US1927091A - Carburation device - Google Patents

Description

Sept. 19, 1933.

H. w. HESS CARBURATION DEVICE Filed Aug. 12, 1929 Patented Sept. 19, 1933 CARBURATION DEVICE Harry W. Hess, Milwaukee, Wis, assignor to Carburetor Control Company, a corporation of Nevada Application August 12, 1929. Serial No. 385,269

8 Claims.

This invention relates in general to the carburation or vaporization and conditioning of fuel for combustion thereof for energy producing purposes, and the invention finds particularly useful application in connection with the admission of a supply of properly mixed liquid fuel and air to the cylinders or manifold of an internal combustion engine, although the utility of features of the invention is of more general scope and application; but, for purposes of presenting the invention, the disclosure will be more particularly directed to the application of the invention for use with an internal combustion engine of the'liquid fuel type, such as is ordi narily used on automobiles.

Control of an internal combustion engine is secured through regulation of the supply of hydro-carbon fuel and air which produce the fuel mixture fed to the cylinders. Inefiiciency of operation and reduced power in the operation of an internal combustion engine are incidents of overrich or over-lean mixtures of fuel and air supplied to the engine cylinders; and the supply of an over-rich mixture has the further defect of causing excessive carbon deposits in the engine cylinders during operation. In order to insure efiicient operation and desired uniformity of power response and regularity of acceleration,

it is ordinarily desirable that, for the various po sitions of the throttle, or valve device regulating the admission of fuel mixture to the engine, the proportions of fuel and air should be constant throughout the entire range of engine speed, or from idling condition to full-open throttle condition.

A general object and purpose of the present invention is the provision of an improved form of carbureting device capable of readily insurring uniformity to the desired degree in the-matter of the proportions of air and vaporized hydro-carbon fuel in the combustible mixture, throughout the full range of control, to the end of attaining smooth operation throughout the entire speed range, with fast acceleration and high maximum power, along with a high degree of general efficiency and economy in the operation of an internal combustion engine with which the carburetor is associated.

The present invention contemplates as a particularly desirable feature thereof the provision of a carburetor for preparing and feeding to an internal combustion engine or the like a mixture of air and vaporized fuel, wherein the supply of fuel is definitely regulated with respect to the particular operating speed or power desired, as may be determined by the position of a throttle, and is coupled with the supply in an automatically controlled manner of just the desired amount of air to produce with the fuel supplied a fuel mixture composed of desirably uniform proportions of air and fuel, to thus insure efiicient operation of the engine. And, in accordance withcertain features of the invention, the control of the supply of liquid fuel is secured through utilization of an improved form of fuel-- controlling valve affording fine regulation and metering of the fuel and rendering the degree of opening of such valve definitely proportional to the degree of opening of the throttle. And a further feature of the invention includes the utilization of an air admission controlling valve whose operation is automatically responsive to the suction drag or degree of depression present in the engine cylinders, or manifold associated therewith, as determined by the position of the throttle, the design and arrangement of parts of this air controlling valve being such as to insure a'readily controlled automatic operation of the valve with an immediate and delicate response, from its minimum-open to its maximumopen position, with consequent maximum available power and maximum economy in the matter of fuel consumption.

Various additional features and objects of this invention, concerned with the controlled supply of airv and fuel to the carburetor and of the combined or mixed air and fuel to the engine, and structural arrangements and mechanical details concerned th rewith, will be apparent from the more detailed description of the invention contained in the specification hereinafter and from the accompanying drawing disclosing embodiments of the invention, and will be more particularly pointed out in the claims.

In the drawing:

Fig. 1 is a broken sectional elevation of a carburetor embodying features of the present invention, the plane of the section being that of the line II of Fig. 2.

Fig. 2 is a view similar to Fig. l, the plane of section being that of the line IIII of Fig. 1.

Fig. 3 is a broken sectional elevation of the device as shown in Fig. 2, the section being in the plane of the line III-III of Fig. 1.

Fig. 4 is a bottom plan view of the device shown in Fig. 2.

Fig. 5 is a View similar to Fig. 3, with parts broken away, and embodying modifications of certain features.

