US 3711069 A
The idle system has separate idle air and idle air/fuel passages. The air passage is branched from the air-borne air inlet portion of the main induction passage and its opposite end opening is straddled by the throttle valve in its idle position. A fuel and air mixing chamber is closely adjacent the idle fuel jet so as to mix the air and fuel in a short period. The fuel and air emulsion passage is of constant cross sectional area, and small and essentially of the same flow area as the orificed outlet of the mixing chamber so as not to noticeably decrease the velocity of the mixture in the emulsion passage. The velocity in the emulsion passage is high and prevents the discreet formation of plugs of fuel and air.
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Description (OCR text may contain errors)
United States Patent 1 m1 3,711,069 1 Jan. 16, 1973 Hideg et a1.
 HIGH VELOCITY CARBURETOR IDLE SYSTEM  Inventors: Laszlo I-Iideg, Dearborn Heights;- Irving N. Bishop, Farmington, both of Mich.
 Assignee: Ford Motor Company, Dearborn,
22 Filed: Aug. 15,1969
] Appl. N0.: 850,456
 US. Cl .Q. ..26l/4l D, 261/121 B  Int. C1 ..F02m 3/08  Field of Search.261/41 D, 41,42, 121 A, 121 B;
[ 56] References Cited UNITED STATES PATENTS 1,384,429 7/1921 Cole "126/41 UX 1,748,472 2/1930 Ensign ..26l/4l.4
1,781,576 11/1930 Goudard .....26l/4l.4
1,799,585 4/1931 Ensign 26l/41.4 X
1,934,130 11/1933 Kirby ..26l/41.4
2,759,716 8/1956 Jones ..26l/4l.4
2,827,269 3/1958 Kittler 261/4l.4 X
' 3,201,097 8/1965 Arndt ..261/4l.4
3,333,833 8/1967 Bimberg 26l/4l.4
1,143,986 6/1915 Muir ..26l/4l 1,259,072 3/1918 'Boverey .....26l/4l 3,554,500 l/197l I-Iideg ..26l/41 3,472,211 10/1969 Meininger ..261/41 D FOREIGN PATENTS OR APPLICATIONS OTHER PUBLICATIONS The Carburetor'l-Iandbook, Knott, 1925, Sir Isaac Pitman & Sons, Ltd. Parker Street, Kingsway WC-Z, London England, pages 10, 288, 289, and 290 relied on T] 787 K6 Primary ExaminerTim R. Miles Attorney-John R. Faulkner and Robert E. McCollum  ABSTRACT mix the air and fuel in a short period. The fuel and air emulsion passage is of constant cross sectional area, and small and essentially of the same flow area as the orificed outlet of the mixing chamber so as not to noticeably decrease the velocity of the mixture in the emulsion passage, The velocity in the emulsion passage is high and prevents the discreet formation of plugs of fuel and air.
9 Claims, 1 Drawing Figure [III I France ..26l/4l.4
HIGH VELOCITY CARBURETOR IDLE SYSTEM This invention relates, in general, to the idle system for the carburetor of an internal combustion engine. More particularly it relates to an idle system design that reduces variations in idle system fuel discharge caused by changes in ambient temperatures and inconsistent mixture formation in the idle system.
Conventional carburetor idle system designs are sensitive to ambient temperature changes because an increase in the rate of fuel vaporization in the idle bypass passage tends to decrease the idle metering vacuum signal. Consequently, the rate of fuel discharge from the idle system decreases with increasing ambient temperatures. The rate of fuel discharge also is lower with fuels having higher vapor pressure. Therefore, to avoid misfiring and engine roughness at high temperatures, generally, either the idle systems are adjusted richer than desirable under average conditions, or an additional temperature compensating device is used on the carburetor.
