Rotary throttle valve carburetor

Information

  • Patent Grant
  • 6431527
  • Patent Number
    6,431,527
  • Date Filed
    Thursday, November 2, 2000
    24 years ago
  • Date Issued
    Tuesday, August 13, 2002
    22 years ago
Abstract
A rotary throttle valve carburetor for a two cycle engine reroutes a portion of intake air and introduces the air around the circumference of a fuel feed tube. A rotary throttle, rotatable and vertically moveable, fits into a cylindrical chamber intersecting an air intake channel through a carburetor body. A needle supported by the rotary throttle fits into the fuel feed tube which extends from a fuel metering chamber within the carburetor body into a throttling bore extending laterally through the rotary throttle. An intake portion of the air intake channel expands conically toward an upstream side. An air guide tube is aligned co-axially and radially outward from a fuel feed tube forming an air passageway there between. The intake air portion flows through the air passage from the intake portion of the air intake channel and into a bottom space of the cylindrical chamber beneath the rotary throttle. From the bottom space, the air flows through the passageway transversely into a fuel stream emitted from a fuel jet orifice of the fuel feed tube. Excessive fuel flow is thereby controlled and fuel vaporization is promoted, resulting in improved fuel burn efficiency and a reduction of exhaust emissions.
Description




FIELD OF THE INVENTION




This invention relates to a carburetor, and more particularly to a rotary throttle valve carburetor for a two cycle engine.




BACKGROUND OF THE INVENTION




A fuel and air mixture is fed into a crankcase of an operating two cycle engine from a conventional rotary throttle valve carburetor via negative pressure. Within the carburetor, fuel flows from a fuel metering chamber into an air intake channel. Within the channel, the fuel mixes with air and is then drawn into the crankcase. From the crankcase, the fuel and air mixture flows into a combustion chamber and is burned. Relative to other combustion engines, the combustion process of conventional two cycle engines is inefficient. The fuel to air mixture does not completely burn and the resultant air pollutants from the exhaust are relatively high. To alleviate some of the air pollutant concerns, the industry is trending toward a leaner fuel to air mixture to achieve a cleaner burn. The dynamics or isolated transients of the mixing and burning process during acceleration and deceleration of the two cycle engine offer a variety of design challenges.




One such transient occurs during deceleration of the two cycle engine when negative pressure within the air intake channel of the rotary throttle valve carburetor increases causing excessive fuel to be drawn through a fuel feed tube and mix with air within the intake channel. When this occurs, the subsequent fuel and air mixture is too rich and the combustion process is not capable of burning all the fuel. The exhaust is therefore affected and the air pollutants rise.




Because the fuel in the fuel metering chamber is directly drawn into the throttling bore of the rotary throttle from a fuel jet orifice through the fuel feed tube, the mixing of fuel and air, i.e. vaporization, is incomplete. Accordingly, it is difficult to attain lean-mixture combustion in the combustion chamber of a two cycle engine.




SUMMARY OF THE INVENTION




A rotary throttle valve carburetor for a two cycle engine has a rotary throttle disposed transversely through an air intake channel through a carburetor body. The rotary throttle rotates and moves vertically within a cylindrical chamber defined by the carburetor body. A throttling bore laterally extends through the rotary throttle and adjustably aligns longitudinally with the air intake channel. The rotary throttle supports a needle extending therefrom longitudinally into a fuel feed tube supported at one end by the carburetor body. The fuel feed tube provides a path for fuel flow from a fuel metering chamber.




An air passage defined by the carburetor body communicates between an intake portion of the air intake channel and a passageway which communicates with the throttling bore of the rotary throttle. The passageway is formed between an air guide tube and the fuel feed tube. Preferably, the rotary throttle supports the air guide tube which is concentric to the fuel feed tube. A bottom space communicates between the air passage and the passageway. An annular face of the carburetor body penetrated by the fuel feed tube and an under annular face of the rotary throttle axially define the bottom space. The air passage communicates with the bottom space through the annular face of the carburetor body. A fuel jet orifice extends laterally through the fuel feed tube thereby emitting fuel transversely into the passageway.




