US2818239A - Automatic choke valve for carburetors - Google Patents

Description

Dec. 31, 1957 E. w. EICKMEI'ER El'AL 2,818,239

AUTOMATIC CHOKE VALVE FOR CARBURETORS Filed April 3, 1956 INi ENTORS Elmer Olson By Edward W E lckme/ef lie/r Attorney AUTOMATIC CHOKE VALVE FORCARBURETORS Edward Wiliiarn Eichmeier, Pontiac, Mich., and Elmer Olson, Rochester, N. Y., assignors to General Motors Corporation, Detroit, Mich., a corporation ot'Deiaware ApplicationApril 3, 1956,.Serial No. 575,759.

2 Claims. (Cl. 261-39) This invention relates to carburetors for internal combustion engines, and, most particularly, to mechanism for automaticallycontrolling the operations of the choke valve thereof which regulates the admission of air to'the mixture passages of a carburetor.

It has-been the general practice for a number of years to provide a choke valve for controlling the admissionof air to the carburetor which could be moved to closed or partially closed position to variably restrict the admission of air to the carburetor in order to provide a richer than normal'mixture of fuel and air for starting purposes. When the engine has started and is operating under its oWn power, it is necessary to progressively open the choke valve as the engine temperature increases to gradually decrease the-fuel content of the mixture until, when normal temperature is reached, the choke valve is wide open and imposes no restriction on'the air inlet.

These choke valves were originally manually operated and were'positioned wholly by the operator of the vehicle. For a good many years, however, it has been customary to provide in most carburetors in commercial use choke valves which are automatically controlled in response to variations in engine-temperature and engine suction, such valves being held closed when the'temperature is low, to facilitate starting and being gradually opened by the effect of suction as the temperature increases after the engine becomes self-operative, until the valves are fully. open when normal operating temperature is reached. Generally, the choke valve is held closed by a bimetallic thermostat one end of which is fixed while the other end engages an arm on the choke valve shaft. Opening of the valve is generally effected by a suction operated piston subject to variations in suction posterior to the throttle and connected'to the valve shaft so as toexert a force in opposition to that of the thermostat, and the valves are also generally unbalanced so as to be responsive to variations in suction effective directly on the valves themselves.

Obviously, an increase in temperature will decrease the force -holding:thevalve:closed, while an increase in suction will increase the force tending to open the valve so that, after the engine is self-operative, the valve will be moved toward open position by the effect of suction as the engine temperature increases and also if the suction is increased without change in temperature. For example, when the engine starts ,to,-run under its own power, there is no immediate-increase intemperature, but there is-a.

I due to.the.redu,ction inthe closing force exerted by the thermostat as the engine temperatureincreases.

To, effectheating of the thermostanhot air is generally drawn from a stove'adjacent the exhaust manifold of the engine throughahousing in which the thermostat is p ositionedor'the thermostatis placedinsuch a position that it is subject to direct radiation from the exhaust manifold 1' nited States Patent 0 so that the temperature variation of the thermostat follows closely the temperature variation of the exhaust manifold. The intake passage of the intake manifold through which mixture is conveyed to the engine also generally receives heat from the exhaust manifold and in some engine installations the intake passage receives so little heat from the exhaust manifold that the increase in temperature of the intake passage is far less rapid than the increase in temperature of the air adjacent the thermostat. In such installations, the choke valve will open too rapidly when the engine first starts to run and the mixture supplied to the engine will be too lean. After the valve is moved to a predetermined open position and the engine temperature has considerably increased, the

suction efiective on the piston is reduced so that after the valve reaches such position the difficulty referred to is not encountered.

It is the primary purpose of the present invention-to eliminate the difficulty above referred to and to provide an automatic choke mechanism having a choke valve controlled in accordance with variations in engine temperature and suction which is provided with means for restricting the application of heat to the thermally re sponsive means during a part of the movement of the choke valve toward open position, butwhich is rendered ineifective after the choke valve makes a predetermined movement toward open position.

It'is'also an object of the invention-to provide in an automatic choke mechanism for a carburetor, having a choke valve movable in response to variations in engine stat, with a valve operable by the thermostat which is elfective to close the direct passage and open.the.by-

' pass at relatively low temperatures, but will close the .by-

pass and open the direct passage after. a predetermined termperature is reached.

Further objects and advantages of the present invention will be apparent from the following description, reference beiug had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawings:

Figure 1 is a fragmentary elevation, partly in section, showing a part of a carburetor equipped with an automatic choke mechanism in which the present invention is incorporated;

Figures 2 and 3 are vertical sectionson the lines 2-2 and 33 of Figure 1, respectively, While Fig. 4 is an enlarged detail of a part of Fig. 1.

Since the invention to which this application relates is concerned solely with the automatic choke mechanism and the specific construction of the carburetor is. in no sense material, the entire carburetor is. not shown, Fig. 1 showing only the upper,or air intakeend of a down-draft carburetor and the automatic choke mechi anism which constitutes the present invention. The carburetor may be of any suitable construction such as'that 'shown in the patent to Olson, 2,339,907, May 26, 1953, for example, and its structure need not be described herein.

As shown in Fig. .1, the reference numeral .2 indicates-a casting'in which is formed a constant level fuel chamber of conventional form which supplies fuel to a mixture the lateral extension '56 of the arm 44 extends, so that when the thermostat'or the suction operated piston moves arm 44, the two arms 98 and 100 are also moved.

