US2250932A - Fuel control - Google Patents

Description

J y 1941. MQ J. KITTLER FUEL CONTROL Filed March 3, 1939 2 Sheets-Shget l h INVENTOR.

ton JIKiZtZer ATTORNEY.

July 29, 1941.

Fig.4. Z1

Fig.2;

M. J. KITTLER 2,250,932

FUEL CONTROL File d March 3, 1959 2 Sheets-Sheet 2 vi a N Q Q Q 7 Q Q oi N s 0 Q o U 0 s :8 s Q 0 V 5 O w I I 7 a 5 a oyz'vg 3.023.212

INVENTOR.

Milton j/fz'ZZZer BY.

ATTORNEY.

L65. #2? Per 4 I Patentea July 29, 1941 ratios at various. rates:

2,250,932 UELcoN'rBoL 'I"Milton J;- Kittler; Detroit, mic'aya signoe to' I 's'eM. I I olley and EarlHolley: I 1 J .ApplicationMarch3,1939,SerialNo.259,566 w q 6'Claims (c1. 261 37) objectiof this invention to control the mixture ratio of an airplane engine of the variable Venturitypein which the fuel is'discharged into the throat of a variable venturi formed between two streamlined throttles. In a car-;- :5 buretor of, this type, asthethrottle valves. are opened,;the: depression in the venturi decreases,

whereas in the normal type of carburetor, when the. throttle-is opened tthe depression in the the pressure of the fuel-in thefuel supply cham- 7 her, so that Igcan utilize the depression. in the .15

venturilto maintain vthe mixture ratio constant when the altitude'varies and also when the load variesdueto change inqthepitch of the propel- -.ler, at any given position of the variable-Venturi throttles- ,v 'I nthedrawingsz Figural showsdiagr mmatica'lly fthe preferred arrangement of. thepar-ts; a

Figure 2 shows thegdesiredp-fuel/air' mixture u e 3 shows :a' detail, being across sectional elevation taken on planefm i E? Figure! shows'a'fcross-section taken on plane H .0f i ure'3;.-."-lt Inliigure 1;: ill -:is the)! aneroi'd bellows which is substantially exhausted of air so that it can respondto variations: of pressure if a chamber 23' whieh-isconnec'ted totan air andiu'elpassage so.

-.'(which: communicates? freely with the variable aventuri) wthrough the 'pas'sa'ge'" 54 so-as to --be "subjected to the depression=- in Lthethrat of the t venturi formed between he throttles W3 "and 44 The tnqws' rota-r 0 iibeef fi b d int alrriurle'ci W16 jufi stati n {515 c ambe -1 51 ofair flow. measured in 2 and -44 are geareds-togeth gears 45- andvli and areoperated by the" gear thus controls the. pre ure of the fuelln the fuel chamber-21. m a

The air chambers 26 and':26 are connected with each other'through a passage 28.-- The chambers are also connected withthe main air entrance '15 of the carburetor, communicating with the vent ring 90 through-a pipe 3|. The area of a restriction-1| in the pipe 3I-thus determines the depression in the chambers 25 and 26 andthus determines the fuel flow as the pressure in 25 and 26 isintermediate the pressure inthe airent-ra'nce l5 and-in the passage. 5

Fuel is supplied-to the diaphragm chamber 21 by anfuel pump TI-which supplies fuel through a ventu'ri 33 which delivers fuel to 1 the needle valves 36-and 35.. vThe fuel supplied by the fuel pump 32 is-maintained' at a substantially constant pressure by meansof :a diaphragm bellows 36, and apressure. relief valve 31.

- As the fuel :flows through thewe'nturi as" it causes a pressure drop which'reflects thequanmy of fuel taken into thedia'phragm chamber 2 1. This fuel .flow causes diiierential-pre'ssure's which operate the diaphragm '36-.1ocated in' -a chamber 18*and overcome v the a spring TI; and thus moves" a- :needle "valve 39; whichv supplies fuel under pressure 1 to rthe passage? 46 which discharges into zthe zp'assagel l which isin free communication :with that "atmosphere through 30 the opening @9 I, and .dischargesdown the. pas

sage 42 into the throatwof thevariable venturi formed between the throttles; 43 and M; Them-ain fuel needle valve is is moved tith throttle 44 by means ofthe'arm 68 anfi the'ball 36 end 69. The'leve'r {66 is 'held"in contact wlth 86, which gear is integral with the cam 66: The

in eedlsvalve 29E isprovided with'tfazcentral air 1 illassage 4'|.=.?which=-"supplies airifor-tidllhg t' the through the air entrance opening 48 wan-aren'- v nular" passage 446 'whichwcommunicatesizwith' the Lpassage 141 siwhenzthe throttlesare closer the needle valve; I 26 acts a's a tval-ve to admit ai-r: to 'thepassagei3fli' winiaddition to the /airifon :Inworder tofprovide Fat lean H I "ing, the manual; controlvalv'eii 6|: "is 'provid'edi. peratedbya 1ever- 52; ';I?his':valve cernes'iaii oilen mg 53 and: the valve iss shownin th'e lean posi v p aztionwsoathat"themort therein :is -located2:in-1 the I} o ;t h e diaghraguis I 9;; and: 3 and 7-65 1 passage communicating with: the fuel; and'i'eir er iby means-pt the the fuel in the chamber 21.

