US 3831910 A
To provide a carburetor in which the fuel/air proportion in the mixture supplied is not materially affected by ambient atmospheric pressure, without introducing problems during engine idling due to the introduction of excessive fuel vapor into the carburetor induction passage, a valve controlled in common with the engine throttle valve which, when the said throttle valve is open connects the fuel chamber to a controlled source of suction, is moved when the throttle valve is closed to connect said fuel chamber to the ambient atmosphere.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 [111 3,831,910 Shadbolt 1 Aug. 27, 1974  CARBURETORS 2,796,243 6/1957 McDuffie 261/72 R 2,894,734 7 1959 w h... 261 D16. 67 Inventor: Francis Shadboll, Lmslade, 3,307,837 3/ 1967 W312i 26l/DIG. 67 England 3,368,326 2/1968 Hervert 26l/DlG. 67  Assigneez The Zenith Carbumter Company 3,730,157 5/1973 Gerhold 26l/DIG. 67
Limited, Stanmore, Middlesex, FOREIGN PATENTS OR APPLICATIONS England 2,034,968 6/1971 Germany 26 1/110. 67  Filed: Dec. 11, 1972 Appl. No.: 313,794
Foreign Application Priority Data Dec. 16, 1971 Great Britain 58494/71 References Cited UNITED STATES PATENTS 1/1936 Wemhoner 26l/DlG. 67 6/1951 Jorgensen 26 l /DlG. 67
Primary ExaminerTim R. Miles Attorney, Agent, or Firm-Clelle W. Upchurch  ABSTRACT To provide a carburetor in which the fuel/air propor tion in the mixture supplied is not materially affected by ambient atmospheric pressure, without introducing problems during engine idling due to the introduction of excessive fuel vapor into the carburetor induction passage, a valve controlled in common with the engine throttle valve which, when the said throttle valve is open connects the fuel chamber to a controlled source of suction, is moved when the throttle valve is closed to connect said fuel chamber to the ambient atmo sphere.
5 Claims, 2 Drawing Figures 23 24 29 2 raa 3i 47 32 28 22 l PAIENTgmuzszmm SHEET 10F-2 PATENTED 6 2 74 sum 20?? 1 CARBURETORS This invention relates to carburetors and has for its object to provide a carburetor in which the proportion of fuel to air in the mixture supplied by the carburetor is substantially unaffected by variations in the ambient atmospheric pressure both due to changes in meteorological conditions and due to changes in altitude.
It has already been proposed to provide a carburetor in which the air pressure acting on the surface of fuel in a fuel supply chamber is varied with atmospheric pressure variations to maintain substantially constant the difference between the pressure on the surface of the fuel and the pressure at a calibrated fuel orifice through which the fuel is delivered into the induction passage of the carburetor, but the previously proposed carburetor had disadvantages which are overcome by the present invention.
According to the present invention there is provided a carburetor comprising an induction passage, a throttle valve in said induction passage, a fuel supply chamber and a metering jet through which fuel from the supply chamber passes into the induction passage, and linkage for controlling the opening and closing of said throttle valve, wherein an air pressure control valve arranged to control the air pressure in said fuel supply chamber above fuel contained therein, comprises a chamber connected to said fuel supply chamber, a valve member movable between two seats in said chamber to connect said valve chamber selectively to an unrestricted vent leading to atmosphere or to both a restricted vent leading to atmosphere and through a variable flow restricting device to a source of suction, the flow restricting device being so controlled by atmospheric pressure as to provide a degree of flow restriction which decreases with decrease of atmospheric pressure and the air pressure control valve being arranged to connect the fuel supply chamber to the unrestricted vent when the throttle valve is closed and to connect it to the restricted vent and to the flow restricting device when the throttle valve is open.
The carburetor may be of the type including an air valve in the induction passage upstream of the throttle valve, which air valve is operated automatically by the depression in a mixing chamber between said air valve and said throttle valve to vary the area of a throat in said induction passage and thereby maintain said depression substantially constant, the said mixing chamber being the source of suction.
