US3494598A - Automatic choke - Google Patents

Description

Feb. 10, 1970 AUTOMATIC CHOKE Filed March 21, 1968 I6 L 7 T L ll;

I0 FIG. I

4 INVENTOR DWIGHT M. GORDON BYW/ZI/4% ATTORNEY D. M. GCRDON 3,494,598

United States Patent O 3,494,598 AUTOMATIC CHOKE Dwight M. Gordon, Farmington, Mich., assignor to ACF Industries, Incorporated, New York, N.Y., a corporation of New Jersey Filed Mar. 21, 1968, Ser. No. 715,065 Int. Cl. F02m 1/10 US. Cl. 261-39 6 Claims ABSTRACT OF THE DISCLOSURE An automatic choke of a carburetor includes a sector arm fixed to the choke valve shaft, and a first rod connected to a suction motor at one end and having an opposite bent end in an arcuate slot of the sector arm. A spring anchored to the sector arm engages the first rod, and the spring is biased to close the choke when the engine is not running and, consequently, the suction motor is not operated. The sector arm is connected by a second rod to a thermostat spring arranged to close the choke at low temperatures and open it at high temperatures. At rather high ambient temperatures, when the thermostat would not close the choke, the first mentioned spring closes the choke to facilitate starting the engine.

BACKGROUND OF THE INVENTION In an automatic choke arrangement, including a suction motor, for opening an unbalanced choke valve immediately after engine starting, the thermostat spring should not present such a high choke closing bias that the opening of the choke is delayed too long, otherwise the engine will run with an overly rich mixture. When the thermostat closing bias is reduced to allow the choke to open shortly after engine starting at normal or low temperatures, the thermostat may not close the choke at rather high ambient temperatures. But an open choke will give an undesirably lean mixture for engine starting, even at high ambient temperatures of, say, 90 degrees Fahrenheit. It is an object of the invention to avoid this difiiculty by maintaining the choke closed during engine starting, while keeping the closing bias of the thermostat spring low enough to permit quick partial opening of the choke after engine starting.

Examples of particular conditions can be cited when it is desirable to close the choke valve even though underhood temperatures may be relatively high. In some types of carburetors fuel enters the accelerating pump over a weir in the upper portion of the pump cylinder. With such an accelerator pump construction, if the car has been driven to normal operating temperatures and is then parked over night or longer, it can be expected that all of the fuel in the pump cylinder will boil out and the cylinder will be dry or substantially dry. Then upon attempting to start the car the normal practice is to step down the accelerator pedal one time and then turn the ignition key. This one shot from the accelerating pump should be sufficient to allow the engine to fire, but under the circumstances described since no fuel is present the engine would not fire and might not start at all.

Another example is the situation where the car has been driven and has become somewhat stabilized in temperature and then is parked for a relatively short time, such as approximately one hour. In this length of time the accelerating pump cylinder can boil out or nearly boil out and yet the thermostatic coil will have a relatively high temperature and will be exerting only a partial closing bias on the choke valve. Under these circumstances cranking would not produce enough vacuum under the choke to draw fuel out of the main fuel nozzle 3,494,598 Patented Feb. 10, 1970 and at the same time the accelerating pump would not have made its initial discharge as would normally be expected. Here, again, the full closing of the choke provided by the invention is very desirable.

SUMMARY OF THE INVENTION A carburetor is provided having an unbalanced choke valve connected to the thermostat spring, as is conventional. An arcuately slotted sector arm is fixed to the choke valve shaft and a rod connects the sector plate to the thermostat spring. A suction motor responsive to intake manifold pressure is linked to a rod having a bent end extending into the arcuate slot, so that the bent end of the rod can ride in the slot when the sector arm is turned by the thermostat spring to open the choke. Before the engine starts, the end of the rod is positioned a short distance from the end of the arcuate slot to provide a predetermined lost motion between the suction motor and the sector arm fixed to the choke valve. A closure spring fixed to the sector arm bears against the rod so as to bias the choke closed when the engine is not running. When the engine starts the suction begins to operate and relaxes the closure spring, and the unbalanced choke valve, due to its weight, opens to a degree dependent on the ambient temperature sensed by the thermostat spring, and then opens further as the suction motor moves the sector arm directly.

BRIEF DESCRIPTION OF THE DRAWING The invention will be fully understood from the following description and the drawing, wherein:

FIG. 1 is a plan view, partly in section of a carburetor, showing the choke actuating mechanism constituting the invention.

FIGS. 2 and 3 are partial views of tWo modifications of the structure shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an embodiment of the invention is illustrated comprising a carburetor 10, the upper end 12 of which is adapted to be fitted to an air filter and the lower end 14 connected to the engine intake manifold. In the air horn 16 of the carburetor is the conventional throttle valve on shaft 18 and unbalanced choke valve 20 on shaft 22. Sector shaped arm 24 is fixed on shaft 22 and has an arcuate slot 26. Rod 28 connects arm 24 to thermostatic coil spring 30. Rod 32 has a bent end 33 extending through slot 26, a looped portion 34, and a re mote end attached to plunger 36 of diaphragm suction motor 38. A torsion spring 40 wrapped round shaft 22 has one end 42 fixed to arm 24 and another end 44 abutting portion 34 of rod 32. Nipple 46 of suction motor 38 is adaped to receive a conduit connected downstream of the throttle, or effectively to the intake manifold.

