US2812932A

US2812932A - Constant fuel-air ratio device

Info

Publication number: US2812932A
Application number: US400499A
Authority: US
Inventors: Homer M Fox
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1953-12-28
Filing date: 1953-12-28
Publication date: 1957-11-12
Anticipated expiration: 1974-11-12

Description

Nov. 12, 1957 H. M. FOX

cons'mu'r FUEL-AIR RATIO DEVICE 3 Sheets-Sheet 1 Filed D80. 28, 1953 m 2 l 0 Z Mm O MA/ I: 3%

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FIG.

INVENTOR.

7 AT TOR N EYS Nov. 12, 1957 H. M. FOX

consmw FUEL-AIR RATIO DEVICE 3 Sheets-Sheet 2 Filed Dec. 28. 1953 RESILIENT MATERIAL I I I l I I I G n0 FIG. 3

METAL ST RIPS INVEVTOR.

' H. M. FOX

ATTORNEYS Nov. 12, 1957 H. M. FOX

consmrr FUEL-AIR 1mm nsvxcza 3 Sheets-Sheet 3 Filed Dec. 28, 1953 AT TORNEYS United States Patent 2,812,932 CONSTANT FUEL-AIR RATIO DEVICE Homer M. Fox, Tuxedo, 0kla., assignor to Phillips Petroleum Company, a corporation of Delaware a device for maintaining a fuel and air mixing device. it relates to carburetors This invention relates to constant fuel-air ratio in a In one of its more specific aspects for internal combustion engines. In another of its more specific aspects, this invention relates to a variable-diameter venturi for automatically maintaining a constant ratio of mass air fiow with respect to the fuel flow. In still another of its more specific aspects, this invention relates to a means for decreasing the linear velocity of air through the venturi of a carburetor as the atmospheric pressure decreases.

Reciprocating internal combustion engines utilizing carburetor devices for forming the combustible mixture of fuel vapor and air to be burned in the cylinders of the engine are usually adjusted with particular atmospheric conditions of air density or temperature and pressure to obtain the development of maximum power and most efficient operation of the engin With changes in operating conditions of the engine, such as a change of pressure resulting from a change in altitude, the density of the air supplied to the engine is considerably different than when the fuel-air mixing devices of the engine were originally adjusted; and inefficient operation of the engine results. For example, as the altitude at which the engine is operating is increased, as in mountain driving, the density of the air decreases so that the mass air flow introduced into the engine is reduced. Since the fuel metering is usually accomplished on a volume basis, this reduction in mass air flow results in the formation of excessively rich fuel-air mixtures and a reduction in the power developed by the engine.

The present invention provides an adjustable air throat in the venturi of a carburetor and comprises means by which the linear velocity of the air to a reciprocating internal combustion engine is regulated in accordance with the pressure of the ambient air supplied to the engine. With the variable throat device of this invention, the effective area of the inlet air passage of the carburetor is varied by expanding and contracting the venturi throat of the air passage, in response to changes in atmospheric pressure, and thereby regulating the linear velocity of air to the engine. Thus, the apparatus of this invention provides improved fuel-air matching for internal combustion engines operating under variable conditions of air pressure.

Each of the following objects will be attained by at least one of the aspects of the invention.

It is an object of this invention to provide a device for maintaining a substantially constant fuel-air ratio regardless of changes in atmospheric pressure.

It is another object to provide a variable-diameter venturi for a carburetor.

It is another object to provide a variable-diameter venturi wherein the diameter is varied in response to the atmospheric pressure.

Another object is to provide an improved carburetor wherein the linear velocity of air can be maintained constant when the atmospheric pressure varies.

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It is still another object to provide a carburetor having a venturi whose throat area is controlled by a pressurescnsitive means.

Other objects and advantages will be apparent to one skilled in the art upon study of this disclosure and the accompanying drawing.

Figure 1 is a vertical sectional view of a preferred embodiment of the invention.

Figure 2 is a view along line 2-2 of Figure 1.

Figure 3 is a vertical sectional view of a modification of the venturi of this invention.

Figure 4 is a vertical sectional view cation of the venturi of this invention.

Figure 5 is a plan view of Figure 4.

Figure 6 is a schematic sectional view of a carburetor embodying a preferred form of this invention.

Referring to Figure 1, the air supply to the carburetor comprises vertical cylindrical tubular casing 10 containing an enlarged center section 11. Fuel is supplied to the carburetor from float chamber 27 by fuel line 12, the end of line 12 being located in the proximity of the vena contracta of venturi 14 and the flow of the fuel-air mixture to the manifold of the engine being regulated by throttle valve 13 located in the lower end of air-supply tube 10 and operated by lever 28.

