US2989293A - Automatic choke - Google Patents

Description

June 20, 1961 F. J. MARSEE 2,989,293

AUTOMATIC CHOKE Filed on. 19, 1959 s Sheets-Sheet 1 INVENTOR. CA J/flM/Pjii 147' TOP/V15) June 20, 1961 F. J. MARSEE AUTOMATIC CHOKE 5 Sheets-Sheet 2 Filed Oct. 19, 1959 INVENTOR. fkDEQ/CKJMORSEE wait? June 20, 1961 F. J. MARSEE 2,989,293

AUTOMATIC CHOKE Filed Oct. 19, 1959 3 Sheets-Sheet 3 I HOKE. OP

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Aria/ewe) United States Patent 2,989,293 AUTOMATIC CHOKE Frederick J. Marsee, Hazel Park, Micln, assignor to Holley Carburetor Company, Van Dyke, Mich., a corporation of Michigan Filed Oct. 19, 1959, 'Ser. No. 847,413 4 Claims. (Cl. 261-39) This invention relates generally to carburetors or other fuel controls for internal combustion engines, and more particularly to means for automatically operating the choking mechanism provided therein.

Most carburetors of present design include a thermo-' static element for controlling the amount of choke opening according to temperature. Additionally, many choke control devices employ a manifold vacuum responsive piston for initially opening the choke a predetermined degree when the cold engine starts and becomes self-sustaining.

Although this general arrangement has been accepted commercially, certain inherent characteristics thereof sometimes cause undesirable results. Some of these results are improper choke come-off and come-on times, the come-off time being that time required to fully open the choke after the cold engine is started and the come-on time being that time required to close the choke after a substantially warmed engine is shut down.

Accordingly, this invention is directly concerned with the above problems and has as its broad purpose the objective of providing means, in a temperature responsive choke control mechanism, for controlling the choke come-off and come-on times.

Other more specific objects and advantages will become apparent when reference is made to the following description and accompanying illustrations wherein:

FIGURE 1 is a perspective view illustrating generally a carburetor embodying the invention, with the carburetor being mounted on an engine.

FIGURE 2 is a fragmentary perspective exploded view illustrating the details of construction of the left-hand portion of FIGURE 1.

FIGURE 3 is an enlarged, fragmentary sectional view illustrating in greater detail the piston and associated elements shown by FIGURE 2.

FIGURE 4 is a cross-sectional view taken on the plane of line 44 of FIGURE 3, and looking in the direction of the arrows.

FIGURE 5 is a fragmentary cross-sectional view taken on the plane of line --5 of FIGURE 4, and looking in the direction of the arrows.

FIGURE 6 is a graph comparing the operation of a choke mechanism embodying the invention with that of presently used choke mechanisms not embodying the invention.

Referring to the drawings in greater detail, FIGURE 1 illustrates acarburetor 10 having a throttle body 12, and an air intake 14 with induction passages therethrough adapted to be controlled by a choke valve 16, which is operatively connected by means of arms 18 and 20 and link 22 to the automatic choke control 24. The carburetor is shown mounted on the engine intake manifold, a

portion of which is illustrated at 25. 1 7

FIGURE 2. illustrates a housing 26 suitably secured, as by screws 28, to the carburetor 10 and having a cylinder 30 formed therein containing a piston 32 which is connected through a linkage 34' to the choke lever 36. A

shaft 38, extending through and rotatable in one wall of the housing 26,"has secured to it at one end thereof a v v 2 7 free outer end 42 of thermostatic element 44 through an arcuate opening 46 in the housing cover plate 48.

The thermostatic housing 50 has a centrally located shaft rigidly secured therein to which the inner end of the thermostatic element 44 is secured. Any suitable means such as the clamping ring 52 may be employed to'hold the cover plate 48 and housing 50 in alignment with and against the housing 26. The ring 52 may be secured by means of screws 54 and the cooperating threaded portions 56.

