US2926895A - Automatic choke improvement - Google Patents

Description

2 Sheets-Sheet l Filed Nov. 24, 1958 R w /Y mfm w mw, W m5 z ,A i,... .i

March l, 1960 R. sEYFAR'rH AUTOMATIC cHoxE IMPROVEMENT 2 Sheets-Sheet 2 Filed Nov. 24, 1958 pations, at least to the extent of creating 2,926,895 AUTOMATIC CHOKE IMPROVEMENT Robert Seyfarth, Mason, Mch., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application November 24, 1958, Serial No. 776,035 7 Claims. (Cl. 261-39) This invention relates to an improvement for an automatic choke device particularly adapted for use on automotivercarburetors. More specifically, the present invention relates to a device adapted to automatically compensate the atoumatic choke mechanism for ambient Operating temperatures and particularly those reflecting seasonal changes.

The automatic choke device with 'which the present invention is concerned is of the type shown in Patent 2,705,484 Jorgensen. In this type of automatic choke device a temperature responsive element, usually a coiled bimetal, is connected to the choke valve and is adapted to urge the same in a closing direction with a force inversely proportional to ambient Operating temperatures. With such a device the choke valve opening force is supplied by making the valve of an unbalanced construction whereby air fiow through the carburetor Will tend to open the choke valve. In addition, a manifold vacuum responsive member is also utilized to modify the 'action of the bimetal during the starting and Warm-up periods.

In general it is apparent that the operation of such an automatic choke device should be adjustable in accordance with the seasons and more specifically between hot and cold Weather operation. It is further apparent that during cold weather operation it is desirable to have the choke remain in a closed or partially closed position longer than is necessary during hot weather operation.

'In present automatic choke construction it is assumed that the thermostatic coil has suflicient range to compensate for seasonal temperature variations. In general this assuinption is correct. However, the coil is actually found to over-compensate for seasonal temperature varistarting and/or running problems during a very short period after start. The problems arise due to the fact that, to a slight extent, the coil unwinds a little too much for Warm Weather operation and tghtens a little too much for cold weather operation. Thus even though the car is Operating during the summer, a cold engine still needs an enriched fuel-air mxture for at least a short period. It has been found, however, that during generally Warm ambient conditions the coil fails to hold the choke closed for a suflicient, albeit short, interval and engine stalling results.

Similarly during cold ambient conditions, the coil tends Vto maintain the choke closed slightly too long immediately after start. Consequently, the engine may either stall or run rough due to over-enrichment.

The present invention avoids these difficulties by provding a simple mechanism whereby the bimetal tension is continuously varied to compensate for changes in ambient Operating temperatures. In the present invention the bimetal coil tension is increased slightly during Warm weather operation and decreased slightly during cold weather operation which adjustment alleviates the problemsof over-compensation by the coil itself.

In the construction of the mechanism illustrated, one end of the coiled bimetal is fixed to an adjustable shaft i enlarged scale;

ice

The details as well as other objects and advantages` of the present invention will be apparent from a of the detailed description which follows.

In the drawings:

Figure 1 shows a carburetor embodying the subject invention; i

Figure 2 shows ambient persual temperature control on an tity of air fiow through which is Controlled by a chokel As seen in Figures 3 and 4, the choke valve is valve 14. operatively connected to an automatic choke controlling device indicated generally at 16. Inasmuch as the present invention relates to an improvement in the automatic choke device, it is deemed to be unnecessary to describe` the carburetor in detail other than to the extent necessary to describe the operation of choke valve 14.

As already noted, automatic choke 16 functions in the same manner as described in the aforenoted Jorgensen patent. As perhaps best seen in the diagrammatic drawing of Figure 4, choke valve 14 is of the unbalanced or air fiow responsive type and is mounted upon a shaft 18. Thus air flow through induction passage 12 will tend to rotate the choke valve in a counterclockwise or opening direction.

Automatic choke 16 includes a coiled bimetal 20 disposed Within a casing 22 and enclosed by a cover 24.'

engine temperature decreases the bimetal will urgethe lever 34 in a clockwise or choke closing direction as viewed in Figure 4. As engine temperature warms the closing force of the bimetal is'decreased Whereby air fiow can more readily open the choke valve thereby leaning the fuel-air mixture which occurrence is compatible With warm engine operation.

As already noted, it has heretofore been assumed that the bimetal coil itself would compensate for Warm or cold weather operation. Since the coil has actually overcompensated, the present atuomatic choke device includes means for modifying the coil tension.

Referring noW more particularly to the subject improvement, it is to be noted that shaft 28 extends exteriorly of cover 24 and includes a pointer lever 36 fixed thereto. As best seen in Figure 2, pointer 36'` is adapted to indicate the setting of bimetal 20 referenced to the indicia 38 formed on cover 24. A second or bifurcated lever 40 is also fixed to bimetal shaft 28.