The flow restricting device may comprise an orifice controlled by a profiled needle, the said needle being connected to an aneroid capsule responsive to changes in ambient atmospheric pressure so as to be moved axially in said orifice by said changes.
The invention will now be described, by way of example, with reference to the accompanying drawings, in which,
FIG. 1 shows diagrammatically an embodiment of the invention in which the carburetor is of the constant depression type; and
FIG. 2 is a similar diagram showing an embodiment of the invention in which the carburetor is of the fixed choke type.
Referring to FIG. 1 of the drawings, the carburetor comprises the usual body, part of which is shown at 10, in which body there is formed an induction passage 11. An air valve slide 12, controlled in the usual manner by the difference in air pressures on opposite sides of a piston or diaphragm, not shown, to which the said slide is connected, co-operates with a bridge 13 in the induction passage 11 to define a variable area throat 14 into which opens a fuel supply jet 15 controlled by a profiled needle 16 carried by the air valve slide 12, the fuel supply jet 15 receiving fuel from a float chamber 17, the fuel level in which is maintained substantially constant by a float valve (not shown) admitting fuel thereto from a supply source. A throttle valve 18 is mounted in the induction passage 11 downstream of the air valve slide 13.
The space in the float chamber 17 above the normal level of fuel therein is connected by a suitable passage or conduit 19 to an air pressure control valve 21 hereinafter referred to as a vent selector valve, comprising a body 22 formed with a bore divided by two apertured partitions 23, 24 into three chambers, 25, 26 and 27 into the central one, 26, of which opens the passage or conduit 19. A valve member 28 in the chamber 26 is movable to and fro between the partitions each of which provides a valve seat capable of being engaged by the valve member to shut off the chamber 26 from the chamber 25 or 27 on the other side of that partition. The valve member 26 is carried by a stem 29 extending through the chamber 25 to the exterior of the body 22 and is acted upon by a spring 31 urging the valve member 28 towards the partition 23. The chamber 25 is connected by an unrestricted vent 32 to the atmosphere, and the chamber 27 is connected by a restricted vent 33 to the atmosphere and through a variable flow restricting device 34 to the mixing chamber constituted by the part 35 of the induction passage 11 between the air valve slide 13 and the throttle valve 18, where a substantially constant depression exists when the carburetor is in operation.
The variable flow restricting device 34 comprises a body in which are two chambers 36 and 37, connected by an orifice 38, and connected respectively to the chamber 27 of the valve 21 and to the mixing chamber 35. A profiled member 39 in the orifice 38 is movable axially therein to vary the effective area of the said orifice, being supported by a stem 41 slidable in a partition 42 separating the chamber 36 from a further chamber 43 in which is an aneroid capsule 44 to which the stem 41 is connected. The chamber 43 is connected to the ambient atmosphere.
The arrangement is such that a fall in ambient atmospheric pressure, and consequent expansion of the aneroid capsule 44 decreases the restriction of the orifice 38.
Linkage for operating the throttle valve 18 is shown diagrammatically in the form of a lever 45 and link 46, it being assumed that the link 46 is suitably coupled, when the carburetor is installed in a vehicle, to the usual throttle control pedal. Suitable means, such as a further lever 47 coupled to the link 46, act on the stem 29 of the valve member 28 in such a way that when the throttle valve is in the idling position, the spring 31 is compressed and the valve member 28 is held seated on the partition 24, thus connecting the float chamber 17 to the unrestricted vent 32, while when the throttle valve is more widely opened, the further lever 47 allows the spring 31 to move the valve member 28 to a position in which it is seated on the partition 23, shutting off the float chamber 17 from the unrestricted vent and connecting it to the restricted vent 33 and to the variable flow restricting device 34.
