US2719706A

US2719706A - Automatic choke

Info

Publication number: US2719706A
Application number: US281237A
Authority: US
Inventors: Albert H Winkler
Original assignee: Bendix Aviation Corp
Current assignee: Bendix Aviation Corp
Priority date: 1952-04-08
Filing date: 1952-04-08
Publication date: 1955-10-04
Anticipated expiration: 1972-10-04

Description

Oct. 4, 1955 A. H. wlNKLER i) 2,719,706

AUTOMATIC CHOKE Filed April a, 1952 /62 /lz [3l /50/1? a I I l 56' A TTOEMS'Y v United States Patent() AUTOMATIC CHOKE A Application April 8, 1952, Serial No. 281,237 8 Claims. Y(Cl. zei- 39) The present invention relates to carburetors for internal combustion engines and more particularly to a choke control device for said carburetors.

One of the types of automatic choke devices widely used commercially on automotive carburetors, consists of a thermostatic element responsive to engine temperature for closing the choke valve when the engine is cold and a piston responsive to manifold vacuum for moving the choke valve to a partially open position when the engine begins to tire. The extent to which the choke valve is opened by the piston is determined by the position of the vacuum conduit port in the sidewall of the cylinder housing the piston. After being partially opened by the vacuum piston, the choke valve on moving to wide open position moves the piston in the cylinder over and beyond this vacuum port. As the piston passes over the port, there is a tendency for the manifold vacuum to restrict or completely prevent further movement of the piston. To overcome this ditiiculty, a longitudinal ilattened portion adjacent the vacuum port has been provided on the piston to relieveV the effect of vacuum 'on the piston side wall. This construction, however, causes a lowering in the degree of effective vacuum available for actuating the piston through the' iirst portion of its stroke and thus tends to decrease the rate at which the piston will operate. It is` therefore one of the principal objects of the present invention to provide a piston and cylinder construction for the aforesaid choke control device which permits the utilization ofl the full manifold vacuum transmitted to the cylinder without creating a condition which prevents the free movement of the piston throughout its full stroke. K

Another object of the invention is to provide an automatic choke control device whichis readily responsive to engine operating conditions.

A further object of the invention is to provide a choke control device in which the parts can be easily arranged to suit any particular type of carburetor or engine installation.

Additional objects and advantages -of the invention will become apparent from the following description and drawings wherein:

Figure l is a side elevation of a carburetor in which an automatic choke control device .is shown in cross section;

Figure 2 is an enlarged, fragmentary cross-sectional view of the piston and cylinder of the choke control device shown in Figure 1; and

Figure 3 is a fragmentary cross-sectional view of the piston and cylinder of a choke control device, showing a modified form of my invention.

Referring more speciiically to the drawing, numeral designates the main body of a downdraft carburetor, 12 a throttle body, 14 a throttle valve and 16 an air horn in which is mounted a choke valve 18 on a shaft 20. The shaft is olset from the center of the induction passage to unbalance the choke valve so that air ilow through the induction passage will tend to open the valve.

2,719,706 Patented Oct. 4,1'955 ICC The carburetor contains, in addition to those elements mentioned, a main fuel system, idle system, accelerating pump, fuel bowl and power enrichment jet, usually found in conventional float typeautomotive carburetors. A description of these elements here is not necessary since their construction is well known.

` The choke valve 18 is controlled by an automatic choke unit mounted on the air horn at one end of shaft 20 and consisting principally of a housing 22, a thermostat 24 of a coiled bi-metallic material connected to the choke shaft through a lever 26, and a vacuumactuated piston 28 connected to lever 26 by a rod 30. 'I'he ythermostat is anchored at its center to a fixed pin 32 and is` hooked at its outer end over a pin 34 on the free end of lever 26. As the engine cools, the thermostat uncoils and urges the lever in a counterclockwise direction, i. e. in the direction to close the choke valve. After the engine has started to run under its own power and is becoming warm, the thermostat gradually coils upon itself and backs the free end thereof away from pin 34, thus permitting the choke valve to open under the inuence of air ilow in the induction passage. Since the larger portion of the unbalanced valve is on the side moving downwardly as the valve opens, the valve tends to move to and stay in open position and must be positively moved to and held in closed or partly closed position. In the unit shown in the drawing, the thermostat is capable of positively moving the choke valve only toward closed position although in some installations it may be desirable to secure the free end of the thermostat to pin 34 so that the choke valve will be positively moved toward open position. j

The piston 28 is disposed in a cylinder 36 and consists of a hollow cylindrical member 40 having a land 42 at its inside end, another land 44 at its outside end, and a central recess formed by ysaid lands and connected by one or more ports 48 with the hollow interior of the piston.

The cylinder which is closed at one end and connected directly at the other end with chamber 38 of the housing is connected at port 49 along the cylinder wall to the induction passage on the engine side of the throttlevalve by conduit 50. The position of port 49 along the cylinder Wall determines theextent to which the piston is moved by manifold vacuum toward ,the right hand end of the cylinder after the engine begins to fire yand thus determines the extent to which the choke valve will be opened to provide the air required for cold engine operation. The port 49 is of larger diameter than the width of land 44 to prevent the land from sealing the port and being held by vacuum as it passes over the port. This arrangement eliminates the necessity of providing the conventional slot in land 44 adjacent port 49 and therefore permits the utilization of the full vacuum transmitted to the cylinder. Whenk the piston arrives at the position shown in Figure 1,A air `from chamber 38 passing through the hollow interiorgof the piston through ports 48 and around recess 46 to port 49 relieves the vacuum atthat port so that it is ineffective to actuate the piston. The, piston can thereafter be easily moved to its full right hand positionas the choke valve is moved toward open position by air ilow in the induction passage.

