US3606983A - Carburetor having an automatic choke - Google Patents

Abstract

A CARBURETOR, HAVING A CHOKE VALVE WITH THERMOSTATIC MEANS ADAPTED TO URGE THE COKE VALVE IN THE CLOSING DIRECTION WHEN COLD, IS PROVIDED WITH PRESSURE RESPONSIVE MEANS WHICH COMMUNICATES WITH A SOURCE OF ENGINE VACUUM FOR MOVING THE CHOKE VALVE IN A DIRECTION OPPOSITE TO THAT OF THE THERMOSTATIC MEANS UPON ENGINE STARTING, THE DEGREE OF EFFECTIVE COMMUNICATION BETWEEN THE PRESSURE RESPONSIVE MEANS THE SOURCE OF ENGINE VACUUM IS CONTROLLED IN ACCORDANCE WITH THE POSITION OF THE CARBURETOR THROTTLE VALVE IS ORDER THAT THE PRESSURE RESPONSIVE MEANS WILL BE EFFECTIVE FOR MOVING THE CHOKE VALVE TO A FIRST PARTLY OPENED POSITION WHEN THE THROTTLE VALVE IS IN THE NOMINALLY CLOSED POSITION AND TO A VARIABLE SECOND MORE FULLY OPENED POSITION WHEN THE THROTTLE VALVE IS MOVED TO A PART THROTTLE POSITION.

Description

Sept. 21, 1971 R. D. MITCHELL CARBURETOR HAVING AN AUTOMATIC CHOKE Filed April 21, 1969 52 ROBE/QTQM/Tf/ffll I N VENTOR.

United States Patent O 3,606,983 CARBURETOR HAVING AN AUTOMATIC CHOKE Robert D. Mitchell, Madison Heights, Mich., assignor to Holley Carburetor Company, Warren, Mich. Filed Apr. 21, 1969, Ser. No. 817,636 Int. Cl. F02m 1/08 US. Cl. 261-39 12 Claims ABSTRACT OF THE DISCLOSURE A carburetor, having a choke valve with thermostatic means adapted to urge the choke valve in the closing direction when cold, is provided with pressure responsive means which communicates with a source of engine vacuum for moving the choke valve in a direction opposite to that of the thermostatic means upon engine starting; the degree of effective communication between the pressure responsive means and the source of engine vacuum is controlled in accordance With the position of the carburetor throttle valve in order that the pressure responsive means will be effective for moving the choke valve to a first partly opened position when the throttle valve is in its nominally closed position and to a variable second more fully opened position when the throttle valve is moved to a part throttle position.

BACKGROUND OF .THE INVENTION Heretofore, automatic choke mechanisms have employed either a diaphragm assembly or a pressure responsive piston in communication with a source of engine or intake manifold vacuum for moving the choke valve, against the resisting force of a thermostat tending to close the choke valve, to a partially open position, often referred to as the qualifying position, after a cold or relatively cold engine has been started. A stepped fast idle cam positioned by choke valve position then controlled idle throttle position.

It has also become accepted practice, in the prior art, to make such pressure responsive diaphragms or pistons of the stopped type; that is with either the stopped diaphragm or piston the initial qualifying position of the choke valve is determined by a positive mechanical stop which precludes any further movement of such diaphragm or piston in the choke opening direction.

However, one disadvantage of the prior art arrangements, including the stopped type of diaphragm or piston employed by the prior art, is that there is no control or modulation of the choke position when the engine operating conditions are changed from cold fast idle to cold engine drive-away. Another disadvantage is that prior art choke systems result in a single fixed qualifying choke valve position for the higher air flow steps on the fast idle cam.

That is, it is generally well known that a cold engine requires a combustible mixture which is of a richer fuelair ratio during cold idle engine operation in order to sustain engine operation and the initial choke opening is selected in order to achieve such a richer mixture. However, upon undergoing cold drive-away conditions, at which higher engine speeds are also experienced, that initial opening of the choke valve usually results in an overly rich fuel-air ratio. This in turn results in the emission of unburned hydrocarbons, a reduction in overall fuel economy and often rough or sporadic engine operation.

