US2646264A - Self-feeding carburetor for internal-combustion engines - Google Patents

Description

\ 8 2 2 ...6. m l J: x 4/0 .n '--w 2 i .M F B mv. O2 2 o I 4 f 3 1 9 IJ. N. MORRIS Filed June 1, 1950 July 21, 1953 SELF-FEEDING CARBURETOR FOR INTERNAL-COMBUSTION ENGINES Inventor T0/417 /V /Varr/L g By Mz f4/ llorney adjustable venturi is so designed as to afford yat duction depression suiciently greatjtocaterfor: pany contingencylikely to arise, this eiipedient would cause some loss of engine power by unduly restricting thecharge and would' detractfunacf- Patented July ,Y 1795-3 t PATENT; oFFlcE SELF-FEEDING LCARBURE'rolt Fon,

INTERNAL-COMBUSTION ENGINES John N. Morris,` Birmingham, England, assignerr tolThe S. U. Carburetter Company Limited,

Birmingham, England 'Application June 1, 195o, serial No. 165,408 Y VIn Great Britain September, 19459 6 Claims.A (o1. zei- 44)V This invention rrelates to self-feeding carburetors forvinternal combustion engines, and,A more specifically, is concerned with vcarburetor-s of thekind in which the contents of the iioat chamber V are subjected'tothe depressionv produced by a venturi ,or variable effective cross-sectionall area which, together with a .tapering needle controlling a main metering jet, is adjustable by pressure-responsive means movable in response to l: variation of the Vpressure drop established by the venturi. j Y

A carburetor of the kind in question is disclosed in the specification of .Patent No. 2,167,892. Its

all times a substantially constant correlation be-V l" tween the depression existing immediately at the up-streamside of rthe engine throttle and that at some particularcross-section of the venturi, the' depression available at that sectionibeing maintained substantially at the minimum value sufficient to raise liquid fuel from a-tank situated at a lower level than the carburetor, without the aid of an extraneous fuel pump.` i

When employed in motor vehicles, the earlier form of carburetor referredto'has beenvfound to function very satisfactorily-so long as the vehicle 'Y is not ascendinga severe gradient.' Uponsuch an f ascent being undertaken the carburetor operates with the drawback of .a very adverse suction head, and this condition is,q of course, worsened "the 3U longer the wheeli'base vofthe vehicle. Although continuityoffuel-feeding in that case couldrbe'i. achieved by so proportioning the Aifactors involvedf` .V thatAtli-e carburetor always operated lwithan incceptably from the. eiciency'of the Vcarburetor under normal running conditfmg v f 40 The drawback mentioned above islobviated byf means of the present invention, which lprovides that whenever thefloat chamber level becomes abnormally low due toa change from the normal sponsive means'tothat obtaining in the venturi, '50

withY the result 'that thel pressure-responsive A means initiates a reduction-of the effective crossf sectional area 'of .the ventur`,-with'.consequent in- -f crease in the depression therein and in thefloat chamber suicient to recommence inspiration of 55 fuel, whereupon the emergency control device becomes arrested in its obstructive action. V-To this end, a carburetor in accordance with thepresent invention comprises -a suction chamber containing a vlooselyfltting piston having a co-axial nosepiece of varying cross-section'which extends from the inlet to beyond the throat of the venturi and is so contoured as to aord a normalr Venturi action for all degrees of entry, and a valve-like member which, whenever the fuel level in the float chamber becomes abnormally low, is moved by neat-actuated means to-obstructl progressively the normal i'low of air which takes place from atmosphere, byA way of the clearance around the piston, ythrough the suction chamber and thence Y to an outlet at .or near the throat of the venturi, whereby the momentarily diminished suction exerted on the piston results in the nose-piece reducing the effective cross-sectional area of the venturi until thedepression in the oat chamber increases to a valuesuicient to recommence inspiration of the fuel, and the oat-actuated means, together with the valve-like member operated thereby, becomes arrested in its action.

[Although theV emergency controlv device or valve-like member referred to may take various forms, it is preferred to employ ya poppet valve which is disposed vertically with its stem depending` above alever operable by the float, ythe head ofthe valve -lying opposite, and normally'remote from, vthe outletv end of a passage by'whichY the suction chamber is placed in communication with the outletv at or near the throat of the venturi.

