US2361132A - Carburetor - Google Patents

Description

s. CQ SMITH CARBURETOR Oct. 24, 1944.

Filed Sept. 23, 1937 4 Sheets-Sheet l INVENTOR. STuYw-:saur C, SMITH TToRNEY.

S. C. SMH-H CARBURETOR l Oct. `24, 1944.

Filed Sept. 25, 1937 4 Sheets-Sheet 2 INVENTOR,

S. C. SMITH CARBURETOR Oct. 24, 1944.

Filed Sept. 25, 1937 I 4 SheetS---Sheel'l 3 S. C. SMITH CARBURETOR Oct. 24, 1944.

Filed Sept. 23, 1957 4 Sheets-Sheet 4 R. Hl m m5 1Q T .N H V w T .5

Patented Oct. 24, 1944 CARBURETOR Stuyvesant C. Smith, South Bend, Ind., assignor 'to Bendix Aviation Corporation, South Bend, Ind., Ia corporation of Delaware ApplicatonSeptember 23, 19377, Serial No. 165,248 Y 1oA claims. (ci. 12s-119) This invention relates .to carburetors and ,more particularly to mechanism adapted for automaticallycontrolling the'carburetor choke.

The present application is a continuation in part of my copending applications `Serial No. 641,898, filed November '9, 1932, and Serial No. 41,439, filed September 20, `1935 (divisionof application Serial No. 653,500,1iled January 25, 1933,

now issuedas Smith-Patent 2,030,331).

Carburetors for internal combustion engines,l in -order to be automatic in operation, must vbe adapted under all conditions to vsupply a fuel mixture proper for the particular stage of operation of the-engine. During engine starting, `when the engine is cold and cranked at a speed =gen erally lower than its normal idling speeds, provision must -be made for an excessively rich mixture, and immediately the lengine commences to iire, and the speed is correspondingly increased, together with lengine suction, the mixture ratio#- must be reduced, and thereafter controlled according to requirements and regulated accordingly. `'Ii'hese varying conditions require `tremendous and rapid changes in the various carburetor control elements to meet the requirements vexisting at various stages of engine operation. This invention is directed Vtoward automatically controlling particularly fthe choke valve and throttle valves during engine starting and running by the utilization of the many variables in engine operation such as temperature, Ymanifold suction, intake suction, speed, etc. in' various novel and related fashions Ito produce substantially correct mixtures for the `various engine operating conditions. p

Certain embodiments of the present invention include a thermostat which is connected to the choke valve of the carburetor to control the .richness of the 4mixture produced thereby, and a vacuumactuated .piston .coupled to the valve and thermostat by a spring which .is tensioned tooppose `the tension of the thermostat, this spring being adjustable so that .the setting of the valve can be accurately controlled.

. .4 An object ofthe invention Ais to provide m a 5 carburetor an automatic choke adapted to .close- `ly follow and respond-'to the variations in engine requirements by :utilization yof engine temperature and speed or dependent variables thereof.

A further object is to provide an automatic choke having thermo-sensitive means with mechanism whereby the effect of the'thermo-sensitive means maybe varied upon engine starting.

Another object is to provide in a carburetork fa novel `mechanism for positively cracking the throttleduring choking.

A still further object yis to .provide an automatic 'choke adapted to .operate a plain balanced choke valve.

Still another `object of the .invention is to pro- ...vide a choke valve of simplified lconstruction and 1- having a minimum of parts.

A still further object is `to provide a thermostatically controlled choke valve, wherein manifold vacuum is adapted to vary the eliect of the i thermostat.

Still lanother object is to provide a `mechanism controllable by the carburetor Ythrottle valve, whereby the choke can be positively opened for airing out after .iiooding Yet a further object is the provision of a thermostatic control adapted to urge a choke valve open or closed dependent on temperature, and vacuum loper-ated Ymechanism for opening the choke slightly upon engine starting, and prior t warming up.

