US2450831A - Carburetor - Google Patents

Description

9 s. F. HUNT 2,450,831

' cmaunn'ron Filed Aug. -11, 1943 mvuma.

AGENT FIG. I

Patented 5, 1948 mm STATES.

l 'zgisasai f cmmme'roa Scott E. Hunt, Mei-iden, assignments, to Niles Conn., 'assignor, by mesn'e -Bement-Pond Company,

West Hartford, Conn., a corporation of New Jersey I Application august 11, 1943, Serial No. 498,151

- 1 The present invention relates to carburetors, and especially to mixture control systems for carburetors associated with internal combustion engines used on aircraft.

An internal combustion engine of the type used on aircraft operates most economically on a lean fuel and air mixture. However, such a lean mixture will not produce the maximum power output of which the engine is capable. Furthermor, the use of a lean mixture under certain conditions, as when operating at high altitudes, for example, will cause the engine to overheat. It is, therefore, customary to" provide, in connection with carburetors used on engines of this type, a manual control. arrangement bywhich.

, the fuel and air mixture supplied to the engine may be selectively set at either a. rich or a lean value; depending upon the various flight conditions encountered. As a further control of the fuel and air mixture supplied to the engine,

there is sometimes provided a valve which opens 1 automatically under high load conditions to enrich'the mixture, regardless of the position of the manual control. This additional valve is usually set to open at a certain value of load' on the engine, as measured by the quantity of air or by the quantity of fuel flowing to the engine. For optimum economy and performance, it would be desirable to open this valve at a higher value of engine load when the mixture control is in its lean position and at a lower value of engine load when'the, mixture control is in it rich position. In previous carburetors, however, this enrichening valve has been set to open at a predetermined value of engine load, regardless of the setting of the manual mixture control. The load value at which this valve opens is a compromise between the load value which would be best when the mixture control isin lean position and the load value'which.

A further object 'of the present invention is.

to provide, in a carburetor equipped witlra con- -trol member movable to a first position in which the carburetor supplies a lean mixture to the I 55 cation of Milton E. Chandler, Serial No. 490,281,

' engine and to a second position in which the '7 Claims. (Cl.- 261- 41) carburetor supplies a rich mixture to the engine,

improved means for enriching themixture sup-. plied to the engine in response to the variations .in the engine load, which means operate at 5v different load values depending upon the position of the mixture control member.

Other objects and advantages of the present Y invention will become apparent from a consideration of the appended specification, claims and drawing, inwhich I Figure l is a somewhat diagrammatic illu'stration of an aircraft carburetor embodying my invention, and r Figure 21s a graphical illustration of the rela-.

tionship between the fuel and air ratio and the air flow thru the carburetor of Figure ,1.

In the drawingjthere is shown, a carburetor body portion ill thru which air flows from an inlet ll thru a passage l2 to an outlet [3. In

flowing thru the passage l2, the air passes a Venturi restriction M, a throttle l5, and a fuel discharge nozzle l6. k

A second air passage connects the inlet l l and the throat of" the Venturi restriction I4. 'This 5 second air 'passage may be traced from the inlet ll thru a plurality of impact tubes I'I, whose open ends project into the inlet il, a vent ring passage l8 interconnecting the impact tubes IT, a conduit 20, an expansible chamber 2| in a 0 pressure meter 22, a restriction 23, an expansible chamber 24 in the pressure meter 22, a con-' duit 28, a chamber 30, and a conduit 3| to the throat of Venturirestriction l4. i A bellows 32 is mounted in the chamber 30,

35 and operates a valve 33 which controls the flow of air from the pas'sage 28 into the chamber 30. The bellows 32 is preferably filled with nitrogen or other inert temperature responsive fluid, so that the position of valve 33 is 40 determined by the temperature and pressure of the air in the chamber 30, and hence'by the density of that air.

- The valve 33 restricts the flow of air thru the second passage just described in such a manner that the pressure differential between chambers 2| and 24 is an accurate measure of the rate pf mass air flow thru the passage l2. Errors;,due

to changes in the density of the air with a1titude and temperature and also those errors due to the inherent limitations of a metering restriction of the Venturi t pe, are substantially eliminated by the operation of valve 33. This type of metering error compensation is more'completely described and claimed in the co-pending appli- P TENT? FFIcB 3 filed June 10, 1943, now Patent No. 2,393,144, issuedJan. 15,1946.

