US2470014A - Carburetor - Google Patents

Description

. c. wfB-Row'N v May l0, 1949.

GARBRE'TOR' l Filed bec. 23; 194s s Smets-sheet 1 May 10, 19.49.- Lc. w. BROWN cARBURET'oR 3 Sheets-Sheet 5 Filed Dec. 23, 1946 Chester W. Brown Patented May 1Y0, 1949 Chester-Wl Brown, Linton, Ind'.

Application December 23, 1946, Serial No; 718,049

20 Claims. l

The present invention relates generally' toA the carburetor art.

More particularly this invention relates to: certain new and useful improvements in carburetors of the downdraft type adapted to' supply proportioned quantities of vaporized liquid uelcandmixture to the intake manifold ofv an internai combustion engine.

In the normal course of operation of the majority of automotive vehicles in which the modern internal combustion engine nds its greatest utility, relatively large variations in engine power and speed requirements arel encountered as a matter of course. The necessary exibilityy of engine operationthus required hask beenl achieved in various Ways, oneof the most im'- portant oi which has been through various renements and improvements in enginel carbure'- tors. l'n the case oi an automobile, forlexample; when the engine is rst started' a relatively. ricla mixture is desirable; as' the enginey warms up the mixture must be leaned out for proper-"op"- eration; and, nally, each different load condi-- tion Which may be occasioned by the vehicle1 traveling up and down hills must be correlatedk with the throttle setting for thel particular enf gine speed at the time, thus necessitating corr-v tinuous mixture changes to secure Atheoretically correct fuel-air ratios.

In the past, in an effort to solve the problem ci maintaining a correct fuel-air ratior under different operating conditions of engine loadand speed, numerous refinements have been made in' the various carburetor designs until thev modern automotive carburetor has become an extremely complicated mechanism involving, as it generally does, numerous passageways, valves, and individual jets, each of which is specically designed principally to improve engine operation for some' one or at most a narrow range of engine operating conditions. Inasmuch as each such additional jet, valve, or other renement is superimposed upon an existing fundamental carburetor circuit designed to function at all times, each has necessitated further adjustments and corrections in the other related circuits so that the final result in practically all cases has been in the nature of a compromise which approaches a correct mixture Within specied operating ranges but which is actually not entirely correct for any particular set of conditions.

Accordingly the principal object of the present invention is to provide a carburetor Whichv will automatically insure a correct fuel-air lmix-y (Cl. 2'61-44) l 2 ture under substantially all conditions of engine opera-tion.

Another object ot thevrinventionis. to provide acarburetor of the'I typey described. wherein-a correct fuel-air ratio is maintained underivarious' engine operating conditi-onsby simultaneouslyl varying the air and` fuel inlets insuchmannen as to meter the quantity of liquid fuel supplied to the carburetor jet in accordance Witltvthe volume ot air'supplied thereto,` While at thais'amei time maintaining the air pressure inrpounds perJ square inch inthe'ventiuin substantially constant.`

An additional object of the'inventionfistoipro vide a carburetor of the type-described,- wherein a correct carburetor adjustment for engine idlingL speed is obtained by controlmeans operatively associated withv the main or high speedacarburetor jet.

Yet another object of the* invention is topro vide aV carburetor for anautomotive vehicleengine incorporating'separate devicesfvfot adjlust' ing the mixture' to prevent overloadingunder acceleration or decelerationby introducing a'time u delay in'variationofl the air inlet opening,.at least" one of said devices being independent,= ofand anotherdependent upon momentumy forces. produced by thevehicle.'v

Astill further object of the invention is. to provide a carburetorof the type described embody',- inganinterconnection between the v throttle valve and the means for vary-ing the airinlet tov prevent ydamage to. theenginecaused by too rapid throttle opening,y andifalso to improve` the engine stalling characteristic under load.

Additional objects of the invention reside't in the` provision of anA adjustable mechanism. fori Varyingy thez carburetor mixture tov uniformly. compensate for variationsiin vacuum-A conditions under bothlight andheavy loads both of a; stead-yand temporary character; `toprovide automatic temperature compensating devicesfor varying thek fuel-air mixture in accordance-vvith thefengine and operating air.temperatureI as welll,A as fuelv vaporization effect; and toeprovide.) ai cushioning'. device forY smoothing they operationi ofthe fuel metering mechanism andacceleratiori` pump action.

A particularly-important object o-f thisr invention is to provide a carburetor of the typede= scribed wherein the various featuresfofadjust.-V ability and compensation, specifically referredfto inY- the preceding-objectsare all. either incorpo-- ratedor have their effectupon a single-jet;-

The'foregoin-g; aswellr as other and:- further oli# jects and advantages of the invention together with a clearer understanding of the precise nature thereof will become more readily apparent to one skilled in the art from a consideration of the following detailed description taken in conjunction with the accompanying drawings illustrating a preferred embodiment thereof wherein similar reference numerals refer to corresponding parts throughout the several views, and wherein:

Fig. 1 is a longitudinal cross-sectional View through a completely assembled carburetor in accordance with the present invention;

Fig. 2 is a longitudinal cross-sectional view similar to but illustrating only a portion of the carburetor of Fig. 1 and showing certain of the parts in another operating position;

Fig. 3 is a longitudinal cross-sectional view to an enlarged scale illustrating in detail the preferred form of jet structure shown in Figs. 1 and 2;

Fig. 4 is an exploded perspective view showing the relationship of certain of the jet elements;

Fig. 5 is a top plan view of the carburetor of Fig. 1 with the top cover removed;

Fig. 6 is a detail view similar to Fig. 3 but illustrating another operating position of the parts;

Fig. '7 is a transverse cross-sectional view through the jet taken substantially along the line 'I--1 of Fig. 6;

Fig. 8 is a top plan View of a preferred form of throttle valve constituting an important part of the present invention; and y Fig. 9 is a side elevational View of the throttle valve of Fig. 8.

Referring now specifically and in detail to the various gures of the drawings and in particular to Fig. 1 thereof, the improved carburetor in accordance with the present invention is seen to comprise a housing in the form of a substantially vertical cylinder IB, preferably formed as a steel casting or the like7 having a cover l2 mounted on its upper end in any suitable manner as by means of the bolts I4 extending through flanges I6 on the cover and into suitably threaded apertures formed in the upper rim I8 of the cylinder I0. The main portion of the cover I2 is tapered inwardly and upwardly and terminates at its upper end in a cylindrical portion I9 constituting an air inlet 20 open to the interior of the cylinder I0 under the control of a choke mechanism illustrated as a conventional buttery valve 22 pivotally mounted as at 24 within the air inlet 20. At its bottom end the cylinder IIJ is provided with a generally cylindrical portion 26 of reduced diameter constituting a mixture outlet 28 provided at its bottom end with a flange 3S having apertures 32 therein and adapted to be attached to the intake manifold of an internal combustion engine. A throttle valve designated generally by reference numeral 34 is pivotally mounted within the mixture outlet 28 for controlling the passage of the fuel-air mixture therethrough to the intake manifold. The construction of the throttle valve 34 involves a number of novel features and will be hereinafter more fully described.