Objects, features and advantages of this invention include reducing air intake vacuum during deceleration transients of the two cycle engine to prevent excessive fuel draw, avoiding overly rich fuel to air mixture, increasing vaporization of the fuel within the throttling bore, and decreasing engine exhaust emissions.











BRIEF DESCRIPTION OF THE DRAWINGS




These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiments and best mode, appended claims and accompanying drawings in which:





FIG. 1

is a side view with portions broken away and in cross-section of a rotary throttle valve carburetor for a two cycle engine according to the present invention;





FIG. 2

is an enlarged cross-section view of the rotary throttle valve portion identified by reference circle


2


in

FIG. 1

;





FIG. 3

is a partial cross-section view of the rotary throttle valve taken along line


3





3


in

FIG. 1

;





FIG. 4

is a side view with portions broken away and in cross-section of a second embodiment of the rotary throttle valve; and





FIG. 5

is an enlarged cross-section view of the rotary throttle valve portion identified by reference circle


5


in FIG.


4


.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




Referring in more detail to the drawings,

FIGS. 1-3

depict a rotary valve carburetor


10


in accordance with the present invention. The carburetor has a body


12


with a through air intake channel


14


which communicates with an air filter on an upstream side and a crankcase of a two cycle engine on the downstream side. The carburetor body


12


defines an intake portion


16


of the air intake channel


14


on the upstream side. The intake portion


16


flares radially outward in the upstream direction.




A rotary throttle


18


partially obstructs, or controls air passage through carburetor


10


by intersecting channel


14


. Rotary throttle


18


rotatably seats and is operatively moveable vertically within a cylindrical chamber


20


defined by a circumferential face


21


of the carburetor body


12


. Chamber


20


communicates with and extends transversely through the air intake channel


14


. Rotary throttle


18


generally inserts into the chamber


20


from above and rotates in assembly about a centerline axis


22


. A throttling bore


24


extends laterally through rotary throttle


18


and communicates operatively with the air intake channel


14


. Throttling bore


24


is substantially perpendicular to the axis


22


and is aligned so that when the carburetor


10


is in the full open throttle position the throttling bore


24


is in fall communication with the air intake channel


14


.




Defining the bottom portion of chamber


20


is an annular face


26


of the carburetor body


12


. A mid surface


28


of the carburetor body


12


defines a mid bore


30


which communicates concentrically with the chamber


20


radially inward of the annular face


26


from beneath. The mid cylindrical surface


28


is congruent to an inner circumference or perimeter


32


of the annular face


26


. Communicating concentrically with the mid bore


30


from beneath is a lower counterbore


34


defined by a lower cylindrical surface


36


of the carburetor body


12


. The circumference of the lower counterbore


34


is slightly larger than the circumference of the mid bore


24


. And the circumference of the chamber


20


is larger than the circumference of the lower counterbore


34


.




A fuel feed tube


40


extending centrally upward into the throttling bore


24


on centerline axis


22


is secured rigidly to the mid cylindrical surface


28


of the mid bore


24


. A fuel jet orifice or aperture


42


extends laterally through the wall of the fuel feed tube


40


and communicates with the throttling bore


24


of the rotary throttle


18


. Fuel is drawn or travels from a fuel metering chamber, past a check valve (not shown), up the fuel feed tube


40


, through the fuel jet orifice


42


, and into the throttling bore


24


. Controlling fuel flow through the fuel jet orifice


42


is an obstructing needle


44


slidably received with a close fit in the fuel feed tube


40


from above. Rotary throttle


18


supports needle


44


from above. As rotary throttle


18


rotates within chamber


20


, it also moves vertically. Likewise, needle


44


also moves vertically within the fuel feed tube


40


thereby adjusting the opening size of the fuel jet orifice


42


.




The carburetor body


12


defines an air passage


52


communicating with the intake portion


16


of the air intake channel


14


substantially near an outer perimeter


54


which defines the outward radial extremity of the flared surface defining the intake portion


16


. Air passage


52


has a downstream end


56


narrowing through a restrictor


58


of the carburetor body


12


. The downstream end


56


inter-communicates with a passageway


60


defined by an air guide tube


62


disposed substantially concentrically with and radially outward from the fuel feed tube


40


. The air guide tube


62


aligns co-axially with the fuel feed tube


40


and extends substantially into the throttling bore


24


.




