US2009412A - Carburetor - Google Patents

Description

Patented July 30, 1935 UNITED STATES PATENT OFFICE GARBURETOR.

Augustin M. Prentiss, San Antonio, Tex. Application January 25, 1932, Serial No. 588,755 23 Claims. (Cl. iii-219) This invention pertains to carburetors and more particularly has reference to compensating carburetors of the pressure feed type wherein the liquid fuel and a portion of the air are fed into the mixing chamber of the carburetor under a super-atmospheric pressure and the flow of liquid fuel is regulated so as to always hear a desired ratio to the flow of air. a

The invention herein disclosed is an improvement upon the invention described in my United States Patent No. 1,329,309, issued January 2'7, 1920.

In this patent I discussed the limitations and deficiencies of suction operated carburetors as' a class and pointed out the impossibility of maintaining a desired ratiobetween the flows of liquid fuel and air under all operating conditions because of the "inherent differences in the laws of flow of liquids and gases. My solution of this problem in the patent cited was to place the liquid fuel under a variable superatmospheric air pressure which was at a minimum (atmospheric) when the vacuum in the mixing chamber was a maximum, and which gradually increased at a predetermined rate as the vacuum in the mixing chamber diminished until it reached a maxi' mum value whenthe vacuum in the mixing chamber was at a minimum.

While that carburetor gave greatly improved operation over the prior art suction operated devices, it was attended with certain practical difficulties in manufacture and adjustment which I have overcome by the greatly simplified construction herein disclosed.

This invention has for its objects:

First; to provide an improved carburetor of this type wherein the liquid fuel is fed into the mixing chamber by positive pressure, that is, a superatmospheric air pressure.

Second; to provide a device wherein the pressure controlling the 'liquid feed varies with the demands of the engine.

Third; to provide an improved apparatus. of this kind wherein the pressure on the liquid fuel is a minimum when the engine is at rest and is gradually increased as the speed of the engine increases until it reaches a maximum value when the engine is operating at highest rated speed.

Fourth; to provide a carburetor wherein the pressure on the liquid fuel varies in general dishowing the operating connections between the rectly with the vacuum in the mixing chamber of the carburetor.

Fifth; to provide a device wherein the ratio of liquid fuel to air is constantly maintained at a predetermined value throughout all changes 5 of operating conditions of the engine, by subjecting the liquid fuel to such a pressure as will make it follow the law of adiabatic gas flow.

Sixth; to provide an improved apparatus of.

this nature having means for supplying air ,un-

der superatmospheric pressure to break up the liquid fuel within the fuel nozzle before it issues therefrom and thus secure a high degree of atomization of the liquid fuel regardless of variations in its specific gravity.

With these and other objects in view which may be incident to my improvements, my invention consists in the combination and arrangement of elements hereinafter described and illustrated in the acompanying drawing in which:

Figure 1 is a central longitudinal section of a carburetor constructed in accordance with the present invention;

Figure 2 is an elevation largely diagrammatic carburetor, air pump and main fuel supply tank;

Figure 3 is an elevation,-on a slightly enlarged scale, of the stem of the liquid fuel pressure valve.

This invention broadly comprehends means for applying a superatmospheric air pressure upon the liquid fuel in the float reservoir of the carburetor whereby the liquid fuel is caused to be fed into the mixing chamber in accordance with the law of adiabatic gas flow by a positive pressure which varies with the demands of the engine, the pressure being continuous and at a minimlun when the engine is at rest and gradually increasing as the speed of the engine increases. The reasons for applying this positive (superatmospheric) pressure were fully explained in my patent cited above and are controlling in this invention also.

Unless specially controlled and regulated to the contrary, the flow of liquid fuel through a carburetor follows the general law of liquid flow and the flow of air follows the law of adiabatic gas flow. As to the air flow, it islogical to assume that the expansion of a gas approaching an orifice, being rapid, is adiabatic, and the authori- 5g ties generally agree that the flow of air through a carburetor is, for all practical purposes, sensibly adiabatic. The observed data support this view. The general formula for liquid flow and adiabatic gas flow respectively as applied to a carburetor, may be expressed as follows:

G1 is the rate of liquid flow in pounds per second.

