Title:
Carburetor cold engine air/fuel mixture enrichment apparatus
United States Patent 3929942


Abstract:
The carburetor throttle plate shaft has fixed to it a lever that normally engages a first stepped edge of a fast idle cam rotated by a temperature responsive element to determine the closed throttle plate, running engine, idle speed position as a function of temperature changes. During engine starting, a second stepped edge of greater projection is engaged with the lever to open the throttle plates wider to initially supply more air and fuel to the engine, the openings varying with temperature. Once the engine attains a running condition, the lever is withdrawn from engagement with the second stepped edge and re-engaged with the first stepped edge to provide a more conventional cold engine running operation, the throttle plates then closing down to less open positions. Simultaneously, during cranking, the temperature control positions a supplemental fuel control needle valve to supply extra fuel to the carburetor during cold engine operation that changes with temperature changes. The extra fuel is inducted along with fuel from the main fuel supply system.



Inventors:
Harrison, Robert S. (Grosse Ile, MI)
Medrick, John D. (Plymouth, MI)
Nowroski, Alvin P. (Livonia, MI)
Application Number:
05/430824
Publication Date:
12/30/1975
Filing Date:
01/04/1974
Assignee:
FORD MOTOR COMPANY
Primary Class:
Other Classes:
261/39.5, 261/44.4, 261/44.7, 261/50.2, 261/52
International Classes:
F02M1/04; F02M1/10; F02M9/10; (IPC1-7): F02M1/10
Field of Search:
261/5A,39A-39E,65,52,5AA,44A
View Patent Images:
US Patent References:
3695591AUTOMATIC COLD STARTING DEVICES FOR INTERNAL COMBUSTION ENGINES1972-10-03Caisley
2747848Carburetor1956-05-29Kehoe
2102428Internal combustion engine fuel system1937-12-14Macauley, Jr. et al.



Primary Examiner:
Miles, Tim R.
Assistant Examiner:
Cuchlinski Jr., William
Attorney, Agent or Firm:
Mccollum, Robert Zerschling Keith E. L.
Claims:
We claim

1. An air fuel mixture enrichment apparatus for cold weather starting and running operation of an internal combustion engine having a carburetor having an induction passage open to fresh air at one end and adapted to be connected at the opposite end to the engine intake manifold, a throttle plate mounted for rotation across the passage between closed and open positions to control the flow of air and fuel therethrough and spring biased to a closed position, a fuel supply port connected to the passage and responsive to movement of the throttle valve to different positions to induce different quantities of fuel into the passage,

2. An apparatus in accordance with claim 1, including spring means normally biasing the second surface into engagement with the first means.

3. An apparatus as in claim 2, including means mounting the cam for axial movement, the spring means normally biasing the cam to a position engaging the second surface and first means.

4. An apparatus as in claim 3, including servo means operably by engine vacuum upon the attainment of an engine running condition to move the cam to a second position engaging the first means with the first series of steps, thereby moving the needle valve to reduce the flow of additional fuel and permitting the throttle plate to move to a less open position to reduce airflow.

5. An apparatus as in claim 1, in which the second surface contains a second series of steps each of greater extent of projection than a step of the first mentioned series of steps.

6. An apparatus as in claim 1, in which the second surface contains a second series of steps corresponding in number and axially aligned with the first series of steps but each of a greater radial extent than the corresponding step of the first series of steps whereby the needle valve is moved further out of the conduit means and the throttle plate is opened wider for the same prevailing temperature level.

7. An air fuel mixture enrichment apparatus for the cold weather starting and running operation of an internal combustion engine having a carburetor having an induction passage open to fresh air at one end and adapted to be connected at its other end to the intake manifold, a throttle plate mounted for rotation across the passage to control the flow of air and fuel therethrough and spring biased to a closed position, a fuel supply port opening into the passage and responsive to movement of the throttle plate to different positions to induce different quantities of fuel into the passage,

8. An apparatus as in claim 7, including a lever between the fast idle cam and needle valve, the lever being engaged and moved by the cam in a needle valve opening direction.

Description:
This invention relates, in general, to an internal combustion engine carburetor. More particularly, it relates to a device for use during cold engine cranking and running operations to supply a mixture of air and fuel to the carburetor that supplements the normal running air/fuel mixture carburetor requirements.