In accordance with the disclosure of the draw- 19110 ing, 5 indicates a fuel float chamber such as is customarily associated with carburetors for use with internal combustion engines of automobiles; and 6 indicates the body portion, of rectangular cross-section, of a riser element or chamber into which the fuel and gas are admitted and wherein they are mixed prior to the supply of the mixture to the engine cylinders. The float chamber and riser chamber are preferably, as indicated, formed separately but are so designed as to be readily assembled as a unit and detachable from one another when necessary. The float chamber is provided with an enlarged hollow extension '7 at one side thereof forming a portion of or having its interior communicating with the main fuel chamber 5, and this extension 7 is provided with spaced projections 8 and 9 extending at substantially right angles from a portion or pad 10 formed on a side wall of the extension 7.

The projection or extension 8 is provided with a bore 11 communicating, as will be described hereinafter, with the interior of theextension 7 of the float chamber; and there is provided at the upper side of the extension 8 at a medial point thereof, an aperture communicating with the bore 11 and in which is mounted, preferably in a detachable manner, a fuel supply nipple 12 having a nozzle portion 13 of suitable known design at its upper end and projecting axially into a central aperture 1% through the bar-like upper projection 9. The diameter of the nipple such that it can be inserted to and from operative p sition through the aperture. 14, and the nozzle portion 13 is sufficiently reduced as to leave annular space of ample size between the outer wall of the nipple and thewall of the aperture 14 to permit the passage therethrough of a supply of air to satisfactorily take care of idling conditions of the engine, the walls of the aperture 14 projecting to a substantial extent above the nipple, thus confining the air passing through the aperture 14 in such a manner as to insure its ready contact and commingling with the fuel drawn through the nozzle 13, during operation of the assembled carburetor.

The bar-like projections 8 and 9 preferably project from the extension 7 of the float chamber to such a point that when the wall of the riser chamber 6 is held against the face of the pad 10, with these projections 8 and 9 extending through an aperture formed in such side wall, the outer end of each of the projections 8 and 9 is in close proximity to or abuts against the inner face of the opposite wall of the riser chamber. The float chamber 5 and the riser chamber 6 are shown assembled in operative position, with the axis of the aperture 14 and the fuel nozzle 13 in alineinent with the axis of the riser chamber, and with the projections 3 and 9 extending through an aperture, with a relatively close fit therein, in the corresponding side wall of the riser chamber, adjacent parts of this side wall abutting fiatwise against the face of the pad 10 on the extension '7 of the float chamber. A raised portion may be formed on the outer face of the pad 10 to enter and fill that portion of the aperture in the adjacent side wall of the riser chamber unoccupied by the projections 3 and 9. Extensions or lugs 16 are preferably formed at the side edges of the pad 10 and embrace the side tvalls of the riser chamber to hold the latter opposite side wall of the riser chamber, and through the latter side wall, these screws 1'? being threaded into apertures in the adjacent ends of the spaced projections 8 and 9. The clamping plate 18 may be provided at its side edges with projections or lugs 19 which engage the faces of the adjacent side walls'of the riser chamber and assist in holding the parts against lateral displacement. With the clamping screws 17 drawn up to position, the riser chamber is securely clamped in operative position relative to the float chamber 5 and its appurtenant fuelfeeding parts in such a manner as to insure the passage of fuel from the float chamber and to and through the fuel discharge nozzle 13.

Fuel is fed from the float chamber 5, a regulating valve 20 controlling the passage of fuel from the hollow extension 7 of the float chamber. This regulating valve comprises a fixed seating element 21 of tubular formation having a slightly flared or conical seating face on its interior, with the larger diameter of the flared seat atthe upper end thereof, where it opens to the fuel in the extension chamber 7, and tapering, in diameter, preferably with a straight taper, toward its lower end. A movable valve element 23 of the needle type, and preferably straight sided or cylindrical throughout its'active controlling portion, is arranged to be reciprocated within and to cooperate with the tapered seating face or bore of the seating element 21, to meter or control the passage of fuel through the valve. As indicated, the seating element 21- is preferably made up in the form of a bushing threaded adjacent its upper end into an aperture formed in the lower wall of the extension 7 of the float chamber. e

