US3231248A

US3231248A - Automatic choke mechanism

Info

Publication number: US3231248A
Application number: US223997A
Authority: US
Inventors: Edward L Nemetz
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1962-09-17
Filing date: 1962-09-17
Publication date: 1966-01-25
Anticipated expiration: 1983-01-25
Also published as: GB989822A

Description

Jan. 25, 1966 E. L. NEMETZ 3,231,248

AUTOMATIC CHOKE MECHANISM Filed Sept. 17, 1962 5 Sheets-Sheet 1 0W4k0 A. IVEMETZ INVENTOR.

Jan. 25, 1966 E. L. NEMETZ 3,231,248

AUTOMATIC CHOKE MECHANISM Filed Sept. 17, 1962 5 Sheets-Sheet 2 50146400 4. A/[METZ INVENTOR ATTOR/VE VJ Jan. 25, 1966 E. L. NEMETZ 3,231,248

AUTOMATIC CHOKE MECHANISM Filed Sept. 17, 1962 3 Sheets-Sheet 5 0 waka 4. A i H5712 I NVENTOR.

United States Patent 3,231,248 AUTOMATIC CHQKE MECHANISM Edward L. Nemetz, 02k Park, Mich, assignor to Ford Motor Company, Dearborn, Micln, a corporation of Delaware Filed Sept. 17, 1962, Ser. No. 223,997 5 Claims. (Cl. 261-39) The present invention relates to automatic choke mechanisms for internal combustion engines.

Internal combustion gasoline engines such as are used in automobiles usually are provided with an automatic choke mechanism for automatically choking the engine for cold-weather starting and operation until the engine has become sufficiently warm for normal operation. Such automatic chokes conventionally are provided with a bimetallic, coiled spring, which, when cold, serves to close the choke valve on the carburetor, and, when heated, to open the valve. The bimetallic spring also serves to move a fast idle cam into operating position to limit closing of the throttle valve at the carburetor when the en e is cold and cause the engine to run at a faster idle to prevent stalling. As the bimetallic spring becomes heated, it progressively rotates the fast idle cam out of operative position to provide less throttle opening at idle until, finally, the cam is rotated completely out of operative position, and closing movement of the throttle is limited by the regular hot engine idle speed stop, thus producing the normal, slow idle of a warm engine.

According to the present invention, the action of the bimetallic spring controlling the choke valve is modulated by a second spring which is energized by return of the throttle to fast idle position, and which tends to open the choke slightly at idle to prevent the engine from running too rich, thus causing uneven engine idling and possible stalling. The present invention also, by thus controlling the choke valve, permits a desirable fast idle speed while the engine is cold without stalling of the engine, and also provides correct enrichment of the fuel-air mixture during driveaway.

Among the objects of the present invention are to provide an improved automatic choke mechanism in which the action of a bimetallic spring is modulated by a second spring etfective as the throttle returns to idle position to reduce choking of the engine at idle; to provide such a mechanism in which the spring is engaged by the fast idle lever of the carburetor as the throttle returns to idle position in order to exert force on the bimetallic spring only at throttle positions one-third open or less; to provide an automatic choke which will choke more in accordance with the requirements of an engine so as to prevent coldengine stalling; to provide such a mechanism in which the choke gives mixture enrichment during driveaway; and to provide a choke mechanism of simple, dependable operation.

Other objects, and objects relating to details and economics of construction and use, will be apparent from the detailed description to follow.

My invention is clearly defined in the appended claims. In the claims, as well as in the description, parts may at times be identified by specific names for clarity and con venience, but such nomenclature is to be understood as having the broadest meaning consistent with the context and with the concept of my invention as distinguished from the pertinent prior art. The best form in which I have contemplated applying my invention is illustrated in the accompanying drawings forming part of this specification, in which:

FIGURE 1 is a perspective view of a carburetor having a choke mechanism according to the present invention, the choke housing and associated parts being separated from the rest of the mechanism for clarity of illustration. The throttle is shown at starting position.

FIGURE 2 is a view similar to FIGURE 1, the throttle being shown at fast idle position.

FIGURE 3 is an exploded view of the choke control parts, the parts being shown in the same general position as FIGURE 2.

Referring now to the drawings, the carburetor has a body 10 which is provided with an air inlet 11. A choke valve or plate 12 is shaped to close the inlet: 111., the plate being mounted on a shaft 14 extending across the air inlet and journaled Within the carburetor body It). Preferably, the choke valve is of unbalanced construction, having a greater area on one side of the shaft 14 than on the other so that the reduced pressure on the underside of the valve when in closed position due to air intake of the engine will tend to rotate the valve towards open position. A lever 15 is secured to an end of the choke 14.