The fuel passing thru the carburetor comes from a fuel pump orother source Of fuel under pressure (not shown). From this source, .the fuel passes thru aconduit 34. a fuel regulator unit 25, a conduit 35, a mixture control valve 36, a jet system 31, a conduit 38, -a pressure regulator valve 48, and a conduit 4| 'to the discharge nozzle |6.--

The pressure meter 22 include a casing 42 which is separated by three flexible diaphragms 43, 44 and 45 into four expansible chambers 46, 24, 2| and 41. A sleeve 48 is attached to the central portions of the diaphragm-s 43, 44 and 45. An annular flange 58 on the interior of one end of the sleeve acts as a valve, and cooperates with a tapered seat formed on a post 52 extending thru the center of the sleeve 48.

The internal diameter of the sleeve 48 is greater than the external diameter of the post 52, so that the position of the valve 58 relative to the seat 5| controls the flow of fluid thru the sleeve 48 between the chambers 46 and 41. v

The fuel regulator unit 25 includes a housing 53 separated by a flexible diaphragm 54 into a pair of expansibie chambers 55 and 56. The diaphragm 54 supports at its central portion a valve 51. The valve 51 controls the flow of fluid between the conduit 34 and the chamber 56,

which is directly connected with conduit 35. The valve 51 is balanced against variations in inlet pressure. The position of valve 51 is determined by the difference between the pressures in the chambers 55 and 56, and by the' compression of a spring 58, which urges the valve 51 in an opening direction. The chambers 55 and 58 are connected by arestricted passage 68.

The mixture control valve 36 includes a disc valve member 6| fixed on a shaft 62 which may be rotated by means not shown, as, for example, a manual lever. The disc valve member 6| is designedto control the flow of fuel from conduit 35 thru a chamber 63 to conduits 64 and 65. When the disc valve 6| is'in the position shown in the drawing, the fuel is free to enter both conduits 54 and 65. As the shaft 62 is rotated, the disc valve 6| may be moved to another position wherein it permits the flow of fuel from chamber 63 only thru conduit 65. If desired, the disc -valve 6|. may also be designed so that in certain angular positions, it completely cuts off the flow of fuel from the conduit 35.

The jet system 31 includes a pair of jets or restrictions 66 and 61 which receive fuel thru the conduit 65, and a jet 68 which receives fuel thru the conduit 64. Fuel flowing thru the jets 61 and 68 also passes thru a jet 10 before flowing out of the jet system 31 into the conduit 38. A poppet valve 1| is positioned in the jet 61 so as to be urged toward open position by-the pressure differential which causes the fuel flow thru the jet. A spring 12 biases the poppet valve 1| .to closed position. A poppet valve 13 is positioned in the jet 88 so as to be urged in an opening direction by the pressure differential which causes the fuel flow thru that jet.

is apertured as at 15, so that even when the valve 13 is seated, a small amount of fuel may pass thru the jet 68 and the apertures 15. It will be readily apparent that a fixed restriction in parallel with the jet 58 may be used instead of the apertures 15 in the valve 13, if desired.

The pressure regulator includes a casing 16 A coil spring 14 biases the valve 13 to closed position. The poppet valve 13 4 separated by a diaphragm 11 into a pair of expansible chambers 18 and 88. The diaphragm 11 carries a valve 8| at its center. The valve-8| controls the flow of fuel from chamber 88, which is connected to conduit 88, to the outlet conduit 4|. The valve 8| is balanced against changes in outlet pressure, so that the position of valve 8|. is determined by the difference in pressures bc-, tween the chambers 18 and 88, and by the tension of the spring 82 whichbiases the valve 8| toward closed position. The chamber 18 is connected thru a conduit 82 to the vent ring l8. The pressure in chamber 18 is small as compared to the sum of that pressure and the strength of spring .82. Therefore the pressure 'in chamber 18' has only a small controlling effect on the position of valve 8|. The connection of chamber 18 thru conduit 82 to vent ring |8 serves as a vent for the chamber 18 so as to permit ready movement of the diaphragm 11 in response to variations in pressure in the chamber 88, and also to vary the pressure in chamber 18 according to changes in barometric pressure.

Operation A portion of fuel entering the fuel regulator 25 passes thru chamber 56, restriction 88, chamber 55, a conduit 83, chamber 48 of pressure meter 22, thru the center of sleeve 48, chamber 41, and a conduit 84 to chamber 88 of the pressure regulator 48. i

The quantity of fuel entering the'carburetor is measured by the jet system 31, and is controlled by varying the pressuredliferential across that system. The pressure downstream from the jet -system 31 is maintained substantially constant by the pressure regulator 48, while the pressure upstream from the jet system 31 is controlled by the fuel regulator 25. The fuel regulator 25 is in 0 turn controlled by the pressure meter 22.

