US3868935A

US3868935A - Automatic choke

Info

Publication number: US3868935A
Application number: US424883A
Authority: US
Inventors: Bernard Liebman; David W Rucinski
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1973-12-14
Filing date: 1973-12-14
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04

Abstract

In a preferred embodiment in a one-barrel carburetor having a choke valve, a throttle, a fast idle cam for controlling the idling speed, and a thermostat responsive to engine temperature, the improvement comprises a pair of connecting links extending from a lever connected to the thermostat to a pair of levers on the choke shaft. The first link extends to a lever secured to the choke shaft, and permits the choke valve to blow open during the first half of the thermostat travel. The second link extends to a cam lever pivoted on the choke shaft and linked to the fast idle cam, and permits delayed fast idle cam come-off during additional thermostat travel.

Description

United States Patent [191 Liebman et a1.

1 1 AUTOMATIC CHOKE [75] Inventors: Bernard Liebman, Pittsford; David W. Kucinski, Rochester, both of NY.

[73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: Dec. 14, 1973 [21] Appl. No.: 424,883

[52] U.S. Cl. 123/119 F, 261/39 B [51] Int. Cl. F02m 1/10 [58] Field of Search 123/119 F; 261/39 B, 64 E [56] References Cited UNITED STATES PATENTS 2,957,465 10/1960 Wagner 123/119 F 3,730.498 5/1973 Keenon 261/39 B 3,785,624 1/1974 Marsee 261/39 B 3.789.814 2/1974 Gilham et a1 123/119 F Mar. 4, 1975 Primary Examiner-Charles .1. Myhre Assistant E.\'aminerS. .1. Richter Attorney, Agent, or Firm-C. K. Veenstra [57 ABSTRACT on the choke shaft. The first link extends to a lever secured to the choke shaft, and permits the choke valve to blow open during the first half of the thermostat travel. The second link extends to a cam lever pivoted on the choke shaft and linked to the fast idle cam, and permits delayed fast idle cam come-off during additional thermostat travel.

1 Claim, 3 Drawing Figures PATENTEU 41975 SHLLI l AUTOMATIC CHOKE The present invention relates to an automatic choke for a carburetor and more specifically to an automatic choke which employs thermostatic means for controlling the operation of both the choke valve and the fast idle cam for ensuring proper operation of the engine under cold starting and warm-up conditions. More specifically, the present invention relates to a novel automatic choke device employing a single thermostatic coil for controlling the operation of the choke valve and fast idle cam in an overlapping or split manner.

The improvement over the prior automatic choke art resides, for the most part, in the provision oflinkage for controlling the choke valve and fast idle cam. With this invention, the control of the choke valve is actually separated from or split, in a manner of speaking, from the control of the fast idle cam; that is, the choke valve is allowed to open fully during the initial portion of the thermostat travel while the fast idle cam is still controlled by the thermostat for the remainder of its travel. In effect, the fast idle cam operation overlaps and is delayed from the operation of the choke valve. This split operation is achieved by the present invention through parallel but overlapping choke valve and fast idle cam controls in a novel linkage combination controlled by a single thermostat.

As will be more apparent from the discussion which follows, the present invention considerably improves the transient or warm-up characteristics of carburetor operation by permitting the choke valve to open or come-off, as commonly expressed, sooner than the fast idle cam allows the throttle valve to obtain its warm idle position.

One of the problematical factors relating to the operation of carburetors using automatic chokes is the following: During and after engine starting, the choke valve reduces the subatmospheric pressure occurring in the metering zone posterior the choke valve and anterior the throttle. This action creates a problem if it provides an enriched fuel-air mixture for a considerably longer period of operation than is necessary to avoid rough running. The foregoing problem can arise when the fast idle cam is operated by the same temperature sensing and positioning thermostat that operates the choke valve. As opposed to the choke valve, the fast idle cam is required to be operative for a longer period (about twice as long) to maintain an increased idling speed during warm-up. If simply linked to the thermostat, the fast idle cam operates simultaneously with and comes off at the same time as the choke valve.