Thus, when the throttle valve I8 is open, the pressure acting in the float chamber 17 above the fuel, which depends on the relation between the restricted vent 33 and the variable orifice 38 through which the chamber 27 is connnected to the mixing chamber, will be reduced in relation to, but will vary with, ambient atmospheric pressure, due to the action of the aneroid capsule 44 varying the area of the said orifice 38. The conditions in the carburetor throat and consequently the rate of fuel supply through the orifice l5, tend to vary with ambient atmospheric pressure, but the variation of air pressure in the float chamber 17 can be arranged to compensate for the effect of the said conditions in the carburetor throat on the fuel supply.
When the throttle valve 18 is closed, the float chamber 17 is connected to the unrestricted vent 32, so that fuel vapor formed due to high temperature conditions which may occur during idling can escape and is not drawn into the engine to produce an excessively rich mixture, nor does it build up a vapor pressure in the float chamber sufficient to cause fuel to spill through the supply jet 15 and cause hot starting difficulty.
Although the pressure acting on the fuel in the float chamber 17 is not reduced in relation to, but varies directly with, atmospheric pressure under idling conditions, some compensation for ambient atmospheric pressure changes is retained under those conditions since the variable orifice provides a flow of air into the mixing chamber which varies with the atmospheric pressure and thus varies the flow through the carburetor throat, since the total flow is governed by the throttle valve characteristics.
Referring now to FIG. 2 of the drawings, only the carburetor shown therein differs from that shown in FIG. I, the remainder of the apparatus being identical with that shown in FIG. I and bearing the same reference numerals.
The carburetor shown in FIG. 2 is of the fixed choke type having a venturi SI in the induction passage 52 and a throttle valve 53 downstream of the venturi. A fuel chamber 54 corresponding to the fuel chamber 17 in FIG. I has a fuel passage 55 leading therefrom to the throat of the venturi 51, and the space in the said chamber 54 above the fuel therein is connected to the chamber 26 of the vent selector valve 21 as previously described. To provide a substantially constant pressure in the chamber 37 of the variable flow restricting device 34, the said chamber is connected to a source of suction, such as a suction pump 56 providing a reduced pressure at a constant value.
The vent selector valve 21 is operated by a throttle valve control linkage 46, 47 as described with reference to FIG. I. In the carburetor shown in FIG. 2, there is no compensation for ambient atmospheric pressure changes when the throttle valve is closed.
1. A carburetor comprising an induction passage, a first throttle valve in said induction passage, a fuel supply chamber, a metering jet through which fuel from the supply chamber passes into the induction passage, passage means for connection to a space in the fuel supply chamber above fuel container therein, and a source of suction, means in said passage means defining a restricted vent to a first area which is at substantially atmospheric pressure and a flow restricting device, the
passage means connecting said space in the fuel supply chamber to said area at substantially atmospheric pressure and at the same time to said source of suction through said flow restricting device, means for providing an unrestricted connection of said space to a second area at substantially atmospheric pressure separate from the restricted vent and a second valve which is associated with the first throttle valve and which is operable to open said unrestricted connection when the first throttle valve is moved to the closed position.
2. A carburetor according to claim 1, including linkage for controlling the opening and closing of the first throttle valve, wherein said second valve associated with the first throttle valve is operated by said linkage.
3. A carburetor according to claim I, wherein said second valve associated with the first throttle valve is operable to close the connection of said space to the first area at substantially atmospheric pressure through said restricted vent and to the source of suction when the first throttle valve is moved to the closed position.
4. A carburetor according to claim 1, wherein said carburetor is of the type including a third air valve in the induction passage upstream of the first throttle valve, which third air valve is operated automatically by the depression in a mixing chamber between said third air valve and said first throttle valve to vary the area of a throat in said induction passage, said mixing chamber being the source of suction.
5. A carburetor according to claim 1, wherein the flow restricting device comprises a variable orifice controlled by a profiled needle, said needle being connected to an aneroid capsule responsive to changes in ambient atmospheric pressure so as to be moved axially in said orifice by said changes.