JP2002276469A - Venturi piston and variable venturi type carburetor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a venturi piston of a variable venturi-type carburetor for improving an output of an engine and generating an effect of improvement of fuel consumption by enhancing atomization performance of fuel supplied from a main nozzle. SOLUTION: A semi-cylindrical guide groove 55 is provided in place of a conventional cut-away within a recessed part 52 at a tip of the venturi piston 50. Air flow velocity at the center part of a main bore 2 is increased in the groove 55. A nozzle of the main nozzle 9 is placed in the air flow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable venturi-type carburetor that mixes gasoline and air and supplies the mixture to an engine such as a motorcycle.

[0002]

2. Description of the Related Art A carburetor for a motorcycle is:
The variable venturi type in which the opening of the venturi portion (hereinafter referred to as the throttle opening) is adjusted by displacing a venturi piston is predominant.

[0003] This variable venturi-type carburetor
A negative pressure operated type in which a negative pressure in a suction chamber is controlled by a throttle valve provided in a downstream main bore and a venturi piston is operated by the negative pressure, and a type in which a venturi piston serving also as a throttle valve is directly pulled by a throttle wire ( Here, for convenience, this is called a VM type).

In both types, the jet needle attached to the axis of the venturi piston is pulled together with the piston, and the amount of fuel (gasoline) ejected from the main nozzle into which the jet needle is inserted increases the throttle opening. It increases according to.

FIG. 4 shows a prior art of a VM type carburetor. Although the details vary depending on the manufacturer, the VM type carburetor basically has a structure as shown in the figure.

In FIG. 1, reference numeral 1 denotes a housing having a main bore 2, a cylinder 3, and a float chamber 4. A venturi piston 5 is slidably incorporated in the cylinder 3 of the housing while preventing rotation, and a spring 7 for returning the piston 5 pulled by a throttle wire 6 connected to a throttle grip (not shown) is incorporated. Have been.

A main nozzle 9 having a main jet 8 is provided between the main bore 3 and the float chamber 4, and the amount of insertion of the jet needle 10 attached to the venturi piston 5 into the main nozzle 9 changes with the displacement of the venturi piston 5. The amount of fuel ejected from the main nozzle 9 is adjusted by the pressure difference between the float chamber and the venturi section.

The fuel injected from the main nozzle 9 is mixed with air introduced from the main air jet 11 as fine bubbles from an air bleed hole provided in the main nozzle 9 in order to promote atomization. Is done.

The housing 1 has a pilot jet 1
2, a pilot outlet 13, a bypass 14, a pilot air hole 15, and a valve 16 for adjusting the amount of air supplied from the pilot air hole 15 are further provided.

When the throttle opening is large, the air-fuel ratio (air:
The ratio of gasoline) is determined by the hole diameter of the main jet 8, and the air-fuel ratio during the throttle opening is adjusted by the throttle of the main nozzle 9 by the jet needle 10. Since the adjustment becomes inaccurate, the fuel introduced by the pilot jet 12 is mixed with air introduced from the pilot air hole 15 and sent out from the bypass 14 and the pilot outlet 13.

Reference numeral 17 denotes a float valve, which keeps the fuel supplied from the fuel tank (not shown) to the float chamber 4 at a constant liquid level. An overflow pipe is also provided to release fuel when the float valve 17 does not operate normally due to some abnormality, but this is not shown.

[0012] In addition, the exemplary VM type carburetor is provided with a starter (also called a choke). The starter, which is a fuel supply path dedicated to starting,
The valve 18 is opened by operating a lever or the like, and the air introduced from the starter air hole 19 and the fuel sucked up from the float chamber 4 are mixed and ejected from the starter outlet 20 into the main bore 2 downstream.

The venturi piston 5 of the VM type carburetor and the venturi piston of the negative pressure actuation type carburetor are provided with an oblique notch called a cutaway at the tip, so that the throttle opening is small (usually 1/4 or less). In this case, the wind pressure is drawn from the cutaway 5a to prevent the fuel from flowing too much from the main nozzle 9.