A choke housing assembly 16 consists of a choke housing 17 secured to the body of the carburetor. A choke housing shaft 19 is journaled within the assembly and is provided with a lever 20 fixed to the end of the shaft adjacent the body of the carburetor and connected with the lever 15 by a link 21 so that rotation of the choke housing shaft opens and closes the choke valve.

The choke housing shaft 19 has a lever 22 mounted on the shaft within the housing. The lever 22 is engaged by a bimetallic spring 24 having spaced coils generally concentric with the shaft 19. The opposite end of the bimetallic spring is supported in a spring housing 25 which forms a cover for the choke housing. The spring 24, when cold, biases the choke valve 12 to closed position. The spring housing 25 is circular and clamped against the choke housing 17 by a generally circular clamping ring 26 held in place by three screws 27 (only two shown in the drawings). By slightly rotating the spring housing 25 on the choke housing, the force with which the choke valve is biased closed may be adjusted.

Heated air is drawn from adjacent the exhaust manifold through the interior of the choke housing 19 and into the intake manifold. The heated air enters the choke housing through the air intake 29 and out of the housing through a passage 36, integral with a leg 31 of the choke housing. Passage of the heated air through the housing serves to heat the bimetallic spring 24, causing the spring to unwind as it becomes heated and thus bias the choke valve 12 to open position. A baflie 32, which may be mounted on the choke housing, prevents excessive chilling of the housing by flow of cold air passing over the engine, so as to permit the spring 24 to become heated at the proper rate.

Conventional throttle plates, not shown, are mounted in the lower portion of the carburetor body by a transversely extending throttle shaft 34. The throttle shaft is operated by a lever and rod, not shown, on the opposite side of the carburetor. An engine idle speed adjusting screw, not shown, adjacent the lever, limits closing movement of the throttle shaft 34 in the customary manner to regulate idle speed of the engine when hot.

Idle speed of the engine when cold is regulated by a fast lever 35 fixed to the throttle shaft 34 and coacting with a fast idle cam as pivota-lly mounted on a stud 37 projecting from the carburetor body a short distance above the throttle shaft. The fast idle cam 36 has a stepped, generally arcuate surface 39 engaged by a stop screw 49 mounted on the fast idle lever 35. Counterclockwise rotation of the cam 36 increasingly limits return movement of the lever 35 and produces a faster idle, while clockwise rotation of the cam reduce-s idle speed until the stop screw 40 no longer contacts the cam and idle speed is regulated solely by the hot engine idle speed adg'ustment on the opposite side of the carburetor.

The fast idle has a lever portion 41 projecting on the opposite side of the mounting stud 37 and connected with a bell crank 42 by a link 44. The bell crank 42 is provided with an arcuate slot 4-5 receiving the link .4 to provide for limited indepenoent movement of the fast idle cam and choke valve.

A torsion spring 46 is mounted on a spring carrier 47 pivotally received on the stud 3'7 beside the fast idle cam. The spring carrier 47 has a tang engaged with one end of the spring 46. A second tang 51 of the carrier is engaged with the other end 52 of the spring 4'! to maintain the spring coiled about the carrier. A third tang 54, extending axially of the carrier 47, is engaged within an o ening 55' in the fast idle cam. A pin 56 extending axially from the fast idle lever engages the outer end portion of the end 52 of the Slilllg 46. An adjusting screw 57 on the fast idle cam may be set against the upper side of the third tang 54 of the spring carrier to adjust the point at which clockwise rotation of the carrier will pick up the fast idle cam and also rotate it clockwise.

The stiffness of the spring 2 5 is such that as the throttle returns to fast idle after a cold engine has been started, the pin 56 on the fast idle lever 35 will pick up the end 52 of the spring 46 and force the choke open slightly against the bias of the bimetallic spring 24 to assure that the choke valve 12; is somewhat opened to prevent too much choking and an excessively rich idle mixture. As the bimetallic spring becomes heated and moves the choke towards open position, it will carry the fast idle cam 36 clockwise so that the engine fast idling speed is reduced. The arcuate slot in the bell crank 42 functions in the usual manner to permit movement of the choke valve under the counteracting influences of the bimetallic spring 24 and intake manifold vacuum without moving the fast idle cam.