A further object is the provision of manifold' vacuum sensitivemeans for varying thermostatic vchoke action.

rl'he above yand :other novel features of the invention will appear more `fully hereinafter from the following detailed-description when taken in connection with the accompanying drawings. It is expressly understood, however, that the `drawings yare employed for purposes of illustration only and are not designed as a definition of the limits of the invention, freference lbeing had for this purposeto the appended claims.

In the drawings wherein like reference numerals indicate like parts;

Figure 1 is a diagrammatic view, partly in section, showing the apparatus of the invention;

Figure 2 is a view similar to Figure 1 showing another modification;

Figure 3 shows the invention adapted to a particular carburetor;

Figure A is a view similar to Figure 1 showing Vanother modication of the invention;

Figure 5 .isa View of the control mechanism of the inventionapplied t'o a carburetor that is located at a point remote from the exhaust manifold;

Figure 6 vis a crosssectional View taken along the line 6--6 of Figure 5.1ooking in the direction of the arrows.

. Figure 'lis a View in elevation partly in section,

fof another form of the invention;

Figure 8 is a view-in elevation partly in section,

of a carburetor embodying a further modified form of the invention;

Figure 9 is an elevation partly in section, of a further modified form of the invention;

Figure 10 is a view in elevation partly section, of a further modified form of the invention; and

Figure 11 is a sectional view of one form of thermostatic element adaptable for use in the modified form of Figure 7.

Referring now to the drawings in more detail, the apparatus shown in Figure 1 includes a car-V buretor I having a balanced choke valve I2 and a throttle I4. The carburetor is shown as a plain tube down draft carburetor, this type being illustrated by way of example only as the invention may be applied to other types of carburetors within the teachings of the invention. The shaft I3 of the choke valve carries a lever I5 fixed thereto and a lever I8 is fixed on the shaft of the throttle. These levers are connected by a rod 20 connected to lever I5 and coupled to lever I8 by a lost motion connection. As the throttleapproaches its wide open position, lever I8 operates rod 26 to crack the choke valve so that ailooded condition of the engine can be corrected. The amount that the choke valve is opened is governed by an adjusting nut 2|. The choke valve I2 is provided with a small poppet valve I6 of known construction to admit air for starting.

A thermostat casing 22 is mounted upon a suitable bracket 23 xed upon the intake manifold of the engine adjacent t0 the carburetor. and a shaft 26 is journaled in the casing. Athermoresponsive element 28 is fixed to the shaft and wound therearound and is disposed so as to be heated by heat radiated from the exhaustmanifold of the engine. The free end of the element bears against astud 36 projecting from the casing. An arm 32 is fixed upon the shaft and its free end is connected to the choke lever I by a rod 34. When the engine is cold thermostat 28 is tensioned to rotate lever 32 and close the lchoke valve and to maintain it closed during starting.

A cylinder 36 is mounted upon the intake manifold 24 and communicates therewith through a 'suitable port 31. A piston 38 is fitted in the cylinder and urged upwardly therein by a spring 40. A rod 4I is iixed to the piston and extends through an ear 42 on lever 32 and therebeyond,

the end of the rod being threaded to receive an adjusting nut 44. A sleeve 45 formed on nut 44 surrounds the rod, and va spring 46 surrounds the sleeve and bears against ear 42 and nut 44.

