US3263661A

US3263661A - Automatic choke

Info

Publication number: US3263661A
Application number: US402093A
Authority: US
Inventors: Frederick J Marsee
Original assignee: Holley Carburetor Co
Current assignee: Holley Performance Products Inc
Priority date: 1964-10-07
Filing date: 1964-10-07
Publication date: 1966-08-02
Anticipated expiration: 1983-08-02

Description

Aug. 2, 1966 F. J. MARSEE AUTOMATIC CHOKE Filed 001:. '7, 1964 2 Sheets-Sheet l F/PED'P/CK JI MARJEE IN V EN TOR.

BY fig W g 2, 1 F. J- MARSEE 3,263,661

' AUTOMATIC CHOKE Oct. 7, 2 sheets-sheet 2 FREDERICK J MA/PJEE IN VEN TOR.

United States Patent 3,263,661 AUTOMATIC CHOKE Frederick J. Marsee, Hazel Park, Mich, assignor to Holley Carburetor Company, Warren, Mich., a corporation of Michigan Filed Oct. 7, 1964, Ser. No. 402,093 13 Claims. (Cl. 123-119) This invention relates generally to carburetors for internal combustion engines, and more particularly to a novel automatic choke control mechanism therefor.

Carburetor automatic choke control mechanisms in which the choke position is influenced by engine temperature and vacuum have been known and used for many years. Such a mechanism is shown by Smitley, U.S. Patent No. 2,988,344.

While these prior art systems have been commercially successful, they involve a substantial number of individual parts, the result being that the assembly is expensive to manufacture.

Many prior art carburetors include a lower throttle body casting and an upper main body casting to which the fuel bowl and the automatic choke mechanism are connected. The two castings are separated by a gasket which tends to prevent the conduction of engine heat to the upper casting. While it is desirable to keep heat away from the fuel bowl, this reduction in radiated and conducted engine heat to the automatic choke mechanism makes the thermostatic element of the choke mechanism less responsive to engine heat. For example, it will coo-1 off faster than the engine when the engine is shut down; thus, the choke will prematurely return to a closed position, as in the case of a relatively short engine shut down, and make restarting diflicult.

Another inherent disadvantage of the choke mechanism shown by Smitley is that the linkage between the thermostatic coil and the choke plate is such that the torque output of the thermostatic coil is substantially constant. This makes it more difiicult or impossible to make small choke adjustments for different engine applications.

The tendency today is toward reduction in cost of manufacture and standardization. Accordingly, a primary object of this invention is to provide an automatic choke control mechanism of the type shown by Smitley, but wherein the number and complexity of the individual parts is substantially reduced as to reduce the over-all cost of the mechanism.

Another object of the invention is to provide a choke control mechanism that forms a part of the throttle body casting so as to be more effectively subjected to conducted andradiated engine heat, which is the desired parameter.

Still another object of the invention is to provide such a mechanism wherein the torque output characteristics of the thermostatic coil can be changed, within limits, so

. as to enable minor adjustments and thus permit a single thermostatic coil to serve more engine applications, or special applications.

These and other objects and advantages of the invention will become more apparent upon reference to the following specification and the accompanying drawings wherein:

FIGURE 1 is a side el-evational view, with portions thereof cut away and in cross section, illustrating a carburetor having an automatic choke control mechanism embodying the invention.

FIGURE 2 is a fragmentary top plan view of the carburetor shown by FIGURE 1, with the cover of the choke control mechanism cut away to better illustrate the internal structure.

FIGURE 3 is a view similar to FIGURE -1, but taken substantially on the plane of line 3-3 of FIGURE 2 to illustrate additional details of construction.

Referring now to the drawings in greater detail, FIG- URE 1 illustrates a carburetor 10 embodying the invention, mounted on an intake manifold 12 of an internal combustion engine. In this particular instance, the carburetor 10 generally comprises three cast sections, including an upper so-calle-d air horn casting 14, an intermediate main body casting 16 and a lower throttle body casting 18. As usual, the assembled carburetor includes an in duction passage 20 having a venturi 22. The usual offset choke plate 24 is secured on a shaft 26 pivotally mounted in the induction passage 20 upstream of the venturi 22, and the usual throttle plate 28 is likewise secured to .a shaft 30 pivotally mounted across the induction passage downstream of the venturi 22. The carburetor also includes a fuel reservoir 32 formed with the intermediate main body section 16, and the carburetor sections are secured together in any suitable manner such as by means of the screws 34, with gaskets 36 positioned between the sections to prevent leakage.