The advent of lower vehicle hoodlines necessitates a change in engine carburetion design. The prior art carburetor designs of the downdraft type generally include in the induction passage a choke valve located above the fuel metering venturi. This adds height to the carburetor and necessitates either providing a hump in the hood or higher hood profiles.

This invention relates to a carburetor design that eliminates the need for a choke valve as such to thereby permit decreasing the overall height of the carburetor. The invention compensates for the lack of a choke system by providing a cold enrichment mechanism that adds additional fuel and air to the carburetor during cold engine starting operations to supplement the quantity of fuel and air normally supplied to the carburetor when the engine has reached its normal operating condition. The conventional choke valve effects an overrich mixture during engine cranking operations, followed by an initial cracking open of the choke valve a predetermined amount to lean the mixture to a less rich but still richer than normal level. The conventional choke valve, therefore, controls the flow of both air and fuel and causes additional fuel to be added to the system during cold engine operation.

The present invention accomplishes the same objectives as a conventional choke valve without requiring the use of one.

More particularly, the invention provides a temperature responsive control mechanism that includes first, a fuel enrichment means variably movable as the temperature decreases to vary the feed of a supplemental supply of fuel to the engine during starting, and secondly, a means to provide an opening of the throttle plates to increase airflow during starting that is greater than during engine running operations, and variable in degree of opening as a function of the temperature level.

It is the primary object of the invention, therefore, to provide a cold enrichment system for an internal combustion engine carburetor to supplement the normal carburetor air/fuel mixture requirements during cold weather engine cranking and running operations.

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 plan view of a variable area venturi type carburetor embodying the invention;

FIG. 2 is a cross sectional view taken on a plane indicated by and viewed in the direction of the arrows 2--2 of FIG. 1;

FIG. 3 is a cross sectional view taken on a plane indicated by and viewed in the direction of the arrows 3--3 of FIG. 7 and looking down on the main or central body portion of the carburetor;

FIGS. 4 and 5 are enlarged cross sectional views taken on planes indicated by and viewed in the direction of the arrows 4--4 and 5--5 of FIG. 3;

FIG. 6 is an enlarged cross sectional view and FIG. 7 is a cross sectional view taken, respectively, on planes indicated by and viewed in the direction of the arrows 6--6 and 7--7 of FIG. 1;

FIG. 8 is a bottom view taken on a plane indicated by and viewed in the direction of the arrows 8--8 of FIG. 7, and looking up at the underside portion of the air horn portion of the carburetor;

FIG. 9 is an enlarged side elevational view taken on a plane indicated by and viewed in the direction of the arrows of FIG. 1;

FIG. 10 is a cross sectional view taken on a plane indicated by and viewed in the direction of the arrows 10--10 of FIG. 9;

FIGS. 11 and 12 are cross sectional views taken on planes indicated and viewed in the direction of the arrows 11--11 and 12--12 of FIG. 10;

FIG. 13 is a cross sectional view taken on a plane indicated by and viewed in the direction of the arrows 13--13 of FIG. 12; and,

FIG. 14 is an enlarged cross sectional view taken on a plane indicated by and viewed in the direction of the arrows 14--14 of FIG. 13.

FIG. 1, which is essentially to scale, is a plan view of a variable area venturi carburetor of the downdraft type. It has a pair of rectangularly shaped induction passages 10, each having one end wall 12 which is pivotally movable and has the profile (FIG. 2) of one-half of a venturi 13. Each opposite fixed cooperating wall 14 is formed with the mating profile of a portion of a venturi. The airflow capacity, therefore, varies in proportion to the opening movements of walls 12 of the induction passages.

As seen more clearly in FIG. 2, movable walls 12 are pivotally mounted at 15 on a stationary pin. The pin actually is fixed to a strut, not shown, that depends from a section of the air horn or upper body portion of the carburetor. Pivotally attached to each of the wall bodies is a fuel metering rod or needle 16 that is tapered for cooperation with a main fuel metering jet 18. The needles have a controlled taper to provide a richer air/fuel mixture at the lower and higher ends of the venturi opening range. Each jet is located in an aperture inside wall 14 at approximately the throat or most constricted section of venturi 13. A fuel float bowl or reservoir 20 has a pair of identical passages 22 conducting fuel to the main metering jets 18. Downstream of the venturis, the carburetor throttle body portion 23 rotatably mounts a shaft 24 on which are fixed a pair (only one shown) of conventional throttle plates 25 that control the flow of air and fuel through induction passages 10.

