US3828745A

US3828745A - Automatic choke control for engines

Info

Publication number: US3828745A
Application number: US00317888A
Authority: US
Inventors: J Medrick
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1972-12-26
Filing date: 1972-12-26
Publication date: 1974-08-13
Anticipated expiration: 1991-08-13
Also published as: CA985108A

Abstract

An automatic choke control for a carburetor of an internal combustion engine having a loosely coiled bi-metallic thermostatic spring generally centered in a cylindrical housing means. One end of the spring is anchored in the housing means and the other end is operatively connected with a movable choke valve pivotally mounted in the air-fuel induction passage of a carburetor. Means are provided for passing a stream of heated air over the thermostatic spring and this means includes an air induction passage in the cylindrical housing means extending generally tangentially with respect to the housing and with respect to the coils of the thermostatic spring and an air exhaust passage located generally centrally of the housing. This structure forms a vortex of heated air in heat transfer relationship to the thermostatic spring.

Description

ilnited States Patent [191 Medrielt Aug. 13, 1974 1 AUTOMATllC CHOKE CONTROL FOR ENGHNES [75] Inventor: John 1). Medrick, Plymouth, Mich.

[73] Assignee: Ford Motor Company, Dearborn,

Mich.

[22] Filed: Dec. 26, 1972 21 Appl.No.:317,888

[52] 11.5. C1. 123/119 F, 261/39 B [51] lint. Cl. F02m 1/10 [58] Field of Search 123/119 F; 261/39 R, 39 B [56] References Cited UNITED STATES PATENTS 2,139,355 12/1938 Coffey 123/119 F 2,188,002 l/l940 Farr 123/119 F 2,848,201 8/1958 Bennett 123/119 F 2,949,102 8/1960 Arkus-Duntonm. 123/119 F 3,180,576 4/1965 Herman 123/119 F 3,246,886 4/1966 Goodyear et a1 123/119 F Primary Examiner-Wendell E. Burns Attorney, Agent, or Firm-K. L. Zerschling; Robert E. McCollum [5 7] ABSTRACT An automatic choke control for a carburetor of an internal combustion engine having a loosely coiled bimetallic thermostatic spring generally centered in a cylindrical housing means. One end of the spring is anchored in the housing means and the other end is operatively connected with a movable choke valve pivotally mounted in the air-fuel induction passage of a carburetor. Means are provided for passing a stream of heated air over the thermostatic spring and this means includes an air induction passage in the cylindrical housing means extending generally tangentially with respect to the housing and with respect to the coils of the thermostatic spring and an air exhaust passage located generally centrally of the housing. This structure forms a vortex of heated air in heat transfer relationship to the thermostatic spring.

8 Claims, 3 Drawing Figures MAN/F010 //[/4 7' J70 Vf PATENTED 31974 3.828.745

- SHEET 1 OF 2 MENIED M181 31974 sum 2 OF 2 dO MAN/F010 AUTOMATIC CHOKE CONTROL FOR ENGINES BACKGROUND AND SUMMARY This invention relates to carburetors for internal combustion engines, and more particularly to automatic choke controls for such carburetors.

At lower engine temperatures, friction within an internal combustion engine increases due to increase in viscosity of the lubricant. In order to prevent stalling of the engine, the idle speed must be increased. Accordingly, a choke mechanism generally is provided to throttle the air intake of the carburetor during cold starting and engine warmup to assure a richer fuel-air mixture.

Generally, the choke apparatus includes a coiled thermostatic spring that rotates the choke valve towards the closed position with decreasing temperatures and progressively opens it as the temperature rises. A manifold-suction responsive device cracks open the choke a predetermined amount when the engine starts. The choke action provides a rich mixture so that sufficient fuel will vaporize to provide smooth starting and running of the cold engine.

The above construction provides satisfactory start and cold engine running conditions, but the rich mixture necessarily results in exhaust gases having fairly high levels of carbon monoxide and unburned hydrocarbons. Accordingly, it is advantageous from the standpoint of fuel economy and low emission levels to reduce the choking operation of the engine as rapidly as possible after the engine is started, consonant with smooth engine operation.

The present invention provides a construction for accomplishing the reduction in the choking operation of the engine as rapidly as possible consonant with smooth engine operations to provide the advantages set forth above. This is done by providing a vortex of hot air that is in heat transfer relationship to the thermostatic spring that is coupled to operate the choke valve. More particularly, an air passage delivers hot air from an exhaust manifold heat stove in a direction generally tangentially with respect to a cylindrical housing which houses a coiled bi-metal choke control thermostatic spring. One end of the spring is affixed to the housing and the other end is attached to a lever which is operatively connected through various mechanisms to the choke valve. At lower temperatures this spring operates to close the choke valve in the air induction passage of the carburetor.