Projecting to the .left ofthe lower end of Larm 98 as seen in *Fig. 1, is .alateral extension 104'which-controls the passage 70 and projecting to the right of the lower end of arm 100 is a lateral extension 106 which controls the passage 80. Normally, at low temperatures, before the engine is started, the parts are in the position shown in Fig. 3, the extension 104 is in registry with the upper end of passage 70 and substantially blocks the how of air from said passage into the chamber A, while the extension 106 is in such a position that the upper end of passage 80 is open and air can flow freely from such passage into the chamber B. With the parts in the position described, the choke valve is closed. Air flowing into the chamber B will flow directly into the suction and on into the carburetor without passing through chamber A, but when passage 70 is open and heated air is admitted to chamber A, it flows through such chamber, heating the thermostat directly, passes through the opening in partition plate 42 into chamber B and then into the suction passage.

When the engine starts to run under its own power there is, as has already been set forth, a very considerable increase in engine suction effective on the piston and also some increase in that directly effective on the unbalanced choke valve. This increase in suction moves the piston 50 to the left, as seen in Fig. 2 and, depending on operating conditions and temperatures, to a position where the forces exerted by suction are balanced by the opposing force exerted by the thermostat. This movement of the piston, of course, effects a movement of the choke valve toward open position, but at low temperatures this initial movement of the valve is not very great. Then, as the temperature of the engine increases, during the warm-up period, the force exerted by the thermostat progressively decreases and the choke valve progressively opens. As already pointed out, this opening of the choke valve occurs too rapidly in some installations if heated air from an exhaust stove is drawn directly past the thermostat, when the application of heat to the intake manifold is insufficient to effect heating of the mixture supplied to the engine in more or less accord with the heating of the thermostat. This results in too much opening of the choke valve and formation of too lean a mixture to effect satisfactory operation of the engine in such installations as are referred to.

In order to eliminate this difficulty, the member 104 is so arranged that it blocks the passage 70 when the choke valve is closed, as it is at low temperatures, but the member 106 is not in position to block the passage 80 until the choke valve has made a very considerable movement toward open position. When the passage 70 is closed and the passage 80 is open, so that hot air is drawn through chamber B, there is some heating of the thermostat, so that its closing force is slowly reduced, but this is not effected nearly as rapidly as if the hot air was drawn directly past the thermostat through the chamber A. The opening of the choke valve is, therefore, delayed by blocking the passage 70, in comparison with a choke mechanism of conventional construction.

As the choke valve opens, the passage 70 is ultimately unblocked and as this occurs, the member 106 is moved into position to block the passage 80. The members 104 and 106 are of such magnitude that the passage 70 is not opened, nor the passage 80 closed until the choke valve is approximately 60 open. By the time the valve reaches this position in this device when the heating of the thermostat is no longer retarded, the manifold is relatively hot and the piston 50 has moved to such a position that there is but little suction effective on the piston. Because of these facts, the heating of the thermo- .statQshould be more rapid. so. that movement of the choke walve-during. the. last part of the opening. movement, i. e. from 60 .on, :will .be. rapid enough to, prevent the formatlOI1 0ff8.miXtu1'e that would -be too rich forxmost-satisfactory operation. It is for this reason that the passage 70 is unblocked when the valve gets 60 open and during further opening movement the thermostat is heated much more rapidly and the choke valve is opened more rapidly.

During all operation after the temperature of the engine has risen sufficiently to effect the unblocking of the passage 70, such passage remains open so that during all normal operation of the engine the thermostat is subject to the full heating effect of the hot air passing directly through the chamber A and the hot air is caused to pass through chamber B only during a part of the warm-up period when the engine is started at relatively low temperatures.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows:

1. In a carburetor for use on an internal combustion engine and which is adapted to supply said engine with a combustible mixture of fuel and air, an air inlet passage for admitting air to said carburetor, a choke valve in said passage controlling the passage of air therethrough, means responsive to temperature and suction for variably controlling the position of said choke valve in accordance with variations in engine temperature and suction, said means being effective to progressively move said choke valve toward open position as the engine temperature increases during the warm-up period following starting of the engine at relatively low temperatures, a housing, a partition in said housing dividing such housing into two chambers in one of which said thermally responsive means is positioned, a conduit for conveying heated air to both of said chambers, a passage communicating the engine suction to said chambers so as to cause a flow of heated air therethrough, valve means for controlling admission of air from said conduit tosaid chambers normally positioned to prevent admission of air to the chamber in which the thermostat is positioned and to admit air to the other chamber when the temperature is low and the choke valve closed, and means for moving the valve means to admit heated air to the first chamber and prevent admission of air to the second chamber as the choke valve is moved toward open position upon increase of temperature.

2. In a carburetor for use on an internal combustion engine and which is adapted to supply said engine with a combustible mixture of fuel and air, an air inlet passage for admitting air to said carburetor, a choke valve in said passage controlling the passage of air therethrough, means responsive to temperature and suction for variably controlling the position of said choke valve in accordance with variations in engine temperature and suction, said means being effective to progressively move said choke valve toward open position as the engine temperature increases during the warm-up period following starting of thte engine at relatively low temperatures, a housing, a partition in said housing dividing such housing into two chambers in one of which said thermally responsive means is positioned, a conduit for conveying heated air to both of said chambers, a passage communicating the engine suction to said chambers so as to cause a flow of heated air therethrough, valve means for controlling admission of air from said conduit to said chambers normally positioned to prevent admission of "air to the chamber in which the thermostat is positioned and to admit air to the other chamber when the temperature is low and the choke valve closed, and means operatively connecting said valve means to the choke valve whereby movement of the choke valve toward open position upon increase of temperature eflFects movement of said valve to a position to admit heated air to the first chamber and References Cited in the file of this patent UNITED STATES PATENTS Coffey Dec. 6, 1938 Coffey July 27, 1943 Olson Dec. 28, 1954

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