' Referring again to Fig. 1, it will be noted that the right-hand side of the cylinder I0 is provided with a float chamber 36 preferably cast integrally there with and closed at its top in any convenient manner as by means of a cover plate 38 held in position by means of a plurality of screws 40. The float chamber 36 is adapted to provide a substantially constant level of liquid fuel such as gasoline therein at all times and to that end is provided with a suitable float 42 depending from pivot arms 44 and operatively connected to a suitable needle Valve mechanism of any wellknown type designated generally by reference numeral 46. The valve mechanism 46 in turn controls in the usual manner the admission of fuel to the float chamber 3B through an elbow 48 and conduit Eil, the latter being connected to any convenient source of supply. The interior of the float chamber 36 is open adjacent its bottom portion to a vertical passage 52 formed in a projection 54 of the cylinder casting III which is connected in turn to a similar horizontal passage ii opening at its opposite end to the interior of the mixture outlet 28. An elbow i'ltting 58 is threaded or otherwise suitably secured as at 60 to the end of the passage 56 and is provided at its other end lwith a tubular conduit 62 connected in any convenient manner thereto as by means of a threaded collar S4. The conduit 62 which is preferably made of copper or brass extends axially upward adjacent the center of the cylinder ID and serves to supply fuel to the carburetor through its connection to the iloat chamber 36 by means of the passages 52 and 56.

As illustrated in Figs. 1 and 2, the space Within the interior of the cylinder Il) is divided into upper and lower working chambers 66 and 68, respectively, by means of a piston designated generally by reference numeral 10. The piston 'I is preferably constructed of a very lightweight material so as to have a relatively small mass and is seen to comprise a cup-shaped portion having a oor 'I2 and a vertical Wall portion 14, the latter being adapted to closely engage the inner wall of the cylinder ID but being relatively freely reciprocable therein. The piston 'IIJ also includes a `downwardly and inwardly tapered intermediate section 'I6 depending from the inner edge of the oor 'I2 and constituting the carburetor venturi l5, and a tubular skirt 'I8 depending from the bottom of the tapered portion 'I6 and reciprocable in pressure-tight relation within the outlet 28.

The piston lil is resiliently supported within the cylinder iii as by means of a plurality of springs titi, preferably three in number, attached at their bottom ends to lugs 82 formed on the upper surface of the piston floor l2, and at their upper ends to the arms 84 of a hanger or spider structure having an outer shouldered rim 86 adapted to be engaged and held in position between the rim i6 of the cover I2 and the upper rim i8 of the cylinder Iii by means of the bolts lil. The arms d4 extend generally radially of the cylinder i5 and are provided adjacent the center of the latter with a generally cylindrical bushing 83 having a key El attached to the inner periphery thereof as by means of a screw @9 for a purpose which will hereinafter be more fully eX- plained. A ring Si@ of a relatively heavy or dense material loosely surrounds the skirt 'I2 and rests upon the inside bottom of the cylinder lil. The ring QQ constitutes a momentum responsive acceleration control and the operation thereof will also be described in detail below.

Referring now particularly to Figs. 1, 3, 4, and 6, there is illustrated a preferred form of jet structure for the improved carburetor in accordance with the present invention. As shown in these figures the top end of the conduit G2 is threaded exteriorly as indicated at 92 for engagement with similar internal threadsprovided atltlie lower central portion of a generally 'cylindrical piston stop 95| extending upward from thetoprof the conduit 52 axially of the cylinder "50. The bottom edge of the piston stop 915 jis beveled as indicated by refererice numeral gli to form a downwardly and inwardly tapering surface having approximately the same incline as the taperedpiston section 'i6 and adapted 'to close-ly engage the latter in one position of the parts to substantially completely close the venturi l5. The top portion of the piston stop ed is slidably received within the bushing 88 and is provided with a pair of diametrically opposite grooves 93 in its side walls one of which slidably receives the key 8'!h to prevent rotation of the stop. The interior of 'the stop 94 is largely hollow providing a central cavity lill! therein which is reduced in size at its bottom portion and is connected to 'the thro-at of the venturi 'l5 by means of a plurality of downwardly inclined radial apertures 'H32 'opening into a groove |04 in the beveled edge 96 of the stop. As shown particularly in Fig. 7, I have provided eight such apertures H12 in the preferred form of apparatus disclosed herein although any suitable number may be provided, and it will also be particularly noted that the outlet groove |04 is adapted to be substantially completely closed by the inner face of the tapered piston section 'I6 when the parts are together as shown for example in Figs. 1, 6, and 7.

The inside of the top en'd of the conduit e2 is also threaded as indicated by reference numeral |96 in Figs. 3 and 6 for engagement with similar threads formed on the outer periphery of the reduced center portion |08` of a generally cylindrical jet body Hl which extends axially upward within the cavity ll'. The upper portion of the jet body l iii is of slightly smaller external dimensions than the cavity so as to form an annular space l2 therebetween. The top vof the jet body EEB is externally threaded to receive va large nut H5, having a tapered lower vedge ile adapted to cooperate with a similarly tapered surface H3 formed within the cavity for controlling the admission of air from the inlet 2e to the annular space H2 and apertures |02. A suitable loclrnut is provided above the nut lill for securing the latter in position after the desired adjustment has been made.

The jet body lli) is 'provided at its lower end with a further reduced portion |22 extending downwardly within the conduit 62 so dimensioned as to provide an annular chamber l2@ therebetween adapted to trap and to retain a certain volume of air or other gas therein. The interior of the jet body l l) is provided with an axial bore |26 extending completely therethrough and providing a metering orifice |28 at its bottom end. A plurality of downwardly inclined radial jets |353 are formed in the body Il!) and serve to connect the bore to the annular space H2. It will be noted that jets 30 are preferably equal in number to the apertures ||l2 and are positioned in such manner as to open directly into the latter.

The metering orifice |28 at the bottom of the bore E26 is under the control of a tapered plunger |32 which extends upwardly through the bore ist and Yis adjustably secured at its top portion by means of a pair of nuts |34 and |35 to a transverse plunger har |38. The plunger bar |33 in turn is attached preferably at four points to the piston 'ill for movement with the latter as shown particularly inrFigs. 1 and 2 is mounted as by means of suitable screws IMJ upon the top flanges |152 "of 'generally dhdnnel lsl'la'pe'd ksupports or brackets ldd preferably formedo'f brass, copper, or the like, havingsiniilar flanges llt at their lower ends for attachment to the upper surface of the piston floor l2 as by means of screws |43. The outer ends of the bar |1358"are preferably slotted as indicated at |56 frattachinent to vflanges 52 formed at the top edge of the vertical wall portion it of the piston 'I fl 'ais by means of suitable screws |54. The cylindrical upper portion of 'the plunger lei is freely slidable within an aperture formed in a washer |56 which rests upon the top surface of the jet body HB and thus serves rto practically close the bore |26 in the latter against the admiss'ion'of air thereto.

