US3917762A

US3917762A - Carburetor and method of carburation

Info

Publication number: US3917762A
Application number: US452654A
Authority: US
Inventors: Dale Herbrandson
Original assignee: Individual
Current assignee: Individual
Priority date: 1974-03-19
Filing date: 1974-03-19
Publication date: 1975-11-04
Anticipated expiration: 1992-11-04

Abstract

An improved carburetor and method of carburetion employs an elongated, flexible reed within the air passage of a carburetor to eliminate the conventional fixed venturi and throttle shaft from the air passage, to function as a variable venturi, to regulate the air flow, and to prevent reversion of a mixture of air and fuel into the upstream portion of the air passage of the engine.

Description

v United States Patent [191 3,917,7 2 Nov. 4, 1975 Herbrandson llllll 2,148,071 2/1939 lrgens....,....,-................. 2,455,775 12/1948 Johnston et a1........

[ CARBURETOR AND METHOD OF CARBURATION [76] Inventor:

2,779,576 1/1957 Morgenroth 3,042,013 3,046,958

Bard et a1. Schneider n o k e N 2 6 9 n. 7

Dale Herbrandson, 1605 Lynngrove Drive, Manhattan Beach, Calif. 90266 3,361,120 3,680,846 8/1972 Bickhaus et a1.

[22] Filed: Mar. 19, 1974 Primary Examiner-Tim R. Miles [21] Appl. No.: 452,654

Attorney, Agent, or FirmBurns, Doane, Swecker & Mathis [52] US. Cl. 261/62; 123/73 A; 123/73 V; 261/DIG. 68

7] ABSTRACT 52 An improved carburetor and method of carburetion employs an elongated, flexible reed within the air passage of a carburetor to eliminate the conventional fixed venturi and throttle shaft from the air passage, to function as a variable venturi, to regulate the air flow, and to preventreversion of a mixture of air and fuel 261/62 into the upstream portion of the air passage of the en- 261/62 gim 123/73 A 261/62 7 Claims, 3 Drawing Figures [51] Int. FOZM 9/10 [58] Field of 123/73 V, 73 A,

261/62, DIG. 68

[56] References Cited UNITED STATES PATENTS 1,552,623 9/1925 Little 1,624,024 4/1927 Svensson et a1.

1,625 ,787 4/1927 Braselton US. Patent Nov. 4, 1975 Sheet 1 of2 3,917,762

U.S. Patent Nov. 4, 1975 Sheet 2 of2 3,917,762

CARBURETOR AND METHOD OF CARBURATION BACKGROUND OF THE INVENTION This invention relates generally to an improved carburetor and method of carburetion for an internal combustion engine. More specifically, the invention relates to an improvement of a carburetor for a two-cycle internal combustion engine in which a flexible, elongated reed functions in conjunction with a variable stop to control the quantity of air and fuel admitted to the combustion chamber of the engine, while concurrently serving as a variable venturi and protecting orifices through which fuel enters the carburetor from pressure developed in the crankcase of the engine.

Many two-stroke engines use a reed valve in series with a carburetor to meet the induction requirements of the engine. In a chain saw, for example, a typical installation mounts the reed valve assembly directly to an adapter on the crankcase. The carburetor is placed upstream from and adjacent to the reed valve. The carburetor functions to form the desired mixture of air and fuel, and to regulate the engine output by providing a means to regulate the air flow. The conventional r'eed valve functions as a check valve allowing the mixture of air and fuel to enter the crankcase, but not to escape. The reed valve is sensitive to the engine air flow demand and does not have fixed timing such as would be found with a cam actuated poppet valve, a piston timed valve, or a rotary valve.

Although the conventional arrangement gives generally acceptable engine operation, there are several areas which could be improved. For example, the conventional carburetor and reed assembly in series requires considerable space. In a chain saw which is carried and operated manually, space means undesirable weight. On a motorcycle, the length of the series arrangement can create a problem in fitting the air filter associated with the carburetor within the space available. I

The venturi in the conventional carburetor must create a pressure drop to operate. Usually the constricted air passage comprising the venturi is sized only for stable operation in the mid-range of the engine power band. Such a venturi may thus be too small for optimal power at high engine speed, and too big to create the desired pressure drop at very low engine speed. A variable venturi could solve this problem.

The conventional air intake passage often may be cluttered. There are three principal restrictions in the air stream of the conventional carburetor and reed installation, viz., the venturi, the throttle shutter and shaft, and the reed valve assembly. Each of these remaintains a contoured surface in contact with the petstrictions, when placed in series, will account for a portion of the pressure loss across the intake system, and

the conventional series placement of the carburetor and reed may require all three restrictions to be in the air stream for proper operation of the engine. The improved carburetor, as will be discussed further on, can eliminate the first two restrictions from the air stream and also offer a more compact assembly. This is accomplished by combining the functions of the throttle, venturi, and reed valve by a unique design. The improved carburetor operates without a conventional throttle shutter or venturi in the air passage.

The throttling requirements in the reed carburetor are met by controlling the lift of the reed petals by use of a movable reed stop. At wide open throttle the movals. During idling, the contoured stop-throttle presses the longitudinal midpoint of the reed against the carbu- 0 retor body while allowing a slight movement of the petal tips from normally closed positions. This movement allows the idling air to pass at relatively high speed over the idling fuel passages under the tips of the petals.

The improved carburetor optimally operates without a conventional venturi upstream from'the reed petals. The venturi in the reed carburetor is located at the V-shaped portion of the air passage formed between the lifting or vibrating tips of the reed petals and the carburetor body. The air flow accelerates in the V- shaped region, reaching its'maximum velocity near the tips of the reed petals. The increased air velocity is accompanied by a reduction in air pressure. The pressure differential aspirates the fuel into the high velocity air stream through orifices disposed adjacent to the tips of the reed petals; Since there are no restrictions upstream from ,the petals, the entire pressure differential in the carburetor throat occurs across the reed petals. When engine air demand decreases due to reduced engine speed under load, the reed does not use all of the available lift even though the variable reed stop is in the wide open position. This diminished lift results in a reduced venturiat the tip of the reed. The reduced area tends to maintain a high velocity across the orifices, maintaining good aspiration of fuel into the air stream.