The quantity of fuel that may pass through the valve is determined bythe degree to which the needle is displaced upwardly from its 10W6Y- most position wherein the lower end of the needle is in engagement, or substantial engagement, along an annular surface or a line, with the adjacent portion of the interior seat 21. By shifting the position of the needle 23 upwards or downwards within its flared seat 21, an annular opening of variable size is formed between the lower end of the needle and the portion of the flared seat adjacent thereto, a feature which per-- mits extremely fine metering or regulation of the amount of fuel discharged downwardly through the valve. Through the presence of a gradual contraction up to the metering throat between the end of the needle 23 and its seat 21, the same being located at a relatively low point in the assembly where it is subjected to considerable head, fuel is discharged through the contracted annular metering passage with. sufficiently velocity to keep even a fine opening clear. Fuel discharges from'the valve 20 into a chamber or supply well 24, preferably formed by a detach able cap or thimbIe-Z H threaded into the wall of a bore or apertured portion at the lower side wall of, the extension '7 of the float chamber. Communication is established between the sup-- ply well 24 and the bore or passage 11 in the prcjection 8 communicating with the nozzle 13, through a passage or bore 25 formed through the lower wall of the extension 7 of the float chamber.

Air enters the carburetor through the lower end of the riser chamber 60f rectangular crosssection, this lower end of the latter, in the form shown herein, being cut away at an angle of approximately 15 degrees so as to facilitate the enxvi trance of the air from a lateral direction. The supply of air through the lower portion of the riser chamber and into the upper portion thereof or mixing chamber, indicated 35, is controlled by means of a special type oi valve which is automatically responsive in its operation to the adjustment or? the throttle control the suc tion drag or depression of the engine cylinders incident thereto. This air controlling valve is shown in the form of a pair of opposed, similarly shaped and symmetrically arranged resilient leaves 28, having their lower secured in position adjacent opposite Walls, hy pivotally mounting these lower ends on pins so as to permit oscillation thereon, as indicated at 39. These ient leaves are of under normal or unbiased cont ons, and are so dimensioned and disposed in the riser chamber that theiintermediate portions are to hear lightly st the side Walls of projection or cross bar 9 which surronids the discharge end of the 13, as indicated in full lines in Fig. 3. The upper ends of these resilient leaves 29 bear against the inner fa es of the adjacent side Walls of the mixing chamber 56, being slightly rounded at these ends, as indicated at 32, to facilitate sliding movement of the ends along the wall of the chamber. Pins 34 through opposed side Walls of the chamber and serve to retain the upper ends of the springs against appreciahle displacement away from the side walls with Whi they engage, While still permitting their. displacement longitudinally along these side Walls as the interined .e portions of the leaves flatten out during. operation of the carburetor.

It is desirable that the intermediate portion of the resilient leaves 28, 29 Where they approach one another most closely be adjacent, preferably slightly above, the discharge end of the nozzle for the air passing through this throat or contracted per at 31, or the venturi formed by the leaves and the side Walls is at maximum velocity and exerts a benericial d ag on the fuel supplied through the nozzle and imparts a desirable breaking-up erlect on the particles of fuel discharged frorn'the nozzle.

The portions of the resilient leaves 28, 29 below the cross par 9, corresponding to the point of greatest contraction slot the passage between the inwardly bulged portions of the opposed resilient leaves, are or full Width, i. they extend across the lull width of the passage through the riser chamber their edges cooperate with opposed straight sided walls of this chamber, preferably with a minimum clearance, so as to permit the desired movement of the spring transversely thereof While at the same time preventing leakage of pressure air to the rear side of the leaves.

portions of the resilient leaves 28, 29above elite on cross bar 9 are recessed or cut away to mit the rear sides of these leaves throughout their full length to be exposed to any depression or vacuu-.. existing in the mixing chamber, due to the suction drag of the engine cylinders. To secure this effect each of the re-' silient leaves 28, 29 may he cut away, as indicated, at its side edges, a point appreciably vs the iwar y bulged intermediate part of the spring which is biased against the cross bar 9. Further, t... ougn this gradual red .ction of the width of the leaves at their upper ends, these portions the leaves have decreased inertia and are more .rlexi lo, and. hence more read ily displaceable or distortable from normal hiase condition during operation of the carburetor.

having the upper ends of the resilient leaves 28,

29 hearing against the walls of the chamber, ency to uncontrolled vibration of t as leaves pulsation during operation is min ed.

