US3823700A

US3823700A - Combined carburetor throttle and choke control for small gasoline engines

Info

Publication number: US3823700A
Application number: US00357879A
Authority: US
Inventors: H Gumtow
Original assignee: Briggs and Stratton Corp
Current assignee: Briggs and Stratton Corp
Priority date: 1973-05-07
Filing date: 1973-05-07
Publication date: 1974-07-16
Anticipated expiration: 1991-07-16
Also published as: CA996825A

Abstract

A manually movable engine control lever swings between defined ''''stop'''' and ''''choke'''' positions, through a range of ''''run'''' positions, its maximum speed setting being nearest the ''''choke'''' position. A second lever is connected with the engine governor spring to tension it for desired engine speed. A cam edge of the first lever cooperates with a cam follower on the second, providing a connection whereby the second lever swings with the first as the first is moved between ''''stop'''' and maximum speed positions but the first swings between maximum speed and ''''choke'''' positions independently of the second while the second remains in maximum speed position.

Description

United States Patent 1191 Gumtow July 16, 1974 COMBINED CARBURETOR THROTTLE 3,126,878 3/1964 Eiler 123/119 F 3,133,532 5/1964 Ball 123/119 F FOR SMALL 3,194,224 7/1965 Lechtenberg et a1. 123/1 19 R [75] Inventor: everbert A. Gumtow, Brookfield, p i w h 1 E. Bums 1s.

[73] Assignee: Briggs & Stratton Corporation, [57] ABSTRACT wauwatosa A manually movable engine control lever swings be- [22] Filed; May 7, 1973 tween defined stop" and choke positions, through a range of run? positions, its maximum speed setting [21] Appl 357879 being nearest the "choke" position. A second lever is connected with the engine governor spring to tension [52] US. Cl. 123/119 F, 123/98, 123/99, it for es ngi e speed- A cam edge of the first 261/64 E lever cooperates with a cam follower on the second, 51 1111. C1. 1 02a 37/00, F02d 9/00 providing a connection whereby e second lever 58 Field of Search 123/97, 98,99, 119 F; swings with the r as e t is moved between 261/64 E stop and maximum speed positions but the first swings between maximum speed and choke posi- 5 References Cit d tions independently of the second while the second re- UNITED STATES PATENTS mains in maximum speed position.

Burkett 123/1191" 3 Claims, 7 Drawing Figures PATENTEDJUHBIW aware-J00 SHEE! 3 BF 3 FIGJ.

a ill! COMBINED CARBURETOR THROTTLE AND CHOKE CONTROL FOR SMALL GASOLINE ENGINES fined choke and stop" positions, through a range of run" positions that provide for operation of the engine at different speeds.

A control device of the general type to which this invention relates is disclosed in Lechtenberg et al. U.S. Pat. No. 3,194,224. Such devices have been commercially successful because they greatly simmplify engine operation, centralizing all engine operating control in a single manually operable instrumentality that is moved in a logical manner to enable the proper control movements to be readily accomplished in the proper sequence.

Thus, when the engine is to be started, the control lever is moved to a defined choke position at one limit of its swinging motion. In the final stages of motion of the lever to that position it effects swinging of the choke valve to a closed position against a torsional bias that tends to hold it open. As soon as the engine starts, the control lever can be moved a short distance to the high speed end of its range of run positions, releasing the choke to swing back to its openposition in response to its bias. By reason of a connection between the control lever and the engine throttle (which connection may include a governor), adjustment of the control lever within its range of run" positions provides for adjustment of the operating speed of the engine. When the engine is to be stopped, the control lever is moved to and beyond the low speed end of its range of run positions to a defined stop position at which a switch element is closed to ground the engine magneto and thus terminate ignition.

Where the engine is equipped with a governor, as is usually the case with lawn mower applications, the control lever is not directly connected with the throttle but instead has a connection with one end of a governor bias spring. The other end of that spring is connected with the governor, and the governor, in turn, has a linkage connection with the throttle. Hence movement of the control lever within its range of run positions effects adjustment of the biasing force that the spring exerts upon the governor and thereby establishes the particular engine speed that the governor will maintain. The governor of course opens and closes the throttle as necessary to maintain the selected speed.

