US2209401A - Carburetor - Google Patents

Description

July 30, 1940.

J. 5. JENNINGS. JR 2,209,401-

CARBURETOR I Filed Mafy 16, 1936 4 Sheets-Sheet l 7 a 37 INVENTOR. (3:5. 5 ,3 JkrVZ-S \5. 7572 713275, J5:-

o JQ cwbw gg i V ATT NEY y 9 J. s. JENNINGS, JR 7 2,209,401

CARBURETOR Filed May 16. 1936 4 Sheets-Shet 4 MAMuAJ THROTTLE I If conuzcnom x7 III Z6 OPgi/ATED GOVERNGR 5A INVENTOR Patented July 30, 1940" CARBUBETOB Jarvis S. Jennings, Jr., Detroit, Micln, auignor to Monarch Governor Company, Detroit, Kick,

it moration of Michigan Application May 16,

18 Claims.

It has been commonly appreciated in the art,

that for delivering maximum power of an engine, the fuel mixture supplied thereto by the carburetor must be as richas possible, while for economical operation the fuel mixture must be as lean as it is possible to fire without missing; it is also commonly known that rich mixture is undesirable in ordinary engine operation, as it greatly decreases the engine operation economy. Therefore, it has been found that the device for enriching the fuel mixture has to be of such a character that it will operate to inject additional fuel into the carburetor only during'the short periods of time when the maximum power is required, and will not operate'to enrich the fuel mixture unnecessarily during the longer periods of operation when economy is important. For

it is quite advantageous to secure better acceleration by enriching the fuel mixture during the short periods of time when high acceleration is desired and economy may be sacrificed, but it is constructed with the expectation that they might perform the function of enriching the fuel mixture in such ways as to satisfythe above requirements. Some of the devices provided have a small reciprocat ing single-acting pump with a piston operated from a rocker arm connected to the carburetor throttle in such a way that when the accelerator foot pedal is stepped upon and the carburetor throttle is opened, the piston of the pump is pushed into the pump cylinder and a charge, of

instance, in a case of a passengermotor vehicle climb a steep hill, but it is desirable, in order to 193s, No. $0,114

gasoline isiniected into the carburetor gas pessage, thus enriching the fuel mixture to be swplied to the engine. The piston at the end of I its stroke comes in contact with a valve admitting the additional gasoline into the carburetor 5 and continues to keep it open so as to permit admission of additional fuel as longas the carburetor throttle is kept open. The devices of such construction have the advantage of positive action and of quick and sure response to the ac- 1o celerator pedal. However, serious disadvantages result from inability of carburetors provided with such devices to supply economical mixture when the same is desired in combination with high engine power output.

The foregoing disadvantage is particularly obiectionable in cases of motor trucks provided with engine governors. when such trucks are operated along the highways the drivers frequently keep the throttle wide open in order to obtain 29 the maximum speed permitted by the governor, in consequence whereof the pump valve is open .an'dthe fuel injecting jet continues to operate, enriching unnecessarily the mixture. Thus, the devices of the above character, usually referred 25 to as mechanically or manually operated power jets, while satisfying the first of the above mentioned requirements, namely, enriching the fuel mixture at sudden demands of maximum power,

prevention of uneconomical enrichment of the mixture in other operation conditions of the engine. Devices which have been provided to avoid the above disadvantage are usually operated by the vacuum created in the gas passage 35 at the down-stream side of the governor valve, and they are known in the art under the name of vacuum-operated power jets. In such devices the fuel injecting piston is pushed into the accelerator pump cylinder by a spring actuatin the rocker arm, such action of the spring being permitted by the'vacuum operated piston when vacuum below the. governor valve decreases. Since the maximum power requirement for the conditions above discussed is, in fact, a maximum torque requirement, and, furthermore, since the' torque of an internal. combustion engine'provided with a governor is roughly inversely proportional to the degree of vacuum existing in operation belowthe governor valve, the vacuum- .controlled mixture-enriching devices accomplish a much better operation control. However, a serious disadvantage of such devices results from the fact that they are not positively-acting, and their response to the accelerator pedal is not so 55 do not satisfy the second requirement, namely 30 quick and dependable as that of the mechanically-operated devices. Besides, their construction is such that regulation of the stroke of fuel pump piston for summer and winter operationof either; particularly, which has the advantage of positive and direct operation of the accelerator pump from the carburetor throttle, or acceleiator foot pedal, and at the same time depends for operative response of the power jet itself upon the vacuum under the governor valve.

