US2808244A - Carburetor - Google Patents

Description

Oct. 1 1957 L. c. DERMOND 2,808,244

cARBuREToR Filed June 2:5, 1954 2 76 lo 2 8O 74 E I I .I 78 g l L A 12 l 88 1o 8 a2 24 so 28 n y 5e 26' *44 n 54 4o 4 56 4 42 64 l2 A l v 4s le It es I as f ,I efe ,fsf M F192 m K l 1 l )QW 93 loo i o "i \m `92 INVENToR. 98 i '04 Lawrence' C. Dermond a IOGBY l |02 611g Wifi/nd los CARBRETOR Lawrence lC. Dermond, Rochester, N. Y., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application Jne 23, 1954,-"SeiialNo. 438,771 s claims. (ci. 261-39) This invention relates to carbiiretors -for internal combustion engines, particularly engines for automotive vehicles 'and more specifically to automatic choke mechanism operable to automatically controlthe-position of an airinlet valve, in order to regulate the air-and fuel ratio thermostatwhich exerts a force tohold the valve closed at low temperatures, and by a suction-operated piston responsive to variations in'suction posterior to the throttle and Iexerting a force tending to `openthe valve as the suction increases.

Devices of this Vkind are Valso old in which a given change in temperature or engine suctiondoes not produce the same movement of the choke valve Vthroughout the entire range of movement ofsaid valve. In other words, if 'the temperature increases a given number of degrees and the suction increases a given number of inches of mercury, the movement of -the valve effected by such changes is different if'the changes occur when the valve is Yin one part of its range-of movement than if the valve is in Va different part of-its range ofmovement when such changes occur.

Devices Aof this kind are provided because characteristcs of different engines vary and with some engines, for example, it is desirable to move the choke valve more rapidly toward open'position upon a vgiven increase in temperature and suction, when the valve is in a certain part of its operating range-than it is with other-engines. `For example, it may be desirable, with some engines, to move the valve more slowly toward open position irnmediately after the engine has been started and is warming up than ywith other engines because some 4engines require Ia richer mixture for best operation under such conditions than do other engines.

It is the primary object or purpose of this-invention vto provide'in a carburetor an automatic-chokevalve which is controlled by variations in temperature and engine suction and novel means for moving such choke valve in States Patent response to variations in 'these `factors `at -such different rates per unit of change therein that its movement throughout Vits operating range will be such as to obtain the mixtre ratiobest suited for operation of'a'particular engine.

More particularly, it is an object ofthe invention `to provide a carburetor having an automatic choke valve of the character described, themovementofwhich toward open position be relatively retarded immediately after its initial movement'which occurs' Whenthe engine starts to run under its own power', and which Willsubsequently be moved more rapidly afterth'e valve is opened Ipiston ineffective to move 'the valve.

to a predetermined extent, and novel means for effecting these movements of the valve.

According tothe presentinvetition, the objects thereof are accomplished by the provision'of a suction operated piston connected to the choke valve and subject rto the effect of suction in the'engine-intake passagerposterior to the throttle when the valve is in closed position, so that immediately `after the engine starts torun under its own Ypower'the valve is moved, by suction effective on such to thethermostat housing througha constantly open passage and draws "heated 'air through said housing to heat up the thermostat 'and 'bring 'aboutthe above-described motion of the valve during the engine Vwarm-up period. As the choker valve -opens the suction operated piston, 'which is connected to said valve and 'moves vwith it,rst 'substantially blocks "the passage through which sliction is communicatedto :the end of -the 1` iston,-to'render the Then as theV choke valve moves on'further-towa'rdopenY position, a second passage leading to -the therm`ostat`-housing is placed in communication with =the suctionpassage at `a Vpredeterminedopen `position of theehoke valve.

