Patent Publication Number: US-7717403-B2

Title: Accelerator device for a carburetor

Description:
REFERENCE TO RELATED APPLICATION 
     Applicant claims priority from Japanese Patent Application Ser. No. 2007-52334, filed Mar. 2, 2007. 
     FIELD OF THE INVENTION  
     The present invention relates generally to carburetors and more particularly to an accelerator device for a carburetor. 
     BACKGROUND OF THE INVENTION  
     Some small internal combustion engines for handheld power tools such as chain saws, grass trimmers, weed trimmers, leaf blowers, and the like have carburetors with an internal accelerator pump which supplies additional fuel to the operating engine as the throttle valve of the carburetor is opened from its essentially closed or idle position toward its wide open throttle position. The accelerator device can temporarily increase the amount of fuel delivered to the engine when the throttle valve is opened fully for improving the acceleration of the engine. This additional fuel is needed to smoothly and rapidly accelerate the engine without stumbling, particularly when the engine is under a load. 
     SUMMARY OF THE INVENTION  
     According to one implementation, a carburetor includes an intake bore, a throttle valve, a main fuel nozzle opening into the intake bore, an accelerator device and a fuel passage. The throttle valve is movable between an idle and wide open positions to control fluid flow through the intake bore and includes a shaft rotatably supported around an axial line extending across the intake bore. The accelerator device may be operable to increase an amount of fuel that flows through the main fuel nozzle when the throttle valve is moved toward its wide open position, and may include a fuel reservoir constructed and arranged to store fuel. The fuel passage communicates with the main fuel nozzle, and may include a first portion communicating with a fuel metering chamber, and a second portion communicating with the main fuel nozzle. The fuel reservoir is provided between the first fuel passage portion and the second fuel passage portion and forms a part of the fuel passage and fuel flows through the fuel reservoir and to the main fuel nozzle both when the throttle valve is opened and when the throttle valve is closed. 
     According to at least one implementation, a carburetor includes an intake bore from which fuel and air are discharged from the carburetor, a fuel chamber from which fuel is supplied within the carburetor, a main fuel nozzle communicating with the fuel chamber and the intake bore and through which fuel flows into the intake bore, a fuel passage communicating with the fuel chamber and the main fuel nozzle, and an accelerator device for increasing an amount of fuel provided to the main fuel nozzle during acceleration of an engine with which the carburetor is used, the accelerator device including a fuel reservoir constructed and arranged to store fuel wherein the fuel reservoir defines at least part of the fuel passage so that fuel flows through the fuel reservoir before the main fuel nozzle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       These and other objects, features and advantages of the present 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 partly broken away sectional view of one embodiment of a carburetor; 
         FIG. 2  is a fragmentary sectional view of the carburetor of  FIG. 1  showing a throttle valve in its idle position; and 
         FIG. 3  is a fragmentary sectional view of the carburetor of  FIG. 1  showing the throttle valve in its wide open position. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
     Referring in more detail to the drawings,  FIG. 1  illustrates one embodiment including a diaphragm type carburetor  1  for an internal combustion gasoline fueled engine with an accelerator device or pump D. The carburetor  1  may be used, for example, in a small general-purpose internal combustion engine. The diaphragm carburetor  1  also has a fuel supply pump assembly E and a fuel metering system C, each of which, if desired, may be of conventional construction. In one embodiment, the carburetor  1  may be a butterfly valve type carburetor. 