The difference in pressure between chambers 2| and 24 of the pressure meter 22 is a measure of the quantity of air entering the carburetor, as previously described. This differential pressure acts on the sleeve 48 in adirection tending to move the valve 58 against the seat 5|. This pressure differential is opposed by the pressure in chamber 46, and is aided by the pressure in chamber 41. The pressure in chamber 41 is the same as that in chamber 88 of pressure regulator 48, and hence is the same as the pressure on the downstream side of the jet system 31. The pres,- sure in chamber 46, on the other hand, is the same as that in chamber'55 of 'fuel regulator 25. Since the latter chamber is connected to the upstream side of the jet system 31 thru the fixed restriction 68, it may be seen that the pressure in chamber 55 is a measure of the pressure on the upstream side of the jet system 31. Therefore, the pressure meter 22 controls the pressure in chamber 55 in accordance with the unbalance between a differential pressure indicative of the quantity of air entering the carburetor and a second differential pressure indicative of th quantity of fuel entering the carburetor. When these two differential pressures become unbalanced, the pressure meter 22 operates to vary the pressure in chamber 55 in a direction to restore the balanced condition, and at the same time varies the flow thru the fuel regulator unit 25 so as to maintain the pressure differential across the let systom 31 proportional to the quantity of air entering the carburetor.

When the mixture control valve 6| is in the position shown in the drawing both the conduits .it and 65 may receive fuel from the chamber 88.

This is the rich. position of valve 8|. When'the valve 61 is in this position. fuel may flow thru all three of the jets 8!, 6,1 and 68. The relationship between the air ilowand the fuel and air ratio 5; under these conditions is illustrated by the characteristic C in Fig. 2. At low values of air flow,

the pressure differential across thejet system 3 as controlled by fuel regulator 25, is also low. The

springs 12 and 14 are strong enough to maintain in.

their associated poppetvalvesflll and I; closed under these conditions; 4 'Iliereforethe fuel flow is determined by the cross-sectional area of jet 66 and the apertures 15 thru the poppet valve 13.

If it is now assumed that the throttle is opened 15 wider so that the air fiow increases, the pressure differential across the jets will be likewise in- I creased by the action of the fueliegulator- 25. When the air fiow exceeds a predetermined value,

' which ma be that value indicated by the ordinate 20 A in Figure'2, the pressure differential across jet 68 becomes sufilcient to overcome the spring H.

The poppet valve 13 then opens, increasing the ratio of fuel to'air' in the mixture supplied to the engine. If the air fiow continues to increase until it reaches a value such as that indicated by the ordinate B in Figure 2, the pressure differential across jet 61 becomes sufilcient to'overcome spring 12 which is stronger than spring 14,

thereby opening the poppet valve .H and further increasing the fuel to air ratio.

When the mixture control valve 6! is in its lean position-the conduit Bills closed, and the conduit 65 remains open. Under those conditions, no fuel fiows thru jet 68. v The relationship between the fuel and air ratio and the air flow then obtained is illustrated by the characteristic D in Figure 2. There it may be seen that as the air fiow increases the fuel to air ratio remains substantially constant until an air fiow indicated by the ordinate B is reached. Then the pressure differential across jet Bl opens the poppet valve ll, acting against spring I2, and increasing the fuel to air ratio.

It may therefore be seen that I haveprovided a mixture control system wherein'th fuel to air ratio is maintained at a low economical value until a very high air. flow is encountered when a manually operable mixture control is in a lean position, but that the fuel to air ratio is increased at a lower .value of air flow when the manually operable mixture control is in its rich position.

While I have shown and described a preferred 4 embodiment of my invention, other modifications thereof will occur to those skilled. in the art, and

I therefore intend that my invention shall be limited only by the appended claims.