Hot air from the exhaust manifold heat stove is injected into the housing in a direction generally tangentially to the cylindrical housing and to the coils of the spring as soon as the exhaust manifold becomes warm. Preferably, this hot air is injected in a direction opposite to the direction that the spring is coiled. The hot air is exhausted from the housing through a centrally located opening which is preferably connected to a source of vacuum, eg. the intake manifold of the engine. This forms a vortex of heated air which is in heat transfer relation to the thermostatic bi-met'al spring and heated air flows between the coils of the spring to the centrally located opening in the housing.

As a result the hot air is in intimate heat exchange contact with the full length of the thermostatic bi-metal spring thereby causing the spring to heat faster than would ordinarily be the case. This causes the choke valve to open faster than with conventional constructions. Consequently, choking action is reduced'in a very rapid manner as soon as the engine is heated sufficiently to no longer require such action. Reduction of the choking action leans the fuel-air mixture and hence reduces the level of unburned hydrocarbons and carbon monoxide found in the exhaust gases of the engine during warm-up operations.

Among the objects of the present invention are to provide an automatic choke construction that will provide good cold weather characteristics and yet reduce to a minimum the output of undesirable emissions; to provide such a construction in which the heating of the coiled thermostatic spring is more accurately controlled for better choke control; to provide such a construction in which there is greater contact of heated air entering the choke housing with the thermostatic spring and generally to improve automatic choke constructions of the type described.

Other objects, features and advantages of the invention will becomemore apparent upon reference to the succeeding detailed description thereof and to the drawings illustrating a preferred embodiment thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional elevational view of a portion of a four-barrel carburetor embodying the invention.

FIG. 2 is an exploded perspective view of the choke mechanism of the present invention, and

FIG. 3 is a vertical section through the choke mechanism of the present invention taken on the line 3-3 of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is obtained by passing a plane through approximately one'half of a known type of four-barrel, downdraft carburetor. The portion of the carburetor shown includes an upper air horn section 12, an intermediate main body portion 14, and a throttle valve flange section 16. The three carburetor sections are secured together by suitable means, not shown, over an intake manifold indicated partially at 18 leading to the engine combustion chambers.

Main body portion 14 contains the usual air-fuel mixture induction passages 20 having fresh air intakes at the air horn ends, and connected to manifold 18 at the opposite ends. The passages are each formed with a main venturi section 22 containing a booster venturi 24 suitably mounted for cooperation therewith, by means not shown.

Air flow through passages 20 is controlled in part by a choke valve 28 mounted in unbalanced relationship on a shaft 30 which is rotatably mounted on side portions of the carburetor air horn, as shown, Flow of fuel and air through each passage 20 is controlled by a conventional throttle valve 36 fixed to a shaft 38 rotatably mounted in flange section 16. The throttle valves are rotated in a known manner by depression of the vehicle accelerator pedal, and move from an idle speed position essentially blocking flow through passages 20 to a wide open position essentially at right angles to the position shown.

The rotative position of choke valve 28 is controlled by the automatic choke control mechanism 40 of the present invention. The latter includes a hollow housing 41 that is apertured for supporting rotatably one end of a choke lever operating shaft 44. The other end of the shaft 44 is rotatably supported in a casting 46. A bracket or lever portion 48 is fixed on the left end portion of shaft 44 for mounting the end of a rod 52 that is connected to choke valve shaft 30. It will be clear that rotation of shaft 44 in either direction will correspondingly rotate choke valve 28 to open or close the carburetor air intake, as the case may be.

Referring now to FIGS. 2 and 3 of the drawings, the automatic choke control mechanism 40 of the present invention includes the housing 41 which may have a portion 42 formed as an aluminum die casting and has means not shown for attaching it to the side of the earburetor 12. The choke lever operating shaft 44 is journaled in the choke housing portion 42 and is operatively connected to operate the choke valve 28 of the carburetor 12 as described above. A generally L- shaped thermostatic spring lever 62 has one leg 64 secured to the end of the shaft 44 within the choke housing portion 42 and has the other end 66 extending in generally parallel spaced relation to the shaft 44.

