GB2179701A

GB2179701A - Carburetor provided with an anti-percolation device

Info

Publication number: GB2179701A
Application number: GB08617882A
Authority: GB
Inventors: Yasuhiko Kamohara
Original assignee: Aisan Industry Co Ltd
Current assignee: Aisan Industry Co Ltd
Priority date: 1985-07-26
Filing date: 1986-07-22
Publication date: 1987-03-11
Also published as: JPS6224048U; JPH036851Y2; FR2585410B1; GB8617882D0; FR2585410A1; GB2179701B; DE3625173A1

Abstract

In a carburetor having a metering needle 4 which controls the flow of fuel through a metering section 9, a perforated bubble breaking member 10 is disposed in a portion of fuel passage 12 adjacent the fuel metering section 9, the bubble breaking member in use breaking-up bubbles generated in the fuel within the fuel metering section into smaller bubbles, thereby preventing occurrence of percolation in the carburetor. The perforated bubble breaking member 10 may be formed of a metal gauze shaped into a cylindrical form or of a coiled spring having a small pitch. <IMAGE>

Description

SPECIFICATION Carburetor provided with an anti-percolation device The present invention relates to a carburetor provided with an anti-percolation device.

As is well-known, when an engine is stopped after running of the engine, the carburetor is heated due to heat transfer from the engine. Thus, the temperature of the fuel in the carburetor is raised and hence the fuel is vaporized to produce air bubbles therein.

As the air bubbles thus produced grow to a fairly large size and move upwardly due to buoyancy force thereof, the fuel near the air bubbles is pushed upwardly towards the main nozzle and passes through the latter into an air-fuel mixture passage of the carburetor.

Such phenomenon is generally referred to as "percolation".

Japanese Utility Model Laid-Open (Unexamined) Publication No. 17255/1984 discloses an anti-percolation device for a carburetor.

This known anti-percolation device has a bubble-separating perforated plate which is detachably secured to the lower inlet end of the main nozzle of a carburetor. A carburetor having this anti-percolation device encounters a problem that bubbles tend to stagnate on the upstream side of the perforated plate. This in turn causes an engine stall when the rate of fuel supply to the engine is small because in such a case the stagnant bubbles prevent the liquid fuel from reaching the main nozzle.

When the fuel supply rate is increased, the gas of the bubbles is sucked through the main nozzle before the liquid fuel reaches the main nozzle, so that the mixture becomes very lean temporarily so as to seriously impair the running of the engine.

According to the present invention there is provided a carburetor having a float chamber for accommodating a fuel and provided in a lower portion thereof with a fuel metering section, a metering needle which controls the flow rate of the fuel flowing through the fuel metering section, a main nozzle opening into an air-fuel mixture passage, and a fuel passage providing a communication between the main nozzle and the fuel metering section, said carburetor including: a perforated bubble breaking member disposed in a portion of the fuel passage adjacent the fuel metering section for breaking-up bubbles generated in the fuel within the fuel metering section into smaller bubbles.

Some embodiments of the invention will now be described, by way of examples, with reference to the accompanying drawings, in which: Figure 1 is a schematic vertical sectional view of a first embodiment of a carburetor with an anti-percolation device in accordance with the present invention; Figures 2 and 3 are sectional views of essential portions of second and third embodiments of the present invention; Figure 4 is a schematic diagram illustrating the relationship between pore size of a perforated bubble breaking member and the amount of occurence of percolation; and Figure 5 is a schematic diagram illustrating the relationship between pore size of a perforated bubble breaking member and the flow resistance encountered by the flow of fuel.

Referring first to Fig. 1, a first embodiment of a carburetor 1 according to the present invention has a float chamber 11 containing fuel 19 and provided at a lower portion thereof with a main jet 9 constituting a fuel metering section. The carburetor 1 further has a metering needle 4 for metering the fuel flowing through the fuel metering section, a main nozzle 3 which opens into an airfuel mixture passage, and a fuel passage 12 which provides a communication between the main nozzle 3 and the fuel metering section 9. An air valve 5 carried by an air valve shaft 8 is arranged to be rotated in accordance with the flow rate of the intake air supplied to the engine. The air valve shaft 8 carries at its one end a cam 6 which is contacted at its peripheral surface by a roller 7 to which attached is the metering needle 4.The arrangement is such that the metering needle 4 is moved up and down within the fuel metering section 9 in accordance with the rotation of the air valve 5, so as to maintain an optimum air-fuel ratio of the mixture. In Fig. 1, the reference numeral 15 denotes a float, while reference numeral 16 designates a stopper which is integrated with the metering needle 4 by being screwed to the upper end of the latter. The reference numeral 17 denotes a compression spring which urges the metering needle 4 normally downwardly.

