US2406114A - Carburetor - Google Patents

Description

Aug. 20, 1946. R, WJSLOANE ErAL CARBURETOR 3 Sheets-Sheet 2 Fil ed June 5, 1942 FIG. 7 LEGEND E K m T S G N O L SHORT STROKE w w w H x n o 4. m x M 5 n a 4 & m I, M A 0L. A. w l E W S 8% M N a .m WM .H w o F m T Rfl P a M 4 w a M w 3 1 m B M III/I I 5 f m .I m 2h. .E= s

R. $I- OANE' ET AL. 2,406,114

' CARBURETOR Aug. 20, 1946.

Filed June 5, 1942 3 Sheets-Sheet s INVENTOR RQBERT W. SLOANE %V1 U N mam PUMP TRAVEL- INCHES BY ELMER M. BIMBERG wI b6 WMIQS ZDDU QJQhi Fla. 6

Patented Aug.'20, 1946 CARBURETOR Robert W. Sloane and Elmer M. Bimberg, Detroit, Mich., assignors to Bendix Aviation Corporation, South Bend, Ind., a corporation of Dela-'- ware ApplicationJune 5, 1942, Serial No. 445,864

This invention relates to carburetors for internal combustion engines such as are generally used in automotive vehicles and the like, and it is more particularly concerned with the matter of securing the proper fuel feed for acceleration of the engine, an important object being to provide an accelerating mechanism which accurately meets the various requirements of the engine.

It is well known to those skilled in the art to provide means for injecting extra fuel during opening of the carburetor throttle valve for accelerating the engine and for opening a power jet when the throttle i near its wide open position and/or the manifold vacuum is very low; One representative type of such devices includes a pump having a plunger or piston actuated by a spring and acting under the control of suction in the intake conduit posterior to the throttle valve. The spring i normally designed so that the piston will approach'one end of its stroke as the manifold vacuum approaches a high value corresponding to idling operations and the other.

end of it stroke as the manifold vacuum approaches a relatively low value, at which time the plunger opens the power jet. In such vacuum operated pumps there is uniform pump travel throughout the entire range 'of manifold vacuum, which means that for an equal drop in vacuum an equal pump travel will be effected whether Or not the throttle is near the wide open position or just off idle. Such uniform 'distri bution of the available pump stroke over the entire manifold vacuum range is objectionable because an accelerating fuel discharge is required only throughout a limited throttle range as the throttle is opened from the idle position and generally any acceleration pump action when the throttle valve is beyond said limited range wastes fuel.

It is therefore another important object of the invention to provide an acceleration pump in which the major portion of the pump stroke occurs through a relatively high vacuum range as the throttle valve is moved through a limited range beyond the idling position; The present invention further provides, in addition to means for delivering extra fuelfor acceleration purposes, means for increasing the flow of liquid fuel during periods of operation when the manifold vacuum is low to thereby enrich the mixture during operation under heavy loads or at high speeds.

7 Claims. (Cl.261-'-34) I Another object of the invention i to provide a device of this character wherein an accelerating 2 rate upon acceleration from low or idlingspeeds and at a relatively slow rate during opening of the power jet or economizer valve.

Still another object of the invention is to provide a compound or multiple stage acceleration mechanism that is under the control of suction in the intake manifold posterior to thethrottle valve and in which the major portion of theacceleration pump stroke occurs upon decrease in manifold vacuum in the high vacuum range and a small portion of the stroke, 'suflicient to open the power jet, occurs in the very low vacuum range, the device being inoperative'throughout a substantial vacuum range intermediate said high and low ranges. A further object of the invention is to provide a device of this character wherein the small por tion of the pump stroke reserved for opening the power jet occurs with a slight change of manifold vacuum in'a relatively low vacuum range. Another object is to provide an'acceleratio n pump of this character wherein the length of the pump stroke is adjustable.

Still another object is to provide a device of this character that is simple in construction, dependable in action and relatively inexpensive to manufacture. 5

Other object and advantages of the invention will be apparent to those skilled in the art from the following description or may be ascertained from a study of the accompanying drawings in which several preferred embodiments of the invention are shown. principles'of the invention may be incorporated in various form and the employment of any structures, arrangements, or modes of operation that are properly within the. spirit of the invention and scope of the appended claims is contemplated.

