Patent Publication Number: US-6983928-B2

Title: Acceleration apparatus for carburetor

Description:
FIELD OF THE INVENTION 
   The present invention relates to an acceleration apparatus in a carburetor used primarily to supply fuel to general-purpose engines. 
   BACKGROUND OF THE INVENTION 
   It is well known in the art that extra fuel, that is, acceleration fuel, is supplied to the suction channel in response to the rapidly increasing quantity of suction air when the degree of opening of the throttle valve is enlarged to increase the rotational speed of the engine. 
   A carburetor, which is one type of fuel supply system, may comprise an acceleration apparatus having a piston-type (or a diaphragm-type) acceleration pump linked to a throttle valve, for example, a carburetor for an automobile engine, as cited in Japanese Patent Application Laid-open No. 53-81831. This acceleration device delivers and supplies acceleration fuel to the suction channel by transmitting the rotation of the throttle valve to the piston (or diaphragm) of the acceleration pump by means of a link mechanism. 
   Despite the fact that the acceleration apparatus described above is easily applied to a carburetor having a butterfly-type throttle valve, providing the link mechanism described above to the exterior of the carburetor main body in a carburetor for general-purpose engines not only unavoidably results in greater complexity and significantly greater size, which is contrary to basic needs and characteristics that the structure be small and simple, but also makes it essentially impossible to apply such an apparatus to a rotating throttle valve-type carburetor often used in general-purpose engines, because the throttle valve moves in the axial direction while rotating. 
   As a result, it has been proposed that an acceleration apparatus be provided to a rotating throttle valve-type carburetor, as cited in Japanese Utility Model Application Laid-open No. 6-67842, such that a piston-type acceleration pump is disposed at a right angle to the throttle valve stem. The piston is operated by a cam formed on the external peripheral surface of the throttle valve to deliver and supply acceleration fuel to the suction channel. 
   The acceleration apparatus provided to the rotating throttle valve-type carburetor described above does not have a complex link mechanism on the exterior to change the rotating movement of the throttle valve to the linear movement of the acceleration pump. However, very troublesome fabrication is required in that a cam in the form of a groove extending in the circumferential direction must be formed on the external peripheral surface of the cylindrical throttle valve so that the acceleration fuel corresponds to the quantity of the suction air. The cam in the form of a groove additionally raises concern that the airtightness of the external peripheral surface of the throttle valve may be impaired, and that air may be sucked into the suction channel during idling depending on the formation site, resulting in a malfunction in idling. 
   SUMMARY OF THE INVENTION 
   The present invention has a simple structure, and provides a solution to the problems described above; primarily, to provide an acceleration apparatus that could be mounted, in particular, in a carburetor for a general-purpose engine without concern that the resulting construction will become significantly bulkier or that the function thereof will become impaired. 
   The present invention provides a solution to the above-stated problems in an acceleration apparatus for a carburetor having a piston-type acceleration pump linked to the throttle valve. In a first embodiment, the portion of a throttle valve stem that protrudes to the exterior of a carburetor main body is provided with a cam whose circular shape is centered about the throttle valve stem and whose cam surface faces the carburetor main body. In the acceleration pump, a piston rod extends from a piston mounted in a cylinder chamber formed inside the carburetor main body is extended to the exterior of the carburetor main body and is disposed parallel to the throttle valve stem. Acceleration fuel is delivered and supplied to a suction channel from the cylinder chamber by the cam pushing the piston rod along the cam surface as the throttle valve rotates in the opening direction of the throttle valve stem. 
   The cam provided on the throttle valve stem which directly pushes the piston rod to deliver and supply acceleration fuel, has a simple configuration that dispenses with a link mechanism, does not greatly enlarge the carburetor, and allows an accelerator to be obtained without concern for impairing the function of the carburetor. 