The venturi section comprises variable venturi tube 14 anchored at its upper end to air duct 10 in truncated annular ledge 15 and rigidly attached at its lower end to end ring 16 which is movably engaged with air duct 10 through a plurality of pins 17 moving in a like number of slots 18 located in the inner wall of air tube casing 10. Slots 18 comprise a plurality of helical slots in casing 10 so that a vertical and rotating movement is imparted to the attached end of venturi 14 when ring 16 is caused to move. The variable venturi tube is constructed of corrugated metal much like a bellows of multiple convolutions wherein the convolutions are helical so that a vertical and twisting force on the movable end of the venturi tube results in a change in the effective cross-sectional area of the throat of the venturi tube. The arrangement of slots 18 in air tube casing 10 is better shown in Figure 2 which is a view of the inner surface of casing 10 taken along line 22 in Figure 1. In Figure 2, it is readily apparent that a downward force on pin 17 in slot 18 causes end ring 16 to be rotated to the right in Figure 2. Any number of pins and slots can be employed, depending on the design of the apparatus, and usually at least two such pins and slots are used.

The pressure-sensing device in the apparatus of this invention comprises an evacuated annular Sylphon bellows 19 located in annular chamber 20 formed between the outer surface of variable venturi 14 and the inner surface of section 11 of tubular air casing 10. Annular chamber 20 is in pressure communication with the atmosphere through a plurality of vents 21 so that atmospheric pressure is present in chamber 20. Bellows 19 is rigidly attached to air casing 10 at the upper end of annular chamber 20 by means of truncated annular ledge 22 so that the lower end of bellows 19 can expand or contract vertically in chamber 20. The expansion and contraction of bellows 19 is transmitted by a plurality of rigid shafts 23 attached to the lower end of bellows l9 and operatively engaged with end ring 16 in such a manner that the downward force on end ring 16 causes it to rotate through the action of pins 17 in slots 18 to expand and twist venturi tube 14 and thereby increase the effective cross-sectional area of the throat of venturi tube 14. The movable contact between the lower end of shafts 23 and end ring 16 is obtained through the use of rollers 24 attached to the ends of shafts 23 by pins 25 and arranged to roll along a circumferential path of another modifialong the surface of end ring 16. Bellows 19 is spring loaded by a compression-type spring 26 having a spring constant of such a value that the smallest elfective crosssectional area of the throat of venturi tube 14 is present with sea level pressure conditions.

The operation of my constant fuel-air ratio device, when employed in the carburetor of an internal combustion engine, is obtained in the following manner. The Sylphon bellows 19 is adjusted so that the smallest diameter of the throat of variable venturi is at sea level atmospheric pressure conditions. As the air pressure is reduced by operation of the internal combustion engine at increased altitudes, for example, the Sylphon bellows re sponds to the decreased pressure by expanding and thus imparts a vertical and rotating movement to the movable end of venturi 14. The elongation of the venturi in combination with the rotational movement which tends to straighten the helical convolutions of the venturi expands the venturi throat and permits the passage of sufficient additional air to compensate for reduction in air pressure. The process is reversed as the air pressure increases.

As the bellows expand with an increase in altitude the throat of the carburetor is enlarged, as described above, and the resulting decrease in linear air velocity aspirates less fuel, thereby preventing the usual increase in fuel-air ratio with altitude and assuring operation at fuel-air ratios closer to stoichiometric. The expansion of the carburetor throat with altitude is adjusted so that the corresponding decrease in the linear velocity of air is that required to cause a decrease in fuel flow commensurate with the decrease in mass air flow. The reduction in fuel fiow required can be obtained from the following table:

Table Altitude, Feet 1 Approximately stolehiometric.

Alt= air-fuel ratl f/A =luel-alr ratio.

Figure 3 illustrates a modification of the venturi of this invention wherein the venturi is constructed of a compressible and resilient material instead of corrugated metal. In this modification rubber, resinous material and similar materials can be used.

Figures 4 and 5 illustrate another modification of the venturi of the invention wherein the venturi is constructed of overlapping flexible metal strips maintained under compression so that the throat is expanded or contracted by varying the compression on the metal strips.

Figure 6 is a detail view of the venturi of Figure 1 as applied to a downflow type carburetor. The invention can be applied with equal advantage to an upflow type carburetor.

The invention is applicable to both automobile engines and reciprocating internal combustion engines operating in aircraft.

Although the invention has been described for use in an automotive engine, it has application in other systems where a constant fuel-air ratio is desired.

Numerous modifications of the apparatus of this invention can be devised without parting from the spirit and scope of the invention. For example, a number of small circular bellows can be used in place of annular bellows 19 for sensing the pressure changes corresponding to changes in altitude of the engine. In addition, rigid shafts 23 transmitting the movement of bellows 19 to end ring 16 can be rigidly attached to end ring 16 and the upper ends of shafts 23 in movable contact with the lower end of bellows 19 to permit end ring 16 to be rotated by the downward force exerted on it. Also, a thin tube a fuel and air throttling means can be used in place of the plurality of shafts 23 to provide a more rigid linkage between bellows 19 and end ring 16.

Other reasonable variations and modifications are possible within the scope of the disclosure of this invention, the essence of which is the provision of a constant fuel-air ratio device comprising a venturi in an air passageway which is expanded and contracted by changes in ambient air pressure.