From the descriptionthus far it will be apparent that the piston "lll is reciprocable within the cylinder lEl and that as it does so, the tapered intermediate section 16 of the piston moves relative to the piston stop Se which is mounted in relatively fixed position by means of the conduit G2. [is the piston 'lll reciprocates it carries with it the plunger lli which moves through the bore i2@ to vary the amount of opening at the metering orifice |38 in accordance with the position'of the piston le. The working chamber e6 within the cylinder ill above the piston 'is of course open to atmospheric air pressure from the inlet 2B at substantially all times except when the choke valve 22 is closed. v

In order to effect reciprocation of the piston 10 the working chamber 68 of the cylinder below the piston is connected to the mixture outlet 28 by means of a lrelatively large passage |58 preferably formed integrally with the cylinder casting Ill and having an opening lil into the mixture outlet 28 above or on the upstream side of the throttle valve 313. The effective `size of the opening |63 is capableof vaislju'stment by means of a threaded needle valve|-62 provided with a spring |64 and movable in or out to provide a variable restriction in the passage |58. A similar passage 6B also preferably'formed integrally at the righthand side of the lower part of the'cylindercasting lll and having an opening |68 into the mixture outlet .28 serves to connect the working chamber 68 below the piston 19 with the outlet 28 at a point below or on the downstream side of the throttle valvel. The passage |66 is also provided with .a variable restriction therein preferably in the form of a needle valve I'ltl pressed outwardly as by means'of a spring |72 but, as will be explained in the description of the operation of the device as set forth in detail below, the function of the passage |68 is substantially different from thatof the passage |58. In both cases, however, these passages |58 and |65 serve to connect the working chamber Gil below the piston 'i6 to the suction or vacuum produced in the intake manifold of the internal combustion engine upon which the carburetor is mounted and thus provide for downward movement of the piston |0 under atmospheric pressure introduced through the Ainlet 2|) to the working chamber 66 above the piston.

As indicated above, the mixture outlet 28. is under the control of a throttle valve designated generally by reference numeral 34 the specific structural details of which are best illustrated in Figs. 8 and 9. As shown in these views the throttle valve 3d is seen'to comprise a generally circular disc or plate |'|4 vattached in any convenient manner as by means k,of a pair of Screws |15 to a flattened* portionrjllY of ash'aft |89. The shaft lso is rotatably mounted within'a, edncentric outer shaft |82 having its central portion cut away throughout the major extent of its periphery to leave a connecting part |84. 'The cut away portion of the outer shaft |82 provides a relatively large gap or opening to accommodate considerable relative rotational movement of the value plate |'|4 and its associated shaft |80 therein. The valve plate |14 is yieldably connected to the part |84 of the outer shaft |82 by means of a spring |66 extending between a lug |88 on the plate |14 and a similar lug |96 on the connectingr part |84 of the outer shaft |82.

The throttle valve plate |14 is also provided with another lug |92 similar to the lug |88 but at the opposite side of the concentric shafts |80--|82. The lug |92 as shown in Fig. 1 is connected to a projecting ear |94 formed at the lower edge of the tubular skirt portion 18 of the piston 'I0 by means of a tie rod |96 which passes through a suitable aperture in the ear |94 and is provided with a stop nut |98 at its top end constituting a one-way abutting connection between the tie rod |96 and the ear |534. The outer shaft |82 of the throttle valve is provided with an arm 2G@ (Fig. 8) adapted to be connected in any suitable manner to the accelerator or other similar throttle control means of the engine with which the carburetor is to be used, and it will now be apparent that as long as the piston 1|! is in a lowered position so that the tie rod |96 is free to move downwardly relative to the ear |94, rotation of the outer shaft |32 by means of the arm 266 will result in corresponding movement of the throttle valve plate |14 by means of the interconnecting spring |86. In the event the piston is fully elevated in the position as shown in Fig. 1 it will be clear that rotation of the outer shaft |82 merely resuits in tensioning the spring |86 so that the throttle valve cannot be opened suddenly unless the piston l@ has first been substantially lowered.

As it is intended that the improved carburetor in accordance with the present invention may be employed in substantially any type of automotive installation it may be desirable in certain cases where extremely rough operation and relatively severe vertical loads are imposed upon the structure to provide some means for counterbalancing the piston I6. Thus in certain cases, as for example where the carburetor is to be mounted upon a tractor engine, I have provided a generally tubular guide 262 securely attached in a generally vertical position in any suitable manner as by welding or the like to one of the arms 84 and in which a weight 2M is adapted to freely reciprocate. The weight 2114, which is suitably selected to approximately equal the weight of the piston assembly, is attached to one end of a cable or flexible line 206 which extends over a sheave 208 rotatably mounted at the top of the guide 202, and the opposite end of the line 236 is connected to the piston 'i at any convenient point such as for example the screw |48. The weight 204 th-us serves to counterbalance any momentum effect of the piston 'Hl under vertical forces imposed a downward direction.

The mode of operation of the device described above may now be set forth in broad terms as follows: Referring particularly to Figs. 1 and 6 the various parts are illustrated in the position which they occupy when the engine is at rest or not operating. It will be noted that the piston is in its upper limit position with the tapered alii intermediate section 16 thereof resting against the beveled edge 96 of the piston stop 94, being held in that position by the tension of the springs 80. The level of liquid fuel within the float chamber 36 is just slightly below the level of the jets |36, and the passages 52 and 56 as well as the conduit 62 and annular space |26 are filled with the liquid fuel up to this same level.

When the engine is started in operation, the various movable parts of the carburetor generally assume the positions as illustrated in Figs. 2 and 3. At this time a certain amount of vacuum from the engine is applied through the passages |58 and |66, respectively above and below the throttle valve 34, to the lower working chamber 68 of the cylinder I6 so tha-t the piston 'l0 is moved downwardly a slight amount in response to the atmospheric pressure of air admitted through the inlet 26 to the upper working chamber Gil. At the same time atmospheric air admit-ted through the inlet 20 commences to flow through the Venturi passage 15 formed between the tapered intermediate piston section 'l and the piston stop 34, creating a low-pressure area at the space between the beveled edge 96 of the stop 94 and the tapered section T6 in accordance with the usual and well-known principles of fluid flow. Liquid fuel from the float chamber 36 is thus induced to flow through the passages 52 and 56, the conduit t2, past the metering orice |28, through `the annular space |26, the jets |36, and the apertures |62 to the groove illl adjacent this region of low pressure. At this point the liquid fuel is vaporized and mixed with the air and subsequently passes downwardly through the tubular skirt lil and mixture outlet 28 to the engine. As mentioned previously a substantially constant level of liquid fuel is maintained in any suitable manner within the float chamber 36 so that as long as the engine is operating and suction is maintained thereby within the lower operating chamber 68 of the cylinder a continuous mixture of liquid fuel and air will take place within the venturi l5 and be supplied to the engine for combustion.

