Patent Publication Number: US-7216856-B2

Title: Accelerator apparatus for diaphragm carburetor

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to accelerator apparatus provided in diaphragm carburetors for supplying fuel to compact, general purpose engines. 
   2. Description of Related Art 
   It is known that an accelerator apparatus having an accelerator pump mechanically coupled to a throttle valve may be provided as a means for increasing a rate of fuel flow delivered to an intake passage of a carburetor in response to an increased amount of air intake, during accelerated operation of an engine. 
   In known diaphragm carburetors, as depicted in conceptual diagrams in  FIGS. 2A ,  2 B, and  2 C, in which fuel delivered from a fuel tank by a fuel pump is held in a fixed fuel chamber at a fixed pressure by utilizing a diaphragm and an atmospheric pressure. Such fuel then is delivered to an intake passage from the fixed fuel chamber and supplied to an engine. 
   Referring to the structure shown in  FIG. 2A , which is described, for example, in Japanese Unexamined Patent Publication No. 60-195365, the disclosure of which is incorporated herein by reference; a main jet  54  defining a maximum rate of fuel flow and a regulating needle valve  55  regulating a rate of fuel flow are disposed in a main fuel passage  53  extending from a fixed fuel chamber  51  to a main nozzle port  52 . Further, a pump chamber  58  of an accelerator pump  57  is connected to main fuel passage  53  downstream of regulating needle valve  55  by a single accelerated fuel passage  59 . Further, referring to the structure shown in  FIG. 2B , which is described, for example, in Japanese Unexamined Patent Publication No. 10-238411, the disclosure of which is incorporated herein by reference; a check valve  56 , which prevents air from flowing into main jet  54  and fixed fuel chamber  51 , and regulating needle valve  55  are disposed in main fuel passage  53 . Accelerated fuel passage  59  is connected to main fuel passage  53  between main jet  54  and check valve  56 . Further, referring to the structure shown in  FIG. 2C , which is described, for example, in Japanese Unexamined Utility Model Publication No. 6-67842 and Japanese Unexamined Patent Publication No. 10-213013, the disclosures of which are incorporated herein by reference; check valve  56  and regulating needle valve  55  are disposed in main fuel passage  53 . Accelerated fuel passage  59  is connected to main fuel passage  53  between check valve  56  and regulating needle valve  55 . 
   Accelerator pump  57  and accelerated fuel passage  59  define an accelerator apparatus. Regardless, whether the throttle valve is a butterfly throttle valve or a rotary throttle valve, as described in each of the Japanese references mentioned above, accelerator pump  57  discharges fuel in pump chamber  58  during acceleration and is coupled mechanically to the throttle valve so as to deliver fuel to main nozzle port  52  from accelerated fuel passage  59  and main fuel passage  53 , and accelerator pump  57  draws in fuel in fixed fuel chamber  51  to pump chamber  58  from main fuel passage  53  and accelerated fuel passage  59  during deceleration. 
   In the accelerator apparatus described above, connecting accelerated fuel passage  59  to main fuel passage  53  has been attempted to improve the carburetor&#39;s acceleration response. Nevertheless, when introducing fuel into a newly manufactured carburetor or after the carburetor has not been in use for a long period of time, it frequently occurs that air remains in pump chamber  58 . Further, if fuel vapor is generated in pump chamber  58  due to engine heat which remains after the engine is shut down, such fuel vapor may accumulate within pump chamber  58  due to a positional attitude of accelerator pump  57  and a configuration of accelerated fuel passage  59 . Further, air and fuel vapor are discharged little by little during engine operation so as to enter into main fuel passage  53 , and disrupt the rate of fuel flow set by main jet  54  and regulating needle valve  55 . In particular, in the structure shown in  FIG. 2A , discharged air and fuel vapor entering main fuel passage  53  adversely affect the regulation of the rate of fuel flow of regulating needle valve  55 . Similarly, in the structures shown in  FIGS. 2B and 2C , discharged air and fuel vapor entering main fuel passage  53  dilutes an air-fuel mixture during discharging. Further, fuel vapor exerts a pumping effect, pushing out fuel within pump chamber  58  due to vibration of the engine during engine operation or a negative pressure pulsation of a venturi portion to which main nozzle port  52  is open. As a result, and fuel may be delivered to the intake passage irregularly so as to make an air-fuel ratio unstable. 
   As a result of these phenomena, undesirable results may occur. For example, engine operation may become unstable, and the content of harmful materials may be increased in the exhaust gas. 
   SUMMARY OF THE INVENTION 
   The present invention prevents an air-fuel mixture from becoming diluted or an air-fuel ratio from becoming destabilized in the known accelerator apparatus mentioned above, in which the single, accelerated fuel passage, which draws and discharges the accelerated fuel to the pump chamber of the accelerator pump, is connected to the main fuel passage from the fixed fuel chamber to the main nozzle port. An object of the present invention is to provide an accelerator apparatus which neither destabilizes engine operation nor causes an increase of a harmful material in the exhaust gas, even if air remains within a pump chamber or fuel vapor is generated. 
   In accordance with the present invention, a means for solving the problem mentioned above is provided by an accelerator apparatus of a diaphragm carburetor, as disclosed herein. Such an accelerator apparatus may comprise an accelerator pump mechanically coupled with a throttle valve; and a single accelerated fuel passage drawing fuel to a pump chamber and delivering fuel as an accelerated fuel. The accelerated fuel passage connects the pump chamber to a fixed fuel chamber in which the fuel is delivered to an intake passage and is stored at a fixed pressure. 
