GB2202007A - I.C. engine carburettor - Google Patents

Abstract

A body A is coaxially supported in the venturi 20 and is actuated by the accelerator. A secondary air passage B provides air flow to the fuel feeding tube 170 and a valve (C, Fig.2) reduces the flow cross-section of the passage (B) when the vacuum downstream of the body A falls. <IMAGE>

Description

TITLE IMPROVED CARBURETOR The present invention relates to an irnproveo carburetor.

Despite the diversity of conventional carburetors, they principally all involve the basic structure comprising a venturi and a butterfly or throttle valve operated by accelerater (See Fig. 5B). The speed of the air stream is controlled by the valve. however, suc deice suffers a disadvantage that the area of the throat into which the fuel spray nozzle empties is unchangeable, therefore it fails to achieve a fine.

atomization and homogenity of the fuel particle in the full range of the tachometrical speed of the engine.

In other words, they may work well under a few specified rpm, but not well for all the engine speed in operation from idling to full speed. The atomized fuel particles are quite uneven and not always finely scattered.(See inset of Fig. 5B) As a result the fuel cannot be burned completely, thus causing considerable waste of fuel and leading to serious pollution of hydrocarbon.

Accordingly, it is the chief object of this invention to provide an improved carburetor, whereby the aforesaid disadvanatages are obviated.

It is another object of this invention to prcicc an automatic choke device.

According to the present invention, revolutionizing carburetor is provide, which comprises an approximately frustal body adjustably supported in the venturi to regulate the effective are of the throat orifice. (See Fig. 5A) The atomization of full particles thus obtained is extremely even and fine.

(See Fig. 5, inset) . Hence the first object is accomplished.

The first object is even better carried out by another feature of this invention. According to the second feature of this invention, the fuel is subject to a premixing with air before it is sucked into the venturi. Thus when the pre-mixture reaches the venturi, it is subject to a further atomization, thereby the resulting fuel particies are exceptionally even and fine. For this purpose, a side airpath is branched upstream of the venturi to the fuel path before the fuel reaches the venturi. The bypassed air amount occupies only a negligibly small portion of the overall airstream, yet its effect is very significant in contributing to the fine atomization of the fuel.

According to a third feature of this invention, an automatic choke device is provided. The choke device comprises a plunger which cooperates with the aforesaid side airpath. As stated before, the side airpath has a significant influence on fuel atomization, if the sidc airpath is partially blocked so that the bypassing airstream decreases, then the resulting fuel/air mixture will become thicker. For this reason, one end of the plunger extends into the side airpath and its another end is in communication with the pipeline connected to intnt electrical power to the air conditioning system.

The foregoing objects and other objects as well as ends into the side airpath and its another end is in communication with the pipeline connected to intth. In so doing, the effective sectional area of side airpath decreases, and the resulting fuel/air mixture becomes thicker, thus carrying out a choking effect.

Numerous other features and advantages will become apparent when read in connection with the accompanying drawing in which: Fig. 1 and Fig. 2 are the elevational sectional views of a preferred embodiment of this invention from different angles; Fig. 3 is a top sectional view of the carburetor in Fig. 1; Figs. 4A and 4B are the perspective view of a "chamber-model" of the side airpath with the fuel feeding tube and the plunger in position; Figs. 5A and 5B are the graphical representation sholfing the venturi of this invention and G conventional standard carburetor, wherein the insets respectively show the enlarged view of their resultant fuel particules.

In the drawings, three-dimensional corrdinates are used to help understand the orientation of each element.

With reference to the drawing, the present invention comprises three main innovations, namely (A) adjustable, approximately frustal body in venturi; (B) side airpath; (C) automatic choking device.

The frustal body A is fixed on a shaft 80. When the shaft 80 is shifted axially, the position of frustal body A is also changed, thus changing the "effective area" (i.e. the annular space between the throat of venturi 20 and the frustal body A.) of the venturi, and resulting in different airstream speed, and therefore, different air/fuel ratio. The shaft 80 is connected through a cable to the accelerator of the motorcycle (not shown) and can be actuated thereby.

When the motorcyclist stresses the accelerator, the shaft 80 and the frustal body A are pulled to the right side of Fig. 1, thus causing a thicker fuel/air mixture.