The foregoing explanation of the method of operation of my improved carburetor constitutes a rather general statement of operation, whereas in the following description the various refinements and improvements which I have provided will be referred to in greater detail. Assuming the engine to be cold prior to starting, the temperature compensating devices are effective to provide an enriched mixture in the following manner. which the piston stop 5M is mounted is preferably made of a material such as brass or copper having a relatively high coefcient of expansion as compared to the steel cylinder lil. Accordingly, when both the carburetor and engine are relatively cold the conduit t2 will be contracted axially or longitudinally of the cylinder l to a slightly greater extent than normal, thus lowering the piston stop S4 and jet body l It and with the latter the jets |60. Thus one effect of the slight extra contraction of the conduit 62 is to lower the position of the jets |30 relative to the liquid fuel level within the oat chamber 36 to thereby increase the effective operating head of the liquid fuel and so enrich the mixture.

At the same time such contraction of the conduit 62 relative to the cylinder I6 results in a lowering of the piston l0 through the abutting contact of the tapered intermediate section 16 with the beveled edge 96 of the piston stop 94.

As mentioned above the conduit 62 on This lowering of the piston results in a slight stretching of the springs 80 causing the latter to operate over a different range which in accordance with the usual characteristics of such springs has the effect of slightly increasing the tension thereof. The effect of increasing the tension of the springs 8|! is to require more vacuum within the lower working chamber 63 in order to produce the required downward movement of the piston lll so that as a result the volume of air which can flow between the beveled edge 95 and the tapered section l5 will be reduced in comparison to the volume of liquid fuel discharged through the jets |30 thus also enriching the mix-ture.

Although the temperature compensating effect produced by expansion and contraction of the conduit 62 relative to the cylinder structure will be found to be adequate in certain installations, I have also provided additional temperature compensating means in the form of the brackets IM. As mentioned above, these brackets |44 are also preferably formed of brass, copper, or some other material having a relatively high coeflicient of expansion relative to the piston and cylinder structure. Thus when the engine is cold the brackets IM are in a slightly contracted condition causing the plunger bar |38 to be drawn slightly downward relative to the piston 'l0 and consequently relative also to the piston stop SLi. Such downward movement of the plunger bar |38 carries with it the plunger |32, causing the latter to move downward relative to the reduced portion |22 and orifice |28 which in turn results in increasing the effective area of the latter due to the taper of the plunger 32. This increase in the effective area of the metering orifice |28 operates to increase the proportion of liquid fuel available at the jets |30 or in other words has a tendency to enrich the mixture supplied to the cold engine.

In the preferred embodiment of the carburetor in accordance with the present invention I have disclosed the temperature compensating eects of the conduit 62 and brackets Idil as being jointly and simultaneously operative to provide an enriched mixture when the engine is `cold although it will be clear that either of these devices may be employed alone to produce a similar result. The reverse of this compensating action, that is to say, the production of a leaner mixture as the engine operating temperature gradually increases, is automatically attained in. each case. Accordingiy, as the engine commences to warm up the conduit 62 tends to expand at a greater rate than the cylinder lil which results in simultaneously raising the level of the jets |3ii relative to the iiuid level of the oat chamber 36 to decrease the effective head of fuel and to raise the stop 94, thus permitting the springs 8d to contract slightly and so operate within a lower tension range or in effect decreasing the spring tension. In similar manner as the engine warms up the brackets Mii also tend to expand at a greater rate than the piston l!) so that the plunger |32 is moved slightly upward relative to the metering orifice |28 to reduce its effective area and thus produce a leaner mixture.

It should also be noted in connection with the temperature compensating effect of the `conduit 62 that the temperature of the mixture as it passes downward around the conduit serves to produce a considerable :cooling effect upon the latter due to the latent heat of vaporization of the fuel, the amount of which will vary in accord- 10 ance with the amount of fuel and air being consumed by the engine. Inasmuch as the quantity of the fuel-air mixture being consumed varies almost directly with the amount of Work being done by the engine, it will be apparent that as.

the engine load increases the conduit |52 will be subject to an increased cooling effect. This increased :cooling effect upon the conduit $2 vthus operates to provide a relatively richer mixture under heavy engine loads and to lean out the mixture under relatively light loads by the same mechanical action which occurs in compensating for ordinary temperature changes.

In arriving at the proper design criteria :for the various elements of my improved carburetor .it must be borne in mind that the relative dimensions of the parte, the tension of the springs,fand the taper of the piston, piston stop, and plunger should be determined accordance with the fundamental concept of providing a correct fuelair mixture for any given set of conditions of constant engine speed and load throughout fthe range from idling to full speed and `no load 'to maximum load. Thus the taper of the plunger |32 will depend in a given case upon the size of the opening between the piston 10 and the piston stop 34 which in turn will vary with the tension of the springs and the weight of the entire piston assembly. The initial adjustment vtou-attain this correct fuel-air ratio vis obtained yby properly setting the nuts ld and |36 to position the plunger |32 within the metering orifice |28 in such manner as to properly meter the -flow of liquid fuel through the latter under a particular set of constant load and speed conditions. The taper of the plunger |32 will then properly vary the effective area of the metering orifice |28 in accordance with the position of the piston 1|) which in turn is determined by the :particular load and speed requirements of the engine at any given time. After this adjustment has once been made the metering action of the plunger |32 lis entirely automatic and although the pressure within the venturi l5 will vary only lslightly during operation, the volume of air drawn therethrough will of course vary greatly and will determine the extent of the fuel metering action 4fby controlling the position of the plunger |32 in accordance with the position of the piston 1l).

In order to permit proper adjustment `of vvthe position of the plunger |32 by means of the'nuts |34| 3B without regard to engine idling requirements, I have provided an auxiliary idling adjustment which may be independently set subsequent to the plunger adjustment. This idling adjustment is made by setting the nut IM and locking it in adjusted position by means of the locknut |20 in such manner as to control ythe relatively small volume of air flowing between the inclined surfaces It and Il and through the annular space I2 to the apertures |02. Since this 'volume of auxiliary air is relatively small compared to the volume of air passing through the venturi 1.5 under practically all operating conditions, fthe idling adjustment may be made subsequent to the adjustment ofthe plunger |32 without substantially affecting the operation of the latter. The auxiliary air admitted past the idle adjusting nut i4 is suitably proportioned relative to the effective area of the metering orifice |28 to provide for smooth engine operation at idling speed-or when the throttle valve 34 is practically closed, and it is to be particularly noted that this idling adjustment is accomplished entirely by modification of the lbasic or high speed jet @circuit without 11 requiring any additional idling or low speed jet circuit.