The invention as herein disclosed and described is directly concerned with the solution of the above as well as other problems.

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SUMMARY OF THE INVENTION According to the invention, a carburetor for an inter- .nal combustion engine comprises a choke valve, a throtpressure responsive means being effective to move said choke valve to a first partly open position when said engine starts and the throttle valve is in its cold or fast idle (closed) position, said pressure responsive means also being effective to move said choke valve to a variable second partly open position more nearly fully open'ed than said first partly open position when said throttle valve is moved from its above-defined idle or closed position toward a part-throttle position.

Accordingly, a general object of the invention is to provide in a carburetor having a choke valve, means for positioning the choke valve in a first partly opened position when the throttle valve is closed and for also positioning the choke valve in a variable second partly opened position more fully opened than said first partly opened position when the throttle valve is moved away from its said closed position to any higher air flow position.

Other more specific objects and advantages of the invention will become apparent when reference is made to the following detailed description and accompanying drawings.

DESCRIPTION OF THE DRAWINGS In the drawings, wherein certain details may be omitted from one or more views for purposes of clarity:

BIG. 1 is a side elevational view of a carburetor, with portions thereof broken away and in cross-section, constructed in accordance with the teachings of the invention.

FIG. 2 is an enlarged fragmentary view of a portion of the carburetor of FIG. 1 sectioned axially through a cooperating pressure responsive choke actuating means constructed in accordance with the teachings of the invention;

FIG. 3 is a fragmentary cross-sectional view, similar to FIG. 2, but of a second embodiment of the invention; and

FIG. 4 is an enlarged fragmentary portion of FIG. 1 illustrating in greater detail certain of the elements shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in greater detail to the drawings, FIG. 1 illustrates a carburetor 10, constructed in accordance with the invention, as comprising a carburetor body 12 formed to provide an induction passage 14 having the usual venturi restriction 16 and a throttle valve 18, Within the induction passage downstream of the venturi 16, pivotally mounted on manually positionable throttle shaft 20. The entire carburetor assembly is suitably secured atop an engine intake manifold 22.

The throttle valve is opened, against the force of a spring 24 urging it closed, in the usual manner as by means of suitable linkage 26 connected between the throttle lever 28 and the operators foot pedal (not shown). As is customary, closure of the throttle 18 may be limited by an adjustable stop screw 30 adapted to be ro tated with the throttle valve and engageable with one of a plurality of cam-like steps (not shown) formed on a fast idle cam (fragmentarily illustrated at 32) which is positioned generally by the choke mechanism 34 as through a lost motion linkage member 36.

The choke mechanism 34 comprises a choke valve 38 mounted on a shaft 40 for pivotal rotation within the induction passage means 14 upstream of the venturi 16. As is often the case, the choke valve 38 may be unbalanced to open by gravity and in response to airflow through the induction passage. In such case the force of the air tending to open the choke valve 38 is opposed by the coiled thermostatic spring 42, which may be mounted on the engine exhaust manifold 44 and operatively pivotally connected to a choke lever 46, which is secured to choke shaft 40 for rotation therewith, by a linkage 48. The opposing force of the thermostat is at a maximum when the engine is cold and is progressive- 1y relaxed as the engine warms up. The choke lever 46 is, in turn, operatively connected to the fast idle cam throng-h a pivotal connection with the upper end of linkage member 36.

In addition to the above described thermostatic arrangement, a vacuum or pressure responsive motor assembly 50 is provided and operatively connected to the choke valve 38 for causing an intial opening of the choke valve 38, against the force of thermostatic spring 42, whenever the engine is started cold.

FIG. 3 illustrates, in enlarged cross-section, a fragmentary portion of the carburetor 10 in combination with the vacuum responsive motor assembly 50 which is shown in axial cross-section.