The size of venturis 13 and the movement of walls 12 is controlled in this case by a spring returned, control vacuum actuated, diaphragm type servo 26. The servo consists of a hollow two-piece casting divided into two chambers 28 and 30 by an annular flexible diaphragm 32. The diaphragm is sealingly mounted along its edge in the casting. Chamber 28 is an air chamber, connected to ambient or atmospheric pressure through a passage 34 (indicated also in FIGS. 1, 3 and 7). Chamber 30 is a vacuum chamber connected to induction passages 10 at a point below the throat but still in the venturi 13. This subjects chamber 30 to changes in a control vacuum that varies with airflow but at a rate that is slightly different than true venturi vacuum. The exact location of the tap of course is a matter of choice. Chamber 30 also is connected to be actuated by ported intake manifold vacuum, for cold weather operation, as will be described in more detail later.

Completing the construction, servo 26 has fixed to one side of diaphragm 32, by a retainer 35, a plunger or actuator 36. The plunger is pivotally connected to a shaft 37 interconnecting cast portions of the movable walls 12. Fixed to the other side of diaphragm 32 is a retainer 38 against which is seated a spring 39. The other end of the spring bears against a seat 40 axially adjustable to vary the spring preload.

FIG. 2 indicates schematically in dotted lines a passage "p" between chamber 30 and induction passages 10. In actuality, as best seen in FIGS. 3, 4, and 5, servo chamber 30 is connected by a restricted line 41 (FIG. 3) to an intersecting passage 42 (FIGS. 3-5). Passage 42 intersects with a vertically downwardly extending passage 44 (FIG. 4) containing a flow restrictor or orifice 46 and terminating in a chamber 48. Chamber 48 is connected by a port 50 to induction passage 10 at a point below the edge of throttle valve 25 when it is in its closed position shown. In the position shown, therefore, as the throttle valve is rotated to an open position, port 50 is progressively subjected to the increased pressure above the throttle valve to bleed the vacuum in passage 42.

Passage 42 also intersects with a right angled passage 52 (FIGS. 4, 5 and 6) that connects to a passage 54 (FIG. 6). The latter passes vertically through the main body portion of the carburetor into a horizontal passage 56 in turn connected by a pair of passages 58 and 60 to the well 62 (FIG. 3) in which is arcuately movable one of the mounting members 70 (FIG. 2) for movable wall 12. While not shown, the well 62 in FIG. 3 and the adjacent induction passage 10 are interconnected by a depressed portion of the main body between the two so that the opening 63 shown in FIG. 6 senses the control or venturi-like vacuum connected by the passages named to servo chamber 30.

Looking now at FIG. 6, the opening 63 to the control vacuum in this case is adapted to be alternately blocked or progressively opened by a needle type valve 72. The valve is movable into and out of the seat 63 in response to a temperature sensitive element, in a manner that will be described more clearly later. Suffice it to say at this point, that during normal engine operating temperatures, the needle valve 72 is completely withdrawn from opening 63 thereby permitting venturi-like vacuum to be sensed through passages 60, 58, 56, 54, 52, 42 and 41 to chamber 30 of the servo, the ported manifold vacuum simultaneously being sensed through port 50, chamber 48, line 42 to line 41 and servo chamber 30.

It should be noted that the size of the venturi-like vacuum passages 60, 58, 56, 54 and 52 are considerably larger than that of the ported manifold vacuum passage 44, coupled with the orifice 46, so that when the needle valve 72 is in the up position, the manifold vacuum is bled to the level of the venturi-like or control vacuum and, therefore, has essentially no effect on the movement of servo 26. The manifold vacuum is used during cold weather operations to modulate the venturi-like or control vacuum to provide a different richness schedule than would be provided by means of the venturi-like control vacuum above, to provide a finer control of engine operation. When the needle valve 72 is in the closed or nearly closed position, the venturi-like vacuum flow will be essentially blocked and manifold vacuum alone will be acting on servo chamber 30. This will cause the movable venturi walls 12 to be moved to a larger area venturi pulling the fuel metering rods 16 out to the desired position.