Lik most conventional carburetors, this carburetor comprises a fuel inlet 140 to introduce in fuel from fuel tank, a fuel reservoir 150, and a float 160 with a needle valve 142. When the accummulation of fuel in reservoir 150 reaches a predetermined level, the fuel inlet 140 is closed by needle valve 142. This is similar to conventional carburetor, thus detailed description is not necessary. A fuel feeding tube 170 is provided to suck the fuel from reservoir 150 to the venturi. Its upper end extends to the vicinity of the throat 30, a suction is created and the fuel in reservoir is drawn up and mixed with the air.

The side airpath B is branched upstream of the throat 30 and leads to the fuel path. In order that the bypassed air can enter the fuel feeding tube 170, the latter is provided with a plurality of perforations 172. The bypassed air enters the fuel feeding tube 170 and pre-mixes with the fuel therein. The fuel/air premixture is then sucked to an annular groove 11 and then enters the fuel spray nozzle 31 through an aperture 12, and then enters the throat to receive a further atomization. As a result, the final fuel particles are extremely even and fine.

In order to compactly built the side airpath B in the carburetor, it is practically a three dimensional double-L tunnel (see the chamber model in Figs. 4A and 4B, where the side airpath is defined by broken lines.) The side airpath has three sections: a Z-section 21 extending from its inlet in the vicinity of the venturi in Z direction, an X-section 22 extending in X direction, and a Y-section 23 extending in Y direction to empty into the fuel feeding tube 170.

The plunger of automatic choke device C comprises a wedge 194 extending into X-section 22 of side airpath B. When the wedge is pushed to the left side, the amount of the bypassed airflow will decrease, thus permitting a thicker fuel/air premixture to reach the venturi. Referring to Fig. 2 and Fig. 3, the wedge 194 is retained in a brass sleeve 190 and slidable along the latter's length. The wedge 194 is carried at one end of a sliding rod 192 with a sealing ring 195 which can make a smooth yet sealing sliding motion in sleeve 190. A retaining tension spring 193 is provided to retain the wedge 194. It's function will be described later. One end of spring 193 is fixed to sleeve 190 while its another end is connected to the free end of sliding rod 192. The sleeve is connected to the intake manifold (not shown) of the engine by means of a connector 191. Since the sealing ring 195 excludes the possibility of any leakage of the air from its one side to its another side, the position of the wedge 194 depends on the balance between the resumptive force of the stressed tension spring 193 and the difference between the pressure on both sides of the sealing ring 195. When the load is high, the operator will stress the accelerator tightly and the degree of vaccum in the intake manifold is lower than that in the venturi, so that the wedge 194 is pushed to the left side to the position shown in broken line in Fig. 2, hence the side airpath B is partially blocked and the side air flow tapped by the side airpath decreases, thus resulting in a significant increase in the concentration of the fuel/air mixture.

On the other hand, when the load is no longer heavy, the operator will apply less stress on the accelerator and the difference of degree of vacuum in the venturi and the intake manifold decreases and the wedge 194 is pulled back to its original position by the resumptive force of spring 193. By properly choosing the modulus of the spring and calculating the variation of degree of vacuum in the venturi and intake manifold under various engine speed, the degree of blockage of the side airpath B can be determined. It is noteworthy that the wedge 194 should not completely block the side airpath B even under the heaviest load, because if this is the case, the air/fuel ratio will increase to an inoperable degree (say below 8.5/1) which results in "sputtering out" or stalling.