G2 is the rate of air flow in pounds per second.

1 is the coefficient of efliux for liquid flow.

m is the coefficient of efliux for adiabatic gas flow.

F1 is the cross-sectional area of the liquid fuel passageway of the carburetorgenerally the area of the metering restriction in the fuel passageway.

F2 is the cross-sectional area of the main air passageway of the carburetor in the zone of the fuel jet orifice--generally the area of the smallest section of the Venturi throat.

71 is the unit weight of the liquid fuel, in pounds per cubic foot at 32 F. temperature.

72 is the unit weight of the air in pounds per cubic foot at normal atmospheric pressure of 32 F.

g is the acceleration of gravity.

Pn is the superior pressure causing the fluid flow, which in suction-operated carburetors, is the atmospheric pressure outside the carburetor.

Pm is the absolute pressure in the mixing chamber of the carburetor in the zone of the fuel jet orifice.

The foregoing nomenclature and formulas are, in accordance with Churchs Mechanics of Engl neering Part IV, Chapter VIII on "Kinetics of Gaseous Fluids.

For convenience of reference in this specification, I shall follow Church's terminology and refer-to the formula for liquid flow (Formula 1) above) as the water formula and the formula for air flow, Formula 2) above, as the adiabatic formula It will also be understood that where I refer, in this specification, to the fuel supply to the mixing chamber of the carburetor as being fed into said chamber in accordance with the law of air flow, I mean in accordance with the Formula (2) above. That is to say, the total weight of liquid fuel passing into the mixing chamber, per unit of time, for any given pressure (vacuum) in said chamber, is that found from the Formula (2) above for Pm equal to the pressure (vacuum) in said chamber, and not from Formula (1) above which normally governs the flow of liquid fuel through a carburetor.

It will be further understood that where I refer, in this specification, to the air supply to the mixing chamber being fed into the mixing chamber in accordance with the normal law of air flow, I mean in accordance with the adiabatic gas formula (Formula (2) above) and where I use the term normal operating conditions I mean conditions of steady flow through the carburetor which excludes momentary fluctuations due to sudden changes in throttle opening.

In the drawing, I have illustrated a preferred embodiment of the invention and the particular construction shown comprises a casing or body I, having a main air inlet 2, Venturi throat 3,

mixing chamber 4 and mixture outlet 5 controlled by a butterfly throttle valve 6, all arranged as in a conventional plain tube suction operated carburetor. The term mixing chamber, as used in this application, designates that part of the main passageway thru the carburetor which lies between the Venturi throat 3 and the throttle valve 6.

Integral with the bottom wall of air intake 2 is a main nozzle 1 which consists of an outer liquid fuel tube 8 and a concentric inner compressed air tube 9, both tubes rising to a point slightly above the center of Venturi throat 3 and surmounted by a cap I0 screw threaded on tube 8 and containing a central aperture Illa through which the main jets of liquid fuel and compressed air are discharged into the mixing chamber 4.

Tube 8 is connected by a passageway I I and port I2 with a liquid fuel reservoir I3 which receives liquid fuel through an inlet I 4 controlled by a valve I5 which is actuated by a float I6 so as to always maintain a constant liquid fuel level, XX, in said reservoir. Port I2 is controlled by a manually adjustable needle valve I7 which regulates the normal flow of liquid fuel. Two idle feed ports I8 and and I9 bestride the throttle 6 (when in closed position) and are connected by a passageway 20 and metering restriction. 2| with tube 8 of nozzle 1, as clearly shown in Figure 1.

Air tube 9 of nozzle 7 is connected through a passageway 22 and pipe 23 (Figure 2) to a compressed air pump 24 which is connected to the engine (to which the carburetor is attached) by a plurality of gears 25, so that whenever the engine is running, pump 24 supplies compressed air through nozzle 7 to mixing chamber 4 of the carburetor. Moreover, pump 24 being constantly geared to the engine runs at a constant speed ratio with respect to the engine, so that as the speed of the engine increases, the speed of the pump 24 increases in direct ratio, and also the amount of air delivered by the pump similarly increases in direct proportion.

