US2495299A - Charge forming device - Google Patents

Description

Jan. 24, 1950 H, TA 2,495,299

CHARGE FORMING DEVICE Filed Sept. 50, 1947 INVENTOR.

HA /WP) 6. 753727? Patented Jan. 24, 1950 2,495,299 CHARGE FORMING DEVICE Henry G. Tarter, South Bend, Ind, assignor to Bendix Aviation Corporation, South Bend, Ind a corporation of Delaware Application September 30, 1947, Serial No. 777,063

4 Claims. (Cl. 128-119) This invention relates to charge forming devices or carburetors for engines, and particularly to so-called injection carburetors commonly used on aircraft engines, and an object of the same is to provide in such devices means whereby when a cold engine is to be started and warmed-up under low temperature conditions preparatory to placing it under load, an enriched fuel mixture may be selectively or automatically supplied to the engine until such time as the latter is able to operate efficiently on normal fuel mixtures;

In the type of injection carburetor and direct injection systems with which the present invention is concerned, fuel mixtures in the idle range and up to low cruise are controlled by a contoured idle valve whose position is varied in relation to throttle opening. This gives satisfactory operation over a wide range of temperatures, but where the surrounding temperature is relatively low, it may prove desirable to enrich the idle and warm-up fuel mixtures; and the present invention provides'improved means for accomplishing this result.

The foregoing and other objects and advantages will become apparent in view of the following description taken in conjunction with the drawings, wherein:

The sole figure is a sectional schematic of an injection carburetor having an idle enrichment control constructed in accordance with the invention.

Referring to the drawing, a main air intake conduit It) leads to a supercharger ll of an internal combustion engine generally indicated at I2. The conduit I is controlled by a throttle l3 operable from the pilots cockpit in a known manner, and anterior the throttle is a large venturi l4 and a small venturi 15. In the type of fuel supply system used to illustrate the present invention, the pilot controls the air supply by manipulating the throttle l3 while the liquid fuel is sprayed under pressure into the air conduit posterior the throttle by means of a nozzle IE, to which the fuel is metered under pressure automatically by the apparatus hereinafter described more or less in detail. It will lbe understood, however, that the nozzle it, instead of discharging into the main air intake conduit, could discharge directly into an engine cylinder and could comprise one of a series of nozzles of a direct injection system as in the copending application of LeRoy J. Evans, Serial No. 475,783, filed February 13, 1943, now Patent No. 2,447,268, issued August 19, 1948.

The fuel metering apparatus is mounted in a casing or housing generally indicated at 20; it may be considered as made up of two main sections, viz., a regulator unit l8 and a control unit IS. The regulator unit comprises a poppet valve 2| arranged to slide in a valve body 22 formed with an annular chamber 23 and a series of inlet ports 23 to which fuel is supplied under substam tially constant pressure by way of conduit 24. Such pressure may be maintained by a conventional fuel pump, not shown, having a by-pass controlled by a valve set to open at a predetermined pressure, for example, sixteen to eighteen p. s. i. An air'diaphragm 25 and a fuel diaphragm 26 have their outer edges secured between adjacent housing sections and their central portions clamped between a series of bushings secured on the stem 21- of the poppet valve 2|. These diaphragms, together with a rigid partition 28 and a sealing diaphragm 29, divide the housing 20 at this point into a series of chambers, viz., air differential chambers A and B and fuel differential chambers C and D. Chamber A is subjected to a measure of air intake pressure by means of a series of impact tubes 30, which have their entrance or intake ends located adjacent the carburetor deck and communicate with chamber A by way of annular chamber 3 I, valve port 32 and passage 33. Chamber B is subjected to Venturi suction by means of annular channel or chamber 34 formed in the throat of the small venturi I5 which communicates with said chamber by way of passages 35 and 35. Chambers C and D. are subjected, respectively, to metered and unmetered fuel pressures. The small diaphragms 36 and 31 serve the purpose of balancing regulator system including the poppet valve 2|; they are connected to opposite ends of the valve and form movable walls of chambers 38 and 39 to which unmetered fuel pressure is communicated from chamber D by small passages 40 and 4|. The diaphragm 31 also has a sealing function. The air chambers A and B are interconnected across the diaphragm 25 by a small passage 42 having a bleed 43 therein, and port 32 in air passage 33 is controlled by a capsule or aneroid shown asa sealed corrugated bellows 44 which is mounted in a housing 45 open to the air intake conduit l0 and carries a valve member or needle 46 adapted to vary the area of said port. The bellows 44 is loaded in a manner such as to render it responsive to changes in both pressure and temperature (see Patent No. 2,376,711 to Frank C. Mock), and is therefore responsive to changes in density. Thus, at relatively high barometric pressures, as for example,

no metering effect.