A bracket 42 is suitably mounted through screws 44V on the automatic choke casing 22. An ambient temperature responsive device indicated generally at 46 is mounted on bracket 42. Device 46 may be of any well known. type including a temperature responsive element or capsule 48 having suflicient force when heated to change: the bias of the bimetal 20. Temperature responsive de- .ly slightly enrichening vice 46 includes a rod 50 vslidably supported within casing 52 and adapted to be moved longitudinally of the casing by the temperature responsive element or capsule 48. The otherV end of rod 50 is adapted to engage p arm 54 'of vthe bifurcated `vlever 40.'

' A spring member 56 'is anchored at one end to bracket 42 and connected at its' other end to arm 58 of bifurcated lever 40. Thus as ambient operating -temperatures increase the temperature responsive capsule 48 will urge rod 50 in an upwardly direction whereby lever 40 and shaft 28 will be urged in a counterclockwise direction increasing the bias on bimetal 20 and consequentthe fuel-air mixture. As ambient temperature decreases, capsule 48 will cause rod 50 to tend to withdraw from lever arm V54. Under this circumstance spring '56 will move lever 40 in a'clockwise direction, maintaining the lever arm 54 in abutting engagement with rod 50, and thereby decreasing the bias on bimetal 20. In this latter instance choice valve 14 is less vstrongly lurged in a closing direction thereby tendng to decrease the richness of the fuel-air mixture avoiding over-enrichment of the charge.

Rod 50 and capsule 48, therefore, positively move lever 40 in one direction and provide a stop to limit the lever movement in the opposite direction by spring 56. In this manner temperature responsive device 46 modifies the ambient temperature adjustment of bimetal 20 and insures improved starting operation of the engine.

Thus a simple device is provided whereby an auto matic choke mechanism is automatically adjusted to sea-- sonal temperature variations insuring increase carburetor efiiciency.

I claim:

1. A charge forming device for an internal combustion engine of the type including a choke valve, means for automatically controlling the operation of the choke valve, said means including a coiled bimetal, a shaft, one end of said bimetaljbeing fixed to said shaft, the otherend of said bimetal being operatively connected to said choke valve to urge the same in a closing direction with a force inversely proportional to engine temperature, a lever fixed to said shaft, an ambient temperature responsive member adapted to engage said lever and urge the same in a direction tendng to increase the closing bias of said bimetal as ambient temperature increases, and a spring member operatively connected to said lever tendng to urge the same in a direction tendng to decrease the choke closing bias of said bimetal.

2. A charge forming device as set forth in claim 1 in which the means for automatically controlling choke valve operation includes an open sided casing, a cover for said casing, said coiled bimetal being disposed within said casing, said shaft being adjustably mounted in said cover.

3. A charge forming device as set forth in claim 2 in which said shaft includes a portion extending exteriorly of said casing and cover, said lever being mounted upon said exterior shaft portion, and the ambient temperature responsive member being mounted exteriorly on said casing proximate said lever.

4. A charge forming device for an internal combustion engine of the type including a choke valve, means for automatically controlling the operation of the choke valve, said means including an open sided casing, a cover for said casing, a coiled bimetal disposed within said casing, a shaft adjustably mounted within said cover, one end of said bimetal being fixed to said shaft, the other end of said bimetal being operatively connected to said choke valve to urge the same in a closing direction with a force inversely Proportional to ngine temperature, a lever fixed to said shaft, a bracket mounted. on said easing, an ambient temperature responsive member mounted on said bracket and adapted to engage lsaid lever and 'urge the same in a direction tendng to JIifcrease the closing bias of said bimetal as ambient temperature increases, and a spring member articulated between said bracket and lever tendng to urge the latter in a direction tendng to decrease the choke closing bias of said bimetal.

5. A charge forming device as set forth in Claim 1 in which the ambient temperature responsive member. comprises a casing, a temperature responsive element within the casing, and a rod slidably mounted within the casing, said rod being adapted to engage said lever, thel element being adapted to control the movernent of said rod and lever with changes in ambient temperature.

6. A charge forming device as set forth in Lclairn 5' in which said lever is bifurcated to provide a pair of arms, said rod being adapted to abuttingly engagleotley of said arms and said spring member 'being articulated` to the other arm.

7. A charge forming device as set forth in clam 4,

in which said lever is bifurcated to provide a pair of arms, said temperature responsive member comprising:

a casing supported on said bracket, a temperature re? sponsive element within the latter casing, a rod slidably; disposed within said latter casing and operatively en-vf gaging said element, said rod abuttingly engaging one arm of the bifurcated lever, said spring member being, articulated between said bracket and the other arm of' said lever, said spring maintaining said lever in :.onst2uit.

engagement with said rod.

No references cited.

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