Pump 24 consists essentially of a cylinder 26 open at the top and closed at the bottom by a wall 21 having a central aperture 28 which is bevelled and serves as a seat for a poppet valve 29. Valve 29 is normally held to its seatby a helical spring 30 which is seated in a cylindrical chamber 3I immediately below cylinder 36, as shown in Figure 2.

Adapted to reciprocate in cylinder 26 is a piston 32 which is connected by a link-33 to one of the gears 25. Cylinder 26 is also provided with a plurality of ports 34 in its side walls which are adapted to be cleared by piston 32 at the top of its stroke. Since valve 29 always closes when piston 32 starts on its up-stroke, a partial vacuum is produced in cylinder 26 as piston 32 ascends, and when piston 32 clears ports 34, atmospheric air enters and fills cylinder 26. This air is then compressed by piston 32 on its next down-stroke until the pressure of this air is sufiicient to unseat valve 29 whereupon valve 29 opens port 28 and the compressed air in cylinder 26 is discharged into chamber 3I. As it requires only a moderate super-atmospheric air pressure to completely atomize liquid fuel with the form of atomizing nozzle shown in Figure 1, pump 24 is designed to deliver compressed air at a pressure between two and three pounds per square inch, gauge.

Connected to chamber 3i are pipes: one, 23,

two discharge leading to the carburetor, as deervoir I3.

scribed above, and the other, 10, leading to a main fuel supply tank 1| Inserted in air line 10, near pump 24 is an adjustable check valve 12 which prevents the return of compressed air from tank 1| to pump 24 when the latter is at rest. Valve 12 also prevents air below a certain predetermined pressure escaping to tank 1 I, so that when pump 24 first commences to deliver compressed air, as when the engine is turned over with the starter, all the air from pump 24 escapes through pipe 23 to the carburetor. In this way, suificient air is delivered by pump 24 to operate the atomizing nozzle I and start the engine. The pressure at which check valve 12 opens is determined by the pressure exerted by its spring 35, the tension of which is regulated by an adjustable nut 36.

Chamber 3| is also provided with an overflow relief valve 31 which is normally held to its seat by a helical spring, the tension of which is regulated by a screw 38 threaded in a yoke 39 depending from chamber 3|.

By means of screw 38, valve 31 may be made to open at any desired pressure, its purpose being to maintain the pressure in chamber 3| at a substantially constant value. This is best effected by making the valve 31 open at a pressure just slightly above the pressure of the air delivered by pump 24 into chamber 3|. Thus supposing that the pressure of the air delivered by pump 24 to chamber 3| is two pounds per square inch, that is, valve 29 opens at two pounds per square inch, then if valve 31 is set to open at 2.1 pounds per square inch, the air in chamber 3| will always be between two pounds per square inch and 2.1 pounds per square inch, or at a substantially constant pressure, regardless of the speed of the pump. With the arrangement just described, the only effect of increasing the speed of the pump will be to increase its'rate of delivery without changing the pressure of the air delivered.

While pump 24 is of the reciprocating type, it is manifest that it may take the form of a rotary pump or any other suitable type, provided its speed is at a constant ratio with engine speed, and it delivers air at a substantially constant pressure irrespective of speed. The capacity of pump 24 is made such that it delivers sufficient air to completely atomize the liquid fuel discharged from main nozzle 7 under full open throttle operation even at low speeds under maximum loads. The excess compressed air, not required for partially open throttle at same speed under light loads, is then discharged through relief valve 31.

From the arrangement shown in Figure 2, it is apparent that as soon as the pressure in chamber 3| reachesa value sufiicient to lift valve 12, (which is usually about half the maximum pressure of pump 24, or about one pound per square inch) the liquid fuel in tank H is subject to this pressure and will be subject to the fuel pressure pump 24 (two pounds per square inch) as long as the engine is running. This pressure is maintained in tank 'H by making the filling plug 40 air tight and is used to lift the fuel from tank II to the carburetor through a liquid fuel supply pipe 4| which connects with the inlet Id of res-' The buoyancy of float I5 is, however, sufficient to close valve I5 and cut off the flow of liquid fuel to reservoir I3, whenever the liquid level in reservoir l3 reaches the line X-X against the maximum pressure of the compressed air in tank 1|.