When it is desired to start the engine the throttle is set to starting position, that is, about one fourth open, and the choke valve is closed by the automatic mechanism just described. The engine is cranked and as soon as it begins firing piston 38 is drawn downwardly against the tension of spring 46. Sleeve 45 engages ear 42 and moves lever 32 to crack the choke valve so that the engine will not stall. Spring 46 is tensioned in opposition to the tension of the thermostat. As the engine warms up, the thermostat tension decreases and spring 46 moves lever 32 to open the choke valve more and thereby reduce the richness of the. fuel mixture. As the choke valve opens the tension of spring 46 decreases as lever 32 moves away from nut 44. When the normal operating temperature of the engine is reached, ther-y mostat 28 will have zero tension and the choke valve will be fully opened. As the thermostat is heated further, as it will be by heat radiated from the exhaust manifold of the engine, the end of the ele-ment moves away from bracket 30 and engages a second bracket 48. The thermostat is then tensioned in the opposite direction to aid spring 46 in holding the choke valve open. The particular type of thermostat shown is not new, being shown and more fully described in the copending application of S. F. Hunt, Serial No. 647,641, filed December 16, 1932. When the engine is stopped, spring 40 raises the piston and the tension of spring 46 is reduced. As the engine cools down, the thermostat is retensioned and le- `ver 32 operated thereby to close the choke valve.

In the modification shown in Figure 2 thermostat shaft 26 carries a multiarm lever 66 and choke valve control rod 34 is connected to the free end of one of the arms. A pivoted lever 68 is connected to piston 38 and provided with an ear 42 through which a rod 10 extends. The rod 10 is connected to one of the arms of lever 66. A sleeve surrounds the rod, and a spring 46 surrounds the sleeve and bears against the ear and a nut 44 as before. A third arm of lever 66 carries a pin 1I against which a lever 12 is adapted to bear. Lever 12 is connected iby rod 13 to the throttle lever and the lever 12 thus moves the pin and lever 66 to crack the choke valve when the throttle is Wide open.

In the operation of the device, the thermostat is tensioned to hold the choke valve closed when the engine is cold. When the engine fires, piston 38 is drawn into the cylinder and spring 46 tensioned to oppose the tension of the thermostat to permit the choke valve I2 to open under the pressure difference on its faces. The tension of spring 46 is adjusted by nut 44 as before.

In Figure 3 I have shown the invention adapted to a carburetor having a choke valve which comprises two leaves 14 which are hinged to the side walls of the structure. A stud 15 is fixed in the carburetor midway between the leaves of the Valve. A collar 16 is mounted on the stud for sliding, and is urged upwardly thereon by a spring 11. Collar 16 is grooved to receive the ends of arms 18 which are fixed on the leaves adjacent to the hinges. Air pressure on the upper face of the leaves and vacuum on the lower faces causes the leaves to swing on their hinges and the collar to move downwardly against the tension of spring 11. In the control mechanism, thermostat arm is fixed on the thermostat shaft and connected by a rod 8| to a pivoted lever 82 which carries an ear 42. Piston 38 is urged upwardly in cylinder 36 by spring 40 and carries rod 4I which extends through the ear and is threaded to receive nut 44 by which spring 46 and sleeve 45 are held on the rod. A bell crank lever 84 is pivoted adjacent to lever-82 and carries an ear 85 through which rod 86 slidably projects. One end of this rod is pivotally connected to lever 82 and the other end is threaded to receive a nut 81. A spring 88 surrounds the rod and bears against ear 85 and nut 81. A crank arm 90 is journaled in the carburetor casing and connected to lever 84 by a rod 9|. The free end of arm 90 bears against one of the leaves of the choke valve.

When the engine is cold and not running, thermostat 28, which is of the type shown in copending application of S. F, Hunt, Serial No. 647,641, above referred to, is tensioned to raise arm 80 and thereby rotate lever 82 clockwise on its pivot. Spring 88 is tensioned to rotate arm 84 and with it arm 96 to close the choke valve. The thermostat is tensioned sufliciently to keep the valve closed during starting of the engine. When the engine fires, piston 38 is drawn downwardly in the cylinder against the tension of spring 4U and spring 46 is -ten'sioned to oppose the thermostat 'and rsleeve =45 engages and moves lever 82 counterclockwise. The tension :of spring 88 is relieved .and the choke valve opened slightly. ySince the tension of spring :opposes the thermostat tension the effective force holding the valve closed is insufficient to resist the air pressure on it. The thermostat is arranged to decrease its'tension as the engine warms up and the valve opens wider, being fully opened when the enginereaches normal operating temperature. As. the valve opens, tension is built up in spring 1.5. When the engine is `stopped spring '48 raises piston 38 to `decrease the tension in spring v46 and as the` engine cools tension Vis built up in the thermostat 'and func tions to rotate farm 98 to fclose the valve with the aid of spring 15. Adjustments of the vchoke setting are made by adjusting nuts A44 `and 81.