The conventional idle system bypass passage generally is long and of a fairly large size or diameter. Consequently, the fuel and air travel through the conventional idle system bypass passage at a relatively low velocity. Under certain conditions, an emulsion of fuel and air cannot be formed because of this low velocity. Under these conditions, a two-phase flow takes place in the form of discrete plugs of liquid fuel and air. The length of the plugs will vary randomly under certain conditions. Consequently, the fuel discharge from the idle system will fluctuate, causing a cycle-to-cycle maldistribution of fuel in the engine cylinders.
To eliminate misfiring and engine roughness, therefore, the idle systems generally are adjusted to provide the correct fuel/air ratio for the leanest cycles. As a result, the rest of the engine cycles are richer than desirable.
Carburetors could be adjusted for leaner mixtures at light loads if the temperature sensitivity and fuel discharge fluctuations of the idle system were decreased. Leaner carburetor adjustment is desirable to improve the exhaust gas composition of the engine.
Therefore, it is a primary object of the invention to provide a carburetor idle system design that obtains the above improvements by reducing the temperature sensitivity and random fluctuations of the fuel flow through the system.
It is a still further object of the invention to provide a carburetor idle system consisting of a dual passage idle bypass system with separate passages for air and for airfuel mixture; and includes a mixing chamber at the outlet of the idle fuel well with the idle adjusting needle valve at the upstream end of the emulsion passage instead of at a location near the throttle valve, as in conventional idle system constructions.
It is also an object of the invention to provide a carburetor idle system design in which the fuel and air mixture flows at a high velocity thereby reducing random fluctuations of fuel flow; also, the idle system fuel flows from the idle jet to the emulsion passage in a short period of time, thereby reduces the temperature sensitivity of the fuel and the likelihood of forming discrete plugs of fuel.
Other objects, features and advantages of the invention will become more apparent upon reference to the succeeding detailed description thereof, and to the drawing illustrating a preferred embodiment thereof; wherein the FIGURE shows a cross-sectional view of a portion of a carburetor embodying the invention.
The figure illustrates a portion 10 of a conventional down-draft type carburetor commonly used with automotive type internal combustion engines. More specifically, carburetor portion 10 includes the usual main air/fuel induction passage 12 having an air inlet 14 and an air/fuel outlet 16. The air inlet is adapted to be connected through a known type of dry element air cleaner, not shown, to a source of air essentially at atmospheric pressure. The lower end 16 is adapted to be connected to the intake manifold of the engine so as to be subjected to the changing vacuum therein upon changes in engine operation, in a known manner.
Induction passage 12 also includes the usual fixed area venturi l8 and a throttle valve 20. The latter is rotatably mounted upon a shaft 22 journaled in the side walls of the carburetor housing, and is movable between the engine idle speed position shown, essentially closing induction passage 12, and a position opening wide the induction passage.
Further details of the main air/fuel metering portion of the carburetor are not given since they are known and are believed to be unnecessary for an understanding of the invention. Suffice it to say, however, that the carburetor would include the usual main fuel discharge nozzle located generally in or adjacent to venturi 18. The latter nozzle would be subject to the change in air flow through the venturi to meter the main supply of fuel to the engine, in a known manner.
Turning now to the invention, the idle system of the carburetor includes a main air inlet 24 connected to air horn or upper air inlet section of induction passage 12. Immediately downstream of the inlet is positioned a flow restricting orifice 26 of fixed cross-sectional area that reduces the pressure and increases the velocity'of air flow therethrough in a known manner. The air passage 28 downstream of orifice 26 has a branch idle by-pass air passage 30 that is connected at its lower end to induction passage 12 at a location adjacent the idle or closed position of throttle valve 20. That is, passage 30 has an outlet consisting of two transfer holes 32 and 33 that are so located as to be traversed by the throttle plate 20 in moving from the idle position shown toward an open throttle position, in a known manner. It will be clear, of course, that it is within the scope of the invention to substitute a vertical slot for the two holes 32 and 33 shown, or to provide more or less than the two holes.