Practically, the frustal body A comprises an approximately frustal head 40 and a bell-shaped element 50. Both of them are provided with internal threads and the shaft 80 is provided with external thread so that the relative axial position of the frustal head 40 and the bell-shaped element 50 on the shaft 80 can be adjusted. The amount of the fuel depends on the width of the gap between the venturi and the fuel spray nozzle (in the case of Fig. 1, it is the distance between points P and Q), whereas the amount of air depends mainly on the distance between the fuel spray nozzle and the front magin of the cylindrical part of bell-shaped element 50 (i.e. the distance between point P and point R). Therefore, the feed of fuel and air can be respectively adjusted by changing the relative position of frustal head 40 and of bell-shaped element 50 on the shaft 80.The shaft 80 is provided with sealing rings 81 so that it can sealingly slide in Y direction in a seat 60 fixed in the main body 10 of the carburetor. A spring 70 is loaded between the bellshaped element 50 and the seat 60 with its both ends respectively fixed to the bell-shaped element 50 and the seat 60, so as to retain the slidable shaft 80 in position. The contacting portion between the frustal head 40 and the bell-shaped bod 50 and the contracting portion between the bell-shaped body 50 and the seat 60 are provided with sealing means 51, 52 so that the frustal head 40 can be sealingly rotated relative to the bell-shaped element 50, and likewise the bellshaped element 50 can be sealingly rotated relative to the frustal head 40 and the seat 60.In order to prevent the unbalance of pressure in the lakless interior of the frustal head 40 and the bell-shaped element 50, which would otherwise lead to the undesirable axial shift of the shaft 80, these elements 40, 50 are respectively provided with a communicating tunnel 43 and 53 to communicate with the interior of the venturi to ensure the balance of pressure. The sealing means 51, 52 are indispensible since their absence may cause sideway leaking, thus leading to undesired unbalance of the pressure between their interior and exterior regardless of the provision of tunnels 43 and 53.

The fuel spray nozzle 31 opens in the vicinity of the frustal head 40, thus by turning the frustal head 40 to change its position on the shaft 80, the effective area of the orifice of the venturi can be changed, and the feed of fuel is also changed.

The frustal head 40 is approximately in form of a paraboloid. The shape of the curve is determined by computer so as to give an optimal air/fuel ratio at any engine speed.

Claims (14)

1. A carburetor for an engine, comprising a venturi; a fuel reservoir with a float valve; a fuel feeding tube for drawing fuel from said reservoir to said venturi; characterized by that an approximately frustal body is coaxially retained in said venturi with its tapering end oriented toward the upstream of said venturi, said frustal body being movable axially in a range between two positions corresponding to the idling and maximal speed of said engine.

2. The carburetor according to claim 1, further comprising a side airpath branched from a spot upstream of the throat of said venturi to the fuel path defifned by said fuel feeding tube before the fuel path opens into said venturi.

3. The carburetor according to claim 2, further comprising automatic choke means which comprises a blocking means retained to move between a first position and a second position, said side airpath being totally unblocked by said blocking means and partially blocked thereby when the latter is respectively in its first position and second position.

4. The carburetor according to claim 1, wherein said frustal body being fastened on a shaft coaxial with said venturi, said shaft being axially movable, one end of said shaft being in mechanical connection with the accelerator for said engine, the position of said frustal body being axially adjustable relative to said shaft.

5. The carburetor according to claim 4, wherein said frustal body comprising an approximately frustal head and a bell-shaped element supported sequentially on said shaft and provided with internal thread, said shaft being provided with external thread engageable with said the internal threads of said frustal head and of said bell-shaped element.

6. The carburetor according to claim 5, wherein said frustal body is approximately in form of a paraboloid, of which the curvature is so determined that the air/fuel ration is optimized under any engigne speed of said engine.

7. The carburetor according to claim 5, wherein the rear part of said frustal head and the rear part of said bell-shaped element. are hollow, the front part of said bell-shaped element being nested in the hollow rear part of said frustal head when they are on their mounting on said shaft.

8. The carburetor according to claim 7, wherein said frustal head and said bell-shaped element are respectively provided with tunnel means, of which the two ends open respectively at their front ends and into the space formed in their hollow rear ends.

9. The carburetor according to claim 2, wherein said side airpath starts immediate upstream of the throat of said venturi and extends a length in a direction perpendicular to the bottom of said reservbir to form a first section and then turn 90 degrees and extends another length in a direction perpendicular to both the axis of said venturi and said first section to form a second section, and then turns 90 degrees and extends a further length in a direction parallel to the axis of said venturi to form a third section which communicates with said fuel feed tube.

10. The carburetor according to claims 3 and 9, wherein said blocking means is a wedge with its tapering end extends from the junction of said first and second sections of said side airpath into said second section thereof.

11. The carburetor according to claim 10, wherein said wedge is spring loaded and retained in a tunnel communicating with said second section of side airpath and the intake manifole of said engine.

12. The carburetor according to claim 11, wherein said wedge being carried on a spring-loaded sliding rod witli a sealing ring, with which said sliding rod can sealingly slide in said tunnel.

13. The carburetor according to claim 1, wherein said shaft is spring-loaded.

14. A carburetor substantially as hereinbefore described, with reference to the accompanying drawings.