A governor on a small engine not only assures smooth operation and reliable power output under varying loads but also performs an important safety function in limiting the maximum speed of the engine. Although no law requires it, the industry has voluntarily established and carefully observed a limitation upon maximum speed for lawn mower engines, and the governors on all such engines are so adjusted as to prevent the engine from exceeding that maximum speed.

Under certain conditions the above described single lever control device, in the form in which it was heretofore available, could cause an engine to run at a slightly higher speed than that for which its governor was adjusted; and while such conditions were unusual, and ordinarily did not result in overspeed running for any prolonged period, the mere possibility of such operation was obviously very undesirable. The condition arose because the choke position of the lever was reached by moving the lever slightly beyond its maximum speed position, and by such movement the tension on the governor spring was increased to a value above that corresponding to desired maximum engine speed. The maximum speed position of the control lever was defined by a detent, and if the detent became worn, or was ignored by the'operator, and if the adjustment of the choke actuating arm was not accurate in relation to its cooperating abutment on the control lever, the control lever could be placed slightly beyond the maximum speed detent, allowing the governor to open the throttle too much without producing an offsetting closure of the choke.

In general, the object of the present invention is to provide a control device for small gasoline engines, of the type that comprises a single member which is manuallymovable to defined choke and stop positions through a range of run positions, which control device does not permit overspeed operation of the engine even in cases where there is substantial inaccuracy in the choke actuating adjustment such that the manually movable member can be moved a substantial distance beyond its maximum speed run" position before it effects closure of the choke.

It can also be said to be an object of this invention to improve the reliability and convenience of engine control devices of the character described, while materially increasing their safety, by reason of the provision of such a control device that does not permit overspeed operation of the engine that it controls even though the detent that defines the maximum speed position of the control lever becomes worn or is ignored by an operator. 1

Inasmuch as the small engine industry is highly competitive and very cost conscious, those familiar with the art will recognize immediately that the present invention must also have among its objects the provision of a control device of the character described that is low incost, very compact, and inherently sturdy and resistant to abuse as well as to normal wear.

With these observations and objectives in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings, which exemplify the invention, it being understood that changes may be made in the specific apparatus disclosed herein without departing from the essentials of the invention set forth in the appended claims.

The accompanying drawings illustrate one complete example of an embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a view in elevation of portions of the crankcase, governor and carburetor of a small engine shown equipped with a control device embodying the principles of this invention, the control device being illustrated in its maximum speed running position;

FIG. 2 is a view generally similar to FIG. 1 but showing only the control device in relation to a part of the governor, the device being illustrated in its stop position;

FIGS. 3-6, inclusive are fragmentary plan views of the two levers comprising the control device, shown in their relationship to one another when the control device is adjusted for various conditions; and

FIG. 7 is a disassembled perspective view of the control device.

Referring now to the accompanying drawings, the numeral 5 designates generally a control device of this invention, mounted on the crankcase portion 6 of a small gasoline engine adjacent to the carburetor body 7. The control device comprises a single manually operable lever 8 which can be swung between a choke" position in which it is illustrated in FIG. 6 and a stop" position in which it is illustrated in FIG. 2, through a range of run positions. The lever 8 can be moved directly, by gripping it at a thumb tab 9 on the outer end of its actuating arm, or can be actuated from a remote location as by means of a bowden cable (not shown) or the like, connected to it at a hole 10 in its actuating arm.

The lever 8, which can be formed as a generally fiat stamping, is carried on a mounting plate 11 that is in turn fixed to the engine crankcase. A rivet 12 through the lever 8 and the mounting plate provides a pivot about which the lever can swing edgewise over the top surface of the mounting plate. Embostures l3 and 14 in the lever define dimples at its underside that have detent cooperation with a small fixed protuberance 15 beneath it. These detents define the maximum speed and minimum speed positions of the lever 8. A wave washer 16 or the like, confined between the lever and the head of the rivet l2, biases the lever flatwise toward the mounting plate and activates the detents.

In the carburetor body 7, near the air inlet thereof, there is a generally conventional choke valve 17, the shaft 18 of which extends through the carburetor air duct and has thereon a laterally projecting actuating arm 19 at the exterior of the carburetor. In FIG. 1 the choke valve is shown in its open position, to which it is biased by a torsion spring 20 which is coiled around its shaft 18 and which reacts between the actuating arm 19 and a part that is fixed on the engine.