During normal operation of the two cycle engine, negative pressure is brought about due to the intake air flowing in the direction of the arrow


64


within the air intake channel


14


. Fuel from the metering fuel chamber flows, via the negative pressure, into the throttling bore


24


through the fuel feed tube


40


and the fuel jet orifice


42


. Simultaneously, the intake air from the air passage


52


flows through the restrictor


58


and into the passageway


60


. The air is mixed therein with the fuel emitting from the fuel jet orifice


42


, whereby atomization or vaporization of the fuel is promoted. The atomized fuel mixes with the remaining intake air flowing through the air intake channel


14


and throttling bore


24


. Consequently, combustion efficiency is improved, promoting a leaner engine operating mixture of fuel to air.




During sudden deceleration of the engine, the alignment of the air intake channel


14


with the throttling bore


24


is minimal. That is, the opening ratio of the throttling bore


24


relative to the air intake channel


14


is reduced. This minimal alignment would produce a strong negative pressure acting upon the fuel jet orifice


42


thereby causing an overly rich fuel to air mixture, if it were not for the intake air supplied through the air passage


52


and the passageway


60


. The intake air moving through the passageway


60


and shrouding the fuel jet orifice


42


alleviates the otherwise strong negative pressures during deceleration. The air passage


52


and passageway


60


act as a bypass passage, whereby excessive fuel draw and combustion inefficiency created by sudden deceleration can be prevented. With the elimination of the high unwanted vacuum during deceleration and the improved fuel to air mixing, the inner circumference or diameter of the fuel feed tube


40


can be enlarged to permit greater fuel flow during acceleration or other operating periods of the two cycle engine. Increasing the inner circumference of the fuel feed tube


40


, or the size of any orifice formed therein, will decrease the potential of foreign debris becoming lodged within the fuel feed tube


40


.




A base tube portion


65


of the fuel feed tube


40


engages the mid cylindrical surface


28


within the mid bore


30


. A smaller portion of the base tube portion


65


extends axially upward beyond the mid bore


30


and above the annular face


26


of the carburetor body


12


. Disposed radially outward and telescopically engaging the smaller portion of the base tube portion


65


is an upper extension tube portion


67


of the fuel feed tube


40


. An end flange portion


71


of the extension tube portion


67


secures rigidly to the annular face


26


thereby supporting the fuel feed tube


40


to the carburetor body


12


. An o-ring


48


seats within the lower bore


34


and seals between mid bore


30


and base tube portion


65


. O-ring


48


thereby prevents leakage of fuel between the mid cylindrical surface


28


of the mid bore


30


and an outer radial surface


46


of the base tube portion


65


or the fuel feed tube


40


.




A lower portion


66


of the rotary throttle


18


has an under annular surface


68


substantially perpendicular to and coaxial with the centerline axis


22


. The under annular surface


68


is positioned above and substantially parallel to the bottom annular surface


50


. The under annular surface


68


and the bottom annular surface


50


axially define a donut-shaped bottom space


70


of the cylindrical chamber


20


. The circumferential face


21


radially outwardly defines the bottom space


70


, and the outer radial surface


46


of the fuel feed tube


40


radially inwardly defines the bottom space


70


. Bottom space


70


interconnects or inter-communicates with the air passage


52


and the passageway


60


. The air guide tube


62


rigidly engages and penetrates the lower portion


66


of the rotary throttle


18


. Air guide tube


62


congruently extends upward from an inner perimeter of the under annular surface


68


and into the throttling bore


24


.