Another object of the invention is to provide a novel fuel mixture-enriching-devlce which ensures ample supply of very rich fuel mixture when the engine is called upon to develop maximum torque, but which does not permit unnecessary enrichment of the fuel mixture when economical operation of the engine becomes important.

Still another object of the invention is to provide a novel fuel mixture-enriching device having simple and positive adjustment means permitting different adjustments of the accelerator pump piston stroke for winter and for summer operation conditions.

A further object of the invention is to provide a novel fuel mixture-enriching device in which the accelerator pump piston is positively operated, and in which the period of injection of the fuel into the carburetor is prolonged beyond the period of the piston stroke, thus preventing throwing of the entire gasoline charge into the. carburetor in a very short time, which action is objectionable as resulting in ineffective waste of said charge, and as causing rough operation of the engine.

A still further object of the invention is to provide a carburetor having a ifuel mixture enriching device of the above character, in which the accelerator pump is operated positively and directly, and in which the advantages of vacuum operated power jet are accomplished by means built-in into the carburetor structure, and without the necessity of changing connection of the accelerator pump from the carburetor throttle lever to the vacuum operated piston, and vice versa.

The above and other objects of the invention will appear from the following description and appended claims when considered in connection with the accompanying drawings forming a part of this specification.

Fig. 1 is a perspective view of a carburetor of the down-draft type provided with a governor and embodying the present invention.

Fig. 2 is a front view of the structure of Fig. 1, partly in section, showing the details of constructlon thereof, particularly the accelerator pump and the two-part rocker arm for operating said pump.

Fig. 3 is a side view of the same structure showing the carburetor throttle lever for operation of the accelerator pump and its connection with-the two-part rocker arm.

Fig. 4 is a front, view of the two-part rocker arm showing the details of its construction.

Fig. 5 is a top view of the rocker arm.

Fig. 6 is an end view thereof.

Figs. 7 and 8 are fragmentary views similar to Fig. 2 illustrating dlflerent positions of certain operating parts.

Fig. 9 is a diagrammatic view of the structure constructed in accordance with the present invention, said view illustrating the interaction of the operative parts of the structure.

Fig. 10 is a perspective view of a conventional governor valve operating mechanism which may be employed in connection with the present invention.

Before explaining in detail the-present invention, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or .carried out in various ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation, and it is not intended to limit the invention claimed herein beyond the requirements of the prior art.

In the drawings there is illustrated, by way of example, a structure embodying my invention which comprises, generally, a carburetor C of the dual down-draft type, which may be generally of any suitable or conventional kind, and a governor G arranged at the downstream side of the carburetor. The carburetor C has a casing 10 provided with suitable dual gas or intake passages H0 which have throttles iii of the butterfly type operatively disposed therein on a spindle or rock shaft it operatedfrom the accelerator pedal in a way well known in the art. A float chamber ll provided with a float and a gasoline connection I2 operates to supply the fuel to the jet disposed in the gas passage of the carburetor. Communicating with said float chamber is an accelerator pump, designated generally by the numeral 23, operating to inject additional fuel into the carburetor gas passage through a suitable auxiliary jet (not shown), usually referred to as a power jet. Although a carburetor and governor structure of the dual down-draft type is illustrated herein, by way of example, it will be understood that a structure with a single passage and a single carburetor throttle valve and,

governing valve,'well known in the art, may be utilized. .Also, a carburetor of the up-draft type may likewise be employed.

The pump 20 comprises a cylinder 2! having a piston 22 slidably fitted therein, said piston being provided with a piston rod 23 and a compression spring 25 arranged above said piston 2i and engaged by a washer 58. Conduit 28 connects the lower part of said cylinder with the power jet and is provided with a check valve 26 normally kept closed by a spring 21. The pump 20 is operated by a two-piece rocker arm R. Said rocker arm R consists (see Fig. 4) of two pieces ormembers, designated generally by numerals and 50, pivoted to the carburetor casing as at "55. The piece is operated from the carburetor lever i3 with the aid of a push-rod ii. The lower and it of the push-rod is connected to said lever through the medium of either the ball pin IE or the ball pin l5 depending upon the desired adjustment. The upper end IQ of the rod i1 is connected to the piece 50 at the ball pin 52. The piece 50 is provided with a bent portion 5! receiving the end of a spring til, the other end of said spring being connected to a lug M bent out from the endv of the piece to.