   To solve the above-stated problems in an acceleration apparatus for a carburetor having a piston-type acceleration pump linked to the throttle valve in the same manner as above, in a second embodiment of the present invention, the portion of a throttle valve stem that protrudes to the exterior of a carburetor main body is provided with a first cam whose circular shape is centered about the throttle valve and whose cam surface faces the carburetor main body, and a second cam whose cam surface is parallel to the cam surface of the first cam and which faces in the opposite direction. In the acceleration pump, a piston rod extending from a piston mounted in a cylinder chamber formed inside the carburetor main body is extended to the exterior of the carburetor main body and is disposed parallel to the throttle valve stem. The piston rod is provided with a first contact portion and a second contact portion that contact the cam surfaces of the first cam and second cam. Acceleration fuel is delivered and supplied to a suction channel from the cylinder chamber by the first cam pushing the first contact portion along the cam surface thereof as the throttle valve rotates in the opening direction of the throttle valve stem, and fuel is suctioned to replenish the cylinder chamber by the second cam pushing the second contact portion along the cam surface thereof as the throttle valve rotates in the closing direction. 
   The reciprocating movement of the piston is performed by the first cam and second cam, so a piston spring in the acceleration pump is unnecessary. In addition to the effects provided by the first means, an acceleration apparatus can be obtained whereby the length of the cylinder chamber is shortened, the acceleration pump can be made small, and the piston can be lengthened to stabilize the reciprocating movement. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal section showing an embodiment of the present invention. 
       FIG. 2  is a cutaway front view showing another embodiment of the present invention. 
       FIG. 3  is a partial cutaway front view showing yet another embodiment of the present invention. 
       FIG. 4(A)  is a partial cutaway front view, and (B) is a partial cutaway top view showing a different embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Describing the present invention with reference to the diagrams,  FIG. 1  is a longitudinal section showing an embodiment in which the present invention has been applied. The carburetor main body  1  has a suction channel  2  that extends in the transverse direction. A cylindrical valve hole  3  that is orthogonal thereto, extends in the transverse direction, and is sealed at the lower end. A cylindrical throttle valve  4  is fitted into the valve hole  3  while allowed to rotate and move in the axial direction. 
   The throttle valve  4  has a throttle through-hole  5  that is set orthogonally to the center axis line thereof and has substantially the same diameter as the suction channel  2 , and further has a metering needle  15  and a throttle valve stem  8  positioned on the center axis line. The throttle valve stem  8  is fixedly fitted in the top portion of the throttle valve  4 , blocks the open end of the valve hole  3 , passes completely through the cover body  12  mounted on the upper surface of the carburetor main body  1 , protrudes to the exterior, and is fixed to a throttle valve lever  10  at the protruding end. 
   In the space between the throttle valve  4  of the throttle hole  3  and the cover body  12 , a valve-closing spring  11  comprising a torsion coil spring fixed to both ends thereof is internally mounted in a compressed state around the throttle valve stem  8 . A fuel control cam  13  comprising a circular end surface cam centered about the throttle valve stem  8  is formed in a protruding configuration on the lower surface of the throttle valve lever  10 , and the cam surface  13 A facing downward therefrom is placed in contact with a contact piece  14  protruding from the cover body  12 . The metering needle  15  is further attached facing downward to the throttle valve stem  8  by threadably mounting a male screw head body  16  at the base end into the female screw hole  9  of the throttle valve stem  8 , and is extended from the upper portion into the throttle through-hole  5  in a manner that allows the length of the protrusion to be adjusted. 
   A constant fuel chamber  17 , which is cut off from the atmosphere by a diaphragm  18 , is disposed on the lower surface of the carburetor main body  1 , holds a fixed quantity of fuel delivered from the fuel tank by way of a fuel pump (not depicted). The fuel from the constant fuel chamber  17  passes through a primary jet  20  that defines the maximum fuel flow rate from the fuel channel  19 , a check valve  21  that prevents air inflow to the constant fuel chamber from the suction channel  2 , and a pipe-shaped fuel nozzle  22 , and is then delivered to the interior of the throttle through-hole  5  by way of a nozzle aperture  23  disposed on the peripheral side surface thereof. The fuel nozzle  22  protrudes from the lower portion into the throttle through-hole  5  disposed on the center axial line of the throttle valve  4 , the leading end portion of the metering needle  15  is inserted therein, and the aperture surface area of the nozzle aperture  23  is made variable. 