An air gauge 42 is connected to the line I and placed upon the instrument board of the car Figure 1.

46, to the liquid fuel reservoir |3. If now,

to show the amount of pressure in tank II at all times.

Since valve 12 prevents the escape of compressed air from tank through pipe 23 andvalve l prevents the escape of liquid fuel through pipe 4|, when the engine is at rest, the only time that the compressed air will escape from tank H is when filling plug 40 is removed to refill the tank. This escape of pressure from tank II will, however, not cause any operating difiiculties, since reservoir I3 of the carburetor is made of sufiicient capacity to run the engine until the normal superatmospheric pressure is reestablished in tank H.

In order to apply the necessary variable pressure to the liquid fuel in the reservoir |3 to cause the flow of liquid fuel to the mixing chamber 4 to always bear the desired ratio to the air flow thereto, I have provided the following novel pressure control mechanism. An auxiliary compressed air chamber 43 is connected by a passage way 44 with passageway 22 and by a passageway 45, supplementary chamber 45 and port 41 withreservoir l3. Passageway 44 is much smaller than air line 22 and passageway 45 may be made only sufficient to maintain a static pressure in reservoir l3, as no air current flows therethrough.

The top wall of chamber 43 has a central screw threaded aperture 48 into which screws a bushing 43 in a position vertically adjustable. A central bore 50 in bushing 49 receives a stem 5| which is attached by screw threads to a piston 52 adapted to reciprocate with an air-tight fit in a cylindrical chamber 53, as clearly shown in Interposed between piston 52 and cover 54 of chamber 53 is a helical spring 55 which tends to force piston 52 downwardly in chamber 53 against the vacuum of mixing chamber 4 which is transmitted to chamber 53 by a passageway 55. Whenever the vacuum in the mixing chamber 4 is greater than the force of spring 55, piston 52 is drawn up to the top of chamber 53 until a lug 13 on piston 52 contacts with cover 54, and conversely, when this vacuum'is weaker than spring 55, piston 52 is forced down in cham ber 53 until stem 5| contacts with the bottom wall of chamber 43.

It will be noted from Figures 1 and 2, that stem 5| is hollow and closed at both ends but has an elongated slot 51 in one wall. This slot is of a peculiar shape, being generally triangular in. outline with the apex of the triangle at the bottom of the slot. The sides of the slot are, however, not strictly straight, that as stem 5| is moved through bushing 49 the area. of the slot exposed to chamber 43 is such that the amount of air escaping from chamber 43 throughslot 51 is sufficient to produce in chamber 43, the pressure desired to be exerted upon the liquid fuel in reservoir |3 for each position of' the stem 5|.

Chamber 53 is provided witha port 58 which is of sufficient size to permit the free escape into the atmosphere of the maximum amount of air which is discharged through slot 51 when stem 5| is in its lowermost position. Port 58 thus prevents any air from collecting in chamber 53 and retarding the movements of piston 52.

From the foregoing description, it is apparent that the pressure of the compressed air in passageway 22 (say two pounds per square inch) is transmitted to chamber 43, through passageway 44, and through passageway 45 and chamber stem 5| is in its uppermost position so that the lower but are slightly curved, s0.

section of passageway end of slot 51 is withdrawn into bushing 49, no air can escape through slot 51, so that the air entering chamber 43 can leave only through passage 45. But since reservoir I3 is closed airtight, by a gasket 59 inserted between the top edge of the reservoir and its cover 60, it is evident that the 'air entering reservoir l3 from chamber 43 cannot escape, and soon builds up a pressure in reservoir l3 equal to that existing in passage 22.

