US3753555A - Carburetors - Google Patents

Abstract

A carburetor of the constant depression type in which liquid fuel is supplied through a fuel metering orifice into a throat defined in the induction passage by an air valve. The effective area of the fuel metering orifice is controlled by a profiled needle carried by the air valve. A transfer passage communicates through a port at one end with the induction passage downstream of the throttle valve when the throttle valve is closed, and, at the other end, with the fuel supply passage between the orifice and the throat through a cavity and a restricted passage. Thus some of the fuel passing through the orifice is passed into the induction passage downstream of the throttle valve when the latter is closed. Air can be drawn from upstream of the throat and mixed with the fuel in the fuel metering orifice to produce an air/fuel emulsion. Air can be fed from a point in the induction passage upstream of the throat and fed to the transfer passage, and valve means may be provided to enable adjustment of the rate of flow of such air fed to the transfer passage.

Description

United States Patent 11 1 Lawrence 1 Aug. 21, 1973 CARBURETORS Prima Examiner-Tim R. Miles [75] Inventor: Geoffrey Lloyd Lawrence Middlesex, Stanmore England AttorneyStevens, Davis, Mlller & Mosher [73] Assignee: The Zenith Carburetter Company 57 ABSTRACT Limited, Middlesex, England [22] Filed: June 4, 1971 A carburetor of the constant depression type in which liquid fuel is supplied through a fuel metering orifice into a throat defined in the induction passage by an air valve. The effective App]. No.: 150,096

"I Foreign Application Priority Data area of the fuel metering orifice is controlled by a 16116 8, 1970 Great Britain 27,627/70 Profiled needle carried y the air valvo- A transfer passage communicates through a port at one end US. Cl. 261/4411, 261/121 B with the induction Passage downstream of the Int. Cl. F02m 19/06 throttle valve when the throttle Valve is closed Field of Search 261/44 R, 121 B and, at the other end, with the fuel p y Passage between the orifice and the throat through a cavity 5 References Cited and a restricted passage. Thus some of the fuel UNITED STATES PATENTS passing through the orifice is passed into the induction passage downstream of the throttle valve :33; i ;2 when the latter is closed. Air can be drawn from 3:278:17l 10/1966 causal 1 3. 2 61/5O A upstream and m'xed the fuel 3,295,839 l/l967 Mitchel1.... 261/56 the fuel metering Orifice Pmduce air/fuel 3,342,463 9/1967 p et 3] 261/441; emulsion. Air can be fed from a point in the 3,409,277 11/1968 Reise 261/51 induction Passage upstream of the throat and fed 3,425,672 2/1969 Seigel et a1.... 261/121 B to the transfer passage, and valve means may be 3,454,264 7/1969 Sarto 261/41 D provided to enable adjustment of the rate of flow FOREIGN PATENTS OR APPLICATIONS Of such air fed E0 the transfer passage. 119,187 9/1918 Great Britain 261/44 R 6 Claims, 2 Drawing Figures Patented Aug. 21, 1973 3,753,555

2 Shoots-Sheet l lllll Patented Aug. 21, 1973 2 Shoots-Sheet 2 CARBURETORS This invention relates to carburetors of the constant depression type, which carburetors are provided, in the induction passage thereof, with a throttle valve to control the admission of fuel/air mixture to the cylinders of an internal combustion engine to which the carburetor is connected, and, upstream of the throttle valve, with an air valve operated automatically in accordance with the depression existing in the chamber defined by the part of the induction passage between the throttle valve and the air valve (hereinafter called the mixing chamber) so as to control the flow of air, into the said mixing chamber and maintain a substantially constant depression therein.

In such carburetors, liquid fuel is supplied through a fuel metering orifice into the induction passage at a position where the effective area of the said passage is controlled by the air valve to define a throat in the said induction passage, and thus varies with the degree of opening of the latter, the effective area of the fuel metering orifice being controlled by a profiled needle which is moved with the opening of the air valve to increase the effective area of the said orifice. Carburetors having the features set out in the two preceding paragraphs are hereinafter termed carburetors of the kind referred to."