. is possible in order to assure proper and smooth length of the slot 00 which exceeds that of thelug 00. The construction is such as to produce as little friction between the pieces 00 and 00 as operation of the device.

In the present embodiment of the invention the governor G, as. well as the carburetor, is of the dual type, although such construction is not essential to the proper functioning of the present device as a governor with a single passage functioning in conjunction with a single passage carburetor may be used. The governor herein shown by way of example, is constructed substantially in accordance with my application, Serial No. 520,060, died March 4, 1931. Said governor, which maybe of any suitable type comprises, in the present instance, by way of example.

a casing suitably affixed to the carburetorcasing I0, and having gas or intake passages, such as 00, "provided therein. Operatively disposed within said passages 08, 00 there are provided suitable governor butterfly valves 00,

secured to a rock shaft I02 and controlled in a way well known in the art. The present illustratedgovernor is substantially similar in construction and mode of operation to the governor illustrated in my co-pending application, Serial No. 520,060, the governing valves 30 being actuated as in said application by means of a vacuum operated piston I00, a main counteracting spring I08, and cam mechanism interposed between the piston and a cooperating crank arm fl xed to the end of the governor valve shaft I022. The can mechanism which may be employed in connection with the present invention is illustrated in detail in Fig. 10. As is clearlyshown in said figure, the piston I00 is provided with a piston rod III-i carrying a cam I05 cooperating with a roller I00 carried by said crank arrn' secured to the shaft I02. Space in each of thetwin intake passages of the engine on the downstream side of the carburetor valve 30 is connected with the space ofthe governor casing on the spring side of the piston I00 by means of a passage I00. With the increase or decrease of engine speed, the vacuum below the governor valve increases or decreases, causing correspondingmovements of the piston I00 against said spring I I, and moving the piston rod I00 and the cam 00. The roller I00 following the outline of the cam actuates the arm 08 and the governor valve shaft I02, thereby closing or opening the governor valve 00.

By means of a conduit 00 the intake passages communicate at the downstream side of the governor valves 20, 00 with a vacuum cylinder the continued pressure on the accelerator pedal pheric pressure. In the illustrated arrangement, particular reference being bad to Fig. 2, it will be understood that, when the engine is idling and a consequent high vacuum exists at ports 2?, the piston 02 under the influence of this vacuum will be drawn down to its fullest extent. In the absence of bumper spring 00 it would draw down lever 00 and extendthe spring 00 until the. ,lug 03 engaged the upper end of the slot .00, thus effecting substantially a solid connection between to parts 00 and 00. This would be undesirable because under such conditions the pump Piston 22 would be immediately responsive to small carburetor throttle movements. In the present arrangement, however, the bumper spring limits the extreme downward movement of piston 32 thereby maintaining the lug or stop 00 preferably about midway of the slot 00. Hence, small or rapid movements of the throttle communicated through rod." to lever 00 are not immediately communicated to lever 00 but are absorbed by spring 00 and the lost motion of lug 00 within its slot. The spring 00 is so designed that when the tbrottleis wide open it is not loaded but when the throttle is closed it opposes somewhat the downward movement of the piston 02 in response to the vacuum in the cylinder sufliciently to assist the action of spring 09. In brief, spring 00 not only maintains under closed throttle conditions lug 03 at an intermediate so point in the slot but also' relieves spring'09 of the high vacuum pull of the piston during such idling or light load positions of the throttle.

It will be understood that in operation the down stroke of pump piston 22 is ,eflected by the lever 00 which is controlled by'the throttle lever is and the vacuum responsive piston 32. Pressing the accelerator pedal causes the throttle lever I3 to push them I? upward and to turn the piece on its pivot 00. Because of the resistance of the pump this results in stretching the spring 00 and exerting an upward pull upon the piece 00. This upward pull transmitted through the spring 00 rocks the lever 00 and forces the piston 22 downward, thereby injecting fuel through the conduit 28 and the power jet into the'Venturi 0 tube operatively disposed within the carburetor intake passage. The action of the spring 00 is gradual and, consequently, the injecting process caused thereby is prolonged; Suflicient pressure on the accelerator pedal will rotate the lever 00 until the lug 00 reaches the upper extremity of the slot 00, thus pomtively engaging the lever 00. Upon establishing such positive engagement,