In other words, so long as slot 51 is closed by bushing 49, and when once the air pressure in reservoir l3 equals that in passage 22, passageway 44, chamber 43, passageway 45, and chamber 46, reservoir I3 becomes a dead end and there is no actual flow of air through passageways 44 and 45, but the pressure of the compressed air in passage 22 is communicated to reservoir l3 by the static column of air in the line of communication. If now, stem 5| descends so as to expose a portion of slot 51 to chamber 43 while the carburetor is in operation, there is at once an escape of compressed air from chamber 43 into cylinder 53 and out through port 58 to the outside atmosphere. But, as long as the area of slot 51, exposed to chamber 43, is less than the cross-section of passageway 44, only a part of the air entering chamber 43 44 escapes, and since the compressed air can flow into chamber 43 faster than it can escape through slot 51, there is no appreciable reduction in pressure in the chamber below that in passage 22. As soon, however, as the area of slot 51 exposed to chamber 43 exceeds the cross- 44, then the compressed air in chamber 43 can escape faster than it can enter this chamber, and there is at once a corresponding drop in pressure of the air in chamber 43 below the pressure in passage 22. This drop in pressure is transmitted to reservoir l3 by the static column of air in passage 45 and chamber 46.

As the area of slot 51 exposed to chamber 43 is still further increased, there is a still further corresponding drop in pressure in chamber 43- until the maximum area of slot 51 is exposed to chamber 43 when the pressure of the compressed air in chamber. 43 is a minimum. Since the maximum area of slot 51 is not infinite as compared to the cross-section of passageway 44 and there is retardation to the escaping air by the friction of passing through a long narrow slot, there is always some super-atmospheric pressure in chamber 43 (and reservoir l3) as long as the carburetor is in operation. This minimum pressure can be regulated by adjusting the maximum size of slot 51 exposed to chamber 43 when stem 5! is in its lowermost position. This is effected by raising or lowering the bushing 49 by screwing it up or down in threaded aperture- 48.

While the carburetor is in operation the pressure in passage 22 is substantially constant due to the action of the regulating valve 31 (Figure 2) and hence air enters chamber 43 at a constant pressure. The pressure in chamber 43 thus depends solely on the area of slot 51 exposed to chamber 43 and this in turn depends on the position of stem 5|. But the position of stem 5| depends upon the movement of piston 52 which is controlled by the vacuum in the mixing chamber 4. It, therefore, follows that the pressure in chamber 43 (and reservoir I3) is at any time dependent upon the vacuum in mixing chamber 4 and varies in general directly therewith, although this, variation is not a strictly linear through passageway function of said vacuum. That is to say, the

greater the'vacuum in the mixing chamber 4, the

that induced by the vacuum in mixing chamber 1 4 alone, if the air pressure in reservoir l3 were only atmospheric. This is the case with all suction operated carburetors. But it has been shown that, due to the difference in laws of flow between gases and liquids, a common vacuum inducing both flows cannot maintain a parity between these fiows as the effective head varies.

In order, therefore, to maintain a desired ratio of flow between the air and liquid fuel under all operating conditions, I subject the liquid fuel flow to a variable head which consists of: (a) the vacuum in the mixing chamber, or more properly, the vacuum produced by the flow of air through a Venturi throat induced by the vacuum in the mixing chamber; (b) the aspirating effect of the air column escaping from the nozzle 1, which is relatively small and sensibly constant, (since the air pressure in nozzle 1 is sensibly constant); and (c) a variable superatmospheric pressure on the liquid fuel in the reservoir I3 which varies from slightly above atmospheric to the maximum required to make the liquid fuel flow maintain its parity with the air flow (or say about two pounds per square inch, gauge). The minimum superatmospheric pressure in 'chamber I3 is adjusted so that, together with the aspirating effect of the air jet in nozzle 1, it is just suiiicient to start the flow of liquid fuel from nozzle 1 under the lowest pressure in the mixing chamber 4.

In this way, I overcome the retarding effects of surface tension and inertia of the liquid column which causes the liquid fuel feed at low vacuum (especially with wide open throttle) to be deficient in suction operated carburetors.