Many carburetors appearing in the prior art may fail to provide effective admission of fuel to the throat of the carburetor when the throttle is closed and the associated engine is idling at low speed. While fuel is admitted to the throat of the carburetor by aspiration within the venturi during operation of the engine at high speed, when the engine is idling, fuel may be drawn into the throat of the carburetor only by a relatively high suction head-developed by the engine downstream from the closed throttle shutter. Since the throttle is closed during idling, the port which is exposed to suction must be located downstream from the shutter. Usually a second port is provided to admit bleed air from the upstream side of the closed shutter to the fuel circuit supplying fuel during idling. This arrangement allows an emulsion of air and fuel to be formed incident to the direct suction of the engine. The emulsion is then mixed with the air passing one side of the closed throttle shutter which is cracked open. The other side of the shutter normally provides only a leakage of air. The same conditions generally continue to prevail as the conventional carburetor is operated at a speed just above idling.

In contrast, the reed carburetor passes all of the air flow over fuel orifices during idling, part throttle, and full throttle. As a result, no leakage occurs as in the conventional carburetor using a throttle shutter and shaft and the fuel may be more efficiently atomized and mixed with the air entering the engine.

Somewhat related to the problem of ineffective induction of fuel into the throat of a carburetor during idling is the problem of maintaining an adequate velocity head within the venturi for efficient aspiration of fuel when the throttle of the carburetor is fully open and the engine is operating under load at less than full speed. Those skilled in the art will appreciate that air flow will be reduced under these lugging conditions. In conventional carburetors the venturi may be comprised simply of an annular constriction in the air passage. The constriction is fixed in size and serves to increase the velocity of air flowing through the throat of the carburetor. The resultant increased velocity results in a pressure drop which aspirates fuel from a port disposed in the constricted area of the throat of the carburetor. As the engine slows under a load, the demand for air may decrease linearly and as a result, the volume of air flowing through the venturi may decrease in a linear fashion. However, while the velocity and volume decrease linearly, the pressure drop across the venturi varies with the square of the air velocity. As engine speed drops and the air velocity decreases, the venturi rapidly becomes unable to aspirate the fuel, and the engine may falter from a too lean mixture. The conventional carburetor approaches this velocity problem by sizing the venturi for stable engine operation at medium values of rpm, and accepting a loss of available power if the flow of air goes sonic, i.e., if the venturi becomes choked at high engine speed. It would therefore be highly desirable if a venturi could be provided which would be variable and which would thereby maintain a velocity head of sufficient magnitude to provide for effective aspiration of fuel for all practical values of engine air flow requirements.

Many carburetors of the prior art are not suitable for use in random positions. For instance, many carburetors of the prior art may not function properly when inverted or when rotated in one or more directions. Such carburetors would not be suitable for use in a tool or other environment in which the engine must operate in a variety of orientations. As suggested by the previous discussion, many carburetors of the prior art may entail separate fuel circuits for the introduction of fuel during idling and during operation of the engine at high speeds. As indicated, the orifices which introduce the fuel during these two phases of operation may open into the throat of the carburetor some distance from one another. Because of the separation of the orifices relative to one another and because of the tendency of the fuel to seek a single horizontal level, if one circuit and orifice is elevated above the other, fuel may drain away from the elevated orifice and may thereby prevent effective induction of fuel into the throat of the carburetor. This problem may be made more difficult by carburetors of the prior art which employ a throttle shutter of the type commonly referred to as a butterfly valve. These engines may depend upon a pressure differential created across the closed throttle shutter by the suction of the engine to directly suck fuel from an idling fuel orifice or port located immediately downstream from the closed edge of the throttle shutter. Since free movement of the butterfly valve may be obstructed by the constriction which forms the venturi, the valve and thus the idling fuel port must of necessity be located a considerable distance downstream from the venturi and the main fuel port. It would, therefore, be quite desirable if a carburetor could be provided in which the idle and the main fuel orifices are disposed in close spatial relation to one another in order to minimize elevational differences incident to various orientations of the carburetor.

Many engines of the prior art employ flexible reed valves as check valves downstream from the carburetor to prevent reversion, i.e., the introduction of back pressure from the crankcase of the engine into the throat of the carburetor. The cyclic negative pressure or suction developed in the crankcase of a two-cycle engine is relied upon to draw air through the throat of the carburetor. However, if the throat of the carburetor were exposed to the cyclic positive pressure developed within the crankcase, the positive pressure could purge the orifices of fuel and prevent proper operation of the carburetor. Therefore, a check valve should be provided for such engines which will allow the flow of air through the throat of the carburetor and into the crankcase of the engine when the pressure of the crankcase is negative and which will isolate the fuel orifices from back pressure which may be developed when the pressure in the crankcase is positive.

Many engines of the prior art provide such valves immediately adjacent the crankcase and these valves may therefore be exposed to rather intense heat and air turbulence from the rotating crankshaft. Exposure may cause oxidation, weakening, or other damage to the valve, particularly if the valve is an epoxy fiberglass composite generally used for this purpose. It would thus be desirable if a carburetor could be provided in which a valve, which would open and close in response to the negative and positive pressures, respectively, of the crankcase, is located at a position away from the areas of the engine generating heat and air turbulence so that damage to the valve may be avoided.