`After the chokevalve reaches-.this position, the heating ofthe-thermostat-ismuch more rapid than previously, so that thernal movement ofthe choke valve to full-open position is considerably faster-than.thelm'ovement of such valve during `the intermediate portion of its range of movemennafter ythe `effect .of suction 4on the piston has become substantially ineffective and before the second passage to the thermostat housing isfopened.

Further objects .and advantages `of the :present invention will be apparent from the followingdescription, 'reference being .had to the accompanying-drawings wherein a-preferred embodiment ofthe present invention is clearly shown.l f

In the drawings:

Figure 1 isa vertical section, partlyin elevation, of a conventional down-draft carburetor embodying they present invention; and v Figure 2 is a detail section on the line 2 2 of Figure l.

The carburetor shown in the-drawings is, in general, of conventional construction and lsubstantially the same as that shown inthe copending application of -Elmer Olson, S. N. 192,035, ledOctober 25, 1950,` now Patent No. 2,698,168 dated Dec. 28, 1954, and comprises three castings 2,- 4 and 6 AsuitablyV secured together by screws 8,-or in jany suitable way. n The casting-2 is the air inlet `casting having apassage 10 for .admission of air. The

-casting4 is theA fuel chamber casting and has a constant level fuel chamber 12 therein, in which vfuel is maintained at a substantially constant level mechanismhwhich Will be very briefly described later. The passage 10 communicates with a chamber or passage' 14 centrally located in the casting 4 into which fuel is yintroduced and which forms the mixing chamber ofthe carburetor.

The casting 4 is immediately above and Vsecured to the casting 6 which is 'the outlet casting 'and is secured in anysiiit'able 'way'to/.the intake manifold of the engine.

iotletlpassage V1'6`is formed in 'the casting 6 and connects with the passage "14, the 4passages "10, T4 and 16,

forming a continuous intake passage through the carburetor through which air entering the inlet flows and 1s mixed with fuel to form a combustible mixture which ows through the outlet passage 16 to the engine.

The flow of mixture from the carburetor is controlled by a suitable throttle Valve 18 secured to a shaft 20 suitably journalled for rotation in the walls of casting 6. This throttle is manually operated in the usual manner by means of an arm 22 secured to one end of the shaft 20 and is variably positioned to control the Volume of mixture supplied to the engine and the speed thereof.

Fuel is supplied to the fuel chamber 12 through-a passage 24 formed inthe wall of casting 2 and communieating with this passage'is a nipple-26 threaded in the wall of casting Zand having a passageV 28 which conveys fuel from passage 24 to chamber 12. The nipple 26 is enlarged at its lower end to form a cylindrical chamber 30 in which is received a'valve 32 which controls ow through passage 28. 'This valve is freely movable and its lower end rests on a tang 34 cut out from and integral with a plate or bracket 36 which is secured to a float (not shown), and is pivoted on a pin 38 mounted in lugs 40 which are integral with and depend from the casting 2 into the chamber 12. When the fuel eaches a predetermined level, the float is raised enough to move the valve 32 against its seat to close passage 28. This is a conventional float valve construction and forms no part of the present invention.

A tube 42 is secured at its upper end in any suitable way to an annular rib 44 projecting from the casting 2 and has a fuel passage 46 formed therein to convey fuel from the chamber 12 to the carburetor mixing chamber. A calibrated plug 48 is screwed intorthe lower end of tube 42 and meters the fuel supplied to the mixing chamber. The passage 46, at its upper end, connects with a cross passage 50 formed in a bridge member 52 which extends across the mixing chamber and is integral with the casting 2. The passage 50 supplies fuel to the main nozzle 54 which extends into a small venturi tube 56 positioned in the mixing chamber and extending into a large venturi 57 which forms the wall of the mixing chamber. A plug 58 having a restricted orifice therein is positioned in the main nozzle to aid in atomizing the fuel. Air is admitted to the passage 50 through two small passages 50 to mix with the fuel flowing therethrough.