As thus far described, during normal engine operating temperatures, the operation is as follows. The rotative movement of throttle plates 25 controls total airflow through both passages 10 to increase as the throttle valves are moved from their closed position. An increase in airflow provides essentially a proportional increase in the control vacuum in chamber 30 from port 63 until diaphragm 32 is moved towards the cup 40. This moves both walls 12 to open induction passages 10 and increase the area of venturis 13 while simultaneously retracting the fuel metering rods 16 to provide a change in fuel flow. Thus, the total airflow and fuel flow vary with changes in throttle plate setting up to a maximum.

Returning now to the general construction shown in FIG. 1, during cold weather operation, as stated previousy, it is desirable to provide an additional supply of fuel to the induction passages to assure sufficient fuel vapor both for starting the engine as well as a different schedule of additional fuel for running the cold engine prior to its reaching normal operating temperature level. These requirements are satisfied by providing a combination fuel enrichment system, a cranking fuel enrichment system, as well as a throttle plate positioner to crack open the throttle plates an additional amount during cold starting operations.

More specifically, FIGS. 3, 6 and 7 show portions of both the cold running enrichment system as well as the cold start cranking fuel system. The body portion of the carburetor is cast with a fuel bowl 20 containing fuel delivered thereto past a conventional inlet needle valve 80 from a supply line 82. The needle valve 80 is moved vertically in a bore 84 by the tab 86 secured to a float member 88 pivotally mounted at 90 on a depending portion of the air horn section of the carburetor.

The inlet valve 80 operates in a known manner. Movement of float 88 downwardly as a result of lowering of the liquid fuel level causes the needle 80 to drop. This permits fuel under pressure to enter the reservoir from line 82 to fill it again to the desired level. Raising of the float raises the inlet valve against a conical seat, not shown, to shut off the supply when the desired level has been reached.

The lower portion of fuel bowl 20 contains a spring opened cranking fuel supply valve 100 (FIG. 6). The latter has a conical valve portion 102 that cooperates with an annular knife edge seat 104 located in the end of a fuel passage 106. Valve 100 has a tapered stem portion 108 and is biased upwardly by a spring 110 to open passage 106 to the flow of fuel from bowl 20. An intersecting passage 112 (FIG. 3) connects with a cross passage 114 to flow fuel into another passage 116 past a solenoid controlled valve unit 118.

As best seen in FIG. 7, unit 118 consists essentially of a valve 120 formed on the end of the armature of a solenoid 122. A spring not shown normally biases valve 120 to close communication between passages 114 and 116. The solenoid normally would be powered from the starter relay of the motor vehicle ignition system so that the solenoid is rendered operative only during engine starting conditions. That is, when the ignition key is turned to the start position, the solenoid 122 would be energized and cause valve 120 to be retracted rightwardly to open communication between passages 114 and 116. A flow of starting fuel would then be permitted from fuel bowl 20 to passage 116. As soon as the engine attained running condition, return of the ignition switch to the on position would de-energize solenoid 122 and again block passage 114 from communicating with passage 116. The solenoid unit could include a manifold vacuum switch so the solenoid is not energized below a vacuum level of say 2 inches Hg., for example. It also could contain a thermal switch to prevent operation above 80°F., for example, when extra cranking fuel usually is not needed.

From passage 114 the fuel passes upwardly through the carburetor main body passage 124 (FIG. 7) where it flows into a plenum 126, shown also in FIG. 8. From the plenum, the fuel is divided equally to be inducted out through passages 128 into each of the induction passages 10 at a location adjacent the venturi but spaced from the fuel jets 18. Thus, it will be seen that for starting operations, energization of the solenoid by turning of the vehicle ignition switch causes additional fuel to be added at times to the induction passages, for starting purposes.

The quantity of cranking fuel to be added to the induction passages, or, on the other hand, the position of cranking valve 100, is controlled by the lower end of a needle valve 140 (FIG. 6) that forms a portion of the engine running fuel enrichment system. More specifically, needle valve 140 is tapered at its lower end as shown at 142 and has threaded to it an abutment portion 144. The latter is adapted to engage the cranking valve 100 when the needle valve is moved downwardly during warmer than the coldest weather operations. The screw connection of member 144 to the needle valve provides axial adjustment for varying the characteristics of the fuel flow.