Downstream of the connection of branch 30 to air supply line 28, the latter opens into an idle air/fuel mixing chamber 34. One portion of the chamber is connected to an idle fuel well 36 open at one end to the carburetor main fuel well 38. An idle fuel jet 40 of fixed cross-sectional area is installed in the upper end of the idle fuel well closely adjacent the connection of the fuel passage to metering chamber 34.
Essentially parallel to the idle fuel well passage 36 is an idle emulsion passage 42 that is connected at its lower end to induction passage 12 at a location below the throttle valve 20. Accordingly, emulsion passage 42 will be subjected at all times to the vacuum in the intake manifold of the engine.
An idle mixture adjusting screw 44 is adjustably mounted in the carburetor body, as shown, so that the needle-like valve portion 46 thereof will project into the connecting portion between the emulsion passage 42 and mixing chamber 34. Thus, the needle valve 46 together with the walls of the emulsion passage form a variable area orifice 48, the. area being determined by the rotated position of the screw 44. in this case, the cross-sectional area or diameter of the emulsion passage 42 is essentially the same as the flow area 48 of the orifice provided by the needle valve 46 so that the increase in velocity caused by the orifice 48 will be maintained throughout the entire length of the emulsion passage for discharge in the induction passage.
Before proceeding to the operation, it is to be noted that the cross-sectional area of air bleed orifice 26 is chosen to be substantially larger than the combined total cross-sectional flow areas of the two transfer holes 32 33 in air bypass passage 30 and the flow area of the needle valve orifice 48. This is so the depression caused by the orifice 26 will be small and only slightly less than atmospheric pressure in the metering chamber 34, and considerably less than the vacuum in the intake manifold acting in emulsion passage 42. Accordingly, the increase in velocity in emulsion passage 42 as the air and fuel pass the orifice 48 isconsiderable.
In operation, therefore, in the idle position of throttle valve 20, it will be assumed that the valve initially is in a position in which the edge of the plate partially uncovers the lower transfer port 33 of air bypass passage 30. Accordingly, with the depression of the intake manifold vacuum acting on the lower port 33 and the discharge end of emulsion passage 42, air essentially at atmospheric pressure will enter the main air inlet 24 and also the upper air transfer port 32 that is now above the throttle valve. A portion of the air will flow through the passage 30 and leave the system through the lower discharge port 33. The remaining portion of air flowing through the orifice 26 will flow into the mixing chamber 34. As stated previously, with the crosssectional area of orifice 26 as stated, the pressure depression across orifice 26 will be only slight; however, it is sufficient, with the proper choice of the crosssectional area of the idle fuel jet 40, to draw the desired amount of fuel from the idle fuel well sump into mixing chamber 34.
Atmospheric pressure, of course, acts on the level of the fuel 38 in the float bowl, and since the idle fuel jet is positioned above the level of the fuel in the fuel well 36, the pressure depression in mixing chamber 34 will be sufficient to draw the desired amount of fuel in the mixing chamber pass the idle fuel jet 40, in a known manner.
Accordingly, the idle fuel and air mix in mixing chamber 34 and pass into emulsion passage 42 for discharge out into induction passage 12 below throttle valve 20. As stated previously, emulsion passage 42 is acted upon by intake manifold vacuum whereas the pressure depression in mixing chamber 34 is only slightly below atmospheric. Accordingly, the pressure drop across orifice 48 provided by the end 46 of needle valve 44 is considerable and induces a high velocity to the fuel and air passing into passage 42. Since this latter passage is essentially constant in cross-sectional area throughout its entire ,length and this cross-sectional area is only slightly larger or nearly the same as the cross-sectional area provided by the orifice 48, there will be essentially no decrease or decay in the velocity of the fuel/air as it travels through the length of the emulsion passage 42.
