JP2000018099A - Rotary throttle valve type carburetor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the individual machining accuracy of a metering pin setting a minimum flow rate at the time of idling and a fixed jet setting a maximum flow rate at the time of full-load and simultaneously to make engine drivability better than over. SOLUTION: A choke valve 22 is installed in the inlet of an intake passage 2 while a check valve 21 to be closed toward a constant fuel chamber 18 is installed in a fuel passage 19, connecting an air bleed passage 24 to the downstream side of the check valve 21 of the fuel passage 19, and any negative pressure acting on the fuel passage 19 and a fuel nozzle 16 is lowered by the induction of bleed air, and further both dimensional accuracies of a metering pin 7 and a fixed jet 20 relaxed. Fuel is evacuated from the air bleed passage 24 in time of cold starting, improving the startability, and further a jet diameter of the fixed jet 20 is enlargeable, whereby a fuel flow rate at the time of full- load driving is secured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a rotary throttle valve type carburetor for supplying fuel to a general-purpose two-stroke engine,
More specifically, the present invention relates to a rotary throttle valve type carburetor that can supply fuel properly during cold start and full load operation.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 58-101253 discloses one type of carburetor for supplying fuel to a general-purpose two-stroke engine used for portable work machines for forestry and agriculture, small vehicles and other power sources. BACKGROUND ART A rotary throttle valve type vaporizer described in a gazette or the like is widely used.

In this carburetor, a cylindrical throttle valve having a throttle hole and a measuring needle is arranged perpendicularly to the intake passage of the carburetor body, and the throttle valve is rotated in accordance with an accelerator operation to control its own center. By moving the throttle in the axial direction, the air flow is controlled by changing the degree of overlap of the throttle hole with the intake passage, and at the same time the fuel flow is controlled from idling to full load operation by changing the depth of the metering needle inserted into the fuel nozzle. Is controlled. Further, the fuel sent from the constant fuel chamber to the fuel nozzle is regulated by a fixed jet or a manually adjusted needle valve.

[0004] A rotary throttle valve carburetor is a metering needle which is a means for setting the minimum flow rate during idling in a single fuel system, and a fixed jet or manual adjustment needle valve which is a means for setting the maximum flow rate in full load operation. It is a vaporizer with a unique structure with

[0005]

However, when such a rotary throttle valve type carburetor is used for supplying fuel to a small general-purpose two-stroke engine, for example, an engine having a displacement of 20 cc or less, the fuel flow during idling is reduced. Is very small. For this reason, even if the choke valve is fully closed at the time of cold start, it is difficult for negative pressure to act on the constant fuel chamber through the small gap, and the number of crankings increases because fuel required for cold start is not sucked out. And it is difficult to start the engine.

On the other hand, even in full load operation, a small displacement engine requires a very small flow rate of fuel, so that there is a difficulty that the diameter of the fixed jet must be processed to a small size with high precision. Alternatively, the troublesome task of requiring a high degree of fineness in the adjustment work of the manual adjustment needle valve cannot be avoided, and any maximum flow rate setting means tends to cause problems such as insufficient output and an increase in harmful substances in exhaust gas. .

The present invention relates to a rotary throttle valve type carburetor, that is, a cylindrical throttle valve having a throttle through hole and a metering needle and arranged perpendicular to an intake passage of a carburetor body, a constant fuel chamber and a fuel passage. A fuel nozzle with a metering needle inserted into the throttle opening and connected to the throttle through-hole, and moving the throttle valve in the direction of its own central axis while rotating the throttle valve in accordance with the accelerator operation, thereby controlling the air flow rate and the fuel flow rate. Solving the above-mentioned problem that the carburetor to be controlled has a carburetor, particularly for a small displacement engine, in which it is difficult to appropriately supply fuel at the time of cold start and at the time of full load operation, It is an object of the present invention to provide a carburetor that can easily start the engine while the required flow rate during full load operation can be easily secured.