[0014]

In a variable venturi-type carburetor, when the air flow velocity in the venturi section (the pressure difference before and after the nozzle outlet, ie, the pressure difference between upstream and downstream) is increased, atomization of fuel injected from the main nozzle is performed. Has been found to be promoted.

[0015] When the atomization performance of the carburetor is improved, the mixing state of air and fuel is improved, thereby improving the combustion efficiency, improving the output of the engine, and improving the fuel efficiency. How to increase the air flow rate at the time of opening and the like is a state of trial and error, and no effective measure has been found.

The cutaway provided in the venturi piston attracts wind pressure to the venturi portion. This cutaway is provided mainly for preventing fuel from flowing too much from the main nozzle when the throttle opening is small. However, the function of increasing the air flow velocity at the main nozzle outlet was not so high, and sufficient atomization performance could not be obtained.

Accordingly, an object of the present invention is to improve the shape of the tip of the venturi piston to improve the fuel atomization performance.

[0018]

In order to solve the above-mentioned problems, according to the present invention, instead of the cutaway conventionally provided at the tip of the venturi piston, the shaft center is shifted from the position facing the inlet of the main bore of the carburetor. And a semi-cylindrical guide groove for directing the air flowing from the inlet toward the jet needle at the axial center.

In this venturi piston, the guide groove whose both sides are surrounded by groove walls is provided in a circular concave portion on the front surface,
It is particularly preferable that the end of the guide groove is open to the recess.

The variable venturi-type carburetor of the present invention adjusts the opening (throttle opening) of the venturi using the above-described venturi piston provided with a guide groove.

[0021]

Operation As shown in FIG.
Has a structure in which the tip is formed in a cylindrical shape, and the cylindrical portion is inserted into a cylindrical groove 21 (see FIG. 6) provided on an extension of the cylinder 3 to narrow the passage area of the venturi portion. In this structure, when the cutaway 5a is provided at the tip of the piston, the air flowing from the cutaway 5b into the recess 5b spreads over the entire area of the recess 5b and hits the leeward (right side in FIG. It flows downstream from the passage 22 formed therebetween.

In such a situation, when the throttle opening is small, the purpose of increasing the pressure in the region where the ejection opening of the main nozzle 9 exists to suppress the fuel ejection amount is achieved, but the increase in the air flow rate is caused by the increase in the passage speed. At the position 22, the effect of improving the air flow velocity at the main nozzle ejection port upstream therefrom is small.

On the other hand, in the venturi piston of the present invention, the air that has flowed into the guide groove does not escape to the periphery until it reaches the axial center of the piston, but concentrates as a fast airflow at the center of the main bore. In addition, the inlet of the guide groove is located upstream of the main nozzle. Therefore, even when the throttle opening is small and the negative pressure of the engine is small, the ejection port of the main nozzle is in the high-speed airflow created by the guide groove. Thus, the fuel is atomized satisfactorily.

Since the guide groove also draws in the wind pressure, similarly to the cutaway, the effect of preventing the fuel from flowing too much from the main nozzle when the throttle opening is small is not impaired.

[0025]

1 to 3 show an embodiment of a venturi piston according to the present invention. The venturi piston 50 is for a VM-type carburetor, and has a cylindrical shape having a partition wall 51 at a position deviated forward. In addition, a slit 53 for taking the throttle wire 6 in and out is provided at one location on the outer circumference over the entire length.
The slit 53 is a key 2 provided on the inner wall of the cylinder 3.
3 is also used to prevent the piston 50 from rotating.

A notch having a tapered surface 54 is provided on the outer periphery of the tip at a position directly opposite to the slit 53. The tapered surface 54 of the notch is for finely adjusting the minimum throttle opening. When the tip of the adjusting screw 24 screwed into the housing 1 is brought into contact with the adjusting screw 24, the screwing amount of the adjusting screw 24 is adjusted. Piston 50
Changes the return end point position and changes the minimum throttle opening.