This problem was recognized in US. Pat. No. 2,957,465 Wagner, which set forth a linkage arrangement for split choke control differing from the present invention. Both the present invention and Wagners arrangement provide choke and cam positioning means controlled by a single temperature responsive thermostat. Also, both permit the normal operation of the fast idle cam when the engine is warming but further permit the choke valve to be opened in advance of the comeoff of the fast idle cam. However, this invention differs from Wagners device by providing two links extending from a lever positioned by the thermostat to a pair of levers on the choke valve shaft. This is an improvement in that it allows a high mechanical advantage linkage at closed choke. Thus, the present invention is an improved way for providing desired split operation of the choke valve and the fast idle cam.

It is therefore the principal object of this invention to provide an automatic choke which acts in a sequenced or split manner for positioning the choke valve and fast idle cam in a split manner. This object is accomplished by the provision of two links extending from a lever controlled by the thermostat to a pair of levers on the choke valve shaft. The first link extends from a-slot in the top of the thermostat lever to a lever secured to the choke valve shaft and provides an operative connection therebetween which permits rapid choke come-off. The second 'link extends from the middle of the thermostat lever to a slot in the bottom of a cam lever pivoted on the choke shaft and connected to the fast idle cam, and provides an operative connection therebetween which permits extended and yet overlapping fast idle cam operation. This novel construction accomplishes the split operation of the choke valve and the fast idle cam.

Other objects and advantages of the present invention will be apparent from the detailed description which follows, when considered in view of the drawings.

In the drawings, the various figures are side elevational views of the present invention as adapted to a one-barrel carburetor with parts broken away to illustrate certain details of construction; where FIG. 1 shows the linkage in a cold start position;

FIG. 2 shows the linkage in an intermediate position corresponding to a wide-open choke; and

FIG. 3 shows the linkage in a position corresponding to full thermostat travel.

Referring to the drawings, the carburetor 10 has a mixture conduit 12 including an air inlet 14 and a mixture outlet 16 which discharges to the engine. A venturi 18 is disposed between the inlet and outlet for accelerating the air flow therethrough, as is conventional practice. Venturi 18 provides a venturi vacuum signal to means (not shown) for metering fuel in accordance with engine air flow.

A throttle valve 20 is rotatably disposed on a throttle shaft 22 in a conventional manner in mixture conduit 12 posterior venturi 18. A throttle lever 24 is secured to throttle shaft 22 for concomitant rotation through a selected path. It should be noted that the counterclockwise direction is the throttle opening direction.

Throttle lever 24 has an upwardly extending finger or cam follower 26. A pivot pin 27 supports a fast idle cam member 28, which is rotatably disposed thereon. Fast idle cam member 28 has a notched portion 29 and series of steps 30 or alternatively a smoothly contoured surface engaged by the cam follower 26. Notched portion 29 is provided at one end of steps 30 to allow the cam follower 26 to come-off or disengage the cam at that point so that the throttle 20 may close to its warm idle position. The cam 28 is disposed in the path of rotation of follower 26 for variably limiting the rotation of throttle lever 24 in the clockwise direction, thereby controlling the idling position of the throttle valve 20.

As the engine warms it is desirable to decrease the amount of air supplied to the engine during idling. Accordingly, the coaction of cam 28 and cam follower 26 enables throttle 20 to close further as the engine warms. This coaction will be described in detail below.

A cam link 32 is pivotally connected at one end 31 to fast idle cam member 28 and at the other end 33 to a cam lever 34. It should be noted that the weight of cam lever 34, cam link 32, and fast idle cam 28 biases cam 28 in the counterclockwise direction, and as the cam rotates counterclockwise under this bias, further closure of throttle 20 is permitted.

A choke valve 36 is rotatably disposed in mixture conduit 12 by means of a choke shaft 38 extending through the mixture conduit 12 in the usual manner. It should be noted that the center of gravity 39 of the choke valve is laterally offset from the choke shaft 38'. Accordingly, this construction provides an unbalanced choke valve, whereby the gravitationally induced clockwise bias of the choke valve, the subatmospheric pressure below and the substantially atmospheric pressure above the valve, and the momentum of air flow through the air inlet 14 past the valve all inpart a clockwise torque on the choke valve 36 about the noncentered choke shaft 38. These torques acting on shaft 38 tend to open the choke valve.