-After land 44 passes port 49, manifold vacuum has no effect on the movement of the piston in either direction. The size of either port 49 or land 44 may be varied in relation to the other in order to vary the vacuum in the closed end of the cylinder at the end of the vacuum actuated portion of the piston stroke to give a gradual transitional movement of the piston from the first part of the stroke to the last part. A restriction 54 may be included in conduit 50 so that the amount of vacuum transmitted to the cylinder may be varied from one installation to another.

A modification of my invention is shown in Figure 3 wherein ableed 60 and/or bleed zconnectconduit 50 with the Vclosed end of thecylinder Vafter land 44 has passed Vover port `52 as it is moved by the choke valve after .completion .of the vacuum stroke. This arrangement .permits the utilization .of a small amount of vacuum to assist in the movement Vof the choke valve to `wide open position, and, by varying the relative sizes of port 48, lrestriction 54 and vbleeds 60 and/or 62, any desired operating characteristic may be obtained. Bleed y60 may be connected to conduit 50 either above or below Yrestriction S4. Other modications and arrange- .ments may be made without departing from the scope of the invention.

'.1. .In a carburetor, an induction passage, a choke valve and a throttle valve in said passage, a shaft for said ychoke valve, a lever secured to said shaft, a cylinder, a piston in said cylinder connected at one end to said vlever and having a land at the other end, and a conduit connecting said cylinder, along the side wall thereof at la point atleast partially traversed by said land, with said passage on the engine side of the throttle valve and having fat the point of juncture with said cylinder a diameter greater than the width of said land.

f2. In a carburetor, an induction passage, a choke valve and a throttle valve in said passage, a shaft for said choke valve, a lever secured to said shaft, a thermostatic means operatively connected to said lever, a cylinder, a piston in .said cylinder connected at one end to said lever and having aland at the other end, and a conduit connecting said cylinder, along the side wall thereof at a point at least partially traversed by said land, with said passage on the engine side of the throttle valve and havling at the point of juncture with said cylinder a diameter greater `than the width of said land.

3. ln a carburetor, an induction passage, an unbalanced choke valve and a throttle in said passage, a shaft for said choke valve, a lever secured to said shaft, a thermostatic means operatively connected to said lever, a cylinder, a piston in said cylinder connected at one end to said lever and having an annular land at the other end, and a conduit connectingv said cylinder, along the side wall thereof at a point at least partially traversed by said land, with said passage on the engine side of the throttle and having at the point of juncture with said cylinder a diameter greater than the width of said land, and a restriction in said conduit.

Y 4. In a carburetor, an induction passage, a choke valve and a throttle in said passage, a shaft for said choke valve, a lever secured to said shaft, a coiled thermostatic means operatively .connected to said lever, a cylinder having a;closed end, a piston in said cylinder operatively connected to said choke valve and having an annular recess in the periphery thereof forming an annular land on the end adjacent the closed end of said cylinder, and a conduit connecting said'cylinder, along the side wall thereof at a point at least .partially traversed by said land, with said passage on the engine side of the throttle and having at the point of juncture with said cylinder a diameter greater than the width of said land.

5. In a carburetor, an induction passage, an unbalanced choke valve and a throttle in said passage, a shaft for said choke valve, a lever secured to said shaft, a coiled thermostatic means operatively connected to said lever, a cylinder having a closed end, a piston in said cylinder operatively connected to said lever and having an annular recess in the periphery thereof forming an annular land on the end adjacent the closedend of said cylinder, a conduit connecting said cylinder along the side wall vthereof with said passageon the engine side of the throttle and having at the point of juncture with said cylinder a diameter greater than the width of said land, and a bleed passage connectingsaid conduitwith said cylinder adjacent the closed end thereof.

6. A control device for a carburetor, comprising a thermostatic means, a housing for said thermostatic means, a cylinder opening at one end into said housing and being closed at the other end, a pistonin said cylinder adapted to be connected to said choke valve and having a recess in the periphery thereof, a land on the end of the piston adjacent the closed end of the cylinder, and a port in the .side wall of said cylinderat ay point at least partially traversed by said land adapted -to be connected with a source of vacuum and having a diameter greater than the width of said land. n

"7. A control device for a choke valve, comprising a thermostatic means, .a housing for said thermostatic means,a .cylinder opening at'one end into said housing andibeing closed at the other end, a hollow piston-in said cylinder adapted tobe operatively connected' to said choke valve andhaving an annular recess in the periphery thereof forming an annular land ,on the end of the piston adjacent the closed end of the cylinder, a passage` way in said piston adapted Vto connect said recess with said housing, and a port in the side Wall of said cylinder at a point atleast partially traversed by said land adapted to be connected with a source of vacuum and having a diameter greater than the width of said land.

8. A control device for a choke valve comprising a thermostatic means, a housing for said thermostatic means, al cylinder opening at one endinto said housing and 'being closed at the other end, a hollow piston in said cylinder adapted to be operatively connected to said choke valve and having an annular recess in the periphery'thereof lforming an annular land on the end of the piston adjacentV the closed end of the cylinder',` a passageway in said piston adapted toy connect said recess with said `housing,.a port in the side wall of said cylinder adapted to `be connected with a source-of vacuum and having a diameter greater than the width of said land, and ableed .passage adapted 'to connect the closed end of the cylinder with a source of vacuum when said land is between said port and said closed Vend References Cited in the tile of this patent j UNITED STATES PATENTS 2,031,709 Hunt Feb.'25, 1936 2,127,735 Hunt Aug. 23, 1938 2,215,682 Winkler Sept. "24, 19.40 2,499,607 Read Mar. '7, 1950 2,523,798 Winkler Sept. 26, 1950