The needle valve 140, in this case, is vertically movable in a well 146 in the upper body portion, and is axially aligned by a pair of seals 148 and 150. The seals define a chamber 152 which is connected by an angled passage 154 to the end 156 of a worm-like passage 158 best seen in FIG. 8. The opposite end 160 of passage 158 connects with a vertical passage 162 (FIG. 7) that intersects an angled passage 164 leading to the plenum 126. As stated previously, plenum 126 also receives fuel from the cranking fuel passage 124. Together then, the fuel passes into each induction passage 10 through the side passages 128. It will be seen then that, depending upon the vertical position of needle valve 140, a quantity of fuel will flow past the tapered portion 142 of the needle valve into the various passages into induction passages 10 to supply additional fuel during cold running operation of the engine.

The vertical movement of needle valve 140 is controlled by a temperature sensitive element that moves the needle valve 140 upwardly to increase fuel flow as the temperature decreases below the normal operating level, and moves the needle valve 140 to a downward position to shut off the fuel enrichment when the temperature reaches the normal operating level. Concurrently, the downward movement of needle valve 140 as the temperature increases will move the cranking fuel valve 100 downwardly against the force of spring 110 in proportion to the temperature increase. Therefore, when the normal operating level is reached, cranking valve 100 will be completely closed against seat 102 and no additional fuel will then be added during starting of the engine.

The upper end of needle valve 140 is pivotally connected to the end of a lever 166. The lever is pivotally mounted on a pin 168 projecting through an aperture in a boss 170 projecting from the carburetor upper body. The opposite end of lever 166 is pivotally connected to an adjustable nut 172 on the upper end of a depending link 174. The link 174 is adapted to be connected to a thermostatically responsive movable element to be described. Adjusting the upper end 172 of course will vary the operating characteristics of the system. Downward movement of link 174 is limited by abutment of the nut 172 against a stop washer 176. Projecting horizontally or laterally from link 174 is a connector 178 pivotally engaging the threaded upper end 180 of needle valve 72. The upper end 180 contains a yoke member 182 adjustably threaded to the end of needle valve 72 as shown to determine the upward and downward limits of movement of the needle valve.

As thus far described, therefore, when link 174 is in the position shown indicating that the temperature is at the lowest below normal engine operating level, the needle valve 140 will have been moved to its upwardmost position to provide maximum fuel flow through this circuit, and the needle valve 72 will have moved to its downwardmost position to block the port or outlet 63 to the induction passage section 62 shown in FIG. 3. Thus, assuming a closed throttle plate position, the higher ported manifold vacuum in port 50 (FIG. 4) will act in servo chamber 30 to move the walls 12 further out than they would be moved by the control vacuum alone, to provide the desired richness schedule by pulling out the metering rods 16. Also, simultaneously, additional fuel will be inducted from the fuel enrichment well 152 into the induction passages 10 and out through the fixed area outlet passages 128.

As soon as the temperature increases from its lowest setting, the link 174 will move vertically upwardly from the position shown. This will gradually and progressively raise the needle valve 72 and lower progressively needle valve 140. The venturi-like control vacuum then bleeds into passage 60 to decrease the vacuum force acting on servo chamber 30 to permit servo spring 46 to slowly close the venturi towards the normal engine idle speed position. While this increases the velocity and fuel metering signal, the additional fuel enrichment will decrease since the tapered portion 142 of needle valve 140 will be closing the opening to the fuel bowl.

Turning now to the temperature responsive control of the movement of link 174 and the throttle valve positioner forming part of the invention, as best seen in FIGS. 9-14, and especially FIG. 10, the lower end of link 174 is pivotally connected to one end of a lever 216 that is fixed on a shaft 218. The shaft extends rotatably through a sleeve 220 that is mounted in a hole 222 in a hollow box-like housing 224. The housing is bolted to the carburetor throttle flange by mounting tabs 225. The opposite end of shaft 218 is enlarged at 226 to constitute a stop for the end of sleeve 220. The end 226 also is riveted to a lever 228 that has leg portions 230 and 232 bent in opposite directions.

