CA1084365A - Carburetor with limited interconnected choke valve and fast idle cam - Google Patents

Abstract

CARBURETOR WITH LIMITED INTERCONNECTED CHOKE
VALVE AND FAST IDLE CAM

ABSTRACT OF THE DISCLOSURE

A carburetor choke valve or plate is interconnected to a fast idle cam mechanism by linkage having a lost motion permitting continued operation of the fast idle cam subsequent to the choke plate attaining a wide open position.

Description

~ ~8 ~3~ S

This invention relates in general to a cold enrichment system for an automotive type car~uretor. ~lore particularly, it relates to an apparatus for at times divorcing the carbure-tor choke valve from the fast idle mechanism to permit comeoff of the choke valve prior to release of the fast idle cam to reduce emiss~ons while at the same time providing favourable operating conditions.
Most commercial carburetors include a choke construc-tion in which the choke valve and fast idle cam are inter-connected in such a way that when the choke valve attains awide open vertical condition, the fast idle cam by that time has caused the throttle valve to be moved to its normal idle speèd essentially closed position. For emission purposes, any delay in opening the choke valve necessarily maintains a richer air/fuel ratio because of the decreased air supply.
In accordance with the present invention, there is ~;
provided a carburetor having an air/fuel induction passage open at one end to air at essentially atmospheric pressure and ~
connected at its opposite engine end to an engine intake ~;
manifold to be subject to the changing vacu~ levels therein, the one end having a choke valve unbalance mounted for a rotatable movement by gravity and airflow thereagainst across the one end between a closed position and a wide open inoper-ative position wherein the choke valve is inoperative to restrict the flow of air into the passage, and a throttle valve secured on a shaft rotatably mounted posterior of the choke valve for movement of the throttle valve across the passage between an engine normal operating temperature level essentially closed engine idle speed position and beyond towards a wide open throttle position to control the volume of flow of an air/fuel mixture through the passage as a func-tion of the position of the throttle valve, the control ! -. _ .
'~'~ . , -: . -~L~843~5 comprising means operable during engine operations below the normal operating temperature to provide a controlled posi-tioning of the throttle valve re].ative to the position of the choke valve, to improve emissions while minimizing engine stalling, the last mentioned means including throttle valve abutment means secured to the throttle valve shaft, a second shaft, a fast idle cam rotatably mounted on the second sha~t and having an edge formed with a number of circumferentially contiguous steps progressively decreasing in radial extent to one which when aligned with the abutment means permits closure of the throttle valve to the normal engine idle speed position, whereby the throttle valve will be.progressively opened beyond the latter position as a function of the particular step engaged by the abutment means, spring means biasing the abutment means and throttle valve towards a closed position and into individual engagement with one of the steps, a thermostatically responsive coiled spring opera-tively effecting the rotation of thè fast idle cam to posi-tions operatively moving the throttle valve to positions pro-gressively more open than the normal idle speed position as afunction of decreases in temperature from a predetermined level, first lever means operatively connected to the choke valve, linkage means connected to the first means, and lost motion means providing a limited interconnection between the fast idle cam and linkage means permitting a limited opening of the choke valve and operation of the fast idle cam indepen-dent of each other.
In this invention the choke valve is interconnec-ted to the fast idle cam mechanism by a lost motion means that permits the choke valve to be fully open while the fast idle mechanism is still on the last step of the cam.

~ - 2 ' , . . .
~: - . .
~ .

- -This causes a leaner mixture to flow to the engine and yet not cause stalling be~ause the throttle valve is still main-tained in a fast idle position permitting a greater volume of flow to the engine.
The present invention i.s described further, by way of illustration, with reference t:o the accompanying drawings, in which:
Figure 1 is a cross-sectional view of a portion of a carburetor embodying the invention;
Figures 2, 3 and 4 are side elevational viewsO on an enlarged scale, with parts broken away and in section~ ~f portions of the Figure 1 showing taken on planes indicated by and viewed in the direction of the arrows 2-2, 3-3 and 4-4, respectively, of Figure l; and ~ :

~ '~

; `~.

IO ~3~ 5 1 I Figure 5 is a to~ plan view of a detail of Figure 4

2 viewed in the direction of the arrows 5-5 of Figure 4.