- passage 36. The application of a portion of the nozzle suction as determined by the relative size of the restricted openings 53 and 1| to theair chambers 26 and 26 through the passage 53 regulates the fuel flow in a well known manner. The pressure in the chamber 25 adjacent to the diaphragm l6 and the chamber 26 which communicates with the chamber 25, adjacent to the diaphragm 20, regulates the relative pressure of This methodof regulating the pressure in the air chambers 25 and 26 is the method that has been in use for years as the means for obtaining the lean mixture customarily used when cruising. The effect of bleeding air to the nozzle passage 36 is incidental and of no material consequence. This port communicates with the chamber 55 through the outlet 56. The chamber 55 is also connected with the passage 24 which communicates with the air chambers 25 and 26. The chamber 55 is bounded on either side with diaphragms 51 and 56 and these diaphragms .in their turn form the walls of fuel chambers 59 and 66. These two fuel chambers communicate with the entrance and the throat of the venturi 33, the chamber 56 connecting with the throat of the venturi 53 through the passage 6|, the chamber 66 communicating with the fuel entrance 63 to the venturi 33 through the passage 62.

A valve seat 66 on a bridge 61 is carried by both diaphragms 51 and 56, the bridge 51 connecting the two diaphragms 51 and 56 together and carrying the valve seat 66 which is adapted to close the passage 56 whenever the velocity of flow through the venturi 33 exceedsthe value determined by a spring 12. Any increase in fuel flow through the throat 33 of the small fuel venturi above the flow determined by the spring 12 causes the diaphragms 51 and- 56 to move over to the left and thus move the disc 66 and thus close high suction on the diaphragms l6 and 26. The actual suction is determined by the relativesize of the opening 53 and of the restriction 1| in the passage 3|. large, the mixture would be relatively rich, and

if this rectriction 1| is made very small, the mixture is relatively lean. Hence the size of the restriction 1| determines the fuel economy.

As the engine ascends into the air the bellows It opens, the valve 2| rises and gradually uncovers the slotted opening 22. The nozzle suction existing in the chamber 23 is thus transmitted to the passage 24 so that as the plane ascends into the air, the mixture does not become richer, despite the fall in density of the air. The characteristic of a variable venturi carburetor is such that the suction in the conduit 54 can never become very slight and is always at a considerable pressure below the atmospheric pressure, but of course as the atmospheric pressure falls the pressure'in 54 also fails, keeping in step with the fall of the atmospheric pressure. The pressure of the atmosphere surrounding the diaphragm |6 is therefore determined by two factors: (1) the pressure of the atmosphere; (2) the.velocity effect of the variable venturi formed between the two throttles 43 and 44. The pressure in 23 is that amount below atmospheric pressure that is determined by the air velocity which is determined by the throttle opening. The only time the suction in 54 is slight is when operating at less than of. power, when close control of the mixture ratio is unimportant. If the pitch of the propeller is reduced, so that the speed of the engine increases for a given throttle position, and the flow through the variable venturi increases to such a point that the density of the air in the throat falls appreciably, there is again an increase of suction in the nozzle passage 36, which is transmitted to the the passage 56. Thereafter, the effect of the suc- The spring 12 unseats the valve seat 66 by moving the bridge 61 to the right, and the bridge moves to the left under the influence of the fuel flow through the venturi 33. As the valve 66 seats it is held on its seat by the vacuum in the pipe 54, which vacuum prevents 'hunting of the valve 66.

- The pressure of the fuel in the chamber 21 is also partially controlled by the tension spring 16 which tends to draw the two diaphragms 26, I6

' together.

Assuming that the plane is in the air having Just left the earth and flying with the valve 5| adjusted, as shown in Figure 1, inthe cruising lean position, then as the throttles 43, 44 move to .the closed position, an increase in suction is developed in the variable venturi between the two throttles 43 and 44, and therefore in the passage 36. This high suction is reflected in the high suction created in the e 54 which communicates through therestriction 53 through the passage 56 to the chamber 55, and communicates chamber 23 and causes a-further opening of the slot 26 and thus causes a further reduction in the pressure in the chambers 25 and 26 acting on the diaphragms l6 and 26, and thus still further reduces the fuel consumption.

Thus, if the density of the air in the throat of the venturi falls either because of an increase in altitude of a decrease in pitch, the mixture remains substantially constant. As the engine approaches sixty per cent of its rated fuel supply there comes a time when there is a critical pressure diflerential between the throat of the venturi 33 and the approach to the venturi; At the time of this critical velocity, the spring 11 in the chamber "and the spring 12 in the chamber 56 yield, and in one case the needle 36 is opened to admit additional fuel to the passage 46 and at the same time. the valve 66 controlling the opening leading to 56 is closed. There is thus an abrupt increase in the mixture ratio due to the lessened effect of nomle suction from the e 36 acting on the diaphragms l6 and 26 as the suction eifect acting through the restriction 53 is eliminated, and also due to the fuel admitted by the needle valve 36.-

For all practical purposes, the manual control 53 is thereafter out of action until the throttles are once more closed and the fuel supply reduced, whereupon the mixture ratio immediately and automatically goes back to the cruising lean value determined by the relative size of the restriction 53. and the restriction 1|.

