US3800762A

US3800762A - Supplemental pulldown mechanism for carburetor automatic choke

Info

Publication number: US3800762A
Application number: US00212362A
Authority: US
Inventors: Cullough C Mc
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1971-12-27
Filing date: 1971-12-27
Publication date: 1974-04-02
Anticipated expiration: 1991-04-02
Also published as: CA967835A; JPS4877219A; DE2261650A1; JPS5012538B2; GB1407600A

Abstract

The carburetor has a conventional automatic choke construction heating a bimetallic coil by engine exhaust stove heat to slowly open the choke valve during cold weather starts; a supplemental temperature responsive power means operable above a predetermined ambient temperature moves the choke valve open faster, to reduce emissions.

Description

United States Patent McCullough Apr. 2, 1974 SUPPLEMENTAL PULLDOWN 2,969,783 1/1961 Braun 123/119 F MECHANISM O CARBURETOR 2,979,047 4/1961 Rapplean et a1. 123/1 19 F 3,190,623 6/1965 Ball 123/119 F AUTOMATIC CHOKE Charles W. McCullough, Detroit, Mich.

Ford Motor Company, Dearborn, Mich.

Filed: Dec. 27, 1971 Appl. No.: 212,362

Inventor:

Assignee:

References Cited UNITED STATES PATENTS 6/1960 Carlson 123/119 F Primary ExaminerWcnde1l E. Burns [57] ABSTRACT The carburetor has a conventional automatic choke construction heating a bimetallic coi1 by engine exhaust stove heat to slowly open the choke valve during cold weather starts; a supplemental temperature responsive power means operable above a predetermined ambient temperature moves the choke valve open faster, to reduce emissions.

5 Claims, 6 Drawing Figures PATENTEUAPR 2:914 3.800 7632 sum 1 or 3 FlG.l

F-MENTEUAPR 21914 SHtEI 2 0F 3 F'IG.3

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 preengine warmup to insure a richer mixture.

Generally, the choke 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 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 I minimum the output of undesirable smog producing elements.

lt is another object of the invention to provide an automatic choke construction that provides a leaner than conventional air/fuel mixture immediately 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, delayed action servo 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 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 predeterminedamount permitting running operation during cold weather; engine exhaust manifold heat being directed to the spring coil to warm it; and, a supplemental vacuum operated servo operable at ambient temperatures above a predetermined level to positively open the choke valve earlier than would normally be the case, the supplemental servo including a temperature actuated valve permitting the application of manifold vacuum to pull the choke valve open, the vacuum acting through a parallel path including an restriction to delay actuation, and a one-way check valve that allows quick recycling of the servo.

Other objects, features and advantages of the inven tion will become more apparent upon reference to the succeeding detailed description thereof, and to the drawings illustrating a preferred embodiment thereof; wherein FIG. 1 is a cross-sectional elevational view of a per tion of a four-barrel carburetor embodying the invention;

FIG. 2 is a perspective view of a carburetor with the automatic choke of the invention;

FIG. 3 is a side elevational view of a portion of the FIG. 2 showing, with parts broken away and in section;

FIG. 4 is an enlarged cross-sectional view of a detail of FIG. 3; and,

FIGS. 5 and 6 are cross-sectional views taken on planes indicated by and viewed in the direction of the arrows 5-5 and 66 of FIG. 4.

FIG. 1 is obtained by passing a plane through approximately one-half of a known type of four-barrel, downdraft type carburetor. The portion of the carburetor shown 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 the engine 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.

Air flow 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 from 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, the opposite end being rotatably supported in a casting 46. 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 valve 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 opposite or righthand end portion of shaft 44. The other leg portion 58 of the lever is secured to the end 59 of a coiled thermostatic spring element 60 through an arcuate slot, not shown, in an insulating gasket 61. The opposite end portion 61 of the spring is fixedly secured on the end of a nipple 64 that is formed as an integral portion of a choke cap 66 of heat insulating material. Nipple 64 is bored as shown to provide

hot air passages

68 and 70, passage 68 being connected to an exhaust manifold heat stove, for example. Cap 66 is secured to housing 42 by suitable means, such as the screw 72 shown, and defines an air or fluid chamber 74 within the two.