3 Figure 1 is o~tained by passing a plane through ap-

4 proximately one-half of a known type of two-barrel, downdraft carburetor 10. It includes an air horn section 12 secured to a 6 main body portion 14, and a throttle body 16. The throttle body 7 is mounted over an intaXe manifold indicated partially at 18 8 leading to the engine combustion chambers.
9 Main body portion 14 contains the usual air/fuel mix-ture induction passages 20 having fresh air intakes at the air 11 horn ends, and connected to manifold 18 at the opposite ends.
12 The passages are each formed with a main venturi section 22 in 13 which is suitably mounted a boost venturi 24.
14 Air flow into passages 20 is controlled by a choke valve 28 that is unbalance mounted on a shaft 30. The choke 16 valve thus may fall open by gravity or be urged to an open 17 position by air flow against it. Shaft 30 is rotatably mounted 18 in side portions of the carburetor air horn, as shown. Flow of 19 the usual fuel and air mi~ture through each passage 20 is con-trolled by a conventional throttle valve 36 fixed on a shaft 38 21 rotatably mounted in the throttle body 16. The throttle valves 22 are rotated in the usual manner by depression of the conventional 23 vehicle accelerator pedal. They move from the idle speed or 24 essentially closed positions sho~n to wide open positions es-sentially at right an~les to that shown.
26 Choke valve 28 rotates from the closed position shown 27 in Figures 1 and 2 to a nearly vertical, wide open, essentially 28 inoperative position. In this latter position, the choke valve 29 provides a minimum obstruction to airflow. The rotative position ~ of choke valve 28 is controlled in part by a thermostatically 3~
,1 1 ¦¦ controlled mechanical operating mechanism 40 located on one side 2 ~ of the carburetor. The latter includes a hollow choke housing 3 ¦ ~ortion 42 that is bolted, by means not shown, to cast extensions 4 1 of the car~uretor main body portion 14. The housing is apertured S ¦ for rotatably supporting one end of a choke valve control shaft 6 ¦ 44, the other end fixedly mounting a bellcrank-t~pe lever 46 (see 7 ! Figure 3). The latter is pivotally connected by a link 48 to a 8 lever 50 fixed on. choke valve shaft 30.
9 It should be noted that lever 46 and link ~8 are inter-lG connected by a lost motion means (Figures 2 and 3) consisting of 11 the right angled end 52 of link 48 constituting a pin engagable 12 in an elongated slot 54 formed in lever 46. It will be clear 13 that rotation of shaft ~4 in either direction as seen in Figures 14 2 and 3 will rotate choke valve 28 in a corresponding direction.
lS This will open or close the carburetor air intake, as the case 16 may be, once the pin end 52 has moved to one or the other end of 17 slot 54, as the case may be. The purpose of this arrangement 18 will become clearer later.
19 The end of shaft 44 that projects into housing 42 has fixed on it ~he body portion 56 of a thermostatic spring 21 lever 58. The lever has one portion 60 that projects outwardly 22 at right angles and through a slot 62 in an insulating gasket 64.
23 It has a bifurcated end that engages the end 66 of a thermosta-24 tically responsive, bimetallic, coiled spring element 68. The inner end portion of the coiled spring is fixedly secured on the ¦
26 end of a nipple 70 formed as an integral part of a choke cap 72 27 of heat insulating material.
28 The thermostatic spring element 68 will expand as a 29 function of changes in temperature of the air in the cham~er 76 ¦ defined within cap 72 and housing 42. Accordingly, changes in 31 ¦ temperature from the normal engine operating level will circum-32 l ferentially move end 66 of spring lever 58 to rotate shaf-t 44 .~ . .