The operation of the throttle plate 28, which is spring loadedto close, through the foot throttle valve is well known in the art. Since it forms no part of this invention, this structure is not shown.

A preferably elongated, generally hollow housing 38 containing the improved choke control mechanism, designated generally as 40, may be formed integral with the throttle body casting 18, or it may be attached thereto. In the carburetor shown, the housing 38 is cast integrally with the throttle body, and a stamped cover member 42 is provided to enclose the mechanism, the cover being secured by any suitable means such as the screws 44 and sealed by gaskets 45 and 47.

The shaft 26 to which the choke plate 24 is fixed extends through the wall of the carburetor and has secured thereto a lever 46. A link 48 is pivotally secured at the upper end thereof to the lever 46 by means of a clip 50, the other end of the link 48 extending downwardly into- -the housing 38, through an eyelet 41 in the cover 42, so as to have the lower transverse end 52 thereof in a position to be engaged by the outer radially extending free end 54 of a thermostatic bimetal coil element 56. The inner end of the coil 56 is fixedly secured in the usual manner through the slot 58 in the shaft 60, the rotational position of which may be set to determine the preload of coil 56 by engagement of the toothed wheel 62 secured to the shaft with a pointed lug 64 formed on the housing 38. Alternatively, the Wheel 62 may be replaced by a slotted plate adapted to receive a screw to hold the plate in any desired position. Bearing openings in the cover 42 locate the shaft 60. i

As is well known in the art, the thermostatic coil 56 is formed so as to expand with decreasing temperature and to contract with increasing temperature. Thus, at lower temperatures, the coil tends to unwind so that the free end 54 thereof tends to close the choke valve 24 through its engagement with the link 48. As alreadly stated, the choke closing force of the thermostatic coil 56 can be varied by adjusting the initial rotational position of the shaft 60.

The housing 38 is preferably formed at the other end thereof with a vertically positioned cylinder 66, the closed end of which is in communication with engine manifold vacuum by means of the passage 68 extending from the induction passage 20 at a point downstream of the throttle plate 28 and communicating with the bottom of the cylinder through the opening 70. The cylinder walls are formed at the upper end thereof with a pair of aligned slots 72 adapted to receive the free end of a wire or other suitably formed beam member 74, the other end 76 of which is rotatably anchored, as by a loop, to the shaft 60 on which the inner end of the thermostatic coil is fixedly mounted. As will be explained, the beam 74 may be rigid, or it may flex at a predetermined rate.

A piston 78 is positioned in the cylinder 66, the piston preferably having only suificient clearance to allow engine vacuum to cause air to flow by the piston and yet to cause the piston 78 to move downwardly in the cylinder in response to the same engine vacuum. The upper portion of the piston is formed to provide an annular groove 80 aligned with the grooves 72 formed in the cylinder wall so that beam 74 member may be received both in the annular groove 80 in the piston and the vertical grooves 72 in the cylinder wall. It will also be noted that the beam '74 passes above the transverse end 52 of the link 48 that engages the free end 54 of the thermostatic coil 56.

Other details of construction of the housing 38 to be noted are the air inlet 82 and the bafile 84 having an opening 86, the bafile causing air, preferably coming from the air cleaner 88 and heated stove 90 positioned in or near the exhaust manifold 92 in the usual manner well known in the art, to pass both over and under the thermostatic coil 56 to heat the same more uniformly. The heated air eventually passes into the open top of the cylinder 66, around the piston 78 and thence into the intake manifold by way of a passage 68, as indicated by the arrows.