According to a further feature of the invention, the pressure-drop constituting the metering head is derived by aiording the float chamber restricted communication with atmosphere through an air jet of small bore so arranged with respect to an outlet duct' that -theair stream ,induced through the bore is compelled tosuifer a reversal of .direction before it can escape'through the out- Y let duct to an outlet at or near the throatof the venturi. 4

The accompanying drawing represents, in somewhat ldiagrammatical form, a central vertical section through a self -feeding down-draught carburetor arranged in accordance with the invention. The carburetor illustratedY has a cylindrical suction chamber l the lower portion of which isi formed with a set of peripheral ports 2 (only one `of which is shown)V open to the atmosphere. Air' enteringthrough these .ports has free access to a region 3 at the inlet end of a'venturi 4 which, 1 adjacent its outlet end, fitted with the usual butterfly throttle 5. A flange 6 is provided for bolting the caruburetor to the inlet manifold of the. engine.

The suction chamber I contains a loosely ntting piston 'l which, together with a depending co-axial nose-piece 8, is slidable on a centrally disposed hollow guide 9, xed to the upper part of the suction chamber I, and is biased downwardly by a helical compression spring I of low rate. The nose-piece 8 is so shaped that it regulates the eifective cross-sectional area of the venturi 4 in accordance with the instantaneous position of the piston '1. In this connection, sinceA the multiplying effect of a venturi istdetermined by the rate of change of cross-sectional area alongv its axis, the profiles of theoverlappingportion of the venturi and the nose-piece 8 need to be such that, whatever the axial position of-the nose-piece within its range of traveLtlidifferf ence between the squares of their diameters at every axial position diminishes progressively towards the point at which the effective crosssectional area of the venturi thatisto say the cross-sectional area of the annular gap between the venturi` and the nose-piece, is required to be a minimum.v The construction in question, Vthereforef aifjords an annular venturi of `variable ow capacity .in which the maximum air velocity (and hence the minimum pressurehead) always ,occurs` at voneparticular fcrosssection. This is at the throat of the Venturi, wherevthere vis an annular slot II through which the meter fuel `is delivered and which will be designated the flowpressure annulus.

The weight of the piston and nose-piece unit, augmentedby the action of the spring IG, tends to cause the Venturi passage to. be closed by the f nosefpiece, This tendency,A however, is opposed bythe depressionfexisting in the upper part of the suctionchamber I whenever the carburetorisfunctioning. The depression referred 4 mospheric region 3 downwards through the annular passage between the venturi 4 and the nose-piece 8. Some degree of depression will thus prevail throughout this passage which, owing to its Venturi form, will be progressively greater as the cross-section of the passage diminishes, Maximum depression will, of course, occur at the low-pressure annulus I'I and the minimum in the neighbourhood of the throttle 5. Maximum value of the ratio between these two degrees of depression has been sought in denose-piece unit only attains maximum lift when; the `engine breathing demand is vat its absolute i maximum.

The degree of depression existing in thelOW- pressure annulus I I also has accessl to theupper side ofthe piston 'l via theY duct I2 andpassage I3. Since the majority of the lower surface of the piston lies within the atmospheric region `3,

to, which acts upon the upper aceof the piston l, isderived fromthe low-pressure annulus II by way. Of a duct I2 anda passagel i3. spaceabove the hollow guide 9,y which issealed from atmosphere by means of ascrew-cap I4, is also permanently in communication .with the low-pressureannulusil througha duct Iwhich communicateswith the passageif.

Solong as the engine is running, thecarburet-4 or automatically raises liquid fuel from a tank The fuelpump; 'The fueh which enters vthrough an inletlfltted with a Acylindrical gauze lter I,

passes into a reservoir I 8 and vthence through. av'

ductV l Bute theseatingof a needle valve 12i) which, inthe usual manner, is contr olled by a pivoted floatZI inavoat chamber 42 2, the fuel being supplied to thenlatter through orifices 2 3 whenever.

thegneedle valve is open. From the float chamber, the fuel passes by way of a duct 2d to a jet,

chamber 25 having va main jet 25 the effective aperture of which is controlled by a tapered metering needle 2'Iv carried by the piston l; The upper end of the needle 21 is held permanently.

