US3174687A

US3174687A - Temperature-compensated carburetor choke control

Info

Publication number: US3174687A
Application number: US204141A
Authority: US
Inventors: John F Gilbert
Original assignee: Individual
Current assignee: Individual
Priority date: 1962-06-21
Filing date: 1962-06-21
Publication date: 1965-03-23
Anticipated expiration: 1982-03-23

Description

March 23, 1965 J. F. GILBERT 3,174,687

TEMPERATURE-COMPENSATED CARBURETOR CHOKE CONTROL Filed June 21, 1962 INVENTOR JOHN F. GILBERT 114, CAME w W BY ATTORNEYS United States Patent 3,174,687 TEMPERATURE-COMPENSATEB CARBURETUR CHOKE (IGNTROL John F. Gilbert, 309 Broadway, Hazard, Ky. Filed June 21, 1962, Ser. No. 204,141 Claims. (ill. 236-91) This invention relates to temperature-responsive devices, and more particularly to mechanisms for controlling the carburetor air inlet opening for an internal com bustion engine, in accordance with the temperature of the engine and the ambient air.

Temperature responsive choke mechanisms for carburetors are well known in the art and almost all of these devices have a bimetallic element as the actuator. The bimetallic element is produced in the form of an elongated strip arranged as a helical coil. The inner end of the coil is secured to a rotating shaft upon which the butterfly valve, or choke, is mounted and the other end of the bimetallic element is attached to a stop mechanism whose position may be adjustably fixed upon the body of the carburetor.

The bimetallic element is contained within a chamber through which air may be drawn, which air has come in contact with a portion of the engine so that as the engine warms up, the rise in temperature Will be communicated to the bimetallic element.

The construction of the helically wound bimetallic element is such that as its temperature increases, the coil will tend to contract or wind-up, the effect of this Winding up being to open the butterfly valve to permit an increase in the amount of air 'fed to the mixing chamber of the carburetor.

One of the disadvantages of the conventional automatic choke mechanisms is that while they are extremely efifective so long as the weather temperatures remain within a fairly constant range, diificulties arise whenever there is a large drop in the temperature of the surrounding air. This lowering of the outside temperature (which tends to cause the bimetallic coil to unwind) tends to increase the pressure with which the choke valve is urged in its closed position. The result of this increased pressure is that the temperature of the air introduced into the chamber containing the helical coil may not be suiiicient to compensate for this initial pressure to open the choke a suhicient amount, with the result that the gasoline and air mixture ted to the engine is excessively rich with gasoline.

In order to partially overcome the difiiculties with prior art devices it is customary to change the setting of the fixed end of the bimetallic element in accordance with the season of the year. This, of course, is an inconvenience to the motorist and so is not a solution to the problem, but only a makeshift compromise with an impractical mechanism.

In order to overcome the diiiicul-ties enumerated above, it is therefore an object of this invention to provide a temperature compensated means whereby the angular movement of the valve mechanism will remain constant regardless of the temperature of the surrounding air.

It is also an object of the invention to provide means for use with a carburetor choke valve such that the force exerted by the valve against its seat when in a closed position will remain the same irrespective of the am bient temperature.

It is another object of the invention to provide automatic choke-operating mechanisms for internal combustion engine carburetors which when initially set in an adjusted position will not require further adjustment in response to seasonal chan es in the range of temperatures of the atmosphere.

Other objects and advantages will become apparent antes? Patented Mar. 23, 1965 "ice to those skilled in the art after reading the following specification in connection with the annexed drawings, in which:

. FIG. '1 is a side elevation of one form of temperaturecompensated carburetor choke control made in accordance the teachings of this invention with a portion of the carburetor housing included;

FIG. 2 is an end elevation of the device shown in FIG. 1 as observed from the right-hand side;

FIG. 3 is an end elevation as observed from the left side as shown in FIG. 1;

FIG. 4 is a cross sectional elevation taken on the line 4-4 of FIG. 3; and

FIG. 5 is a perspective View of a helical bimetallic coil strip.