The sides of the housing 38 are formed with suitable projections 94 and 96 providing oppositely disposed aligned slots 98 to receive the shaft 60 and a second pair of slots 100, the outermost of which is adapted to guide the lower transverse end 52 of the link 48. It is understood that the slots 98 may be initially formed to provide either a deeper or a shallower seat for the shaft 60, as indicated by the dotted lines A and B in FIGURE 1. Since the link 48 must move through the fixed opening 41 in the cover member 42, the outer slot is formed with an angular cam portion 102 to guide the lower end of the link in a manner to permit the upper end of the link to move outwardly, as it must due to the arcuate movement thereof resulting from its pivotal connection to the choke lever 46, as shown in dotted lines in FIGURE 1. It will thus be noted that while the upper end of the link moves at a fixed radius, the lower end of the link does not move at a fixed radius.

The extent to which the piston 78 can move downwardly in response to engine vacuum may be manually adjusted by means of the screw 104 having a cone end. Alternatively, the piston itself can be formed so as to enable variation in its travel.

As best seen in FIGURES 2 and 3, a fast idle and dechoke lever 106 is pivotally secured at one end thereof to the fuel bowl portion of the carburetor by means of a washer 108 and screw 110. Lateral movement of the lever is prevented by means of the bosses 112 extending from the fuel bowl, movement of the lever being thus limited to pivotal movement about the screw 110 in the plane of the lever.

It will be noted that the link 48 has a transverse portion 114 intermediate the ends thereof at a point above the cover 42. An upper arm 116 of the lever 106 extends over this transverse portion 114 and is positioned thereby. In other words, the lever 106 is free to pivot and will always fall in a counterclockwise direction about the screw until it engages the transverse portion 114. It is apparent that movement of the choke plate 24 to the closed position, as shown in dotted lines, will raise the link 48, and at the same time pivot the lever 106 clockwise.

The intermediate left-hand portion of the lever 106 is formed with a series of

steps

118, 120 and 122 which comprise a fast idle mechanism co-operating with the free, laterally extending end 124 of the lever 126 secured to pivotwith the end of the throttle shaft 30 protruding through the wall of the carburetor. Since the throttle 28 is spring loaded to close, the tap 124 on the lever 126 will either be free of or engage one of the

steps

118, and 122, depending upon the choke position when the throttle is released. The tap 124 may be formed with an opening adapted to receive a tool, such as a screwdriver, with which the tab may be suitably bent to provide fast idle settings intermediate that provided by the steps, correct for misalignment, etc.

The lower left-hand arm 128 of the lever 106 is formed with a portion 130 turned into the carburetor so as to be engaged by the intermediate contoured portion of the lever 126 so as to cam the lever 106 counterclockwise andopen the choke when the throttle is opened fully.

Operation When an engine is shut down after a run, the engine is at normal operating temperature and the choke 24 is open, as shown in solid lies in FIGURE 1. The fast idle lever 106 would thus be in its most counterclockwise position, and the lever 126 would have been positioned above the first step 118. The thermostatic coil 56 would be wound up so as to be positioned below and away from the bottom transverse end 52 of the link 48.

As the engine cools, the thermostatic coil 56 cools so as to unwind until it engages the bottom transverse end 52 of the link 48, thereafter urging the link upwardly and the choke closed. However, the first step 118 coming into engagement with the tap 124 on the lever 126 prevents the lever 106 from pivoting clockwise and the choke from closing. Since there is no engine vacuum, the piston78 is free, and it falls to the bottom of the cylinder, the beam 74 being pivotally connected to the shaft 60.

The first step in starting a cold engine is to depress the foot throttle. This opens the throttle 28 and causes the lever 126 to move counterclockwise in FIGURE 3, disengaging the tap 124 from the first step 118 and allowing the stressed coil 56 to unwind and raise the link 48, thereby closing the choke valve 24. The lower transverse end 52 of the link will also raise the beam 74, and thus the piston 78, to its uppermost position. At the same time, link 48 will rotate lever 106 clockwise so that the tab 124 will engage the fast idle step 122 when the throttle is released.

The ignition key is then turned on and the engine is cranked. As soon as the engine starts and becomes selfsustaining, and while the coil is still in the cold condition and tending to close the choke 24, the piston 78 will be drawn downwardly by engine vacuum to the stop 104, causing the beam 74 to move the link 48 downwardly and partially opening the choke plate, against the closing force of the still cold unwound thermostatic coil.