1 ¦ and lever 58 in one or tne other directions, as the case may be.
2 ¦ The force of bimetallic spriny 68 is chosen such that at the nor-3 1 mal engine operating temperature, the circumferential movement 4 ¦ of the spring will have moved the choke valve 28 to a wide open S vertical position. Decreases to levels below the normal tem-6 perature will progressively increase the biasing force on the 7 choke valve in a closing direction.
8 As seen in Figure 2, opposing the force of spring 68 9 is a modulating tension spring 76. It is hooked at its upper end to an extension 78 of spring lever 58 and anchored at its 11 opposite end to an adjustable screw 80. The force of modulating 12 spring 76 is chosen such that at temperature levels between 13 60-F and lOO-F, the spring force will exceed the torque or 14 closing biasing force of thermostatic spring 68. The position at lS which thermostatic spring 68 and tension spring 76 are in equili-16 brium will determine the position of spring lever 58.
17 As shown in Figure 2, the thermostatic spring normally 18 biases lever 58 against an adjustable stop 82. The latter deter-19 mines the cold engine minimum pulldown or engine running position of choke valve 28. That is, the coldest position of the end 66 21 of thermostatic spring 68 will position an extension 84 of spring 22 lever 58 against stop 82, and locate lever 46 as shown. The most 23 the choke valve 28 then can open is to fall by gravity or be 24 moved by airflow against it to move the pin end 52 of link 48 upwardly to the top of slot 54. As the temperature rises to 26 above 65-F, however, the modulating force of tension spring 76 27 causes the levers 58 and 46 to be moved clockwise to new equili-28 brium positions, as stated above, which increases the choke pull-29 down for choke valve 28. Thus, it allows the choke valve to have 3o a greater opening that is more in line with the leaner air/fuel 1 l~ ratio the warmer temperature level is calling for to maintain 2 1I the engine running.
3 ! At some warm engin~e temperature level around lOO~F, 4 ¦ for example, th~ force equilibrium between springs 68 and 76 will be such as to permit spring 76 to retract to its dead 6 height, and thereafter have no effect on the decreasing closing 7 force of thermostatic spring 68. The adjustability o-f screw 80 8 will determine the amount of modulating force applied to thermo-9 static spring 68, and also the temperature range over which the modulation will occur.
11 During cold engine operation, it is necessary to open 12 throttle valves 36 from their normal, essentially closed idle 13 speed positions to allow enough extra air/fuel mixture into the 14 engine to prevent it from stalling due to the extra friction, greater viscosity of the lubricant, etc. Then as the engine 16 ¦ warms, it is desirable to progressively close the throttle 17 valves to the idle speed positions to reduce engine speed. As 18 best seen in Figures 1 and 3, a fast idle cam 86 is rotatably 19 mounted on a shaft ~8. The cam has a lever 90 projecting from one side that is pivotally connected by a link 92 to a second 21 lever 94. The latter is rotatably mounted on shaft 44 and 22 adjustably mounts a screw 96. The screw has a one-way engage-23 ¦ ment with a finger or right angle tab 98 that is integral with 24 and projects laterally from choke lever 46. The weiyht and location of lever 94, link 92, lever 90 and fast idle cam 86 is 26 such that the cam will always fall by gravity in a clockwise 27 direction so that screw 96 will follow the movement of ta~ 98 28 of lever 46. This will effect rotation of the fast idle cam 29 clockwise ox counterclockwise progressively as the temperature of thermostatic spring 64 increases or decreases, respectively.