Positioned in the bridge piece 52 at the right of the main nozzle is a sleeve 62 having a passage therethrough for idling fuel and at its right end this sleeve is somewhat reduced in size so that it is spaced from the wall of the passage t), as shown in Fig. 1. The fuel which flows through the sleeve 62 ultimately reaches vthe passage 64 which supplies fuel to idling fuel supply inlets (not shown), which deliver fuel adjacent the edge of the throttle valve 18. Y

The admission of air to the passage is controlled by an automatically operated choke valve 70, secured to a shaft 72 suitably journalled for rotation in the wall of the casting 2. This shaft has secured to the left end thereof, as seen in Fig. l, an arm 74 which has a horizontally extending portion 76. The shaft 72 extends into a housing 78 which is a part of casting 2 and is provided with a removable and adjustable cover-plate 80 which may be either metal or a suitable plastic and is held in any adjusted position by screws 82. The arm 76 at the end of the choke shaft and cooperating parts, about to be described, are positioned in this housing.

The arm 76 is engageable by the hooked end 84 of a thermostat 86 the other end of which is secured to a pin 88 which is fixed in the cover-plate 80, as Shown in Fig. l. Upon reduction of temperature, the hooked end 84 moves counter-clockwise to engage the extension 76 of arm 74 and exerts a pressure thereon to hold the choke valve in closed position, as shown in Fig. 2. By adjustment of plate 80, the pin 88 is rotated and changes the pressure exerted by the thermostat at any given temperature to hold the choke valve closed.

The lower end of the arm 74, as seen in Fig. 2, is pivotally connected to a link 90 which is pivotally connected to a cross-pin 92 extending across a slot 93 in the right end of a piston 94slidable in a horizontal cylinder 96 integral with the housing 78 and to which the suction maintained in the intake passage posterior to the throttle 18 is communicated through a passage 98. The passage 98 may connect with the carburetor outlet between the throttle and the manifold or with the intake passage in the manifold itself. The particular position of this connection is not material as long as it is on the engine side of the throttle.

rPhe mechanism so far described is substantially the same as that shown and described in the co-pending application previously referred to.

In the device disclosed in such application the suction passage comparable tothe passage 98 connects with the cylinder in which the suction operated piston slides substantially at the end of such cylinder, so that the suction, which is communicated through such passage, is effective on the piston throughout the whole range of movement of the choke valve and exerts a pulling force on the piston until the valve reaches fully open position.

ln the device disclosed herein the passage 9S connects with the cylinder 96 by means of an orice 100 in the wall of the cylinder. This orifice is of rectangular shape, as shown, but may be triangular or of any other shape desired, but this orice is positioned relatively close to the end of the piston when the valve is in closed position so that the' valve cannot open very far before the orice is completely blocked by the side wall of the piston. As illustrated, the piston reaches approximately the position designated by the dotted line A when the choke valve is about 20 open. The piston 94 is slightly loose in the cylinder in which it slides so as to permit leakage of air past the piston and when the piston reaches the dotted-line position, the area of the orifice not covered by the piston is very little greater than this leakage space. When the parts are in such position, air can enter the cylinder at almost the same rate as it is withdrawn therefrom, by action of the suction passage 98. Hence, there is very little partial vacuum maintained in the D cylinder 96 when the piston reaches line A and the suction communicated through the passage is ineffective to move the choke valve further toward position.

The choke valve will be moved to this position by suction almost immediately after the engine starts to run under its own power, and this position of the valve is that which has been found most desirable for the beginning of the warm-up operation of some particular engine. It might be desirable to secure a greater or less substantially immediate opening of the choke valve for some other engine and this could be accomplished by appropriate positioning of the orifice 100.

It also should be apparent that there may be some slight difference in the position assumed by the valve when it first is moved by engine suction when the engine starts to run under its own power, due to the difference in force exerted by the thermostat at different temperatures. This difference will be very slight, however, as the valve will move immediately to a position where the opening and closing forces are balanced and this will be very close to the line A with the piston end somewhere opposite the orilce 100, and very quickly the thermostat will warm up enough for the piston to move to` lineA. Obviously, in view of the foregoing, the choke valve will move, almost immediately and quite rapidly after the engine starts, to a position about 20 open, which has been found desirable for some particular engines.