As thus far described, it will be clear that the thermostatic spring element 60 will contract or expand as a function of the changes in ambient temperature conditions of the air entering tube 68, or, if there is no flow, the temperature of the air within chamber 74. Accordingly, changes in ambient temperature will rotate the spring lever 54 to rotate shaft 44 and choke valve 28 in one or the other directions, as the case may be.

The leg 56 of spring lever 54 is pivotally fixed to the rod 76 of a piston 78. The latter is movably mounted in a bore 79 in housing 42. The under surface of piston 78 is acted upon by vacuum in a passage 80 that is connected to the carburetor main induction passages by a port 82 that is located just slightly below throttle valve 36. Piston 78, therefore, is always subject to the vacuum existing in the intake manifold passage portion 18.

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 vaporized. Therefore, the choke valve is shut or nearly shut to increase the pressure drop thereacross and draw in more fuel and less air. Once the engine does start, however, then the choke valve should be opened slightly to lean the mixture to prevent engine flooding as a result of an excess of fuel.

The known choke mechanism described automatically accomplishes the action described. That is, on cold weather starts, the temperature of the air in chamber 74 will be low so that spring element 60 will contract and rotate shaft 44 and choke valve 28 to a closed or nearly closed position, as desired. Upon cranking the engine, vacuum in passage 80 will not be sufficient to move piston 78 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 80 moves piston 78 downwardly and rotates shaft 44 a slight amount so that choke valve 28 is slightly opened so that less fuel is admitted to induction passage 20. Shortly thereafter, the exhaust manifold stove air in line 68 will become progressively warmer and cause choke element 60 to unwind slowly and rotate shaft 44 and choke valve 28 to a more open position. Further details of construction and operation are not given since they are known and believed to be unnecessary for an understanding of the invention.

FIG. 2 shows the carburetor as including a supplemental choke valve pulldown servo device 90 that is connected to the choke rod lever 48. More specifically, and referring to FIGS. 2-6, the servo 90 has a three piece housing consisting of a left hand check valve and a vacuum line adapter portion 92, a main body portion 94, and a cup shaped shell portion 96.

Portion 92 has a press fit within an annular flange 98 projecting from body portion 94, and contains a vacuum passage 100. The latter is connected by a tube 102 to the carburetor bore at a location below the throttle valve to be subject to manifold vacuum at all times.

Passage 100 communicates with an enlarged stepped diameter bore 104 containing a sintered metal anular plug 105. The wall of the housing portion defining bore 104 contains an axially extending keyway like slot 106 (see FIG. 5) communicating around the left end of plug with passage 100. Seating at times against the right end of restrictor 105 is a thin elastomeric check valve 108. It has an outer ring 110 connected by a flexible neck portion 1 12 (FIG. 5) to an inner flexible disc 1 14. The disc 114 has a central hole 116 constituting a flow opening. he total restriction to flow through the sintered metal restrictor 106 is chosen to provide the desired delay in communication of vacuum in line 100 to the opposite side of check valve 108, as will become clearer later. The check valve is held against the recess shoulder of housing portion 92 by a retaining ring 118. The latter is held in place as shown by the staked end 120 of the housing.

Body portion 94 contains an annular flange 122 and a central vacuum passage 124. A Belleville type bimetal disc 126 is floatingly mounted within flange 122, and is biased towards the left by a spring 128. The central portion of disc 126 has an elastomeric valve 130 fixed to it that is adapted to seat against the passage 124 to control flow through it. In assembly, an enlarged flexible integral portion 132 of the valve is pulled through a small hole 131 in disc 126 until the valve is seated, as shown.

The bimetal disc 126 is responsive to ambient temperature changes of the servo to flip over-center from the full line position shown, to the dotted line position 133, in a known manner, at say, temperature levels above 65:t, for example, to open passage 124. Reduction of the ambient temperature below the predetermined level will again flip-flop the disc to close passage 124.