     FIG. 1  shows the condition during idling. When the driver turns the throttle valve lever  10  by operating the accelerator, the throttle valve  4  rotates in an integral manner while twisting the valve-closing spring  11 , and the suction airflow rate is increased by enlarging the degree of overlap with the suction channel  2  and the throttle through-hole  5 . At the same time, the contact piece  14  in contact with the cam surface  13 A pushes up the throttle valve lever  10 , the throttle valve stem  8 , and the throttle valve  4  in accordance with the increase in the height of the fuel control cam  13 , and the fuel flow rate is increased by reducing the insertion depth of the metering needle  15  into the fuel nozzle  22  and enlarging the aperture surface area of the nozzle aperture  23 . When the accelerator operation is lessened or released, the contact piece returns to the idling position along the cam surface  13 A by the action of the valve-closing spring  11 . The above description is the same as for conventional rotary throttle valve-type carburetors. 
   In the acceleration pump  25  comprising the acceleration apparatus of the present invention, a rod-shaped member of uniform diameter, with the top side serving as a piston rod  28  and the lower side serving as a piston  27 , is fitted into a cylinder chamber  26  that extends in the vertical direction and is sealed at the lower end. The space below the piston  27  of the cylinder chamber  26  is connected to the fuel channel  19  between the check valve  21  and the primary jet  20  by way of a conduit  31  to form a pump chamber  29  in which a piston spring  30  comprising a compression coil is mounted. The piston rod  28  is extended completely through the cover body  12  above the carburetor main body  1  and is disposed parallel to the throttle valve stem  8 . 
   A cam  33  comprising a circular end surface cam centered about the throttle valve stem  8  is formed in a protruding configuration on the lower surface of the throttle lever  10 . A contact portion  32 , comprising a sphere rotatably mounted and held on the upper end of the piston rod  28 , is kept in constant contact with the downward facing cam surface  33 A of the cam  33  by means of the piston spring  30 . 
   During idling, the contact portion  32  is in contact with the lowest portion of the cam surface  33 A, as shown in  FIG. 1 . This reduces the friction resistance by rolling in contact with the cam surface  33 A when the throttle valve lever  10  turns due to the driver operating the accelerator, and prevents bending of the piston rod  28  and any wear due to direct contact. The piston rod  28  and the piston  27  integrated therewith are pushed downward as the height of the cam  33  increases, and acceleration fuel from the pump chamber  29  is delivered and supplied to the suction channel  2  from the nozzle aperture  23  by way of the conduit  31  and fuel channel  19 . When the throttle valve lever  10  is returned in the direction of the idling position by a reduction or release in the accelerator operation, fuel from the constant fuel chamber  17  is suctioned to replenish the pump chamber  29  from the fuel channel  19  and the conduit  31  by means of the piston spring  30  pushing up the piston  27  and the piston rod  28  in preparation for the subsequent throttle-opening action, that is, acceleration operation. 
   According to the present embodiment, the piston rod  28  and the cam  33  are disposed in the space between the throttle lever  10  and the cover body  12 . The piston rod  28  is directly moved in a straight line by means of the cam  33  that moves in the circumferential direction in association with the rotation of the throttle valve  8 . The structure is very simple because a mechanism that enlarges the carburetor overall or that is externally disposed is dispensed with, allowing the components to be accommodated in conventionally available space. 
   In the present embodiment, when the throttle valve  4  rotates from the idling position to the completely open position, the contact location on the cam surface  13 A of the contact piece  14  moves from the lowest portion in the idling position to the highest portion in the completely open position. The difference in height H T  is the quantity of movement of the metering needle  15 . In order for the acceleration pump  25  to supply and deliver acceleration fuel to the suction channel  2 , the piston  27  must be pushed downward despite the throttle lever  10  moving upward by H T . For this reason, the difference in height H P  between the location in which the cam surface  33 A is in contact with the contact portion  32  in the idling position, and the contact location in the completely open position in the present embodiment is made larger than H T , and the difference H P −H T  is set to the maximum stroke of the piston  27 . This approach allows acceleration fuel to be reliably delivered and supplied to the suction channel  2 . 