     When the engine is operating, the fuel pump assembly E supplies fuel to the metering system C of the carburetor  1 . The fuel pump assembly E has a flexible diaphragm or membrane  5  received and sealed between an upper face of the carburetor body  26  and a lower face of an upper cover  28  and defining in part a fuel pump chamber  6  and a pulsating pressure chamber or pulse chamber  55  to which pressure and vacuum pulses in the crankcase of an operating engine are introduced through a passage  30  to displace or actuate the diaphragm  5 . The fuel pump chamber  6  communicates with an external fuel tank (not shown) via an inlet passage  32  formed in the carburetor main body and a one-way check valve  7  and a reciprocating movement of the diaphragm  5  caused by the pulsating pressure draws fuel from the fuel tank and feeds it into the pump chamber  6 . The movement of the diaphragm  5  draws the fuel through inlet passage  32  and one-way check valve  7  into the pump chamber  6  and supplies the fuel under pressure through an outlet passage  34 , one-way check valve  8 , and a screen  36 , to the fuel metering system C through a flow control valve  9 . A fuel-intake movement of the pump diaphragm  5  causes the check valve  8  to close and the check valve  7  to open and to thereby allow fuel to be drawn from the fuel tank. A fuel expelling movement of the pump diaphragm  5  causes the check valve  8  to open and the check valve  7  to close and to thereby force the fuel from the fuel tank into a fuel chamber or fuel metering chamber  11  of the fuel metering system C through which fuel is supplied within the carburetor. 
     The fuel metering system C has a flexible diaphragm or membrane  12  received and sealed between a lower face of the carburetor body  26  and a lower cover  40 . The diaphragm  12  defines on one side the fuel metering chamber  11  and on the other side an atmospheric air chamber  13 . The atmospheric air chamber  13  communicates with the atmosphere exteriorly of the carburetor through a port  42  in the lower cover  40 . The flow valve  9  is opened and closed to control the admission of fuel to chamber  11  by movement of the diaphragm  12  which is operably connected to the valve  9  by a lever  15 . At one end, the lever  15  is connected to the flow valve  9 , and at the other end the lever  15  bears on a projection  46  attached to the center of the diaphragm  12 . The lever  15  is rotatably supported by a pivot shaft  14  and yieldably biased by a spring  48  bearing on the lever  15  to bias the valve  9  to its closed position. In one embodiment, the lever  15  is resiliently urged in the direction to abut an end of the lever  15  against projection  46 . 
     When the pressure of the atmospheric chamber  13  is higher than the pressure of the fuel metering chamber  11  to such an extent that the diaphragm  12  is displaced in a direction reducing the volume of the fuel metering chamber  11 , the projection  46  pushes on and moves the lever  15  about its pivot  14 , and the resulting counter clockwise rotation of the lever  15  opens the fuel feed control valve  9 . Fuel then flows into the fuel metering chamber  11 . 
     The carburetor  1  has an intake bore or air and fuel mixing passage  2  with an air inlet  52 , downstream of the inlet a restricted venturi section  54 , and downstream of the venturi  54  an outlet  56  which communicates with an intake passage of the engine. A throttle valve head  3  is received in the intake bore  2  downstream of the venturi  54  and is mounted on a throttle valve shaft  4  extending transversely through the bore and journalled for rotation in the carburetor body  26 . 
     In operation of the carburetor  1 , fuel is supplied from the metering chamber  11  to a main fuel nozzle  21  opening into the intake bore  2  via a check valve  17 , a first fuel passage  16   a , a fuel reservoir chamber  18   a , a second fuel passage  16   b , a fuel metering needle valve  19 , and a check valve  22 . Fuel is also supplied from the metering chamber  11  to a series of low speed fuel nozzles or ports  38  which may open into the intake bore  2  both upstream and downstream of the throttle valve  3  in its idle or closed position, via a passage  58 , an adjustable low speed fuel regulating needle valve  60 , and a passage  62 . 
     In operation, air flowing through the intake bore  2  creates a pressure differential causing fuel to flow through the low speed nozzle  38  downstream of the throttle valve  3  (in its idle position) into the intake bore  2  and in the engine under idle and near idle operating conditions, and to flow through the main fuel nozzle  21  into the intake bore  2  and the engine when the engine is in the range from near idle to wide open throttle operating conditions. This pressure differential acts on the diaphragm  12  to open and close the valve  9  to maintain a predetermined quantity of fuel in the metering chamber  11  and at a substantially constant pressure when the engine is operating to supply fuel to the low speed nozzle  38  and the main fuel nozzle  21 . 