During normal carburetor operation under any particular xed set of conditions or at constant engine speed and load the air-fuel ratio of the carburetor is determined by the position `of the -piston 10 which controls the amounts of the Venturi air opening, and effective area of the metering -orice |28 and is in turn controlled -by the amount of suction or vacuum transmitted from the engine through the passages |58 and |66 to the lower working chamber 68 of the cylinder l0. The piston 'I0 under such fixed engine operating conditions accordingly will assume a position such as to provide a balance between the difference in air pressure in the chambers ltti and 68 above and below the piston, respectively, and the tension of the springs 88. In the event the engine vacuum should gradually increase Ior ydecrease, Ithe piston 'i8 will move slightly in response to the new conditions and will readj-ust itself automatically to provide the proper Afuel-air ratio. However, in the event the engine vacuum should increase, for example, and the piston l should be restrained against its automatic movement to a new balanced position for the altered engine operating conditions, it will be apparent that due to the relatively inelastic nature of the liquid fuel as compared with the relatively highly elastic air a greater volume of fuel will -be delivered at the jets |30 in comparison 4to the volume of air -owing past the venturi 15 under such increased vacuum. Stated in more general terms, it is thus possible to superimpose a mixture variation upon the carburetor over and above that automatically provided by the balanced position of the piston and plunger by any means which tends to restrain the piston 'l0 against such automatic movement.

One of the principal reasons for superimposing an additional controlled effect upon the movement of the piston 'I0 is to provide a slightly enriched mixture during engine acceleration. As one means of accomplishing this result, I have provided the adjustable needle valve |62 which presents a variable restriction within the passage |58 connecting .the lower working chamber B8 of the cylinder I0 with the mixture outlet 28 above the throttle valve 34. As the throttle valve 34 is opened for acceleration the vacuum above the throttle valve is momentarily `increased thus tending to produce a relatively larger air ow through the venturi 15 which -in turn produces a higher suction at the Venturi throat and a greater ow of liquid fuel through the jets |30 and apertures |02. However, because of the restriction presented by the needle valve |62, IJthis increased vacuum is not immediately effective upon the piston 10 so that a time `delay is introduced in the downward movement of the latter. The amount of this time delay is of course determined by the amount of the restriction imposed by the needle valve |62 within the passage |58 and is so calculated as to provide for an increase in the volume of liquid fuel flow `as compared to the volume of air flow for -a sufficient interval of time to permit the enriched `mixture to be effective during the period of acceleration. The increased engine vacuum will of course gradually become fully effective within the lower working chamber `68 of the cylinder Ill, thus causing the piston 'l0 to ultimately assume a new balanced position wherein the fuel-air ratio is determined by the respective size of the openings of the venturi 'andthe metering orifice |28.

retors.

TheY .passage U66 opening at |68 into the mixture outlet 28 below the throttle valve 35i is intended primarily to function as a load regulating device. Thus when 4the throttle valve is substantially fully closed there will be practically no vacuum thereabove so that the passage |58 despite its large size will be relatively ineffective to more the piston lil downward. A very small suction effect is accordingly provided through the passage I'S under the control of the needle valve ift so that under any constant engine load and speed a slight additional suction is operative upon the piston '10. It will be apparent that when the throttle is substantially fully closed the vacuum -below the throttle `valve is relatively very high as compared with the vacuum above the thr tle valve so that the additional suction effect illO- duced by the passage |66 will be relatively high under no load engine conditions. On the contrary, when the engine is under heavy load and the throttle valve 34 substantially fully opened the vacuum differential above and below the throttle valve is quite small so that the additional suction effect of the passage tot is negligible. It will thus be apparent that the passage it operates as a load control having an effect upon the piston 'i0 such as to produce a slightly richer mixture under high engine load conditions than under low engine load conditions. An additional effect of the passage L86 should vbe noted in connection with its effect upon the 'piston lil under acceleration. When the throttle valve Se is opened suddenly the pressure within lthe outlet 28 below the throttle valve tends to increase so that during the acceleration period a relatively smaller degree of suction will be transmitted through the passage i with the result that the piston 'fil will not be urged downwardly thereby at as great a rate as runder closed throttle conditions.

As my improved carburetor is particularly adapted for use upon an automotive vehicle it will be apparent that the motion of the vehicle itself during sudden acceleration will `tend to introduce a time lag in operation of the piston l due to the greater friction effect of the latter caused by its inertia. In addition to this inertia effect, I have also provided the ring E@ of a relatively heavy lor dense material which surrounds the depending tubular skirt i3 of the piston and which will :be moved due to its inertia upon vehicle acceleration to increase the effective weight of the piston 'e0 and thus mechanically impose a further delay or time lag upon movement of the latter during the acceleration period.

All of the factors mentioned above as having a control eifect upon the piston it to enrich the carburetor mixture during acceleration are equally effective under conditions of deceleration to provide a leaner mixture during such period. In other words, the effect of each of the instrumentalities described above during deceleration is substantially equal and opposite to its effect under acceleration conditions.

Disregarding for a moment the various factors tending to restrict the motion of the piston 'lil under acceleration it will be noticed that as the throttle valve 34 is opened causing the piston lli to move downward the plunger |32 also moves downward into the conduit 62 and in this respect operates somewhat similarly to the usual acceleration pump provided in conventional carbu- However, as the requirements for liquid fuel is suddenly increased at this time, there is a certain amount of inertia in the fuel itself which tends to delay its action in reaching the jets l30. At this time the air or other gas trapped within the annular space H24 lying between the reduced bottom portion H22 of the jet body and the conduit 62 operates to cushion and smooth the operation of the fuel circuit due to the elasticity of the gas therein which permits it to expand. The air or gas within the annular space |24 is ordinarily trapped therein from the usual air or gas bubbles occluded with the liquid fuel during normal carburetor operation and is thus continuously replenished.