Thermostat spring 30 is normally designed to hold choke 20 closed at cold temperatures and to open the choke at elevated temperatures. For reasons already set forth, the thermostat itself may not cause closing of choke 20 during engine cranking under conditions when choke closing is desirable or even necessary. When cold, spring 30 contracts, raises rod 28 and tends to close choke 20, and during heating spring 30 expands, pulls rod 28 down and tends to open the choke. Before the engine starts suction motor 38 is inoperative and hence its diaphragm and plunger 36 are in their uppermost positions. End 33 of rod 32 is then spaced from the right hand end of arcuate slot 26, as indicated at 48. Since end 44 of spring 40 is cocked against rod 32, the other end 42 of spring 40 acts on arm 24 to turn it counterclockwise and close choke 20, even though the thermostat may be at a temperature which will not cause it, of itself, to quite close the choke. Torsion spring 40 needs little force to act against the relaxed thermostat spring 30 sufficiently, or overcome the unbalanced weight of the choke valve, in order to hold the choke closed before the engine starts. After the engine starts, suction motor 38 begins to operate and move plunger 36 and rod 32 downward, thereby relieving the pressure on the end 44 of spring 40, so that the latter no longer urges the choke closed. Due to the unbalanced nature of choke 20, it is opened by gravity and the higher pressure on its top side when spring 40 relaxes. As the engine continues running suction motor 38 pulls rod 32 down and turns sector arm 24 to open choke 20 further, to a predetermined degree. Thereafter, the opening of the choke can proceed still further as the engine heats up and thermostat spring 30 pulls rod 28 downward. As sector shaped arm 24 turns with the choke, the end 33 of rod 22 rides in slot 26. It can be seen then, that even when thermostat 30 is at such a temperature that it would not close the choke, the choke is closed by torsion spring 40, to facilitate starting, and proper operation is obtained after engine starting.

In FIG. 2 there is shown a modified torsion spring 50 and its connection to rod 51, which differs from rod 32 in that there is no bent portion 34. The end 52 of spring 50 is anchored to sector arm 53 and end 54 of the spring is looped round rod 51. The latter is spaced from the end of arcuate slot 55 as indicated at 48 in FIG. 1, when rod 51 is in its normal non-operated position, so that initially there is a lost motion between rod 51 and sector arm 53. It will be evident that the structure of FIG. 2 functions in substantially the same manner as that of FIG. 1.

FIG. 3 shows another type of choke closing spring. Spring 60 is a bowed, preferably flat spring fixed to arm 62 by screws 63, 64. Rod 66 has a bent end 67 spaced from the end of arcuate slot 68 when the rod is in its non-operated position. In this position of rod 66, a bend 70 thereof bears against spring 60 to urge choke valve 20 closed. As rod 66 moves downward in response to engine starting, the pressure on spring 60 is relieved, allowing choke valve 20 to open, as a result of its weight. As rod 66 moves down further, the end 67 thereof reaches the end of slot 68, and thereafter moves arm 62 along with it, and opens choke 20 further. It will be understood, although connection to the thermostat is not shown, that choke valve shaft 22 is actuated by a thermostat in essentially the same manner as in FIG. 1, and the operation of the choke otherwise is like that of FIG. 1.

I claim:

1. In a carburetor having an automatic choke including an unbalanced choke valve; a thermostat connected to said choke valve for positioning the same in response to temperature so that the choke valve is not closed by the thermostat when it is above a predetermined temperature; a suction motor adapted to be actuated in response to intake manifold pressure and having linkage providing a lost motion connection to the choke valve, the improvement comprising spring means connected to said choke valve and tensioned for closing the same even when said thermostat is above said predetermined temperature, said spring means engaging said linkage and being arranged so that actuation of said suction motor produces a limited lost motion travel of said linkage in a direction to reduce the tension of the spring means to enable the choke valve to be opened by the thermostat above said predetermined temperature.

2. The invention according to claim 1, wherein said spring means is a torsion spring having one end fixed to said choke valve and its other end in engagement with said linkage.

3. The invention according to claim 2, wherein said choke valve has a pivot shaft and an arm fixed to said shaft, said arm having a slot, said linkage including a rod connected to and actuated by the suction motor and having a remote end extending into said slot to form said lost motion connection, said other end of the torsion spring being normally pressed against said rod.

4. The invention according to claim 3, wherein said other end of the torsion spring is connected to the remote end of said rod.

5. The invention according to claim 1, wherein said spring means is a fiat spring having at least one end thereof fixed to said choke valve and another portion thereof in engagement with the suction motor linkage.

6. The invention according to claim 5, wherein said choke valve is an unbalanced valve having a pivot shaft and an arm fixed to said shaft, said spring being a bowed spring having both ends thereof fixed to said arm and an intermediate portion engaging said linkage.

References Cited UNITED STATES PATENTS 2,998,233 8/ 1961 Marsee. 3,167,254 1/ 1965 Goodyear. 3,253,781 5/ 1966 Schefl'ler. 3,284,061 11/1966 Gordon. 3,321,193 5/1967 Highley.

TIM R. MILES, Primary Examiner

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