US2509994A

US2509994A - Carburetor

Info

Publication number: US2509994A
Application number: US624177A
Authority: US
Inventors: John H Stresen-Reuter
Original assignee: Niles Bement Pond Co
Current assignee: Niles Bement Pond Co
Priority date: 1945-10-24
Filing date: 1945-10-24
Publication date: 1950-05-30
Anticipated expiration: 1967-05-30

Description

May 3U, 1950 J. H. STRESNREUTR 2,5@99994 CARBURETOR Filed OG. v 24, 1945 AGENT Patented May 30, 1950 CARBURETOR John H. Striesen-Reuter, Golf, Ill., assigner, by mesne assignments, to Niles-Bement-Pond Company, West Hartford, Conn., a corporation of New Jersey Application October 24, 1945, Serial No. 624,177 8 Claims. (Cl. 261--39) The present invention relates to carburetors for internal combustion engines, especially for carburetors for use in aircraft engines.

In carburetors for internal combustion engines, it is usual to provide some means for measuring the rate of ilow of combustion air to the engine, and to provide means responsive vto the measured rate of air now for controlling the fuel flow so as to maintain the fuel-air ratio substantially constant. It is also usual to provide either manual or automatic means, or both, for varying the fuel-air ratio within selected limits.

yThe density of the usual liquid fuel remains rsubstantially constant, but the density of the air varies with its pressure and temperature. In order to maintain aconstant fuel-air ratio, it is necessary to proportion the mass of air flowing per unit time to the mass of fuel flowing per unit time. The variations in the air density make it dicult to measure the mass of air flowing per unit time.

It may be shown, as set forth in detail in my co-pending application, Serial No. 624,179, filed October 24, 1945, that a constant fuel-to-air ratio may be obtained under varying air density conditions, if the ratio between the fuel pressure differential which measures the velocity of the fuel ow and the air pressure differential which measures the rate of air flow is made proportional to the ratio between the air pressure and the air temperature. In other words, a constant fuel-air ratio is maintained if the carburetor is constructed to operate in accordance with the following equation:

K 1li-P2 k t1 (l) where p1 represents the absolute air pressure at the Venturi inlet, p3 represents the absolute air Venturi throat, P1 represents the absolute fuel pressure on the upstream side of the metering restriction,

P2 represents absolute fuel pressure on the downstream side of the metering restriction,

t1 represents the absolute temperature of the air at the Venturi entrance, and

7c is a constant, depending on the physical characteristics of the air and fuel meters, the temperature and pressure units chosen, and the particular fuel-air ratio selected.

It is an object of the present invention to provide an improved carburetor operating in accordance with the equation set forth above.

pressure at the Another object is to provide a carburetor of the type described in which the air pressure differential produced by a venturi is balanced against the fuel pressure differential across a metering restriction, and in which the mechanical advantage of the balance mechanism is varied by means responsive to the pressure and temperature of the air in the venturi.

Other objects and advantages of my invention will become apparent from a consideration of the appended specification, claims and drawing, in which the single figure represents, somewhat diagrammatically, a carburetor for an internal combustion engine built in accordance with' the present invention.

Referring to the drawing, there is shown an air passage I0 thru which air flows from an entrance I2, past a fixed Venturi restriction I4, a throttle I6, and a fuel discharge nozzle I8 to a mixture outlet 20.

' A supercharger is commonly used between the mixture outlet 20 and the intake manifold of the engine. In some cases the supercharger is mounted ahead of the entrance I2, or two superchargers may be used, one in each location.

Fuel owing to the engine comes from a pump provided with means for maintaining a substantially constant discharge pressure and'flows thru a conduit 22, a mixture control 24, a jet system 26, an idle valve 28, a fuel regulating valve 3U, and a conduit 32 to the discharge nozzle I8.