In the drawings:

Figure 1 is a vertical section of a carburetor embodying the invention;

Figure 2 is an enlarged vertical section through the acceleration device showing the piston thereof in an intermediate position;

Figure 3 is a horizontal section of the plump plunger taken on line 33 of Figure 2;

Figure 4 is a ectional view of a carburetor em bodying a modification of the invention;

\Figure 5 is a fragmentary sectional view of a carburetor embodying another modification of the invention;

Figure 6 is a chart illustrating the character istics of conventional acceleration pump action and the characteristics of the action of the pres.-

It will be evident that the v justable needle valve 6.2.

ence characters represent similar parts although where such parts are modified in structure'andoperation they are given a erence character. 7

Referring more particularly to Figure 1 there is shown, for purposes of illustration only a pl'ain' tube downdraft carburetor I6 having an inducfurther differing ref tion passage including an air inlet I2, large and small venturis I4 and I6 respectively and a mixture outlet I8 which is attached to the intake manifold 2| of an internal combustion engine. IPhe air inlet is controlled by the usual offset choke. valve 22 and the mixture outlet is ,controlled byathrottle valve 24. 7 r

The carburetor is provided with a liquid fuel chamber 26 having a wen known air connection with the air inlet by means of an impact tube 21 and, having the usual floatmechanism 2B. A

mainlfuel system includes a calibrated fuel jet 36 which receives fuel fromythe fuel chamber 26 and disoharges'same by way'of: fuel passages 32 and 34 into an annular channel 36' in the small venttlri I6 from which it; isdrawn by suction into. the air stream of the. induction. pass through a slot 38; air being bledto the main fuel system through passages 46 and42, and openings 44 in a, tube 46.. There is further provided V an idling. systemincluding an idlin tube 48'. calibrated' jet 56. and fuel passages -2, 54 and 56,, the

idling fuel being discharged through the well known idling jet or plug 58, adjacent one ed e of the throttle valve- '2 4, and air is bled to said idling fuelthrough a passa e 66 communicatingwith theinduction passage and controlled by an ad'- present acceleration device of the-compound type wherein the operation thereof is in a plurality'of distinct stages having difierent characteristics as will be described hereinafter; one embodiment of 'thejinvention being 1 shown" in Figures-,1. 2 and. 3. The device comprises'a fuel: cylinder I0 disposed. within the fuel chamber 26, althou h if desired said cylinder may be. suitably mounted'externally of the'carbnreton' An accelerating fuel plunger or piston" is. reciprocably received in the cylinder 19, the complete. piston assembly of the device including a vacuum actuated piston. I4 connected with piston 12 by a rod I6; The rod'IG is secured to piston 14in the known manner by a clip I8 in an annular groove in the end of said rod which extends into. the interior of piston I4. The piston 12: is attached to the rod I6 by means of a keyhole slot 13. c0- operating with. groove I5. A. second groove TI is I also provided for a purpose that will be herein into an annular recess provided therefor, closes- 7 tom, fuel enters the cylinder I6 through an inlet fin g the piston I2.

the lower end of cylinder 80, and a vent from said cylinder opens into the fuel chamber 26 to relieve any undesired pressure that might otherwise occur below the vacuum piston I4. If desired, the vent 96 may open into the air inlet passage I2.

The collar 88 has a central opening for slidable reception of a sleeve 92 which is slidable on rod I6, said sleeve having "a flange 94 adjacent its lower end and below collar 88 and against which one end of a small relatively strong spring 96 reacts, the other end of said spring reacting against the fuel piston I2. A second spring, 96, which is large and relatively weak, reacts between the collar 88 and said piston I2.

In the supplementary 0r auxiliary fuel syspassage II4 communicating with the fuel chamber 26, passage having a check valve II6 therein to prevent return flow of fuel during the discharge stroke of t should be noted that fuel'that may accumulate above piston I2 may flow over the upper end of cylinder I6 and return to the fuel reservoir or chamber 26.

Twoj auxiliary fuel discharge systems from cylinder III. are shown in the embodiment of the invention illustrated in Figures 1 and 2, both of which discharge fuel into the annular. channel 36 of the small venturi.

One discharge system, termed the, power or economizer system, includes passages I26, I22 and I24 and is .provided with a power jetregulator including a body' I26 and power. jet regulator or economizer valve I28 integral with a stem I36 and positioned intermediate the ends thereof.' One end of said stem extends into the fuel cylinder 16 whereby the piston I2, may engage same and open the valve I28. 'A spring I32 yieldingly urges, said valve I28 closed.