     FIG. 2  is a partial cutaway front view showing another embodiment of the present invention, in which the lower edge  35 A of a driven member  35  with an inverted U-shape profile is fixedly attached to the upper end of the piston rod  28  of the acceleration pump  25 . The piston rod is extended upward completely through the cover body  12  and is disposed parallel to the throttle valve stem  8  in the rotary throttle valve-type carburetor in the same manner as in  FIG. 1 . 
   In the driven member  35 , the external circumferential portion of the throttle lever  10  is inserted between the lower edge  35 A and the upper edge piece  35 B, and a first contact portion  36  and second contact portion  38 . The first and second contact portions  36  and  38  are positioned on the extended center axis line of the piston rod  28 , are configured as rotatably mounted and held spheres, and are set facing each other. The lower edge  35 A has a bifurcated end portion  35 C. The throttle valve stem  8  is interposed to prevent the driven member  35  from rotating in concert with the turning of the throttle valve lever  10 . The bifurcated end portion and throttle valve stem  8  constitute a direct-acting guide  35 D for the piston rod  28 . 
   A first cam  37  and a second cam  39 , which comprise circular end cams centered about the throttle valve stem  8 , are formed in a protruding configuration on the lower surface and upper surface of the throttle valve lever  10 . These cam surfaces  37 A and  39 A are parallel to each other. The cam surface  37 A of the first cam  37  faces the carburetor main body  1  and is brought into contact with the first contact portion  36 . The cam surface  39 A of the oppositely directed second cam  39  is brought into contact with the second contact surface  38 . 
   During idling, the first contact portion  36  makes contact with the lowest portion of the second cam  37 , and the second contact portion  38  makes contact with the highest portion of the second cam  39 , as shown in  FIG. 2 . As a result, when the driver turns the throttle valve lever  10  by operating the accelerator, the piston rod  28  and the driven member  35  are pushed downward in association with the increase in height of the first cam  37 , and acceleration fuel from the pump is delivered and supplied to the suction channel. 
   When the throttle valve lever  10  returns in the direction of the idling position due to the accelerator operation being lessened or released, fuel is suctioned to replenish the pump chamber by the second contact portion  38  pulling up the piston rod  28  and driven member  35  in association with the increase in height of the second cam  39 . 
   According to the present embodiment, a piston spring indispensable to a conventional acceleration pump or the acceleration pump in the embodiment of  FIG. 1  is unnecessary because two cams  37  and  39  perform the action of the acceleration pump  25 , which includes a delivery stroke and a suction stroke. The length of the cylinder chamber, and the pump chamber in particular, can be shortened, the acceleration pump  25  can be made smaller, or the portions that slide within the cylinder chamber of the piston rod  28  and the piston can be extended and the stability of linear reciprocation can be ensured. Rendering the piston spring unnecessary also has the advantage of not increasing the load on the valve-closing spring  11 , which works in the opposite direction. The driven portion  35  is disposed around a side portion of the throttle valve lever  10 , and because it does not greatly project to the exterior of the carburetor, the entire carburetor is not significantly enlarged. 
   In the present embodiment, two contact portions  36  and  38  are kept in constant contact with the cam surfaces  37 A and  39 A. This approach allows the movements of the acceleration pump  25  to precisely follow the opening and closing action of the throttle valve. However, considering dimensional errors in components and deviations in assembly, it is actually preferable to make the space between the two contact portions  36  and  38  slightly larger than the space between the two cam surfaces  37 A and  39 A. Such a configuration reliably prevents the friction resistance from decreasing and acting in concert with the direct-acting guide  35 D to bend the piston rod  28 , and allows the acceleration pump to operate smoothly because the second contact portion  38  is maintained in a state slightly separated from the cam surface  39 A of the second cam  39  when the throttle valve opens, and because the first contact portion  36  is maintained in a state slightly separated from the cam surface  37 A of the first cam  37  when the throttle valve closes. 
     FIG. 3  is a partial cutaway view showing yet another embodiment of the present invention, in which the lower edge  41 A of a driven member  41  with an inverted U-shape profile is fixedly attached to the upper end of the piston rod  28  of the acceleration pump  25 . The piston rod is extended upward completely through the cover body  12  and is disposed parallel to the throttle valve stem  8  in the rotary throttle valve-type carburetor in the same manner as in  FIGS. 1 and 2 . 