In the embodiment of the invention shown in Figure 4, the shaft of thermostat 28 `carries a cam `82 upon which is mounted a pin 9'3. A lever 52 is pivotally mounted adjacent to the cam and connected to the throttle of the carburetor by suitable means 53. When the throttle is moved to wide open position, lever 52 lengages and moves cam 92 to partially open, the choke valve. VA 'shaft .94 is journaled in thecasing of the'mechah nism and carries a lever 96which is fixed thereto and carries a roller 85 that engages the cam. A second lever 88 is fixed upon shaft 94 and connected by rod 34 to the choke valve I2. A lever 31 floats upon shaft 94 and is connected to piston 38. Spring 48 urges piston38 upwardly tomove lever 91 counterclockwise on shaft 94. Lever `86 carries an ear 89 which overhangs lever 91 so that the tension of'spring 48 is applied to lever 88 to hold the choke valve closed. i

When the engine is cold, shaft -25 is urged `counterclockwise by the tension in the thermo; stat. A shoulder I8I on the cam strikes roller 95 to apply the thermostat tension to lever 98 to aid in keeping the choke valve closed while the engine is being cranked. Immediately the en gine fires piston 38 is drawn downwardly against spring 48 and lever 91 is moved away from ear 99 so that the tension of spring 48 is removed from the valve and it is partially opened against the tension of the thermostat by the diierenoe of air pressure on its faces. As the thermostat is heated cam 92 isi-rotated clockwise. RollerA 95 rides over cam surface |88 to move lever 96 counterclockwise and thereby open the choke valve. When the engine reaches normal .operating temperature, vroller 95 engages a concentric portion of the earn to lock the choke valve open, and further rotation of the cam is without effect. Movement of lever 96 reengages ear 99 with Alever 91 to lock the piston in its operated position so that it will not be vibratedby variations in pressure in the intake manifold during operation. This feature s more fully explained in S. F. Hunt Patent 2,015,752, granted October 1, 1935. When the engine is shut down, spring 48 raises piston 38 and closes the choke valve as soon as the tension in thermostat 28 rotates cam 82 back so that roller 95 engages surface IDD.

In many V-type engines the intake manifolds and carburetor are located on Ytop of the engine' and the exhaust manifolds are outside and under the cylinders. In an arrangement of this kind the thermostat of the control mechanism cannot be located sufficiently close to the exhaust manifold to permitit to be operated by heat radiated therefrom. In Figures 5 and 6 I have shown a modification of the invention adapting it to an which air escapes engine of 'this type. In this arrangement a casing |582 is mounted upon the boss |83 on the air horn of the carburetor `in which choke valve 'shaft .I3 .isjournaled A cylinder |84 projects from the bottom of this casing 'and Vis connected by a pipe |85 to the intake manifold `Iila of the engine. .A stove |86 is placed over the exhaust manifold IIlSa of the engine and Iconnected to the casing vby .a pipe |81 so that hot air will be 'conducted to the casing- Y Shaft I3 projects through the casing, and thermostat element 28 is fixed to and wound around the shaft. A piston 38 iits in the cylinder and carries -a rod H8 having a bent end over which the free end of the thermostatis hooked. A lever |08 oats on shaft I3 and the bent end of rod lI I8 extends through and is guided by the lever. A spring y48 fits in cylinder |84 and urges piston 38 upwardly to tension the thermostat so as to hold the choke valve closed when the engine is cold. A valve I-I2 oats upon shaft I3 and is connected to thermostat element 28 by a suitable clamp yI I3.

