US2015752A - Carburetor - Google Patents

Description

Oct. 1, 1935. s. F. HUNT CARBURETOR Filed Jan. 25, 1953 2 Sheets-Sheet 2 I INVENTOR. ficoff /T Hum 4- Q fir g ATTORNEY Patented 1, 1935 UNITED STATES PATENT oFFIcE cancuan'ron i Scott F. Hunt, South Bend, Ind., assignor' to Bendix Aviation Corporatiom South Bend, Ind.,

a corporation of Delaware Application January 25, 1933, Serial No. 653,518

' 9 Claims. (01. 123-119 The present invention relates generally to carburetors, more especially to fuel mixture control -valves therefor, and specifically provides a valve which, when the engine is not running or is rotating at cranking speed, is set to produce a rich .mixture and this setting automatically altered, under the joint control ofthe engine temperature and intake manifold pressure, to grade down the richness of the mixture. 1U Carburetors, designed to form a mixture of liquid fuel and air for consumption in an internal combustion engine, are. usually provided witha manually operated choke valve for governing the air supply to the Ecarburetor. Certain prior art devices, of which I am aware, provide for automatically operating the choke valve, and the instant invention provides certain improvements in such automatic devices.

In the copending application of Hunt and '20. Olson, SerialNo. 575,025, filed November 14, 1932,

there is disclosed an automatic choke valve 'arrangement over which the instant invention broadly is an improvement. This copending application' provides an unbalanced 'choke valve which is maintained'closed by toggle links. A

piston is connected between the intake manifold of the engine and atmosphere and is actuated by the pressure difference imposed on it by the negative pressure or vacuum produced in the 30 manifold when the engine is running. The piston moves into its operated position against'the tension of a spring, this movement serving to unlock the toggle links so that thechoke valve may be opened by the difference in pressure on its anterior and posterior faces. The opening of the valve is opposed by tension in a thermostat when the'engine is-cold. This tension decreases as the motor warms up, becoming zero when the normal operating temperature is reached.

40 In accordance with the teachings of the present invention the fuel mixture control valve, which may be' either a. choke valve or a fuel valve, is held closed by the pressure of a spring, against which the vacuum piston works and by the ten- 45 sion, in the thermostat when'the engine iscold.

The spring is eflfective when the engine is not running and when it is being crankedpreparatory to starting. As soon as the engine begins firing and a predetermined vacuum is built up in the intake manifold, the piston is actuated to remove the pressure of the spring from the control valve, leaving the control valve to be controlled solely by the thermostat.

Should the vacuum in the intake manifold fall 55 below this. predetermined amount during the warming up period of the engine, as it will if the engine is accelerated rapidly or loaded heavily, the piston is restored and the tension of the spring reapplied to'the control valve and the valve is operated to enrich the fuel mixture. d

When once the control valve has been moved.to one of its extreme positions,'it' is locked by toggle links which also serve to hold the piston in its operated position so that itcannot be moved by pressure variations produced in the intake manio fold during the operation of the engine.

An important object of the present invention resides in the provision of aconnection between the throttle and an automatically controlled choke valve which facilitates cleaning the engine after it has been flooded, as by cranking it with the ignition circuit open. By opening the throttle completely the piston is mechanically moved to its operated position, and the choke valve is placed under the control of the thermostat. The pressure difference built up on the two faces of the valve by cranking the engine is sufllcient to open the valve, and an excess of air is drawn through the carburetor to clean the same.

The" teachings of my invention will be best understood from the detailed description and claims which follow, reference being had to the accompanying drawings in which a preferred embodiment is shown by way of example and in which; i '80 Figure 1 is' an elevational view, partly in section, showing a carburetor and associated mechanism embodying the invention;

Figure 2 is a cross sectional view along the line 2-2 of Figure 1;

Figure 3 is a diagrammatic view of the apparatus shown in Figure 1; 2

Figure 4 is a diagrammatic sectional view showing the choke valve;

Figure 5 is a fragmentary sectional view taken along the line 5-5 of Figure 2;

Figure 6 is a perspective .view of a modified form of control unit;

Figure 7 is a fragmentary view showing tb leverage system of Figure 5 in one of its extreme positions;

Figure 8 is a view similarto Figure 7 showing the other extreme position of the levers; and

Figure 9 shows another modification of the invention.