Many carburetors of the prior art used in conjunction with a reed valve may present the problem of the two units in series being larger than desired for use with an engine employed in a particular environment. For instance, if the engine is to be employed in a chain saw, it must be covered with a protective shroud and the entire assembly must be small enough to allow use in relatively restricted areas. Also, when the tool must be handled manually, the weight of the tool is a major consideration and every saving which can be made in weight is important. If an engine is to be used to power a motor-cycle it must fit within a rather small structural framework. An unnecessary protrusion, such as that which may occur if the air intake system is excessively long, must be avoided in order to use efficiently the space available for the engine and associated hardware. In many reed valve applications of the prior art a considerable portion of the length of the induction system is taken up by the space required to place the reed valve and associated connective structure between the carburetor and the engine. Therefore, it would be highly desirable if a carburetor could be provided in which the reed valve assembly is simply included within the length of the carburetor, for a substantial savings in size of the assembly.

Other carburetors of the prior art which employ conventional venturis may be subject to the problem that when the engine is operating near its maximum power the flow of air through the venturi may go sonic. That is, the flow of air may reach a velocity which simply cannot be increased, regardless of the demand of the engine, and the venturi is said to be choked. A choked venturi limits engine output because the volume of combustible mixture delivered to the engine is proportional to the air velocity through the carburetor venturi. It would, therefore, be highly desirable if a carburetor could be provided which avoids the phenomenon of the air passing through the venturi reaching a maximum velocity before the engine reaches its air intake limit.

OBJECTS AND SUMMARY OF THE PREFERRED FORMS OF THE INVENTION Objects In light of the foregoing it is therefore a general object of theinvention to provide an improved carburetor and method of carburetion intended to obviate or minimize the problems of the type previously noted.

It is a particular object of the invention to provide an improved carburetor and method of carburetion wherein the venturi varies in response to the demand of the engine to maintain the velocity of air passing through the venturi needed to effectively aspirate fuel from a main fuel port disposed therein.

It is another object of the invention to provide an improved carburetor in which the orifices, through which fuel is admitted to the throat of the carburetor during both idling and operation at high, speeds, are located in close proximity to one another and in a location close to the center of the fuel reservoir so that both orifices will experience only a small change in the static head of the fuel regardless of the position in which the unit is operating.

It is yet another object of the invention to provide an improved carburetor and method of carburetion in which fuel is introduced during idling by aspiration from a fuel port into the carburetor incident to the passage of air through a venturi in which the port is disposed.

It is still another object of the invention to provide an improved carburetor in which a valve, which allows the flow of air and fuel into the engine and which isolates the fuel ports from any positive pressure developed by the engine, is located away from areas of high temperature and turbulence to at least partially avoid oxidation, weakening, or other damage to the valve.

It is a further object of the invention to provide an improved carburetor incorporating the desirable operating characteristics of a series reed valve, but which is compact and therefore suited to use with an engine employed to power chain saws, motorcycles, or other devices in which only a limited amount of space is'available for the engine and associated hardward.

It is still a further object of the invention to provide an improved carburetor and method of carburetion in which the volume of the air passing through the carbu retor does not reach a premature maximum before the air intake limits of the engine are reached at high speed, without compromising the ability of the carburetor to form the correct air/fuel ratio needed to effectively operate the engine at lower .values of engine speed.

Brief Summary An improved carburetor according to a preferred embodiment of the invention intended to accomplish at least some of the foregoing objects includes an air ini the correct mixture of air and fuel. A flexible elongated reed is cantilevered across the air passage and functionsas. a reed check valve to prevent reversion of the mixture of air and fuel, and also to throttle the air flow. The reed may be moved from its normally closed position to a variably open position by the decreased pressure caused by the engine inducting air through the carburetor air passage. When air flows past the tip of the reed petals, a pressure drop is created by the increased air velocity, which aspirates fuel into the airstream from passages located at the tip of the reed petals. The extent to whichthe reed may open is controlled by a regulating'device which may be employed to selectively limit the lift of the reed to regulate the quantity of air and fuel entering the engine. Thus, the reed valve may be employed to concurrently control the quantity of fuel and airadmitted to the engine and to isolate the fuel orifices withinthe carburetor from any positive pressure developed by the engine incident to reversion.

An improved method of carburetion according to the I present invention mixes fuel and air and introduces this mixture into an internal combustion engine. This induction is accomplished by the proper use of the cyclic positive and negative pressures within the crankcase of the engine created by the reciprocating piston. Fuel is introduced into a carburetor connected to the engine in response to these cyclical pressures. Air and fuel are introduced into the interior of the air passage of the carburetor in response to the negative pressures and are mixed therein ,as the air flows through the air passage into the engine. The orifices through which the fuel enters the air passage are isolated from the positive pressures by closing a reed valve disposed in the carburetor and normally closing the air passage in response to positive pressures. The orifices are exposed to the negative pressures when the reed valve opens in response to the negative pressures. The quantity of fuel and air entering the engine and the power output thereof are controlled by regulating the degree to which the reed valve opens. I

THE DRAWINGS Other objects and advantages of the present invention will become apparent from the detailed description which follows considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of an embodiment of the invention shown in position on a typical small internal combustion engine; i v

FIG. 2 is a transverse sectional view of an embodiment of the invention taken along the lines 2-2 of FIG. 1 showing the improvement of the subject inventionas applied to a typical carburetor; and

FIG. 3 -is an exploded perspective view of a portion of the improved carburetor according to a preferred embodiment of the invention.

into reservoirs adjacent the interior of the air passage 16 by means of the pump 20. The manner in which this is accomplished will be described in more detail in connection with the discussion of FIG. 2. A throttle is disposed in the carburetor and is operated by means of a throttle lever 22 and associated pivot pin 24. The function of the throttle will also be hereinafter more fully described. The carburetor is secured to the engine by means of a throttle support plate 26 which is secured to the carburetor and an insulating base plate 28 which is secured both to the support plate 26 and the engine 10.