The jet needle 10 is passed through a hole formed in the center of the partition wall 51 and is prevented from coming off by the circlip 25. The jet needle 10 is provided with a plurality of grooves arranged at a fine pitch in the axial direction, and the amount of fuel injected from the main nozzle 9 is adjusted by changing the position of the groove for locking the circlip. .

The above configuration has no difference from the conventional venturi piston. That is, in the present invention, the guide groove 55 whose both sides are surrounded by the groove wall 55a is provided in the concave portion 52 at the tip of the venturi piston 50 instead of the conventional cutaway, which is different from the conventional product. The guide groove 55 is a straight groove having a semi-cylindrical shape, and is provided in a range from the position facing the center of the inlet of the main bore 2 on the outer peripheral surface to the axis of the piston. Also,
The end of the guide groove 55 is opened to the recess 52 at a position slightly beyond the axis of the piston.

The venturi piston 50 constructed as described above is mounted on the carburetor housing 1 shown in FIG.
When incorporated in place of the above, the variable venturi-type carburetor of the present invention is completed.

For an experiment for confirming the effect, a running test of a motorcycle was performed by replacing the venturi piston of a commercially available VM type carburetor assembly φ24 with the product of the present invention shown in FIG. 1. Improvement,
The effect of reducing fuel consumption was recognized. This may be attributed to the improvement in atomization performance.

The startability of the engine was better when the venturi piston of the present invention was used. The smaller the throttle opening, the greater the difference in atomization performance between the invention product and the conventional product, which seems to have been affected.

In addition, when tuning the engine, etc., conventionally, fine adjustment of the cutaway size, replacement of the main jet (deformation of the hole diameter), replacement of the jet needle (change of the taper degree of the needle), venturi The condition of the engine was adjusted by changing the fixed position of the jet needle with respect to the piston, and the work was very troublesome, but when using the venturi piston of the present invention, the range that can be handled without adjustment was widened .

Although the above description has been made with reference to a VM type carburetor as an example, the guide groove 55 which characterizes the present invention exerts its effectiveness even if it is provided in a venturi piston of a negative pressure operated carburetor. .

[0034]

As described above, in the venturi piston of the present invention and the variable venturi type carburetor using the same, the air flow velocity of the main nozzle ejection port is increased by the action of the guide groove at the tip of the piston to atomize the fuel. Is promoted, and a mixture with a high degree of mixture is supplied to the engine, so that the combustion efficiency is increased, and the output of the engine is improved and the effect of reducing fuel consumption is obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a venturi piston of the present invention.

FIG. 2 is a sectional view showing a main part of a carburetor to which the piston of FIG. 1 is assembled.

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

FIG. 4 is a structural diagram showing a basic principle of a VM type carburetor.

FIG. 5 is a perspective view of a conventional venturi piston employed in the carburetor of FIG. 4;

6 is a sectional view of a main part of the carburetor to which the venturi piston of FIG. 5 is assembled.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Main bore 3 Cylinder 4 Float chamber 6 Throttle wire 9 Main nozzle 10 Jet needle 17 Float valve 21 Cylindrical groove 24 Adjust screw 50 Venturi piston 51 Partition wall 52 Depression 53 Slit 54 Tapered surface 55 Guide groove 55a Groove wall

Claims (3)

[Claims] 1. A semi-cylindrical guide groove which extends from a position facing an inlet of a main bore of a carburetor to an inlet to an axial center portion and directs air flowing from the inlet toward a jet needle at the axial center portion is replaced with a cutaway. The venturi piston of the variable venturi type carburetor provided at the tip. 2. The venturi piston according to claim 1, wherein said guide groove is provided in a circular concave portion on the front surface, said guide groove being surrounded on both sides by a groove wall, and an end of said guide groove is opened to said concave portion. 3. The method of claim 1, wherein the opening of the venturi is adjusted.
Or a variable venturi-type carburetor that is operated by the venturi piston according to 2.