   In the driven member  41 , the external circumferential portion of the throttle lever  10  is inserted between the lower edge  41 A and the upper edge piece  41 B, and the following components are set facing each other: a first contact portion  42  positioned on the extended center axis line of the piston rod  28  and configured as a sphere that is rotatably mounted and held on the lower edge  41 A, and a hemispherical second contact portion  45  formed at the leading end of an adjustment screw  44 , which is threadably mounted in the upper edge piece  41 B. A vertically extending side edge  41 C is fitted into a vertical guide groove  12 A formed in the cover body  12  to prevent the driven member  41  from rotating in concert with the turning of the throttle valve lever  10 . The side end  41 C and guide groove  12 A constitute a direct-acting guide  41 D for the piston rod  28 . 
   An annular stopper  47  that surrounds the adjustment screw  44  and protrudes upward is integrally provided to the upper edge piece  41 B. The head of the adjustment screw  44  is configured to prevent excessive threadable insertion of the adjustment screw by making contact with the stopper  47 . The stopper may be an annular piece separate from the upper edge piece  41 B. 
   A first cam  43  and a second cam  46 , which comprise circular end cams centered about the throttle valve stem  8 , are formed in a protruding configuration on the lower surface and upper surface of the throttle valve lever  10 . These cam surfaces  43 A and  46 A are parallel to each other, the cam surface  43 A of the first cam  43  faces the carburetor main body  1  and is brought into contact with the first contact portion  42 , and the cam surface  46 A of the oppositely directed second cam  46  is brought into contact with the second contact surface  45 . 
     FIG. 3  shows the state during idling, in which the first contact portion  42  is slightly separated downward from the lowest portion of the first cam  43 . When the adjustment screw  44 , which causes the second contact portion  45  to come into contact with the lowest portion of the second cam  46 , is turned in the screw-in direction, the space between the two contact portions  42  and  45  is reduced and the first contact portion  42  moves to come into contact with the first cam  43 . The stopper  47  prevents the drawback in which the adjustment screw  44  is excessively threadably inserted, causing both contact portions  42  and  45  to bite into the cam surfaces  43 A and  46 A, and resulting in reduced performance. When the adjustment screw  44  is turned in the removing direction, the space between the two contact portions  42  and  45  is increased and the first contact portion  42  further separates from the first cam  43 . 
   When the throttle valve lever  10  is turned from the state shown in  FIG. 3  by the driver operating the accelerator, the height of the second cam  46  that is in contact with the second contact portion  45  is reduced, the acceleration pump  25  is stopped in an inoperative position without being operated by friction resistance of the piston or piston rod  28 , by the fuel pressure within the pump chamber, the channel resistance of the fuel, or the like, and the second contact portion  45  separates from the second cam  46 . On the other hand, when the height of the first cam  43  increases, the cam surface  43 A thereof comes into contact with the first contact portion  42 , the piston rod  28  and the driven member  41  are thereafter pushed downward in association with the increasing height of the first cam  43 , and acceleration fuel from the fuel chamber is delivered and supplied to the suction channel. The first cam  43  pushes the driven member  41  down, and the second contact portion  45  is thereafter held in a state separated by a fixed space from the cam surface  46 A of the second cam  46 . 
   When the accelerator operation is lessened or released, the throttle valve lever  10  returns in the direction of the idling position, the first contact portion  42  separates from the gradually lowering first cam  43 , the piston rod  28  and the driven member  41  stop in the pressed-down position, and the gradually rising second cam  46  makes contact with the second contact portion  45  and then lifts the piston rod  28  and driven member  41  to suction in the fuel and fill the pump chamber. 
   The linear reciprocating movement of the acceleration pump  25  is performed by the two cams  43  and  46  in the present embodiment as well, so the same effects exhibited in the embodiment shown in  FIG. 2  can be achieved, making it possible to provide a smaller acceleration pump  25 , to ensure the stability of linear reciprocation, and to increase the size of the entire carburetor only slightly. 
