US3906912A

US3906912A - Two-phase choke system with primary and secondary heating

Info

Publication number: US3906912A
Application number: US416556A
Authority: US
Inventors: Delma J Jackson; John D Medrick
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1973-11-16
Filing date: 1973-11-16
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23
Also published as: JPS5079635A; CA1027436A; GB1449990A; AU7401574A; DE2452341A1

Abstract

The choke has a housing divided into two chambers, one of which contains a thermostatically responsive coil spring that is attached to the choke valve and is warmed by engine exhaust manifold heated air as the primary heat source, the second chamber at times containing exhaust gases constituting secondary heating to warm the coil spring by radiation, flow of exhaust gases to the second chamber being controlled by a splitter type fluidic device using airflow past a thermostatically controlled air inlet as a switching control to divert the gases to the second chamber, the final rotative degrees of movement of the coil spring as it warms up closing off the air supply to permit the fluidic device to revert to its original flow condition shutting off flow of gas to the second chamber.

Description

United States Patent Jackson et al.

[ Sept. 23, 1975 TWO-PHASE CHOKE SYSTEM WITH PRIMARY AND SECONDARY HEATING lnventors: Delma J. Jackson, Dearborn; John D. Medrick, Plymouth, both of Mich.

Ford Motor Company, Dearborn, Mich.

Filed: Nov. 16, 1973 Appl. No.: 416,556

Assignee:

U.S. Cl. 123/119 F; 123/117 A; 261/39 R Int. Cl. F02]! 33/00 Field of Search 123/119 F, 117 A;

References Cited UNITED STATES PATENTS 2/1964 Boller 123/119 F 2/1974 Hunt 123/119 F 4/1974 McCullough.... 123/119 F 4/1974 Winkley 123/119 F Primary Examiner-Charles .1. Myhre Assistant Examiner-Daniel J. OConnor Attorney, Agent, or FirmRobert E. McCollum; Keith L. Zerschling [57] ABSTRACT a splitter type fluidic device using airflow past a thermostatically controlled air inlet as a switching control to divert the gases to the second chamber, the final rotative degrees of movement of the coil spring as it warms up closing off the air supply to permit the fluidic device to revert to its original flow condition shutting off flow of gas to the second chamber.

13 Claims, 5 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of3 3,906,912

US Patent Sept. 23,1975 Sheet 2 of3 3,906,912

Sept. 23,1975 Sheet 3 of 3 3,906,912

US Patent TWO-PIIASE CHOKE SYSTEM WITH PRIMARY AND SECONDARY HEATING This invention relates, in general, to a carburetor for a motor vehicle engine. More particularly, it relates to an automatic choke to provide cold weather starts of an engine, while at the same time minimizing the output of undesirable emissions.

As ambient temperature drops, friction within the engine and the viscosity of the lubricants increase significantly. Therefore, at low temperatures, the speeds at which an engine normally would idle must be increased to prevent stalling. Accordingly, a choke mechanism is generally provided to lessen the air intake during cold starting and pro-engine warmup to insure a richer mixture.

Generally, the chole apparatus includes a coiled thermostatic spring that operatively rotates the choke valve towards a closed or nearly shut position with decreasing temperatures, and progressively opens it as the temperature returns towards a chosen level. A manifold suction responsive device generally cracks open the choke a predetermined amount when the engine starts. The choke action provides a rich mixture so that sufficient fuel can be vaporized to permit smooth starting and running of the engine.

The above construction, while generally satisfactory, is a compromise between good cold weather running conditions on the one hand and low emission outputs on the other hand. The richer than normal mixture existing during the choking operation may result in higher emission outputs such as, for example, CO.

It is an object of this invention to provide an automatic choke construction that will provide good cold weather starting characteristics and yet reduce to a minimum the output of undesirable smog producing elements.

It is another object of the invention to provide an automatic choke construction that provides a leaner than normal air/fuel mixture sooner than is conventional after the start of a warm engine by pulling open the choke valve faster than would be by conventional choke systems.

It is also an object of the invention to provide an automatic choke construction including a temperature responsive, secondary heating apparatus operable above a predetermined ambient temperature to shorten the length of time required for the normal operation of an automatic choke.