When the engine is not running and is cold, piston 38 is at the top of the cylinder and the thermostat is tensioned to hold the choke valve closed. Immediately the` engine res, piston 38 is drawn into the cylinder against the tension of spring 48 andthe effective tension holding the valve closed is reduced to permit the valve to partially open. As the engine warms up, heat from the exhaust manifold heats stove |86 and hot air passes through pipe I 81 into casing |82 to heat the thermostat. The casing is closed by a cover |I4 which has a central opening into which the end of shaft I3 projects and through yfrom the casing. Thermostat it is heated and with this loss of tension, valve I2 is permitted to open more nearly wide open. Preferably the thermostat will be adjusted so that the valve will be wide open when the engine reaches its normal operating temperature. Further heating of the thermostat raises the hooked end of the element off of rod I I8 and the element can move without damage to itself or to the casing. This movement of the element carries valve I I2l across the opening of pipe I 81 into the casing to block oit the heat therefrom. When the engine is stopped spring 48 raises piston 38. As the thermostat cools, its hooked end is reengaged with rod I I 8 and the element is tensioned to close the valve. Valve I I2 is moved to unblock pipe |81 and the apparatus is in readiness for another operation.

In vFigures l to 4 inclusive I have shown the control mechanism as a separatev unit mounted adjacent to the carburetor to simplify the figures, but it should be understood that` the control mechanism may be included as an integral part of the carburetor within the teachings of the invention. Throughout the figures parts which are not materially different in construction and function bear the same reference numerals.

In the embodiment illustrated in Figure 7 a carburetor `2I8, secured to an intake manifold 2| 2 has provided therein a Achoke valve 2| 4 and throttle 2I6. The choke valve may be of the unbalanced buttery type having a valve disc 2I8 28 loses tension as mounted upon an offset shaft 228, the valve disc proper being preferably provided with an inwardly opening relief valve 222 of the poppet type as shown which is spring pressed to cover relief apertures provided thereunder in the valve disc 2I8. suitably secured on the end of the valve shaft 228 is a crank 228 which is connected to a` rod 238 having sliding engagement with a tube 232 pivotally secured to the carburetor as at 234. Fitted between the free end of the tubel 232 and the end of the rod which projects beyond the free end of the tube is a series or pile of thermostatic elements 234' which may be inthe form of pairs of oppositely arranged bimetallic discs which tend to dish upon. heating, thereby tending to expand. When vapor filled sylphon discs 233, (see Figure 1i), are used, there is provided a tubular sylphon core 235 to permit the passage of the rod 238 therethrough. l

Preferably the rod 238 and tube 232 are so positioned as to bring the thermostatic element when cold close to a point on the motor which is quickly heated upon engine starting, which is preferably the exhaust manifold or an exhaust heated portion of the intake manifold. Upon being heated the thermostatic element not only opens the choke valve .but moves to a position (shown in dotted lines in Figure '1) further from the source of heat and thereafter regulates the choke in a modified manner. Such an arrangement provides for relatively high initial choking and gradual lessening thereof upon engine starting.

Although when cold, the thermostat resiliently Urges the choke closed, the unbalanced valve may open slightly against the resilient urge of the thermostat in response to engine suction created when starting and prior to any heat exchange between the manifolds and the thermostat.

For proper starting it is necessary that the mixture passage of the carburetor be opened partially so that substantial fuel charges may be drawn into the engine and for this purpose a bypass 248 around the throttle valve is provided. A spool valve 242 having a connection 246 with the choke by means of the arm244 of the choke crank 228 is adapted to actuate the spool valve, thereby opening the bypass during choking. The contour of the spool valve may be such as to provide a gradually decreasing area of cross section for the channel as the choke moves to open position or may be otherwise constructed as to provide a different characteristic as may be desired.