A choke cap 68 forms a portion of the choke housing 41 and is adapted to close the open side of the choke housing portion 42. The choke cap 68 is formed of molded plastic and is generally circular or cylindrical in form. A peripheral flange 70 is provided to hold the cap in assembled position on the choke housing portion 42. A circumferential ridge 72 on the flange 70 is in sealing engagement with the gasket 74 interposed between the choke cap 68 and the choke housing portion 42.

A choke cap retainer washer 76 extends about the cap 68 and is held in position by a series of screws 78 threadably engaged in bosses 80 spaced about the periphery of the choke housing portion 42. The retainer washer 76 is of the general form indicated in the drawing and is formed so as to resiliently engage and press the circumferential ridge 72 of the flange 70 of the choke cap 68 against the gasket 74.

The choke cap 68 is provided with a central inwardly projecting boss 82 which is slotted to receive the diametrically extending inner end 84 of a thermostatic spring 86.

The thermostatic spring 86 is formed of a strip of loosely coiled bi-metallic material that lies within the choke housing 41. The outer end 88 of the spring 86 is formed into a loop that engages the leg 66 of the thermostatic spring lever 62 as indicated in the drawings.

The choke housing 41, preferably the choke housing portion 42, is provided with a hot air passage 90 extending through the generally cylindrical peripheral side wall 92 of the choke housing portion 42. The passage 90 is connected to an exhaust manifold heat stove 92 which supplies a stream of hot air to the automatic choke control mechanism 40 a short time after the engine is started. The air passage 90 extends generally tangentially of the generally cylindrical peripheral side wall 92 of the choke housing portion 42 and in a direction opposite to the direction in which the thermostatic spring 86 is coiled. An exhaust passage or opening 94 is located centrally of the choke housing 41, i.e., in the end wall 95 of the housing portion 42 and communieates with the intake manifold 18 via conduit 96, passage 98 in the carburetor body and port 100 located just below throttle valve 36.

The port 100 is always under a slight vacuum due to the throttling of the air flow by the venturi 22 and the throttle valve 36. Consequently, the heated air that enters the passage exits from the choke housing 41 via the exhaust passage or opening 94 and then flows through the conduit 96, the passageway 98 and the port into the intake manifold 18. The hot air from the exhaust manifold heat stove 92, it can readily be appreciated, is injected tangentially with respect to the generally cylindrical side wall 92 of the choke housing portion 42 and therefore generally tangentially with respect to the coils of the bi-metal spring 86. Moreover, in the preferred form of the invention this air is injected tagentially and in a direction opposite to that in which the thermostatic spring 86 is coiled.

As can be seen from the drawings, the bi-metal spring 86 substantially fills the cavity formed by the choke housing 41. It will also be noted by reference to FIG. 2 that the exhaust passage or opening 94 that is under a vacuum via the structure previously decribed, is located at the center of the coiled thermostatic spring 86. Thus, the hot air that is injected tangentially through the passage 90 from the exhaust manifold heat stove 92 forms a vortex that has an axis coincident to the axis or center of the exhaust passage or opening 94 and coincident with the axis of the coils of thermostatic bi-metal spring 86. Consequently, the heated air is in contact with a major portion of the length of the coiled thermostatic spring 86. This provides for a very efficient heat transfer between the hot air injected into the choke housing 41 via air passage 90 and the whole of the thermostatic spring 86. This rapid heat transfer rapidly heats the bi-metal spring 86 thereby rapidly opening the choke valve 28 as soon as hot air is available in the exhaust manifold heat stove and this air is available shortly after the internal combustion engine is started.

Thus the present invention provides an automatic choke control mechanism in which the choke valve is opened as rapidly as possible after the internal combustion engine is started and is sufficiently warm to provide heat to the choke mechanism. At this time, of course, the throttling action of the choke valve is no longer needed and the rapid opening of the choke valve leans the fuel air mixture thereby reducing the amount of unburned hydrocarbons and carbon monoxide contained in the exhaust gases emitted from the engine as rapidly as is feasible.

What I claim and desire to secure by US. Letters Patent is:

I. An automatic choke control for use with a carburetor having an air-fuel induction passage and a choke valve pivotally mounted across the passage, said automatic choke control comprising a housing having a generally cylindrical side wall mounted on said carburetor, a coiled thermostatic spring positioned in said housing, one end of said spring being anchored in said housing, means operatively coupling the other end of said thermostatic spring with said choke valve for positioning said choke valve in response to the temperature of said thermostatic spring, means coupled to said housing for injecting a stream of heated air into said housing in a direction generally tangential with respect to said generally cylindrical side wall of said housing, said housing having an exhaust passage positioned therein approximately on the axis of said generally cylindrical side wall whereby a vortex is formed in heat transfer relationship to said thermostatic spring.