Referring now to the drawings in detail, the choke control mechanism generally is indicated by the numeral 19 and is shown as being attached to that portion of the housing 11 which usually forms the chamber through which air heated by the engine exhaust manifold is drawn to actuate the conventional automatic choke control; it being understood that the provision of such a chamber in a carburetor and the method and means of supplying such heated air to the chamber, are well known in the art and form no part of the present invention.

Preferably, the control means of the present invention is contained within a cup-shaped housing 12 having an end wall 13. The open end of the cup-shaped housing is closed by a circular plate 14 which may be provided with a radially extending flange 15, adapted to be received within a recessed seat 16, usually provided at the open end of the carburetor housing 11.

The inner face of the end wall 13 is provided with a centrally located socket 17 containing a bushing 18 for rotatably receiving one end of a shaft l9. The plate 14 is also provided with a centrally located opening 29 to re ceive the bushing 21 in alignment with the bushing 1'3 to additionally support the shaft ll? medially of its ends. The bushing 21 is annularly recessed as at 22 to receive a resilient O-ring seal 23 to prevent leakage of air from one side of the plate 14 to the other side through the shaft opening.

The inner periphery of the open end of the housing 12 may be annularly recessed as at 24 to assist in positioning the housing on the carburetor housing 11 and to enable the housing as a whole to be rotated about the axis of the shaft 19. The end Wall 13 may also be annularly recessed as at 25 to receive the clamping ring 26 which is, itself, secured to the carburetor housing 11 by a plurality of bolts 27 received Within threaded openings 28 which are usually provided about the periphery of the opening in the carburetor housing.

In the conventional carburetor having an automatic choke, the portion of the housing indicated by the numeral 11 is closed by a cover, which in this invention is replaced by the plate 14 to provide a closed chamber indicated by the numeral 29, through which chamber, as previously stated, air is circulated after being brought into contact with, and heated by, a portion of the manifold of the engine.

One of the ends of the shaft 19 extends into the chamber 29 and is provided with an axially extending diametrically cut slot 30, within which is received the flattened inner end 31 of a helically coiled bimetallic strip 32.. The outer end of this bimetallic strip is provided with an outwardly projecting leg 33 which bears against the actua ing arm 34 of a butterfly valve numeral 45 placed in the air inlet of the carburetor 46. Bimetallic strips of this type are well known in the art and have the characteristic that it the inner portion 31 of the strip is held in a fixed position, the outer leg 33 will move angularly about the axis of the coil 32. in one direction or the other in response to changes in the temperature of the coil. In common practice, the coil tends to unwind (or to move the leg 33 in a clockwise direction as viewed in FIG. 5) when subjected to a decrease in temperature. However, it will be understood that the principles of operation of this invention would be equally applicable if the reverse were the case.

The other end of the shaft 19 is also axially slotted at 35 to receive the flat inner end 31 of a bimetallic coil strip 32' which has the same physical and mechanical characteristics as the metallic coil 32. The projecting leg 33 may be set in a slot in a fixed anchor 36 attached to the inner face of the end wall 13. Between the coil 32 and the bushing 21, the shaft 19* is provided with an annularly projecting shoulder 37. An L-shaped stoplever 38, which may be fabricated of sheet metal, is provided with an opening 39 to enable the arm to be pressfitted on the shaft 19 against the shoulder 37 and thus held fixedly with respect to the shaft. The other endof the stop-lever may bear against one side of an adjustable stop member 40 which is received Within a circular slot 41 provided in the end wall 13 and having its axis of curvature coaxial with the shaft 19.

In understanding the operation of the invention, it should be realized that the purpose of a temperature-compensated choke mechanism is to control the admission of air to the carburetor only during the initial operation of the engine, it being necessary to reduce the proportion of air when the engine is cold and to gradually increase the proportion of air as it warms up. Once the engine has reached its normal operating temperature, the choke valve should be completely open and there should be no reduction in the air intake regardless of the speed or load under which the engine is operating.