Once the piston 78 reaches the stop 104, further choke opening due to air flow on the unbalanced choke plate 24 is resisted only by the force of the coil 56. As warm air is drawn through the housing and around the thermostatic coil, the coil is progressively heated, causing it to wind up and offer less and less resistance to choke sirable to provide a choke control mechanism in which the characteristics of the bimetal movement may be readily changed.

Since the lower end of the link 48 does not traverse afixed radius, as opposed to the typical prior art structure of Smitley, a maximum mechanical advantage occurs at some given point, which can be adjusted by simply repositioning the bimetal post or shaft 60 vertically, either up or down from the position shown in FIGURE 1.

Such a shift in shaft position will also adjust the torque characteristics, within a limited range of choke plate travel, and can be accomplished by changing the depth of the slots 98, as already stated above.

With the proposed choke mechanism, the above changes or adjustments in choking characteristics can be easily made, without resorting to complicated lever modifications, as would be required in the case of the Smitley structure wherein the choke link does traverse a constant radius.

It will also be noted that the beam 74, which is pulled downwardly by the piston so as to move the link 48 downwardly and open the choke plate against the force of the thermostatic element, may be of a wire spring construction. It is apparent, if the bending movement of the beam is lower than the force of the thermostatic element, that under certain predetermined temperature conditions the beam will be forced to bend a predetermined amount. This bend of the beam will prevent the choke plate from being opened to the same angle, for a constant piston travel, as it would be if the beam were rigid. Thus, the fuel-air mixture can be modulated in accordance with temperature changes.

By actual count, the number of separate pieces required for a complete Smitley type choke system is approximately 39; with the proposed structure, the number of pieces required for a complete choke system is reduced to approximately 28.

Furthermore, since the housing containing the thermostatic element is located at the lower portion of the carburetor near the engine,'it is more responsive to conducted and radiated engine heat, which is the desired parameter. Also, such a location reduces the length and exposure of the passage required to connect the vacuum cylinder with manifold vacuum and the housing with the stove.

It should be apparent that various modifications may be possible within the scope of the appended claims.

What I claim as my invention is:

1. In an internal combustion engine carburetor automatic choke mechanism of the type wherein a thermostatic force opposes a choke plate unbalance force substantially at all times during engine operation and an engine vacuum force overcomes the thermostatic force when the engine first starts, a member pivotally connected at one end thereof to said choke plate and means whereby said thermostatic and engine vacuum forces are applied to said member from opposite sides thereof, said structure being free of any pivotal connections at the point of application of said forces.

2. In an internal combustion engine carburetor automatic choke mechanism of the type wherein a thermostatic force opposes a choke plate unbalance force substantially at all times during engine operation and an engine vacuum force overcomes the thermostatic force when the engine first starts, a link pivotally connected at one end thereof to said choke plate and means whereby said thermostatic and engine vacuum forces are applied in opposite directions directly to the other end of said link.

3. In a carburetor automatic choke mechanism of the type wherein the opening of a choke plate olfset to open in response to flow of air to the engine is opposed by a thermostatic coil element anchored atits inner end and responsive to engine heat so that opposition to choke opening decreases with increasing engine temperature and assisted by a pressure responsive member actuated fully by any engine vacuum exceeding engine cranking vacuum, means for connecting said choke plate, said thermostat and said vacuum responsive member, said means comprising a link pivotally connected to an arm extending from said choke plate, the free end of said link having a lateral extension passing between elements extending from said coil and said pressure responsive member so as to be acted upon by said elements from opposite sides thereof and so that the torque output characteristics of said coil may be varied by varying the location of said coil anchor.