Another object of the invention is to provide an automatic choke construction including a thermostatically controlled bimetal coil spring normally urging the choke valve closed with decreasing ambient temperature changes and opposed by a manifold suction operated motor device that initially cracks open the choke 'valve to a predetermined settingpermitting running operation during cold weather; engine exhaust manifold heat being directed at all times to the spring coil to warm it; and, a supplemental heating system connectable to the choke at ambient temperatures above a predetermined level to warm the bimetal spring faster than would normally be the case, the supplemental system including an air controlled valve that diverts a protion of the hot engine exhaust gases from their normal path directly to the choke housing adjacent the bimetal spring, the final stages of unwinding of the springopening of the chokevalve blocking the 1 revert the exhaust gas flow to its normal path and terminate the supplemental application of heat to the choke spring.

Other objects, features and advantages of the invention will become more apparent upon reference to the succeeding detailed description thereof, and to the drawings illustrating the preferred embodiment thereof; wherein,

FIG. 1 is a perspective view of a two-barrel carburetor and associated controls embodying the invention;

FIG. 2 is an enlargedplan view of the carburetor shown in FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken on a plane indicated by and viewed in the direction of the arrows 33 of FIG. 2;

FIG. 4 is an enlarged side elevational view of a portion of the carburetor of FIG. 2 taken on a plane indicated by and viewed in the direction of the arrows 4--4 of FIG. 2; and,

FIG. 5 is a schematically illustrated, exploded view of the details of the invention shown in FIG. 1.

FIG. 1 shows a two-barrel, downdraft type carburetor, which, except for the choke mechanism to be described, is conventional. As more clearly seen in FIG. 3, the carburetor includes an upper air horn section 12, an intermediate main body portion 14, and a throttle valve flange section 16. The three carburetor sections are secured together by suitable means, not shown, over an intake manifold indicated partially at 18 leading to theengine combustion chambers.

Main body portion 14 contains the usual air-fuel mixture induction passage 20 having fresh air intakes at the air horn ends, and connected to manifold 18 at the opposite ends. The passages are each formed with a main venturi section 22 containing a booster venturi 24 suitably mounted for cooperation therewith, by means not shown.

Airflow through passages 20 is controlled in part by a choke valve 28 unbalance mounted on a shaft 30 rotatably mounted on side portions of the carburetor air horn, as shown. Flow of fuel and air through each passage 20 is controlled by a conventional throttle valve 36 fixed to a shaft 38 rotatably mounted in flange portion 16. The throttle valves are rotated in a known manner by depression of the vehicle accelerator pedal, and move form an idle speed position essentially blocking flow through passage 20 to a wide open position essentially at right angles to the position shown.

The rotative position of choke valve 28 is controlled by a semiautomatically operating choke mechanism 40. The latter includes a hollow housing portion 42 that is formed as an extension of the carburetor throttle flange. The housing is apertured for supporting rotatably one end of a choke lever operating shaft 44. A bracket or lever portion 48 is fixed on the left end portion of shaft 44 for mounting the end of a rod 52 that is pivoted to choke shaft 30. It will be clear that rotation of shaft 44 in either direction will correspondingly rotate choke valve 28 to open or close the carburetor air intake, as the case may be.

An essentially L-shaped thermostatic spring lever 54 has one leg 56 fixedly secured to the right-hand end portion of shaft 44, and pivotally fixed to the rod 58 of a piston 60. The latter is movably mounted in a bore in housing 42 as shown. The under surface of piston 60 is acted upon by vacuum in a passage 64 that is connected to the carburetor main induction passages 20 by a port 66 located just slightly below throttle valve 36. Piston 60, therefore, is always subject to the vacuum existing in the intake manifold passage portion 18.

The other leg portion'68 of lever 54 is secured to the outer end of a coiled thermostatic spring element 72. The inner end portion-76 of the spring is fixedly sc- 'cured on the end of a nipple'78 that is formed an an integral portion of a partition 80. Partition 80 divides the choke housing into a first chamber 82 containing coil spring 72, and a second chamber 84. The first chamber 82 has an inlet 85 for air that is heated by an engine exhaust manifold stove (not shown) in a known manner. This provides the primary source of heat for coil spring 72 in aconventional manner.