Through the arrangement of the arts of the valve, all of air admitted to the in her is metered or controlled, by reason of its passage through the throat 3' of Venturi tube of automatically va formed between the inwardly .ilged or contracted portions of the s its 23, 29, the e r of the lower portions or l or with the opposed Walls of the chamber s that there is no appreciable or. air heen the edges of the leaves and the side Walls of the charnloer'at the inlet of the contracted throat, such might cause undesirable variations the proportion of air and fuel admitted to the mi ing chamber. With this arrangement, the lower portions of the resil suction a variahle degree toward flattened condi ion, dc Li pending upon the speed of operation engine, a material factor in avoiding sluggish ness in the opening and closing movements of the air controlling valve and in insuring the de sired ready and delicate responsiveness of this air valve in automatically providing the required how of air to the mixing chamber and t e uniformity of proportions of and Fuel drawn in vapor form into t. mixing chamber from the nozzle 13 is surrounded by and quite thoroughly mixed with through the opening 14 in the cross bar 9 and between the Walls of Venturi throat "1e size formed between the inw dly bul c. mediate portionsof the res-ill nt leaves 2 I which, as they are distorted more or less from their normal biased positions during oi the engine, have the effect of varying the crosssectional area of this mixing chamber at its lower portion.

The mixture oi air and vaporized iuel is fed from the mixing chamber 3'5 the engine cylindel's, or the manifold. associated therewith, through a controlling throttle valve ll of butterfly type, indicated outline for cooperation. v; passage of rectangular cross-s upper portion of the chard: r tle valve mounted on a through the side Walls of the eraloly mounted in der; enlarged cap portion of the riser. The t 'llOL may through spindle 42 and an actua. nected to a crank arm 45 fl: the spindle, by a handle or any position convenient to 0 here shown in the form of a in a projection i"! on th ci r With a fixed stop or projection to variably determinative closed, position or" the re desired idling conditions of cap portion 43 is preferably separate casting, particularly Where chamber can be formed of stock shapes and sizes and the machine work necessary to constitute a suitable mounting for the throttle valve and parts, may be done on the part 43 before the latter is attached to the riser.

While certain features of the present invention may be realized with a carburetor wherein there is a single fixed or manually controllable opening for supply of fuel to the carburetor, some variation inthe amount of fuel supplied being aiforded by differences in suction drag exerted by the engine due to variations in speed of the latter, nevertheless, the most desirable operating characteristics attained in a carburetor of the general type described above wherein the supply of fuel to the carburetor is to correspond more definitely and assuredly to the requirements of the engine in the n atter of speed and power. Accordingly, the niov ile needle element 23 of the fuel. regulating valve is caused to be actuated to a position to produce an opening through the valve 28 which always bears a desired definite relation to the position of the throttle valve, and hence, to the required speed and power of the engine.

As indicated, the needle valve 23 is fixedly attached to a rod 51, as by having the upper end of the needle valve fitting within a socket at the lower end of the rod 51 and having flexible side walls which, after the needle is inserted into position in the socket, be clamped and held in position about the needle by means of a clamping nut 52 threaded upon the flexible side walls of the socketed portion of the rod. This rod 51 preferably passes out of the chamber formed in the extension 7 of the float chamber, through an apertured cap or bushing 53 secured, as by threading, in an opening formed in the upper wall of the extension 7 of the float chamber. This opening in which the bushing 53 is detachably secured, is of suiiicient size to permit the ready removal and replacement therethrough of the tubular seating element 21 of the fue regulating valve 20 which is formed at its upper end for engagement with a suitable tool. A compression spring 5 1 surrounds the rod 51, bearing at its upper end against the under side of the cap portion of the bushing 53, and at its lower end against the clamping nut at the lower end of the rod 51; and this spring serves to bias the needle valve downwardly toward closed or desired idling position, insuring automatic return to lower position whenever the needl is relieved of operating pressure.