     As shown in  FIG. 1 , in one embodiment the accelerator device or pump D is provided inside the carburetor body  26  adjacent the throttle shaft  4  in an area spaced or remote from or outside of the intake bore  2 . The accelerator pump D may increase the amount of fuel discharged from the main fuel nozzle  21  and into the intake bore  2  when opening the throttle valve  3 . The accelerator pump D may include a piston  23  axially slidably received in a cylindrical chamber  18  and a cam  4   a  which may be carried by or formed in the throttle valve shaft  4 . In one embodiment the piston  23  may be a short, cylindrically shaped piston. In one embodiment, the other end of the cylindrical chamber  18  is closed by a plug  64  press fit therein. A fuel reservoir chamber  18   a  is defined by the cylindrical chamber  18  and an end surface of the piston  23 . The fuel reservoir chamber  18   a  is configured to store fuel and communicates with both the fuel metering chamber  11  and the main fuel nozzle  21 . The accelerator pump D draws fuel into the fuel reservoir chamber  18   a  when closing the valve  3  and expels fuel out of the fuel reservoir chamber  18   a  when opening the valve  3 , in synchronism with a valve opening and closing movement of the valve shaft  4 . 
     The piston  23  may be located laterally adjacent to the intake bore  2 . The intake bore  2  includes a block member to communicate an upstream part of an intake passage with a downstream part thereof. The valve  3  is provided in the downstream part of the intake bore  2  to selectively close and open the intake bore  2 . The valve  3  may be integrally secured, for example by using screws, to a valve shaft  4 . The valve shaft  4  may be rotatably supported around an axial line extending perpendicularly to the intake bore  2  or across the intake bore  2 . An end of the valve shaft  4  that extends out of the carburetor main body is fixedly fitted with a throttle lever (not shown) so that the intake bore  2  can be opened and closed by actuating the throttle lever. 
     The first fuel passage  16   a  communicates with the fuel metering chamber  11  and the chamber  18   a . The check valve  17  may comprise a disk-shaped valve member which is configured to selectively close the first fuel passage  16   a  facing the fuel metering chamber  11  under gravitational force and to be lifted by the force of the flow of fuel, and comprises a retainer that limits the opening movement of the valve member and has a cutout or holes to permit the flow of fuel through the retainer even when the valve member is engaged with the retainer. 
     The first fuel passage  16   a  and the second fuel passage  16   b  open into the fuel reservoir  18   a . The fuel reservoir  18   a  may be provided in an intermediate part of the overall fuel passage  16   c  comprising the first and second fuel passages  16   a  and  16   b , and forms a part of the fuel passage  16   c . The fuel passage  16   c  communicates with and may extend from the fuel metering chamber  11  to the main fuel nozzle  21  and passes through and/or includes the fuel reservoir  18   a . The first fuel passage  16   a  communicates with the second fuel passage  16   b  via the fuel reservoir  18   a . The second fuel passage  16   b  communicates with a main fuel nozzle  21  via the fuel metering needle valve  19 . The main fuel nozzle  21  may have the shape of a cylindrical cup, and may include a head formed with a fuel ejection orifice and projecting into the venturi  54  formed in the intake bore  2 . The fuel ejection orifice may be selectively closed by the check valve  22 . In one embodiment, the check valve  22  may have an identical structure as the check valve  17 . 
     The valve shaft  4  extends across a part of the cylinder chamber  18  that is located on the opposite side of the fuel reservoir  18   a  with respect to the piston  23 . A ball  24  is disposed in the cylinder chamber  18  and between the valve shaft  4  and the piston  23 . In this implementation, the piston  23  is actuated by a cam  4   a  that is connected to, carried by or actuated by the valve shaft  4  and engages the spherical ball  24  disposed between them and received in a recess  66  in an end of the piston  23 . As shown in  FIGS. 2 and 3 , the valve shaft  4  may include a portion with a D-shaped cross section defining at least part of the cam  4   a  in this implementation. The cam  4   a  displaces the piston  23  in synchronism with a valve opening and closing movement of the valve shaft  4 . 