4. A carburetor for an internal combustion engine, comprising a body formed with (1) an induction passage having a venturi restriction, (2) a choke plate mounted on a pivotable shaft and positioned upstream of said venturi, (3) a throttle plate mounted on a pivotable shaft and positioned downstream of said venturi, and (4) an automatic choke control mechanism, said mechanism including (a) a housing extending from said body adjacent one end of said throttle shaft;

(b) a cylinder formed at one end of said housing, said cylinder having a slot formed lengthwise through the wall thereof;

(0) a piston in said cylinder, said piston having an annular groove formed in the outer surface thereof;

(d) adjustable means for limiting the travel of said piston;

(e) a passage communicating between the induction passage downstream of said throttle plate and a source of air heated by said engine, said passage including said cylinder and said housing;

(f) a thermostatic element positioned in said housing, said thermostatic element comprising a bimetallic coil spring having the inner end thereof secured to a rotatably adjustable shaft extending across said housing and the outer free end thereof formed to provide a radially extending abutment;

(g) a lever secured to said choke shaft;

(h) a link pivotably mounted at one end thereof to said lever and extending into said housing through the top wall thereof, said link having a transverse portion intermediate the ends thereof, the free end of said link within said housing having a lateral extension engaging said abutment formed on the free end of said thermo static element so that said element tends to close said choke plate through said link when it is cold; and

(i) a beam having one end thereof pivotally secured on said shaft to which said inner end of said thermostatic element is secured, said beam extending across said lateral extension of said link toward said cylinder and the free end thereof being positioned both in said slot in said cylinder and in said groove in said piston, said beam being in engagement with said lateral extension when said choke is closed so as to open said choke against the force of said thermostatic element when said piston is moved downwardly to its stop due to engine vacuum when the engine is started.

5. In a carburetor for an internal combustion engine including a body formed with (1) an induction passage having a venturi restriction,

(2) a choke plate mounted on a pivotable shaft and positioned upstream of said venturi,

(3) a throttle plate mounted on a pivotable shaft and positioned downstream of said venturi, and

(4) an automatic choke control mechanism, said mechanism comprising (a) a housing extending from said body adjacent one end of said throttle shaft;

(b) a cylinder formed at one end of said housing, said cylinder having a slot for-med lengthwise through the wall thereof;

(d) adjustable means for limiting the travel of said piston;

(e) a passage communicating between the induction passage downstream of said throttle plate and a source of air heated by said engine, said passage including said cylinder and said houss;

(g) a lever secured to said choke shaft;

(h) a link pivotably mounted at one end thereof to said lever and extending into said housing through the top Wall thereof, said link having a transverse portion intermediate the ends thereof, the free end of said link within said housing having a lateral extension engaging said abutment formed on the free end of said thermostatic element so that said element tends to close said choke plate through said link when it is cold; and

6. In a carburetor for an internal combustion engine including a body formed with (1) an induction passage having a venturi restriction,

(4) an automatic choke control mechanism, said mechanism comprising (a) a substantially sealed housing;

(b) a cylinder formed in said housing, said cylinder having a slot formed lengthwise through the wall thereof;

(c) a piston in said cylinder, said piston having an annular abutment formed on the outer surface thereof;

(d) a passage communicating between the induction passage downstream of said throttle plate and a source of air heated by said engine, said passage including said cylinder and said hous- (e) a thermostatic element positioned in said housing, said thermostatic element having one end thereof adjustably secured to said housing and the other free end thereof extending toward said cylinder;

(f) an arm extending from said choke shaft;

(g) a link pivotably mounted at one end thereof to said arm and extending into said housing through a wall thereof, said link having a transverse portion intermediate the ends thereof and the free end of said link within said housing having a lateral extension engaging said free end of said thermostatic element so that said element tends to close said choke plate through said link when it is cold; and

.(h),a beam having one end thereof pivotally secured to said housing, said beam extending across said lateral extension of said link toward said cylinder and the free end thereof being engaged in said slot in said cylinder and adjacent said abutment on said piston, said beam being in engagement with said lateral extension when said choke is closed so as to open said choke against the force of said thermostatic element when said piston is moved downwardly due to engine vacuum when the engine is started.