those usually prevailing at or near sea level, the bellows tends to collapse and open port 82 and passage 33, while at relatively low barometric pressures, as for example those usually prevailing at high altitudes. the bellows tends to expand and close port 31 and restrict flow of air through passage 33. As passage 33 becomes more and more restricted, the differential across air diaphragm 25 is reduced, tending to reduce travel of the poppet valve 2| for a given change in throttle position and conseqently the fuel-air ratio, as will be more fully explained in the description of the operation of the invention.

richment fuel during the early part of the power enrichment range, the Jet [53 taking overat higher power flows. The metering jets are located in flow channels which open into a fuel discharge conduit 53 through ports controlled by a manual mixture control valve 51 secured on a rotatable shaft 58 provided with a lever or handle as. Metered fuel pressure is communicated back to chamber C of the regulator unit it by way of a duct or conduit 60. VA regulator fill valve 8i, operated by a cam on the shaft 58, permits chamber C to fill with fuel through duct or conduit Gil when the carburetor is to be placed in operation after it has emptied, said valve 6! being held open in all positions of the mixture .control valve 57 except idle cut-off. For a more detail description of the fill valve, see Patent No. 2,361,227 to F.- C. Mock. Conduit 58 conducts metered fuel under pressure to the discharge nozzle it, which may be set to open at a predetermined pressure, for example, ten p. s. i. A passage or duct 62 vents chamber C to discharge conduit 56 to insure removal of any accumulation of air or vapor in said chamber.

An idle spring is indicated at 65. Its purpose is to provide an enriched fuel-air ratio for idling speeds. A screw 66 is readily accessible for adjustment by removing cap 61, the said spring preferably being set so as to act on the poppet valve 2| and urge it toward open position only when the said valve is nearly closed.

In the passage 50 which conducts unmetered fuel to the jets is an idle valve port 68 which is controlled by idle valve 53, the latter being connected to the throttle linkage in a manner such that when the throttle is closed or nearly so, the idle valve comes into play and controls or meters the idle flow permitted by the action of spring 65 to the desired value. Part of the linkage which connects the idle valve to the throttle is indicated at 10. As the throttle opens more and more, the idle valve opens and increases the idle flow, until when the low cruise range is reached, the valve attains its fully open position and has Any preferred type of idle system may be adopted, that shown being for the purposes of illustration only. For other types see for example the copending applications of Frank C. Mock, Serial No. 538,153, filed May 31, 1944, and Arthur J. Volz et al., Serial No. 696,690, filed September 13, 1946.

While the idle system may provide a sufliciently rich starting and warm-up mixture for average temperatures, yet when operating in cold weather or unusually cold climates, it may prove desirable to further enrich the fuel-air ratio to facilitate warming-up of the engine preparatory to placing it under load. and also for starting the engine, if desired. Withthis in view, a bypass channel or conduit II has its inlet end disposed to receive fuel upstream of the idle valve 89 and its discharge end located downstream of said valve, a restriction 12 being removably inserted in said by-pass. A valve 13 controls flow through conduit H, and this valve is preferably operated automatically in response to an engine condition. Accordingly, said valve is shown as mally urged toward closed position by a spring ii. A solenoid coil 15 is supported in the housing H, and this coil is energized when an electric circuit, comprised of wires H and 78 and a battery 19 or other suitable source of potential, is closed by a switch 80. As shown, the switch 80 is of the thermal type, it being connected by a rod 8| to a piston 82, the latter being slidingly mounted in a cylinder loaded with a temperature responsive material or fluid in heat exchange relation to a thermal element 83 located at a point with respect to the engine where it will respond to engine operating temperature, as for example, cylinder head temperature, oil temperature, or any other point indicative of engine temperature. A spring 84 normally urges the switch 80 to closed position. The electric circuit is preferably connected up with a master or main ignition switch 85 so that the circuit will be broken when the ignition is turned off.

Operation When the engine is running, air is drawn into the air intake conduit ill and through the boost venturi l5 and main venturi M, and a differential pressure is created between the throat of the small venturi and. the air inlet which at constant entering air density is proportional to the square of the quantity or air flowing. These respective pressures are transmitted to chambers A and B of the fuel regulator unit on opposite sides of the air diaphragm 25 and create a net force on the diaphragm tending to open the fuel valve 2|, this force usually being termed the air metering force. If this force were unopposed, the fuel valve 2| would tend to move to full open position; but when the valve opens, fuel under pressure flows into unmetered fuel chamber D and through conduit 50 to the fuel control unit,