A metering device 34 controls the fuel regulating valve 30, and thereby determines the rate of flow of fuel to the engine. The metering device 34 includes a casing 35 containing a sealed bellows 38, one end of which is attached `to-the casing 36. The interior of bellows 38 is connected thru a conduit 4I) to a series of impact tubes 42, whose open ends receive the impact of the air entering the carburetor. The interior of casing 36 is connected thru a conduit; 44 to the throat of venturi I4. Therefore, it may be seen that the pressure differential established between the entrance and throat of the venturi acts on the bellows 38 in a direction to expand it. The free end of bellows 38 carries a wear plate 46, which engages a roller 48 carried by a shaft 50 on the end of a rod 52. The rod 52 is positioned by a sealed bellows 54, which is evacuated, so that it expands and contracts in accordance with the variations in pressure inside the casing 36.

An extension of shaft 50 passes thru a slot 55 in the end of a lever 58 which is centrally pivoted at 60.

The casing 3E carries a projection 14 on which are mounted a pair of opposed aligned bellows 16 and 18. The free ends of these bellows are connected by a stem 8! having valves 82 and illl formed thereon. The interior ci bellows is is connected thru a conduit B6 to the iue'l 'line at a point downstream from the jet system. The interior of bellows '18 is connected thru a conn duit 88 to the fuel line at a point upstream on the jet system. The free end of bellows 'E8 carries a wear plate Si! which engages roller 8S.'

The bellows 38 produces a clockwise mozrne'ni'. on lever 5E. This moment is egual to the torce produced by the air pressure "derentfal acting on 'bellows 38 times -the moment farm fof thatiorca which is determined by A'the pressure the ycasing 35, acting -thru the beilcws Similarly, the 'fuel pressure differential Vacross 'the iet system produces -a counterclcckwise -AInoment on the 'lever 58. This moment is measfured by the product of iuel pressure ldliif-ern ientia'l which 'produces the torce acting `downward on 'the rol-ler 615 and the moment oi ima-'t itorcemvhich is determined by the tempera- `turev 'in the casing, acting thru the bellows '112.

The mixture control 24 includes a disc valve f 9| fixedon a rotatable shaft 82. When the'valve M is in the ifull 'iine position on the drawing, fuel may flow thru *the mixture control unit to the iet system 2t only thru a corrizluit B4. The valve il 'may be 'moved by rotation :of vshaft Si. Ito the i position shown in dotted lines iin the drawing, L

whereupon may new to the iet 28 thru lcond-uit Bil and thru another conduit 85. The 'fuli line position of disc 9| is known as its lean position and 'the dotted line position' is known as 'its rich position. The 'valve 9| may also 'be moved ito a fout-off position in which it prevents fthe 'flow :of iuel vthru either conduit t59%# Fuel entering the -iet system fthr-u the conduit "et passes thru -a jet A'or restriction 298. lvThis fuel may also pass th--ru fa kres-triction 150s controlled by a valve |02, which is biased to ielosed position by ta spring i114. Fuel entering 'the jet system thru Lconduit @E passes thru a fixed re- 'striction IUS. Fuel passing thru the restrictions lill) and W6 'passes thru vanother xed restriction Hi8.

The idle valve `28 may 4"be reciprocated by a lever "|08 connected 'by a link lH11 tto an arm iff-2 jmounted 'on the rshaft "H4 `which 'carries the throttle T6.

The fuel regulating valve 30 includes a diaphragm l |6 attached `a't aits center 'to avalve H'B .which is .balanced .against discharge pressure.

lFuel .from the jet system 26 enters a chamber above the diaphragm |.I'6 'is connected thru a .conduit |24 to the .metering device '34. A spring |26 biases 'the valve ||8 flor .movement toward closed position. 1

@perdition When the forces acting on. lever 5B 'are balanced, uel may 'flow from the 'inlet thru a conduit Y88 'to the interior of bellows "I8 Land .then

valves

82 and 84 are the same size, the pressure in chamber |22 of the fuel regulator 30 is not changed, and the fuel flow remains steady.