   According to the present embodiment, the space between the two contact portions  42  and  45  is additionally made steplessly adjustable according to the depth of the threadable insertion of the adjustment screw  44 . These portions can be arbitrarily adjusted from a state in which a maximum stroke is provided to the acceleration pump  25  in contact with the cams  43 A and  46 A, to a state in which the first contact portion  42  comes into contact with the first cam  43  in a position proximate to the one in which the throttle valve of the throttle valve lever  10  is completely open, and in which a minimum stroke is provided to the acceleration pump  25 , allowing the acceleration fuel flow rate to be steplessly adjusted so as to correspond to a variety of engine demands. 
   In the embodiments in  FIGS. 2 and 3 , the difference in height H P   1  between the contact locations in the completely open positions and those in the idling positions of the cam surfaces  37 A and  43 A on these first cams  37  and  43  in relation to the first contact portions  36  and  42 , and the difference in height H P   2  between the contact locations in the completely open positions and those in the idling positions of the cam surfaces  39 A and  46 A on these second cams  39  and  46  in relation to the second contact portions  38  and  45  must be mutually equal and greater than the movement quantity H T  in the axial direction of the throttle valve stem  8  shown in  FIG. 1 . However, it is apparent in relation to a carburetor in which the throttle valve is a butterfly-type and the throttle valve stem does not move in the axial direction, that H P  in  FIG. 1  and H P   1  and H P   2  in  FIGS. 2 and 3  need merely be set with consideration of the piston stroke of the acceleration pump  25  only, without regard to H T . 
   Next,  FIG. 4  shows yet another embodiment of the direct-acting guide for the piston rod in a device having two contact portions and two cams in the same manner as the embodiments of  FIGS. 2 and 3 . 
   The driven member  51  in this embodiment is configured such that the first contact portion  53  protrudes upward from the lower edge  51 A, and the second contact portion  55  protrudes downward from the upper edge piece  51 B, in the same manner as the driven members  35  and  41  described above. Protruding edges  52   a  and  52   b  facing the external circumference  10 A of the throttle valve lever  10  are disposed with a small space therebetween on both sides of the side edge  51 C of this driven piece  51 . The two contact portions  53  and  55  are disposed on the extended center axis line of the piston rod  28 . A first cam  54  that pushes the piston rod  28  downward and a second cam  56  that lifts it upward are formed on the lower surface and upper surface of the throttle valve lever  10 , in the same manner as the embodiments of  FIGS. 2 and 3 . The region along the first cam  54  and the second cam  56  of the external circumference  10 A of the throttle lever  10  is made circular with the throttle valve stem  8  as the center, and the two protruding edges  52   a  and  52   b  are configured so as to be constantly facing the circular portion when the throttle lever  10  turns between the idling position and the completely open position. 
   When the throttle lever  10  turns, the first contact portion  53 , which is in contact with the first cam  54 , and the second contact portion  55 , which is in contact with the second cam  56 , move in the turning direction and attempt to pull and rotate the driven member  51 , one of the protruding edges  52   a  and  52   b  stops the co-rotation by making contact with the external circumference  10 A, and the piston rod  28  linearly reciprocates without bending even when the throttle valve rotates in either the opening direction or the closing direction. In other words, the circular external circumference  10 A and the two protruding edges  52   a  and  52   b  in the present embodiment constitute a direct-acting guide  51 D for the piston rod  28 . 
   In the implementation of the present invention, the cam  33  of  FIG. 1 , the first cams  37 ,  43 , and  54 , and the second cams  39 ,  46 , and  56  in  FIGS. 2 to 4  may be attached to the throttle valve stem  8  as respectively independent components, but attaching these to the throttle valve lever  10  as in the depicted embodiments has advantages in that the throttle valve stem  8  need not largely protrude from the carburetor main body, and the size of entire carburetor is not significantly increased. 
   As described above, according to the present invention, a piston-type accelerator pump can be linked to the throttle valve and operated in a simple configuration that dispenses with a link mechanism and does not greatly enlarge the carburetor. An accelerator particularly suitable for the carburetors of general-purpose engines can be obtained without concern of impairing the function of the carburetor.