Referring now to the drawings in'more detail, in Figure l I have shown a carburetor I0 which is provided with a choke valve l2 and a throttle l4. As shown, the carburetor I0 is of the plain tubefdowndraft type, and the choke valve and throttle are mounted for rotation about horizontal axes. may be substituted within the teachings of the invention. The choke valve I2 is of the unbalanced type, that is to say the shaft I3, by which it is mounted in the carburetor, is located to one side of the center of the vane portion of the valve, and when the upper face of the valve is exposed to a pressure higher than that on the lower face, the valve will tend to move into a vertical position.

As shown, the choke valve control mechanism comprises a casing I 6 which is fixed. upon the intake manifold I8 of the engine, but it is to be understood that this casing may be formed as an integral part of the carburetor within the teachings of the invention. A shaft 28 is journaled in the casing and extends therebeyond in both directions. An arm 22 is fixed to the one end of shaft 28, and a rod 24 connects the free end of this arm with the free end'of crank arm 26, which is fixed upon the shaft I3 to operate the valve I2. The opposite end of shaft 28 projects into a thermostat casing 28 in which is disposed a spiral wound bimetallic thermostat element 38. One end of the element 38 is fixed in a slot 3| in the end of the shaft 28, and the other end is hooked over a suitable post 32 carried by the casing. The element 38 is arranged to place the shaft 20 under a torque tending to rotate it clockwise (Figures 1-4) when the element is cold, that tension decreasing as the element is heated by the engine. The casing I6 is mounted so as to bring the element 38 into heat exchange relation to the exhaust manifold of the engine, and when hot the element 38 may unhook itself from the post32, during the normal operation of the device, to prevent stressing the element unnecessarily.

' The shaft 28 also carries a crank lever 36 which is keyed thereto, and to the free end of which a link. 38 is pivotally secured. A second shaft 48 is journaled in the casing I6 in parallel relation to the shaft 28. A lever 42 is journaled upon the shaft 48 for rotation therearound, andthe free end of'the link 38 is pivotally secured to lever 48 to form a toggle.

A cylinder 44 is located in the casing I6 and communicates with the region posterior to the throttle valve I4 through a suitable port '46,

which may if desired contain a check valve, such s as is shown in the above mentioned copending application. Within the cylinder is a piston 48 which is urged upwardly therein by a spring 50. The shaft 40 carries a second lever 52, journaled for rotation therearound and containing an ear 54 Which overhangs the lever 42. The shaft 48 also carries a lever arm 56 which-is fixed thereto and connected'at its free end to the throttle operating lever 68 by a suitable rod 58. An arm 82 is fixed upon shaft 48 adjacent to the lever 52 and is provided with an ear 64 which overhangs the lever 52. The assembly thus formed is protected by a suitable cover 66 which is fixed upon the casing I6.

When the engine is cold, thermostat 38 is tensioned to rotate shaft 20 in a clockwise direction, as represented by the vector 30 in Figure 3, and spring 58, acting through lever 52, ear 54, lever 42, link 38, and lever36, acts in the same direction. Shaft 28 is rotated clockwise and the choke valve I2 is closed through the movement of lever 22, rod 24, and lever 26. When the engine is cranked, preparatory to starting, a relatively small amount of air is drawn into the car-- Other types of carburetors and valves buretor' around the choke valve, and a rich mixture is formed. During cranking, the vacuum in the intake manifold is not suflicient to overcome the tension of spring'58 and piston 48 is not moved. a

As soon as the engine fires, high vacuum is built up in the intake manifold I8, and piston 48 is drawn downwardly against the force of sprirm 58, lever 52 being rotated thereby to raise the ear 54 out of contact with the lever 42. This leaves the choke valve held closed only by the tension of the thermostat 30, and since the tension in the thermostat is rather small the choke valve is opened by the difference in pressure on its two faces. With the choke valve opened part 1 way, an increased amount of air isv available to the carburetor and the mixture delivered to the engine is sufllciently lean to prevent stalling.

The vacuum .in the intake manifold decreases when the engine is heavily loaded or is being accelerated rapidly, and should this occur during the warming up period of the engine, the vacuum may be insuflicient to hold down piston 48 against the force ofspring 58. Piston 48, on rising in cylinder 44, reengages ear 54 with lever 42 so 5 that the force of spring 50 is again exerted on choke valve I2, to partially close that valve and enrich the fuel mixture.