causes a corresponding downward movement of the accelerator pump piston 22, effecting a plentiful and quick fuel injection. As the piston 22 reaches the end of its downward stroke, itcontacts the .valve 20. If the accelerator pedal is kept pressed down, keeping the throttle wide open, the valve 20 continues to stay open and under these conditions the vacuum existing in the conduit 20 opens a check valve (see Fig. 9) provided in the cylinder 20, opening therein from the float chamber II, thus permitting drawing of additional fuel through the power jet and enriching the fuel mixture supplied to the -engine.

It will be appreciated that under conditions when the carburetor throttle is wide open very little vacuum or pressure drop exists in the pressure zone at the downstream side of the governor valve, and consequently, the spring 09 will move the lever 00 to bring the piston. 22 into contact with the valve 26. Thus, under the conditions when maximum torque is suddently demanded,- the present device responds substantially as quickly to the accelerator pedal as does a con- 5' ventional mechanically operated power jet, but

the action of the spring 49 causes a more prolonged injecting process, just as required for the most effective and efilcient use of the gasoline charge available in the accelerator pump cylm inder. It will be appreciated from a consideration of the explanation given above, that if the carburetorthrottle is kept continuously open and the speed of the engine increases beyond the governed speed, the governor valve begins to close,

45 decreasing the speed of the engine. .With the conventional mechanically operated power jets, the accelerator pump does not respond operatively to this change of conditions and the engine continues to operate on a very rich and 20 uneconomical fuel mixture. The present fuel enriching device, in spite of the fact that its accelerator pump is positively operated by the throttle lever, does operativeiy respond to such change of conditions, and it precludes unneces- 25 sary enrichment of the fuel mixture and uneconomical operation of the engine under such con- 4 ditions.

As the governor valves. 39, 39 move toward closed position the vacuum or pressure drop in- 30 creases at the downstream'side thereof, and said vacuum operates to retract the piston 32 to approximately the position shown in Fig. 7, thus overcoming the resistance of the spring 48. The movement of the piston 32 into such position 35 causes the link 48 to exert a pull on the member 48 at H, raising the piston 22 sumciently high to permit closing of the valve 26 by the pressure of the spring 21. It' should be noted that, since at the end ofthe injecting stroke of the piston 22 the lug 53 is in contact with the lower extremity of the slot 56 (Fig. 8), sufilcient movement of the piston 22 is permitted, because of the elongated shape of the slot 4t, to lift the piston 22 out of contact with the valve 126 to permit 5 the same .to close without, however, transmitting this return movement of the piston 22 to the carburetor throttle lever. -Glosing of the valve 26 prevents unnecessary enrichment of the fuel mixture. By a proper selection of the springs 35 and 50 25 as to their respective resistances, and of the area of the piston 32, the above-described operative response of the present device may be caused to occur at any predetermined degree of vacuum existing on the downstream side of the 55 governor valve. In view of the foregoing, therefore, operation Wof the present device in accordance'with the following brief statement will be readily understood. Assuming that'the carburetor throttle III is in 60 the partially closed or idling position, the accelerator pumppiston 22 will be retracted to or near the position shown in Fig. 2. Under such a condition the lever 40 will be pulled down by the rod 48, thereby extending spring 49, this action being caused by the high vacuum in the economizer cylinder 3! with closed ornearly closed throttle. If the carburetor throttleis then suddenly opened, producing an upward thrust of rod I! on lever 50, lever 40 will follow or swing in 70 accompaniment with lever 5U, thus directly actu ating the pump, but unless the carburetor throttle is almost fully open, the spring 49 will remain extended or stretched to a degree sufficient to stop rotation of lever 40 and cause the b pump piston 22 to stop at a point sufficient above the bottom of the accelerator pump cylinder so that it will not engage or open the valve 26, see Fig. 7. If, however, the carburetor throttle is opened to the greatest extent, the vacuum in the economizer cylinder will drop to a point where it 5 will no longer exertsuificient force to extend the spring 49. The lever 40 will then be drawn upward by the spring and'the other end of the lever will be lowered sufllciently for the piston 22 to engage and open the power jet valve 26, 10 see Fig.8. If, however, the throttle is held open continuously for a sumcient period, the vehicle speed will eventually reach the point where the governor valves will start to close, and at a predetermined rise in the vacuum downstream from these valves the spring 49. will again be extended by the piston 32 acting through link 48, thus lifting the piston 22 from contact with the power jet valve, as shown in Fig. '7.