As illustrated, the carburetor is located so that the throat 16 opens directly into the crankcase 32 of the engine. A valve located in this area and employed to isolate the carburetor from the interior of the crankcase may therefore be subject to damage by heat and turbulence developed in this area. This potential is neutralized by the unique placement of the valve as will be more fully described in connection with FIG. 2.

It will be noted that the truncated nature of the throat 16 of the carburetor allows the carburetor to occupy less space and to be oriented in a manner which reduces the degree to which the carburetor protrudes from the engine. As suggested in the preceeding, the compactness of this arrangement renders the carburetor more suitable for use with engines operating within closely confined areas. In particular, such an arrangement may render the improved carburetor more advantageous for use in a chain saw, motorcycle, or other engine powered device.

FIG. 2 illustrates a transverse sectional view of an embodiment of the invention taken along lines 22 of FIG. 1. It should be noted at the outset that the particular type of carburetor to which the improvement is applied was chosen only as exemplary of a typical carburetor and should not be construed as a limitation upon the applicability of the improvementto other types of carburetors. The invention, for instance, could equally well be applied to those carburetors commonly. referred to as float carburetors.

While the particular structural characteristics of thecarburetor illustrated are not in themselves significant, it may be helpful to a full understanding of the improvement according to the present invention if the function of the carburetor is briefly described. In this connection and as illustrated, a fuel hose 18 admits fuel through conduit 36 to an annular filter 37 which feeds to a temporary reservoir 38 from which the filtered fuel is drawn through conduit 40 and associated check valve 44 into a pump chamber 42. The fuel is drawn from the reservoir 38 into the pump chamber 42 by the suction effect created in the pump chamber 42 by the displacement of a pump diaphragm 46 downward. The diaphragm 46 moves downward, away from the pump chamber 42, in response to suction introduced to chamber 43 through conduit 48 from the crankcase of the engine. Once fuel is drawn into the pump chamber 42, the check valve 44 closes.

The suction introduced through conduit 48 to cham- 8 in use, the main and idle fuel reservoirs may be interconnected or merged into a single central reservoir which contains all of the fuel used both during idling and high speed operation. It should be appreciated in this regard that only the particular configuration of the reservoirs illustrated in FIG. 2 would be altered in such carburetors. The main and idle fuel circuitry would remain essentially unchanged.

As indicated in connection with the earlier discussion of FIG. 1, the carburetor 8 shown in FIG. 2 is connected to, the engine through the throttle support plate 26 by means of the insulating base plate 28. Within the body of the carburetor 12, upstream from the throttle support plate 26 and away from the crankcase 32 (see h FIG. 1), is disposed a flexible, elongated reed 64. The reed 64 is secured to a seating means or surface 90 on body 12 by means of threaded fasteners 66 and a formed clamp 68. The configuration andsequential arrangement of these elements can perhaps best be seen in the explodedperspective view shown in FIG. 3. The flexible, elongated reed 64 is cantilevered across the truncated throat or air passage 16 of the'carburetor and normally closes the air passage. The flexible elongated reed 64 therefore isolates the air passage 16 into an upstream portion 74 and a downstream portion 76. This serves to protect fuel orifices disposed in the upstream portion of the air passage from the crankcase pressure developed by the engine in the downstream portion.

The reed 64 has been moved to a position within the body of the carburetor away from the engine crankcase 32. At such a location the valve is less subject to. the high temperatures, or turbulence developed within the crankcase tending to cause oxidation, weakening, or other damage to the reed.

In extending across the air passage 16, the tip 70 of the reed directly seals an idling fuel port or orifice 72 through which fuel is conducted from the idling fuel circuit '62 into the downstream portions 76 of the air passage 16. Thus, in this closed posture the'reed 64 not only isolates the upstream portion 74 of the air passage 16 from'pres'sures' 'which may develop in the ,downstream portion 76, but the tip also directly seals the I idling port to ensure that this port is not subjectedto ber 43 is followed by a period of positive pressure in which the pump diaphragm 46 is displaced upward. The fuel contained in pump chamber 42 is thereby forced through a second check valve 50 into conduit 52 and ultimately into a primary fuel reservoir 54. From the reservoir 54 the fuel can enter either a main fuel reservoir 56 or an idling fuel reservoir 58 through variable orifices 55 and 57, respectively. From the main fuel reservoir 56, fuel can enter main fuel circuitry 60. Similarly, fuel from the idling fuel reservoir can enter an idling fuel circuit 62. In some carburetors presently any pressure sufficient to purge the orifice or. circuit of fuel. 1

The fuel from the main fuel reservoir passes through the main fuelcircuitry 60 and enters the air passage 16 through main ports or orifices 82. FIGS. 2 and 3 illustrate that-the main ports 82are-disposed in very close relation to the idle port 72, and that there are provided dual, laterally opposed sets of orifices. This arrangement of dual sets of orifices will be more fully described in subsequent discussion. The very close proximity between the idle port and the main port ensures that, regardless of the position of the carburetor, the elevation head of the orifices will be very nearly the same. This will minimize the tendency of fuel to drain away from either orifice. By minimizing the difference in elevation head and the possibility of fuel draining from one of the orifices, more effective operation of the fuel induction process may be insured in an all position application.

The downstream portion of the idling fuel circuit is bifurcated and is in this regard characterized by a branch 78, through which fuel for idling enters the downstream air passage 76, and a branch 80, through which bleed air from the upstream air passage 74 may enter during idling. The second branch also may serve as a fuel passage during the transition from idling to higher speeds of operation. The operation of the second branch will hereinafter be more fully described. A second bleed air passage 84 is provided to introduce air into fuel being drawn through the main fuel circuitry 60. It has been found that the introduction of bleed air into the main fuel circuit provides a more crisp throttle response. That is, when the throttle is opened, the response of the engine is more immediate.