As indicated, the throttle valve 41 is connected to the operating rod 51 of the needle 23 of the fuel metering valve, for one-way positive operation of the latter, through a link 55 flexibly connected to the upper end of the rod 51 and to a crank 56 loose upon the spindle 42 of the throttle and provided with an off-set lug or extension 58; and an adjustable stop 59 threaded through a projection so on a crank arm 61 fixed to the spindle e2 bears against the upper side of the projection 58. With this arrangement, operation of the throttle ll toward full-open position, that is, in a clockwise direction, as viewed in Fig. 2, causes the opening of the needle 23, through the action of the stop 59 bearing upon the projection 58 on the loose crank 55 to which the connecting link 55 is attached. ihis operating connection is such that as the throttle opened, the needle valve is opened to a corresponding desired amount, definitely determined by the lever arm of the crank 55 and the degree of taper of the valve seat 21; and then, as the throttle is released or closed, the needle 23 of the fuel metering valve is immediately forced, through the ac-v tion of the biasing spring 54, to a closed or partly closed position, corresponding to the new position of the throttle, at which time the projection 58 on the loose crank 56 abuts against the adjustable stop 59 associated with the operating parts of the throttle.

The initial or idle position of the fuel metering valve, and the amount of fuel supplied for a particular throttle opening may be adjusted at will by adjusting the position of the stop 59 against which the projecting lu 58 on the crank 56 abuts, this adjustment, coupled with the effect of the biasing spring 54, serving to raise or lower the needle 23 relative to its seat 21 to thereby vary the opening through the valve. Further adjustment of the fuel metering valve may be accomplished by replacing the needle 23 with another of different diameter which, for a given needle position, affords a correspondingly larger or smaller passage between the lower end of the needle and the seat 21.

In order to provide for opening of the fuel metering valve 20 independently of the throttle and its adjustment relative to the fuel valve, such as may be necessary for cold-weather starting, a crank 63 is mounted loosely on the spindle i2 of the throttle and is provided with a projecting nose 63" which, on suitable actuation of this crankin a clockwise direction, as by means of a connecting rod passing to the operators position, engages with the outer end of the extension 58 on the crank 55, shiftingthe latter in a clockwise direction and thereby lifting the needle 23 of the fuel valve away from its tubular seat to the desired degree. On relieving the crank 53 of operating pressure, the biasing spring 54 immediately shifts the needle valve to a closed or other position, corresponding to the position of the throttle at the time.

An auxiliary supply or bypass for the feeding of fuel from the float chamber 5 to the fuel nozzle 13 maybe provided through a port 6% in the lower side wall of the hollow extension 7, this port com municating with the well 2 A needle valve 65 cooperates with this port for varying the size thereof or closing the port, a portion of this valve passing through the upper wall of the hollow chamber '7 and formed at its upper end to permit adjustment from the outside of the casing of the degree of opening of the valve. Or, this valve 65 may have its upper end formed for connection to a loose crank such as 53 for adjustment thereby, through an operating connection, from the operators position.

Assume that the engine has been started and is operating under idling conditions, the throttle being opened or cracked slightly, as determined by the adjustment of the stop screw 45, and with the fuel metering valve open to its predetermined or nearly closed position, and the air valve with the inwardly bulged intermediate portions against the sides of the cross bar 9, as

ure is drawn therefrom throughfuel is fed under these conditions, just enough to maintain the engine in operation with no load thereon.

In order to bring the engine up to any desired operating speed, the throttle is actuated to a position corresponding to the desired speed, and the fuel metering valve, through the operating connection therebetween and the throttle during its opening adjustment, is alsoopened to a degree corresponding to the particular settingof the throttle. The suction of the engine cylinders is immediately effective to draw an increased amount of fuel through the supply nozzle 13 and, likewise, the increased suction due to the opening of the throttle, is immediately efit'ective to cause an increased supply of air through the air valve, the leaves 28, 2 of the air valve moving outwardly toward their flattened position, due to the differential pressure exerted thereon by the incoming air passing through the throttle of the venturi formed by the intermediate bulged portions of the resilient leaves. These leaves are distorted or flattened to a position determined by the design of the leaves and the particular setting" of the throttle, the result being that the opening between these leaves is just sufficient to supply under the suction drag conditions incident to the particular degree of opening of the throttle, just the required amount of air for mixture with the supply of fuel passing through the fuel metering Valve whose position is likewise determined by the position of the throttle.