Second chamber 84 is defined by a spacer 86 and and end cap 88 of heat insulating material. The end cap has an exhaust gas inlet 90 and an outlet 92. Outlet 92 re- .turns the exhaust hases to the exhaust manifolding. A

retaining flange 94 sealingly secures the end cap to housing by screws through bosses 96.

The flow of exhaust gas to chamber 84 is controlled by a flow splitter type fluidic device 100, of a conventional construction. It has an input 102, a main outlet flow path 104, an auxiliary outlet flow path 106, and a switching signal air passage 108. The input 102 would be connected to a portion of the exhaust manifolding containing hot exhaust gases. The main flow path 104 likewise would return the gases to the exhaust system. The auxiliary path 106 is connected to choke housing chamber 84 so as to warm the coil spring mounting ahaft 78 at times to transfer heat to the coil 72.

The air in switching passage 108 is supplied through a tube 110 connected to a thermostatically and mechanically controlled air valve 112 that is located on the carburetor body. More specifically, a groove 114 is cast in the carburetor body surrounding an air inlet opening 115 to tube 110. A compressible O-ring 116 seats in the groove and supports a bimetallic thermo statically responsive disc 118. Below temperature levels of 65iF, for example, the disc assumes a concave attitude, as viewed from the top, to compress the O- ring. This prevents the flow of air through a hole 120 flow to protect the bimetal coil spring 72 from beingoverheated and thus overstressed. Hinged at on a pedestal 126 is an L-shaped lever 128. At one end it has a button type rubber valve 130 located over the hole 122. The other end of lever 128 has a tab 132 adapted to be engaged by the end of a lever 134. The latter is fixed to the choke shaft 30 at such an attitude that its coounteclockwise movement causes rubber valve 130 to close hole 122 only as the cold enrichment system is shut off the by the last few degrees of rotation of the travel of bimetal spring 72. That is, when the heat to the bimetal 72 is sufficient to relax the coil spring force so that the choke valve can open wide, then this opening of the choke valve will close ,off hole 122. If the temperature of the bimetal drops, the hole will be opened again.

' As is known, a cold weather start of a motor vehicle requires a richer mixture-than a warmed engine start because considerably less fuel is vaproized. Therefore, is operation, .the choke valve initially is shut or nearly shut to increase the pressure drop thereacross and draw in more .fuel ,and less air. Once the engine does start, then the choke valve is opened slightly to lean the mixture to prevent engine flooding as a result of an excess of fuel, and then progressively opens as the coil spring is warmed.

v The choke mechanism described automatically accomplishes the action described. That is, on cold 'wcather starts, the air temperature in both choke chambers ,82 and 84 will be low so that the spring coil 72 will contract and rotate shaft 44 and choke valve 28 to a closed valve 28 to a closed or nearly closed position, as desired. Upon cranking the engine, vacuum in passage 64 will not be sufficient to move piston 60 to open the choke valve. Accordingly, the engine will be started with a rich mixture. As soon as the engine is running, high vacuum in passage 64 moves piston 60 downwardly and rotates shaft 44 an amount sufficient to open choke valve 28 slightly. As a result, less fuel will be drawn into induction passage 20. Shortly thereafter, the now warming exhaust manifold stove air in line 83 will begin warming choke coil 72, which will then begin to unwind slowly and rotate shaft 44 and permit rotation of choke valve 28 to a more open position. 7

Below 65F ambient, the bimetal disc 118 will remain in a concave valve closed position, and no air will pass to tube 110. Therefore, no exhaust gaswill be diverted to choke chamber 84. Increases in choke housing temperature, caused by the increases in exhaust manifold heat in line 83, therefore, cause the bimetal 72 to slowly unwind and permit opening of the choke valve by airflow against it. During this stage, therefore, the entire choking action will then be controlled solely by the heat in line 83.

