US2396031A - Pressure carburetor - Google Patents

Description

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SQM. UDALE ETAL PRESSURE CARBURETOR Filed Nov. l, 1945 March 5, 1946.

Patented Mar. 5, 1946 2,396,031 i PRESSURE CARBURE'TOR Stanley M. Udale and Bert Beard, Detroit, Mich., asslgnors to George M. Holley and Earl Holley Application November l, 1943, Serial No. 508,573

1 Claim.

-'I'he object of this invention is to devise the simplest possible carburetor of the pressure type which will give correct metering for changes in load, altitude and temperature.

In the drawing, .I is the air entrance. is the small venturi which creates the necessary pressure difference between the entrance and the throat in response to airilow so that this double venturi acts as an air meter. I2 is the pipe connecting the throat of the small venturi II with a chamber I3, the right-handside of which is formed by a exible diaphragm |4 supported by a spring I5 which is adjusted by an adjusting screw I6. The diaphragm I4 carries a tapered needle I 1 which controls the ow of fuel from the passage I8. The ow of fuel in the passage I8 is supplied by an engine driven pump I9.- The chamber IIll communicates with the passage I8 through an elongated restricted passage 36 and the right-hand wall of this chamber IIl1 is formed by a diaphragm 34. This diaphragm is supported by a spring which controls a valve admitting fuel to the passage 2| and thus controls the pressure drop pastthe needle I1.

This diaphragm 34, when it is moved to the left by the spring 20, admits fuel into the pipe 2| by moving the Valve 35 to the left and the fuel discharges past the spring-loaded valve 22 into the inlet passage of the engine or into the center of the supercharger (not shown).

Changes in altitude and temperature are corrected by a barometric element 25 located in a chamber 26, which chamber is connected by a large passage 21 with the air entrance I0 at the downstream end of the venturi and on the engine side of the throttle 23. A relatively small pipe 28 connects chamber 26 with the throat of the venturi. A tapered valve 29 vallows air to flow from chamber 26 to the chamber I3. It will be noted that there is a restriction 31 in the pipe 28. The pipe l2 is connected to the throat of the venturi Il through the opening 38. A stop screw prevents the valve I1 from seating entirely. This prevents damage to the valve or to the valve seat and also permits a minimum quantity of fuel to ow so that the engine can idle. A throttle stop 3| prevents a throttle lever 32 from entirely closing the throttle 23. A pressure release valve 33 prevents the pressure in the chamber I3 vfrom becoming excessively high so that the pressure in passage I8 does not vary more than 3 or 4 lbs. per square inch,

In order to equalize the variation of air pressure in the air entrance, a pipe. 34 connects the right-hand side of'the diaphragm I4. This pipe 34 takes its air from theair entrance leading to the venturi Ill. As a rule, air is blown into a scoop from the propeller; alternatively, a supercharger provides the air entrance with air under pressure.

Operation Assume that the engine is in a plane ilying at low altitudes, say below 7,000 feet. The valve 29 is closed and the full depression in the'venturi acts on the diaphragm I4. The valve I1 opens and fuel flows under a pressure which may vary from 10 to 14 lbs. per square inch. The vconstruction of the diaphragm 34 and the spring' 20 limits the pressure drop at the needle |1 to the stiffness of the spring 20 which is a constant. Hence, the fact that the pump I8 and the relief valve 33 will not control the pressure anywhere near constant does not matter. At altitude, that is, say above 7,000 feet, the barometric element 25 begins to expand and admits air from chamber 26 into the chamber |3 reducing the fuel flow so as to keep the mixture ratio constant. At extreme altitudes the venturi Ill will choke the engine unless a supercharger be connected so as to force air into entrance pressure being transmitted through the pipe 34.

The pipe 28 causes a flow down the unrestricted passage 21 and yup the passage 28. The restriction 31 in the pipe 28 causes the pressure in the chamber 26 to equal the pressure downstream below the venturi I0. At air flows higher than normal, there is a tendency for the mixture ratio to become rich because the air expands and the liquid gasolinefdoes not. When the air expands due to high velocity and also expands due to high a1titude, in both events the capsule 25 expands the. valve 29 travel to the right. The travel of the valve 29 to the right bleeds air into I3 at a higher pressure than the pressure in the throat of the smaller venturi 11 transmitted through the opening 38. Hence, the valve 29 corrects for alti tude and also for load and for temperature. By the circulation oi?v air through chamber 26, the

air entrance with a chamber 35 located to the 55 element 25 is held at the temperature in I0.

2 asomar What we claim is:

A carburetor having an air entrance, a double venturi therein comprising a small venturi discharging into the throat. of a larger venturi, 'an air chamber having a passage communicating with the downstream side of said larger venturi, a source of fuel under constant pressure, a. second air chamber, a moving wall therefor, a fuel control valve connected to said moving wall, a

passage connecting said nrst air chamber to the 10

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