- . . . . ~.,.. ,. ~

I
~8~36S

1 ~ The o2posite side of fast idle cam 86 is formed with 2 ¦ an edge 100 having in this case, three circumferentially conti-3 ! guous steps, a high cam step 102 and lower cam steps 104 and 4 1 106. Each step in counterclockwise circumferential succession S is defined by a face that is of less radial extent from the axis ¦
6 ~ of rotation 108 of the cam than the previous one, 'che lower step ¦
7 1 106 being followed by an opening 110. The steps and opening 8 ~ constitute abutments or stops in the path of movement of a screw ¦
9 ¦ 112. The latter is adjustably mounted on a lever 114 fixed on l throttle shaft 38. The radial depth of opening 110 is chosen 11 such that when the fast idle cam is rotated to pexmit movement 12 of screw 112 into the opening 110, throttle valves 36 then will 13 be permitted to rotate to their normal engine operating tempera-14 ture level idle speed positions essentially closing the induction passages. Engagement of the screw 112 with each of the steps 16 106, 104 and 102 as the cam is rotated counterclockwise upon 17 temperature decreases then will progressively locate the idle 18 speed position of the throttle valves at more open positions.
19 The fast idle cam is repositioned for a cold start to its fastest idle speed position by depressing the conventional 21 accelerator pedal to open the throttle valves to move the abut-22 ment screw 112 away from the face of cam 36. That is, even 23 though the engine temperature may decrease to a level calling 24 for counterclockwise rotation of fast idle cam 86 by the thermo- I
static spring 68, if screw 112 engages steps 104 or 106, the 26 frictional resistance between the two prevents rotation of the 2 7 cam.
28 A kickdown operation of a warm engine is also provided.l 29 Depressing the conventional accelerator pedal to the floor rotates '':'' ~ ' . , 1 the throttle valve shaft 38 a ma~cimum amount. Fixed on the 2 throttle shaft is an actuator 116 which when rotated engages a 3 pin 118 projecting from the fast idle cam 86. The movement of 4 the pin moves the fast idle cam and through links and levers 90, 92, 94, 46, ~8 and 59 opens c:hoke valve 28 to relieve the 6 flooded or rich mixture stall condition by leaning the mixture.
7 The choke valve usually is positioned essentially 8 closed for cold engine starts. This lessens airflow and in-9 creases the vacuum fuel metering signal to draw in enough extxa fuel to provide sufficient vapor for starting the engine. Once 11 the engine fires, however, the throttle plates must be open 12 enough to permit the engine to draw in enough fuel and air to 13 raise the engine cranking speed of say 100 r,p.m. to a 1,000 14 r.p.m. fast idle speed that will sustain engine operation. Once the engine running operation is attained, then the overrich 16 starting mixture no longer is required and it becomes desira~le 17 to reduce both the choke valve and throttle plate openings to 18 lower settings, but still ones that provide a richer setting 19 than that which provides the normal idle speed when the engine has warmed up.
21 ~he position of the throttle valve, therefore, is 22 important. The more it i5 crac~ed open from the closed position 23 during engine cranking operations, the greater the volwne of 24 air and fue} inducted. Therefore, for englne starts, the throttl~ , valve stop screw 112 is scheduled to be located against the high 26 step 102 of fast idle cam 86 to provide the richest cranking 27 air/fuel mixture. Once the engine has started, however, then 28 the throttle valves are automaticall~ closed do~m b~ a small 29 amount that will reduce the airflow and consequentlv the engine 108436~

1 idling speed, without disengaging the throttle valve stop or 2 abutment from the high step of the fast idle cam.
3 More particularly, the fas-t idle cam is eccentrically 4 secured on the end of a shaft 120 rotatably mounted in the car buretor body and having an axis of rotation 122. Secured to the 6 opposite end of shaft 120 is a lever 124 that is pivotally con-7 nected to a manifold vacuum actuated servo 126.
8 The servo 126 consists of a hollow two-piece housing 9 128 between which is edge mounted an annular flexible diaphragm 130. A pair of retainers 132 are riveted to the diaphragm and 11 to the cup shaped housing 134 of a flexible connector assembly.
12 Slidable within housing 134 is an actuating rod 136, the base 13 of which is formed as a seat for a spring 138. The opposite 14 end seats against a retaining ring 140. Rod 136 is screwed to an adaptor 142 that is pivotally connected to lever 124.
16 Servo diaphragm 130 divides housing 128 into an air 17 chamber 144 and a vacuum chamber 146. Air at ambient pressure 18 communicates with chamber 144 through the opening 148. A tube 19 150 connects engine manifold vacuum from any suitable source to vacuum chamber 146. A spring 152 normally urges diaphragm 130 21 and thus the fast idle cam 86 to the positions shown.
22 In brief, when the engine starts, manifold vacuum is 23 communicated to the vacuum side of diaphragm 130 via tube 150.
24 As diaphragm 130 strokes leftwardly, compressing s~ring 152, lever 124 is rotated about center 122. Fast idle cam 86, having 26 its center of rotation at point 108 on shaft 88, moves right 27 wardly as diaphragm 130 strokes leftwardly. Due to throttle re-28 turn cable and other throttle closing forces, screw 112 is held 29 in contact with and follows the rightward movement of fast idle cam 86. This closes down the throttle valves. Therefore, by 108~365 1 ¦ using a diaphragm motor to eccentrically reposition the fast 2 ¦ idle cam, automatic and gradual speed decay is achieved.
3 ! Adjustment of rod ]36 qualifies the diaphragm assembly 4 1 to the eccentric lever 124. Adjustment of screw 112 determines S the cranking throttle angle, and also the engine run-up speed 6 that will occur before manifold vacuum is realized by diaphra~m 7 130. By employing delay restrictors, not shown, between mani-8 fold vacuum tube 150 and diaphragm 130, the elapsed time for 9 automatic speed decay can be varied to suit any calibration.
Adjustment of stop screw 154 sets the stroke of diaphragm 130 11 and the subsequent speed to which the engine will run down after 12 start-up. If adjusting screw 112 is in contact with any step on 13 cam 86, the initial run-up speed will be higher than the after 14 automatically reduced speed established by the step radius. If adjusting screw 112 is not in contact with fast idle cam 86, 16 the idle speed will be as determined by the conventional throttle 17 anti-dieseling solenoid or idle speed adjusting screw, not shown.
18 As sta~ed previously, the start of a cold engine 19 requires a richer mixture than that of a warmed engine because ¦ less fuel is vaporized. Therefore, the choke valve must be 21 shut or nearly shut to restrict air rlow and increase the 22 pressure drop across the fuel inlet to draw in more fuel and 23 less air. Once the engine does start, however, then the choke 24- valve should be opened slightly to lean the mixture to prevent 1 engine flooding as a result of an excess of fuel.
26 The mechanisms shown in Figures 4 and 5 and indicated -27 partially on the left hand side of the carburetor in Figure 1 28 accomplish this objective.
29 The choke valve shaft 30 has a lever 156 fixed to it for cooperation with the right angled tab end 158 of an actuating ~ 3~