It has been found that, in internal combustion engines using carburetors of this type, idling is not always satisfactory, and it is the object of the present invention to provide a carburetor of the constant depression type in which more satisfactory idling can be obtained.

According to the invention there is provided a carburetor of the kind referred to, wherein provision is made for causing a part of the total fuel flow passing through the fuel metering orifice to pass, when the throttle valve is closed or substantially closed, into the induction passage downstream of the throttle valve.

Preferably, the fuel metering orifice is provided by a restricted portion of a fuel supply passage leading from a fuel storage chamber to the throat in the induction passage which restricted portion is connected to the said throat through a portion of the fuel supply passage of larger diameter than the said fuel metering orifice.

A fuel transfer passage may be provided which extends from said portion of the fuel supply passage connecting the fuel metering orifice to the throat to a position in the induction passage downstream of the throttle valve.

Means may be provided for mixing fuel passing through the fuel metering orifice, in the said orifice, with air, so that an emulsion of fuel and air is supplied both to the throat and to the induction passage downstream of the throttle valve.

There will now be described, by way of example and with reference to the accompanying drawings, two embodiments of carburetors of the constant depression type embodying the present invention.

In the drawings FIG. 1 is a partial longitudinal section of one form of carburetor embodying the invention; and

FIG. 2 is a partial longitudinal section similar to FIG.

-I but showing a modification in which provision is made for admitting extra air to the fuel transfer passage through an adjustable flow restricting unit. For convenience of drawing, the adjustable flow restricting unit has been shown in the plane of the section, and the float chamber has been omitted, but it will be understood that the said flow restricting unit would in fact be positioned so as to be clear of the float chamber.

Referring to FIG. 1, the carburetor comprises the usual body, part of which is shown at 10, having an induction passage 11 extending through it. A bridge member 12 formed in the induction passage 1] has a flat surface 13, chordal to the axis of the passage 11, co-operating with a flat end surface 14 of an air valve slide member 15 movable across the passage 11 in a direction normal to the flat surface 14 to vary the area of a throat l6 defined between said bridge member and said slide member.

A butterfly throttle valve 17 is provided in the induction passage 11 downstream of the air valve slide 15, and the position of the air valve slide 15 is controlled, in the known manner, by the depression in the mixing chamber 18 defined by the part of the induction passage between the said air valve slide 15 and the throttle valve 17.

Fuel is supplied to the induction passage 11 of the carburetor, from a fuel supply chamber, partly shown at 19, in which the fuel level is controlled by the usual float (not shown), through a jet 21 mounted in a bore in the carburetor body 10 opening into the flat surface 13 of the bridge 12, the jet 21 having a bore portion of reduced diameter at 22 which constitutes the fuel metering orifice. The said metering orifice 22 is spaced from the upper end of the jet 21 by a bore portion 23 of larger diameter. A profiled needle 24 carried by the air valve slide 15 extends through the metering orifice 22 so that the effective area of the said orifice varies with the position of the air valve slide.

A flat formed on the exterior of the jet 2] as its upper end defines, between itself and the wall of the bore in the body, a cavity 25 connected by a radial passage 26 in the jet to the bore portion 23 above the metering orifice 22, and a transfer passage 27, formed in the carburetor body 10, connects the said cavity 25 to a port 28 opening into the induction passage 11 at a position such that it is downstream of, but close to, the edge of the throttle valve 17 when the throttle valve is closed, the said throttle valve edge passing across the port 28 during a very small angle of movement from its closed position.