It will be appreciated that the provision of bleed air may enhance the induction of fuel into the air passage 16 from either the main or the idling fuel circuits by virtue of the tendency of the bleed air to form an emulsion with the fuel prior to induction into the air passage. Thus, the fuel may already be partially aerated before it is aspirated into the air passage and atomization within the air passage may therefore be more complete. If the fuel is partially emulsified prior to aspiration and if the aspiration is thus rendered more effective, the fuel and air mixture may comprise a lighter mass which will be more easily accelerated into the air stream.

A check valve 59 is placed between main fuel reservoir 56 and the junction of passages 84 and 60. This prevents the emulsified mixture of fuel and air from being forced back into reservoir 56 in the event 'the throttle is snapped shut while there is a high velocity flow of air in the air passage 16.

The quantity of the bleed air which will be introduced into either the main fuel circuit or the idle fuel circuit can be adjusted by varying the diameter and/or the length of the bleed air passage to increase or decrease the head loss experienced by the air in passing through the passages. Also, the farther the opening 85 of the bleed air passage 84 is located from the orifices 82, the greater the pressure differential will be between the main fuel orifice 82 and the opening 85 of the bleed air passage 84 due to the increased air velocity approaching the tip of the reed in the air passage 74. The greater the pressure differential, the greater will be the quantity of air drawn through the bleed air passage. A non-linear amount of bleed air may be introduced into the main fuel orifice 82 by proper placement of orifice 84 in the upstream air passage 74.

As indicated in connection with the discussion of FIG. 1, the air flow through a carburetor improved according to the present invention can be controlled by means of a throttle lever 22 and an associated pivot pin 24. As illustrated in FIG. 2 a regulating means or stopthrottle 86, which controls the lift of reed 64 is secured to the pivot pin 24. FIG. 3 presents an exploded perspective view of the stop-throttle, pivot pin, and lever assembly and should be referred to for a more complete understanding of the configuration and arrangement of these elements. Rotation of the throttle lever 22 rotates the pivot pin 24 and moves the stop-throttle 86 relative to the air passage 16 to alter the position of the reed 64.

When the engine is idling, only a small amount of air and fuel is required and the throttle lever and pivot pin are moved to position the stop-throttle 86 to hold the reed 64 in the position shown in solid lines. The tip 70 of the reed, however, is free to vibrate from the position shown in solid lines to generally the position shown in broken lines at A. In other words as the engine cyclically develops a negative intake pressure, air is drawn from the upstream portions 74 of the air passage 16 past the reed 64 to displace the tip 70 of the reed to the position illustratedby the broken lines at A. Only a small opening is created by the displacement of the reed and the air moves past the idle jet 72 at a relatively high velocity, aspir'ating fuel fromthe orifice 72. The velocity of the air passing the idle jet 72 develops by reason of the small aperture or venturi formed between a venturi surface 88 surrounding the fuel ports and the tip of the reed. This aspiration should not be confused with the direct suction employed by certain carburetors of the prior art to draw fuel into the air passage. Aspiration through the venturi may afford more effective atomization of the fuel than does direct suction. As the pressure within the crankcase cyclically reaches a zero value, the tip of the reed moves back to the position shown by the solid lines, thereby directly sealing the orifice 72. Therefore, when a positive pressure is cyclically developed within the crankcase, the orifice 72 has been directly sealed and the main fuel jet 82 and the transition fuel passage are isolated from the positive pressure.

When the engine is operating under load at full throttle, the stop-throttle 86 is located in the position shown by the broken lines at C while the reed 64 vibrates between the position shown by the solid lines and a position of generally more extreme flexure as indicated by the broken lines at B. When the engine is functioning in this manner, the stop-throttle does not contact the reed, instead the reed flexes to a variably open position dependent upon. the quantity of air flowing through the air passage 16 in response to the demand of the engine. The variably open position of the reed forms a variable venturi between the tip of the reed 70 and the venturi surface 88 which maintains the velocity head of the air passing through this variable venturi in direct proportion to the flexural stiffness of the reed. In other words, the stiffer the reed, the greater will be the velocity head for a given demand by the engine. This relation will continue until the engine reaches top speed, when the reed will vibrate between the position shown in solid lines and that shown by the broken lines at C. Contact with the retracted stop-throttle 86 in position C preempts the proportional relation. The relation may also be preempted by movement of the stop-throttle into contact with the reed.

With the velocity head dependent upon the flexural stiffness of the reed, the velocity should remain relatively constant and the requisite amount of fuel should be effectively aspirated into the downstream portion 76 of the air passage 16 while the engine operates under load at full throttle. It will be recalled from the earlier discussion that a constant area venturi does not provide this advantage. In the carburetors of the prior art, if the engine lugs down or decreases in speed due to loading, a smaller quantity of air flows through the venturi with the result that the velocity head decreases and less fuel may be aspirated into the air passage. With a carburetor improved according to the present invention, an adequate quantity of fuel will be aspirated into the air passage even though the demand for air by the engine decreases.

It will be recalled from the earlier discussion of the bleed air circuitry that the branch 80 of the idling fuel circuit was described as admitting bleed air during idling and as a fuel passage during transition by the engine from idling to higher speeds. With regard to the latter function, this branch will be useful as the reed moves from the position shown generally at A to that shown generally at B or C. As the reed moves more toward a position at B, the narrowest portion of the opening or venturi formed between the tip 70 of the reed and the venturi surface 88 moves slightly upstream from its original position near the idling fuel port 72. As this movement occurs, the venturi may become less effective with regard to aspirating fuel from the idling fuel port 72. Furthermore, until the engine begins operating at higher speeds, the velocity head may not be of sufficient magnitude to effectively aspirate fuel from the main fuel ports located slightly farther upstream. Therefore, an intermediate port is provided in the form of the transition port 80 so that fuel may be progressively aspirated from the idling fuel port, the transition port, and ultimately the main ports as the speed of the engine increases.

Whenever it is desired to control the speed with which the engine operates, the stop-throttle 86 may simply be rotated to a desired position within the range defined by the solid and broken line representations to contact and partially close the vibrating reed 64. The degree of closure regulates the flow of air and fuel into the engine and therefore the speed with which the engine will run. Engine speed is thus principally dependent upon and regulated by the position of the stopthrottle. The engine will produce less power the more nearly the stop-throttle approaches the position shown in the solid lines. Accordingly, to the extent the engine can overcome a load, the engine will run at a higher speed as the stop-throttle is moved more nearly to the position shown in the broken lines. Regardless of the position of the stop-throttle, the reed will continue to vibrate from a variably open to a closed position in order to prevent reversion by cyclically admitting the flow of air into the engine and isolating the fuel delivery system from positive pressures developed by the engine.

FIG. 3 is an exploded perspective view illustrating the arrangement of the elements comprising the improvement. The body 12 of the carburetor is illustrated in broken lines. The base surface 90 or other suitable seating means of body 12 terminates the upstream portion 74 of the air passage and provides a base to which the flexible elongated reed 64 can be secured and a seat against which the reed may snugly rest when closed. The reed 64 is bifurcated into identical petals 96 in the embodiment illustrated. The connective base of the reed is secured to the base surface 90 of body 12 by means of a formed backup clamp 68 and threaded fasteners 66 which thread into the apertures 92. The reed clamp 68 is flat in the area used to secure the reed to surface 90. The clamp is formed into a slight radius beginning at crease 98 in order to control the bending stress in the petals 96 of the reed 64. At wide open throttle the stop-throttle 86 forms an extension of the curvature begun in clamp 68 (see FIG. 2). When the reed 64 is in place on the surface 90, dual openings 100 which provide communication between the upstream and the downstream portions of the air passage are fully and snugly covered. The tips 70 of the reed fully cover and directly seal the idle ports 72. The dual openings 100 are separated by a septum 102 which extends a distance into the upstream portion 74 of the air intake passage 16.

The embodiment shown here uses two openings 100 in body 12, and two petals on reed 64. A carburetor designed to provide less air flow would use only one opening 100 in body 12, and a single petal on reed 64. Likewise, a carburetor designed to provide more air flow would use three openings covered with three petals in a single body.

The throttle lever, pivot pin, and stop-throttle can be seen at 22, 24, and 86, respectively. As illustrated, the stop throttle is secured to the pivot pin by inserting an edge 104 of the stop-throttle into a longitudinally extending slot 106 in the pivot pin 24. The stop-throttle is then securely fastened therein by means of threaded fasteners 108 which are threaded through the apertures 110 and 1 12. Of course, those skilled in the art will appreciate that the stop-throttle could be connected to the pivot pin by a number of suitable methods. For instance, a longitudinal portion of the pivot pin could be machined to provide a flat abutting surface. The stopthrottle could then be secured against this surface by means of threaded fasteners passing through the stopthrottle into the pivot pin.

When in position, the pivot pin 24 rotates in the bearing 114 of the throttle support plate 26. The entire assembly is enclosed by the throttle support plate 26 which is secured to the surface by threaded fasteners threaded through the apertures 1 16. The assembled carburetor can then be secured to the insulating base plate 28 as illustrated in FIG. 1 by threaded fasteners disposed in apertures 1 18 of the throttle support plate SUMMARY OF ADVANTAGES It will be appreciated that in providing an improved carburetor according to the present invention certain significant advantages are obtained.

Of particular importance is the advantage that the improved carburetor is more compact and therefore better suited to use in engines employed to power chain saws, motorcycles, and other devices in which little space is available for the reed valve and carburetor on the engine.

Also quite important is the advantage gained by the removal of a restrictive venturi and throttle shaft in the air passage upstream from the reed. The resulting uncluttered air passage will permit more air to flow to the engine, giving better peak engine power.

At lower engine speeds, the reed carburetor provides the advantage of a variable venturi which ensures an adequate velocity head for effective aspiration of fuel from the fuel ports when the engine is operated both at full throttle and at low speed. The variable venturi created beneath the reed petal adds to the lugging ability of the engine at low speed, in spite of the decreased volume of air required by the engine.

Also quite important is the improvement in which the main and idling fuel ports are positioned in very close proximity to one another and to the center of the fuel reservoir so that the static fuel head will remain essentially equal for both ports regardless of the position of the carburetor.

Furthermore, the unique provision of a venturi for the aspiration of fuel from an idling fuel port provides the important advantage of ensuring efficient atomization of the fuel into a mixture which can be effectively inducted into the engine when the engine is idling.

A still further advantage resides in the improvement in which the reeds are moved from a position of very close proximity with the crankcase to a position within the carburetor in which they are exposed to less heat and air turbulence.

In describing the invention, reference has been made to a preferred embodiment. However, those skilled in the art and familiar with the disclosure of the invention may recognize additions, deletions, substitutions, or

13 other modifications which would fall within the perview of the invention as defined in thelclaims.

What is claimed is: w I l. A method of carbureting fuel and air comprising: providing induction passage means having an air receiving inlet and a fuel and air discharging outlet; providing fuel supplying orifice means communicating with said induction passage means and operable to discharge fuel thereinto; providing flexible reed valve means extending transversely across said induction passage means, said flexible reed valve means being concurrently operable to throttle the flow of air through said induction passage means in response to operation of engine throttle control means, prevent a reverse flow of air through said induction passage means from the outlet thereof toward the inlet thereof, and induce aspiration of fuel from said fuel supplying orifice means into said induction passage means; providing throttle linkage means connected with said engine throttle control means; providing and deploying throttle movement limiting means to define selectively variable throttling positions of said flexible reed valve means with respect to said induction passage means and said fuel supplying orifice means; and manipulating said throttle movement limiting means on said throttle linkage means to cause said throttling action of said flexible reed valve means, as determined by selective positioning of said throttle movement limiting means, to be responsive to operation of said engine throttle control means. 2. A carburetor apparatus operable to supply air and fuel to engine means and comprising:

induction passage means having an air receiving inlet and a fuel and air discharging outlet; fuel supplying orifice means communicating with said induction passage means and operable to discharge fuel thereinto; flexible reed valve means extending transversely across said induction passage means, said flexible reed valve means being concurrently operable to throttle the flow of air through said induction passage means in response to operation of engine throttle control means, prevent a reverse flow of air through said induction passage means from the outlet thereof toward the inlet thereof, and induce aspiration of fuel from said fuel supplying orifice means into said induction passage means; throttle linkage means operable to be connected with said engine throttle control means; throttle movement limiting means operable to define selectively variable throttling positions of said flexible reed valve means with respect to said induction passage means and said fuel supplying orifice means; and means mounting said throttle movement limiting means on said throttle linkage means to cause said throttling action of said flexible reed valve means, as determined by selective positioning of said throttle movement limiting means, to be responsive to operation of said engine throttle control means.

14 3. A carburetor apparatus as described in claim 2, wherein:

said flexible reed valve means is operable to provide a freely movable, outer end portion projecting beyond said throttle movement limiting means,

said outer end portion of said flexible reed valve means is operable to undergo flexing movement beyond said throttle movement limiting means while an anchored, innerendportion of said flexible reed valve means is engaged with said throttle movement limiting means at relatively lower speeds of said engine means so as to permit induction passage opening, flexing movement of said freely moveable outer end portion of said flexible reed valve means operable to induce aspiration of fuel into such induction passage means from said fuel supplying orifice means at said relatively lower speeds of said engine means, while said inner end portion is restrained by said throttle movement limiting means; and

said flexible reed valve means is operable, at relatively higher speeds of said engine means, to undergo flexing movement of both said inner and outer portions, with said flexing of said inner and outer portions of said flexible reed valve means being operable to induce aspiration of fuel into said induction passage means through said fuel supplying orifice means.

4. A carburetor apparatus as described in claim 3 including:

check valve means included in said fuel supplying orifice means and operable to prevent a flow of air from said induction passage means through said fuel supplying orifice means associated with said check valve means.

5. In a carburetorsfor mixing and introducing fuel and air into an internal combustion engine, said carbureto including;

an air intake port for admitting air into said carburetor,

an air passage through which air may be conducted from said intake port to said internal combustion engine,

a fuel inlet for admitting fuel into said carburetor,

idle and main fuel orifice means opening into said air passage for introducing fuel into said air passage, and

idle and main fuel circuit means, connected to said fuel inlet and further connected with said air pas-' sage through said orifice means, for conducting fuel from said fuel inlet to said air passage wherein air and fuel are mixed and from which the mixture is introduced into said internal combustion engine, an improvement which comprises:

flexible elongated means, within and connected to said carburetor, for admitting air and fuel to said engine and for preventing exposure to said orifice means to back pressure developed by said engine, said flexible elongated means being disposed in a cantilevered posture across said air passage to normally cover said passage and being movable to a variably open position by air passing through said passage;

regulating means, connected to said carburetor and operably associated with said flexible elongated means, for selectively engaging and releasing said flexible elongated means to regulate the quantity of air and fuel entering said engine; and

seating means, disposed in said air passage, for seating said flexible elongated means to isolate air within said passage upstream of said seating means from air within said passage downstream of said seating means, said seating means having an opening for the passage of air therethrough and surface means adjacent thereto for forming a variable venturi with the free end of said flexible elongated means when said flexible elongated means is in said variably open position in response to the flow of air through said air passage; said idle and main fuel orifice means being positioned relative to said free end of said flexible elongated means with sufficient proximity to cause aspiration of fuel from said orifices by air passing through said variable venturi; said seating means including a transverse member disposed across said air passage having dual openings therein through which air can pass from an upstream portion of said air passage to a downstream portion, and a septum means connected to said transverse member, said septum means being oriented to 16 extend generally longitudinally of said air passage, transversely intersect said planar member, and divide said air passage adjacent said transverse member into dual channels. 6. An improved carburetor, for mixing and introducing fuel and air into an internal combustion engine, as defined in claim 5 wherein said flexible elongated means comprises:

a bifurcated reed having elongated petals for covering said dual openings. 7. An improved carburetor, for mixing and introducing fuel andair into an internal combustion engine, as defined in claim 5 wherein said regulating means comprises:

contact means for contacting each of said elongated petals of said bifurcated reed, across the width thereof, to selectively close said bifurcated reed to regulate the quantity of air and fuel entering said engine, said regulating means clamping said elongated petals against said seating means when said regulating means is in a position of full closure.

Claims

1. A method of carbureting fuel and air comprising: providing induction passage means having an air receiving inlet and a fuel and air discharging outlet; providIng fuel supplying orifice means communicating with said induction passage means and operable to discharge fuel thereinto; providing flexible reed valve means extending transversely across said induction passage means, said flexible reed valve means being concurrently operable to throttle the flow of air through said induction passage means in response to operation of engine throttle control means, prevent a reverse flow of air through said induction passage means from the outlet thereof toward the inlet thereof, and induce aspiration of fuel from said fuel supplying orifice means into said induction passage means; providing throttle linkage means connected with said engine throttle control means; providing and deploying throttle movement limiting means to define selectively variable throttling positions of said flexible reed valve means with respect to said induction passage means and said fuel supplying orifice means; and manipulating said throttle movement limiting means on said throttle linkage means to cause said throttling action of said flexible reed valve means, as determined by selective positioning of said throttle movement limiting means, to be responsive to operation of said engine throttle control means.