Conduit '58 communicates between a source of heated air, such as the stove 59 which may be formed within the engine exhaust manifold, and the chamber formed by the cover plate 48 and housing 50. The purpose of conduit 58 is to deliver a controlled amount of air, which is at a temperature indicative of engine temperature, to the there mostatic element 44 in order that the element 44 may react to it and influence the position of the choke valve 16 accordingly. The general path of this heated air is indicated by the arrows in FIGURE 2, its ultimate exit being to the intake manifold 25 through a porting means between the piston 32 and the walls of the cylinder 30; the latter is to be described more fully in connection with FIGURE 3.

Conduit 60 communicates generally between the cylin: der 30 and a source of engine manifold vacuum in such a manner as to cause movement of the piston 32 in a direction resulting in a clockwise rotation of lever 36, and at the same time to draw the heated air referred to above through conduit 58.

The construction described above is well known to those skilled in the art as the standard automatic choke employed on most carburetors. Other features, such as a fast idle mechanism, are normally associated therewith, but they need not be described since they form no part of the invention.

Referring now to FIGURE 3, piston 32 has a cavity 66 formed therein which is adapted to receive the linkage 34. The other end of the piston is closed and is subjected to manifold pressures as previously described. One end of the linkage 34 may be secured to the piston 32 by any suitable means such as pin 62; the other end of linkage 34 has a slot 35 therein which is adapted to slidably receive a pin 64 which is secured to the lever 36. The slots 68, which constitute the porting means already referred to above, may be formed in the wall of cylinder 30.

FIGURE 4, a fragmentary cross-sectional view taken on the plane of line 4-4 of FIGURE 3, illustrates in greater detail the preferred form of the valving means 76 employed by the invention. A conduit 70 formed through shaft 38 is adapted to communicate between conduit 72, which leads to the atmosphere, and chamber 74, which leads to the chamber formed generally by the housing 26 and cover plate 48. I 7

FIGURE 5, a cross-sectional view taken on the plane of line 55, illustrates the relative angular position of conduit 70 with respect to conduit 72 and chamber 174 at some intermediate point when the choke valve 16 is between a fully opened and a fully closed position.

Operation of invention Assuming for the purpose of illustration that the engine is cold and is being cranked, the thermostatic element 44 may be in its unwound condition, thereby causing its end 42 to position projection 40 of lever 36 in its egrtreme counterclockwise position. The lever 36 being secured to shaft 38 rotates the shaft and arm 20 which is secured to it counterclockwise to cause the choke valve 16 to assume a position which substantially closes off the flow of air through the carburetor induction passage 514. 'All of these elements will continue to occupy these respective positions while the engine is being cranked.

Assoon as the engine fires and becomes self-sustaining, manifold vacuum rises to a value sufficient to move the vacuum piston 32 downwardly in opposition to the force of thermostat 44. The extent of movement of this piston is determined by the position of the porting means, that is, the slots 68 within the cylinder 30.

As soon as the piston 32 uncovers the ends of the slots 68, the effect of the manifold vacuum on the piston is reduced to such a degree that the piston is unable to further overcome the opposing force of the thermostat 44. As the engine continues to run, air is drawn from any suitable stove 59 through conduits 58, 82, and 84 through orifice 86 in cover plate 48, and into the chamber formed by the housing 50 and cover plate. This air warms the thermostat 44 and passes through the arcuate opening 46 within the cover plate. The air is then drawn through the slots 68 in cylinder 30. Ultimately, the air is drawn through orifice 88 into conduit 90 leading from the cylinder 30 to conduits 92 and 60, which are in turn connected to a source of manifold vacuum.

After the piston has performed its function of opening the choke 16 a predetermined degree, the thermostatic element 44 is then required to control the choke position until it has been fully opened. One of the most serious defects of this arrangement, which till this point of the discussion is common to those mechanisms currently used, is that the come-off time is excessive. Attempts to correct this defect by the substitution of a higher rate thermostatic element failed because the combustible mixture supplied by the carburetor during the period that the choke was progressively opening was made overly lean.