As the engine warms up, the force exerted by thermostat 30 decreases, finally reaching zero 30 when the normal operating temperature of the engine is reached. The choke valve will then be moved, by the force of the air drawn past it, into the fully opened position in which it is shown in locked position. v

I While the toggle is moving toward its locked position, lever 42 engages the ear 54, depressing in Figure 1. This movement rotates the shaft 5 22, rod 24 and lever 26 hold the toggle mechanism the piston 48, and when the lever 42 is locked in' its uppermost positionby the toggle, the piston 48 is held in its lowermost position mechanically and cannot be vibrated by the variations in pressure occurring in the intake manifold during the operation of the engine. Since the piston does not vibrate or operate unnecessarily, it is not subjected to great wear and its useful life is in-, creased.

As will be seen in Figure 4, the effective area (horizontal projection) of the choke valve I2 upon which the pressure diflerence is exerted to move the piston, decreases as the valve moves from its closed position, shown in full lines, through intermediate positions A and B to'its open position C, and becomes zero in position C. It willbe seen from Figure 3 that the arrangement of levers 26, 24 and 22 is such that the moment exerted by the choke valve about shaft I3 has a definite mechanical advantage in rotating shaft 28, which mechanical advantage is 70 words, a given moment developed by the differential of air pressures on opposite faces of the choke valve exerts but a relatively slight force on shaft 20 when the choke valve is closed or nearly closed, but during the later stages of the warming up operation, when the choke valve is approaching its open position, the same force may materially flex the thermostat to widely varying theopening of the choke in response to the changing demands of the engine;

It will also be noted that the mechanical advantage of the force exerted by spring upon shaft 20 is greatest when the choke valve is .closedand levers 38 and 36 are in the positions shown in Figure 3, which mechanical advantage decreases as the levers move toward the dead center position shown in Figure 1. It will therefore be seen that the force generated by a given differential of air pressure on the unbalanced,

valve, the mechanical advantage of the resulting moment about shaft l3, andthe mechanical advantage of the force of spring 50 inrotating shaft 20, all vary with the choke valve-position, and these forces may be varied to obtain any desired operation, within reasonable limits. In the preferred'form the parts are so arranged that when the engine is running but not warmed up and the throttle is opened, spring 50 will move the choke valve approximately to position A against the forces of the thermostat and the moment developed by the choke valve. At about position A, however, the horizontal projection of the choke valve has increased sufiiciently to enable the moment developed by the choke valve to balance the as by being cranked with the ignition circuit open,

the choke valve may be opened to supply an excess of air to clean the engine, by moving the throttle valve l4 to its fully opened position. Le-

ver is rotated by this movement and through link 58 and lever 56 rotates shaft 40 and crank 62 in a counterclockwise direction. Ear 64 'is forced downwardly carrying with it the lever 52 and piston 48. Movement of lever 52 raises ear I 54 off of lever 42 and the tension of spring 50 is.

removed from the choke valve l2. The pressure difference built up on the valve I2 by rotating the engine at cranking speed is sufllcient to open the valve, and an excess amount of air is drawn into the carburetor and hence into the engine to clean the same.

As will be seen in Figure 5, lever 60 contains a cam surface 6| which engages the adjacent edge of link 38 as the throttle is moved to fully closed position, indicated by the dotted lines. If the toggle is in locked position, the cam 6| will move links 38 into the dotted line position, thereby unlocking the toggle. This arrangement is particularly advantageous on an engine which must be choked when started even though it is at operating temperature. The feature whereby closing the throttle unlocks the toggle is not claimed herein, but is further disclosed and claimed in my copending application SerialNo. 653,519, filed January 25, 1933.

In the modification shown in Figure 6 the choke valve is locked open and also looked closed by 'a toggle. In this modification, shaft III has fixed thereto the thermostat I2, lever 14 and the lever 22 by which it is connected to the choke valve operating lever. Shaft 16 is parallel to shaft 10 and carries a lever I8 which is loosely journaled thereon. A link 15 (connects the free ends of le- 5 vers l4 and 18, being pivotally connected thereto. Shaft 16 also carries a lever 80, journaled for rotation thereon, and connected tothe piston 82 which isurged upwardly by the spring 84. Shaft 16 carries a lever 56, keyed thereto and connected 10 to the throttle control lever, and also carries a lever 62 keyed thereto "and carrying an ear 64 which overhangs the lever 80. In this modification, lever 18 carries an ear 86 which overhangs the lever 80. Levers I4 and 18 and link 15 form 15 a toggle which may be adjusted to lock the choke valve in open position by adjustment of a stop 13 with which the ear II -on the lever 14 engages, as shown in Figure 7. With the toggle locked, car