where it flows through any one or more of the respective metering orifices, depending upon the position of the manual control valve 51, and thence to the discharge conduit 56 and discharge nozzle it, from which it is discharged under pressure to the air stream flowing to the engine. Chamber D is subjected to unmetered fuel pressure and chamber 0 to metered fuel pressure, and the differential between these respective pressures acts upon the diaphragm 26, tending to move the fuel valve 2| to the left, or in a direction to close the valve. This force is commonly termed the "fuel metering force" and it opposes the air metering force. The valve 2| is thus caused to adjust itself to a point of equilibrium such that the differential pressure across the fuel 5. manner substantially constant fuel-air proportioning is maintained. As engine speed is decreased, the rate of air flow to the venturi is decreased, thereby decreasing the differential pressure acting on the diaphragm 25, causing the valve 42 to move towards closed position and thus decrease the fuel flow to compensate for decreased air flow. Thus, the air metering force controls the fuel metering force. Since the Venturi-toair scoop differential pressure increases upon a decrease in entering air density, the differential pressure across the diaphragm 25 will tend to a increase, thereby increasing the fuel flow and enriching the mixture. The automatic control unit including the bellows 44 coacts with the calibrated bleed 43 in channel 42 to prevent such enrichment, said bleed bein substantially ineffective to vary the differential pressure in these chambers and across the air diaphragm 25 at such times when the needle valve 46 is in open position, as at ground level, by becoming increasingly effective in reducing the differential pressure when said needle progressively restricts the port 32 and consequently the passage 33 with increase in altitude. Thus,,for any given mass air flow, the needle 46 will so restrict the passage 33 with variations in altitude that the differential pressures in chambers A and B will remain constant notwithstanding that the differential in pressure at venturi l and the impact tube 30 increases with a decrease in entering air density.

At low air flows, the differential across the air diaphragm may be reduced to a point where the poppet valve will not open sumciently to provide adequate head for idling purposes, and it is therefore desirable to provide some means of holding the valve open at idling and near-idling speeds of the engine. It is for this reason that the idle spring 65 (or some other idling arrangement such as those disclosed in the copending Mock and Smith applications) is provided, the said spring 65 being adjusted in a manner such that it holds the fuel valve open when the air differential drops to a predetermined value. This will insure an ample fuel metering head for the idle valve 69, which comes into play at low air flows and meters the idle fuel.

Under low temperature conditions, however, it may become desirable to provide an added enrichment for idlin and near-idling speeds; and

it is under these conditions that the valve 13 comes into operation to open the passage 1| and permit fuel to by-pass the idle valve and enrich the idling or near-idling mixture. In the form of the invention illustrated,'the valve 13 is operated automatically, the circuit TI, 18 being rendered operative when the master switch 85 is turned on or closed; and assuming at this time that the temperature of the engine is such as to cause the thermal switch 80 to close, then the I solenoid 16 will be energized and the valve 13 will be opened and fuel will not only flow through the idle valve port 68 (assuming an idle setting of the throttle), but will also flour through the channel ll to the discharge nozzle 16. As soon as the engine attainsv a predetermine operating qtemperature, the thermal element 3 expan s and opens the switch SIM the latter remaining open'untilthe temperature again dro s to a'relatively low value. If desired, an additional manual switch may be introduced into the circuit, so that valve 13 may be operated automatically only at such times as conditions warrant. For selective manual operation, the solenoid valve I3 could be operated by the pilot, in which event the thermal switch -83 could be dispensed with. Another example would be to substitute a mechanical valve for the solenoid valve 13 and operate the mechanical valve by a. hydraulic circuit with a thermal indicator acting to open and close the valve.

Although only one embodiment of the invention has been illustrated and described, it will be obvious that others will be obvious in view of the teaching of the invention, and that various changes in the form and relative arrangement of the parts may be made to suit requirements.

I claim:

1. In a, fuel supply system for an engine, a flow channel provided with a metering restriction, a fuel valve for regulating the metering head adapted to respond to differential pressures constitutin a function of the flow of air and fuel to the engine, an idle orifice in series flow relationship with said restriction, an idle valve for controlling said orifice and arranged to meter idle fuel at low air flows, a conduit by-passing said orifice and valve, a valve controlling said conduit, and means for operating said latter valve.

2. A fuel supply system as claimed in claim 1 wherein said valve operating means includes a thermal device responsive to changes in engine operating temperature.

3. In a fuel supply system for an engine having a throttle controlled air intake, a flow channel provided with a metering restriction, a fuel valve for regulating the metering head across said restriction, diaphragm means connected to said valve and arranged to respond to differential air and fuel pressures constituting a measure of the flow of air and fuel to the engine, means for maintaining a minimum head of fuel irrespective of low air flows, an idle valve movable in relation to throttle position for metering the fuel at idle and near idle speeds of the engine, a fuel conduit by-passing said idle valve and having a meterin restriction therein, a valve controlling said latter conduit, and means for operating said latter valve to enrich the idle fuel.

4. A fuel supply system as claimed in claim 3 wherein the valve controlling said by-pass conduit is of the electric type and the means for operating the valve comprises an electric circuit having a thermal switch therein including a thermal element responsive to changes in the operating temperatures of the engine.

HENRY G. TARTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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