in contact with the base of; the piston'v 'I by means -of a spring clip 28` which. is anchored ,in-a,

groove 29 formed rat the. junction betweenthe piston and its nose-piece.. The needle` is mount-v an upward pneumatic load is exerted upon the;l

piston and nose-piece unit, which, in consequence, rises until the upward nforce becomes balanced bythe vcombination `of the weight of that unit and the load of the 'spring I0. When this conditionof balance isachieved the piston and nose-piece unit willhave attained a condition of stability, with the piston suiciently lifted and, therefore, with the nosefpiece 8 sufficiently withdrawn from the venturi i'to ensure iat the resultant'elfective cross-sectional area remains substantially constant,' it is clear that the degree of depression effective upon the upper face of thepistonz'l must also be substantially" constant throughout the normal range of opera-l tion.

2'! is also progressively withdrawn from the main jet 26. i Thecontour of the effective part of the needle can, ofcourse, be so chosen as to give any required fuel/ air ratio corresponding to any Y degreeof piston lift and, therefore, of air flow to the engine.;V Fuel drawn from the neat chamber 22, having been metered on passing the main jet 26, flows upwards'within a well 3| Vand enters the low-pressure annulus I I from'the annular slot of which it issues, mixing with .the air at'thisr region of minimum pressure and, therefore, maximum Velocity.V Exceptionallygood pulverisation" of the fuel is consequentlyachieved.

Instead of the upperpart of the viioat cham# ber 22 being freely vented to atmosphere (as is the normal practice), it is placed in. communica# tion with thelow-pressure annulus IIr by way of i ducts 32.` and 33 and the duct I2; It is, however, afforded restricted communication with atmosphere through an air jet l3l! ofsmall bore which permits a slight amount of air to be drawn into the, duct 32 under the influence of the sub-atmospheric pressure prevailing Vin the low-pressure As the piston assembly rises the metering needle annulus II and, therefore, in the float chamber 22.1' Since the arrangement is such that the stream Yv of air induced through the jet vIIII can only leave the duct 32 by proceeding throughthe duct 33-(there being no other air outlet from the Y float chamber), the air stream in question has to suffer a reversal of direction within the duct 32 in order to enter the duct' 33 from which it passes, by way ofthe duct I2 and the low-pressure annulus I I, into the mainair stream in the venturi 4. In consequence ya finite diferenceof static pressure is established between the ends of the duct 32, and -hencel between the float chamber 22 andthe low-pressureV annulus II.

This pressure-drop, whichV is n'laintained across the main jet 26, constitutes the metering head.

` Its magnitude is afunction of the dimensions of the jet 34 and the duct 32, and 'it canbe consistently kept'without diflicultyv at a value equivalent to .approximately 5 ins. water head. This'v metering head isalso made available for Aan enrichment or cold-starting`H vjet 35 which is connected to the iloat chamber 22 by a passage 36` andsupplies additional fuel tothe low-pressure annulus II by way of a duct 31 when, by rotation of a mixture control lever 38, Vthe end of a projection 39 formed on a screwethreaded shank 40 is withdrawn from the facing containing the enrichment jet 35. Although not indicated in the drawing, a linkage is provided between the mixture control` lever 38 and theV throttle 5 to effectpartial opening of the throttle when the enrichmentjet 35 is brought into use by a manual control. A Y

So long as normal operating conditions preuntilthe'loat'chamber depression produced is 'just' suicient to maintain the required flow of fuel from the tank.

velocity of. `fl 'ow`throughY theY Venturi 4, but .simultaneously a slight weakening effect results from the abnormally low oat chamber level. At the y same time' atemporary increase in depression at theVenturi throatl implies a corresponding iny n crease in the unmultiplied depression in the region,

vail, a small poppet valve 4I remains inoperal `tive in the position shown, its hea-d being suficiently remote fromthe bottom of the passage I3 to afford no 'obstruction thereto. If, howeven'under conditions of exceptionallylhigh fuel-lift (suchasmay arise due to a combination of severe gradientand long wheel base), the