Thus, when the throttle valve is closed, or nearly closed there is a high degree of suction acting on the port 28 and some of the metered fuel passes directly to the induction passage 11 downstream of the throttle valve 17, being sucked from the larger diameter bore portion 23 of the jet 21 through the radial passage 26, the cavity 25 and the transfer passage 27, the remainder of the metered fuel passing into the throat 16 in the usual manner. Due to provision of the cavity 25, the degree of suction applied to the radial passage 26 is less than that acting on the port 28 and is dependent upon the volume of the cavity 25, the greater the volume of the cavity 25 the greater the difference between the degree of suction acting at the port 28 and the degree of suction applied to the radial passage 26. Thus the cavity 25 provides a tuning feature. When the throttle valve has opened beyond a certain position, the suction acting on the port 28 is no greater than that acting in the throat l6 and substantially the whole of the metered fuel passes to the throat, the total supply of fuel at all times being determined by the effective area of the jet orifice. When the throttle valve is closed again,

fuel is drawn initially from the cavity 25 and fed through the transfer passage 27 to the port 28, such initial fluid flow being fed from within the cavity 25 at the instant of throttle valve closure, or being fuel drawn into the cavity 25 from the bridge face 13 into which the cavity 25 opens. Thus the flow of fuel through the transfer passage 27 is initiated more quickly than would be so if the transfer passage 27 communicated with the larger diameter bore portion 23 of the jet 21 solely through the restricted radial passage 26.

A valve (not shown) may be provided in the passage leading from the lateral orifice in the jet to the ports opening into the induction passage, to control the flow of fuel in the said passage.

Air is supplied to the fuel metering orifice 22 through an air passage 29 opening laterally into the said orifice 22 and receiving air from the induction passage 11 upstream of the air valve slide 15, so that an air/fuel emul sion is formed in the jet 21, and it is this air/fuel emulsion which is supplied to the induction passage 11 downstream of the throttle valve 17. The air passage 29 preferably leads downwardly to its connection with the fuel jet, to reduce the risk of fuel being deposited in the said passage which could prevent the emulsion air bleed from working.

The provision of an air supply to the fuel metering jet as above described is more fully described and is claimed in our co-pending Application No. 55836.

In the embodiment of the invention shown in FIG. 2 of the drawings, provision is made for supplying extra air to the transfer passage to mix with the fuel or fuellair emulsion passing through that passage. In my earlier filed United States patent application Ser. No. 127,206, filed Mar. 23, 1971 (executed March 15, i971), also entitled IMPROVEMEIXIS IN OR RE- IJATING TO CARBURETORS, I have described and claimed a carburetor of the kind to which the present invention relates, wherein a further passage provided for supplying air directly to the induction passage at a position downstream of the throttle valve, when the said throttle valve is in the idling position, is so controlled by operation of the throttle valve that the supply of air through said further passage to the induction passage downstream of the throttle valve ceases when the said throttle valve has in the arrangement shown in FIG. 2 of the accompa nying drawings, in which parts corresponding to those shown in FIG. I, bear the same reference numerals, a further passage as described in my said earlier filed application is provided by the part of the transfer passage 27 adjacent the port 28, and an air supply passage connected into the said transfer passage.

The said air supply passage comprises a part 31 leading from the induction passage 11 upstream of the air valve slide to an adjustable flow restricting unit 32, and a part 33 leading from the said unit 32 into the transfer passage 27, the said unit 32, although shown in the section plane in FIG. 2, being in practice, arranged in some other position around the axis of the induction passage so as to be clear of the float chamber, which is not shown in FIG. 2.

The flow restricting unit 32 has formed in it a first passage 34 connecting with the air supply. passage part 31, a second passage 35, parallel to the passage 34 and closed at one end, a third passage 36 connecting the other end of the passage 35 to the passage 34, and a fourth passage 37 connecting the passages 34 and 35 which is connected intermediate its ends, by a fifth passage 38, to air supply passage part 33.