The leg portion 230 is adapted to engage or move between a pair of drive lugs 234, 235 (FIG. 12) formed on a fast idle cam 236. The cam is rotatably mounted on a second sleeve 238 slidably mounted on sleeve 220. The cam is fixed axially on sleeve 238 between an annular collar 240 at one end and a snap ring 242 at the other end. The cam has a portion 244 in which is mounted a ball 246 of chosen weight, and a fast idle portion 248. The fast idle portion, as best seen in FIGS. 12-14, has two peripheral circumferentially stepped edge surfaces 250 and 252. Each surface contains, in this case, a series of four steps 250', 250", 250'", and 250"" and 252', 252", 252'" and 252"", in sequence each of a greater radial extent than the circumferentially contiguous previous one. The series of steps on surface 250 are axially aligned with and correspond to the series of steps on surface 252. Each of the steps on surface 252, however, extend or project radially outwardly a greater distance than the steps on surface 250.

The steps are adapted to be engaged individually or one at a time by the end of a plunger 254 shown in FIG. 12. The plunger is slidably mounted within a sleeve 256 fixed in the housing 224 within a hole 258. A spring 260 biases the opposite button end 262 of the plunger to a retracted, inoperative position. The plunger end is engaged by the cam end 264 of a lever 266 that adjustably mounts a screw 268. The end of the screw abuts a tang 270 formed on a lever 272 fixed on the throttle shaft 24. The throttle shaft thus is free to move in a counterclockwise direction to open the throttle plates, but is stopped in its movement in a closing direction by the position of screw 268. The throttle shaft 24 is biased in a closing direction against the screw by a coiled spring not shown.

As stated previously, plunger 254 is adapted to engage only one of the fast idle cam steps at a time on the two surfaces 250 and 252. As seen in FIG. 13, the surfaces are in two different planes. The plunger, however, is movable but in a single plane along the axis of the hole 258. The fast idle cam, therefore, is adapted to be shifted axially to alternately align the plunger end with one or the other of surfaces 250, 252.

As best seen in FIGS. 10 and 11, the sleeve 220 is slipped through a hole 280 in a reaction plate 282 until a collar 283 on the sleeve abuts the plate. The plate then is anchored to the sleeve by a snap ring 284. The plate has a stamped tab portion 286 that is bent upwardly to form a fulcrum 287 for a flat lever 288. The right-hand end of lever 288 is formed as a fork 290 with ears 292 engaged in the channel of collar 240 of slidable sleeve 238. The lever end 290 is biased downwardly in FIG. 10 by a spring 294 stretched over the top surface of lever 288 in a groove 296. The spring is anchored on opposite ends as shown in FIG. 11.

The lever 288 in the position shown in FIG. 10 locates sleeve 238 and fast idle cam 234 so that the less projecting cam surface 250 is aligned with the axis of plunger 254. When the lever 288 is pivoted about the fulcrum 287 in a counterclockwise direction, it raises the sleeve 238 and fast idle cam so that the more projecting cam surface 252 is then aligned with the axis of plunger 254.

The lever 288 is pivoted by a vacuum controlled servo 300. The servo is defined in part by a formed portion 302 of housing 224 and a cover 304 bolted to housing 224. An annular flexible diaphragm 306 subdivides the housing into an air chamber 308 and a vacuum chamber 310. The air chamber is vented to the ambient air inside the housing 224 through a hole 312. A plunger 314 riveted to diaphragm 306 projects through hole 312 against the end of lever 288. The vacuum chamber 310 contains a spring 316 that biases plunger 314 and lever 288 downwardly in FIG. 10 to the dotted line position 318 aligning cam surface 252 with plunger 254. Vacuum applied to the servo retracts diaphragm 306 and plunger 314 to the full line position shown aligning the fast idle cam surface 250 with plunger 254. Engine vacuum is applied to chamber 310 from an engine intake manifold port in the induction passage through a passage 320 (FIG. 12) connected through another passage in a hollow mounting bolt, not shown, adapted to be inserted in hole 321.