` fuel-lift called for exceeds the depression'available in the iioat chamber, the fuelY flow begins to diminish and the iioat 2I drops. -In dropping, Vthe oat at rst opens the needle valve 20 to its fullest extent and then, by means of an associated lever 42, begins to raise the valve 4I sovthat the normally free communication provided by the passage I3 becomes partiallyobstructed. As this obstruction occurs, the small flow lof 'air which inevitably takes place from atmosphere in vthe interior of the suction chamber I through the clearance provided between the suction chamber and the piston 1, can now no longer be freely evacuated via the passages I3 and I2. The degree of depression in the suction chamber therefore commences to drop below its normal Value, with the result that the piston 1 sinks somewhat and the nose-piece 8 enters the venturi to 'a greater extent than normal. The additional obstruction thereby imposed upon flow through the venturi then results in an increment in the depression normally obtaining in the low-pressure annulus II and hence in the oat chamber 22. This effect is progressively intensiiied as the head of the valve 4I continues to approach the outlet of the passage I3, untilr the increased depression in thefloat chamber reaches a value sucient to recommence the inspiration of fuel.

When fuel commences to flow again into the oat chamber the raising of theV float permits the valve 4I to descend,` and consequently the restricting influence of this valve diminishes of the throttle, which may thereby increase from y the normal value of 10 ins. water head to, say, 11 ins; or 12 ins. The adverse eiect of an increment in induction depression of this order upon power output-is, of course, slight. Nevertheless, i-t is considered preferable to arrange for the carburetor to operate normally upon the lower manifold depression iigure and tov bring into operation the emergency high-lift mechanism to meet ex- -`ceptional conditions only, rather than to operate,

at all "times, with suiciently high depression throughout the system to Ymeet circumstances` which rarely occur.

muttering of the piston assembiy is' prevented" by hydraulic damping. This is effected by retaining'a quantity of lightoil 43 in the bore of the nose-piece 8 and the lower part of the guide 9, the end of which is closed except for a small orifice 44, and providing a loosely iitting cylindrical baf-r fle 45 within the guide 9. Thus, movementof the piston assembly cannot take place without corresponding displacement of the oil and the steadying eifect which this engenders. The momentary high pressure created inthe oil beneath the endl of the guide 9, uponsudden upward movement ofA the piston assembly, may result in someV oil being forced upwardly in the working clearance between the periphery of the guide 9 and the surrounding portion of the b oreof the nose-piece 8. Any oil so displaced is received in thespace betweenthe guide 9 and an inner Vannulus 46 provided on the piston 1, and eventually returns to the interior of the guide 9 through a small hole vAlthough the contour of the metering needle 21 is initially so chosen as to afford the ,mostv appropriate mixture ratios throughout' the workingY range, provision is made for the mixture ratio under idling conditionagwhen the mainY jet is almost whollyv obstructed by the needle, to be readily adjustable.- To this end, the portion of the piston 1 against which the head of the `needle 21 is spring-loaded, as already described, is formed as a circular ramp 48 the face of which has a series of uniformly spaced small protuberances (not shown) the intervals between these defining the successive positions of adjustment. Thus, by manually rotating the piston 1 the head vof the needle 21 is caused to override the protuberances and click into the desired location, thedegree to which the needle enters the'main j et 25 for any given position of the piston 1 being determined by the direction in which the Vpiston is rotated.

long asl an ab-v Thus themixture ratios. tend to, become slightly .richer due .to-the ,higherv aware IlShQuldJ Perhaps. be mentioned.herewthatwhen the piston andv Vnose-piece assumes l its" l'ovvl"u est positionit is arrested bythe "engagemfent"` of the lower face ofthe pistonwithan annular rib v"The carburetor incorporates an acceleration pump whiclrautomatica'lly produces' a temporary 1 enrichment of `the mixture upon sudden opening l ingin the float chamber under'normal'.qsteady'- running conditions. is suddenly opened a When, howeveryv the throttle momentary increase in the normal depression occurs in all internaljspaces communicating with the low-pressure annulus l i due partly to the inability of rthe piston assembly to lrespond instantly tothe 1s fully. distended to the' right by vrmeans 'of itsVV increased air-dow demand vby reason of its inertia, andpartly to the damping which momentarily delays its' 'upward movement. This momentary abnormal depression within the float chamber space is transmitted to the chamber 5l.; bounded by the accelerator pump diaphragmf, via the injector tube 52 and a passage Sti-Which `communicates with the top ofthe chamber' 5 lv. The strength of the diaphragm spring 53 is so chosen that under these conditions the diaphragm will collapse inwards (as permitted by an air hole 55) displacing 'fuel from' the chamber" 5I and causing it to discharge rapidly from the injector tube 52. YThe resulting injector eec't produced at the mouthof the duct 2e Willv cause a momentary increase of head within this duct, and thus give rise to a momentary increase inthe discharge past the main jet 25.