A further important advantage of the present invention resides inthe provision of means permitting the stroke of the accelerator pump piston to be changed in accordance with changing operating conditions in summer and in winter. In the present embodiment of the invention,- said ,3 means are exemplified by the two points of attachment of the rod H to the lever I3. Ball points I! and [6 are provided on the carburetor lever l3 at different distances from the center of the rotation thereof, and consequently, rotation of the lever l3 through the same angle causes the ball pin it to go through a longer arcuated path than that covered by the point l5. Therefore, when the end l8 of the push rod I1 is attached to the lever i3 at the ball pin IS, the stroke of the accelerator pump piston 22 is longer than it is when the rod i1 is attached to the lever at the ball pin l5, and a larger charge of fuel is injected into the carburetor. Connection of the rod I! at the'point I6 is desirable for winter 40 operation, while for summer operation the end Id of said rod is transferred to the ball pin I5 in order to produce a shorter stroke of the piston 22. Under these conditions the degree of vacuum at which the power jet is taken out of action is very r, slightly lowered, as is desirable for summer operation.

Thus, in one of its broader aspects my invention contemplates providing a novel fuel mixture enriching device having means whereby the accelerator pump piston is operated directly from the throttle lever, with prolonged period of injection, and whereby the enrichment of the fuel mixture is precluded under conditions where economy of engine operation becomes important.

I claim:

1. In a carburetor and governor installation for an internal combustion engine having an intake passage, said carburetor having a throttle valve and said governor having a governing valve no in said passage, a throttle valve actuating lever,

a device for injecting additional fuel into the carburetor and actuated by said carburetor valve lever, a device cooperating with the injecting device for enriching the mixture under heavy ento glue loads, and means responsive to the vacuum in said passage for rendering said enriching device inoperative at predetermined engine working conditions.

2. In a carburetor and governor installation for an internal combustion engine having an intake passage, said carburetor having a throttle vaiveand said governor having a governing valve in said passage, a throttle valve actuating lever,

a devicefor injecting additional fuel into the 7 carburetor and actuated by said carburetor valve lever, a device cooperating with the injecting device for enriching the mixture under heavy engine loads, and means responsive to the vacuum at the downstream side of said governing valvefor rendering said enriching device inoperative at predetermined engine working conditions.

3. In a carburetor and governor installation for an internal combustion engine having an intake passage, said carburetor having a throttle valve and said governor having a governing valve in said passage, a throttle valve actuating lever, a device for injecting additional fuel into the carburetor..means connected to'said carburetor valve lever for operating said device, a device cooperating with the injecting device for em'lching the mixture under heavyengineloads, and piston means responsive to the pressure. in said passage at the downstream side of said governing valve for rendering said last named device ineffective to enrich the mixture at predeter- Y mined engine working conditions.

4. In a carburetor and governor installation for an internal combustion engine having an intake passage, said carburetor having a throttle valve and said governor having a governing valve in said passage, a fuel mixture enriching device for introducing additional fuel into the carburetor, a pair of members for operating said device, one of said members being connectedto said carburetor throttle valve, vacuum responsive means connected to the other of said members, and a yieldable connection betweensaid members.

5. In a carburetor and governor installation for an internahcombustion engine having an intake passage, said carburetor having a throttle valve and said governor havinga governing valve in said passage, a device for introducing fuel into the carburetor, a pair of members for operating said device, one of said members being connected to said carburetor throttle valve, vacuum responsive means connected to the other of said members, and a yieldable lost motion connection between said members.

6. In a carburetor and governor installation for an internal combustion engine having an intake passage, said carburetor having a throttle valve and said governor having a governing valve in said passage, a fuel injection device including an accelerator pump having a piston adapted to be operated in its buretor throttle, and means actuated by the vacuum in the intake passage at the downstream side of the carburetor valve for modifying the length of the stroke of said piston.