It will be apparent from a consideration of the control eiects described in connection with the above instrumentalities which operate to enrich the carburetor mixture under acceleration conditions that under certain circumstances such, for example, as a very rapid opening of the throttle valve at very low speed the mixture might be unduly richened thereby wasting fuel and adversely affecting acceleration. In order to guard against this eventuality I have provided the impositive throttle valve mounting having a oneway abutting connection with the piston lil. The eiIect of this throttle valve arrangement is to prevent the throttle valve from opening too Wide before the engine speed has increased sufliciently. Thus at very low engine speeds and corresponding high manifold vacuum, operation of the arm 263i! by the engine accelerator rotates the outer shaft |82 and by means of the spring connection E86 tends to rotate the valve plate l'lbl upon its shaft 853. However, the valve plate IM is prevented irom rotating (counterclockwise in Fig. l) when the piston lil is in raised position due to the fact that the stop nut E98 abuts against the ear left which restrains the valve plate lill by means of the tie rod 95. The effect of a sudden throttle opening is thus to open the throttle valve slightly and impose a tension upon the spring l tt, the valve plate El@ opening somewhat more gradually as the piston 'lll moves downward.

An additional operational advantage of my improved throttle valve structure is found in the fact that it provides for automatic engine stalling under extreme or harmful load conditions. The throttle valve and tie rod dimensions are so proportioned that when the valve is open a substantial amount, the piston l@ must be down a certain distance suicient to accommodate such opening. Thus if the engine should slow down under extremely heavy load while the throttle valve is retained in approximately wide open position, the piston 'lu will gradually move upward in the cylinder Iii to a point where it will engage the stop nut w8 and start to close the valve plate Hd. If the overload upon the engine is main tained the throttle valve will eventually be substantially completely closed in this fashion so that the engine will be unable to operate.

It will be noted that in the operation oi the jet structure of my improved carburetor the liquid fuel admitted through the conduit 6E and jets l 3G is subjected to a slight mixing action within the apertures IiiZ by the auxiliary air admitted through the annular passage l l2. In addition to this mixing action the fuel as it leaves the groove llll in the beveled edge 55 is relatively widely dispersed about the sharp edge of the latter and accordingly Will be more finely vaporill-ed mixes with the air in the Venturi throat than is the case where a single jet is employed. My improved jet structure in addition to giving a more completely vaporized mixture also tends to retain the richer portion toward the center of the outlet Z8L andthus tends to discourage con,- densation on the sides thereof.

Obviously numerous other modiications, a1- terations, and deviations from the specific structure disclosed herein as a preferred embodiment solely for the purpose of illustration will occur to one skilled in the art and it is to be understoody that numerous changes can be madein size, ma,- terials, and arrangement of parts without departing from the principles of this invention as set forth in the appended claims.

Having thus described my invention, what I claim as novel and desire to secure by Letters Patent of the United States is:

1. A downdraft carburetor comprising, a cylinder having an inlet at its upper end and a .mixture outlet at its lower end provided, with a throttle valve therein and adapted to be connected to the intale ma bustion engine, a piston reciprocable Within said cylinder including a tapered intermediate section having a depending tubular skirt reciprocable within said outlet, a plurality of springs sup.- porting said piston from the upper portion of said cylinder, a float chamber formed atone side of said cylinder and providing a substantially constant level of liquid fuel therein, a tubular conduit connected to said float chamber and mounted in said outlet to extend axially upward adjacent the center of said cylinder, a generally cylindrical piston stop mounted on the top of said conduit having a beveled lower edge and including a central cavity having a plurality of radial apertures extending therefrom to said beveled edge, a generally cylindrical jet body secured in said cavity with a reduced diameter lower portion extending downwardly intov said conduit including an axial bore therein having a metering oriiice at its lower end and a plurality of radial jets connected to said bore and opening into said apertures, a plunger bar mounted on said piston, a 'tapered plunger adjustably secured to said bar and extending through said orifice, and an air passage interconnecting the interior of said cylinder below said piston and said outlet above said throttle valve whereby said piston may move in response to the pressure dierential between said inlet and said outlet.

2. A carburetor comprising, a cylinder having an air inlet and a mixture outlet provided with a throttle valve therein and adapted to be connected to the .intake manifold of an internal combustion engine, a piston reciprocable Within said cylinder including a tapered intermediate section and a depending tubular skirt reciprocable within said outlet, resilient means for supporting said piston within said cylinder, a conduit mounted to extend axially adjacent the center of said cylinder, means for supplying liquid fuelto said conduit, a generally cylindrical piston stop mounted on the top of said conduit havingl a beveled lower edge and including a central cavity having a plurality of radial apertures extending therefrom to said beveled edge, a generally cylindrical jet body secured in said cavity with a reduced diameter lower portion extending downwardly into said conduit including an axial bore therein having a metering orice at its lower end and a plurality of radial jets connected to said bore and opening into said apertures, a plunger bar mounted on said piston, a tapered plunger adjustably secured` to-said bar and extending through said orice, and an air passage interconnecting the interior of said cylinder below'said piston and saidoutlet above said;l

old of, an internal com-v throttle valve whereby said piston may move in response to the pressure differential between said inlet and said outlet.

3. A carburetor comprising a cylinder having an air inlet and a mixture outlet provided with a throttle valve therein and adapted to be connected to the intake manifold of an internal combustion engine, a piston reciprocable within said cylinder including a depending tapered section, resilient means for supporting said piston within said cylinder, a conduit mounted to extend axially adjacent the center of said cylinder, means for supplying liquid fuel to said conduit, a piston stop having a beveled lower edge and including a central cavity connected to said conduit and having a plurality of radial apertures extending therefrom to said beveled edge, a jet body secured in said cavity with a reduced diameter lower portion extending downwardly into said conduit including an axial bore therein having a metering orifice at its lower end and a plurality of radial jets connected to said bore and opening into said apertures, a plunger bar mounted on said piston, a tapered plunger adjustably secured to said bar and extending through said orifice, and an air passage interconnecting the interior of said cylinder below said piston and said outlet above said throttle valve whereby said piston may move in response to the pressure diierential between said inlet and said outlet.

e. A carburetor comprising, a cylinder having an air inlet and a mixture outlet provided with a throttle valve therein and adapted to be connected to the intake manifold of an internal combustion engine, a piston reciprocable within said cylinder including a depending tapered section, resilient means for supporting said piston within said cylinder, a conduit mounted to extend axially adjacent the center of said cylinder, means for supplying liquid fuel to said conduit, a piston stop having a beveled lower edge and including a central cavity connected to said conduit and having a plurality of radial apertures extending therefrom to said beveled edge, a jet body secured in said cavity with a reduced diamete-r lower portion extending downwardly into said conduit including an axial bore therein having a metering orifice at its lower end and a plurality of radial jets connected to said bore and opening into said apertures, a tapered plunger having mechanical connection with said piston and extending through said orifice, and an air passage interconnecting the interior of said cylinder below said piston and said outlet above said throttle valve whereby said piston may move in response to the pressure differential between said inlet and said outlet.