If the air ow now increases, which may, for example, be due to an opening movement of the throttle, then the air pressure differential at the venturi increases and, acting thru bellows 38, rotates the lever 58 clockwise. The valve stem 80 is thereby moved upwards, gradually closing the valve 82 and opening valve 84. This allows .more :duid to pass out the drain conduit |33 than is supplied by the valve S2, so that the pressure in chamber |22 is reduced, and the valve ||8 is opened wider to increase the fuel flow. As the fuel ow increases, the pressure on the downstream side of the jets decreases, and the bellows "I6 collapses partially so that the stem 80 moves back toward its original position. When it reaches a position where 'the ,system 'is again in balance a Vnew `lower Avalue of pressure `is maintained in chamber 122. The new balanced 'position of valve stem'will not be exactly the same as its `previous baianced position, but will be slightly above Iit in order that vaive 82 may be slightly more closed so as to reduce the pressure in passage 428, which iis the .same 4as `fthe pressure chamber 122.

An analogous operation takes place if the air flow decreases except that the valve stein 0 then moves downwardly-and the press-ure `in chamber |21 increases.

If the atmospheric pressure decreases, 'then a given :air pressure fdierentia'l at the venturi indicates a smaller mass .of air owing thruthe venturi than was the case when `the atmospheric pressure was higher. efect is compensated for by the beliows 54- As the atmospheric pressure decreases this bellows moves 'the roller 48 to the left thereby decreasing the moment arm of 'the *force due to the pressure '.diiflerentiaL The `'clockwise moment acting 4.on `lever 58 is thereby 'compensated for errors iin fthe 'measurement :of :the mass air flow due 'to atnros-pheric pressure variation.

if 'the spring rate of the bellows and `its internal spr-ing is constant, which may be safely assumed to be true over lthe required range of -hellows travel, then the xdistance 'through which the bellows moves iin response to a 'given change -in kthepressure ldifferential acting on it isin direct proportion tothatachan'ge mpressuredifferential. Consequently, the parts mary be so designed that the distance between pinot 60 and shaft 58 varies 'in direct proportion -to lthe atmospheric pressure.

Changes in air temperature, which likewise cause changes in the mass of air flowing `for a given value .of air pressure ldiierentia.l .are .compensated by the bellows '|2. For example, .if the .air temperature increases, .the bellows l2 .expands and increases the moment arm of .the .duel pres- .sure .differential on :the lever .58. This permits a given value ofiuel .pressure ditierential .to .balance a greater air pressure diferential .than before, so that the higher .air A.pressure differential result- ,ing trom the .increased Aair ,temperature .is there by compensated.

nFrom .the .oregoing explanationit .may be seen that an .equation 'describing .the balancing .of .the ,moments acting on lever .58 .may he written:

where "the various terms are defined asvin Equation 1.

Equation 2 may be rewritten:

which is the same as Equation 1.

It may be noted that the equations have been written as though bellows 54 responded to p1 rather than to p2. As a matter of fact, either p1 or p2 may be used to operate bellows 54. There is an advantage in the use of pz, as shown, in that it compensates for variations in the Venturi meter constant which occur with increasing air flows. The advantage gained by using the Venturi throat pressure to compensate the action of a carburetor is more completely described in the copending application of Milton E. Chandler, Serial No. 490,281, filed June 10, 1943, now Patent No. 2,393,144, issued January 15, 1946.

While I have shown a preferred embodiment of my invention other modifications thereof will readily occur to those skilled in the art and I therefore intend my invention to be limited only by the appended claims.

I claim:

1. A carburetor for an internal combustion engine, comprising an air conduit, means associated with said air conduit for producing two unequal pressures Whose difference is a measure of the velocity of flow of air therethru, a fuel conduit, a metering restriction in said fuel conduit for regulating the fuel flow in accordance with the fuel pressure differential established thereacross, means for varying said fuel pressure differential to control the fuel flow including a normally balanced lever, means responsive to the difference of said two unequal pressures for applying a first moment to said lever in one direction, means for varying the moment arm of said first moment in accordance with the atmospheric pressure only, means responsive to said fuel pressure differential for applying a, second moment to said lever acting in opposition to said first moment, and means for varying the moment arm of said second moment in accordance with the atmospheric temperature only.