As illustrated in FIG. 3, the housing 52 of assembly 50 may be comprised of first and second housing portions 54 and 56 which are suitably retained in assembled relationship so as to peripherally retain therebetween a pressure responsive diaphragm 58. If desired, suitable annular seals 60 and 62 may be disposed on opposite sides of the diaphragm 58 so as not to have the housing portions directly contact the diaphragm. Housing section 54 may in fact, as illustrated, be formed integrally with carburetor body 12 by having an extending portion defining an opening therein for the reception of certain of the elements of the pressure responsive assembly 50.

The diaphragm or pressure responsive member 58 in effect defines two variable but distinct chambers 64 and 66 of which chamber 64 is vented to a source of relatively high pressure. In this case, such venting or communication is accomplished by means of an aperture or conduit means 68 in communication with a source of atmospheric pressure as may exist above the choke valve 38 and below the air cleaner commonly associated with the carburetor 10 and fragmentarily illustrated at 70.

Cup-like reinforcing and clamping members 72 and 74 disposed on opposite sides of diaphragm 58 are retained thereagainst by means of a mounting stem 76, which includes an integrally formed flange portion 78 and a first threaded shank portion 80, and a washerlike retainer 82. Nut 84 threadably engaged with shank portion is effective for maintaining the washer 82, cups 72 and 74, and diaphragm 58 in assembled relationship against flange 78.

The left-most end of stem 76 is provided with an extension 86 which is pivotally connected, by means of a pivot pin 88, to one end 89 of a lost motion connecting linkage 90 which has, at its other end, an elongated slot 92 formed therein. A lever arm 94 operatively connected to or carried at one end by choke valve 38 is connected at its other end to linkage 90 by means of a pivot pin 96 which is carried by lever arm 94 and slidably retained within slot 92. As shown, the connecting link 90 may actually freely pass through the aperture 68 formed backing cup 74. Rotation of nut 102 will, in view of the above, evidently vary the preload force of the compression spring 108.

Finally, an adjustable stop member is threadably engaged with housing section 56 and positioned so as to be at times in axially abutting engagement with the face 112 of spring perch or abutment 106. Preferably, stop member 110 is provided with an annular or O ring type seal 114 for preventing leakage between chamber '66 and the ambient atmosphere. A tool-engaging surface is preferably provided as at 116 by which stop member 110 can be rotated in order to achieve axial adjustment thereof. A chamber-like opening 118 is formed at the left end of stop member 110 in order to accommodate the end of stem 76 as well as nut 102, as when surface 112 of spring abutment 106' is in abutting engagement with end 120 of stop member 110, for example.-

A second axially adjustable stop member 126, which may be threadably carried centrally of the stop 110, is also provided with an O ring type seal 128 and a toolengaging slot by which axial adjustment of stop 126 relative to stop member 110 can be achieved.

While, as previously stated, chamber 64 is in communication with a source of relatively high pressure, chamber 66 is in communication with a source of relatively low pressure as by conduit means 122 leading to port 124 formed in the carburetor 10 so as to be in communication with the induction passage 14 at a location adjacent (slightly above and/or below) the throttle valve 18 when the throttle valve 18 is in its abovementioned nominally closed position.

OPERATION The general operation of the invention is as follows. For purposes of illustration, let it first be assumed that the engine is cold and not running. At this time, the throttle valve 18 will be in its shown nominally closed position and thermostatic element 42 will have closed the choke valve 38 moving it to the position shown in either of FIGS. 1 or 2. Typically, at this time, the lip of throttle valve 18 is so situated with respect to port 124 (as also illustrated in FIG. 4) as to present some degree of communication between port 124 and the induction passage 14 on the upstream side of the throttle valve 18, and a lesser degree of communication between the port 124 and the induction passage 14 on the engine side of the throttle valve 18. Depending upon the particular engine requirement, the degrees of communication of port 124 below and above the throttle valve 18 could be varied or reversed.

Now with the engine and thermostat 42 still cold, let it be assumed that the engine is started and running. At this time manifold vacuum existing below or posterior to the throttle valve 18 is communicated via port 124 through conduit means 122 to chamber 66 of the vacuum responsive motor assembly 50. It should be evident that in the embodiment disclosed, the value of the vacuum communicated to chamber 66 will be somewhat less than the actual value of the manifold vacuum generated by the engine because of the slight bleed effect created by the port 124 communicating to some degree with the induction passage 14 upstream of the throttle valve 18.