1 ¦ lever 160. Lever 160 s pivoted on a shaft 162 mounted on a 2 pedestal 164. A return spring 166 is hooked against one arm 3 portion 168 of lever 160, th~e opposite end 170 of the spring 4 being anchored in the choke housing. Spring 166 urges lever 160 downwardly out of engagement with choke shaft levar 156 to 6 permit the choke valve 28 to fall open by gravit~ or he forced 7 open by the air load or air flow against it, to a position as 8 dictated b~ the pulldown mechanism descri~ed in connection with 9 Figure 2.
The choke valve 28 is forcea~ly closed during engine 11 starts, i.e., the cranking cycle, by a conventional solenoid 12 172. The latter is adjustably mounted on the carburetor air 13 horn 12 and has a slidable armature 174. The armature is con-14 nected by an extending spring 176 to arm 168 of lever 160.
The solenoid is wired by a lead 178 to the engine ignition or 16 starting circuit, not shown, so that it will be energized when-17 ever the ignition switch is turned to the start position and 18 deenergized when the ignition st~itch is released to the engine 19 running position.
With the ignition switch in the start position, 21 solenoid 172 pulls in extending spring 176 and actuating lever 22 160. When rotated a~out pivot 162, the ta~ end 158 of lever 23 160 contacts lever 156~ as seen in dotted lines, closing choke 24 valve 28. In order to achieve engine speed run-up, spring 176 extends against the air load on choke valve 28. At this point, 26 the driver realizes the engine is running and he releases the 27 ignition switch. With a hold-in force no longer applied at 28 solenoid 172, spring 170 returns lever 160 to its deenergized 29 position so that the choke valve 28 can rotate freel~ as the engine warms up.

10t3~365 1 ¦ For starts in ambient temperatures above lOO-F, the 2 thermostatic spring 68 will have positioned choke valve 28, and 3 likewise lever 156 to the fu:Ll line position shown so that when 4 solenoid 172 is energized, the end of lever 160 no longer will contact lever 156, and the choke valve will remain open.
6 In overall operation, except for Figure 4, the parts 7 are shown in the positions they attain when the engine is 8 conditioned for a start or cranking operation below lOO~F. As 9 seen in dotted lines in Figure 4, when the engine ignition switch is turned to the on or start position, solenoid 172 is 11 energized and pulls down on extending spriny 176. This moves 12 the actuating lever 160 up against the edge of lever 156 and 13 positively closes the choke valve. At t~e same time, as seen 14 in Figure 2, the thermostatic spring 68 has pushed lever 58 against the minimum stop 82, which predetermines the minimum 16 pulldown opening of the choke valve. As soon as the driver 17 realizes that the engine is running, he releases the ignition 18 switch which then deenergizes solenoid 172 and allows choke 19 valve 28 to drop by gravity and the air load against it. As 1 seen in Figures 2 and 3, the choke lever link 48 is free to 21 move within slot 54 of lever 46 so that the degree of opening 22 is determined by the position of lever 46 and lever 58. Ac-23 cordingly, the choke valve will move to a slightly cracked 24 open position which allows more air to enter the carburetor to ¦ lean out the previously rich starting mixture.
26 Simultaneously, as seen in Figure 3, rotation of 27 thermostatic spring 68 in the choke valve closing direction 28 locates the lever 46 as shown thereby moving the fast idle cam 29 linkage 94, 92 and 90 to its counterclockwisemost position 1 shown. Upon depression of the conventional accelerator pedal, l -12-... ~ ..
.