Assume now that the ambient temperature is above 65F. Initially, upon engine start-up, vacuum pulldown operation occurs as above described. However, now air can be applied to switching passage 110 because the thermostatically responsive disc 118 has now flipped over center to a convex position. This allows air to pass over the O-ring tube 110. i

The existence of air pressure in line 108 now switches, in a known manner, the flow of exhaust gases from the main path 104 to the auxiliary path 106. The

heat of theexhaust gases is then applied to chamber 84 and through the bimetal post 78 to coil 72. Thus the primary heat source in in line 83 warming coil 72 is supplemented by the heat transferred from chamber 84. The coil spring will therefore unwind at a much faster rate than with just the heat in line 83 above applied. Y

Finally, the last few degrees of roatation of coil spring 72 will cause lever 128 to engage lever 134 and move the rubber valve 130 ohm the hole 122. This will block off the air supply to the fluidic device and cause a reversion of it to its initial state. That is, the flow will be switched so that the exhaust gases flow only along path 104 to the exhaust system, and supplemental heat to chamber 84 is cut off. If the temperature of coil spring 72 is not able to be maintained by the flow of hot air through line 83. then the rotation of coil spring 72 in the reverse or cold direction will again effect opening of hole 122 and supply of hot gases to chamber 84. The system thus will hunt until the coil spring 72 is warm enough to maintain the choke or cold enrichment system in the off position.

While the invention has been shown and described in its preferred embodiment, it will be clear to those skilled in the arts to which it pertains, that many 1 changes and modificatons may be made thereto without departing from the scope of the invention.

We claim:

1. A two phase automatic choke system for use with a carburetor having an air/fuel induction passage open at one end and adapted to be connected to an engine intake manifold at the other end for subjecting the passage to varying manifold vacuum, the passage having a throttle valve mounted for a variable movement between positions opening and closing the passage to control air/fuel flow through it,

the choke system including an unbalance mounted, air movable, choke valve mounted anterior of the throttle valve for variable movement across the passage to control airflow towards the throttle valve,

thermostatic spring means operably connected to the choke valve urging the choke valve towards a closed position with a force that increases with decreases in the temperature of the thermostatic means from a predetermined level,

a first heat source of engine heated air transferring engine heat to the thermostatic means to warm it and reduce its choke valve closing force comprising a hot air duct operably connected to flow air past the engine exhaust system to the thermostatic means,

and a second heat source intermittently operable for at times transferring additional engine heat to the thermostatic means to and concurrent with the heat transferred to it by the first source for further reducing the choke closing force of the thermostatic means, comprising a duct conducting hot engine exhaust gases to an area contiguous to the thermostatic means.

2. A choke system as in claim 1, including other temperature responisve means for controlling the application of heat from the second source to the thermostatic means.

3. A choke system as in claim 1, including control means responsive to a predetermined opening of the choke valve to discontinue the tranfer of heat form the second source.

4. A choke system as in claim 1, the duct being the auxiliary path of a fluidic flow splitter device having a main path through which the exhaust gases normally flow, and diverter means to switch the flow from the main path to the auxiliary path.

5. A choke system as in claim 4, the diverter means comprising an air passage, and valve means to control the admission of air to the passage.

6. A choke system as in claim 5, including Control means responsive to a predetermined opening of the choke valve for closing the air passage and permitting the fluidic device to switch flowback to the main path.

7. A choke system as in claim 6, the valve means comprising temperature responsive means movable above a predetermined temperature from a position How of air through the passage to a position permitting the flow. I

8. A choke system as in claim 7, wherein the temperature responsive means is a bimetallic overcenter type disc valve.

9. A two phase automatic choke system for use with a carburetor having an air/fuel induction passage open at one end and adapted to be connected to an engine intake manifold at the other end for subjecting the passage to varying manifold vacuum, the passage having a throttle valve mounted for a variable movement between positions opening and closing the passage to control air/fuel flow through it,

the choke system including an unbalance mounted, air movable, choke valve: mounted anterior of the throttle valve for variable movement across the passage to control airflow towards the throttle valve,

a hollow housing having first and second chambers, the first chamber enclosing the spring means and having a hot air inlet and outlet situated to flow the air past the spring means,

means connecting the outlet to the induction passage below the throttle valve for inducing flow through the first chamber to warm the spring means to decrease the choke valve closing force,

the second chamber having an inlet and outlet, a duct containing engine exhaust gases, diverter valve means in the duct selectively shiftable to divert flow of exhaust gases to the second chamber from a normal flow path so as to further warm the spring means, temperature responsive means operable above a predetermined temperature to operate the valve means to divert flow of gases to the second chamber,

and control means operable in response to movement of the choke valve open a predetermined amount to render inoperable the temperature responsive means and return the flow of the exhaust gases to the normal fiow path so as to decrease the additional heat to the spring means.