A screw plug 39 mounted in a screw-threaded bore aligned with the passage 36 has a tapered end 41 seating in the passage 36 and is formed with intersecting bores 42, 43 providing a fixed flow restriction between the passages 34 and 35, and a second screw plug 44, mounted in a screw-threaded bore 45 aligned with the passage 37, has tapered portions 46 and 47 cooperating respectively with the parts of the passage 37 on opposite sides of the passage 38 to provide an ad justable restriction of flow between the passages 34, 35 and the passage 38. Thus the actual rate of flow of air through the passage 31,33 is determined by the area of the bores 42, 43 in the plug 39, and the position of each of the tapered portions 46 and 47 relative to the respective parts of the passage 37 with which they co-operate. The rate of flow of air can be varied by movement of the screw plug 44 in or out to alter the position of the tapered portions 46 and 47 relative to the respective parts of the passage 37 with which they co-operate. The degree of control of the actual rate of flow of air through the passage 31, 33 which can be achieved by movement of the screw plug 39 is related to the position of the screw plug 44, and the extent by which movement of the screw plug 39 can effect the rate of flow of air for a particular position of the screw plug 44 is limited to a minimum value by the area of the bores 42 and 43, and to a maximum value by the position of the tapered portion 47 relative to the respective part of the passage 38 with which it co-operates.

It has been found that the provision of the transfer passage 27 has additional advantages in that, by reason of its connection to the induction passage 11 downstream of the throttle valve, a higher suction is applied to the air/fuel emulsion supply system than would 0therwise be the case. This higher suction has been found to exercise a stabilizing influence on the action of the air/fuel emulsion supply system particularly in regard to the initiation of air flow to the fuel jet.

I claim:

1. A carburetor of the constant depression type comprising:

a. a body having an induction passage which extends therethrough;

b. a throttle valve connected within the induction passage;

c. an air valve in the induction passage upstream of said throttle valve, said air valve defining a throat area within the induction passage, said body also having an opening into the throat area;

d. a fuel supply jet, located in the opening, having a fuel metering orifice wherein fuel is fed to said orifice, said fuel supply jet also including a bore, having a larger diameter than said orifice, through which fuel flows from said orifice to said throat;

. first means for supplying air to said fuel metering orifice to form an emulsion of air and fuel in said orifice; and

f. a fuel transfer passage having one end open to said bore and the other end open to said induction passage downstream of said throttle valve, whereby when said throttle valve is substantially closed part of the fuel-air mixture will be supplied to said throat and part will be supplied through said fuel transfer passage downstream of said throttle valve.

5. The carburetor according to claim 1 wherein said one end of said fuel transfer passage has a cavity open to said throat and a radial passage extending from said cavity and open to said bore whereby said fuel supply passage receives a fuel-air mixture from said throat and from said fuel supply jet.

6. The carburetor of claim 1 wherein said first air supply means comprises an air supply passage which slopes downward to said orifice.

Claims (6)

1. A carburetor of the constant depression type comprising: a. a body having an induction passage which extends therethrough; b. a throttle valve connected within the induction passage; c. an air valve in the induction passage upstream of said throttle valve, said air valve defining a throat area within the induction passage, said body also having an opening into the throat area; d. a fuel supply jet, located in the opening, having a fuel metering orifice wherein fuel is fed to said orifice, said fuel supply jet also including a bore, having a larger diameter than said orifice, through which fuel flows from said orifice to said throat; e. first means for supplying air to said fuel metering orifice to form an emulsion of air and fuel in said orifice; and f. a fuel transfer passage having one end open to said bore and the other end open to said induction passage downstream of said throttle valve, whereby when said throttle valve is substantially closed part of the fuel-air mixture will be supplied to said throat and part will be supplied through said fuel transfer passage downstream of said throttle valve.

2. The carburetor according to claim 1 further comprising second means incuding an air supply passage for supplying extra air to the fuel flowing from said fuel metering orifice and entering the induction passage downstream of said throttle valve.

3. The carburetor according to claim 2 wherein said extra air supply passage is connected to said fuel transfer passage.

4. The carburetor according to claim 2 wherein said extRa air passage includes an adjustable flow restricting unit for controlling the flow of extra air.

5. The carburetor according to claim 1 wherein said one end of said fuel transfer passage has a cavity open to said throat and a radial passage extending from said cavity and open to said bore whereby said fuel supply passage receives a fuel-air mixture from said throat and from said fuel supply jet.

6. The carburetor of claim 1 wherein said first air supply means comprises an air supply passage which slopes downward to said orifice.

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