The modified form shown in Figure 8 comprises the usual carburetor 258 having a choke valve 256 and a throttle 254. To automatically regulate the choke valve, the same comprises an unbalanced valve disc 256 mounted on a shaft 258 which is thermostatically controlled by the spiral bimetallic thermostatic element 268. To give the desired choking effect during cranking the valve 256 necessarily must be substantially locked closed and for this purpose the thermostatic element is made sufficiently stiff and placed under the required tension.

Since the tension required to produce the desired choking effect at cold motor cranking speeds is greater than that required once the engine commences to operate, a vacuum responsive motor 262, connected either to the carburetor mixture passage on the engine side of the throttle valve as at-264 or to the intake manifold, is provided together with a connection 266, through resilient means to a lever arm 268 mounted upon the choke shaft 258. As illustrated the resilient means may consist of a spring 218 threaded upon the rod 266 so as to bear upon a swivel collar 212 secured to the lever 268 and upon an adjustable nut 214 upon the end of the rod. Upon high manifold vacuum, the piston 216 will be drawn downwardly within the suction motor 262 resiliently tending to open the choke valve 256. By properly balancing the resiliency andtension of the spring 218 and the thermostatic coil 268, an operating combination results which is capable of supplying the proper mixture to the engine under substantially all circumstances, and by further proper selection of the spring characteristics and by proper adjustment, the control may be applied to a choke utilizing a common balanced butterfly valve, of the same lgeneral type as the throttle valve 254.

Since it often occurs that an engine is cranked with the ignition circuit open by mistake, or for some reason or other the engine becomes flooded, there may be provided a connection between the choke valve and throttle so that the choke valve can be positively opened to air the motor out and discharge excess fuel into the vexhaust passages. For this purpose there is illustrated a connecting link 288 pivotally connected between the lever 268 on the choke valve and the crank 284 on the throttle valve 254. So that ordinarily the operation of the throttle may not disturb the automatic operation of the choke valve, the link 288 is preferably connected to the throttle by a lost motion connection as shown wherein the rod or link 288 slidably engages a swivel collar 285 secured to the crank 284, and provided at its end with a collar 286, which is adapted to engage the swivel collar upon opening the throttle wide, so that further movement may open the choke.

Referring to the modification of Figure 9, there is shown a downdraft carburetor 298 having an unbalanced choke valve 292 and throttle 294. Secured to the choke valve shaft 286 is a double crank member 298, operatively connected through a link 38| to a crank 382 actuated by a thermostat 384. A lever 386, pivoted on the choke shaft 296 is adapted to operate between spaced pins 388 on the crank member 298, thereby providing a lost motion connection. A vacuum operated cylinder 38T having a piston 388 is connected to the intake manifold preferably at any point on the engine side of the throttle valve 294, and is adapted through the piston 388 and link 3|8 to actuate the lever 386 during the high vacuum which will in turn engage the lower stop pin 380 and positively open the choke a small amount. At such times as substantially no vacuum exists in the manifold the piston may take the upper position shown by reason of the urge of spring 3l2 thereby causing the lever 386 to engage the upper stop pin 388 and urge the choke closed.

The thermostatic bimetallic element 384 isl preferably secured at its inner end so as to rotate the crank 382, and at its outer end is adapted to hook upon a stud 385. Upon heating of the element, due to its position adjacent some member of the internal combustion engine such as the exhaust manifold, tension tending to close the choke valve is gradually released due to the coiling action of the thermostat element, and when the element becomes hot enough, the outer end of the element may leave the stud 385 and coil in a clockwise direction until it strikes the abutment 383, whereupon the thermostat element will commence to urge the choke valve to an open position. It will be readily appreciated that for adjustment purposes the stud 385 and stop 383 may be secured to a revolvable shell 386 which may be frictionally or otherwise secured in any position to adjust the tension on the thermostatic ribbon or element.

