided. A passage 45 communicating with 38 is formed. Therefore, the pressure in the large diameter chamber 40 is always the same as that in the needle chamber 38, and the pressure in the large diameter chamber 40 does not change when the fuel adjusting needle 30 is adjusted. As a result, the flow rate of fuel flowing through the main jet 31 can be stabilized immediately after adjustment.

Next, the operation of the above embodiment will be described. When the starting pump 25 is repeatedly operated before starting, negative pressure acts on the inside of the diaphragm chamber 7, and the fuel is sucked into the chamber 7 via the fuel pump 10 from a fuel tank (not shown). The fuel that has flowed into the diaphragm chamber 7 is returned to the fuel tank through the discharge passage 28 in accordance with the subsequent operation of the starting pump 25.

When the engine is operating, the intake negative pressure generated in the intake passage 3 acts on the diaphragm chamber 7 from the fuel nozzle 5 through the main jet 31 and the check valve 34, and the fuel is sucked into the intake passage 3. This raises the diaphragm 19 and opens the fuel valve 20. At the same time, the fuel pump 10 is driven by the operating pressure of the engine, and the fuel is sent to the diaphragm chamber 7 according to the opening degree of the fuel valve 20. In this way, the diaphragm chamber 7 is always kept at a predetermined pressure by the diaphragm 19.

The fuel sucked from the diaphragm chamber 7 to the fuel nozzle 5 is controlled by the main jet 31, and the throttle diameter of the main jet 31 is adjusted by the fuel adjusting needle 30. At the time of adjusting the fuel adjusting needle 30, the volume of the large diameter chamber 40 is reduced or expanded by advancing and retracting the adjusting needle 30 in the central axis direction, but the large diameter chamber 40 is communicated with the needle chamber 38 by the groove 44. Therefore, the pressure fluctuation generated in the large diameter chamber 40 at the time of adjusting the fuel adjusting needle 30 is instantly eliminated. Therefore, in the adjustment work of the fuel adjusting needle 30, the fuel flow rate of the main jet 31 is stabilized immediately after the adjustment, and the adjustment of the fuel adjusting needle 30 can be performed quickly and accurately.

Next, another embodiment for forming the passage will be described. 4 and 5 show a passage that connects the large diameter chamber 40 and the needle chamber 38 upstream of the main jet 31 by providing the thread portion 35 of the fuel adjusting needle 30 with the notch 47 in the central axis direction of the fuel adjusting needle 30. This is an example of forming 45.

6 and 7 show the screw portion 4 of the screw hole 32.
8 is an embodiment in which a groove 50 extending in the direction of the central axis of the fuel adjusting needle 30 is provided to form a passage 45 that connects the large diameter chamber 40 and the needle chamber 38 upstream of the main jet 31.

FIG. 8 shows a passage 4 connecting the large-diameter chamber 40 to the carburetor body 2 and the fuel supply passage 6 upstream of the main jet 31.
5 is an example in which 5 is provided. Further, in this case, in the case of a diaphragm type carburetor of the type in which the check valve is not provided in the fuel feed passage 6, the passage 45 may be connected to the diaphragm chamber 7 formed upstream of the fuel feed passage 6. It is possible.

[0024]

As described above in detail, according to the present invention, since the large diameter chamber is connected to the fuel feed passage upstream of the main jet by the passage, the large diameter chamber is generated in the large diameter chamber when the adjusting needle is rotated. The pressure fluctuation disappears instantly. Therefore, in the operation of adjusting the fuel adjusting needle, it is possible to prevent the deviation of the fuel flow rate immediately after the adjustment, and to adjust the fuel adjusting needle quickly and accurately.

Further, when the passage is formed by providing a groove or notch in the thread portion of the fuel adjusting needle or by forming a groove in the thread portion of the screw hole of the carburetor body, the machining is easy. The formation of the passage can be performed at an extremely low cost.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a diaphragm type vaporizer of the present invention.

FIG. 2 is an enlarged sectional view of a main part of the present invention.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is an enlarged cross-sectional view of an essential part showing another embodiment of the present invention.

FIG. 5 is a sectional view taken along line BB of FIG. 4;

FIG. 6 is an enlarged sectional view of a main part showing another embodiment of the present invention.

FIG. 7 is a sectional view taken along line CC of FIG. 6;

FIG. 8 is an enlarged sectional view of an essential part showing another embodiment of the present invention.

FIG. 9 is a cross-sectional view of essential parts showing a conventional diaphragm type carburetor.

[Explanation of symbols]

 1 Diaphragm vaporizer 3 Intake passage 5 Fuel nozzle 6 Fuel supply passage 7 Diaphragm chamber 30 Fuel adjusting needle 31 Main jet 35 Fuel adjusting needle screw part 44 groove 47 Notch 48 Screw hole screw part 50 groove

Claims (5)

[Claims] 1. A diaphragm type carburetor in which a main jet whose throttle diameter is adjusted by a fuel adjusting needle is formed in the middle of a fuel supply passage from a diaphragm chamber to a fuel nozzle of an intake passage. A fuel adjusting needle for a diaphragm-type carburetor, characterized in that a passage is provided to connect a large-diameter chamber for accommodating thereinto and a fuel feed passage on the upstream side of the main jet. 2. The passage for connecting the large-diameter chamber and the fuel supply passage upstream of the main jet is formed by providing a groove in the central axis direction in the thread portion of the fuel adjusting needle. A fuel adjusting needle for the diaphragm type carburetor described. 3. The passage for connecting the large diameter chamber and the fuel feed passage upstream of the main jet is formed by providing a cutout in the central axis direction in the thread portion of the fuel adjusting needle. A fuel adjusting needle for the diaphragm type carburetor described in 1. 4. A passage for connecting the large diameter chamber and a fuel feed passage upstream of the main jet is formed by providing a groove in the central axis direction in a thread portion of a screw hole of the fuel adjusting needle provided in the carburetor body. The fuel adjusting needle of the diaphragm type carburetor according to claim 1, wherein 5. The fuel adjusting needle for a diaphragm type carburetor according to claim 1, wherein the carburetor body is provided with a passage communicating with the large-diameter chamber and a fuel feed passage upstream of the main jet.