7. In a carburetor automatic choke mechanism of the type wherein the opening of a choke plate offset to open in response to flow of air to the engine is opposed by a thermostatic coil element anchored at its inner end and responsive to engine heat so that opposition to choke opening decreases with increasing engine temperature and assisted by a pressure responsive member actuated fully by any engine vacuum exceeding engine cranking vacuum, means for connecting said choke plate, said thermostat and said vacuum responsive member, said means comprising a link pivotally connected to an arm extending from said choke plate, the free end of said link having a lateral extension passing between elements extending from said coil and said pressure responsive member so as to be acted upon by said elements from opposite sides thereof, said element extending from said pressure responsive member having a predetermined bending moment so as to provide modulation of the effect of said thermostat.

8. In a carburetor automatic choke mechanism of the type wherein the opening of a choke plate offset to open in response to flow of air to the engine is opposed by a thermostatic coil element anchored at its inner end and responsive to engine heat so that opposition to choke opening decreases with increasing engine temperature and assisted by a pressure responsive member actuated fully by any engine vacuum exceeding engine cranking vacuum, means for connecting said choke plate, said thermostat and said vacuum responsive member, said means comprising a link pivotally connected to an arm extending from said choke plate, the free end of said link having a lateral extension passing between elements extending from said coil and said pressure responsive member so as to be acted upon by said elements from opposite sides thereof, and so that the torque output characteristics of said coil may be varied by varying the location of said coil anchor, said element extending from said pressure responsive member having a predetermined bending moment so as to provide modulation of the effect of said thermostat.

9. In a carburetor automatic choke mechanism of the type wherein the opening of a choke plate offset to open in response to flow of air to the engine is opposed by a thermostatic coil element anchored at its inner end and responsive to engine heat so that its opposition to choke opening decreases with increasing engine temperature and assisted by a pressure responsive member actuated fully by any engine vacuum exceeding engine cranking vacuum, means for connecting said choke plate, said thermostat and said vacuum responsive member, said means comprising a link pivotally connected to an arm extending from said choke plate, the free end of said link having a lateral extension merely passing between and being free of positive connections to elements extending from said coil and said pressure responsive member.

10. In a carburetor automatic choke mechanism of the type wherein the opening of the choke plate is opposed by a thermostatic element responsive to engine heat and assisted by a pressure responsive member actuated by engine vacuum, means for connecting said choke plate, said thermostat and said vacuum responsive member, said means comprising a link pivotally connected at one end thereof to an arm extending from said choke plate, said link being arranged so that said pivoted end of said link traverses a constant radius arc, the other free end of said link traversing a different path so as to have a distinct maximum mechanical advantage at some particular point,

said point being variable by varying the direction of forces acting thereon.

11. In a carburetor automatic choke mechanism of the type wherein the opening of the choke plate is opposed by a thermostatic element responsive to engine heat and assisted by a pressure responsive member actuated by engine vacuum, means for connecting said choke plate, said thermostat and said vacuum responsive member, said means comprising a link pivotally connected at one end thereof to an arm extending fromsaid choke plate, said link being arranged so that said pivoted end of said link traverses a constant radius arc, the other free endof said link traversing a ditferent path so as to have a distinct maximum mechanical advantage at some particular point.

12. An internal combustion engine carburetor automatic choke mechanism comprising an offset choke plate, a thermostat heated by the engine, and a link extending between said choke plate and said thermostat so that opening of said choke plate is resisted by the force of said thermostat, said link being arranged so that its maximum mechanical advantage occurs at a single fixed point, whereby said point can be varied merely by varying the direction of application of said thermostat force.

13. An internal combustion engine carburetor automatic choke mechanism comprising an offset choke plate, a thermostat heated by the engine, a link extending between said choke plate and said thermostat so that opening of said choke plate is resisted by the force of said thermostat, said link being arranged so that its maximum mechanical advantage occurs at a single fixed point, whereby said point can be varied merely by varying the direction of application of said thermostat force, an engine vacuum responsive device assisting initial opening of said choke plate, and means to modulate the effect of said thermostat.

References Cited by the Examiner UNITED STATES PATENTS 2,862,488 12/1958 Nastas 123-119 2,956,558 10/1960 Sterner 123-119 2,957,465 10/1960 Wagner 123-119 2,962,014 11/1960 Durler 123-119 2,988,344 6/ 1961 Smitley 261-39 MARK M. NEWMAN, Primary Examiner. KARL J. ALBRECHT, Examiner.