It should also be understood that after an internal combustion engine has been out of operation for a certain length of time, it becomes cooled to the temperature of the surrounding air circulating over its exposed surfaces. Therefore, prior to the starting of an engine, the bimetallic coiled strip 32 will be at approximately the same temperature as the bimetallic strip 32', regardless of the fact that the strip 32 is contained within a closed chamber, while the strip 32' is in more direct contact with ambient air through slot 41 in the end plate.

Further, it should be understood that the elements 32 and 32' are arranged on the shaft 19 so that the resultant angular movement of one of the elements is neutralized by the resultant angular movement 'of the other element. This is accomplished by placing the respective coils 32 and 32' on the shaft 19 so that the direction of rotation of the convolutions of both helical coils is in the same direction. It can be seen in FIG. 2 that the coil 32 spirals outwardly from the center in a counterclockwise direction, and therefore the coil 32' should also be arranged so that it spirals outwardly from the center when viewed from the rear end of the shaft. Conversely, when viewed from the front of the housing (as in FIG. 3) both coils 32 and 32' would be observed as spiraling outwardly from the shaft in a clockwise direction.

The result of such an arrangement is as follows: so long as the engine is not operating, a temperature drop of the surrounding air will affect both of the bimetallic elements to cause both coils to tend to unwind on the shaft. As viewed from the front of the housing, this unwinding of coil 32 will turn'shaft 19 angularly a certain amount in a clockwise direction, since the leg 33 is fixed to anchor 36. If the shaft 19 were connected to the actuating arm 34 of the choke valve, the effect of the unwinding of coil 32' would be to tend to move the arm 34 with the shaft. However, since the arm 34 is connected with the shaft 19 by the bimetallic coil 32, and, since it is the inner end 31 of the coil 32 that is anchored to the shaft, the resultant unwinding of the coil 32 will be a counterclockwise rotation of the leg 33 with respect; to the shaft and, because the characteristics of the two coils are identical, the counterclockwise angular movel ment of the leg 33 with respect to the shaft will be equal and opposite to the clockwise angular rotation of the shaft by the coil 31'. There is thus no change in the angular position of the leg 33 with respect to the housing 11 and no change in the effects exerted against the arm 34.

If there is a subsequent rise in the ambient temperature, so long as the engine is not running, the shaft 19 will be rotated by cell 32' in a counterclockwise direction in accordance with the temperature change; but there will be a corresponding winding of coil 32 which will nullify the rotation of the shaft to maintain the same force against the actuating arm 34.

To install the temperature-compensated actuating mechanism, the complete assembly with the cover 14 covering the open end of the cup-shaped housing 12 and the coiled strip 32 in place at the end of shaft 19, is inserted in place at the open end of the housing 11 with the protruding leg 33 angularly spaced to the right of the choke actuating arm 34, as viewed from the outer end in FIG. 3; the housing 12 is then rotated in a counterclockwise direction until the leg portion 33.contacts the arm 34 and this rotation is continued until the choke valve is closed and placed under slight tension by the combined effect of a slight winding force applied to spring 32 and the equal and opposite unwinding force applied to coiled strip 32'. The end plate of the cup-shaped housing may be provided with boss 43 provided with a diametrically extending slot 44 adapted to receive the blade of a screwdriver or other similar tool to assist in rotating the housing. With the housing in this position, the clamping ring 26 is applied and tightened on the. outer end of the hous ing by the bolts 27. To complete the adjustment, the stop member in the slot 41 is wound in a clockwise direction until it is placed in contact with the downwardly projecting end of the stop-lever 38, and the adjusting a screw 42 is tightened to hold the stop member 40 in this position.