In assembly of carburetor


10


, a cap plate


72


and a metal reinforcement plate


74


close off the cylindrical chamber


20


with rotary throttle


18


received in the carburetor body


12


. Plates


72


,


74


secure to the carburetor body


12


by bolts


76


. Rotation of the rotary throttle


18


is achieved by a throttle lever


82


. Lever


82


secures substantially perpendicularly to an upper end of a shaft portion


80


of the rotary throttle


18


which extends through the cap plate


72


. Rotation of the rotary throttle


18


is restricted by an idle adjustment screw


78


which threads through an upwardly projecting wall on the cap plate


72


. Vertical movement of the rotary throttle


18


, and therefore vertical movement of the needle


44


in the fuel feed tube


40


, is achieved coincidentally to the rotational movement of the rotary throttle


18


. A non-shown cam surface of a groove which changes its depth along a circumferential direction forms on a lower surface of the throttle lever


82


. The cap plate


72


rigidly supports an upward extending follower (not shown) which makes slidable contact with the cam surface. The slope of the cam surface is such, that the rotary throttle


18


lifts upward with the needle


44


when the throttling bore


24


increasingly aligns to the air intake channel


14


.




Remote actuation or rotation of the throttle lever


82


and therefore the rotary throttle


18


is conducted via a control cable. An outer tube of the remote control cable is fixed to a wall portion


84


by a metallic mount fitting


86


. Wall portion


84


extends upward from the metallic reinforcement plate


74


and is a unitary part thereof. An inner wire of the remote control cable is connected to a swivel


88


supported rotatably by the throttle lever


82


.




The throttle lever


18


is biased rotationally against a threaded end of the idle adjustment screw


78


by a return spring, not shown. When the throttle lever


82


is in contact with the idle adjustment screw


78


, the opening ratio of the throttling bore


24


to the air intake channel


14


is set at an idle position. When the throttle lever


82


rotates about centerline axis


22


against the force or resilience of the return spring toward a full-open position, the opening ratio of the throttling bore


24


increases, the rotary throttle


18


and the needle


44


are pushed upward by the contact between the circumferential cam surface and the follower, and the opening ratio of the fuel jet orifice


42


increases. To open the throttle, an operator exerts a force through the control cable which radially winds the return spring as the rotary throttle opens. When the control cable is released, the wound return spring unwinds and the rotary throttle


18


automatically returns to an idle position.




The return spring is received within a circular spring groove


90


formed into the shaft portion


80


of the rotary throttle


18


from above. The return spring is capable of winding upon rotation of the rotary throttle


18


because one end of the return spring is engaged with the rotary throttle


18


and the other end is engaged with the cap plate


72


.




With the rotary throttle fully open, not only is the return spring fully wound, but it is under axial tension. As the rotary throttle opens, or rotates away from the idle position, the contact of the follower with the circumferential cam surface of the throttle lever


82


causes the rotary throttle


18


to lift and the needle


44


to move outwardly from the fuel feed tube


40


against the axial resilience of the return spring. When the operator releases the control cable, the circumferential cam surface of the throttle lever


82


is biased against the follower by the axial tension of the return spring. The cam surface slides against the follower until the throttle lever


82


presses upon the idle adjustment screw


78


as a result of the wound or radial tension of the return spring.




A resilient or pulsation membrane


90


interconnects and seals between an intermediate wall


92


and a bottom end of the carburetor body


12


. Furthermore, resilient membrane


90


is part of fuel pump


94


further comprising a pulsation pressure chamber and a pump chamber with the resilient membrane disposed communicatively there between. A suction check valve is disposed at an inlet side of the fuel pump


94


and a discharge check valve is disposed at an outlet side of the fuel pump. The fuel pump


94


draws fuel from a fuel tank, not shown, through an inlet tube


96


and into the pump chamber. From the pump chamber, the fuel flows through an inflow valve and into the fuel metering chamber. A constant pressure fuel supply mechanism


98


comprises a lower wall


100


disposed beneath the intermediate wall


92


with a resilient membrane


102


disposed sealably between them. An upward facing surface of the membrane


102


defines the constant pressure fuel chamber, and a downward facing surface of membrane


102


defines an atmospheric air chamber.




A suction pump


110


is formed on the lower end of the lower wall


100


. It has, a resilient dome or chamber-wall


104


with its periphery attached to the lower end of the lower wall


100


by a circumferential clamp plate


106


and bolts


108


. The fuel or suction pump


110


has a suction valve at an inlet side and a discharge valve at an outlet side formed or defined by the resilient membrane


102


. By repeatedly manually alternately pushing and releasing the resilient dome


104


of the suction pump


110


before starting the two cycle engine, the vaporized fuel and/or air in the fuel metering chamber is drawn into the resilient chamber-wall


104


and returned to the fuel tank through a discharge tube


112


, and, liquid fuel is supplied from the fuel tank to the fuel metering chamber through the fuel pump


94


.