In the modification shown in Fi 5, the riser chamber 6 is indicated as being of special shape particularly designed to provide space for receiv-- ing the opposed leaves 28, 29 constituting the air valve when the latter is in maximum open position, to the end that, when this valve is in maximum open position, there will be a through passage between the opposed leaves which is substantially equal in cross-sectional area to the.

inlet portion of the riser chamber. As indicated, opposed side walls of the riser chamber are distorted outwardly adjacent the leaves, from'the pivotal point to the upper end th reof, thus providing recesses which receive the springin its maximum open position, indicated in dotted lines.

While the inherent resilience'of the leaves 28 and 29 themselves, constituting the automatic air valve, is relied on wholly in the particular embodiments of the invention described herein,

to insure the properopening of the air valve at" times, certain desirable results are attainable 'th valve leaves in connection with which separate springs are utilized in whole or in part to bias and return the leaves to minimum open position.

"it is an interesting feature of the operation .of the present carburetor that the response in the matter of an increased or decreased supply of air, corresponding to any opening or closing adjustment of the throttle is immediate, for the operation of the throttle varies to pressure to .which the rear sides of the resilient leaves are exposed, thus distorting or destroying the normal equilibrium or balance existing for the theretofore existing throttle adjustment. Through the above described several, features of design, the highly desirable result is attained that a uniform proportion of air and fuel is supplied to the engine from the minimum opening or idling position of the throttle and associated parts to the maximum opening thereof, corresponding to maximum speed of operation of the engine. And further, through this design and arrangemerit of parts, the depression or suction available in the mixing chamber or at the discharge side of the air: valvevaries at a uniform rate from idling or minimum open position of the throttle, corresponding to minimum operating speed, to maximum opening, or maximum speed condition of the engine, the general result being that maximum power and maximum economy of fuel is available under all operating conditions the engine. 'While the riser chamber 6 is shown asbeing of rectangular cross-section throughout, any piion of the sameabove the activecontrolling portion of the leaves 28, 29 of the air valve may, with reasonably satisfactory results, be of a section other than rectangular. However, with a butterfly valve of rectangular outline cooperating with a correspondingly shaped casing, the open area or passage through the latter more readily provides a passage of uniformly varying area as the throttle is opened. Likewise, the rectangular form of throttle cooperates better with a simple design of fuel metering valve of relatively straight taper, to secure the desired uniformity of proportions of fuel and air, as the throttle is opened.

It should be understood that the invention claimed is not limited to the details of construction and operation described hereinabove, for obvious modifications within the scope of the appended claims will occur to those skilled in the art and are to be considered as included within the general scope of the invention.

't isclaimed and desired to secure by Letters Patent:

l.v In a carburation device, the combination of a fuel mixing chamber, means for automatically controlling the admission of air to said mixing chamber, said means comprising a leaf valve having an intermediate portion resiliently urged toward a position to close the through passage of air and movable transversely across a portion of thecasing element having opposed parallel sidewalls with which the edge portions of said leaf valve cooperate to prevent the passage of air from the inlet side thereof between said edges and said walls of the valve chamber, while perinitting free exposure of the rear side of said leaf valve to the pressure conditions present in said mixing 1 chamber.

, 2. In a carburation device, the combination of a fuel mixing chamber, of an automatically operated valve for controlling the admission of air to said mixing chamber, said valve being resiliently biased to closed position and being movable to open position in response to the suction available in said mixing chamber, said valve including a plurality of symmetrically disposed and opposed leaves providing a Venturi throttle of variable throat opening, and a casing element therefor having opposed parallel side walls with which the edge portions of said leaves cooperate in a substantially fluid tight manner during movement of said leaves from their closed position wherein they approach each other to a maximum extent, whereby the inlet sides of each of said leaves is open to the pressure of incoming air whereas the rear side of said leaves is freely exposed to the suction available in said mixing chamber.