2. A carburetor for an internal combustion engine, comprising an air conduit, means associated with said air conduit for producing two unequal pressures Whose difference is a measure of the velocity of flow of air therethru, a fuel conduit, a metering restriction in said fuel conduit for regulating the fuel flow in accordance with the fuel, pressure differential established thereacross, means for varying said fuel pressure differential to control the fuel flow including a normally balanced lever, means responsive to the product of the atmospheric pressure and the difference of said two unequal pressures for applying a first moment to said lever in one direction, and means, independent of said last mentioned means responsive to the product of the atmospheric temperature and said fuel pressure differential for applying a second moment to said lever acting in opposition to said rst moment.

3. A carburetor for an internal combustion engine, comprising an air conduit, means associated with said air conduit for producing two unequal pressures whose difference is a measure of the velocity of flow of air therethru, a fuel conduit, a metering restriction in said fuel conduit for regulating the fuel flow in accordance with the fuel pressure differential established thereacross, means for varying said fuel pressure differential to control the fuel flow including a normally balanced lever, means responsive to the unbalance of said lever for operating said fuel pressure differential varying means in a sense dependent upon the direction of unbalance of said lever, means responsive to the difference of said two unequal pressures for applying a first moment to said lever in a fuel flow increasing direction, means for varying the moment arm of said first moment directly in accordance with the atmospheric pressure only, means responsive to said fuel pressure differential for applying a second moment to said lever acting in opposition to said moment and means for varying the moment arm of said second moment directly in accordance Awith the atmospheric temperature only.

4. A carburetor for an internal combustion..

engine, comprising an air conduit, means associated with said air conduit for producing two unequal pressures whose difference is a measure of the velocity of flow of air therethru, a fuel conduit, a metering restriction in said fuel conduit for regulating the fuel flow in accordance with the fuel pressure differential established thereacross, valve means for varying said fuel pressure differential to control the fuel flow, means for operating said valve means including' a normally balanced lever, means responsive to the difference of said two unequal pressures for applying a first moment to said lever in one direction, means for Varying the moment arm oi' said first moment in accordance with the atmospheric pressure, means responsive to said fuel pressure differential for applying a second moment to said lever acting in opposition to said first moment, and means for varying the moment arm of said second moment in accordance with the atmospheric temperature, said two moment applying means and said two moment arm varying means cooperating to balance said lever in accordance with the equation:

p1 represents the air pressure at the Venturi inlet,

p2 represents the air pressure at the Venturi throat,

P1 represents the fuel pressure on the upstream side of the metering restriction,

P2 represents fuel pressure on the downstream side of the metering restriction,

t1 represents the temperature of the air at the Venturi entrance, andv 7c is a constant.

5. A carburetor for an internal combustion engine, comprising an air conduit, means associated with said air conduit for producing two unequal pressures whose difference is a measure of the velocity of flow of air therethru, a fuel conduit, a metering restriction in said fuel conduit for regulating the fuel fiow in accordance with the fuel pressure differential established thereacross, valve means for varying said fuel pressure differential to control the fuel flow, and mechanical means, including a fixed pivot lever operatively associated with an element responsive to atmospheric temperature and an independent element responsive to atmospheric pressure for operating said valve means in accordance with the equation:

:zu ,rennesents :the air .at vtire Venturi r2.2 represents air pressure @at :tlie Nenturi nlnroat, Pi represents the :fuel pressure .the :.unstceam sigle .of une metering restriction. Rareprese. .ts nel .pressure -on the downstream ,f side .ci .ne .metering nes:trietionJ si :represents the @temperature .of air at the entrance, and 1st-:is aconstant.