Consequently, at this time the vacuum in chamber 66 is sufficient to make the diaphragm 58 move to the right (as viewed in FIG. 2), against the resistance of thermostatic element 42, .until end face 112 of spring seat 106 abuts against end 120 of the first stop or abutment member 110. Such movement of diaphragm 58, of course, causes a like movement of stem assembly 76 thereby moving the connecting linkage 90 to the right and causing the choke valve 38 to be moved to a first partly opened or qualifying position as fragmentariily illustrated in phantom line at 38a. If the engine and throttle valve 18 remain at the above described conditions, the diaphragm 58 will not move any further to the right because of the preloaded force in compression spring 108.

However, if it is assumed that the vehicle is driven away, under for example part throttle operation, while the engine is still cold, it can be seen that the throttle valve 18 is rotated some degree counterclockwise (as viewed in FIGS. 1 and 4) thereby causing the port or slot 124 to either experience a further reduction in the degree of permissible communication with the induction passage upstream of the throttle valve 18 or to have such communication completely terminated. Assuming that the throttle valve 18 has been sufficiently rotated as to place the lower surface 132 thereof above the top of the slot or port 124, it can be seen that the full manifold vacuum generated by the engine is applied directly through port 124 and conduit means 122 to chamber 66.

As a consequence of such full manifold vacuum being applied to chamber 66, the pressure differential thusly created across diaphragm 58 is sufficient to overcome the preloaded force of spring 108 causing the diaphragm 58 to compress spring 108 and thereby move stem assembly 76 further to the right. Such movement of diaphragm 58 and stem assembly 76 will continue until the right end of stem 76 approaches or actually abuts against the second adjustable stop or abutment member 126. Connecting linkage 90 will have been correspondingly moved causing the choke valve 38 to move from the first partly open position 38a to a second more nearly fully opened position as illustrated fragmentarily in phantom line at 38b. Such additional movement of the choke valve to a position as at 38b serves to have the effect of leaning out the fuel-air ratio of the combustible mixture being supplied to the engine.

The provision of adjustable stops 110 and 126 along with the adjustment nut 102 enables the adjustment of the preload force in spring 108 as well as the adjustment of the positions to which the choke valve will initially move both upon starting of the engine and during cold engine drive away.

FIG. 2, in which all elements which are like or similar to those of FIG. 3 are identified with like reference numbers, illustrates a second embodiment of the invention as comprising a housing 140 having formed therein a cylindrical chamber 142 for the slidable reception therein of a piston assembly 144. The piston assembly 144, is, in turn, comprised of a first piston member 146, in sliding engagement with the wall of chamber 142, operatively connected, as by a pivot -148, to end 89 of the connecting linkage 90 (as also shown in FIG. 3). A stem-like extension portion 150 carried by piston 146 passes through an aperture 152 formed in end 154 of a second piston member 156 serves to connect both pistons 146 and 156 together. An end stop portion 158, which may be adjustable in a manner similar to nut 102 (in FIG. 3), formed on or carried by stern 150 serves to prevent separation of the pistons 146 and 156 while a compression spring 160, generally contained between pistons 146 and 156 serves to resiliently urge the pistons away from each other and thereby resiliently maintain piston 156 against the end stop 158.

A first threadably adjustable stop member 162 passing through a wall of the housing 140 has a contoured tip 164 which, as illustrated, is placed in the path of travel of piston 156 so that abutting engagement will be achieved therebetween whenever the engine is initially started. It should be apparent that as adjustable stop 162 is withdrawn that piston assembly 144 will travel further to the right before abutting against the contoured tip 164. Of course, the vacuum is communicated to end 166 of chamber 142 via conduit means 122 and port or slot 124 as in the embodiment of FIG. 3.