As the lever 8 is swung clockwise (as shown in FIG. 1) beyond its detent-defined maximum speed position, a tab-like arm 22 on the lever collides with the choke actuating arm 19 and then swings that arm through about 90 to bring the choke valve to its closed position. When the lever 8 is swung back into itsrange of run positions the choke valve is of course returned to its open position'under the bias of the torsion spring 20. The tab-like arm 22 on the lever 8 is in upwardly offset relation to the remainder of that lever. I

The position of the throttle valve (not shown) corresponds to the position of a conventional throttle actuating lever 24 which is anchored on the throttle valve shaft at the exterior of the carburetor body. The governor that controls the particular position that the throttle occupies at any momentcan be conventional and therefore is not shown except for a swingable arm 26 that comprises a connection between it and the control device and also a connection between it and the throttle. An adjustably variable biasing force is applied to the arm 26 by means of a tension spring 27 that is connected at one end with the arm 26 and has its other end connected with the control device 5215 hereinafter described. A conventional link 28 connects the governor arm 26 with the throttle lever 24.

In general, the governor maintains higher engine speeds when higher biasing forces are imposed upon its arm 26 by the spring 27. To provide for control of the biasing force normally maintained by that spring, and thusafford a means of adjusting engine speed, the governor spring has its end remote from the governor arm connected with a lever 30 which comprises a part of the control device and is positioned by the manually actuatable lever 8.

The lever 30 overlies the mounting plate 11, in flatwise sliding engagement with its upper surface, and swings about a rivet 31 that extends through it and the mounting plate. To provide clearance between the govenor spring 27 and other parts, the lever 30 has an upwardly offset free end portion 33 to which the governor spring is connected. Note that the rivet 31 which provides the fulcrum' or trunnion for the lever 30 is spaced a small distance from the rivet 12 that pivots the manually actuatable lever 8, and that those two pivot axes are parallel to one another.

Because of a peculiar motion transmitting connection 34 (described hereinafter) between the lever 8 and thelever 30, the latter is constrained to move with the lever 8 throughout its range of run positions, to thereby tension the governor spring in accordance with the position in which the manually adjustable lever 8 is set. When the lever 8 is in its maximum speed position, the lever30 engages an abutment 35, defined by an upturned lug on the mounting plate. The abutment 35 thus fixes the upper limit of tension that can be applied to the governor spring. However, the connection 34 permits the manually actuatable lever 8 to be swung independently of the lever 30 through that portion of the swing of the lever 8 at which it actuates the choke valve. I

The lever 8 is in partly overlying relation to the lever 30 and also to the rivet 31. To provide clearance for the lever 8, it flatwise overlies a spacer member 38 which is secured to the mounting plate by the rivet 12. A locating pin 39 at the underside of the spacer member engages in a hole in the mounting plate and confines that member against rotation about the rivet 12. The locating pin 39 and detent protuberance 15 can be formed integrally with the spacer, as shown. An upwardly projecting abutment 40 that is engaged by the lever 8 to define the position thereof at which the choke valve is fully closed can be carried by a portion of the spacer member that extends edgewise beyond the mounting plate.

The motion transmitting connection 34 between the lever 8 and the lever 30 comprises an upwardly projecting protuberance or cam follower 41 on the lever 30, spaced from the axis thereof and engageable with edge portions of the lever 8 that are shaped to provide a cam. Specifically the cam defining edge of the lever 8 comprises one portion 43 which is of rapidly changing radius relative to the swinging-axis of the lever 8 and another portion 44 of uniform radius aboutthat-axis.

As the lever 8 is swung away from its stop position (i.e., clockwise from its position shown in FIG. 2), the rapidly changing radius cam portion 43 cooperates with the cam follower 41 to swing the lever 30 more or less in unison with the lever 8, increasing the tension on the governor engine speeds. FIG. 4 illustrates the relative positions of the

levers

8 and 30 at about the midpoint of the run range.

The changing radius portion 43 of the cam edge merges into the uniform radius portion 44 at a point on the cam edge that the cam follower 41 passes just as the lever 30 is brought into engagement with its stop abutment 35, as illustrated in FIG. 5.