As in the modification of Figure 8, the carburetor 298 may have a means for positively opening the choke by extreme movement of the` agenten V throttle valve,` there: beingr provided for this purpose, a rod 314 pivot-,ally secured: in: one end of the double crank 2&8, and slidably engagingfa swivel 'collar 3.164 on the cra-nk 3|f8 controlling the throttle. A fixed collar 32ll-on the` end. of the rodi serves to engage the swivel collar upon` open.- ing the. throttle wide, therebyv allowing the choke valve to be opened by extrememovement of. the throttle valve.

The further modified form ofrFi'gui-.e 10\isw also illustrated. asa adapted .to aA downdraft` carburetor 33D 'having a choke. valve 332 and throttle 334,. 'llhe choke valve mayv beof the unbalanced. type and isl carriedkon ae shaft 336 to whichf is also secured a cam 338 and spiral' thermostatic. ele:- ment` 3.411 Api-voted: lever 342 havingpreferably a roller follower 34141` is adapted to engage the outer cam, surface 346, and engage the inner cam surface 348. byv the: spur 3501 oni the lever, vto which is; also. secured.` the outery endof the. thermostatic` element 3.40. By: the.` usel of. a suction motor connectedto theintake manifoldasfatr35fl., which. motor comprises. an cylinder 352'` andi piston 354, actuation; of' the levery 342: through the connecting link 356 takes place in accordance with the manifold; vacuum-except as modified by' the heat of the resilient thermostatic element, which is exposed to a source of ht resulting either directly or indirectly from engine operation.

The outer cam surface 346 has a steep nearly radial portion 341 and alow pitched spiral portion 345 which are adapted to engage the roller follower 344. The steep portion 341 acts as a choke lock preventing the choke from opening due to suction on the unbalanced valve, without the aid of the suction motor 352, the mechanical advantage of the steep cam surface when driving the roller being too low to permit choke opening due to suction alone. The generally spiral section 348 provides a means for determining the position of the lever 342 once the choke has opened, and thereafter may regulate the tension on the thermostat since movement of the lever, through the spur 350 varies the position of the outer end of the thermostatic ribbon. Should the choke for any reason stick after the engine commences to run, manifold vacuum acting on the piston 354 will tend to rock the lever, urging the spur 350 against the inner cam surface 348 thereafter forcing the choke open.

Operation of the device illustrated in Figure produces a change in thermostat adjustment with changes in manifold vacuum. For example, lupon sudden opening of the throttle, a cold motor is often prone to .back fire due to the temporary existence of too lean a mixture, but with the structure shown, upon sudden drop in manifold vacuum as when the throttle is quickly opened, the piston 354 is released, allowing the spring 353 to urge the piston upward and rotate the lever 342 counterclockwise thereby instantaneously tightening the thermostat ribbon, and Inomentarily increasing the tendency to choke, which as a result enriches the mixture and tends to compensate for the sudden variations in throttle opening. It of course will be understood that the low pitch cam surface 345 regulates at all times the maximum tension which may be applied to the thermostatic ribbon for any given throttle position, and that the above operation occurs only at such times as when manifold vacuum is suiciently high to actually remove the roller from the cam contour. This action may be termed an economizer action, for in normal steady operation, the choke. is olered: little resistance to opening. permitting economical operation while upon sudden departure from steady operation, the. resistance i is instantly increased:r

Thoughf several: embodiments. of.y the. invention have. been illustrated` and described, it isito` be understood that: the invention is not limited thereto but may be embodied in variousfmechanicalzforms. For: example;k various;` elements ofthe modification-szmay` be interchanged, a's one may .benfound morer..desirable. irr. a specific easel than another. As many such'. changes in construction and; arrangement of' parts may bei made without departing from the spiritiof the. invention, as will be` apparent. tothosefs-killed. in the` art, reference will lnefliaditof` theapp'en'de'd claims. for a defnitionl ofi` ther limits 1 off the invention;V

Featuresl not claimed herein; are claimed in-my cnpending.-application, Serial. No; 395531, filed September 7-, 1.935,. as' a; divisioni. of my copending application" Serial; No.. 6.4.1,898gabo-ve referred to;

I claim; y

1.In` a, carbureton. an unbalanced choke valve; resilient thermostati'csm'eansfor urging saidvalve towards closed; positiom and: aamanifoldi vacuum' operatedr piston. having.: ai resilient: operating connection with said valve for urging said valve toward open position against the urge of said thermostatic means.