These adjustments having been made, no further adjustment will be necessary regardless of seasonal changes in temperature. When the engine is started, the air circulating in the chamber 29, as previously explained, will begin to warm up in response to an increase in the temperature of the engine manifold. As the air in this chamber increases in temperature, the bimetallic coil 32 which is exposed to this air, will tend to wind up. However, since the bimetallic coil 32' is exposed to the temperature of the ambient air only, there will be no change in the angular position of the shaft 19. But, since the shaft 19 does remain in the same position, the wind-up of the element 32 causes angular movement of the leg portion 33 in a clockwise direction, together with choke valve arm 34. This clockwise movement continues until the air in the chamber 29 having reached its operating temperature, the clockwise movement of the leg 33 and arm 34- has been sufiicient to completely open the choke butterfly valve- When the engine is stopped, the drop in temperature of the air in the chamber will gradually cause the bimetallic strip 32 to unwind in a counterclockwise direction until the choke is again closed.

During the initial period of warming up of the engine, the bimetallic element 32 will be substantially unaffected by the presence of heated air in chamber 29 due to the presence of the O-ring seal 23 surrounding the shaft 19, and to the fact that the heat transferred by conduction through the shaft and the housings l1 and 1.2, will not appreciably affect the element 32' until after the warm-up period has been completed. During continued operation of the engine, the temperature of the element 32 will normally become elevated due to heat transfer by conduction and also because of the possibility that the air in the immediate vicinity of the carburetor which enters through the slot 41 will have its temperature elevated. Since an increase in the temperature of element 32' would tend to cause it to wind up, the effect of this would be to rotate the shaft in a counterclockwise direction. At this point, the air in chamber 29 having reached its operating temperature, there would be no further change in the condition of the element 32, thus, the counterclockwise rotation of the shaft by the element 32' would cause bodily rotation of the element 32 in addition causing the leg 33 to move in a counterclockwise direction and urging the choke lever 34 towards its closed position. Since this is an undesirable condition, once the engine has reached operating temperature, the stop member 40 prevents such counterclockwise movement of shaft 19 by limiting coun terclockwise rotation of the stop-lever 38. t will thus be seen that the stop member 46 will permit any amount of clockwise rotation of the shaft 19 induced by the unwinding of the bimetallic element 32' in response to dropping temperatures, but will limit counterclockwise rotation of the shaft (tending to close the choke valve) which may be induced by increases in the ambient air to which the element 32' may become exposed.

In the claims, it should be understood that the phrase engine temperature refers to the temperature of the air circulated in the chamber 29 or to any medium employed to affect changes in the bimetallic element 32 as a function of the operating temperature of the internal combustion engine with which the carburetor is associated. The phrase ambient air is intended to refer to the temperature of the air in the environment in which the internal combustion engine and its associated mechanisms are being operated.

Having disclosed one form in which the invention may be practiced it will be understood that modifications and improvements may be made which would come within the scope of the annexed claims.

I claim:

1. In temperature-compensated carburetor choke control mechanisms for internal combustion engines having a valve actuated by an arm rotatable about a fixed axis in one direction from a closed position to a plurality of open positions, the combination including, a shaft mounted for rotation about an axis concentric with said fixed axis, first temperature-responsive means connected between said shaft and said arm to move said arm in said one direction With respect to a given angular position of said shaft With increases in an engine temperature, second temperatureresponsive means connected with said shaft to rotate said shaft in a direction opposite to said one direction in response to decreases in ambient temperature, and enclosure means in communication with air heated by an internal combustion engine surrounding one of said temperature-responsive means for heat-exchanging relationship between said one temperature-responsive means and an engine, said other temperature-responsive means being exposed to ambient air.

2. The invention as defined in claim 1, wherein stop means is provided to limit movement of said shaft in said opposite direction.

3. The invention as defined in claim 1, wherein both said temperature-responsive means comprises substantially identical helical bimetallic strips.

4. The invention as defined in claim 1, wherein a casing having a wall disposed normal to the axis of said shaft is provided, said shaft having a radially extending member fixed thereto, said end wall being provided with an arcuate slot concentric with said shaft axis, and an element slidable in said slot to limit movement of said radial member in one direction at a plurality of predetermined positions.