A by-pass from one side of valve I26 to the other includes a longitudinal passag I34 through the. valve stem I36, opening atone end into the cylinder I0. and provided with a lateral duct I36 adjacent said end. Below the valve I28 a lateral, calibrated metering jet I38 connects the passage I 34 with theinterior of the body I26,.said body, having a calibrated power'jet I46, larger thanthe jet I38, communicating with passage I26. Thus when the valve I28 is closed there is a fiow of fuel through the economizer system metered by the jet I36 andjwhen said valve is open the fuel is metered by jet I48, the advantage of the by-pass arrangement being that it'eliminates the "flat spot or hole which normally tends to appear upon slight accelerations from the low' speed or idling operation just off idle. .If desired, however, the by-pass I36, I34, and I38 may be eliminated.

The other auxiliary fuel discharge system, termed the accelerating discharge system, includes passages I42, I44 and an accelerating nozzle I46 received in passage I24, said nozzle I46 discharging fuel through'a calibrated jet I48; It should'be noted that nozzle I46 is of less diameter than the passage I24 to permit the how of has a gravity actuated check vavle I56 adjacent the lower end, urged to closed position by aweight I52; The upper end of passage I44 'is-vented at I54 to the upper portion of the fuel chamber 26 to prevent fuel'from being sucked fromjet I48 when the acceleration pump is not operatin'g',"said II4 being normally open but.

vent being controlled bya check valve I 56 which is closed by the pressure of the acceleration fuel in passage I44 while the pump is discharging.

The operation of this device is as follows: Whenthe throttle is at idle the suction in the intake manifold below the throttle is approximately 18 or 19 inches of mercury, which will raise the vacuum piston I4 to its upper limit of movement, drawing piston I2 correspondingly upward and compressing or loading springs 96 and 98.

The discharge stroke of the pump is divided primarily into two stages. The first stage comprises the major portion of said stroke and includes the piston travel from the upper limit of movement, as shown in Figure 1, to the point at which piston I4 engages the upper end of the sleeve 92, as shown in Figure 2. It is effected by both springs 96 and '98 upon a drop in manifold vacuum through the relatively high vacuum range when the throttle is opened off idle, and due to the combined strength of springs 96 and -98 the discharge is forceful and at a rapid rate. It will benoted that at the end of the first stage ofthe pump stroke piston I2 is closely adjacent to but spaced slightly from the upper end of valve stem I351.

When piston I4 engages the end of sleeve 92 no further expansion of spring 96 can occur. Thereafter, said spring is ineffective to actuate the pis ton I2 and is carried along with the piston assembly throughout the remaining portion or second stage of piston travel which comprises only a small part of the total stroke. This second stage is effected solely by the comparatively weak spring 98 and said stage is reserved primarily for opening thepower regulating valve I28 by piston I2, although as said piston is opening the valve it will also effect a slow accelerating fuel discharge which improves the operation of the engine during this transition period. In this connection, before the assembly can progress on downward, the

vacuum above piston 14 must be diminished by an amount sufiicient to equal the preloaded force or initial tension in spring 96 when restrained to the length shown in Figure 2.

Fromthe foregoing description of the invention and its operation it will be understood that there is a substantial difference in the pressure characteristics of the spring action of the two stages and consequently there is a substantial intermediate vacuum rang wherein "no movement of the piston occurs. The lower limit of this range is that value of vacuum just sufficient to overcome the force of spring 98 and a slight drop in vacuum through a very low vacuum range below this value will permit said spring to actuate the piston I2 which will thereupon engage valve stem I30 and open valve I28. During the opening of said valve the counter force of valve spring I32 must be overcome and this spring will tend to retard or interrupt the movement of the piston. However the force, of spring I32 is relatively slight and is readily overcome by spring 98 so that it does not adversely affect the proper functioning of the device. i

It should be further noted that spring I32 is preferably so calibrated that neither the pressure of the fuel-in the cylinder during thedownward movement of the piston I2, nor suction from the induction passage on the power or economizer discharge system, nor the combination of said force and vacuum will open the valve I28 prior to its actuation by the piston I2.

When the piston I2 is at the lower limit of movement it will rest on the upper face of the valve body I 26 and the flow of fuel into said body will be by way of a slot I60 and an annular pass sage I62 about the valve stem I30.