153~34365 1 ¦¦ the throttle valve shaft 30 rotates to release fast idle screw 2 ¦ 112 from engagement with the fast idle cam face 100, thereby 3 1 permitting the fast idle cam to be moved to the position shown 4 ¦ aligning the high step 102 with screw 112. No vacuum exists in tube 150 so that servo 126 is in the position shown eccentrically rotating the fast idle cam axis 108 clockwise about the axis 122 of lever 124. This locates the fast idle cam leftwardly its 8 maximum amount so that the throttle lever screw 112 causes the 9 throttle valves 36 to be opened the maximum amount desired for a cold engine start.
11 Assume now that the engine has ired. The firing 12 vacuum is still insufficient to move servo 126 so that the 13 throttle valves remain in the positions indicated in Figure 3.
14 As soon as the engine reaches sustained operation, however, the manifold vacuum present in tube lS0 moves diaphragm 130 leftward-16 ly to pivot lever 124 about its axis 122. This simultaneously 17 moves the eccentrically mounted fast idle cam 86 counterclock-18 wise about the axis 122 as seen in Figure 3O In effect, the fast 19 idle cam moves rightwardly, with the throttle lever screw 112 remaining in contact with the high step face 102 to slightly 21 close down the throttle valves by an increment that decreases 22 the air flow through the carburetor and thus reduces the fast idle 23 speed of the engine. From this point forward, so long as the 24 ! engine remains running, all fast idle action will occur as a result of pivotal movement of the fast idle cam 86 about its 26 axis 108 rather than a lateral movement of the cam.
27 As the engine warms, the end 66 of thermostatic spring 28 68 will move arcuately or circumferentially clockwise so as to-29 gether with the force of modulating spring 76 rotate levers 58 and 46 clockwise to progressively open the choke valve wider.

l ~ 3'13~5i 1 At the same time, as seen in Figure 3, the clockwise rot~tion 2 of lever 46 permits the fast idle cam linkage to follow and ac-3 cordingl~ rotate the fast idle cam clockwise. This will progres-4 sively present the lesser radial extent steps 104, 106 and finally opening 110 for engagement with throttle lever screw 6 112. This will progressively decrease the throttle valve open-7 ings until the screw finally engages in recess 110 of the fast 8 idle cam, at which point the throttle valves will have closed to 9 their engine normal operating temperature idle speed positions essentially closing the induction passage. Similarly, if the 11 temperature should decrease, the force of the thermostatic spring 12 68, as modulated by spring 76, exerts a closing force on the 13 choke valve 28 and fast idle cam 86 by urging the levers 46 and 14 58 in a counterclockwise direction to gradually close the choke valve and also reposition the fast idle cam towards its high cam 16 step 102 setting upon disengaging of the screw 112 from the cam 17 face engaged and reengagement with step 102.
18 It should be understood that during all engine opera-19 tions, the air load on the choke valve will normally cause the link 48 and pin 52 to be located at the upper edge of the slot 21 54 in lever 46. Therefore, regardless of whether the lever is 22 moving clockwise or counterclockwise, the air load on ~he choke 23 valve will maintain the end 52 in the position indicated.
24 An additional feature provided by the construction is to provide a maintained fast idle speed position of the 26 throttle valve for a period of time even though the choke valve 27 is rotated to its wide open position. This permits larger 28 volume air flow at temperature levels which in a conventional 29 carburetor would close down the throttle valves to their normal : . ~ : , . .