[0008]

As a means for solving the above-mentioned problems, the present invention provides a choke valve at an inlet of an intake passage, a check valve which closes toward a constant fuel chamber in a fuel passage, and a suction valve. An air bleed passage connecting the throttle valve upstream of the passage and the check valve downstream of the fuel passage is provided.

When the choke valve is fully closed, a high negative pressure is generated in the intake passage, and fuel is sucked out of the air bleed passage into the intake passage, thereby facilitating the start of the engine during cold start. In addition, since the bleed air introduced into the fuel passage lowers the negative pressure of the fuel nozzle, the required flow rate of the fuel during full load operation can be easily secured.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, an embodiment of the present invention will be described. A carburetor body 1 has an intake passage 2 penetrating forward and backward and a valve hole 3 perpendicular to the intake passage 2 and having one end closed. A cylindrical throttle valve 4 is fitted into the valve hole 3 so as to be rotatable and movable in the direction of its own central axis.

The throttle valve 4 has a throttle through hole 5 having a diameter substantially the same as that of the intake passage 2 perpendicular to the center axis thereof, and a nozzle insertion hole 6, a measuring needle 7, a valve Axis 8
have. The nozzle insertion hole 6 is provided on the closed end side of the valve hole 3 so that the fuel nozzle 16 is inserted. Further, the valve shaft 8 is formed integrally with the end of the throttle valve 4 located on the open end side of the valve hole 3, and projects through the cover body 11 of the valve hole 3 to the outside of the carburetor body 1. Further, the measuring needle 7 is formed so as to protrude from the tip of an adjusting screw 9 screwed into a screw hole 8 a of the valve shaft 8.
The length of the protrusion in the fuel nozzle 16 at the idle position, and thus the depth of insertion into the fuel nozzle 16 at the idle position, is adjustable and held by the throttle valve 4.

A throttle valve lever 12 which is turned by a driver's accelerator operation is fixed to the shaft end of the valve shaft 8, and a torsion coil between the throttle valve 4 and the cover body 11 has both ends fixed thereto. A valve closing spring 13 composed of a spring is inserted around the valve shaft 8. Also, the valve shaft 8 of the throttle valve 4
A flange 4a is provided at the side end, and a cam 14 is formed on a surface facing the intake passage 2, and this cam 14 contacts a pin 15 protruding from the carburetor body 1.

When the throttle valve lever 12 is turned by the accelerator operation, the throttle valve 4 rotates integrally and the degree of overlap between the throttle passage 5 and the intake passage 2 changes, thereby controlling the intake air flow rate of the engine. At the same time pin 1
The throttle valve 4 moves in the direction of its own central axis in accordance with the cam 14 contacting the cam 5, and the insertion depth of the metering needle 7 into the fuel nozzle 16 changes, so that the fuel flow sucked out from the fuel injection hole 17 opened on the side surface. Is controlled.

On the end face of the carburetor main body 1 opposite to the cover body 11, a constant fuel chamber 18 similar to a widely known membrane carburetor is provided, which is separated from the atmosphere by a diaphragm (not shown). The fuel in the constant fuel chamber 18 passes through the fuel passage 19 and passes along the fixed jet 2 which is the main jet.
At 0, the maximum flow rate is regulated and sent to the fuel nozzle 16.
A well-known fuel pump that includes a diaphragm that operates by a pulse pressure generated in the crankcase of the engine and supplies fuel from a fuel tank (not shown) to the constant fuel chamber 18 is provided at an appropriate position on the outer surface of the carburetor body 1. It is installed in.

A well-known elastic cantilevered check valve 21 formed by making a U-shaped cut in a rubber plate is provided at a portion of the fuel passage 19 adjacent to the fixed jet 20 on the downstream side of the fixed jet 20.
The check valve 21 prevents air from flowing into the constant fuel chamber 18 from the intake passage 2 through the fuel passage 19. Further, a plate-shaped choke valve 22 is provided so as to overlap with the end face of the carburetor body 1 on the air cleaner side. It turns to open and close the entrance of the intake passage 2.

Further, an air bleed passage 24 is provided which connects the intake passage 2 upstream of the throttle valve 4 and the fuel passage 19 downstream of the check valve 21. An air bleed jet 25 is provided.