6,- .n carburetor for an internal combustion engine. y.compulsing .air conduit, -rneans associated with said air conduit for producing itu/o unequal pressures vwhose dinerenoe a :measure .ofwtne relecity of :new loi tneretnru. sepa-irate fnieans independently fresnonsive ,respectively -fto ftneateniperature anrl'nressure of :the air ente seid tir conduit. a :fuel conduit.. a metering restriction' in .said ifuel conduit :for regulating :the :fuel new accordance ..vvizth the :fuel nressure ninenential established tnereaeross. y.val-.ve :in-earns for vary-ang .saisi ffuel pressure differential fte reen.- .trol tnefuel new, .and mechanical balancing fnoeens, .comprising .a leser .-aetuateel :by renee 'ebetxveen Atl-.ie Monnet @1f-.said :fuel apr uiierential times .fthe temperature of e entering air and zthe product of .a keeristant :..tirnies saisi air nressure differential times tine pressure ci the entering .tor operating salire nica-ns `to ,varrsaici tuelfnressure differential in .fa :ni n--:.to maintain fsaiti mechanical means i.bal-ance.-

.A carburetor -for .an combustion engine. comprising an air connu-it. ineens asso- .ci ted .with sain air conduit for @reducir-.is two unequal pressures whose rdiiierence is a :measure .of the velocity new of air tneretnru. a fuel conduit, a metering restrietion said ,fuel en.- duit for regulating the fuel flow in accordance with the fuel pressure differential established thereacross, valve means .for varying said fuel pressure diierential to control the fuel flow,

means for measuring the temperature of the air l sin sain air conduit. rneans for measuring the pressure of the air in said air conduit, mechanical including .nnen pivot lever. ier balancing the product of said fuel pressure diierential and sain temperature against tneprorluet of said air pressure dinerential .and said pressure. and means responsive .to unbalanceicf'saitl mechanical means for operating .said valve means -to .vary .said .tfuel pressure difierential a direction .to rebalance said mechanicalneans.

8. A carburetor dor an internal combustion engine, comprising an air conduit, means assoelated with said air conduit for producing two unequal pressures Whose ldifference is a measure of the velocity of new .of air .tneretnra a .fuel conduit. .a metering restriction .in .said fuel conduit .for regulating the fuel flow in accordance .with :the fuel jpressure differential established thereaeross. valve means ier varying said ,fuel lpressure diferential to .control the fuel new. .a

normally .balanced .iev-er, means responsive ,to

the difference .of .said two .unequal pressures for applying a .first .montent to .said lever .in one directiongmeans ,for tarying .the .moment .arm oi said Anrst `rnoinent in .accordance Vwith .the .atmosptieric :pressureJ means responsive to said fuel nressune isiifierential for appl-ying `a .second moment to saidYleMer-,acting ,ifnpposition to .said moment. 'means ,for varying the .moinentarm .of said .second .mon-lent .in .accordance with .ine teninerature .of .the air .in .said air conduit. nulo motor jmeans for operating .said yalve means., :a source of fluid at high pressure, asource ,ci Huid at low pressure, a pilot valve for selectivelyonnectins .said sources to .said fluid v.inotor ineans. said pilot l.valve .having .a .normal .position .in .which no now takes place .between .saiol .motor means .and .either .of .said sources and ,being eiiectire upononnosite movements from sain normal position to ,connectsaid motor means .to one .or ,the other .of .said .sources depending .upon .the .direction of Isuoli increment, .and .a connection .be- .tweensaid rlever .and .said .pilot .valve for .ooerat ina saine .ir1 accordance .with the .unbalance of saidlever, .said ,uilot yalve being effective .upon unbalance .of .said lever .to cause .operation ,of .said .fluid inctornieans and said salire .means to .vary said nel .pressure .diii'erential in `a direction .to .rebalance .said .lever- .J.O.H N STRESEN-.REUTER REEERENCES oir-ED :..ne .following references are .of record .in .tbe v`iile of .this ,.natent.: