Automatic choke actuator for small engines

United States Patent

111] 3,578,293

<td> [72]</td><td> Inventor</td><td> John D. Santi West Allis, Wis.</td>

<td> [21]</td><td> Appl. No.</td><td> 781,940</td>

<td> [22]</td><td> Filed</td><td> Dec. 6,1968</td>

<td> [45]</td><td> Patented</td><td> May 11,1971</td>

<td> [73]</td><td> Assignee</td><td> Briggs &amp; Stratton Corporation Wauwatosa, Wis.</td>

<td> 1,995,452</td><td> 3/1935</td><td> Harbison.................</td><td> ..... 261/64( .4)X</td>

<td> 2,979,047</td><td> 4/1961</td><td> Rapplean et al.........</td><td> ..... 261/39( ,2)X</td>

<td> 3,181,843</td><td> 5/1965</td><td> Brown et al..............</td><td> ..... (261/DCIV)</td>

<td> 3,190,623</td><td> 6/1965</td><td> Ball.........................</td><td> 261/39(.2)</td>

<td> 3,284,063</td><td> 11/1966</td><td> Bichhaus et al..........</td><td> ..... 261/39(.2)X</td>

Primary Examiner—TimR. Miles Attorney—Ira Milton Jones

[54] AUTOMATIC CHOKE ACTUATOR FOR SMALL ENGINES

Claims, 3 Drawing Figs.

[52] US. Cl....................................................... 261/64

[51] Int.CI......................................................... F02m 1/14

[50] Field of Search............................................ 261/64.4,

64, (DCIV), 39.2

[56] References Cited

UNITED STATES PATENTS

1,969,358 8/1934 Coffelder..................... 261/64(.4)

ABSTRACT: In an automatic choke actuator wherein the choke is spring-biased toward closed position and is opened by suction in a suction chamber acting on a pressure responsive actuator linked to the choke, the suction chamber is communicated with the fuel induction zone of the carburetor induction passage through a duct controlled by a pressure responsive throttling valve opened opened by suction in the induction passage and which closes to restrict flow of air back into the suction chamber.

<img file="US3578293A_D0001.tif" />

Patented May 11, 1971

3,578,293

<img file="US3578293A_D0002.tif" />

3,578,293

2

AUTOMATIC CHOKE ACTUATOR FOR SMALL ENGINES

This invention relates to automatic choke actuators for the carburetors of small internal combustion engines, and more particularly to automatic choke actuators of the general type disclosed in the pending patent application of Joseph V. Reichenbach, Ser. No. 667,032, now abandoned, for “Carburetor for Small Internal Combustion Engine having Automatic Choke Actuator.”

In the carburetor of the Reichenbach application, the choke valve is biased toward a closed position by means of a spring, and is moved toward its open position by suction acting on a pressure responsive actuator that is connected with the choke valve through a simple linkage. The actuator comprises a diaphragm or membrane which overlies the open top of a welllike suction chamber and closes and seals the same. The upper side of the diaphragm is exposed to air at atmospheric pressure. When the engine is running, the suction chamber at the underside of the diaphragm is normally at subatmospheric pressure because air is then drawn out of the suction chamber through a restricted duct which communicates the suction chamber with a zone of the carburetor induction passage at which fuel is inducted thereinto. The spring that biases the choke valve toward its closed position is located in the suction chamber and reacts upwardly against the diaphragm. Suction in the suction chamber of course offsets the bias of the spring, to effect opening of the choke valve.

The apparatus just described has proven to be highly satisfactory for many small engines, and especially on those used for power lawn mowers. However, on engines used for some types of installations, and particularly on those employed for driving high inertia loads (e.g., certain pumps and generators) some difficulty was experienced with that choke mechanism in achieving satisfactory acceleration of the engine through a range of speeds just above the lowest operating speed.

The present invention is based upon the discovery that the cause of the difficulty presented by the above-described automatic choke actuating mechanism resided in the restricted duct communicating the suction chamber with the induction passage.

When an engine having such an automatic choke was manually cranked, the suction manifested in the suction chamber was low enough to allow the biasing spring to maintain the choke in its substantially closed position, as Was desired. But when the engine began to run, and picked up speed to just above its minimum running r.p.m, the suction in the suction chamber should have increased in step with increasing suction in the induction passage, in order for the choke valve to open just the right amount to maintain a substantially constant suction at the fuel jet and thus assure maintenance of the desired fuel-air mixture ratio: Instead, however, the opening of the choke valve lagged the development of suction in the induction passage, and the mixture became so rich that the engine could not accelerate satisfactorily under any substantial load.

To understand why this delayed opening of the choke valve was caused by the substantially constant restriction to airflow through the duct communicating the suction chamber with the induction passage it should be observed that suction is manifested in the induction passage of the carburetor of a single-cylinder four-cycle engine only during the intake stroke. During the remaining three strokes of the engine cycle the pressure in the induction passage tends to rise back to the value of ambient atmospheric pressure, even when the choke valve is closed. Hence, with the above-described automatic choke arrangement, air was drawn out of the suction chamber during each intake stroke and bled back into it during the remainder of the engine cycle.

Because the duct communicating the suction chamber with the induction passage was necessarily a restricted one, the pressure in the suction chamber during the first intake stroke after the engine started running was not brought all the way down to the value of the pressure in the induction passage, and it began to rise again at the termination of the intake stroke and continued to rise through the remainder of the engine cycle. Not until the engine had run for a few cycles did pressure in the suction chamber accurately correspond to the pressure in the induction passage during the intake stroke.

As a result of the circumstances just described, the opening of the choke valve was always too little and too late, until such time as the engine had accelerated to a speed at which suction in the induction passage became great enough to maintain the choke valve substantially wide open. With the choke thus closed a little too much, the mixture was excessively rich, and during the time that the engine was running with such a mixture it had low torque.

As indicated above, an engine having a low inertia load like a rotary mower blade could successfully accelerate through the low speed range in which opening of the choke valve in effect lagged the development of suction in the induction passage, and it could readily get into the higher speed range at which sufficient suction was developed in the induction passage (and hence in the suction chamber) to effect opening of the choke valve substantially all the way, to where the engine ran with its normal operating mixture ratio. But if an engine having such an automatic choke device was driving a high inertia load, it had very low torque at its lowest speeds, due to the excessively rich mixture resulting from lagging actuation of the choke to its open position, and it would therefore accelerate only very slowly, if at all.

With the foregoing considerations in mind, it is a general object of the present invention to provide a very simple and inexpensive improvement in automatic choke mechanisms of the above-described character, whereby the choke valve is rendered accurately responsive to suction conditions in the induction passage of the carburetor at all speeds of the engine crankshaft.

More particularly, it is an object of this invention to provide means for maintaining in the suction chamber of an automatic choke actuator of the character described a pressure throughout each engine cycle which closely corresponds to the pressure in the induction passage during the intake stroke of the cycle, so that the position of the choke valve during starting and slow speed running will always be such aS to maintain such suction in the induction passage as will assure the desired fuel-air mixture ratio.

Thus is another general object of this invention to provide a very simple and inexpensive improvement in automatic choke control mechanisms of the character described whereby an engine equipped with such a mechanism is enabled to accelerate smoothly and rapidly from its lowest running speed, regardless of the nature of the load on the engine.

With these observations and objects in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying draw55 ing. This disclosure is intended merely to exemplify the invention. The invention is not limited to the particular structure or method disclosed, and changes can be made therein which lie within the scope of the appended claims without departing from the invention.

The drawing illustrates one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

FIG. 1 is a view in elevation, with portions broken away, of a 65 carburetor equipped with an automatic choke actuator embodying the principles of this invention;

FIG. 2 is a fragmentary vertical sectional view of the choke control mechanism of this invention shown under conditions where little or no stiction exists in the carburetor mixing 70 passage; and

FIG. 3 is a view generally similar to FIG. 2 but illustrating the condition during the intake stroke of an engine on which the carburetor is installed.

Referring now to the accompanying drawing, the numeral 5 75 designates generally the body of a carburetor for a single

3,578,293 cylinder internal combustion engine, in which there is a choke valve 6 that is moved to and from a closed position by means of an automatic choke mechanism which is designated generally by 7 and which embodies the principles of this invention. The choke valve 6 is located in the mixing or induction passage 8 of the carburetor, upstream from the fuel induction zone 9 of the induction passage where the conventional throttle butterfly 10 is situated.

In general the automatic choke actuating mechanism 7 comprises a pressure responsive actuator 11, a rodlike link 12 which connects the actuator 11 with an eccentric arm 13 on the shaft 14 of the choke valve, and a spring 15 which biases the choke valve toward its closed position.

Although it could as well comprise a piston or a bellows, the actuator 11 is shown as a diaphragm, comprising a part of a membrane 16 that serves as a gasket between the underside of the carburetor body 5 and the top wall of a fuel tank 17 that is supported by the carburetor body. Where the actuator 11 comprises a part of a membrane, as here illustrated, other parts of the membrane can of course perform other functions. For example, as disclosed in the aforesaid Reichenbach application, certain portions of the membrane can provide the diaphragm and flapper valves of a fuel pump (not shown).

As here illustrated, the fuel tank 17 has its top wall formed to provide an upwardly opening well 18, and the actuator 11 overlies the mouth of said well and closes it to define a suction chamber 19. There is a hole 20 in the carburetor body, directly above the actuator, through which the link 12 extends with a substantial clearance, and therefore the upper surface of the actuator is exposed to air at atmospheric pressure. When the engine is running, there is a substantial suction in the suction chamber 19, by reason of the provision of means described hereinafter by which the suction chamber is communicated with the fuel induction zone 9 of the induction passage 8. Such suction in the suction chamber draws the actuator 11 downwardly, against the bias of the spring 15, and thus tends to swing the choke valve toward its open position.