The net result of these various devices is that if the-mixture ratio, Figure 2, is at A with an air flow of twenty per cent (20%) of maximum and w the D Se .24 which impos s a elatively 7 remains at the sameflgure at thepoint B when If this restriction 1| is made verythe air flow is sixty per cent (60%) when it abruptly jumps to the mixture ratio C due to the closing of the valve seat 58 on the opening leading to the passage 56, and then as the needle 39 continues to open so as to admit more and more fuel to the passage 40, the mixture ratio is increased along the line Q D. The point B at which the mixture ratio takes the abrupt jump from B to C is sixty per cent (60%) of the maximum horsepower of the engine as air flow and horsepower are substantially equivalent to each other at this end of the horespower range.

If the valve II is moved, so as to disconnect the restriction 53 and completely block the flow through the passage M, then the mixture ratio at twenty per cent (20%) of maximum horsepower is at A andremains at this mixture ratio until the point C is reached, at which time the valve 39 opens and the mixture ratio becomes progressively richer, as shown at the rising line C-D. The valve 39 therefore is responsible for the portion of the curve C-D and the valve 66 is responsible for the portion of the curve 3-0. The fact that this mixtureratio diagram remains constant at all altitudes is due to the mechanism contained in the chamber 23. This device also is responsible for the fact that this diagram remains unchanged regardless of any change in the pitch of the propeller.

What I claim is:

1. In a carburetor having antair entrance, an air throttling means, adapted to form a variable Venturi passage, an air vented fuel nome discharging into the throat of said variable venturi, said nozzle having a restricted communication 'with the air entrance and a relatively unrestricted fuel and air outlet into the throat of said variable venturi, a fuel supply for said carburetor comprising a fuel pump adapted to supply fuel at a substantially constant pressure above the atmospheric pressure, a low pressure fuel supply chamber communicating with said pressure fuel supply, pressure reducing mechanism in said chamber, an air chamber associated with said fuel chamber adapted to control the pressure in* said fuel supply chamber, and communicating with the air entrance of the carburetor through a restriction, a second air passage connecting said air chamber with said nozzle. a variable restriction in said passage, barometric means responsive to the absolute pressure in the air vented nozzle adapted to vary said variable restriction whereby the pressure in said air chamber associated with said fuel chamber is decreased as the absolute pressure in said nozzle decreases and is increased as increases.

2. A device as set forth in claim a ,restricted passage permits additional nozzle 1 suction to be imposed on said air chamber restricted passage inoperative when the fuel flow to said fuel chamber exceeds a predetermined maximum fuel flow.

3. A device as set forth in claim 1 in which a restricted passage permits additional nozzle suction to be imposed on said air chamber throughout the cruising range, manual means for obstructing said restricted passage, a pipe connecting said passage with said. air chamber, means responsive'to the fuel flow to the fuel chamber for obstructing said pipe so as to render said restricted passage inoperative when the fuel flow to said fuel chamber exceeds a predetermined maximum fuel flow.

4. In a carburetor. having a variable Venturi mixing chamber, an air entrance leading thereto, a fuel nozzle discharging into the throat of said variable venturi and responsive to the air flow therethrough, a fuel supply chamber connected to said fuel nozzle, an air chamber associated with said fuel chamber and adapted to regulate the pressure in said fuel supply chamber, a restricted-passage connecting said air chamber with the air entrance, suction control means for I responsive to the pressure in the said second air the absolute pressure therein 1 in which throughout the cruising range, a pipe connect-- ing said passage with said air chamber, means responsive to the fuel flow from the fuel chamber for obstructing said pipe so as to render said chamber for controlling said valve means.

5. In a. carburetor having an air entrance, an air passage leading therefrom, a fuel supply chamber, a fuel nozzle connected thereto and discharging into said air passage and responsive to the air flow therethrough, an air chamber associated with said fuel supply chamber and adapted to regulate the pressure in said fuel sup ly chamber, a restricted passage connecting sai air chamber with said air entrance, a man ally operated economizer valve adapted to l pose a suction on the air chamber so as to counteract the effect of the atmospheric pressure in said air entrance, means responsive to the fuel flow into sa'id fuel chamber to render said economizer valve ineffective whenever the fuel fig; exceeds a predetermined maximum velocity 0 ow.

6. In a carburetonan air passage, a fuel supply chamber, a fuel'nozzle supplied therefrom directly responsive to the air flow through said air passage, a manually-operated device for restricting the fuel supply, means responsive to the rate of fuel flow for rendering said manually operated device suddenly ineffective whenever the fuel flow exceeds a predetermined maximum.-

' MlLTON J. KI'I'ILER.

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