I claim:

1. In a carburetor for an internal combustion engine comprising an air supply passage, a fuel supply inlet and a fuel and air throttling means positioned in said air supply passage, the improvement comprising a section of said air passage having an enlarged diameter, a helical corrugated venturi member positioned within said enlarged section and having its upstream end secured in sealing communication with the walls of said air passage; an annular member secured to the downstream end of said venturi in movable contact with the walls of said air passage; a plurality of helical slots in the inner wall of said air passage adjacent said annular member; a plurality of pin members positioned around the periphery of said annular member and extending into said slots; an evacuated cylindrical bellows member positioned in the annular chamber between the venturi member and the walls of the enlarged section of said air passage, having one end secured to the upstream end of said enlarged section and the other end opcratively connected to said annular member; a compression spring member positioned in said cylindrical bellows member; and means for communicating atmospheric pressure to said cylindrical bellows member.

2. In a carburetor for an internal combustion engine comprising an air supply passage, a fuel supply inlet and positioned in said air supply passage, the improvement comprising a section of said air passage having an enlarged diameter; a deformable venturi, the diameter of which is decreased by iongitudinal compression and increased by longitudinal tension, positioned within said. enlarged section and having its upstream end secured in sealing communication with the walls of said air passage; an annular member secured to the downstream end of said venturi in movable contact with the walls of said air passage; a plurality of helical slots in the inner wall of said air passage adjacent said annular member; a plurality of pin members positioned around the periphery of said annular member and extending into said slots; an evacuated cylindrical bellows member positioned in the annular chamber between the venturi member and the walls of the enlarged section of said air passage, having one end secured to the upstream end of said enlarged section and the other end operatively connected to said annular member; a compression spring member positioned in said cylindrical bellows member; and means for communicating atmospheric pressure to said cylindrical bellows member.

3. In a carburetor for an internal combustion engine comprising an air supply passage, a fuel supply inlet and a fuel and air throttling means positioned in said air supply passage, the improvement comprising a section of said air passage having an enlarged diameter, a flexible, deformable venturi constructed of flexible, coaxially disposed, overlapping metal strips, the diameter of which is decreased by longitudinal compression and is increased by longitudinal tension positioned within said enlarged section and having its upstream end secured in sealing communication with the walls of said air passage; an annular member secured to the downstream end of said venturi in movable contact with the walls of said air passage; a plurality of helical slots in the inner wall of said air passage adjacent said annular member; a plurality of pin members positioned around the periphery of said annular member and extending into said slots; an evacuated cylindrical bellows member positioned in the annular chamber between the venturi member and the walls of the enlarged section of said air passage, having one end secured to the upstream end of said enlarged section and the other end operatively connected to said annular member; a compression spring member positioned in said cylindrical bellows member; and means for cornmunicating atmospheric pressure to said cylindrical bellows member.

4. In a carburetor for an internal combustion engine comprising an air supply passage, a fuel supply inlet and a fuel and air throttling means positioned in said air supply passage, the improvement comprising a section of said air passage having an enlarged diameter, a deformable venturi constructed of rubber the diameter of which is decreased by longitudinal compression and is increased by longitudinal tension positioned within said enlarged section and having its upstream end secured in sealing communication with the walls of said air passage; an annular member secured to the downstream end of said venturi in movable contact with the walls of said air passage; a plurality of helical slots in the inner wall of said air passage adjacent said annular member; a plurality of pin members positioned around the periphery of said annular member and extending into said slots; an evacuated cylindrical bellows member positioned in the annular chamber between the venturi member and the walls of the enlarged section of said air passage, having one end secured to the upstream end of said enlarged section and the other end operatively connected to said annular member; a compression spring member positioned in said cylindrical bellows member; and means for communicating atmospheric pressure to said cylindrical bellows member.

5. In a carburetor for an internal combustion engine comprising an air supply passage, a fuel supply inlet and a fuel and air throttling means positioned in said air supply passage, the improvement comprising a section of said air passage having an enlarged diameter; a deformable venturi, the diameter of which is decreased by longitudinal compression and increased by longitudinal tension, positioned within said enlarged section and having its upstream end secured in sealing communication with the walls of said air passage; an annular member secured to the downstream end of said venturi and contacting the walls of said air passage for simultaneous longitudinal and rotational movement; an evacuated cylindrical bellows member positioned in the annular chamber between the venturi member and the walls of the enlarged section of said air passage, having one end secured to the upstream end of said enlarged section and the other end operatively connected to said annular member; a compression spring member positioned in said cylindrical bellows member; and means for communicating atmospheric pressure to said cylindrical bellows member.

6. The device of claim 5 wherein the deformable venturi is constructed of flexible, helically corrugated metal.

7. The device of claim 5 wherein the deformable venturi is constructed of flexible, axially disposed, overlapping metal strips.

8. The device of claim 5 wherein the deformable venturi is constructed of compressible, resilient material.

References Cited in the file of this patent UNITED STATES PATENTS