At the same time by supplementing the air flow through the main air intake 2 and Venturi throat 3, with a compressed air jet, I am able to make the size of the Venturi throat smaller than in a plain tube suction carburetor without sacrificing volumetric efiiciency of the engine, and am thus able to deliver more mixture and develop more power athighest speed of the engine.

Since, with a constant pressure in passage 22, the pressure in chamber 43 depends only upon the relative sizes of the passageway 44 and slot 51 and not upon their absolute sizes, the passageway 44 is made as small as possible without causing too great a friction loss with the maximum flow of air therethroughL It is thus made only a fraction of the size of passage 22 so that even when slot 51 is fully open, the actual flow ofair through passageway 44 will be only a small percentage of the flow through passage 22. Thus the maximum escape of air through 44 is not sufficient to materially affect the flow through passage 22. The capacity of pump 24 is made sufficient to supply the maximum flow of air required through nozzle 1 at highest speed of the engine and since slot 51 is always closed at highest speed, there is no escape of air through passageway 44 at this time.

At slower speeds the capacity of the pump is sufficient to care for the maximum escape .of air through passage 44 and at the same time supply sufficient air to nozzle 1.

Since there is no appreciable how of air through passage 45 it may be made as small as practicable from a manufacturing viewpoint.

The sole function of chamber 46 is to prevent the entrance of liquid fuel into passageway 45, due to splashing, and when the carburetor is tilted at an angle.

The operation of my device is as follows. When the engine is at rest, the pump 24 is also at rest and there is no air pressure in pipe 23 or passage 22, since air tube 9 communicates with the outside atmosphere through the aperture in cap Ilia and air intake 2, and affords a means of escape of any air in this line when the pump stops. On the other hand, pressure from previous operation is retained in pipe 10, tank H and pipe 4| by check valve i2 and valve i5.

When the engine is turned over by the starter, the throttle is in the restricted position shown in Figure 1 and the high suction above throttle 8 acting through port It and passage 26 on the liquid fuel in passage 20, which stands at the static level XX, lifts this fuel up through port 68 into mixture outlet 5. At the same time air enters port is and mixes with this fuel, forming a rich starting mixture in the conventional way. As the starter is turning the engine over, pump 24 supplies all of its air through pipe 23 and passage 22 to nozzle l, since valve I2 is not opened by this slight pressure. The current of air thus supplied is suflicient to atomize the liquid fuel issuing from tube 8 of nozzle 1, by the aspirating effect of the escaping air. Thus nozzle I starts into action just as the engine starts to fire from its priming mixture, and little or no choking is required. be opened somewhat wider at starting, thus increasing the suction on the main nozzle 1.

Since the air pressure in passage 22 is relatively low while the engine is being turned over by the starter, and since slot 51 is in its open position, there is little or no pressure in chamber 43 and reservoir i3. As soon, however, as the engine starts and the throttle is opened, the increase in speed of the engine increases the pressure in passage 22 and at the same time the increase in vacuum in mixing chamber 4 causes stem 5! to be drawn up, thus restricting slot 51 and transmitting an increased pressure to reservoir I3. Thereafter, the pressure in reservoir I3, during the operation of the carburetor, will vary with the vacuum in the mixing chamber and as vacuum varies with the demands of the engine, the superatmospheric pressure upon the liquid fuel in reservoir l3 will likewise vary therewith and a parity of liquid fuel and air flows will automatically be maintained under-all operating conditions.

This is the same result as is partially secured by air bleeding the main jet which is called compensation, so that in addition to increased atomization, compensation is also secured by my variable air pressure.

While I have shown and described the preferred embodiment of my invention, I desire it to be understood that I do not limit myself to the constructional details or values indicated, as these may be varied by those skilled in the art without departing from the spirit of my invention, or exceeding the scope of the appended claims.

I claim:

1. In a carburetor having a mixing chamber If a choke is used, the throttle can and a fuel nozzle, a constant level fuel reservoir supplying fuel to the fuel nozzle, means for maintaining in said reservoir such a superatmospheric pressure as will cause the fuel to be fed into the mixing chamber at a rate which varies in accord: ance with the law of adiabatic gas flow, said pressure varying in general directly as the vacuum in the mixing chamber.