As shown in FIG. 1, a thermostat housing 42 extending from the carburetor encapsulates a bimetallic coil 44, one end of which is anchored at a pin 43 to a housing cap 45 adjoining housing 42. Housing cap 45 is rotatably adjustable relative to stationary housing 42 to provide for initial adjustment of the coil 44. The other end 46 of bimetallic coil 44 is hooked over and positions a thermostat lever 47 (internal to housing 42). Thermostat lever 47 is secured to a central thermostat shaft 48 which extends through cap 45 and is secured to an outboard, upwardly extending thermostat lever 50 in a conventional manner.

Air heated in response to engine operating temperature may be admitted to the housing 42 via a port 51 to circulate in the housing, thereby providing means for communicating engine operation temperature to bimetallic coil 44. Alternatively, a heating element may be disposed adjacent the coil to heat it electrically.

As coil 44 warms, end 46 will move and allow lever 47, shaft 48, and lever 50 to turn in the counterclockwise direction.

A first link 52 has an end 53 disposed in an arcuate slot 54 in the top 55 of thermostat lever 50. Link 52 extends to a short choke lever 56 secured to the choke shaft 38 in the usual manner. A second link 58 extends from an intermediate location 59 on thermostat lever 50 to an arcuate slot 60 formed in the bottom 61 of cam lever 34. Accordingly, lever 50 has a long lever arm controlling movement of link 52 and rotation of choke shaft 38. Also, lever 50 forms a short lever arm positioning link 58 to control movement of fast idle cam 28. These differences in lever arms permit link 52 to travel faster than link 58.

The split sequence of operation of the present invention can be best illustrated by referring to FIGS. 1-3, which illustrate the positions of the invention as coil 44 warms. In operation, the unbalanced choke valve 36 will open until end 53 of first link 52 slides leftwardly in and abuts the leftmost end 63 of slot 54. As coil 44 warms, it moves and permits thermostat lever 50 to rotate counterclockwise from the initial (cold) position shown in FIG. 1. As thermostat lever 50 rotates through an angular displacement up to and including an angle A, as shown in FIG. 2, arcuate slot 54 in the thermostat lever 50 is repositioned counterclockwise to allow leftward movement of link 52 and concommitant choke opening. Accordingly, during this initial stage of travel of thermostat lever 50, up to and including angle A, air flow past the choke pushes or biases the end 53 of link 52 to the left end 63 of slot 54. As coil 44 is heated, it permits counterclockwise rotation of thermostat lever 50 and thus permits increased choke opening movement.

Simultaneously, as thermostat lever 50 rotates through angle A, second link 58 moves from the initial position shown in FIG. 1 to the intermediate position shown in FIG. 2. Link 58 is shifted leftwardly and end 62 of link 58 slides in arcuate slot 60 of cam lever 34. Cam 28 is prevented from rotating by engagement with follower 26 when throttle 20 is closed, thereby restraining cam lever 34. However, cam 28 is gravitationally urged counterclockwise by its weight and the weight of link 32 and lever 34. When the throttle is opened, lever 24 and follower 26 are rotated counterclockwise, thereby disengaging follower 26 from cam 28 and allowing cam 28 to move. In turn, link 32 is lowered and lever 34 rotates clockwise.

The counterclockwise rotative movement of cam lever 34 is limited by the coaction of end 62 of second link 58 with the rightmost end 64 of arcuate slot 60. As thermostat lever 50 rotates counterclockwise as the engine warms, second link 58 is shifted leftwardly. End 62 of link 58 can travel in slot 60 away from end 64 when cam lever 34 is held by cam 28 and follower 26. However, when the throttle is opened, cam lever 34 rotates until end 62 of second link 58 again engages the rightmost end 64 of arcuate slot 60. Accordingly, the rotative movement of cam lever 34 is limited in the clockwise direction which further limits the counterclockwise movement of cam 28 and the rotation of throttle 20. It is in this manner that the thermostat coil 44 repositions the fast idle cam to allow the throttle to close in accordance with increasing engine temperature during the extended warm-up period.

It should again be noted that cam follower 24 engages and restrains fast idle cam 28 when the throttle is closed. Since link 32 and cam lever 34 are also re strained, link 58 may slide in a lost-motion manner in slot 60. This occurs until such time as the throttle lever 24 is moved counterclockwise so that cam 28 may rotate counterclockwise to allow follower 26 to engage a lower step 30 on the cam. In this manner, the temperature-varying, counterclockwise position of cam 28 is determined by the relationship between and position of coil 44, thermostat lever 50, link 58 (end 62 abutting rightmost end 64 of slot 60), cam lever 34 and link 32.