10. A choke system as in claim 9, the diverter valve means comprising a fluidic splitter valve having a normal flow path connected to the duct and an alternate flow path connected to the second chamber, an air pas sage connected to the diverter valve to trigger switching of flow from the normal to the alternate paths, the temperature responsive means permitting or blocking flow of air through the air passage as a function of change in temperature from a predetermined level.

11. A choke system as in claim 10, the temperature responsive means comprising a bimetal overcenter type disc, a second housing having a second air inlet and a second air outlet, means connecting the second outlet to the passage past the disc, the disc in alternate positions permitting and blocking respectively communication between the second air inlet and second air outlet.

12. A choke system as in claim 11, the control means including additional valve means to block the second air inlet in resposne to opening of the choke valve a predetermined amount.

13. A choke system as in chaim 12, including means operably connecting the thermostatic means and the additional valve means, the thermostatic means comprising a coil spring with an end having an accurate movement, the final movements of the coil in response to the heat transferred thereto and the air directed against the choke valve applying a force to the additional valve means to block the second air inlet.

Claims

1. A two phase automatic choke system for use with a carburetor having an air/fuel induction passage open at one end and adapted to be connected to an engine intake manifold at the other end for subjecting the passage to varying manifold vacuum, the passage having a throttle valve mounted for a variable movement between positions opening and closing the passage to control air/fuel flow through it, the choke system including an unbalance mounted, air movable, choke valve mounted anterior of the throttle valve for variable movement across the passage to control airflow towards the throttle valve, thermostatic spring means operably connected to the choke valve urging the choke valve towards a closed position with a force that increases with decreases in the temperature of the thermostatic means from a predetermined level, a first heat source of engine heated air transferring engine heat to the thermostatic means to warm it and reduce its choke valve closing force comprising a hot air duct operably connected to flow air past the engine exhaust system to the thermostatic means, and a second heat source intermittently operable for at times transferring additional engine heat to the thermostatic means to and concurrent with the heat transferred to it by the first source for further reducing the choke closing force of the thermostatic means, comprising a duct conducting hot engine exhaust gases to an area contiguous to the thermostatic means.

7. A choke system as in claim 6, the valve means comprising temperature responsive means movable above a predetermined temperature from a position flow of air through the passage to a position permitting the flow.

9. A two phase automatic choke system for use with a carburetor having an air/fuel induction passage open at one end and adapted to be connected to an engine intake manifold at the other end for subjecting the passage to varying manifold vacuum, the passage having a throttle valve mounted for a variable movement between positions opening and closing the passage to control air/fuel flow through it, the choke system including an unbalance mounted, air movable, choke valve mounted anterior of the throttle valve for variable movement across the passage to control airflow towards the throttle valve, thermostatic spring means operably connected to the choke valve urging the choke valve towards a closed position with a force that increases with decreases in the temperature of the thermostatic means from a predetermined level, a hollow housing having first and second chambers, the first chamber enclosing the spring means and having a hot air inlet and outlet situated to flow the air past the spring means, means connecting the outlet to the induction passage below the throttle valve for inducing flow through the first chamber to warm the spring means to decrease the choke valve closing force, the second chamber having an inlet and outlet, a duct containing engine exhaust gases, diverter valve means in the duct selectively shiftable to divert flow of exhaust gases to the second chamber from a normal flow path so as to further warm the spring means, temperature responsive means operable above a predetermined temperature to operate the valve means to divert flow of gases to the second chamber, and control means operable in response to movement of the choke valve open a predetermined amount to render inoperable the temperature responsive means and return the flow of the exhaust gases to the normal flow path so as to decrease the additional heat to the Spring means.

10. A choke system as in claim 9, the diverter valve means comprising a fluidic splitter valve having a normal flow path connected to the duct and an alternate flow path connected to the second chamber, an air passage connected to the diverter valve to trigger switching of flow from the normal to the alternate paths, the temperature responsive means permitting or blocking flow of air through the air passage as a function of change in temperature from a predetermined level.