If the suction which is communicated through the passage 98 continuedto be effective Yon the piston so that the valve would continue to be moved by the effect of suction during the warm-up period, it has been found for aannam@ some engines that the vmovement would be vtoo rapid and the mixture would become too llean lfor ventirely satisfactory operation. It is, therefore, desirable .to `retard the further opening movement ofthe valve relative to its rate of movement at the beginning-of such movement, sothat its opening from .20 -tosomepredetermined position, more than open, isrelatively slow. Therefore, the oriiice 100 is so positioned that .after the valve opens about 20 the suction becomes substantially ineffective and the subsequent movement ofthe valve is controlled by the rate at which the thermostat is heated.

To this end, Lthe :passage '98 connects `with Va passage 102 formed in the casting 2 xwhich leads @to the interior of the housing 78 and also a passage 104 formed in a threaded nipple V106 extendingfrom the housing 78 'communicates with 'the interior-thereof. This nipple may be positioned at any point on the housing where it gives the best results. Connected to the nipple 106 is a conduit 108 leading to a source of hot air (not shown), for example, a stove on the exhaust manifold.

The engine suction is communicated through passage 102 to the interior of housing 78 and draws heated air through passage 104 through the housing to heat the thermostat. During the warm-up period, after the piston has reached line A, the heated air passing through housing 78 progressively heats the thermostat so that the hooked end 84 moves clockwise and away from the extension 76 of arm 74. As the end of the thermostat so moves, the choke valve is moved toward open position, at a rate which is determined by the thermostat, by the force exerted by the entering air directly on the choke valve 70. This movement is relatively slow until the choke valve reaches a predetermined open position when the rate of movement of the choke valve is considerably increased and the valve continues to move at the increased rate until it reaches full open position.

To effect this increased rate of movement, the piston 94 is cut away on the lower side thereof, as indicated at 110 and this cut-away portion of the piston is brought into registry with the orifice 100 when the choke valve is about 55 open. As soon as this occurs, the eect of suction communicated to the interior of the housing 78 is much increased and much larger quantities of heated air per unit of time are drawn through housing 78. This eiects heating of the thermostat more rapidly after the choke valve is opened to the extent referred to and more rapid opening movement of the choke valve is effected from that point to its full open position, than its movement from 20 open to the position at which the cutaway portion 110 becomes effective. l

It will be apparent from the foregoing that in the device disclosed the choke valve is moved very rapidly by the eect of engine suction, when the engine starts to run under its own power, to a position about 20 open, the effect of engine suction is then substantially eliminated, the valve is then moved more slowly at a rate controlled primarily by the thermostat to a position about 55 open, and finally is moved more rapidly from 55 open to full open position, this being effected by more rapid heating of the thermostat after the valve is opened to that extent. These movements of the valve could be brought about at dilerent points in its operating range by changing the position of the orifice 100 or changing the length of the cut-away part 110 of the piston. By suitable dimensioning of the parts, substantially any desired rate of movement of the choke valve can be obtained at different parts of its operating range.

It may be said that, upon acceleration during the warmup period, the operation of the device disclosed herein is somewhat different from the conventional automatic choke. ln the latter, when the throttle is opened to eect acceleration, the choke moves somewhat toward closed position, due to the drop in suction effective on the piston corresponding to piston 94. In this device, since the suction is substantially ineffective on the piston after the valve `is .20 i open, v-the 'drop in Ysuction in passage 98 `when' sthe throttle iszopened is substantially vwithout etfectland the Yvalve will probablybe opened-slightly due tothe increase in pressuredilferential across the vvalve 70 itself. Therefore, -the -desired mixture vfratio for .acceleration must be effected by'theaccelerator pump which is probably `beneficial because tthe :pump is morefeasily =and;accurately.c'on trollable.