When valve I28 is open the jet I40 becomes the primary metering restriction and the by-pass I36, I34, I38 is substantially. without effect. Consequently, the by-pass is effective during part throttle operation only.

In order that the operation of the present acceleration mechanism and its advantages over conventional vacuum controlled acceleration devices will be better understood, reference is now made to Figure 6. The solid line illustrates the characteristics of the conventiona1 or common vacuum operated acceleration pump action. It will be seen that there is uniform pump travel throughout the entire range of manifold vacuum which means that for an equal'drop in vacuum in the intake manifold, which is determined by the speed of the engine and the position of the throttle valve, an equal pump travel will result whetheror not the throttle is adjacent Wide open position or just off idle.

The dotted line curve illustrates the characteri'stics of the action of the present invention, disregarding the effect of the power jet valve spring I32. The manifold vacuum points in inches of mercury, used on the curve, are for illustration only, for by proper proportioning of the strength of the springs, the length of sleeve 92, and/or varying the total length of the piston stroke these points can be varied over a large range.

As shown in said dotted line curve, the fuel pistonwill travel from the extreme retracted end of the stroke of approximately .425" to .1" from the oppositeend of piston travel upon a drop of manifold vacuum throughthe range between 13" and 12" of vacuum. There is then no further piston travel until the manifold vacuum has dropped to V 5.5" of Hg, the remaining .1" of pump travel occurring between approximately 5.5" and 5" of manifold vacuum during which portion or stage of the pump stroke the valve I28 of the power regulator is opened.

If desired the pump stroke may be adjusted by attaching the piston I2 to groove I't instead of to the groove i5. This will vary the total length of the stroke inasmuch as the upward travel of thepiston assembly is limited by the distance the vacuum piston 14 can travel before reaching the top of the vacuum cylinder 80. Attachment of the pistonin the groove I5 provides a short piston stroke, and attachment in the groove TI provides a longer stroke. Other spachowever be provided or other means for adjust ing :the position of the piston I2 on the rod I6 or adjusting the total stroke of the device may be used,'the illustrated arrangement being a preferred one. Variation in the length of the piston stroke could also be made by means of an adjusting arrangement between the vacuum piston I4 and the rod I6.

In Figure 7 the characteristics of the action of the present invention are shown according to two piston adjustments. The solid line curve indicates the characteristics of the action whenthe adjustment is for the short stroke, the longer stroke being indicated by :the broken line curve. The hook or drop in the curve around 5.5 to 4.5 inches of mercury is caused by the amount of pre-loading of spring I32 of the power jet regulator valve. It will be noted that the vacuum points of the device charted in this figurevary somewhat from those shown in Figure6. This p 7 I is. due to different. spring? maracteriistics: These poin s, however, are also used only by way of ex- 3 ample and may be altered as. desired;

It will be further noted that adjustment of the piston stroke varies the; values of vacuum, in the higher vacuum, range, required to startthe device in motion; This is. due tothe fact that varying the length of therpiston asscmbly variesthe relativ spacing from the piston 72 to th c ll r 88 and. the flange 94 of the sleeve 92 when the as- 'sembly is in the uppermost position. This re-i vacuum range will occur after h same am t of pump travel from'the upperposition, regardless of the'groove into whichthe piston 52 is assembled. i It wil be app r nt from the f re oin hat th aracteristi s f. th device m y be ed. y varying the length, of the stroke. Moreovenby also varying the length of sleeve, 92, and by vary ing the. thickness of the flangofli i of sleeve 92, in.

order to vary the amount of initial tension in spring 5 and inorder to change the time of transition from, thehigher tothelo-wer vacuum range, a considerable number oi operative combinations become available without changing the springs" If the springs rates are also varied;

innumerable other, operative combinations are, possible; resultingjin a device which maybe read-j ily adapted to meet the various: acceleration and.

eoonomizer requirements of different-makes, types: and sizes of engines;

Attention is particularly'called to the fact that by lengthehing the sleeve 92;, the length of the V first stage'of the stroke is shortened inthe higher i being connected with the fuel chamber and air is bled in the well-known manner to said main fuel system.

Within the tube 412; and discharging fuel therein, is a calibrated power and accelerating nozzle 424 of smaller diameter than the inside dimension of tube 412. The power and accelerating nozzle 4.24 is supplied with fuel by way of a horizontal passage 426 and a vertical passage 4281 having a regulator adjacent the upper end.