Because of the proximity of the idle fuel jet 40 to the discharge restriction 48, the fuel flows through the mixing chamber 34 in a very short period of time. This short residence time minimizes the vapor formation in the chamber and consequent temperature-sensitive variations of the fuel metering. In addition, there is no opportunity for the fuel and the air to form plugs in the chamber. No plugs of fuel and air can form in emulsion passage 42 because the passage diameter, as stated previously, is made relatively small and essentially the same as the flow area of orifice 48 to maintain the high flow velocity caused by the orifice. The absence of plug formation, of course, minimizes fluctuations of the fuel discharge.
During transfer operation, both orifices 32 and 33 are subjected to the manifold depression below throttle valve 20, thus increasing the vacuum signal in air passage 30 and feeding more air downwardly through said passage.
From the foregoing, therefore, it will be seen that the invention provides a high velocity idle system that minimizes the forming of discrete plugs of fuel that cause cycle-to-cycle variations in fuel flow. Also, it will be seen that the idle air and fuel are mixed in a relatively short duration of time because of the compactness or closeness of the idle fuel jet and air supply to the mixing chamber and the shortness of the mixing chamber. It will further be seen that random fluctuations of the fuel flow is minimized by separation of the idle system into dual passages, one containing air alone, while the other contains air fuel flow, this permitting a reduction in size of the passages to maintain high velocity flow therethrough.
1. An idle and part throttle fuel and air supply system for a carburetor having a main air/fuel induction passage with an air inlet at one end and its opposite end adapted to be connected to an engine intake manifold so as to be responsive to the changes in vacuum therein, and a throttle valve pivotally movable across said passage and movable between idle and wide open throttle positions essentially closing and opening wide respectively said passage to control air/fuel flow therethrough, said system comprising, an air inlet connected to the essentially atmospheric pressure airhorn portion of said carburetor and containing an orifice providing a pressure drop and air flow velocity increase thereacross, a fuel and air mixing chamber from which fuel and air are metered also connected to said air inlet closely downstream of said orifice; an idle system fuel jet connected on its upstream side to a source of fuel and on its downstream side to said mixing chamber, a
fuel/air emulsion passage of constant cross-sectional area connected at one end to said mixing chamber adjacent the airhorn section and at its other end to the induction passage downstream of said throttle valve, and adjustable needle valve means in the connection between said emulsion passage and chamber for metering flow of fuel and air therefrom and providing a second adjustable orifice of an area effecting a substantial pressure drop and high velocity increase thereacross, the downstream diameter of said emulsion passage being essentially the same as the flow area provided by said latter second orifice to minimize the decrease in flow velocity through said emulsion passage into said induction passage and thereby minimize the formation of discrete plugs of fuel therein, and an idle system air passage open at one end to said air inlet downstream of said air inlet orifice and connected at its opposite end by an opening to said induction passage at a location traversed by said throttle valve during its movements so as to vary the total flow area of said idle system as a function of the position of said throttle valve.
. 2. An idle and part throttle fuel and air supply system for a carburetor having a main air/fuel induction passage with an air inlet at one end and its opposite end adapted to be connected to an engine intake manifold so as to be responsive to the changes in vacuum therein, and a throttle valve pivotally movable across said passage and movable between idle and wide open throttle positions essentially closing and opening wide respectively said passage to control air/fuel therethrough, said system comprising, separated idle air and idle air/fuel supply lines connected in parallel circuits to a common air inlet connected to said induction passage at a location above said throttle valve with the connection of said air supply line to said inlet being upstream of that of said air/fuel line, flow restricting means in said inlet to increase the flow velocity of and decrease the pressure of air flow therethrough, means connecting the downstream flow discharge end of said air supply line to said induction passage at a location adapted to be traversed by the edge of said throttle valve during a portion of its movements to thereby vary the pressure in said supply line as a function of movement of the said valve, means connecting the discharge end of said air/fuel supply line to said induction passage below said throttle valve so as to subject said latter supply line to the changing vacuum therein, connecting means connecting a source of fuel to said air/fuel line adjacent the upstream end of said air/fuel supply line,
and a further flow restricting means in the upstream.