While the Vembodiment of the .present invention 'as herein disclosed constitutes :a ypreferred form, itis to kbe understood that other .forms mightfbefadopted.

What is claimed is as follows:

=l. In a charge 'fortningrdevice for aninternal combustionrengine Ahaving a-constant level fuel supply chamber, anlintake passagehavingfuel and air inletsand a mixture outletfor lsupplyi'ng la combustible mixture .to lsaid engine, a :throttle -valve lfor,c-:ontrolling' fthe itlow of ksaid mixture, an unbalanced choke valve operable in response to variations in the intake passage for controlling the admission of air through said inlet; mechanism for automatically controlling the operation of said choke valve comprising a thermostat operable to exert a force tending to hold said valve closed upon a reduction in temperature, a suction operated member connected to said valve and operable to move said valve toward open position upon an increase in suction, a conduit to communicate the engine suction to said member, said conduit being so positioned that it is blocked by said member when the valve reaches a partially open position, a housing in which the thermostat is positioned, a source of heated air, a suction passage communicating with said housing and effective to draw heated air from said heat source through said housing to progressively heat the thermostat whereby the valve closing force of the thermostat is progressively reduced and the choke valve is moved further toward open position only by the suction effective on the valve itself after said conduit is blocked by said suction operated member, and a second means for drawing heated air through said housing which is rendered effective when the choke valve reaches a predetermined open position to effect more rapid heating of the thermostat so as to bring about more rapid movement of the valve toward open position after it has been opened to a predetermined extent.

2. In a charge forming device for an internal combustion engine having a constant level fuel supply chamber, an intake passage having fuel and air inlets and a mixture outlet for supplying a combustible mixture to said engine, a throttle valve for controlling the ow of said mixture, an unbalanced choke valve operable in response to variations in the intake passage for controlling the admission of air through said inlet; mechanism for automatically controlling the operation of said choke valve comprising a thermostat operable to exert a force tending to hold said valve closed upon a reduction in temperature, a suction operated piston slidable in a cylinder and operatively connected to the valve so as to move the valve toward open position upon an increase of suction, a suction conduit connected to said cylinder intermediate its ends and adapted to be blocked by said piston when the valve is moved to partially open position so that the piston is rendered ineffective to move the valve further toward open position, a housing surrounding the thermostat, a source of heated air, a constantly open passage connecting said conduit with the housing and effective to draw heated air from the heat source through the housing to heat the thermostat and reduce its valve closing force so as to permit further opening of the valve by the suction effective on the valve itself, and a second normally closed passage connecting said conduit with the housing, said last named means being rendered effective after the choke valve reaches a predetermined open position.

3. In a charge forming device for an internal combustion engine having a constant level fuel supply chamber, an intake passage having fuel and air inlets and a mixture outlet for supplying a combustible mixture to said engine, a`throttle valve for controlling the flow of said mixture, an unbalanced choke valve operable in response to variations in the intake passagefor controlling the admission of air through said inlet; mechanism for automatically controlling the operation of said choke valve comprising a thermostat operable to exert a force tending to hold said valve closed upon a reduction in temperature, a suction operated piston slidable in a cylinder and operatively connected to the valve so as to move the valve toward open position upon an increase of suction, a suction conduit connected to said cylinder intermediate its ends and adapted to be blocked by said piston when the valve is moved to partially open position so that the piston is rendered ineffective to move the valve further toward open position, a housing surrounding the thermostat, a source of heated air, a constantly open passage connecting said conduit with the housing and eiective to draw heated air from said heat source through the housing to heat the thermostat and reduce its valve closing force so as to permit further. opening of the valve by the suction effective Von the valve itself, said piston having a passage in the wall l0 position as the valve approaches its fully open position.

References Cited in the le of this patent UNITED STATES PATENTS Winkler Sept` 26, 1950 v2,719,706 Winkler Oct. 4, 1955

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