As the lever 8 is swung clockwise beyond that point, toward its choke position illustrated in FIG. 6, the uniform radius portion 44 of the cam edge is engaged with the cam follower, and hence the lever 30 cannot swing with the lever 8. However, since the pivot axis of lever 30 is spaced to one side of the line through the cam follower and the pivot axis of lever 8, the lever 30 is maintained in engagement with its stop 35 to hold the throttle fully open while the engine is being choked, as is desired for engine starting. a

As the lever 30 is swung away from the choke position towards the stop position, successively through the positions shown in FIGS. 6, 5 and 4, the biasing force of the governor spring tends to swing the lever 30 counterclockwise, towards its low speed position.

However, when the lever 8 is moved all the way to its stop position illustrated in FIGS. 2 and 3, a portion of the lever 30 engages a magneto grounding switch element 47, and therefore a positive driving connection between the two levers is desired in the final stage of counterclockwise movement of the lever 8. To that end the edge of lever 8 is formed with another cam portion 49 that opposes the changing radius cam portion 43 and defines a slot 50 therewith. The cam portion 49 comes into engagement with the cam follower 41 near the low speed end of the range of run positions of the lever 8. Note that engagement of the studlike cam follower in the bottom of the cam slot 50 prevents further counterclockwise motion of both levers beyond the stop" position.

The switch element that provides for magneto grounding is described in detail in the above mentioned U.S. Pat. No. 3,194,224. In general, it comprises a resilient metal member mounted beneath the mounting plate, in insulated relation thereto, having an arm 51 which projects up through a hole in that plate to be engaged by a portion of the lever 30. The upper edge of the switch arm 51 is inclined so as to be cammed downwardly in consequence of its engagement with the lever 30. There is a fairly strong biasing force on the switch arm that insures its having good grounding contact with the underside of the lever 30, hence its camming engagement by the lever 30 affords a detent action that identifies the stop position.

From the foregoing description taken with the accompanying drawings it will be apparent that this invention provides a single-element type of control device for small gasoline engines which has the simplicity and sturdiness of control devices of that type heretofore available, but which prevents any possibility of overspeed operation of the engine as the manually actuated control member is moved towards its choke posiiton.

Those skilled in the art will appreciate that the invention can be embodied in forms other than as herein disclosed for purposes of illustration.

The invention is defined by the following claims:

I claim:

1. An internal combustion engine control device of the type that comprises a lever manually swingable about a fixed axis through and beyond a range of increasing running speed positions to a defined choke position, and means providing a connection between said lever and the throttle actuator of the engine through which adjustment of the lever in its range of running positions effects adjustment of the throttle actuator, said control device being characterized by the last mentioned means comprising:

A. a second lever pivoted to swing about a second fixed axis which is spaced from and-parallel to the first mentioned axis, said second lever having 1. an arm connected with the throttle actuator and 2. a cam follower spaced from said second axis;

B. fixed abutment means engageable by said second lever to define one limit of swinging motion thereof at which the engine is caused to run at its maximum speed; and Y C. cam means on the first mentioned lever cooperable with said cam follower to swing the second lever towards engagement with the fixed abutment means in consequence of movement of the first lever towards its choke position, said cam means having a portion which is of uniform radius about the first axis and which thus permits the first lever to be swung a limited distance to and from its choke position independently of the second lever while the later remains engaged with said abutment means.

2. A manually actuatable control device for an internal combustion engine that has a choke valve which is biased to an open position and which hasa laterally projecting actuating arm on its shaft, a throttle actuator comprising a movable governor member, and a spring connected at one end with said governor member to impose upon the latter a biasing force that can be varied to afford control of engine running speed, said control device comprising: i

A. a first lever to which the other end of said spring is connected and which is mounted to swing about a first fixed axis to and from a defined limit which corresponds to maximum engine running speed;

B. a second lever mounted in partially overlying relation to the first lever for swinging motion about a second fixed axis spaced from and parallel to the first axis and having an abutment which collides with said actuating arm and swings it to a choke closing position in a final stage of motion of the second lever in one direction toward a defined limit;

C. a projection on one of said levers providing a cam follower slidingly engageable with edge portions of the'other lever; and

D. cam means on said other lever comprising edge portions thereof which cooperate with said projection to constrain the two levers to move substantially in unison toward and from said limit of swinging motion of the first lever but which permit the second lever to move through said final stage of its motion, to and from its said choke closing position, independently of the first lever while the latter remains at its said limit of motion.