5. A device of the character described for attachment to internal combustion engine carburetors provided with temperature-responsive choke means, said choke means including a chamber in communication with air heated by an engine and having a circular opening and a bimetallic helical element mounted on an axis concentric with said circular opening to regulate a choke control arm, the combination including, a generally cup-shaped casing having its open end adapted for adjustably rotatable engagement with the circular opening in a carburetor chamber, plate means to isolate the interior of the cup-shaped casing from a carburetor chamber, a shaft, said cup-shaped casing having a bushing for concentrically rotatably supporting one end of the shaft Within the casing, concentrically positioned sealed bushing means in said plate means for rotatably supporting said shaft with the other end projecting into a carburetor chamber, means at said other end of the shaft to support the central end of a bimetallic helical element, a second bimetallic helical element similar to said first helical element, means to support the central end of the second bimetallic element at the one end of the shaft, and means to connect to outer end of the second bimetallic element to the cup-shaped casing said casing being in communication with ambient air.

6. The invention as defined in claim 5, wherein adjustable stop means is provided to limit rotation of said shaft in one direction.

7. The invention as defined in claim 6, wherein said stop means includes a radially projecting element on said shaft, and an arcuately movable member adjustably fixed on said casing.

8. In temperature-compensated choke control mechanisms for carburetors for internal combustion engines of the character wherein temperature-responsive means is provided tending to exert force to close the air inlet of a carburetor in response to decrease in engine temperature and to open said inlet in response to increase in engine temperature, the combination including, second temperature-responsive means in communication with ambient air, means to isolate said second temperature-responsive means from heat-exchanging relationship with an engine, and means to connect said second temperature-responsive means with said air inlet to exert an equal and opposite force on said first temperature-responsive means in response to changes in ambient air temperature when an engine is inoperative.

9. In automatic controls for internal combustion engine carburetors having a choke valve means movable in one direction to a closed position, yieldable temperature-influenced compound actuating means for said choke valve means, said compound actuating means including first and second temperature-responsive mechanisms, means for placing one of said mechanisms in communication only with an engines air, and means for placing the other mechanism in communication only with ambient air, said actuating means being adjustable in a plurality of positions to exert a predetermined force on said choke valve means in closed position when an engine is inoperative, said predetermined closing force being uninfluenced by changes in ambient air temperature.

10. The invention as defined in claim 9, wherein means is provided to subject said compound actuating means to both ambient air temperature and engine temperature, said actuating means being responsive to increase in engine temperature due to operation thereof to relieve said closing force on said choke valve means and to progressively open said valve means.

References Cited by the Examiner UNITED STATES PATENTS 2,043,834 6/36 Marbury 73363.1 X 2,145,230 1/39 Arrighi 236101 2,939,445 6/60 Sterner 261-392 FOREIGN PATENTS 135,591 11/33 Austria.

EDWARD 1. MICHAEL, Primary Examiner.

FREDERICK L. MATTESON, IR., Examiner.

Claims

9. IN AUTOMATIC CONTROLS FOR INTERNAL COMBUSTION ENGINE CARBURETORS HAVING A CHOKE VALVE MEANS MOVABLE IN ONE DIRECTION TO A CLOSED POSITION, YIELDABLE TEMPERATURE-INFLUENCED COMPOUND ACTUATING MEANS FOR SAID CHOKE VALVE MEANS, SAID COMPOUND ACTUATING MEANS INCLUDING FIRST AND SECOND TEMPERATURE-RESPONSIVE MECHANISMS, MEANS FOR PLACING ONE OF SAID MECHANISMS IN COMMUNICATION ONLY WITH AN ENGINE''S AIR, AND MEANS FOR PLACING THE OTHER MECHANISM IN COMMUNICATION ONLY WITH AMBIENT AIR, SAID