I claim as my invention: l 1. A fuel supply system for an internal combustion engine, comprising a first main conduit for conveying combustion air t-o'said engine, a second main conduit for conveying fuel to said engine,

first and second parallel branch conduits connected in series with said second main conduit, a

mixture control valve located at a junction of said parallel branch conduits and said second main conduit, said mixture control valve being movable between a first position wherein only said first parallel branch conduit is opened to the flow of fuel and a second position wherein both 7 of said parallel branch conduits are openedto the flow of fuel, first and second fixed metering restrictions in said first and second parallel branch conduits, respectively, means responsive to the rate of fiow of air thru said first main conduit for I. 7 anneal.

regulating" the fuel pressure diflerential across said restrictions to control the rate of fiow' offuel therethru, said pressure differential regulating means, said restrictions and said mixiture control valve cooperating w en said mixture control valve is in said first p ition to maintain a first predetermined fuel-to-air ratio and when said mixture control'valve is in said second position to maintain a-second predetermined fuel-to-' air. ratio'greater than said first ratio, first and second enrichment valves connected in parallel with said first and second restrictionsrespectiVely. each said enrichment valve beingwtedupon in an opening sense by said fuel pressu differential, and first and second springs assoc ated with said first, and second en'richmentvalves, 'respec;= tively, to bias said valves toward closed position,

said first spring being stronger than said second spring, said valves and springs cooperating with, said pressure differential regulating means to in-' crease the fuel-t-o-alr ratio above said, fi rst predetermined value at a first fuel pressure differen- 'f tlal value when said mixture control valve isii-in' said first position and to increase the fuel-to-air ratio above said second predetermined value at a second lower fuel pressure differential value when said mixture control valve is in said second position. v

2. A fuel supply system for an internal combustion engine, comprising a first main co nduit for conveying combustion air to said engine .a second main conduit for conveying fuel to sd d engine. first and second parallel branch conduits connected in series with said second main conduit,-a

mixture control valve located at a junction of'said parallel branchconduits and said second main conduit, said mixture control valve being movable between a firstposit-ion wherein only said first parallel branch conduit'is opened to the flow of fuel and a second position wherein both of said parallel branch conduits are opened to the fiow of fuel, first and second fixed metering restrictions in said first and second parallel branch conduits, respectively, means responsive to the rate of flow of air thru said first main conduit for reg-v ulating the fuel pressure differential across said restrictions to control the rate of fiow of fuel therethru, said pressure differential regulating means, said restrictions and said mixture control valve cooperating-when said mixture control valve is in said firs-t position to maintain a first predetermined fuel-to-a'ir ratio and when said mixture control valve is in said second position to maintain a second predetermined fuel-to-air ratio greater than said first ratio, enrichment valve means connected in parallel with said restrictions, said enrichment valve means being acted .upon in an opening sense by said fuel pressure differential, and spring means for biasing said enrichment valve means toward closed position, and means to vary a force acting on said enrichment valve means in a valve-opening sense upon movement of said mixture control valve from said first to said second positions, said enrichment valve means and said force varying means cooperatin with said pressure differential regulating means to increase the fuel-to-air ratio above said first predetermined value at afirst fuel pressure differential value when said mixture control valve is in said first position and to increase the fuelto-air ratio above said second predetermined value at asecond lower fuel pressure differential value when said mixture control valve isin said second position. 5 a 3. A fuel supply system for an internal combustion .engine, comprising a first main conduit for c ying combustion air to said engine, second main conduit for conveying fuel to said engine, first and second parallel branch conduits connected in series with said second main conduit, a mixture control valve located at a junction of said parallel branch conduits and said second main conduit, said mixture control valve being movable between a first position wherein only said first parallel branch conduit is opened to th: flow of fuel and a second position wherein both of said parallel branch conduits are opened to the fiow of fuel, first and second fixed metering restrictions said first position to maintain a first predeter-' mined fuel-to-air ratio and when said mixture control valve is in said second position to maintafn a second predetermined fuel-to-air ratio greater than said first ratio, an enrichment valve connected in parallel with one of said restrictions, said enrichment valve being acted upon in an opening sense by the pressure drop across said econd restriction, and a spring for biasing said enrichment valve toward closed position, said onrichment valve cooperating with said pressure differential regulating means only when said mixture control valve is in "said second position to in-- crease the fuel-to-air ratio above said second predetermined value at a predetermined fuel pressure differential value.