86 mechanically holds the piston 82 in its lower- 20 I most position. g

In Figure 8 I have illustrated the position assumed by the levers and links in locking the choke valve closed. An adjustablestop 11 engages the ear H on lever 14 to fix the locking 25,

position-of the toggle. Lever carries a projection or arm 90, and when the piston is drawn down by the vacuum in cylinder 44 this arm is moved into engagement with the pivotal connection between lever 18 and link 15 to break the 30 toggle. The air pressure on the choke valve then works against the tension of thermostat 12, ultimately moving the valve to open position- In the modification shown in Figure 9, the toggle formed by levers 14, I5 and 18 locks the choke 35 valve closed. Vacuum piston 94 operateslever 96 to break the toggle and return the choke valve to the control of the thermostat in the manner set forth in the foregoing copending application of Hunt and Olson. A lever 98 is pivotally mount- 40 ed adjacent to the toggle and rotated in a clockv wise direction by the rod I00 as the throttle, not shown, is moved into wide open position. Arm I02, fixed to the lever 98, engages the junction of levers I5 and 18, to unlock the toggle. Thus 45 by moving the throttle to wide open position, the toggle may be unlocked and a flooded condition of the engine corrected by the excess airdrawn into it at cranking speed.

What is claimed is: 1. The combination of a carburetor, a pressure responsive choke valve in said carburetor, a spring, a thermostat, means connecting said spring and thermostat to said valve toclose the same, and pressure responsive means for discon- 55 necting saidxspring from said connecting means. 2. The combination with a carburetor having a choke valve, of a thermostat element, means connecting said element to said valve, a spring, levers connecting said spring to said means to assist in holding said valve closed, pressure responsive means for disconnecting said spring from said element and means to permit said valve to open, and means including said levers for locking said valve. in open position. 3. A control mechanism for a carburetor having a pressure actuated air valve and a throttle, comprising a thermostat for controlling the degree of opening of the valve, a toggle mechanism for lookpressure responsive means. 75

e. A control mechanism for a carburetor having a pressure actuated air valve and a throttle, comprising a thermostat for controlling the degree of opening of said valve, a spring for biasing said valve closed, means operated responsive to a predetermined suction on the posterior side of said throttle for rendering said spring inoperative, and toggle mechanism for holding said suction operated means operated and for locking said valve open.

5. A control mechanism for a carburetor hava'rotatable shaft, a thermostat operable to rotate said shaft, means operably connecting said shaft to said valve, a second shaft, toggle links connecting said shafts, a lever joumaled on said second shaft, a spring connected to said lever, and means connecting said lever to one of said toggle levers whereby said spring aids said thermostat in maintaining said valve closed.

'7. A control mechansm for an internal combustion engine carburetor having a pressure act'uat'ed valve and a throttle, comprising a spring connected to the valve to close the same, toggle mechanism included in said connection and operative to lock the valve closed, means operated aoiarea gle and disconnecting said spring from the valve,

means associated with said throttle for manually operating said suction responsive means, a thermostat tensioned when cold to bias said valve closed, said tension decreasing to permit the de- 'gree of valve opening to increase with an increase in engine temperature, and means including said toggle mechanism for locking the valve open and 1 holding said suction responsive means operated when the engine reaches normal operating temperature.

8. A control mechanism for a carburetor having a pressure actuated air valve and a throttle, comprising a thermostat arranged to control said valve to permit the same to open an amount increasing with the temperature of the thermostat,

a spring tensioned to aid the thermostat in tend- .ing to keep the valve closed, suction operated means 'for disabling said spring, toggle mecha nism locked by the movement of the valve into open position to hold the valve open and to hold said suction operated means in operated position, the tension in said thermostat when cold unlocking said toggle to permit the valve to be closed by said spring and thermostat jointly.

9. A control mechanism for a carburetor-having a pressure actuated air valve and a throttle, comprising a temperature responsive element for governing the degree of opening of the air valve, toggle mechanism for locking the valve closed, vacuum operated means for unlocking the toggle mechanism, and mechanical means associated with the throttle for unlocking the toggle mecha anism.

SCO'I'I F. HUNT.

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