The spring 15 is a coiled expansion spring which, as shown, is received in the suction chamber 19 and reacts between the bottom of the well 18 that defines said chamber and the underside of the actuator. Where the actuator comprises a diaphragm of rubber or the like, it preferably has a reinforcing disc 21 overlying at least its bottom surface, to receive the thrust of the spring and carry it into the link 12. Desirably there is also a reinforcing disc 22 overlying the upper surface of the diaphragm, and the two disc 21 and 22 can be flatwise clamped into sealing relationship with the membrane by means of a fitting 23 that is secured to the lower end of the link and extends through aligned closely fitting holes in the diaphragm and the two discs.

The suction chamber 19 beneath the actuator is communicated with the fuel induction zone 9 of the carburetor induction passage by means of a communicating passage or duct 24 in which there is a pressure responsive throttling valve element 25. The portion of the duct 24 that opens directly to the suction chamber 19 is defined by a pair of intersecting bores in the top wall structure of the fuel tank, one of them, designated by 26, being substantially horizontal and opening substantially radially from the suction chamber, and the other, designated by 27, being vertical and opening upwardly into a counterbore 28 which in turn opens to the flat top surface of the fuel tank. The junction of the vertical bore 27 with the counterbore 28 defines an upwardly facing seat for the pressure responsive valve element 25, which in this case is shown as a poppet having a stem 29. For guidance of the poppet 25 in its up and down motion, its stem 29 is received in a well or blind bore 30 that is smaller in diameter than the bore 27 and extends coaxially downwardly therefrom.

Other portions of the duct 24 are formed in the carburetor body 5, including a vertical bore portion 31 which aligns with the counterbore 28 and is communicated therewith through a hole in the membrane 16. As disclosed in the above-identified Reichenbach application, the segment of the duct 24 that is in the carburetor body can have a portion 32 which is at a level above the bottom surface of the fuel induction zone 9 of the induction passage 8, to prevent any spit back fuel from getting into the suction chamber 19.

To insure a relatively free flow of air past the valve element 25 when it is off of its seat, its head has a substantially smaller diameter than the counterbore 28 in which it is received, and it has a plurality of tits 33 on top of its head that engage the underside of the membrane 16, around the hole therein. Thus air can flow around and over the head of the valve in passing from the bore 27 to the bore 31.

It will be apparent that the pressure responsive valve element 25 opens when pressure in the fuel induction zone 9 of the induction passage 8 is lower than that in the suction chamber 19 and closes when pressure in the suction chamber exceeds that in the induction zone. Stated another way, the valve 25 opens to permit evacuation of the suction chamber during the intake stroke and closes to prevent air from entering the suction chamber during the remainder of the engine cycle.

However, some bleeding of air back into the suction chamber 19 must always be permitted, for otherwise the choke valve would remain open at times when it should be closed; and therefore the valve element 25 performs a throttling function, merely restricting the duct 24 when· it is in its seated position. To enable air to bleed back into the suction chamber, there is a duct portion 34 in bypass relation to the pressure responsive valve element. One manner of affording such a bypass is to provide the top wall 16 of the fuel tank with a narrow and shallow groove 34 in its upper surface, extending from the mouth of the well 18 that defines the suction chamber 19 to the mouth of the counterbore 28. The groove 34 can be formed by means of a coining tool, and to assure against closure of the end thereof that opens to the well 18, that end of the groove may be extended down into the side wall of the well.

Because the valve element opens to permit substantially free flow of air out of the suction chamber and closes to restrict flow of air back into it, suction in the fuel induction zone 9 will be promptly manifested in the suction chamber, and the pressure in the suction chamber throughout each engine cycle will correspond closely to pressure in the fuel induction zone during the intake stroke of that cycle. Hence the choke valve 6 will be accurately positioned in accordance with suction conditions in the induction passage, with no delay in its opening motion as the engine accelerates through its lowest range of speeds.

Because the duct 24 is substantially unrestricted when the throttling valve 25 of this invention is open, pressures in the suction chamber 19 during engine operation will normally be much lower than they would be if the duct 24 had a fixed restriction, as in the prior device of the Reichenbach application. It is therefore necessary that the spring 15 be substantially stronger than it would be if the passage 24 had a fixed restriction. However, as in the prior mechanism, the spring should have a relatively flat springing rate, that is, it should respond with a relatively large expansion or contraction to a small change in applied force, so that it will effect the desired actuation of the choke valve in accordance with the relatively small changes in pressure that occur in the induction passage through the speed range of the engine.

From the foregoing description taken with the accompanying drawings it will be apparent that this invention provides a simple and very inexpensive improvement in suction actuated automatic choke control mechanisms for small single-cylinder engines, whereby acceleration of the engine through its lowest speed range is materially improved, even when the engine is coupled to a high inertia load.