The invention, in order to correct these problems of improper come-off and come-on times, provides means such as illustrated by the valving arrangement of FIG- URES 4 and 5 for varying the responsiveness of the thermostat 44.

The graph of FIGURE 6 illustrates three separate curves A, B, and C of choke valve position in relation to time. Of course, the choke valve position corresponds to the position assumed by the free end 42 of the thermostat 44 until it is fully opened, after which the end 42 continues to move some amount away from the projection 40 of arm 36. The points Y and Z illustrate such over travel by the free end 42. I 7

Referring now to FIGURES 4 and 6, let it be assumed, for purposes of illustration, that the engine on which the carburetor is to be used has the characteristic which requires that the choke valve 16 be at a point P at some time X after the engine is started. In order to accomplish this, a thermostat 44 is provided which will have a particular rate whereby the performance slope passes through points M and P. When this is done, however, the come-off time, as determined at point N, is excessive; this causes overly rich combustible mixtures and poor economy.

Realizing that the desired come-01f time is at some point R, a thermostatic element of higher rate could be used so as to have a slope passing through points M and R. With this change, however, it is to be noted that, for the same time X, the choke 16 will have assumed a more nearly open position S than it had previously at point P. In other words, with such a change the come-0E time would be proper but the combustible mixture supplied as a consequence of choke position would be too lean for proper engine operation during the warm-up period.

In contrast to the curves A and C, the invention pro- 'vides means whereby the performance curveof a particular thermostat having a definite rate can be controlled so as to deliver the proper richness of the combustible a arms and yet attain the desired come-off time. Such a curve'isillustrated at B in FIGURE 6.

The method by which the invention accomplishes this is by the use of the valving assembly 76 of FIGURES4 and 5. That is, as the engine is started cold and the vacuum piston 32 has performed its function, the shaft 38 will have been rotated to a position whereby conduit 70 will be in a position substantially as illustrated in FIGURE 5. As a result of this, the vacuum which exists generally within the chamber 26, as described previously, causes some unheated atmospheric air to be drawn in through'conduits 70 and 72 with the heated air through the conduit 58. By such means, the heating effect upon the thermostat 44 is minimized generally during the time X.

As the thermostatic element 44 becomes heated because of some warm air coming from conduit 58, the lever 36 is caused to rotate clockwise (FIGURES 2 and 3) thereby turning the shaft 38 in the same direction. As the shaft 38 rotates, conduit 70 becomes continuously and progressively closed off by virtue of its end 78 passing beyond the effective opening of conduit 72, thereby allowing less unheated atmospheric air to be drawn in, and conversely more heated air to be supplied to the thermostat 44. In this manner, the performance curve can be shaped so as to pass through the desired points M, P and R.

Additionally, an added feature of this invention is that the come-on time can be prolonged. That is, the present choke mechanisms are too quick in their responsiveness after the engine is shut down. This usually occurs as a result of the use of low rate thermostats which, when exposed to the full heat of the warmed engine, have only a slight movement away from the lever 40, as illustrated by the position of point Z on the ordinate scale.

By the use of a high rate thermostat 44 in the invention, a point Y can be attained which is substantially increased ordinate-wise over the point Z. As a result of this, the engine has to cool to a greater degree, which in turn requires a longer period of time, before the choke 16 will again begin to close. This feature again improves the economy and permits easier starting of an already warm engine.

The preferred embodiment is illustrated and discussed from the standpoint of the atmospheric bleed being open when the choke valve is closed and conversely that the bleed is closed when the choke valve is open. It is evident, however, that the reverse relationships are also possible if the particular engine characteristics are such to warrant the reversal. If such a reversal were desired, then the atmospheric vent 70 would be closed when the choke valve was closed and progressively increase the amount of ambient air introduced into the housing 26 as the choke valve moved toward wide open position. As a result of this, the choke valve movement would initially have a relatively high rate and subsequently diminish in accordance with the degree of ambient air bleed.