In starting a cold engine having an automatic choke according to the present invention, the throttle plates should be moved to a position at least one-third open by holding the accelerator pedal down. This movement of the throttle plates moves the pin of the fast idle cam away from the end 52 of the torsion spring as, making the spring inoperative in opposing the bimetallic spring 24, and thereby making the full force of the bimetallic spring available for completely closing the choke valve 12 for easy starting in cold weather and permitting the bimetallic spring to select prope positioning of the choke valve for starting a partially warm engine.

In driveaway with a cold engine, as the throttle is moved from idle position, the pin of the fast idle cam moves away from the end 52 of the torsion spring 46. As above described in conn ction with cold engine starting, the spring 24 is unopposed by the torsion spring 46 as soon as the throttle is partially opened, which makes the full force of the bimetalli spring available for moving the choke valve 12. towards closed position to enrich the mixture for acceleration.

As the bimetallic spring becomes heated during operation of the engine, it will move the choke valve towards open position. As soon as the Valve has moved beyond the partially open starting position shown in FIGURES 2 and 3, the torsion spring 46 will have no further affect on operation of the automatic choke I claim:

1. In an automatic choke assembly for a carburetor having an air inlet, a throttle valve, and a choke valve for closing the air inlet; a bimetallic spring mounted on the carburetor and exposed to heat due to engine operation, linkage connecting the bimetallic spring with the choke valve to bias it between open and closed position responsive to temperature of the spring, a fast idle cam pivotally mounted on the carburetor for selectively limiting closing movement of the throttle, means linking the bimetallic spring to the fast idle cam to rotate between operative and non-operative positions responsive to temperature of the bimetallic spring, means to resiliently bias tl e fast idle cam towards non-operative position against the bias of the bimetallic spring, and means to stress said biasing means upon return of the throttle towards closed position so as to render said biasing means operative Only at idle and part-throttle operation, the bias of the fast idle cam overcoming the bias of the bimetallic spring and, acting through the linking means between the bimetallic spring and the fast idle cam, causing the choke valve to be opened slightly at cold engine idle.

2. in an automatic choke assembly for a carburetor having an air inlet, a th ottle valve, and a choke valve for closing the air inlet; a bimetallic spring mounted on the carburetor and exposed to heat due to engine operation, linkage connecting the bimetallic spring with the choke valve to bias it between open and closed position responsive to temperature of the spring, a fast idle Cam pivotally mounted on the carburetor for selectively limiting closing movement of the throttle, means linking the bimetallic spring to the fast idle cam to rotate it between operative and non-operative positions responsive to temperature of the bimetallic spring, means to resiliently bias the fast idle cam towards non-operative position against the bias of the bimetallic spring, and means to stress said biasing means upon return of the throttle towards closed position so as to render said biasing means operative only at less than about one'third throttle opening, the bias of the fast idle cam overcoming the bias of the bimetallic spring and, acting through the linking means between the bimetallic spring and the fast idle cam, causing the choke valve to be opened slightly at cold engine idle.

3. In an automatic choke assembly for a carburetor having an air inlet, a throttle valve, and a choke valve for closing the air inlet; a tc-mperature-sensitive spring mounted on the carburetor and exposed to heat due to engine operation, linkage connecting the temperatureperature sensitive spring with the choke valve to bias it between open and closed positions responsive to temperature of the spring, a fast idle cam pivotally mounted on the carburetor for selectively limiting closing movement of the throttle, means linking the temperaturesensitive spring to the fast idle cam to rotate it between operative and nonoperative positions responsive to ternperat-ure of the temperature-sensitive spring, a torsion spring engaged with the fast idle cam and means to stress the torsion spring upon return of the throttle valve to wards closed position so as to render said biasing means operative only at idle and part-throttle operation for resiliently biasing the fast idle cam towards non-operative position against the bias of the temperature-sensitive spring, the bias of the fast idle cam overcoming the bias of the temperature sensitive spring and, acting through the linking means between the temperatitre-sensitive spring and the fast idle cam, causing the choke valve to be opened slightly at cold engine idle.