5. A carburetor comprising, a cylinder having an air inlet and a mixture outlet provided with a throttle valve therein and adapted to be connected to the intake manifold of an internal combustion engine, a piston reciprocable within said cylinder including a depending tapered section, a conduit mounted to extend axially within said cylinder, means for supplying liquid fuel to said conduit, a piston stop having a beveled edge and including a central cavity connected to said conduit and having a plurality of radial apertures extending therefrom to said beveled edge, a jet body secured in said cavity and forming with the latter an annular space connecting said a-pertures to said air inlet, adjustable means for controlling the admission of air to said space, said body further including a lower portion extending downwardly into said conduit of smaller diameter than the latter to form an air chamber therebetween, an axial bore in said body providing a metering orifice in said lower portion, and a plurality of radial jets opening from said bore into said apertures, a tapered plunger having mechanical connection with said piston and extending through said orice, resilient means urging said tapered section against said beveled edge, and an air passage interconnecting the interior of said cylinder below said piston and said outlet above said throttle valve whereby said piston may move in response to the pressure differential between said inlet and said outlet.

6. A carburetor comprising, a cylinder having an air inlet and a mixture outlet provided with a throttle valve therein and adapted to be connected to the intake manifold of an internal combustion engine, a piston reciprocable within said cylinder including a depending tapered section, a conduit mounted to extend axially Within said cylinder, means for supplying fuel to said conduit, a piston stop having a beveled edge and including a central cavity connected to said conduit and having a plurality of radial apertures extending therefrom to said beveled edge, a jet body secured in said cavity and forming with the latter an annular space connecting said apertures to said air inlet, adjustable means for controlling the admission of air to said space, an axial bore in said body having a metering orince therein and a plurality of radial jets opening from said bore into said apertures, a tapered plunger having mechanical connection with said lpiston and extending through said orice, resilient means urging said tapered section against said beveled edge, and an air passage interconnecting the interior of said cylinder below said piston and said outlet above said throttle valve whereby said piston may move in response to the pressure differential between said inlet and said outlet.

7. A carburetor comprising, a cylinder having air inlet and a mixture outlet provided with a throttle valve therein and adapted to be connected to the intake manifold of an internal combustion engine, a piston reciprocable within said cylinder including a depending tapered section, a conduit mounted to extend axially within said cylinder, means for supplying fuel to said conduit, a piston stop having a beveled edge and including a plurality of radial apertures connected to said conduit and extending therefrom to said beveled edge, means forming a metering orice between said apertures and said conduit, a tapered plunger having mechanical connection with said piston and extending through said orifice, resilient means urging said tapered section against said beveled edge, and an air passage interconnecting the interior of said cylinder below said piston and said outlet above said throttle valve whereby said piston may move in response to the pressure dierential between said inlet and said outlet.

8. A carburetor comprising, a cylinder having an air inlet and a mixture outlet provided with a throttle valve therein and adapted to be connected to the intake manifold of an internal combustion engine, a piston reciprocable within said cylinder and having an opening in its center portion, a conduit mounted to extend axially within said cylinder, means for supplying fuel to said conduit, a piston stop adapted to contact said piston adjacent said opening and including a plurality of radial apertures connected to said conduit and extending therefrom to the contact region of said piston and said stop, means forming a metering orifice between said apertures and said conduit, a tapered plunger having mechanical connection with said piston and extending through said orifice, resilient means urging said piston against said stop, and an air passage interconnecting the interior of said cylinder below said piston and said outlet above said throttle valve whereby said piston may move in response to the pressure differential between said inlet and said outlet to cause said plunger to variably meter the quantity of fuel flow through said orifice in accordance with the volume of air now Vpast said apertures to automatically maintain a correct fuel-air ratio at various engine speeds.

9. A carburetor comprising, a cylinder having an air inlet and a mixture outlet provided with a throttle valve therein and adapted to be connected to the intake manifold of an internal combustion engine, a piston reciprocable within said cylinder and having an opening in its center portion, a piston stop adapted to contact said piston adjacent said opening and including a plurality of radial apertures therein, means for supplying fuel to said apertures, a metering orince interposed between said fuel supplying means and said apertures, a tapered plunger a ing mechanical connection with said piston and extending through said orifice, resilient means urging said piston toward said stop, a rst air passage extending from the interior of said cylinder below said piston to said outlet above said throttle valve, adjustable means for restricting iiow through said lirst passage, a second air passage extending from the interior of said cylinder below said piston to said outlet below said throttle valve, and adjustable means for restricting flow through said second passage, said piston and plunger being simultaneously movable in response to vacuum transmitted through said first passage to maintain a correct fuel-air ratio at various engine speeds and being simultaneously movable in response to vacuum transmitted through said second passage to vary said fuel-air ratio under varying conditions of engine load.

10. A carburetor comprising, a cylinder having an air inlet and a mixture outlet provided with a throttle valve therein and adapted to be connected to the intake manifold of an internal combustion engine, a piston reciprocable within said cylinder having an opening in its center portion, a piston stop adapted to contact said piston adjacent said opening and including a plurality oi radial apertures therein, means for supplying fuel to said apertures, a metering orifice interposed between said fuel supplying means and said apertures, a tapered plunger having mechanical connection with said piston and extending through said orifice, means urging said piston toward said stop, a first air passage extending from the interior of said cylinder below said piston to said outlet above said throttle valve, adjustable means for restricting flow through said rst passage, and a second air passage extending from the interior of said cylinder below said piston to said outlet below said throttle valve, said piston and plunger being simultaneously movable in response to vacuum transmitted through said rst passage to maintain a correct fuel-air ratio at Various engine speeds and being simultaneously movable in response to vacuum transmitted through said second passage to vary said fuel-air ratio under varying conditions -of engine load.

11. A carburetor comprising, a cylinder having an inlet and an outlet provided with a throttle valve therein and adapted to be connected to van internal combustion engine, a piston recipkrocable within said cylinder having an opening in its center portion, a piston stop adapted to contact said piston adjacent said opening and including a plurality of radial apertures therein, means for supplying fuel to said apertures, a metering orifice interposed between said fuel supplying means and said apertures, a tapered plunger having mechanical connection with said piston and extending through said orice, means urging said piston toward said stop, a passage extending from the interior of said cylinder below said piston to said outlet above said throttle valve, and adjustable means for restricting ow through said passage, said piston and plunger being simultaneously movable in response to vacuum transmitted through said passage to maintain a correct fuel-air ratio at various engine speeds.

12. A carburetor comprising, a cylinder having an inlet and an outlet provided with a throttle valve therein and adapted to be connected to an internal combustion engine, a piston reciprocable within said cylinder having an opening therein, a piston stop adapted to contact said piston adjacent said opening and including an aperture therein, means for supplying fuel to said aperture, a metering orifice interposed between said fuel supplying means and said aperture, a tapered plunger having mechanical connection with said piston and extending through said orice, means urging said piston toward said stop, and a passage extending from the interior of said cylinder below said piston to said outlet above said throttle valve, said piston and plunger being simultaneously movable in response to vacuum transmitted through said passage to maintain a correct fuel-air ratio at various engine speeds.