Referring to

FIGS. 4 and 5

, a second embodiment of the present invention is shown. The air guide tube


262


engages rigidly to the annular face


226


of the carburetor body


212


. Preferably, the annular face


226


concentrically defines an upward or axially extending collar


227


. A radial inward surface of the collar


227


engages a radial outward surface of the air guide tube


262


. The lower portion


266


of the rotary throttle rotates and substantially seals about the air guide tube


262


. The air passage


252


with restrictor


258


directly communicates with the passageway


262


, and the bottom space


270


is generally isolated from any air intake flow.




While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention as defined by the following claims.



Claims
  • 1. A rotary throttle valve carburetor comprising:a carburetor body having an air intake channel, a cylindrical chamber, and an air passage, the air intake channel extending through the carburetor body, the air intake channel having an intake portion disposed upstream, the cylindrical chamber communicating laterally through the air intake channel downstream of the intake portion, and the air passage communicating between the intake portion and the cylindrical chamber; a rotary throttle disposed rotatably and vertically moveably within the cylindrical chamber, the rotary throttle having a throttling bore extended laterally through the rotary throttle and aligned communicably with the air intake channel; an air guide tube disposed within the cylindrical chamber and extending transversely into the throttling bore; a fuel feed tube disposed radially inward of the air guide tube and concentrically to the rotary throttle, the fuel feed tube engaged at one end to the carburetor body and extending transversely into the throttling bore; and a passageway defined radially between the air guide tube and the fuel feed tube, the air passage communicating with the passageway, and the passageway communicating with the throttling bore.
  • 2. The rotary throttle valve carburetor according to claim 1 comprising a needle engaged concentrically with the rotary throttle and extending transversely through the throttling bore and longitudinally into the fuel feed tube.
  • 3. The rotary throttle valve carburetor according to claim 2 wherein the fuel feed tube has a fuel jet orifice communicating with the passageway.
  • 4. The rotary throttle valve carburetor according to claim 3 wherein the air guide tube is engaged rigidly with a lower portion of the rotary throttle.
  • 5. The rotary throttle valve carburetor according to claim 4 wherein the cylindrical chamber has a bottom space defined axially by an under annular face of the lower portion and a face of the carburetor body, the under annular face parallel to the face of the carburetor body, and the bottom space communicating between the air passage and the passageway.
  • 6. The rotary throttle valve carburetor according to claim 5 wherein the carburetor body defines a restrictor adjacent a downstream end of the air passage.
  • 7. The rotary throttle valve carburetor according to claim 6 wherein the downstream end of the air passage communicates with the bottom space through the face of the carburetor body.
  • 8. The rotary throttle valve carburetor according to claim 7 wherein the face of the carburetor body is annular and concentric to the under annular face of the lower portion.
  • 9. The rotary throttle valve carburetor according to claim 8 wherein the air guide tube is concentric to the fuel feed tube.
  • 10. The rotary throttle valve carburetor according to claim 3 wherein the carburetor body has a mid surface and an annular face, the mid surface defines a mid bore communicating concentrically with the cylindrical chamber, the fuel feed tube is engaged circumferentially to the mid surface and extends through the annular face, and the air guide tube is engaged with the annular face.
  • 11. The rotary throttle valve carburetor according to claim 10 wherein the carburetor body has a restrictor adjacent a downstream end of the air passage, and the downstream end communicates with the passageway through the mid surface.
  • 12. The rotary throttle valve carburetor according to claim 11 wherein the annular face of the carburetor body defines a collar engaged with an outer radial surface of the fuel feed tube.
Priority Claims (1)
Number Date Country Kind
11-323875 Nov 1999 JP
RELATED APPLICATION

Applicants claim priority of Japanese patent application, Ser. No. 11-323875, filed Nov. 15, 1999.

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