3. In a carburation device, the combination of a casing having therein, a fuel supply chamber, a fuel mixing chamber, and means for controlling the supply of fuel from said supply chamber to said mixing chamber, said means comprising a nozzle disposed adjacent said mixing chamber, and a fuel controlling valve controlling the passage of fuel from saidsupply chamber, said valve including a seat member of tubular formation having a flared internal seat, mounted in the lower wall of said fuel supply chamber, a movable controlling needle disposed within said tubular seat having its end portion of a cross-sectional area at least equal to that of the shank portion of said needle, said end portion constituting the effective valve element for varying the size of the effective passage therethrough between said seat and the end'of said needle.

4. In a carburation device, the combination of a fuel supply chamber, a fuel mixing chamber, and means for controlling the supply of fuel from said supply chamber to said mixing chamber, said means comprising a nozzle disposed adjacent said mixing chamber, and a fuel controlling valve controlling the passage of fuel from said supply cham-' her, said valve including a seat member of tubular formation having a flared internal seat, a movable controlling needle disposed within said tubular inlet having its end portion of a cross-sectional area at least equal to that of the shank portion of said needle, said end portion constituting the effective valve element for varying the size of the effective passage therethrough between said seat and the end of said needle, a throttle for controlling the fuel mixture discharged from said mixing chamber, and a mechanical connection between said throttle and said fuel supply valve for insuring the opening of said fuel supply valve to a degree proportionate to the opening of said throttle.

5. In a carburetor, the combination of a fuel mixing chamber, means for controlling the admission of air to said mixing chamber, said latter means comprising a plurality of leaves uniformly distributed about the axis of said mixing chamber and cooperative with wall portions at the inlet side of said mixing chamber to produce a Venturi throttle of variable throat opening, the rear faces of said leaves being exposed to only the pressure in the mixing chamber at the discharge side of said air valve, and a fuel supply nozzle having its discharge opening between said leaves adjacent the point of greatest constriction therebetween.

6. In a carburetor, the combination of a fuel mixing chamber, an automatically operable valve for controlling the admission of air to said mixing 'chamber, said valve comprising a plurality of leaves symmetrically disposed about the axis of said mixing chamber and forming a variable ven'- turi therein and yielding biased toward each other to decrease the size of the Venturi passage formed therebetween, said leaves cooperating with the walls of said chamber to close the rear faces of said leaves to pressure other than that existing in the mixing chamber beyond the throat of said venturi, an element extending across said chamber and serving as a stop to limit the movement of said valve members toward each other, said stop being apertured in substantial alinement with the axis of said mixing chamber, and a fuel discharge nozzle extending into the aperture in said stop and spaced from the walls thereof, to insure an air passage about the discharge end of said nozzle when said leaves are in position to provide minimum opening therebetween.

'7. In a carburetor, the combination of a mixing chamber, a throttle valve of rectangular outline cooperating with the walls of a passage of rectangular cross-section for controlling the discharge from said mixing chamber, and a reciprocating valve for controlling the supply of fuel to said mixing chamber, said fuel valve being asso ciated with said throttle for actuation in synchronism therewith and being biased toward closed position independently of said throttle, the operating connection between said throttle and said fuel valve insuring the positive actuation of said fuel valve to open position and the automatic return of said fuel valve following closing movement of said throttle.

8. In a carburetor, a two-part casing structure, one part of said casing including a fuel supply chamber, a fuel discharge nozzle, and a valve for controlling communication between said fuel supply chamber and said fuel nozzle, and a second part of said casing including a mixing chamber, a throttle valve for controlling the discharge from said mixing chamber, and an air admission controlling valve comprising a plurality of separable leaves biased toward each other for controlling the admission of air to said mixing chamber, and means for securing the two parts of said casing in operative position relative to each other, with said fuel discharge nozzle disposed in substantial alinement with the axis of said mixing chamber and located at the point of minimum opening between

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