3. A manually actuatable control device for an internalcombustion engine that has a choke valve which is biased to an open position and which has a laterally projecting actuating arm on its shaft, a throttle actuator comprising a movable governor member, and a spring connected at one end with the governor member to impose upon the latter a biasing force that can be varied arm and swings the choke closed in a final portion of motion of said second member to its said limit; and

C. cooperating means on said members providing a motion transmitting connection between them whereby in all other portions of the motion of the second member the first member is constrained to move substantially in unison therewith but whereby said second member can move independently of the first member through its said final portion of movement while the first member remains at its maximum speed limit of motion.

II l *8

Claims

1. An internal combustion engine control device of the type that comprises a lever manually swingable about a fixed axis through and beyond a range of increasing running speed positions to a defined ''''choke'''' position, and means providing a connection between said lever and the throttle actuator of the engine through which adjustment of the lever in its range of running positions effects adjustment of the throttle actuator, said control device being characterized by the last mentioned means comprising: A. a second lever pivoted to swing about a second fixed axis which is spaced from and parallel to the first mentioned axis, said second lever having 1. an arm connected with the throttle actuator and 2. a cam follower spaced from said second axis; B. fixed abutment means engageable by said second lever to define one limit of swinging motion thereof at which the engine is caused to run at its maximum speed; and C. cam means on the first mentioned lever cooperable with said cam follower to swing the second lever towards engagement with the fixed abutment means in consequence of movement of the first lever towards its ''''choke'''' position, said cam means having a portion which is of uniform radius about the first axis and which thus permits the first lever to be swung a limited distance to and from its ''''choke'''' position independently of the second lever while the later remains engaged with said abutment means.

2. a cam follower spaced from said second axis; B. fixed abutment means engageable by said second lever to define one limit of swinging motion thereof at which the engine is caused to run at its maximum speed; and C. cam means on the first mentioned lever cooperable with said cam follower to swing the second lever towards engagement with the fixed abutment means in consequence of movement of the first lever towards its ''''choke'''' position, said cam means having a portion which is of uniform radius about the first axis and which thus permits the first lever to be swung a limited distance to and from its ''''choke'''' position independently of the second lever while the later remains engaged with said abutment means.

2. A manually actuatable control device for an internal combustion engine that has a choke valve which is biased to an open position and which has a laterally projecting actuating arm on its shaft, a throttle actuator comprisiNg a movable governor member, and a spring connected at one end with said governor member to impose upon the latter a biasing force that can be varied to afford control of engine running speed, said control device comprising: A. a first lever to which the other end of said spring is connected and which is mounted to swing about a first fixed axis to and from a defined limit which corresponds to maximum engine running speed; B. a second lever mounted in partially overlying relation to the first lever for swinging motion about a second fixed axis spaced from and parallel to the first axis and having an abutment which collides with said actuating arm and swings it to a choke closing position in a final stage of motion of the second lever in one direction toward a defined limit; C. a projection on one of said levers providing a cam follower slidingly engageable with edge portions of the other lever; and D. cam means on said other lever comprising edge portions thereof which cooperate with said projection to constrain the two levers to move substantially in unison toward and from said limit of swinging motion of the first lever but which permit the second lever to move through said final stage of its motion, to and from its said choke closing position, independently of the first lever while the latter remains at its said limit of motion.

3. A manually actuatable control device for an internal combustion engine that has a choke valve which is biased to an open position and which has a laterally projecting actuating arm on its shaft, a throttle actuator comprising a movable governor member, and a spring connected at one end with the governor member to impose upon the latter a biasing force that can be varied to afford control of engine running speed, said control device comprising: A. a first member having a connection with the other end of said spring and which is constrained to movement in opposite directions toward and from a defined limit which provides for maximum engine running speed; B. a second member constrained to move in opposite directions to and from a defined limit and arranged to be manually actuated, said second member having an abutment which collides with said actuating arm and swings the choke closed in a final portion of motion of said second member to its said limit; and C. cooperating means on said members providing a motion transmitting connection between them whereby in all other portions of the motion of the second member the first member is constrained to move substantially in unison therewith but whereby said second member can move independently of the first member through its said final portion of movement while the first member remains at its maximum speed limit of motion.