2. In a carburetor, a choke valve, a throttle valve, a manifold vacuum responsive motor, resilient thermostatic means for urging said choke valve closed, a resilient connection between said motor and choke valve for urging said choke valve open upon high vacuum in said motor, and means for positively opening said choke valve upon movement of said throttle valve to substantially Wide open position.

3. In a carburetor choke, an unbalanced butterfly choke valve, thermostatic means forcibly urging said valve closed when cold, and forcibly urging said valve open when heated, and manifold vacuum sensitive means operatively connected to said valve for positively Yopening said valve upon existence olf normal operating vacuum in the manifold.

4. In a carburetor, a pressure responsive choke valve, a throttle valve, thermostatic means for closing and opening said choke valve, manifold vacuum sensitive means including a cylinder and a piston for opening said choke valve, and connecting means between said choke valve and throttle valve to open said choke valve when said throttle valve is opened substantially wide.

5. A control mechanism for an internal combustion engine carburetor having a choke valve and a throttle, comprising a thermostat connected to the choke valve and tensioned when cold to hold the choke valve closed for starting and to permit the same to fully open when the engine reaches a predetermined temperature, a piston actuated by vacuum posterior to the throttle when the engine is running, and yieldable means connecting the piston to the valve in opposition to the thermostat.

6. A control mechanism for an internal combustion engine carburetor having a choke valve and a throttle, comprising a shaft, a lever xed on the shaft, means connecting the lever to the choke valve, a thermostat connected to the shaft and arranged to rotate the same to close the choke valve when the engine is cold, an ear on the lever, a rod extending through the ear, a

" spring fixed on the rod and bearing against the ear, and means connected to the rod and actuated by vacuum posterior to the throttle for tensioning said spring to oppose the thermostat and open the choke valve.

7. A carburetor havinga choke valve, a carbureting passage, athrottle valve controlling the carbureting passage, temperature responsive means adapted to urge the choke valve toward the closed position when cold and to permit the choke valve to fully open when heated to a predetermined temperature, pressure responsive means communicating with the carbureting passage posterior to the throttle valve, and yielding means connecting the pressure responsive means to the temperature responsive means.

8. A carburetor having an air inlet passage, a pressure responsive choke valve controlling the air inlet passage, a carbureting passage, a throttle valve controlling the carbureting passage, temperature responsive means controlling the choke valve, iluid pressure actuated means communicating with the carbureting passage posterior to the throttle valve to modify the action of the temperature responsive means, and yielding means between the temperature responsive means and the uid pressure actuated means.

9. A control mechanism for a carburetor having an air inlet passage and a carbureting' pas* sage, a pressure responsive choke `valve controlling the air inlet passage, a throttle valve controlling the carbureting passage, temperature responsive means `adapted to exert aforce when cold and to discontinue said force when heated to a predetermined temperature, connecting means -between the temperature responsive means and the choke valve, and pressure responsive means yieldingly connected t0 said connecting means.

10. A control mechanism for-a carburetor having an air inlet passage and a carbureting passage, a pressure responsive choke valve controlling the air inlet passage, athrottle valve controlling the carbureting passage, temperature responsive means adapted to exert a force when cold and to discontinue said force when heated to a predetermined temperature, connecting means between the temperature responsive means and the choke valve, and pressure responsive means communicating with the carbureting passage beyond the throttle valve and yieldingly connected with the connecting means to modify the action of the temperature responsive means.

STUYVESANT C. SMITH.

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