The disc spring 128 is seated against a cup shaped spring retainer 134. The latter is held in place in the ring flange 122 by a ring 136, and has a central aperture 138.

The housing portions 94 and 96 together define a hollow interior. Between them is clamped the edge of an annular flexible diaphragm that divides the interior into an air chamber 142 and a vacuum chamber 144. Holes 145 in housing portion 96 permit a free communication of chamber 142 with the ambient air pressure surrounding the servo.

A pair of retainers 146 fixedly mount a plunger or link 148 on the diaphragm, a spring 150 normally biasing the plunger to the position shown. The plunger has a lost motion connection to choke lever 48 consisting of an elongated slot 152 that receives the bent end 154 of a link 156 pivotally connected to lever 48.

Completing the construction, a pair of bosses 158 are welded to housing portion 96 for the attachment of a mounting bracket 160 that is secured at its opposite end to a portion of the throttle valve body portion of the carburetor, as shown.

In operation, below 65 F ambient, the bimetal disc 126 remains in a valve closed position as shown, and no vacuum is applied from passage 100 into servo chamber 144. Therefore, the servo is inoperative. The choke valve is initially closed by coil 60, and cracked open upon engine startup by the pulldown servo 78. Increases in choke housing temperature, caused by the increases in exhaust manifold heat, cause the bimetal 60 to slowly unwind and permit opening of the choke valve by air flow against it. This is permitted by the sliding movement of the pin 154 in slot 152. The entire choking action will then be controlled solely by the coil 60.

Assume now that the ambient temperature is above 65 F. Initially, the same operation occurs as above described. Check valve 108 will still be seated because of the pressure differential acting on opposite sides. Therefore, bleed of air can only occur through the hole 1 16 past the sintered restrictor 106. However, now vacuum can be applied to chamber 144 because the thermostatically responsive disc 126 has now flipped over center to position 133. This unseats valve 130 and opens passage 124. Manifold vacuum in passage 100 now is applied slowly, as determined by the combined restrictions of restrictor 106 and hole 116, to begin drawing diaphragm 140 and plunger 148 to the left. This will continue without any effect on the choke valve until the pin 154 is engaged by the end of slot 152. Continued leftward movement of the plunger until it bottoms, at dotted line position 162, against retainer 134, will then positively open the choke valve against the force of the coil 60.

The maximum delay is scheduled in this case to be approximately forty seconds. It will vary, of course, from the maximum to a minimum as a function of the initial position of the pin 154 in the slot 152, upon engine startup, which will depend upon the initial ambient temperature conditions affecting the force of coil 60.

Assume now that the engine is shut off, or quickly accelerated, so that the manifold vacuum decays suddenly. It is desirable at this time that the servo 90 recycle itself so as to be in a position to provide the desired choking action when restarted or the acceleration phase terminated. The check valve 108 provides this action since the sudden change in pressure conditions now places the higher pressure level in passage 100, and a lower vacuum in chamber 144. This bends or deforms the check valve outwardly to the right off its seat to permit free communication between passage 100 and chamber 144 by flow around the sintered restrictor 106 through the slot 105. This immediately permits spring 150 to stroke the diaphragm and plunger 148 to the right to the positions shown.

In summary, therefore, below an ambient temperature level of 65: F, the choke hot air system provides the only control for choking functions. The bimetal coil 60 will unwind, therefore, only as a function of the increased heating by the hot air from passage 68.

Above 65 F, however, the conventional exhaust manifold stove heat system constitutes the primary choke control, while the vacuum operated servo device 90 acts as the suplemental force to pull open the choke valve faster than were it being controlled by the primary control alone. This leans the fuel/air mixture earlier than with conventional choke arrangements, and lowers undesirable emission outputs.

With the above described two phase choke construction, therefore, it will be seen that it is possible to provide a reliable and accurate short duration choking effect thereby minimizing vehicle exhaust emission without jeopardizing the cold weather choking function.