With the elements in the positions shown in FIG. 2, the choke valve 38 would assume a position as shown at 38a of FIG. 2. That is the abutting of piston 156 against stop 162 would be equivalent to the spring seat 106 of FIG. 3 being in abutting engagement with end of I stop 110. Also, as throttle valve 18 was opened to a part throttle condition the increased vacuum supplied to end 166 would be transmitted through one or a plurality of passages 168, formed in end 154 of piston 156, to the space between the pistons 156 and 146 and thereby create a pressure differential across piston 146 sufficient to overcome the preload force of spring 160. Consequently, piston 146 would move to the right until the end 158 of stem abuts against the second adjustable stop member 126. As in the case of member 100, however, a stable condition could result where end 158 is not positioned against stop 126. Such movement of the piston 146 would cause connecting linkage 90 to move the choke valve 38 to a position corresponding to 38b of FIG. 3.

In view of the preceding, it can be seen that the invention provides means for modulating the choke position, during cold engine operation, in accordance with throttle valve position. This is accomplished through the use of a timed vacuum pick-up port means; that is, by timed it is meant that the porting means is brought progressively further into full communication with a source of manifold vacuum as the throttle valve is moved from its nominally closed position to a part throttle position. In conjunction with this, pressure responsive means are provided so as to be acted upon by the manifold vacuum in order to establish a first partly opened position of the choke valve whenever the engine is cold and running with the throttle valve in a nominally closed position, and a second partly opened position, more nearly fully open than the first position, whenever the throttle is moved from its nominally closed position toward a part throttle position. In this respect it can be seen that the porting means 124 and the edge of the throttle valve 18 combine to form a valving means or mechanism by which a tailored or regulated degree of vacuum communication is permitted with the pressure responsive assembly such as 50.

By means such as above, the invention enables the fuelair ratio to be sufliciently rich during curb idle cold engine operating conditions and still to some degree lean-out the fuel-air ratio of the combustible mixture when the cold engine has to operate at driving conditions.

As a consequence of the above, the degree of unburned hydrocarbon exhaust emission usually experienced with the prior art arrangements is reduced, fuel economy is increased and significantly smoother engine operation is achieved especially in the drive-away condition.

It should also be made clear that various configurations and positions of Vacuum porting means could be employed in place of porting means 124. As one further example, porting means 124 could be replaced by a series of generally vertically spaced small cross-sectional passages or ports each interconnected to the others and ultimately connected to conduit means 122, much in the manner as sometimes employed for controlling the advance mechanism of a pressure actuated ignition distributor assembly. Any such arrangement may, of course, be employed without departing from the spirit of the invention. Further, it should be apparent that since the porting means 124 and the edge of throttle valve 18 form a valving means, that other forms of valving means could be employed for performing the desired function. For example, the throttle shaft 20 could be formed to either form a portion of a suitable valving mechanism or to control a re lated valving mechanism which would in turn be effective for varying the manifold vacuum in the pressure responsive motor means in accordance with throttle valve position.

Although basically only two embodiments of the invention have been disclosed and described, it should be apparent that other embodiments and modifications of the invention are possible in View of the teachings herein disclosed.

I claim:

1. In a carburetor for internal combustion engines, a

throttle valve, a choke valve, means including a heat responsive device to close said choke valve at low temperatures, a device responsive to engine vacuum for causing at least a partial opening of said choke valve against the tension of said heat responsive device upon starting of the engine, and abutment means adapted to limit the amount of choke opening due to said engine vacuum responsive device, said abutment means including a first portion eifective for establishing a first maximum partly open choke valve position when said engine is operating with said throttle valve in a closed throttle position, and a second portion effective for establishing a second maximum partly open choke valve position more nearly fully opened than said first partly open choke valve position when said throttle valve is moved away from said closed throttle position...

2. A carburetor according to claim 1 wherein said vacuum responsive device comprises a pressure responsive, movable wall member, said carburetor further including connecting means operatively interconnecting said choke valve and said movable wall member, said first portion including first stop means operatively engaged by said wall member upon application of a first pressure differential across said wall member, and said second portion including second stop means spaced from said first abutment means, said second stop means being operatively engaged by said wall member upon application of a second predetermined pressure differential greater than said first pressure differential across said wall member.