During idling with the accelerator released, the throttle valve 4 minimizes the degree of overlap of the throttle hole 5 with the intake passage 2 and maximizes the depth of insertion of the metering needle 7 into the fuel nozzle 16, ie, sets the fuel flow rate. It is placed in a position that minimizes these gaps.

When cranking is performed with the choke valve 22 fully closed during cold start, the intake passage 2 and the throttle
A high negative pressure is generated in the fuel chamber 18 and the fuel in the constant fuel chamber 18
7 and at the same time as the air-bleed passage 24, the high-concentration air-fuel mixture is supplied to the engine.
For this reason, the engine is started with a small number of crankings, and the engine can be easily started at the time of cold start.

On the other hand, during idling when the choke valve 22 is open, the bleed air flows from the air bleed passage 24 to the fuel passage 1 due to the high negative pressure in the throttle hole 5.
9. Introduced to the fuel nozzle 15. For this reason, the high negative pressure of the throttle passage 5 does not act on the constant fuel chamber 18, and the fuel suction amount is smaller than that without the air bleed passage 24.
Therefore, the measuring needle 7 for setting the fuel flow during idling is set.
It is not necessary to make the gap between the fuel nozzle 16 and the fuel nozzle 16 extremely small, and the processing accuracy of the measuring needle 7 can be reduced to increase the gap. This also increases the amount of fuel sucked out of the fuel injection port 17 at the time of a cold start, thereby reliably achieving the purpose of facilitating engine start.
In addition, idling can be stably performed.

Next, when the throttle valve 4 is located at a predetermined position between the idle position and the full load position in response to the accelerator operation, the fuel in the constant fuel chamber 18 mixes with the bleed air in the fuel passage 19. As a result, the negative pressure sucked from the fuel nozzle 17 into the throttle hole 5 and acting on the fuel nozzle 16 is lower than that without the air bleed passage 24. For this reason, the jet diameter of the fixed jet 20, which sets the maximum flow rate of the fuel, is made larger due to the lower negative pressure. Therefore, it is not necessary to process the jet into a minute size with high precision. It is easy to make the fixed jet 20 without any.

In the case of the structure in which the maximum flow rate is set by the manual adjustment needle valve, the fuel passage 19 can have a required constant effective cross-sectional area without requiring a fine adjustment work. As described above, in combination with the fact that the fixed jet 20 having the required constant effective area can be easily obtained, no harmful substances in the exhaust gas are increased in the vaporizer provided with any of the maximum flow rate setting means, and The engine can be properly and stably operated over the entire operation range without causing output shortage during load operation.

[0022]

As described above, the processing of the metering needle and the fixed jet can be facilitated by the simple means of connecting the air bleed passage to the fuel passage downstream of the check valve, or the manual adjustment needle valve can be used. Easy adjustment work, improved engine startability during cold start, stable idling,
By ensuring output during full load operation and suppressing harmful substances in exhaust gas, the engine can be operated stably over the entire operation range.

[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, 2 intake passage, 4 throttle valve, 5
Throttle hole, 7 measuring needle, 16 fuel nozzle, 1
8 constant fuel chamber, 19 fuel passage, 20 fixed jet, 21 check valve, 22 choke valve, 24 air bleed passage

Claims (1)

[Claims] 1. A column-shaped throttle valve having a throttle hole and a measuring needle and arranged perpendicular to an intake passage of a carburetor body;
A fuel nozzle connected to a constant fuel chamber and a fuel passage, the fuel nozzle having the metering needle inserted and opened in the throttle through hole,
In a rotary throttle valve carburetor that controls the air flow rate and the fuel flow rate by moving the throttle valve in the direction of its own central axis while rotating in response to an accelerator operation, a choke valve is provided at an inlet of the intake passage. And a check valve that closes toward the constant fuel chamber is provided in the fuel passage, and an upstream side of the throttle valve in the intake passage and a downstream side of the check valve in the fuel passage. A rotary bleed valve carburetor, which is provided with an air bleed passage connected to the carburetor.