1. A CARBURETOR APPRATUS OPERABLE TO SUPPLY AIR AND FUEL TO ENGINE MEANS AND COMPRISING: INDUCTION PASSAGE MEANS HAVING AN AIR RECEIVING INLET AND A FUEL AND AIR DISCHARGING OUTLET, FUEL SUPPLYING ORIFICE MEANS COMMUNICATING WITH SAID INDUCTION PASSAGE MEANS AND OPERABLE TO DISCHARGE FUEL THEREINTO, FLEXIBLE REED VALVE MEANS EXTENDING TRANSVERSELY ACROSS SAID INDUCTION PASSAGE MEANS SAID FLEXIBLE REED VALVE MEANS BEING CONCURRENTLY OPERABLE TO THROTTLE THE FLOW OF AIR THROUGH SAID INDUCTION PASSAGE MEANS IN RESPONSE TO OPERATION OF ENGINE THROTTLE CONTROL MEANS, PREVENT A REVERSE FLOW OF AIR THROUGH SAID INDUCTION PASSAGE MEANS FROM THE OUTLET THEREOF TOWARD THE INLET THEREOF AND INDUCE ASPIRATION OF FUEL FROM SAID FUEL SUPPLYING ORIFICE MEANS INTO SAID INDUCTION PASSAGE MEANS, THROTTLE LINKAGE MEANS OPERABLE TO BE CONNECTED WITH SAID ENGINE THROTTLE CONTROL MEANS, THROTTLE MOVEMENT LIMITING MEANS OPERABLE TO DEFINE SELECTIVELY VARIABLE THROTTLING POSITIONS OF SAID FLEXIBLE REED VALVE MEANS WITH RESPECT TO SAID INDUCTION PASSAGE MEANS AND SAID FUEL SUPPLYING ORIFICE MEANS AND MEANS MOUNTING SAID THROTTLE MOVEMENT LIMITING MEANS ON SAID THROTTLE LINKAGE MEANS TO CAUSE SAID THROTTLING ACTION OF SAID FLEXIBLE REED VALVE MEANS AS DETERMINED BY SELECTIVE POSITIONING OF SAID THROTTLE MOVEMENT LIMITING MEANS, TO BE RESPONSIVE TO OPERATION OF SAID ENGINE THROTTLE CONTROL MEANS.

3. A carburetor apparatus as described in claim 2, wherein: said flexible reed valve means is operable to provide a freely movable, outer end portion projecting beyond said throttle movement limiting means, said outer end portion of said flexible reed valve means is operable to undergo flexing movement beyond said throttle movement limiting means while an anchored, inner end portion of said flexible reed valve means is engaged with said throttle movement limiting means at relatively lower speeds of said engine means so as to permit induction passage opening, flexing movement of said freely moveable outer end portion of said flexible reed valve means operable to induce aspiration of fuel into such induction passage means from said fuel supplying orifice means at said relatively lower speeds of said engine means, while said inner end portion is restrained by said throttle movement limiting means; and said flexible reed valve means is operable, at relatively higher speeds of said engine means, to undergo flexing movement of both said inner and outer portions, with said flexing of said inner and outer portions of said flexible reed valve means being operable to induce aspiration of fuel into said induction passage means through said fuel supplying orifice means.

4. A carbUretor apparatus as described in claim 3 including: check valve means included in said fuel supplying orifice means and operable to prevent a flow of air from said induction passage means through said fuel supplying orifice means associated with said check valve means.

5. In a carburetor for mixing and introducing fuel and air into an internal combustion engine, said carburetor including; an air intake port for admitting air into said carburetor, an air passage through which air may be conducted from said intake port to said internal combustion engine, a fuel inlet for admitting fuel into said carburetor, idle and main fuel orifice means opening into said air passage for introducing fuel into said air passage, and idle and main fuel circuit means, connected to said fuel inlet and further connected with said air passage through said orifice means, for conducting fuel from said fuel inlet to said air passage wherein air and fuel are mixed and from which the mixture is introduced into said internal combustion engine, an improvement which comprises: flexible elongated means, within and connected to said carburetor, for admitting air and fuel to said engine and for preventing exposure to said orifice means to back pressure developed by said engine, said flexible elongated means being disposed in a cantilevered posture across said air passage to normally cover said passage and being movable to a variably open position by air passing through said passage; regulating means, connected to said carburetor and operably associated with said flexible elongated means, for selectively engaging and releasing said flexible elongated means to regulate the quantity of air and fuel entering said engine; and seating means, disposed in said air passage, for seating said flexible elongated means to isolate air within said passage upstream of said seating means from air within said passage downstream of said seating means, said seating means having an opening for the passage of air therethrough and surface means adjacent thereto for forming a variable venturi with the free end of said flexible elongated means when said flexible elongated means is in said variably open position in response to the flow of air through said air passage; said idle and main fuel orifice means being positioned relative to said free end of said flexible elongated means with sufficient proximity to cause aspiration of fuel from said orifices by air passing through said variable venturi; said seating means including a transverse member disposed across said air passage having dual openings therein through which air can pass from an upstream portion of said air passage to a downstream portion, and a septum means connected to said transverse member, said septum means being oriented to extend generally longitudinally of said air passage, transversely intersect said planar member, and divide said air passage adjacent said transverse member into dual channels.

6. An improved carburetor, for mixing and introducing fuel and air into an internal combustion engine, as defined in claim 5 wherein said flexible elongated means comprises: a bifurcated reed having elongated petals for covering said dual openings.

7. An improved carburetor, for mixing and introducing fuel and air into an internal combustion engine, as defined in claim 5 wherein said regulating means comprises: contact means for contacting each of said elongated petals of said bifurcated reed, across the width thereof, to selectively close said bifurcated reed to regulate the quantity of air and fuel entering said engine, said regulating means clamping said elongated petals against said seating means when said regulating means is in a position of full closure.