In operation, the shaft 8 and, hence, the cam 6 are rotated in accordance with the rotation of the air valve 5, so that the roller 7 rolls up and down along the contour of the cam 6. This in turn causes the metering needle 4 to move up and down, so as to control the flow rate of the fuel flowing from the float chamber 11 to the main nozzle 3 through the fuel passage 12. Since the above-noted construction of carburetor is known per se, no further description will be needed in this connection.

A cylindrical bubble breaking perforated member 10, which is fitted into the hole constituting the downstream end of the fuel metering section 9, is arranged to break-up air bubbles which are formed when the fuel is heated. The term "perforated member" is used in this specification to include various types of member which are perforated or provided with pores or holes in their surfaces, as well as mesh-like members such as gauze wire and a cylindrically wound spring which provides spiral continuous small clearance serving as a "perforation". The perforated member 10 includes a cylindrical metal gauze wire of a suitable mesh size and made of a material which is resistant to corrosive environment created by the fuel, e.g., stainless steel.More specifically, the perforated member 10 is formed by rounding a sheet of a metal gauze wire and fixing and reinforcing the overlapping ends, i.e., the seam, and both the upper and lower circumferential edges by resin moulding. The cylindrical perforated member 10 has an inside diameter which is considerably greater than the outside diameter of the metering needle 4, so as not to impede the vertical movement of the metering needle 4 within the perforated member 10.

When the engine is stopped after a continuous running, the forced cooling system of the engine is stopped also, so that the fuel in the carburetor 1 is heated by the heat transmitted from the engine by radiation and conduction.

As a result of the heating, bubbles are generated in the fuel within the fuel metering section 9 or around the edge portion of the main jet 9. The bubbles, however, cannot be relieved into the float chamber 11 due to the presence of the metering needle 4. Consequently, the bubbles accummulate in the fuel metering section 9 so as to fill up the portion of the fuel passage immediately downstream of the fuel metering section 9. The bubbles then ascent through the fuel passage 12 so as to push the liquid fuel up to the main nozzle 3 so that the operation of the engine is rendered unstable. This unfavourable effect is known as "percolation".

According to the invention, the percolation is effectively prevented by virtue of the bubble breaking member 10 which is disposed at the downstream end of the fuel metering section.

Namely, large bubbles are broken into tiny ones, so that the force for pushing the liquid fuel is decreased to minimize the tendency for percolation. Another advantage is that the fine bubbles form good emulsion of the fuel when mixed with the fuel, so that the operation of the engine is not adversely affected by the bubbles.

Fig. 2 shows a second embodiment of the present invention. This second embodiment incorporates a bubble breaking member 10 similar to that shown in Fig. 1 and disposed in a second passage 12b' of the fuel passage 12.

In this embodiment also, the bubbles generated in the fuel metering section are broken into tiny ones.

More specifically, referring back to Fig. 1, the fuel passage 12 has a first passage 12a having one end (upper end as viewed in Fig.

1) connected to the main nozzle 3 and extending downward therefrom through the wall la of the carburetor 1, the first passage being provided therein with an emulsion tube 13, and a second passage 12b corresponding to the above-mentioned second passage 12b' and connecting the other end (lower end as viewed in Fig. 1) of the first passage 12a to the fuel metering section 9. As will be seen from Fig. 1, the second passage extends through the wall 1 a of the carburetor obliquely downwardly from the lower end of the first passage. Thus, the second passage 12b makes a predetermined angle to the first passage 12a.In the first embodiment described before, therefore, the perforated member 10 fitted in the downstream end of the fuel metering section 9 is positioned at the right-side end of the second passage 1 2b. In contrast, according to the second embodiment, the bubble breaking member 10 is disposed at the juncture between a passage 12b' corresponding to the second passage 12b shown in Fig.

1 and a passage 12a' corresponding to the first passage 1 2a shown in Fig. 1. In operation, the bubbles in the second passage 12b' are broken by the bubble breaking member 10 into tiny bubbles before they enter the first passage 12a'.

In the second embodiment, the left-side end of the second passage 12b' as viewed in Fig.

2 extends through the wall la of the carburetor 1 into the airfuel mixture passage lb in the carburetor. The second passage 12b', however, does not communicate with the mixture passage 1b because a plug 18 is driven into the second passage 12b' in such a manner as to interrupt the communication between the second passage 12b' and the air-fuel mixture passage 1 b. In the assembly, the perforated member 10 is inserted into the second passage 12b' from its end which opens into the air-fuel mixture passage 1 b and is fixed in the second passage 12b' by a suitable means.

Thereafter, the plug 18 is driven into the end of the second passage 12b' so as to interrupt the communication between this passage 12b' and the air-fuel mixture passage 1 b.

