US3622131A

US3622131A - Choke plate closing retarding means for a carburetor automatic choke

Info

Publication number: US3622131A
Application number: US885157A
Authority: US
Inventors: Timothy R Keenon
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1969-12-15
Filing date: 1969-12-15
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23

Abstract

A choke plate closing retarding means device for a carburetor automatic choke having a thermostatic spring element. A lever arm attached to the choke plate shaft engages a cantilever spring during a portion of lever arm travel which thereby retards initial choke plate closing.

Description

BACKGROUND OF THE INVENTION One of the basic functions of a gasoline engine carburetor is to mix fuel and air iri appropriate ratios to provide a combustible mixture under all operating conditions of the engine. When a cold engine is to be started, especially at cold winter temperatures, the carburetor must supply an exceptionally rich mixture to assure that enough vaporized fuel reaches the combustion chambers to support initial combustion. This is because fuel at cold temperatures vaporizes more slowly than at moderate temperatures and also because a portion of the fuel vaporized in the carburetor is condensed in the cold intake manifold before it reaches the combustion chambers. A choke system is generally employed in the carburetor to provide this exceptionally rich mixture needed to start and sustain initial combustion in a cold engine.

A conventional choke system consists primarily of a butterfly valve mounted within the carburetor barrel upstream of the throttle valve. When the choke valve is closed the quantity of air entering the carburetor is at a minimum and the pressure within the carburetor barrel is significantly reduced. The reduced pressure increases the pressure differential between the fuel bowl and the carburetor barrel and thus, increases the fuel flow into the carburetor barrel. The increased fuel flow plus the reduced airflow results in the rich mixture necessary to start the cold engine.

Most choke systems used in automobile engines today are automatically controlled. The automatic control generally consists of a bimetal thermostatic spring and a vacuum-actuated piston or diaphragm. The thermostatic spring is installed in a stream of air from the exhaust manifold.

When the engine is cold, the spring is coiled tightly and exerts a closing force on the choke. The choke is thus fully closed until the engine starts. As soon as the engine is started, the vacuum on the piston or diaphragm pulls the choke valve partly open allowing the entry of more air.

With the use of a conventional automatic choke, as described above, a problem arises when the engine is restarted after having been stopped for a period of time of about 20 to 40 minutes. Especially at cold winter temperatures, the thermostatic spring cools much more rapidly than does the engine block when a hot engine is stopped. Consequently, when the engine is restarted after a cold soak period" of about 20 to 40 minutes, the choke valve is often fully closed, but the engine block temperature and intake manifold temperature have dropped considerably less. The fuel-air mixture provided on restart may be too rich to support combustion or will stall the engine upon initial warrnup.

This invention provides an economical and reliable means to prevent premature choke closing before the engine has cooled sufficiently to require full choking on restart.

SUMMARY OF THE INVENTION An automatic choke closing retarding means constructed in accordance with this invention includes a lever arm connected to the choke plate shaft and movable therewith and a spring means engageable with the lever arm during the first portion of its closing travel. To close the choke plate, the force of the spring means must be overcome by the force of the automatic choke thennostatic spring. This delays the initial closing of the choke valve until the engine has cooled and prevents engine restarting failures and stalling due to overly rich mixtures.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an elevational view of a gasoline engine carburetor with portions broken away showing the automatic choke assembly, the choke plate and the linkage interconnecting them. The choke plate of FIG. 1 is in a partially closed position.

FIG. 2 is an elevational view of the carburetor with portions broken away showing the choke plate in a wide open position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A portion of a carburetor 12 is shown in the drawing having an upper body or air horn 14 and a lower body 16 joined by threaded fasteners 18. An air inlet opening 20 is formed in the upper body in which a butterfly choke valve 22 is pivotally mounted by means of a choke shaft 24. A lever arm 25 is secured to one end of shaft 24 and is movable therewith. A bimetallic thermostatic spring assembly 26 is mounted to the lower body of the carburetor and is connected to a lever 28 which is movable in response to temperature changes sensed by the assembly 26. An adjustable link member 30 is pin jointed to the lever arm 25 and the lever 28.

A cantilever spring 32 is mounted to the upper body 14 by fastener 34 and extends upwardly toward lever arm 25. The spring has a convex surface 36 which is slidingly engageable with the end of lever arm 25 during the initial portion of the lever closing travel.

The lever arm 25, in moving from the choke open position of FIG. 2 to the partially closed position of FIG. 1, must deflect spring 32 sufficiently far to obtain clearance. Thus, the choke plate 22 does not close more than slightly until the thermostatic spring assembly 26 imparts a moment to lever arm 25 which exceeds the force necessary to obtain deflection clearance of spring 32. This has the effect of delaying the closing of the choke plate until the temperature experienced by the thennostatic assembly is sufficiently low to warrant a fully or nearly fully choked condition. As mentioned previously. such a delay is desirable because after the engine is stopped the thermostatic spring assembly cools much more rapidly than the remaining portions of the engine such as the engine block and manifold.

Further modifications and alterations will occur to those skilled in the art, which are included within the scope of the following claims.

Iclaim:

1. In an internal-combustion engine having a carburetor, said carburetor including a body portion, a choke plate pivotally mounted to said body portion, and temperature responsive means connected to said choke plate,

a choke plate closing retarding device comprising:

a lever means secured to said choke plate and pivotal therewith,

cantilevered spring means secured to said body and engageable with and deflectible by said lever means during a portion of the pivotal movement thereof,

said spring means including a generally convex surface engageable with said lever means to delay initial closing of 50 the choke plate,

said lever means being undeflected and spaced from said spring means during the later portion of choke plate closing travel. 2. In an internal-combustion engine having a carburetor, 5 said carburetor including a body portion, a choke plate pivotally mounted to said body portion, and temperatureresponsive means,

a choke plate closing device comprising:

a first lever arm connected to said temperature responsive means for pivotal movement in response to changes in ambient air temperature,

a second lever arm connected to the choke plate for pivotal movement therewith,

linking means joining said first and second lever arms,

cantilevered spring means engageable with and deflectible by the end of one of said lever arms during pivotal movement thereof,

said spring means has a generally convex surface engageable with said one lever arm to delay initial closing of the choke plate,

said one lever means being undeflected and spaced from said spring means during the later portion of choke plate closing travel.

Claims

1. In an internal-combustion engine having a carburetor, said carburetor including a body portion, a choke plate pivotally mounted to said body portion, and temperature responsive means connected to said choke plate, a choke plate closing retarding device comprising: a lever means secured to said choke plate and pivotal therewith, cantilevered spring means secured to said body and engageable with and deflectible by said lever means during a portion of the pivotal movement thereof, said spring means including a generally convex surface engageable with said lever means to delay initial closing of the choke plate, said lever means being undeflected and spaced from said spring means during the later portion of choke plate closing travel.

2. In an internal-combustion engine having a carburetor, said carburetor including a body portion, a choke plate pivotally mounted to said body portion, and temperature-responsive means, a choke plate closing device comprising: a first lever arm connected to said temperature responsive means for pivotal movement in response to changes in ambient air temperature, a second lever arm connected to the choke plate for pivotal movement therewith, lInking means joining said first and second lever arms, cantilevered spring means engageable with and deflectible by the end of one of said lever arms during pivotal movement thereof, said spring means has a generally convex surface engageable with said one lever arm to delay initial closing of the choke plate, said one lever means being undeflected and spaced from said spring means during the later portion of choke plate closing travel.