Finally itV may be mentioned thatv this carburetor is "remarkablyneiectiye in suppressing induction roar. Its silencing capability is attributable lto theV 'extremely high velocity of airflow at thev throat of the venturi, preaching s'uiciently closely to that of sound (under the conditions of temperature and so forth prevailingthere) to` reduce induction tract noise to such an extent'that only the simplest form of air-silencer, suilicient to ldeal Withthehigh-frequencycomponentsof the noise (such as foonstituted by the throttle-edge hiss), is required.

I'claim: I

1. A self-feeding carburetor comprising a fuel chamber having a float therein and a suction chambensaid suction chamber havingV an air inlet and a venturi serving as its outlet, said chamber containing a loosely fitting piston having a 'co-axial nose-piece of varying cross-section which extends from said air inlet tobeyond the throat of the venturiv and which is so contoured as to aiord la normal Venturi action for all degrees of entry into said outlet, a suction this velocity lappassage'system intersecting' the throat of said venturrand Aconnecting it to said suction cham` bei" on theopposite side of the piston vfrom the Y venturi and to said fuel chamber; through which system there is a normal dow of air drawn from the atmosphere by Way of the clearance around the loosely tting ypiston through the suction chamber and suction passage system to 'the venturi, and a valve member located in said s uction passage systemand means: forV transferring themovement of said float to said valve member Aaftersaid floathas fallen below a predetermined level soas to obstructprogressively said normal Vilovv of 'air wherebythe momentarily di-4 minished suction exerted on the piston resultsv in movement ofvits nose-piece to reduce theeffectve cross-sectional decrease the lpressure therein, ing, the pressure in the suction passage system andlcausin'g inspiration of fuel thereinto.

2. A carburetor accordingto pheric l pressure. from 'said ased downwardly against. springk means bearing against its top.

3. A" self-feeding carburetor accordingrv to air, inlet and is. Ibiclaim 1 in which the valve-like memberis a.. poppetvalve disposed vertically with itsstemV dependingabove a lever operatedby .the float, the head of the Y themovement of sage system.

4. A carburetor accordingto claiml in which ain through said Ysuction pas.-

a pressure drop between said fuel chamber and. Venturi throatis *maintained vby affording the fuel chamber restricted communication. Withthe. through an air. jet of small bore so.`

atmosphere arranged with respect to an outlet duct leading to said .Venturi of Vdirection before it can escape through .said outlet.

5. A'carburetor according to claiml having said fuel chamber, pressure Aresponsive means in y inlet,l a variable venturi in said outlet,ra suction passage system. to transfer the pressure at said venturi to said .l

communication with saidvair pressure responsive means and to saidfuel cham.- ber, means whereby.. said y pressure responsive means contro-ls the efective*cross-sectional` area` of and consequently. theY pressure in said venturi, valve means. in said Ysuctionlpassage systeinyfor of pressure to reduce the ratio vof the depression acting upon` theA restricting said transfer pressurey responsive means to that obtaining in the venturi so'that said, reduction in ratiovinitiates a reducticnin'said effective cross-sectional areakand` a consequent I'decrease'in the pressure 1n said venturi, at the pressure responsive means and in the `fuel chamber, and means for transfferring the movementof said oatto said valve means after' saidI iloat determined level.

JOHN N. MORRIS.v

References .cites .in the. fue or this patent UNI'IED STATES l-A'I'EN'IS Number Name Date 1,472,660` Meisingeiy Oct. k30, 1923. 1,581,837 .l Brou/'neet al. Apr..20, 1926 2,051,820 Chandler Aug. 25, 1936 2,131,036 l Brackey V septal ,1938. 2,167,892" Kent et al. Aug. i, 1939v 2,399,637 Jones May 7,1946

area of the venturi and thereby decreasel l l* l I claiml in which said'piston is exposedat itsbottomto atmossuch. pressure .by

valve lying in and controlling..

Y throat that the air drawn. inv through the jet is compelledto suiera reversal with a circular ramp` haswfallen below a pre-

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