2. The combination of claim l in which said thermostatic spring is formed in a loose coil, said first mentioned end of said thermostatic spring is anchored approximately on the axis of said generally cylindrical side wall of said housing adjacent said exhaust passage and said other end of said thermostatic spring is positioned radially outwardly of said first end.

3. The combination of claim 2 in which said means for injecting a stream of heated air into said housing in a direction generally tangential with respect to said generally cylindrical side wall is positioned to inject said stream of heated air in a direction opposite to that in which said thermostatic spring is coiled.

4. The combination of claim 11 and further comprising an intake manifold, the carburetor being mounted on said intake manifold and means connecting said exhaust passage to said intake manifold.

5. The combination of claim 1 in which said means coupled to said housing for injecting a stream of heated gas into said housing comprises an exhaust manifold heat stove.

6. An automatic choke control mechanism for use with an internal combustion engine, the combination comprising a carburetor having an air induction passage, a choke valve pivotally mounted in said air induction passage, a housing mounted on said carburetor, a thermostatic spring positioned in said housing, one end of said spring fixed in said housing, means operatively coupling the other end of said thermostatic spring with said choke valve for positioning said choke valve in response to the temperature of said thermostatic spring, and means coupled to said housing for providing a vortex of heated air in said housing in heat transfer relationship to said thermostatic spring, said thermostatic spring being formed in a loose coil with the axis of the coil being positioned generally coincident with the axis of said vortex of heated air, said housing having a generally cylindrical side wall and an end wall, and said means for providing a vortex of heated air comprising an opening in said end wall positioned approximately on the axis of the coil of said thermostatic spring and means for injecting heated air into said housing in a di rection substantially tangential to said generally cylindrical side wall.

7. The combination of claim 6 in which the internal combustion engine includes an intake manifold connected to the air induction passage, and means are provided for connecting said opening in said end wall of said housing with said intake manifold.

8. The combination of claim 7 in which the internal combustion engine is provided with an exhaust manifold heat stove and said means for injecting heated air into said housing comprises a passage connected to said exhaust manifold heat stove and to said generally cylindrical side wall of said housing.

Claims

1. An automatic choke control for use with a carburetor having an air-fuel induction passage and a choke valve pivotally mounted across the passage, said automatic choke control comprising a housing having a generally cylindrical side wall mounted on said carburetor, a coiled thermostatic spring positioned in said housing, one end of said spring being anchored in said housing, means operatively coupling the other end of said thermostatic spring with said choke valve for positioning said choke valve in response to the temperature of said thermostatic spring, means coupled to said housing for injecting a stream of heated air into said housing in a direction generally tangential with respect to said generally cylindrical side wall of said housing, said housing having an exhaust passage positioned therein approximately on the axis of said generally cylindrical side wall whereby a vortex is formed in heat transfer relationship to said thermostatic spring.

2. The combination of claim 1 in which said thermostatic spring is formed in a loose coil, said first mentioned end of said thermostatic spring is anchored approximately on the axis of said generally cylindrical side wall of said housing adjacent said exhaust passage and said other end of said thermostatic spring is positioned radially outwardly of said first end.

4. The combination of claim 1 and further comprising an intake manifold, the carburetor being mounted on said intake manifold and means connecting said exhaust passage to said intake manifold.

6. An automatic choke control mechanism for use with an internal combustion Engine, the combination comprising a carburetor having an air induction passage, a choke valve pivotally mounted in said air induction passage, a housing mounted on said carburetor, a thermostatic spring positioned in said housing, one end of said spring fixed in said housing, means operatively coupling the other end of said thermostatic spring with said choke valve for positioning said choke valve in response to the temperature of said thermostatic spring, and means coupled to said housing for providing a vortex of heated air in said housing in heat transfer relationship to said thermostatic spring, said thermostatic spring being formed in a loose coil with the axis of the coil being positioned generally coincident with the axis of said vortex of heated air, said housing having a generally cylindrical side wall and an end wall, and said means for providing a vortex of heated air comprising an opening in said end wall positioned approximately on the axis of the coil of said thermostatic spring and means for injecting heated air into said housing in a direction substantially tangential to said generally cylindrical side wall.