13. A carburetor comprising, a cylinder having an outlet adapted to be connected to an internal combustion engine, a piston reciprocable within said cylinder including a tubular Skirt reciprocable within said outlet and deiining an'opening in said piston, a piston stop engageable'with said piston to vary the size of said opening and including an aperture therein, means for supplying fuel to said aperture, a metering orice interposed between said fuel supplying means and said aperture, a tapered plunger having mechanical connection with said piston and extending through said orice, means urging said piston toward said stop, a counterbalance connected to said piston for resisting vertical inertia forces thereon, a ring of heavy material loosely surrounding said skirt and engageable with the latter by inertia to increase the effective weight thereof under horizontal acceleration loads, a throttle valve in said outlet, means impositively interconnecting said skirt and said valve to limit opening movement of the latter in accordance with the position of said piston, and a passage extending from the interior of said cylinder below said piston to said outlet above said valve whereby.

said piston and plunger may move simultaneously in response to vacuum transmitted through said passage to maintain a correct fuel-air ratio at various engine speeds.

14. A carburetor comprising, a cylinder having an `outlet adapted to be connected to an internal combustion engine, a piston reciprocable within said cylinder including a tubular skirt reciprocablewithin said outlet and defining an opening in said piston, a piston stop engageable with said piston to vary the size of said opening and including an aperture therein, means for supplying fuel to said aperture, a metering orice inter- .vposed between said fuel supplying means and saidiaperture, a tapered plunger having mechanical connection with said piston and extending through said orifice, means urging said piston toward said stop, a ring of heavy material loosely surrounding said skirt and engageable with the latter by inertia to increase the effective weight thereof under horizontal acceleration loads, a throttle valve in said outlet, means impositively interconnectingr said skirt and said valve to limit opening movement of the latter in accordance withl the position of said piston, and a passage extending from the interior of said cylinder below 4said piston to said outlet above said valve whereby `reciprocable within said outlet and dehning an opening in said piston, a piston stop engageable with said piston to vary the size of said opening and including an aperture therein, means for supplying fuel to said aperture, a metering orice interposed between said fuel supplying means and said aperture, a tapered plunger having mechanical connection with said piston extending through said orifice, means said piston toward said stop, a throttle valve in said outlet, means impositively interconnecting said skirt. and said valve to limit opening movement of the latter in accordance with the position of said piston, and a passage extending from the interior of said cylinder below said piston to said outlet above said valve whereby said piston and plunger may move simultaneously in response to vacuum transmitted through said passage to maintain a correct fuel-air ratio at various engine speeds.

1,6. A carburetor comprising, a cylinder having an outlet adapted to be connected to internal combustion engine, a piston reciprocable Within said cylinder having an opening therein, a piston stop engageable with said piston to vary lthe size of said opening and including an aperture therein, means for supplying fuel to said aperture, a metering oriiice interposed between said; fuel supplying means and said aperture, means having mechanical connection with said piston for varying the eifective size of said orifice, means urging said piston toward said stop, and a.. passage extending from the interior of said cylinder below said piston to said outlet whereby said piston may move in response to vacuum transmitted through said passage tomaintain a correct fuel-air ratio at various engine speeds. 1.7. A carburetor comprising, a cylinder having an outlet adapted to be connected to an internal combustion engine, a piston reciprocable within said cylinder having an opening therein., a fuel supply conduit secured to said cylinder, a` piston stop mountedon said conduit and erigageable with said piston to vary the size of said opening, said stop including an aperture opening into said conduit, a metering orifice in said conduit, a tapered plunger loperatively associated with said orifice for varying the effective size thereof, bracket means mounting `said plunger on said piston, means urging said piston toward said stop, and a passage extending from the interior of said cylinder below said piston to said outlet for applying vacuum to said piston to simultaneously vary the size of said opening and of said orice, said conduit and said bracket means being made of a material having a coecient of expansion different from that of said piston and cylinder whereby slight relative movements between said plunger and oriiice are eifected in response to temperature changes to automatically vary the fuel-air mixture in accordance therewith.

18. A carburetor comprising, a cylinder having an outlet adapted to be connected to an internal combustion engine, a piston reciprocable within said cylinder having an opening therein, a fuel supply conduit secured to said cylinder, a piston stop mounted on said conduit and engageable with said piston to vary the size of said opening, said stop including an aperture opening into said conduit, a metering orifice in said conduit, means for varying the effective size of said orice, means urging said piston toward said stop, and a passage extending from the interior of said cylinder below said piston to said outlet for applying vacuum to said piston to simultaneously vary the size of said opening and of said orice, said conduit being made of a material having a coefcient of expansion dii'- ferent from that of said cylinder whereby slight relative movements between said plunger and orice are eifected in response to temperature changes to automatically vary the fuel-air mixture in accordance therewith,

19. A carburetor comprising, a cylinder having an inlet and an outlet provided with a throttle valve therein and adapted to be connected to an internal combustion engine, a piston reciprocable within said cylinder having an opening therein, a piston stop adapted to contact said piston adjacent said opening and including an aperture therein, means for supplying fuel to said aperture, a metering orice interposed between said fuel supplying means and said aperture, a plunger having a substantially cylindrical upper portion and a variably tapered lower portion, said plunger having mechanical connection with said piston and extending through said orifice, a washer surrounding the cylindrical portion of said plunger for preventing the admission of air to said orice, means urging said piston toward said stop, and a passage extending from the interior of said cylinder below said piston to said outlet above said throttle valve, said piston and plunger being simultaneously movable in response to vacuum transmitted through said passage to maintain a correct fuel-air ratio at various engine speeds.

20, A carburetor comprising, a cylinder having an inlet and an outlet provided with a throttle valve therein and adapted to be connected to an internal combustion engine, a piston reciprocable within said cylinder having an opening therein, a piston stop adapted to contact said piston adjacent said opening and including an aperture therein, means for supplying fuel to said aperture, a metering orice interposed between said fuel supplying means and said aperture, a plunger having a substantially cylindrical upper portion and a variably tapered lower portion, said plunger having mechanical connection with said piston 21 22 and extending through said orifice, means urging said piston toward said stop, and a passage eX- REFERENCES CITED tending from the interior of said cylinder below The following references are of record in the said piston to said outlet above said throttle valve, le of this patent: said piston and plunger being simultaneously 5 UNITED STATES PATENTS movable in response to Vacuum transmitted through said passage to maintain a correct fuel- Number Name Date air ratio at various engine speeds. 1,995,110 Wahlmark Mar. 19, 193:; CHESTER W. BROWN, 2,393,118 Oswald Jan. 15, 1946

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