JPH0134693Y2 - - Google Patents

Description

[Detailed Description of the Invention] The structure of a conventional carburetor for a general-purpose engine will be explained with reference to FIG. General-purpose engines are used for many purposes, and some work machines have an air cleaner 1 installed far away from an outer air vent type carburetor 3 and connected to it by a long pipe 2, as shown in FIG. If the specifications of the carburetor 3 are constant, if the long tube 2 is used, the air-fuel ratio characteristics of the carburetor 3 will be thinner than when the long tube 2 is not used, causing engine malfunction. Therefore, a carburetor flow rate adjustment test is performed by changing either or both of the main jet 4 and the main air jet 5 so that the air-fuel ratio characteristics are appropriate even if the long meandering pipe 2 is employed. The drawback was that the carburetor adjustment test required a lot of time. 6 is a joint, and 7 is a breather pipe connected to the engine crankcase (not shown).

The present invention has been devised for the purpose of eliminating the above-mentioned drawbacks by inexpensive means.

The present invention provides an outer air vent type carburetor for a general-purpose engine in which the air cleaner is installed far away from the carburetor and has a long pipe. Consisting of an outlet passageway whose cross section is larger than the inlet passageway, (c) an airflow resistance adjusting element uniformly distributed within the outlet passageway, and (d) a blowback prevention plate disposed on the end face of the outlet passageway. The purpose of this invention is to provide a carburetor that is characterized by having a joint that can be used to reduce the development and testing time, and is applicable to all small general-purpose engines.

An embodiment of the vaporizer of the present invention will be described with reference to FIG. FIG. 2 shows a schematic diagram of an embodiment of the vaporizer of the present invention. 1 is the air cleaner, 2 is the long pipe, 3
is a carburetor, 4 is a main jet, 5 is a main air jet, and 7 is a breather, which are similar to conventional carburetors. Reference numeral 11 denotes an element made of, for example, a cylindrical foamed porous body for adjusting ventilation resistance. Reference numeral 12 denotes a blowback prevention plate (a plate used in ordinary air cleaners with appropriate holes drilled in it). 1
6 is a joint with a step for positioning the element 11, and a blowback prevention plate 12 is attached to the vaporizer 3.
There is a positioning step between the two.
That is, an inlet passage 16-1 with a reduced passage cross-sectional area is formed on the upstream side of the joint 16, followed by an outlet passage 16-2 with a step and a passage cross-sectional area larger than that of the inlet 16-1. This exit passage 1
6-2 houses an airflow resistance adjusting element 11 made of a foamed porous material with uniform distribution. The blowback prevention plate 12 also serves to prevent the element 11 from flowing out.

The operation of the present invention will be explained.

(1) Reasons why the air-fuel ratio becomes lean Figure 3 shows the pressure at each part when the long tube 2 is used and when it is not used.

When the long tube 2 is used, the long tube 2 serves as a surge tank, and the pressure in front of the main air jet 5 becomes smaller than when the long tube 2 is not used. Furthermore, since most general-purpose engines have single cylinders, the long pipe 2 plays a large role as a surge tank. Further, the negative pressure after the main air jet 5 is smaller when the long tube 2 is used than when it is not used.

On the other hand, the fuel flow rate supplied by the carburetor is proportional to the pressure difference between the atmospheric pressure and the back of the main jet 4. Therefore, if long tube 2 is used, compared to not using it,
Since the negative pressure after the main jet 4 is reduced, the fuel flow rate supplied by the carburetor is reduced.

On the other hand, in the case of a general-purpose engine, the air flow rate to the engine hardly changes depending on the length of the long tube 2.
That is, the reason why the air-fuel ratio becomes thinner when the elongated pipe 2 is adopted is because the negative pressure in front of the main air jet 5 becomes smaller and the fuel flow rate decreases.

(2) Effect of the present invention In order to reduce the influence of the long flexible pipe 2, the negative pressure in front of the main air jet 5 should be brought close to the negative pressure when the long flexible pipe 2 is not used. That is, the negative pressure can be easily adjusted by the restriction by the inlet passage 16-1 of the joint 16 in front of the carburetor 3 and the fine adjustment function by the presence of the porous foam element 11 and the blowback prevention plate 12. The pressure is made to be almost the same even when the long tube is used as when it is not used. That is, the pressure at each part approaches that when the long tube 2 is not used.

The present invention has the above configuration and has the following effects.

(1) Despite the adoption of a long serpentine tube, the pressure before the main air jet changes less than when it is not used, so the fuel flow characteristics of the carburetor can be easily adjusted to an appropriate value.

(2) Therefore, development adjustment time is significantly reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a conventional vaporizer, Fig. 2 is a schematic diagram of an embodiment of the vaporizer of the present invention, and Fig. 3 shows the pressure in various parts when a long meandering tube is used in the vaporizer and when it is not. FIG. 1... Air cleaner, 2... Long pipe, 3... Vaporization, 4... Main jet, 5... Main air jet,
11...Airflow adjustment element, 12...Blowback prevention plate, 16...Joint, 16-1...Inlet passage,
16-2...Exit passage.

Claims (1)

[Scope of utility model registration request] In an outer air vent type carburetor for a general-purpose engine in which the air cleaner 1 is installed far away from the carburetor 3 and has a long pipe 2, (a)
(b) an inlet passage 16-1 with a narrow passage cross-section; and (b) an outlet passage 16-2 with a passage cross-section larger than the inlet passage.
and (c) a joint consisting of an airflow resistance adjusting element 11 uniformly distributed within the outlet passage, and (d) a blowback prevention plate 12 disposed on the end face of the outlet passage. Characteristic vaporizer.