4. A fuel supply system for an internal combustion engine, comprising a first main conduit for conveying combustion air to said engine, a second main conduit for conveying fuel to said engine, first and second parallel branch conduits connected in series with said second main conduit, a mixture control valve located at a junction of said parallel branch conduits and said second main conduit, said mixture control valve being movable between a first position wherein only said first parallel branch conduit is opened to the ilow'of fuel and a second position wherein both of said parallel branch conduits are opened to the flow of fuel, first and second fixed metering restrictions in said first and second parallel branch conduits, respectively, means responsive to the rate of flow of air thru said first main con-' duit for regulating the fuel pressure diiferential across said restrictions to control the rate of flow of fuel theretliru, said pressure differential regulating means, said restrictions and said mixture control valve cooperating when said mixture control valve is in said first position to maintain a first predetermined fuel-to-air ratio and when said mixture control valve is in said second position to maintain a second predetermined fuel-toair ratio greater than said first ratio, enrichment valve means connected in parallel with said restrictions, said enrichment valve means being movable in response to the pressure in said second branch conduitbetween said mixture control valve and said second restriction, spring means for biasing said enrichment valve means, toward closed position, said mixture control valve means being effective upon movement to said second position to vary said pressure in an enrichment valve opening sense, said enrichment valve means cooperating with said pressure difierential regulating mean to increase the fuel-to-air ratio above said first predetermined value at a first fuel pressure differential value when said mixture control valve is in said first position and to increase the fuel-'to-air ratio above said second predetermined value at a second lower fuel pressure differential value when said mixture control valve is in said second position.

5. A charge forming device for an internal combustion engine, comprising a conduit for combustion air flowing toward said engine, means for controlling the flow of air thru said conduit, a conduit for fluid fuel flowing toward said engine, means for controlling the flow of fuel thru said fuel conduit, means for coordinating the operation of said fuel fiow control means and said air fiow control means to maintain a predetermined fuel-to-air ratio, first means associated with said coordinating means for varying said ratio, an operator for said first means movable between a first position wherein said coordinating means and said ratio varying means cooperate to maintain a first predetermined ratio and a second position wherein said coordinating means and said ratio varying means cooperate to maintain a second greater ratio, and second means including a plurality of successively opening fuel valves in said first means for varying said ratio to increase :c'aid ratio above said first value when said operator is in" said first position and the rate of air fiow exceeds a first predetermined value, and to increase said ratio above said second value when said operator is in said second position and the rate of air flow exceeds a second value lower than said first value.

6. Fluid fi-ow controlling apparatus, comprising first and second parallel conduits leadingfrom a common inlet to a common outlet, first and second restrictions in said first and second conduits, respectivcly, a selector valve in series with said conduits and movable between a first position wherein flow is permitted only thru said first conduit and a second position wherein flow is permitted thru both said conduits, first and second by-pass conduits connected in parallel with said first and second restrictions, respectively, first and second pressure responsive valves in the respective bypass ccnduits, said pressure responsive valves being movable in an opening direction in response to the fluid pressure differential across said restrictions, first and second springsbiasing said first and second valves, respectively, toward closed position, said second spring being weaker than said first spring so that said second valve opens at a lower value of fluid pressure-differential than said first valve.

, 7. Fluid fiow control apparatus, comprising a main conduit, 0, pair of parallel branch conduits connecting two spaced portions of said main conduit, a selector valve at one of the junctions of said branch conduits with said main conduit, said selector valve being movable between a first position wherein only one of said branch conduits is open and a second position wherein both of said branch conduits are open, a metering restriction in each of said branch conduits, said selector valve being effective upon movement to said first and second positions to establish respectively first and second relationships between the fluid pressure differential between said portions of said main conduit and the quantity of fiuid per unit of time therethru, passage means arranged for fiow parallel to said branch conduits, valve means in said passage means subject to said fluid pressure differential, said diiierential acting on said valve means in an opening sense, springnmeans biasing said valve means to closed position, and

means including said selector valve to vary a force acting on said valve means in a valve-opening sense upon movement of said selector valve from said first to said second positions, so that said valve means commence to open when said selector valve is in said first position at a first predetermined value or said pressure differential and when said selector valve isin said second position at a second lower value or said pressure diflerential.

sco'rr I.

Romances cum The following reference: are of record in the tile of this patent:

Number Number 523395 15 cameo Automotive Industries, June 15, 1941, pages 10 mm'nn s'rarns rwmma Name Date Reeder Mar. 31, 1914 MacBryde June 15, 1920 Abernethy et a1 Nov. 9, 1926 Lister June 20, 1939 Boyce June 11, 1940 Udale Dec. 2, 1941 Mock et al Feb. 16, 1943 Mock Oct. 24, 1944 FOREIGN PATENTS Country Date Great Britain July 25, 1940 France May 15, 1935 o'rm ammnucss

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