'7. In a carburetor and governor installation for an internal combustion engine having an intake passage, said carburetor having a throttle valve and said governor having a governing valve in said passage, a fuel injection device including an accelerator pump having a piston adapted to be operated in its injection stroke from the carburetor throttle, and means actuated by the vacuum in the intake passage at the downstream side of the governing valve for modifying the stroke of said piston. Y

8. In an internal combustion engine having an intake passage provided with a carburetor valve and a governing valve, an accelerator pump having a piston and a fuel injection conduit provided with a fuel valve, means connected to the carburetor valve for operating said piston in its injection stroke, said piston being adapted at the end of its injection stroke td maintain said fuel enriching injection stroke from the car- 7 valve in open position, and means responsive to the vacuum in the intake passage on the downstream side of said governing valve for moving said piston into position to permit closure of said I fuel valve in open position, and means responsive to the vacuum in the intake passage for moving said piston into position to permit closure of said fuel valve without affecting the position of the carburetor valve.

10. In an internal combustion engine having an intake passage provided with a carburetor -valve and a governing valve, an accelerator pump having a piston and a fuel injection conduit provided with a fuel valve, means connected to the carburetor valve for operating 'said piston in its injection stroke,

valve in open position, and a piston responsive to the vacuum in the'intake passage on the downstream side of said governing valve for moving said accelerator pump piston into position to permit closure of said fuel valve.

11. In an internal combustion engine provided with an intake passage having a carburetor valve and a governing valve therein, a fuel mixture enriching device including an accelerator pump provided with a piston, a pair of spring con nected members for operating said piston, means for connecting one of said members to the carburetor valve, and means actuated by the vac= uum in the intake passage and connected to the other member for operating the same at predetermined engine working conditions.

12. In a carburetor and governor installation for an internal an intake passage having a carburetor valve and a governing valve mounted'therein, a fuel mixture a. pair of swinging levers for operating said plunger, a piston responsive to the pressure in the intake passage and connected to one of said levers, means for connecting the other lever to said carburetor valve, and a lost motion connection between said levers.

13. In a carburetor and governor installation for an internal combustion engine provided with an intake passage having a carburetor valve and a governing valve mounted therein, a fuel mixture enriching device including a reciprocable plunger, a pair of swinging levers for operating said plunge ,a second piston responsive to the pressure in the'intake passage and connected to one of said levers, means, for connecting the other leverto' said carburetor valve, and a yielding lost motion connection between said levers.

14'. In an internal combustion engine provided with an intake passage having a carburetor valve and a governing valve therein, a fuel mixture enriching device including an accelerator. pump said piston being adapted atthe end of its injection stroke to maintain said fuel device including a reciprocable plunger,

combustion engine provided with havinga piston adapted to be operated from the carburetor throttle valve, means actuatedby the vacuum in the intake passage on the downstream side of the governing valvefor controlling the operation of said piston, said carburetor throttle valve having a throttle lever and a plurality of means for operativeiy connecting the throttle lever at any one of a pluralityoi points spaced di'flferent distances from the axis of rotation of said throttle valve, and means responsive to the vacuum in the intake passage at the downstream side of said governing valve for controlling the operation of said pistorf.

16. In an internal combustion engine provided with an intake passage having a carburetor throttle valve and a governing valve mounted therein, said carburetor valve having a throttle lever secured thereto, a fuel injection device, an oscillatable lever including a pair of relatively movable spring connected members for actuating said device, means for connecting one of said members to the throttle lever at any one of a plurality of points spaced diflferent distances from the axis of rotation of the throttle valve, :2.

vacuum responsive device, and means for connecting the latter to the other or said members.

17. In an internal combustion engine provided with an intake passage having a carburetor throttle valve and a governing valve mounted therein, a fuel injection device, a vacuum responsive member, an oscillatable lever including a pair of relatively movable spring connected parts,

means for connecting one of said parts to the throttle valve, and means for connecting the other part to said member.

' 18. In a carburetor and governor installation for an internal combustion engine having an intake passage, said carburetor having a throttle valve and said governor having a governing valve in said passage, an accelerator pump having a piston, a spring loaded piston responsive to the vacuum at the downstream side of said goveming valve, said spring loaded piston interconnecting saidpump and said throttle valve and adapted to resiliently transmit to the pump an actuating force adapted to move the pump piston through a stroke oi predetermined length, and means adapted to effect a positive connection between said pump and said throttle valve under,

predetermined engine operation conditions.

JARVIS s. JENNINGS, JR.

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