The rotative position of fast idle cam 234 to determine which step on either surface 250 or 252 will be engaged by plunger 254 is controlled by a coiled thermostatic bimetal spring 322 shown in FIG. 10. The outer end of the spring engages in a slot in the leg 232 of lever 228 to rotate the same with contractions or expansions of the coiled spring upon changes in temperature level. The inner end 324 of the coil spring is mounted in a slot on a stub shaft 326. The shaft projects loosely through a cover 328 that closes the end of housing 224 with a gasket 329 between, and is attached to an indexing plate 330. Turning the plate places a preload or removes the preload on coiled spring 322 by coiling or uncoiling the spring. The plate is held frictionally in adjusted position by tightening a cover plate 332 against the plate by means of screws 334.

As best seen in FIGS. 9 and 10, the lowermost portion of housing 224 includes a tube 336. The tube is adapted to be connected to a conventional exhaust manifold heat stove whereby fresh air flowing past the stove into the tube is heated. The chamber defined within housing 224 in turn is connected to the manifold vacuum in passage 320 (FIG. 9) by means of a small hole 338 in the lowermost wall section 340 and a connecting passage 342 formed in the casting. Thus, when the engine is running, vacuum acting through hole 338 will pull hot air along the lowermost portion of the housing, as seen in FIG. 10, past the coiled spring 322 to heat it.

Warming of the coiled spring 322 will cause a circumferential movement of the outer end 232 of lever 228 in a counterclockwise direction (FIG. 12) to permit the fast idle cam 236 to follow by gravity. This then will place a lower step or none, as shown, of surface 250 in the path of the plunger 254, upon depression and release of the accelerator pedal. Similarly, cooling of the coil 322 will cause it to rotate lever 228 in the opposite direction. This of course simultaneously rotates the fast idle cam 236 by abutment of lever 230 against the projection 234, so that, depending upon the temperature level, one of the higher steps of surface 250 will be presented opposite the end 254 of plunger 254. Thus, the throttle plate idle speed setting will be determined by which step is engaged by plunger 254, during running operations of the engine. During cold start operations, the fast idle cam is raised by the servo spring 316 so that the cam surface 252 is aligned with plunger 254. The engagement of the plunger with one of the steps of the higher cam surface thus opens the throttle plates more for starting purposes than they are during normal cold running conditions.

It will be seen, therefore, that regardless of what rotative position the fast idle cam 236 assumes because of the prevailing ambient temperature, the throttle plates will be opened more during starting than for normal, cold running operation. The degree of opening will vary to agree with the ambient temperature level so that a correct starting air/fuel mixture is obtained. This is in contrast to the conventional constructions in which there is only one fast idle start position, accomplished only by positioning a highest step against the throttle stop. At the inbetween temperature levels, this is too high and results in too fast an idle speed, and one that may provide undesirable emissions.

The overall operation of the carburetor is believed to be clear from the above description and by reference to the drawings. Therefore, it will be repeated now only briefly. Assume that the engine is off and the ambient temperature is essentially 0°F. The coiled bimetallic spring 322 will have contracted a maximum amount biasing lever 228 clockwise (FIG. 12). By opening the throttle plates, plunger 254 will be retracted by its spring, allowing lever 228 to rotate the fast idle cam 236 clockwise. This will locate the highest cam step opposite the plunger 254. Simultaneously, the servo spring 316 will move plunger 314 downwardly to pivot lever 288. This will shift the fast idle cam upwardly to align the higher cam surface 252 opposite plunger 254, and in particular, the highest cam surface 252'. Release of the throttle plates now will engage the plunger with the step 252' and the plates will be opened a maximum amount for the coldest start positions. The induction passages 10 at this time are at their smallest cross section because the servo spring 46 has moved walls 12 to this position. The greater opening of the throttle plates, however, exposes the passages to a larger cranking vacuum signal so that the airflow across the fuel metering jets 18 is increased.

The rotation of lever 216 moves link 174 downwardly to its extreme position until the stop 172 shown in FIG. 6 abuts the washer 176. This pivots needle valve 140 to its uppermost position allowing a maximum amount of fuel past the tapered lower portion from fuel bowl 20. This upward position also permits the upward movement of the cranking valve 100 by the spring 110 to open wide the passage 106 to flow fuel to passage 112. Therefore, when the ignition switch is turned to an on or start position, the solenoid 118 will withdraw the valve 120 to permit fuel to flow from passage 114 to 116.