1S)t3~3~;5 1 idle speed position. When tllermostatic spring 68 has rotated 2 levers 46 and 58 to a position where choke valve 28 is positioned 3 in the vertical or wide open position, ~ast idle throttle lever 4 screw 112 will still be in a position engaging the lower cam step 106, thus ~roviding additional fast idle air flow. Fur-6 ther rotation of lever 46 by tlle t~ermostatic spring 68 is per-7 mitted by the end 52 of the choke lever link 48 moving the length of the slot 54 from top to bottom. This small movement, 9 which amounts to appro~imately 14-, is sufficient to permit the fast idle cam to rotate to a position wherein the screw 112 will 11 then align with the opening 110 and finally permit tlle throttle 12 valves to close to their engine normal idle close positions.
13 Upon engine shutdown, the parts will take the positions 14 determined by the thermostatic spring 68 and modulating spring 76. The fast idle cam 86 will be repositioned according to the 16 position of the springs, and will be eccentrically rotated clock-17 wise about the axis of rotation 122 by the servo spring 152, to 18 reposition the throttle valve screw 112 for an opening of the 19 throttle valves in porportion to that called for by the position of the thermostatic spring 68 and modulating spring 76.
21 It will be understood that the starting o. the engine 22 under conditions that are warmer than the coldest conditions 23 described will locate the choke valve 28 and fast idle cam 86 24 for greater choke openings and less engine speeds, respectively, in proportion to the richness of the air/fuel ratio and engine 26 speed called for by that particular temperature level. That is, 27 as the engine warms, the air/fuel ratio will become progres-28 sively leaner for starting purposes, and the engine speed need 29 be less since the friction and viscosity of the lubricant, etc., is correspondingly less.

,. .

10~34365 1 From the foregolngl it will be seen that a carburetor 2 has been described that provides a choke plate pull-close 3 solenoid for starting purposes, improved pull-down modulation, 4 an eccentrically mounted fast: idle cam for automatic gradual S speed reduction after engine startup, and continued fast idle 6 cam operation subsequent to choke valve inoperativeness.
7 While the invention has been shown and descri~ed in 8 its preferred embodiment, it will be clear to those skilled in 9 the arts to which it pertains, that many changes and modifica-tions may be made thereto without departing from the scope of 11 the invention.

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A carburetor having an air/fuel induction passage open at one end to air at essentially atmospheric pressure and connected at its opposite engine end to an engine intake manifold to he subject to the changing vacuum levels therein, the one end having a choke valve unbalance mounted for a rotatable movement by gravity and airflow thereagainst across the one end between a closed position and a wide open inoper-ative position wherein the choke valve is inoperative to restrict the flow of air into the passage, and a throttle valve secured on a shaft rotatably mounted posterior of the choke valve for movement of the throttle valve across the passage between an engine normal operating temperature level essentially closed engine idle speed position and beyond towards a wide open throttle position to control the volume of flow of an air/fuel mixture through the passage as a func-tion of the position of the throttle valve, the control comprising means operable during engine operations below the normal operating temperature to provide a controlled posi-tioning of the throttle valve relative to the position of the choke valve, to improve emissions while minimizing engine stalling, the last mentioned means including throttle valve abutment means secured to the throttle valve shaft, a second shaft, a fast idle cam rotatably mounted on the second shaft and having an edge formed with a number of circumferentially contiguous steps progressively decreasing in radial extent to one which when aligned with the abutment means permits closure of the throttle valve to the normal engine idle speed position, whereby the throttle valve will be progressively opened beyond the latter position as a function of the particular step engaged by the abutment means, spring means biasing the abutment means and throttle valve towards a closed position and into individual engagement with one of the steps, a thermostatically responsive coiled spring opera-tively effecting the rotation of the fast idle cam to posi-tions operatively moving the throttle valve to positions pro-gressively more open than the normal idle speed position as a function of decreases in temperature from a predetermined level, first lever means operatively connected to the choke valve, linkage means connected to the first means, and lost motion means providing a limited interconnection between the fast idle cam and linkage means permitting a limited opening of the choke valve and operation of the fast idle cam indepen-dent of each other.

2. A carburetor as in claim 1, including a second lever operatively connected to the linkage means and having a portion extending into the path of rotative movement of the fast idle cam towards a position positioning the throttle valve to the normal idle speed position, the fast idle cam being rotatable by gravity against the lever portion upon disengagement of the abutment means with a fast idle cam step, the lost motion means connecting the linkage means and second lever and comprising a pin and slot type connection.

3. A carburetor as in claim 2, the lost motion means permitting the fast idle cam to be rotated from a first posi-tion engaged with a step on the cam while the choke valve is in wide open position to a second position out of engagement with the abutment means while the choke valve is still main-tained in a wide open position.