end of said latter line downstream of the point of connection thereto of said fuel, the cross-sectional area of said air/fuel line downstream of said latter flow restricting means being constant and essentially the same as the flow area of said flow restricting means whereby the increase in velocity of the air and fuel in said air/fuel line is maintained throughout the length of the line for minimization of random fluctuations of fuel flow and formation of discrete plugs of fuel prior to discharge into said induction passage 3. An idle fuel and air supply system as in claim 2, said further flow restricting means comprising an adjustable needle-like valve movably projecting into said air/fuel line.
4. An idle fuel and air supply system as in claim 2, wherein the cross-sectional flow area of said air inlet flow restricting means is substantially larger than the combined cross-sectional flow areas of the discharge end of said air supply line and the flow area of said further flow restricting means whereby the pressure depression thereacross is substantially lower than the intake manifold vacuum.
5. An idle air and fuel supply system as in claim 2, wherein said air inlet is connected to the air horn section ofthe carburetor, and the constant small cross-sectional area portion of said air/fuel line extends for a substantially length from a position essentially at the level of the airhorn to a point below the throttle valve.
6. An idle and part throttle fuel and air supply system for a carburetor having a main air/fuel induction passage with an air induction opening at the airhorn end and its opposite end adapted to be connected to an engine intake manifold so as to be responsive to the changes in vacuum therein, and a throttle valve pivotally movable across said passage and movable between idle and wide open throttle positions respectively closing and opening wide said passage to control air/fuel flow therethrough, said system comprising, an idle system air/fuel emulsion passage of constant crosssectional area operatively connected at its discharge end to said induction passage at a location posterior of said throttle valve so as to be subjected to changing intake manifold vacuum therein, an idle system air supply line connected at an inlet end to said induction passage at the airhorn location anterior of said throttle valve wherein the incoming air is at essentially atmospheric pressure or thereabouts, an idle system fuel supply line connected at one end to a source of fuel, a fuel and air mixing chamber having individual connections to each of said idle system air and fuel supply lines and to said emulsion passage for mixing said air and fuel prior to passage out through said emulsion passage, said air and fuel supply lines each containing a flow restricting means increasing the velocity and decreasing the pressure of the fluid flow therepast, the fuel flow restricting means being closely adjacent the connection between said fuel supply line to said mixing chamber to minimize duration of travel of fuel vapor through said chamber to said emulsion passage and thereby minimize the formation of discrete plugs of fuel in said chamber and said emulsion passage, said emulsion passage having a cross-sectional area less than that of said mixing chamber whereby flow of air and fuel there through is accelerated to provide a relatively high velocity thereto minimizing random flow of fuel and fuel vapor, said air supply line having a branch connected thereto downstream of said air supply line flow restricting means and upstream of the connection of said fuel supply line to said mixing chamber to prevent the flow of idle fuel therethrough, the opposite end of said branch line having an opening into said induction passage at a location to be transversed by the said throttle valve during its opening movements to thereby vary the inlet and outlet air flow areas of said idle system as a function of the movement of said throttle valve.
7. An idle fuel and air supply system as in claim 6, said emulsion passage at its mixing chamber end containing a flow restricting orifice having a flow area essentially the same as the cross-sectional area of said emulsion passage thereby minimizing the velocity decrease downstream of said flow restricting means due to the size of said passage.
8. An idle fuel and air supply system as in claim 6, wherein the area of the air line flow restricting means is substantially larger than the combined flow areas of the branch line opening and the emulsion passage orifice whereby the pressure depression across said air line flow restricting means is slight and substantially less than the intake manifold vacuum depression.
9. An idle fuel and air'supply system as in claim 7, wherein said emulsion passage orifice comprises an adjustable needle-like valve providing a variable area orifice.