The regulator comprises a body member 439. screwed into passage 428 and in which, is oper-l ably received avalve 432 intermediate the ends of a; longitudinally bored valve stem 34. One end of stem lt lextends through fuel passage:

435 which is controlled by the valve 432, said stem being of smaller cross-section than the fuel pas-j sage 43,6 and'extends into fuel cylinder 440. Lateral ,f;.ue l orifices 444 are provided adjacentthe upper end ofgstem 434 andthelower end of the} bore is shown as having a] calibrated regulator l t.- Mt. A spring 8 yieldinglvurees th'evalve 432 closed and is calibrated to maintainsaid valve in this position against suction on the jet 416.

In the embodiment of the invention, shown in Figure 4 a modified type of fuel piston Aj iZis shown which 'is'provided with a disk 45%) having a keyhole'orifice similar to the orifice '13 shown in Figure 3 sothat said piston may be attached to rod To prevent closing of fuel passage V 435 by the piston 442 when at its lower limit of movement, lug 452 are provided which are adapted to engage head 43%! of member 530 and space the piston 442 from the head 438; However, if desired, lugs 452jmay be dispensed with and the head-433 may be slotted as shown in. Figures 1 and 2 orany other suitable arrangement may be provided to insure the fiow of fuel from the cylinder 440. into passage 5218 when the piston see is at its lower limit of movement.

Cylinder MEI is providedpadjacentthe' ubher end with an overflow passage 45b and the upper 7 end of vacuum cylinder 85 is connected with the induction passage posterior to the throttle valve 24 by a passage Q62, said cylinder 80 also has a vent 454; from a point adjacent the lower end thereof to the induction passage anterior to the throttle valve.

In this embodiment of the, invention the fuel is metered by jet 4% when the valve 432 is closed as said jet is smaller than the calibration of the metering jet Mil. Upon discharg movement of the accelerating piston 4 32,, the volume of fuel discharged from the cylinder 440 is such that it cannot all pass through jet tlfi and consequently the valve 532 is forcedopen-by the pressure of said fuel. The metering-jet ll-00f the power and accelerating nozzle 4524 then meters the accelerating fuel charge. Said jet also-serves to meter the fuelfor. the power mixture when'th'e power regua lator valve 432 is openedbypistonMZ.

The embodiment of the invention illustrated in Figure 5 is shown as incorporated in a carburetor of similar construction as thatshown in Figure 1 and the regulator is also similar to that hown in the latter figure. The accelerating fuel piston,- however, is similar to the one shown in Figured.

Pistons l4 and 442 are connected by a rod 516 which is similar to the rod 16 except that the upper end is enlarged at 5% to provide a shoulder 5M and there is an enlarged; head EModisposed within piston it whereby said piston raises said rod and piston M2. The enlarged p t on 5 is adapted to pass through an opening 505 in collar 38 so that shoulder 532 will pick up a washer 506 on the accelerating stroke of the pump, the washer being slidable on rod'blfi and engageable with the under side of collar 88 when the pistons are raised, Spring 96 reacts betweenwasher 506 and piston 442 and spring 98 reacts between said piston and the collar'88; When the shoulder 502 engages the washer 506" further expansion of spring 95 is prevented. Varying the length of the enlarged portion 5% effects changes in the opera, tion of the device comparable to changes-in the length of sleeve $2 in Figures 1, 2 and 4. a

In' this embodiment there is also but one fuel discharge passage, 568, from the accelerating pump cylinder 10 which is controlled by the regulator, the passage 508 including: a power and" ac.-

celerating jet 510 discharging into a passaige'5l2' V which communicates with channel 36 in the small venturi. 2

When the valve I28 is'closed, fuel is metered by the jet I38; and'when' the valve is. open, jet

5 I ll meters the. iEuel tor the power mixture as well as the charge of accelerating fuel, orifices 530 having a combined area large enough so that they are not calibrating factors.

While certain modifications of the invention have been shown and described it is to be understood that one or more of the Various features of one modification may be substituted for corresponding features of another modification, or may be added thereto. Further, a diaphragm type of accelerating mechanism, incorporating the functions and features of the illustrated piston type pump mechanism, may be used and the invention may be incorporated in a horizontal delivery type of carburetor or the like as well as the types shown and described herein. If desired, there may be an independent accelerating discharge jet or nozzle discharging directly into the induction passage and the control of the mechanism may be by other means than manifold vacuum.