When the engine is cranked for starting purposes, the cranking vacuum signal is sufficient acting across the induction passage outlets 128 (FIG. 8) to draw fuel up cranking fuel circuit passage 124 into plenum 126. Simultaneously, fuel is drawn past the engine running fuel circuit needle valve 140 into the worm passage 158 (FIG. 8) to plenum chamber 126, where both circuits combine and the fuel is inducted to provide the necessary starting richness. Once the engine has been started, release of the ignition switch to the engine running position de-energizes solenoid 122 to then again block the connection between the cranking supply line 114 and the line 116. However, with the link 174 in its downwardmost coldest position, the valve 72 will also be down blocking off port 63. Accordingly, engine running manifold vacuum will act in servo chamber 30 and draw the walls 12 of the venturis to open or enlarge the venturi area. This will also withdraw the fuel metering rods 16. The reduced air velocity reduces the fuel metering signal and therefore leans out the overall mixture at this time even though the fuel jet orifices are enlarged. Thus, a richer than normal idle but less rich than cranking mixture is provided at this time.

Simultaneously, upon the engine attaining a running condition, the manifold vacuum established in servo chamber 310 will be sufficient, once the throttle lever 264 is pivoted counterclockwise to release plunger 254, to retract plunger 314. This will permit the fast idle cam 234 to drop down to the full line position shown in FIG. 10. Now the lever 264 will abut the step 250 of the fast idle cam and thereby close down the throttle plates to less open positions than during starting. This provides less fuel and airflow for cold running operations, which is desired because a less rich air/fuel mixture now is required once the engine has attained its idle speed horsepower.

As the temperature increases, the bimetallic coiled spring 322 will rotate the lever 216 in a counterclockwise direction away from the fast idle cam. The cam then can move in the same direction by gravity when the throttle plates are opened beyond the fast idle position so that the end of lever 266 gradually moves progressively clockwise to permit the progressive closure of the throttle plates. Simultaneously, the counterclockwise rotation of lever 216 effects an upward movement of link 174 to progressively move the needle valve 140 downwardly and thereby progressively close off the additional fuel flow past the valve. This movement also causes an upward movement of needle valve 72 permitting the venturi-like vacuum to decay the ported manifold vacuum signal acting in servo chamber 30.

Thus, the lowering vacuum signal in pressure chamber 30 will permit the venturi walls 12 to move to contract the venturi area and move the metering rods 16 into the jets 18. This richens the main fuel mixture because the fuel metering signal now increases. But at the same time, the supplemental fuel is being cut off. So for the same airflow, the mixture will lean as the temperature increases. Eventually, the throttle plates will be returned to their normal idle speed closed positions, the needle valve 72 will be drawn essentially completely out of port 63 so that movement of the venturi walls will be controlled solely by control or venturi-like vacuum changes, and the supplemental fuel needle valve 140 will be moved downwardly to shut off completely the supply of additional fuel to the system. At this time, the cranking valve 100 will be shut so that even if solenoid 122 opens during engine start condition, no additional cranking fuel will be added to the engine when the engine is started at a normal operating temperature level. It should be noted that during cold engine operation, when the throttle plates are in the fast idle speed positions, the high manifold vacuum provides excess fuel vaporization. This is why the venturi is enlarged, to lean the mixture at this time. The moment the throttle plates are moved off idle to accelerative positions, the manifold vacuum drops, and a richer mixture is required for better engine drivability. The traversing of port 50 by the throttle plates decreases the manifold vacuum progressively to the control vacuum level existing above the throttle plates, and therefore closes the venturi progressively to progressively increase the richness.

From the foregoing, it will be seen that the invention provides a throttle plate positioner to provide variable additional throttle plate openings during cold engine starts regardless of the fast idle cam position, to provide increased air and fuel flow for cold weather operation, and, therefore, improved emissions. It will also be seen that the invention provides an enrichment system to supply fuel to the engine during cranking and cold running that supplements the fuel supplied by the main fuel metering system, to provide extra richness at this time.

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 changes and modifications may be made thereto without departing from the scope of the invention.