Although only two embodiments of the invention have been disclosed and described, it is apparent that other modifications of the invention are possible within the scope of the appended claims.

What I claim as my invention is:

1. Ina carburetor having a choke valve therein, an automatic choke control device comprising, a choke shaft secured to said valve, a member secured to said shaft and adapted to be rotated therewith, a housing, a second shaft mounted through one side of said housing and adapted to be rotated therein, an arm secured to one end of said second shaft externally of said housing so as to be rotatable therewith, means connecting said member with said arm, a second arm having a projection thereon secured to the other end of said second shaft within said housing adapted to rotate said second shaft, thermostatic means within said housing adapted to bias said projection in a direction so as to close said choke valve, first conduit means leading from said housing and communicating with a source of heated air at substantially atmospheric pressure, second conduit means leading from said housing and communieating with a source of engine vacuum, and valve means formed integrally with said second shaft and said housing adapted to provide a variable degree of communication between a source of ambient air and said housing, said valve means being positioned so as to provide an everdiminishing degree of communication with said ambient air as said choke valve moves from fully closed to fully open position.

2. In a carburetor having a choke valve therein, an automatic choke control device comprising, a choke shaft secured to said valve, a member secured to said shaft and adapted to be rotated therewith, a housing, a second shaft mounted through one side of said housing and adapted to be rotated therein, an arm secured to one end of said second shaft externally of said housing so as to be rotatable therewith, means connecting said member with said arm, a cylinder open at one end and substantially closed at its other end, a piston in said cylinder, a second arm having a projection thereon secured to the other end of said second shaft within said housing adapted to rotate said second shaft, first conduit means leading from the space between the said piston and the closed end of said cylinder and communicating with a source of engine suction, second conduit means leading from said housing and communicating with a source of heated air at substantially atmospheric pressure, thermostatic means within said housing adapted to bias said projection in a direction so as to close said choke valve, connecting means between said second arm and said piston enabling said piston to oppose the movement of said thermostat whenever said engine is running, and valve means formed integrally with said second shaft and said housing adapted to provide a variable degree of communication between a source of ambient air and said housing, said valve means being positioned so as to provide an ever-diminishing degree of communication with said ambient air as said choke valve moves from fully closed to fully open position.

3. In a carburetor having a choke valve therein, an automatic choke control device comprising, a housing, a shaft mounted through one side of said housing and adapted to be rotated therein, an arm secured to one end of said shaft externally of said housing so as to be rotatable therewith, means connecting said choke valve with said arm, a second arm having a projection thereon secured to the other end of said second shaft within said housing adapted to rotate said second shaft, thermostatic means within said housing operatively engaging said shaft so as to bias said shaft in a choke closing direction, first conduit means leading from said housing and communicating with a source of heated air at substantially atmospheric pressure, second conduit means leading from said housing and communicating with a source of engine vacuum, and valve means in series with said second conduit means and formed integrally with said shaft adapted to provide a variable degree of communication between a source of ambient air and said housing, said valve means being positioned so as to provide an ever-diminishing degree of communication with ambient air as said choke valve moves from fully closed to fully open position.

4. In a carburetor having a choke valve therein, an automatic choke control device comprising, a choke shaft secured to said valve, a member secured to said shaft and adapted to be rotated therewith, a housing, a second shaft mounted through one side of said housing and adapted to be rotated therein, an arm secured to one end of said second shaft externally of said housing so as to be rotatable therewith, means connecting said member with said arm, a second arm having a projection thereon secured to the other end of said second shaft within said housing adapted to rotate said second shaft, thermostatic means within said housing adapted to bias said projection in a direction so as to close said choke valve, first conduit means leading from said housing and communicating with a source of heated air at substantially atmospheric pressure, second conduit means leading from said housing and communicating with a source of engine vacuum, and valve means formed integrally with said second shaft and said housing adapted to provide a variable degree of communication between a source of ambient air and said housing in accordance withthe position of said choke valve.

References Cited in the file of this patent UNITED STATES PATENTS

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