2. In a carburetor, a mixing chamber, a constant level liquid 'fuel reservoir communicating therewith, means for maintaining upon the liquid fuel in said reservoir such a variable pressure as will force said liquid fuel into said chamber at a rate which varies in accordance with the, law of gas flow, and means for varying said pressure in general directly with the vacuum in said mixing chamber.

3. In a carburetor, a mixing chamber, means for feeding liquid fuel thereinto at a rate which varles in accordance with the law of adiabatic gas flow, and means for maintaining on said fuel a superatmospheric pressure which varies in general directly with the vacuum in said mixing chamher.

4. In a carburetor, a mixing chamber, a constant-level liquid fuel reservoir communicating therewith, means for maintaining a superatmospheric pressure in said reservoir and for varying said pressure in general inversely with the pressure in said mixing-chamber to force said liquid fuel into said chamber at a rate which varies in accordance with the law of gas flow.

5. In a carburetor, a mixing chamber, a fuel feeding nozzle associated therewith and comprising an air tub-e and a liquid fuel tube; means for supplying compressed air to the air tube, and means controlled by the vacuum in said chamber for supplying liquid fuel to the liquid fuel tube under a superatmospheric pressure derived from said compressed air.

6. In a. carburetor, a mixing chamber, a fuel feeding nozzle associated therewith and comprising an air tube and a liquidfuel tube, means for supplying compressed air to the air tube, means for supplying liquid fuel to the liquid fuel tube under a superatmospheric pressure derived from said compressed air, and automatic valve means for coordinating said pressure with the vacuum in said mixing chamber.

'7. In a carburetor, a mixing chamber, a compiessed air supply thereto, a liquid fuel reservoir in communication therewith, means for maintaining liquid fuel in said reservoir at a constant level, means for maintaining a superatmospheric pressure upon said liquid fuel from said air supply to force said liquid fuel into said mixing chamber, said pressure being coordinated with the vacuum in said mixing chamber. 1

8. In a carburetor, a mixing chamber, a compressed air supply thereto, a liquid fuel reservoir in communication therewith, means for maintaining liquid fuel in said reservoir at a constant level, means for maintaining a superatmospheric pressure upon said liquid fuel from said air supply to force said liquid fuel into said mixing chamber, and a vacuum controlled valve for coordinating said pressure with the vacuum in said mixing chamber.

9. In a carburetor, a pressed air supply thereto,

mixing chamber, a coma liquid fuel reservoir in communication therewith, means for maintaining liquid fuel in said reservoir at a constant level, means for maintaining a superatmospheric pressure upon said liquid fuel from said air supply to force said liquid fuel into the mixing chamber, and means for coordinating the pressure upon said liquid fuel with as the pressure in the mixing chamber, said last mentioned means including a regulating valve actuated by a piston responsive to the vacuum in the mixing chamber.

10. In a carburetor, a mixing chamber, a compressed air supply thereto, a liquid fuel reservoir in communication therewith, means for maintaining liquid fuel in said reservoir at a constant level, means for maintaining a superatmospheric pressure upon said liquid fuel from said air supply to force said liquid fuel into said mixing chamber, and a vacuum-controlled valve for varying said pressure in general directly as the vacuum in said mixing chamber so as to make said liquid fuel fiow from said reservoir to said chamber in accordance with the law of gas flow.

11. In a carburetor, a mixing chamber, a subatmospheric air supply, a compressed air supply and a liquid fuel supply thereto, and means for controlling the liquid fuel supply comprising a superatmospheric pressure derived from said compressed air supply and so coordinated with the vacuum in said mixing chamber as to make said fuel supply always bear a predetermined ratio to the total air supply which latter is in accordance with the law of adiabatic gas ,flow.

12. In a carburetor, a mixing chamber, a compressed air supply thereto, an air supply thereto under a subatmospheric pressure from said compressed air supply, and a liquid fuel supply thereto under a superatmospheric pressure, said pressures being so coordinated with each other that all of said supplies always enter said chamber in accordance with the law of gas flow.