In an automatic choke assembly for a carburetor having an air inlet, a throttle shaft, a throttle valve mounted on said shaft, and a choke valve for closing the air inlet; a temperaturecensitive spring mounted on the carburetor and exposed to heat due to engine operation, linkage connecting the temperature-sensitiye spring with the choke valve to bias it between open and closed positions responsive to temperature of the spring, a fast idle cam pivotally mounted on the carburetor for selectively limiting closing movement of the throttle, an arm fired to the throttle shaft and engaging the fast idle cam to limit closing movement of the throttle valve, means linking the temperature-semilive spring to the fast idle cam to rotate it between operative and non-operative positions responsive to temperature of the temperature-sensitive spring, and a torsion spring engaged with the fast idle cam and engaged and stressed by the arm upon return of the throttle valve towards closed position for resiliently biasing the fast idle cam towards non-operative position against the bias of the temperature-sensitive spring, the bias of the fast idle cam overcoming the bias of the bimetallic spring and, acting through the linking means between the bimetallic spring and the fast idle cam, causing the choke valve to be opened slightly at cold engine idle.

5. In an automatic choke assembly for a carburetor having an air inlet, a throttle shaft, a throttle valve mounted on said shaft, and a choke valve for closing the air inlet; a temperature-sensitive spring mounted on the carburetor and exposed to heat due to engine operation, linkage connecting the temperature-sensitive spring with the choke valve to bias it between open and closed positions responsive to temperature of the spring, a fast idle cam pivotally mounted on the carburetor for selectively limiting closing movement of the throttle, an arm fixed to the throttle shaft and engaging the fast idle cam to limit closing movement of the throttle valve, means linking the temperature sensitive spring to the fast idle cam to rotate it between operative and non operative positions responsive to temperature of the temperaturesensitive spring, and a torsion spring concentric with the pivotal mounting of the fast idle cam and engaged and stressed by the arm upon return of the throttle valve towards closed position for resiliently the fast idle cam towards non-operative position against the bias of the temperature-sensitive spring, the bias of the fast idle cam overcoming the bias of the bimetallic spring and, acting through the linking means between the bimetallic spring and the fast idle cam, causing the choke valve to be opened slightly at cold engine idle.

References Cited by the Examiner UNITED STATES PATENTS 2,124,778 7/1938 Hunt 261-39 2,786,657 3/1957 Sutton 261-39 2,880,978 4/1959 Winkley 261-39 2,998,233 8/1961 Marsee 261-39 3,085,792 4/1963 Hill 261-39 HARRY B. THORNTON, Primary Examiner. HERBERT L. MARTIN, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,231,248 January 25, 1966 Edward L Nemetz ror appears in the above numbered pat- It is hereby certified that er tters Patent should read as ent requiring correction and that the said Le corrected below.

Column 4, line 40, strike out "perati lre"; column 6, line 4, after "resiliently" insert biasing Signed and sealed this 6th day of December 1966.

( L) Attest:

ERNEST W. SWlDER Attesting Officer Commissioner of Patents EDWARD J. BRENNER-

Claims

1. IN AN AUTOMATIC CHOKE ASSEMBLY FOR A CARBURETOR HAVING AN AIR INLET, A THROTTLE VALVE, AND A CHOKE VALVE FOR CLOSING THE AIR INLET; A BIMETALLIC SPRING MOUNTED ON THE CARBURETOR AND EXPOSED TO HEAT DUE TO ENGINE OPERATION, LINKAGE CONNECTING THE BIMETALLIC SPRING WITH THE CHOKE VALVE TO BIAS IT BETWEEN OPEN AND CLOSED POSITION RESPONSIVE TO TEMPERATURE OF THE SPRING, A FAST IDLE CAM PIVOTALLY MOUNTED ON THE CARBURETOR FOR SELECTIVELY LIMITING CLOSING MOVEMENT OF THE THROTTLE, MEANS LINKING THE BIMETALLIC SPRING TO THE FAST IDLE CAM TO ROTATE IT BETWEEN OPERATIVE AND NON-OPERATIVE POSITIONS RESPONSIVE TO TEMPERATURE OF THE BIMETALLIC SPRING, MEANS TO RESILIENTLY BIAS THE FAST IDLE CAM TOWARDS NON-OPERATIVE POSITION AGAINST THE BIAS OF THE BIMETALLIC SPRING, AND MEANS TO STRESS SAID BIASING MEANS UPON RETURN OF THE THROTTLE TOWRDS CLOSED POSITION SO AS TO RENDER SAID BIASING MEANS OPERATIVE ONLY AT IDLE AND PART-THROTTLE OPERATION, THE BIAS OF THE FAST IDLE CAM OVERCOMING THE BIAS OF THE BIMETALLIC SPRING AND, ACTING THROUGH THE LINKING MEANS BETWEEN THE BIMETALLIC SPRING AND THE FAST IDLE CAM, CAUSING THE CHOKE VALVE TO BE OPENED SLIGHTLY AT COLD ENGINE IDLE.