I 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 be- 6 tween 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 air flow towards the throttle valve,

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

initial and supplemental power means each having force transmitting means connected in an individual power relationship to the choke valve and movable by engine manifold vacuum connected by first and second conduits thereto to open the choke valve sequentially by varying degrees, the supplemental power means including a flow restriction in the second conduit connecting manifold vacuum thereto to at all times delay application of vacuum to the supplemental power means until after the initial power means has operated, lost motion means connecting the supplemental power means force transmitting means to the choke valve and initial power means force transmitting means for a limited lost motion movement whereby initially the initial power means upon application of vacuum thereto cracks open the choke valve a predetermined amount and subsequently in sequence the supplemental power means upon application of vacuum thereto after the delay caused by the flow restriction and the taking up of slack in the lost motion connection sufficient to retard operation of the supplemental power means moves the choke valve open a greater amount than moved by the initial power means,

and on-off temperature responsive valve means in the second conduit in series with the flow restriction and movable to block flow of vacuum to the supplemental power means below a predetermined ambient temperature.

2. An automatic choke system as in claim 1, including means for bypassing the flow restriction means at times to provide a fast change in pressure levels on opposite sides of the flow restricting means in response to increases in pressure level of the manifold vacuum over that in the vacuum chamber, the last mentioned means comprising a flexible check valve having an orifice constituting the flow restricting means, a higher pressure level on the supplemental power means side of the check valve than the manifold vacuum closing the check valve permitting flow only through the orifice, a lower pressure on the supplemental power means side of the check valve than manifold pressure opening the check valve to provide free connection between the conduit means and the supplemental power means.

3. An automatic choke construction as in claim 2, the temperature responsive valve means comprising a Bellville type disc having a valve member along its axis, the overcenter action of the disc in response to temperature changes from a predetermined level seating and unseating the valve means.

4. An automatic choke system as in claim 1, wherein the flow restriction comprises a sintered metal flow restrictor in the second conduit delaying communication of pressure changes between the manifold vacuum in the second conduit and the supplemental power means.

5. A two phase automatic choke system for use with an internal combustion engine 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 rotatably mounted across the passage adjacent the lower end 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 rotatably mounted across the passage adjacent the upper end for variable opening and closing movements to control air flow towards the throttle valve,

a thermostatically responsive spring coil operably connected to the choke valve and normally urging the choke valve towards a closed position with a force increasing with decreases in the temperature of the coil from a predetermined level,

initial and supplemental power means each having force transmitting means connected in an individual power relationship to the choke valve and movable by engine manifold vacuum connected by first and second conduits thereto to open the choke valve sequentially by varying degrees, the supplemental power means including a flow restriction in the second conduit connecting manifold vacuum thereto to delay application of vacuum to the supplemental power means until after the initial power means has operated, lost motion means connecting the supplemental power means force transmitting means to the choke valve and initial power means force transmitting means for a limited lost motion movement whereby initially the initial power means upon application of vacuum thereto cracks open the choke valve a predetermined amount and subsequently in sequence the supplemental power means upon application of vacuum thereto after the delay caused by the flow restriction and the taking up of slack in the lost motion connection sufficient to retard operation of the supplemental power means moves the choke valve open a greater amount than moved by the initial power means,

the initial power means including a vacuum operated movable piston means, and a heat source transferring engine heat to the coil and comprising a hot air containing duct operably connected from the engine exhaust system to the coil for warming the coil to reduce its choke valve closing force,

the supplemental power means comprising a vacuum servo having a vacuum chamber and an ambient pressure chamber defined by a movable diaphragm, a plunger secured to the diaphragm, the lost motion means connecting the plunger to the choke valve, the second conduit connecting manifold vacuum to the servo vacuum chamber, the flow restricting means in the second conduit providing a pressure differential thereacross to delay the change in pressure in the vacuum chamber upon change in pressure in the second conduit, and means for bypassing the flow restriction means to provide a fast change in pressure levels on opposite sides of the flow restricting means in response to increases in pressure level of the manifold vacuum over that in the vacuum chamber, the last mentioned means comprising a flexible check valve having an orifice constituting the flow restricting means, a higher pressure level in the vacuum chamber than the manifold vacuum closing the check valve permitting flow only through the orifice, a lower pressure in the vacuum chamber than manifold pressure opening the check valve to provide free connection between the conduit means and the vacuum chamber, a temperature responsive valve means in the second conduit comprising a Bellville type disc having a valve member along its axis, the overcenter action of the disc in response to temperature changes from a predetermined level seating and unseating the valve means.