It will also be apparent to those skilled in the art that Various other changes may be made in the form, construction and arrangement of the parts without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the forms hereinbefore described being merely preferred embodiments of the invention.

We claim:

1. In a charge forming device for an internal combustion engine: an induction passage; a throttle valve controlling said passage; a source of fuel; a main fuel system adapted to deliver fuel to the induction passage from said source; an accelerating device adapted to receive fuel from said source and deliver it to the induction passage, said devic including a pumping member having a predetermined discharge stroke and controlled by manifold vacuum; relatively strong yielding means for forcefully eifecting a predetermined major portion of the discharge stroke of the pumping member during decrease of vacuum in a high manifold vacuum range; and relatively weak yielding means for effecting the remainder of the discharge stroke upon a slight decrease of manifold vacuum in a low vacuum range.

2. The combination with a carburetor having an induction passage controlled by a throttle valve, of an acceleration device having a piston with a predetermined discharge stroke and controlled by a vacuum posterior to the throttle; a pair of springs in parallel for effecting discharge movement of the piston, one of said springs being stronger than the other; means for limiting the effectiveness of the stronger spring to a predetermined major portion of the discharge stroke of the piston; the weaker spring being effective throughout the entire stroke of the piston and adapted to independently complete said stroke; and a valve controlling a passage from the acceleration device and openable by the piston during that portion of its stroke effected solely by the weak spring.

3. In a carburetor having an induction passage controlled by a throttle: an acceleration device having a piston controlled by vacuum posterior to the throttle, said piston having a predetermined discharge stroke; and a pair of springs for effecting discharge movement of said piston; one of said springs being effective throughout the entire discharge stroke of the piston, the other spring being effective in cooperation with the one spring to actuate the piston through part of its stroke only. 1

4. In a carburetor for an internal combustion engine, an induction passage controlled by a throttle, a fuel chamber, and a main fuel delivery system: an auxiliary fuel system subject to suction by air flow in the induction passage; a regulator valve controlling said auxiliary system; an acceleration device connected with the fuel chamber, a pumping member for said device controlled by manifold vacuum; yielding means for actuating the pumping member throughout a major portion of its discharge movement; means for rendering said yielding means inoperative throughout the remaining portion of the movement of the pumping member; weaker yielding means for effecting said remaining portion of the discharge movement of the pumping member; said pumping member opening the regulator valve during the movement effected by the weaker yielding means; and a discharge passage for accelerating fuel from the acceleration device to the induction passage.

5. In a carburetor having an induction passage controlled by a throttle valve: an acceleration device including a fuel cylinder; a fuel piston operative therein; a vacuum cylinder connected with the induction passage posterior to the throttle; a vacuum piston operative therein; a rod connecting said pistons; a fixed member; a spring reacting between said fixed member and the fuel piston; a sleeve slidable relative to said rod and adapted to engage the fixed member; and a second spring adapted to react between the sleeve and the fuel piston; said sleeve being so arranged that the vacuum piston will engage one end of same as it approaches one end of its stroke.

6. In a carburetor having an air passage controlled by a throttle: an acceleration device having a fuel cylinder; a piston therefor; a piston rod secured to said piston; means for controlling the piston by vacuum posterior to the throttle valve; a fixed member adjacent the piston rod;

a slidable member on said rod and engageable.

with the side of the fixed member adjacent the piston, a pair of springs, one of said springs reacting between the piston and the fixed member and the other spring reacting between the piston and the slidable member; a shoulder on said rod adapted to engage the slidable member upon a predetermined movement of the piston in one direction.

'7. In a carburetor having an induction passage controlled by a throttle valve: an acceleration device including a fuel cylinder; a piston operable therein; a vacuum cylinder connected with the induction passage posterior to the throttle; a vacuum piston operative therein; a rod connecting said pistons; a fixed member; a spring reacting between said fixed member and the fuel piston; a sleeve slidable relative to said rod and adapted to engage the fixed member; a second spring adapted to react between the sleeve and fuel piston; said sleeve being so arranged that the vacuum piston will engage one end of same as it reaches a predetermined position adjacent the end of its discharge stroke thereby rendering said second spring inoperative for further discharge movement; an auxiliary fuel system; and a valve controlling same, said valve being opened by the fuel piston upon discharge movement beyond said predetermined position.

ROBERT W. SLOANE. ELMER M. BIMBERG.

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