3. A carburetor according to claim 1, wherein said abutment means is constructed so that said second choke position is variable up to its maximum partly open position, depending upon the vacuum applied to said device.

4. A carburetor according to claim 1 wherein said vacuum responsive means comprises a movable pressure responsive member operatively connected to said choke valve, said carburetor further including valving means for variably applying said engine vacuum to one side of said movable member, said first portion including first stop means for at times operatively engaging said movable member in order to thereby establish said first partly opened choke position, and said second portion including second stop means for at times operatively engaging said movable member in order to thereby establish said second more nearly fully opened choke position.

5. A carburetor according to claim 4, wherein at least one of said stop members is provided with means for adjustment thereof.

6. A carburetor according to claim 1 wherein said temperature responsive means normally resists opening movement of said choke valve when said engine is cold, wherein said pressure responsive device comprises a housing defining a general chamber therein, a pressure responsive movable wall member contained within said general chamber and defining at opposite sides first and second variable but distinct pressure chambers, said first pressure chamber being in communication with a source of relatively high pressure, conduit means effective for completing communication between said source of engine vacuum and said second pressure chamber, said first portion including a first stop member and a first abutment member operatively carried by said pressure responsive movable wall member, means resiliently urging said first abutment member away from said wall member, and said second portion including a second stop member and a second abutment member operatively carried by said pressure responsive wall member, said first stop member and said first abutment member being effective to engage each other upon the admission of a first value of engine vacuum to said second pressure chamber thereby arresting further 8 movement of said wall member, and said wall member being further effective upon admission of a second value of engine vacuum greater than said first value to move against the resistance of said resilient means until such time as said second abutment member engages said second stop member.

7. A carburetor according to claim 6 wherein said conduit means terminates in porting means formed in and communicating with said induction passage, said porting means comprising at least one aperture positioned so as to be partly closed to communication with said source of engine vacuum by said throttle valve when said throttle valve is in its closed position.

8. A carburetor according to claim 6 wherein said conduit means terminates in porting means formed in and communicating with said induction passage, said porting means being so positioned as to be partly exposed to the source of engine vacuum downstream of the throttle valve when said throttle valve is in its closed position and simultaneously partly exposed to the atmospheric pressure upstream of said closed throttle valve.

9. A carburetor according to claim 6 wherein said pressure responsive movable wall member comprises a pressure responsive diaphragm, wherein said first abutment member comprises a movable spring seat, and wherein said resilient means comprises a compression spring contained generally between said diaphragm and said spring seat.

10. A carburetor according to claim 6 wherein said pressure responsive movable wall member comprises a pressure responsive piston, wherein said first abutment member comprises a spring seat, and wherein said resilient means comprises a compression spring contained generally between said piston and said spring seat.

11. A carburetor according to claim 6 wherein said pressure resonsive movable wall member comprises a pressure responsive diaphragm assembly, a stem portion carried by said diaphragm assembly and extending generally axially thereof, wherein said first abutment member comprises a movable spring seat slidably situated on and retained by said stem portion, wherein said resilient means comprises a compression spring contained generally between said diaphragm assembly and said spring seat, including adjustment means carried by said stem portion for adjusting the preload force of said compression spring, wherein said first stop member comprises a threadably adjustable stop carried by said housing and generally extending into said second pressure chamber, and wherein said second stop member comprises a threadably adjustable second stop also operatively carried by said housing in a manner so as to have an end thereof generally within said second pressure chamber.

12. A carburetor according to claim 6, wherein means are provided to adjust the preload of said resilient means.

References Cited UNITED STATES PATENTS 787,480 4/1905 Tanner 92-65X' 2,506,374 5/1950 McMahon 92-65X 2,988,344 6/ 1961 Smitley 261-39(.2) 3,159,692 12/1964 Kittler 261-39(.2) 3,171,868 3/1965 Hamilton 26139(.2) 3,187,640 6/1965 Young et a1. 92-65X 3,279,771 10/ 1966 Herman et al. 26139(.2) 3,321,194 5/1967 Oarlson 26l39(.2)

TIM R. MILES, Primary Examiner U.S. Cl. X.R, 926 5

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