     In one embodiment, a seal may be provided between the piston  23  and the bore  18  by an O-ring (not shown) and the piston  23  is yieldably biased towards its retracted position and into engagement with the ball  24  which in turn is urged into engagement with the cam  4   a  by a spring  25  received in the reservoir  18   a  and bearing on the piston  23 . In one implementation, the cam  4   a  consists of a flat cutout surface  4   b  of the throttle shaft  4 . In the fully closed state of the throttle valve  3  illustrated in  FIG. 2 , the ball  24  engages the cutout surface  4   b  so that the volume of the fuel reservoir  18   a  is maximized. 
     Referring to  FIG. 2 , when the valve shaft  4  is turned in the direction indicated by arrow A (or counter clockwise as viewed in  FIG. 2 ) to open the throttle valve, the ball  24  is displaced toward the piston  23  so that the piston  23  is displaced in the direction indicated by arrow B ( FIG. 3 ). In this manner, the movement of the piston  23  resulting from the rotation of the valve shaft  4  toward the fully open position reduces the volume of the fuel reservoir  18   a , and the amount of the fuel corresponding to the reduction in the volume of the reservoir  18   a  is moved into the fuel passage  16   b . Because the first fuel passage  16   a  has the check valve  17 , the fuel that is pushed out from the fuel reservoir  18   a  is forwarded to the second fuel passage  16   b , and discharged into the intake bore  2  via the main fuel nozzle  21 . Therefore, the amount of fuel ejection can be increased at the time of opening the throttle valve, and a favorable acceleration performance can be achieved. 
     When the valve shaft  4  is turned from the state illustrated in  FIG. 3  (fully open state) in the valve closing direction, the ball  24  rides onto the flat cutout surface  4   b  of the valve shaft  4 . The further rotation of the valve shaft  4  in the valve closing direction allows the point of contact between the cutout surface  4   b  and the ball  24  to move away from the fuel reservoir  18   a . Because the return spring  25  urges the piston  23  toward the valve shaft  4 , the piston  23  is pushed back to the initial position (fully closed position). 
     As can be appreciated from the foregoing description, the fuel reservoir  18   a  may be provided in an intermediate part of the fuel passage  16   c  and forms a part of the fuel passage  16   c  through which the fuel flows from the metering chamber  11  to the intake passage  2 . Even when the accelerator pump D is not operating, fuel flows to the main fuel nozzle  21  through the fuel passage  16   c . All the fuel therefore passes through the fuel reservoir  18   a  before being delivered to and expelled from the main fuel nozzle  21 . If bubbles are produced in the first and second fuel passages  16   a  and  16   b  due to the transfer of heat from the engine main body and/or the vibrations of the carburetor main body  1 , or for any other reason, the bubbles are carried away by the flow of the fuel through the fuel passage  16   c  and do not remain trapped in the fuel reservoir  18   a . As a result, when the amount of fuel to be discharged through the main fuel nozzle  21  is temporarily increased by opening the throttle valve  3 , this fuel contains few, if any, bubbles, and a favorable accelerating performance can be achieved at all times. This may not be true in accelerator pump arrangements wherein a reservoir is disposed downstream of the main fuel nozzle and communicates therewith by a branch passage. When the accelerator pump is not operating, fuel does not flow through the reservoir but rather passes directly to a fuel nozzle and hence, vapor bubbles may collect or increasingly form in the reservoir and thereby reduce the volume available for liquid fuel. When this happens, less fuel is displaced by the accelerator pump and engine performance can be adversely affected. 
     In the embodiments shown in the figures, the pump arrangement includes a piston slidably received in a cylinder or chamber to move fuel into and out of the chamber. In other embodiments, the pump arrangement is not limited by such a cylinder/piston pump, but may consist of any pump as long as it is capable of achieving a pump action in synchronism with the rotation of the valve shaft  4 . Likewise, the throttle valve is shown as a butterfly type-throttle valve but other construction and arrangements may be used. Still other modifications and alternatives are possible and contemplated to be within the scope of the following claims.