13. In a carburetor, a mixing chamber, an air supply and a liquid fuel supply thereto, and automatic means for controlling the liquid fuel supply so as to make it flow into said chamber at a rate which varies in accordance with the law of gas flow, the pressure in said means varying in general directly as the vacuum in said chamber.

14. In a carburetor, a mixing chamber, an air supply and a liquid fuel supply thereto, and means to apply such a variable superatmospheric pressure to the liquid fuel supply as to make it enter said chamber at a rate which varies in accordance with the law of gas flow, said pressure varying in general directly as the vacuum in said chamber.

15. In a carburetor, a mixing chamber, a liquid fuel supply and a compressed air supply thereto, means for applying a superatmospheric air pressure to said liquid fuel supply from said air supply, and means for varying said pressure so as to make said liquid fuel supply flow into said chamber at a rate which varies in accordance with the law of gas flow. I

16. In a carburetor, a mixing chamber, a subatmospheric air supply, a compressed air supply and a liquid fuel supply thereto, means for applying a superatmospheric air pressure to said liquid fuel supply from said compressed air supply, and means for varying said pressure so as to make said liquid fuel supply always bear a predetermined ratio to the total air supply to said chamber which latter is in accordance withthe law of adiabatic gas flow.

17. In a carburetor, a mixing chamber, an air supply thereto, an atomizing nozzle therein, means for supplying liquid fuel and air under superatmospheric pressure to said nozzle, the pressure on said liquid fuel varying in general directly as the vacuum in said chamber and supplementing said vacuum so as to cause said liquid fuel to flow into said chamber at a rate which varies in accordance with the law of gas flow.

18. In a carburetor, a mixing chamber, a subatmospheric air supply, a compressed air supply and a liquid fuel supply thereto, means for applying a superatmospheric air pressure to said liquid fuel supply from said compressed air supply, said pressure being controlled by the vacuum in said chamber and supplementing said vacuum so as to cause said liquid fuel supply to enter said chamber at a rate which varies in accordance with the law of gas flow.

19. In a carburetor, a mixing chamber, a subatmospheric air supply, a compressed air supply and a liquid fuel supply thereto, means for applying a superatmospheric air pressure to said liquid fuel supply from said compressed air supply, said pressure being controlled by the vacuum in said chamber and supplementing said vacuum so as to cause said liquid fuel supply to always bear a predetermined ratio to the total air supply to said chamber.

20. In a carburetor having a mixing chamber, a constant level liquid fuel reservoir, an atomizing nozzle, means for supplying compressed air 'to said nozzle, and means for supplying liquid fuel from said reservoir to said nozzle under a superatmospheric pressure from said air supply, and means for varying said pressure so as to make said liquid fuel supply flow into said chamber at a rate which varies in accordance with the law of gas flow.

21. The method of carburetion characterized by introducing into a flowing subatmospheric air component, a compressed air component, and a liquid fuel component under a superatmospheric pressure derived from the pressure acting on said compressed air component, said pressure being so coordinated with the pressure causing the subatmospheric air flow that said fuel component is made to flow always in a predetermined variable ratio with said air components flowing in accordance with the law of gas flow.

22. The method of carburetion characterized by commingling an air stream and a liquid fuel stream, both flowing under heads comprising a common vacuum and a plurality of superatmospheric air pressures, said vacuum and pressures derived from a common source and so coordinated with one another that the quantities of air and fuel delivered to the commingling zone by said respective" streams are the same as though all streams were flowing in accordance with the law of gas flow.

23. In a'carburetor, a mixing chamber having an air supply, an atomizing nozzle in said chamber, a compressed air supply and a' liquid fuel supply to said nozzle, and means for controlling the rate of liquid fuel supply comprising a superatmospheric pressure from said air supply so coordinated with the vacuum in said mixing chamber as to make said liquid fuel supply always bear a predetermined ratio to the total air supply to said chamber which latter is in accordance with the law of adiabatic gas flow.

AUGUSTIN M. PRENTISS.

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