As thermostat 44 warms further, the rotation of thermostat lever 50 will exceed angle A, which is associated with the wide-open position of choke valve 36. For example, in FIG. 2 the choke valve wide-open position is clockwise rotation from the fully-closed position shown in FIG. 1. The FIG. 2 position is, in this instance, the maximum amount of choke opening possible. An arcuate slot 54 in the top of lever 50 is provided to allow end 53 of first link 52 to slide therein in a lostmotion manner. Accordingly, as rotation of thermostat lever 50 exceeds angle A, link 52, choke lever 56, choke shaft 38 and choke valve 36 are not repositioned further.

After the choke valve has fully opened but before full warm-up, thermostat lever 50 continues to shift second link 58 leftwardly during the overlapping and extended cam control operation. End 62 of link 58 persists in limiting the clockwise rotative movement of cam lever 34, link 32, and the counter-clockwise rotative movement of fast idle cam 28. As fast idle cam member 28 continues to rotate counterclockwise under its own weight and that of link 32 and lever 34, cam follower 26 engages lower steps 30 of the cam to decrease the throttle opening. (Again, cam 28 can move only when the throttle is opened.) This decreases the air flow as the engine warms to control the idling speed.

It is important to note that this thermostatically controlled repositioning of the cam proceeds even though the choke valve has previously reached its wide-opened position. Repositioning of fast idle cam 28 will continue until thermostat lever 50 passes through an angular displacement B, with B about twice as large as angle A. At this point follower 26 will disengage cam 28 by falling into notch 29, so that the throttle has .come-off" the control of the fast idle cam.

To prevent the choke valve 36 from closing while the engine temperature equals a normal operating temperature, slot 54 of thermostat lever 50 has a second function. As thermostat lever 50 continues to rotate as coil 44 warms, the rightmost end 65 of slot 54 and end 53 of link 52 come into engagement to hold the choke valve wide open. The coaction of end 53 of link 52 with rightmost end 65 of slot 54 will prevent closure of the valve while the engine is warm.

As previously described, the manner of operation of the present invention which accomplishes the positioning of

links

32, 52 and 58 in relation to levers 34, 39 and 50 provides a split, overlapping sequence of actuation between the choke valve 36 and the fast idle cam 28. The portion of the automatic choke mechanism defined by links 52 and 58 in combination with thermostat lever 50 and cam lever 34 causes the choke valve 36 to open in about half the time required for the fast idle cam 28 to come off. This relationship ensures an optimal compromise of desirable rapid choke opening and extended repositioning of the fast idle cam to control engine idling speed until the engine is fully warmed.

What is claimed is:

1. For use in an internal combustion engine, a carburetor comprising an air intake, a throttle rotatably disposed in said air intake for controlling air flow to the engine, a throttle lever secured to said throttle for concomitant rotation through a selected path, a cam disposed in said path for variably limiting the rotation of said throttle lever in a throttle closing direction and thus controlling the idling position of the throttle valve, a choke shaft rotatably disposed in said air inlet anterior said throttle, a choke valve secured to said choke shaft, a choke lever secured to said choke shaft, a cam lever having an arcuate slot and rotatably disposed about said choke shaft, a cam link operatively connecting said cam lever and said cam, and positioning means responsive to temperature and including a housing, a thermostat shaft rotatably disposed in and extending through said housing, a bimetallic coil enclosed within said housing and having one end anchored to the housing and further having the other end positioning said thermostat shaft, a thermostat lever secured at one end to said thermostat shaft outside said housing and having an arcuate slot adjacent the opposite end, a first link extending from said slot in said thermostat lever to said choke lever for limiting the opening of said choke valve, and a second link extending from the middle of said thermostat lever to said slot in said cam lever; whereby as the temperature responsive positioning means warms, said coil permits said thermostat lever, said first link, and said choke lever to allow said choke valve to blow open, whereby as said thermostat lever moves, said second link, said cam lever, said cam link and said cam move under their own weight to allow said throttle lever to close said throttle, and whereby said choke valve is permitted to open before said cam is permitted to come off.