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 air flow towards the throttle valve, bimetallic thermostatic spring means operably connected to the choke valve urging the choke valve towards a closed position with a force increasing as a function of decreases in the temperature of the spring means from a predetermined level, initial and supplemental power means each having force transmitting means connected in an individual power relationship to the choke valve and movable by engine manifold vacuum connected by first and second conduits thereto to open the choke valve sequentially by varying degrees, the supplemental power means including a flow restriction in the second conduit connecting manifold vacuum thereto to at all times delay application of vacuum to the supplemental power means until after the initial power means has operated, lost motion means connecting the supplemental power means force transmitting means to the choke valve and initial power means force transmitting means for a limited lost motion movement whereby initially the initial power means upon application of vacuum thereto cracks open the choke valve a predetermined amount and subsequently in sequence the supplemental power means upon application of vacuum thereto after the delay caused by the flow restriction and the taking up of slack in the lost motion connection sufficient to retard operation of the supplemental power means moves the choke valve open a greater amount than moved by the initial power means, and on-off temperature responsive valve means in the second conduit in series with the flow restriction and movable to block flow of vacuum to the supplemental power means below a predetermined ambient temperature.

5. A two phase automatic choke system for use with an internal combustion engine 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 rotatably mounted across the passage adjacent the lower end 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 rotatably mounted across the passage adjacent the upper end for variable opening and closing movements to control air flow towards the throttle valve, a thermostatically responsive spring coil operably connected to the choke valve and normally urging the choke valve towards a closed position with a force increasing with decreases in the temperature of the coil from a predetermined level, initial and supplemental power means each having force transmitting means connected in an individual power relationship to the choke valve and movable by engine manifold vacuum connected by first and second conduits thereto to open the choke valve sequentially by varying degrees, the supplemental power means including a flow restriction in the second conduit connecting manifold vacuum thereto to delay application of vacuum to the supplemental power means until after the initial power means has operated, lost motion means connecting the supplemental power means force transmitting means to the choke valve and initial power means force transmitting means for a limited lost motion movement whereby initially the initial power means upon application of vacuum thereto cracks open the choke valve a predetermined amount and subsequently in sequence the supplemental power means upon application of vacuum thereto after the delay caused by the flow restriction and the taking up of slack in the lost motion connection sufficient to retard operation of the supplemental power means moves the choke valve open a greater amount than moved by the initial power means, the initial power means including a vacuum operated movable piston means, and a heat source transferring engine heat to the coil and comprising a hot air containing duct operably connected from the engine exhaust system to the coil for warming the coil to reduce its choke valve closing force, the supplemental power means comprising a vacuum servo having a vacuum chamber and an ambient pressure chamber defined by a movable diaphragm, a plunger secured to the diaphragm, the lost motion means connecting the plunger to the choke valve, the second conduit connecting manifold vacuum to the servo vacuum chamber, the flow restricting means in the second conduit providing a pressure differential thereacross to delay the change in pressure in the vacuum chamber upon change in pressure in the second conduit, and means for bypassing the flow restriction means to provide a fast change in pressure levels on opposite Sides of the flow restricting means in response to increases in pressure level of the manifold vacuum over that in the vacuum chamber, the last mentioned means comprising a flexible check valve having an orifice constituting the flow restricting means, a higher pressure level in the vacuum chamber than the manifold vacuum closing the check valve permitting flow only through the orifice, a lower pressure in the vacuum chamber than manifold pressure opening the check valve to provide free connection between the conduit means and the vacuum chamber, a temperature responsive valve means in the second conduit comprising a Bellville type disc having a valve member along its axis, the overcenter action of the disc in response to temperature changes from a predetermined level seating and unseating the valve means.