Fig. 3 shows a third embodiment which is substantially the same as the second embodiment except that the perforated bubble breaking member 10 is constituted by a coiled spring having a small pitch. The left-side end of this coiled spring is seated on and fixed to a small boss 18' formed on the right-side end of the plug 18. It will be seen that this third embodiment offers the same advantage as that produced by the second embodiment.

In the first embodiment described before, the perforated bubble breaking member 10 is constituted by a metal gauze wire which is rounded in the form of a cylinder and resinmoulded along its seam and both circumferential edges, such that both axial ends of the cylinder are opened. This cylindrical perforated bubble breaking member may be modified such that it has a bottom constituted by a metal gauze wire fixed to one axial end thereof by resin moulding. It is also possible to form the cylindrical perforated bubble breaking member with or without a bottom wholly from a resin. Similarly, the perforated bubble breaking members in the second and third embodiments may be substituted by a cylindrical perforated member which is provided with a bottom fixed to the right-side end thereof by resin moulding.

Fig. 4 shows a relationship between the size of the mesh of the metal gauze wire constituting the perforated bubble breaking member and the amount of generation of percolation.

This relationship has been obtained through an experiment conducted by the present inventors. From this Figure, it will be seen that the mesh size of the metal gauze wire is preferably greater than 90 in terms of the number of apertures per inch in weft and warp directions, because the percolation is substantially nullified when the mesh becomes finer.

Fig. 5 shows a relationship between the mesh size of the metal gauze wire and the flow resistance encountered by the flow of the fuel, as observed through an experiment conducted by the inventors. From this Figure, it will be seen that, when the mesh size exceeds 120, the flow resistance is gradually increased as the mesh becomes finer.

It is possible to obtain an optimum design of the carburetor of the first and the second embodiment by making an effective use of the characteristics shown in Figs. 4 and 5. For instance, the mesh size of the metal gauze wire is selected to be 140 upon consultation with the graph shown in Fig. 4, in order to nullify the possibility of occurrence of percolation. Then, the metering needle is designed in view of the flow resistance characteristics shown in Fig. 5, in such a manner that the desired air-fuel ratio is obtainable when the flow of fuel encounters the flow resistance produced by the bubble breaking member constituted by the metal gauze wire having the mesh size of 140.

As has been described, according to the invention, the bubbles generated in the fuel within the fuel metering section are broken into tiny bubbles by a perforated bubble breaking member which is disposed in a portion of the fuel passage adjacent the fuel metering section. Therefore, bubbles generated by the heat applied to the fuel can be broken into tiny bubbles, so as to remarkably suppress the percolating tendency of the fuel, thereby preventing troubles such as difficulty in restarting of the engine which may otherwise be caused by percolation of the fuel, i.e., undesirable discharge of the fuel from the main nozzle. In addition, the tiny bubbles form a good air-fuel emulsion when mixed with fuel, so that any deterioration of the drivability due to a temporary leaning of the air-fuel mixture can be avoided. Furthermore, any tendency for the bubbles to stagnate in the bubble breaking member can be suppressed if the perforated bubble breaking member has a sufficiently large surface area, as is the case of the cylindrical metal gauze wire or a cylindrical coiled spring with or without a bottom which are used in the described embodiments.

Claims

1. A carburetor having a float chamber for accommodating a fuel and provided in a lower portion thereof with a fuel metering section, a metering needle which controls the flow rate of the fuel flowing through said fuel metering section, a main nozzle opening into an air-fuel mixture passage, and a fuel passage providing a communication between said main nozzle and said fuel metering section, said carburetor including a perforated bubble breaking member disposed in a portion of said fuel passage adjacent said fuel metering section for breaking-up bubbles generated in the fuel within said fuel metering section into smaller bubbles.

2. A carburetor as claimed in Claim 1, in which said perforated bubble breaking member comprises a metal gauze wire shaped into the form of a cylinder.

3. A carburetor as claimed in Claim 1 or Claim 2, in which said perforated bubble breaking member is disposed at the downstream end of said fuel metering section.

4. A carburetor as claimed in Claim 1 or Claim 2, in which said fuel passage includes a first passage having one end connected to said main nozzle, and a second passage connected between the other end of said first passage and said fuel metering section, said second passage extending at a predetermined angle to said first passage, said perforated bubble breaking member being disposed at the juncture between said first and second passages.

5. A carburetor as claimed in Claim 1, in which said fuel passage includes a first passage having one end connected to said main nozzle, and a second passage connected between the other end of said first passage and said fuel metering section, said second passage extending at a predetermined angle to said first passage, said perforated bubble breaking member including a coiled spring disposed at the juncture between said first and second passages.

6. A carburetor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.