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