   The fixed fuel chamber is set at a negative pressure slightly lower than atmospheric pressure, and the fuel is delivered from an idle port, a slow port, and a main nozzle port in a butterfly-type throttle valve system and is delivered from the main nozzle port in a rotary-type throttle valve system, in correspondence to a difference from the negative pressure in the intake passage. The accelerated fuel, which the accelerator pump discharges during acceleration, is fed to the fixed fuel chamber so as to reduce the negative pressure or set a positive pressure, and increases the pressure difference from the negative pressure in the intake passage so as to increase the delivered fuel to the intake passage. In other words, the increased fuel flow corresponds to the accelerated fuel. 
   On the other hand, because the air and the fuel vapor within the pump chamber enters into the fixed fuel chamber although being discharged little by little, a rate of fuel flow delivered to the intake passage is not disrupted. Further, because the fuel, which is extruded from the pump chamber due to the pumping effect of the air and the fuel vapor, enters into the fixed fuel chamber, the flow rate of fuel flow delivered to the intake passage does not become irregular. 
   In accordance with the present invention, a deviation of the fuel flow rate and an irregular fluctuation are not generated by the air remaining in the pump chamber and the generated fuel vapor while achieving a desired, accelerated fuel supplying function. Thus, it is possible to reduce or eliminate the risk that the harmful material in the exhaust gas will increase and to stabilize the engine operation during steady operation. 
   Further objects, features, and advantages of the present invention will be understood from the following detailed description of preferred embodiments of the present invention with reference to the accompanying figures. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention now are described with reference to the accompanying figures, which are given by way of example only, and are not intended to limit the present invention. 
       FIG. 1  is a vertical, cross-sectional view showing an embodiment in accordance with the present invention. 
       FIGS. 2A ,  2 B, and  2 C are diagrams of known diaphragm carburetors. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   A description id provided below of an embodiment in accordance with the present invention with reference to  FIG. 1 . A fixed fuel chamber  8  is separated from an atmospheric chamber  9  by a diaphragm  7 , and fixed fuel chamber  8  is provided in a lower surface of a carburetor main body  1 . Carburetor main body  1  is provided with a horizontal intake passage  2  having a choke valve  3 , a venturi tube  4 , and a throttle valve  5 . A manual start pump and a pulsation-type fuel pump, which are not illustrated, additionally are provided in carburetor main body  1 . Fuel in a fuel tank (not shown) is fed to the fixed fuel chamber  8  by the start pump or the fuel pump. Diaphragm  7  is displaced due to a difference between the pressure in fixed fuel chamber  8  and the atmospheric pressure in the atmospheric chamber  9  so as to open and close an inlet valve (not shown). Diaphragm  7  controls a fed fuel flow rate so as to cause fixed fuel chamber  8  store the fuel at a fixed negative pressure slightly lower than the atmospheric pressure. 
   The fuel in fixed fuel chamber  8  is delivered to a main nozzle port  13  open to venturi tube  4  through a main fuel passage  10 , and is delivered to an idle port and a slow port open to intake passage  2  in a side portion of butterfly-type throttle valve  5  through a low speed fuel passage (not shown). Main fuel passage  10  has a main jet  11  defining a maximum fuel flow rate, and a manual regulating needle valve  12  inserted into main jet  11  and regulating the fuel flow rate. Main nozzle port  13  is provided with a check valve  14  which prevents air in intake passage  2  from entering into fixed fuel chamber  8 . 
   A notch is provided in an axial end portion of a throttle valve shaft  6  attaching to throttle valve  5 , and a notched surface and a hemispherical surface form a cam  22 . Cam  22  is arranged in a cylinder chamber  23  formed in the carburetor main body  1  so as to be orthogonal to throttle valve shaft  6 . A protruding piston rod  25  is brought into contact with a piston  24  fitted to the cylinder chamber  23 . A space opposite to cam  22  with respect to piston  24  of cylinder chamber  23  forms a pump chamber  26 , and a push spring  27 , which urges piston rod  25  into contact with cam  22 , is fitted therein. Cylinder chamber  23 , piston  24 , piston rod  25 , pump chamber  26 , and push spring  27  mentioned above constitute an accelerator pump  28 . 
   Pump chamber  26  is connected to the fixed fuel chamber  8  by a single, accelerated fuel passage  29 , and accelerator pump  28  and accelerated fuel passage  29  constitute an accelerator apparatus  21 . 
   When throttle valve  5  is at an idle position, piston rod  25  is brought into contact with the notched surface of cam  22  so as to increase pump chamber  26  to a maximum volumetric capacity. When throttle valve  5  is opened, piston rod  25  is brought into contact with the hemispherical surface of cam  22  so as to push piston  24 , thereby feeding fuel in pump chamber  26  to fixed fuel chamber  8  from accelerated fuel passage  29 . Accordingly, in fixed fuel chamber  8 , the negative pressure is reduced and becomes a positive pressure, and the pressure difference between the negative pressure generated in the region of throttle valve  5  of intake passage  2  and venturi tube  4  increases, so that the amount of fuel delivered from the idle port, the slow port, and main nozzle port  13  is increased. The increased fuel is supplied as accelerated fuel to the engine. 
   Because an amount of fuel fed to fixed fuel chamber  8  from pump chamber  26  is relatively small and because a pressure increase within fixed fuel chamber  8  is temporary, the delivery of accelerated fuel is finished quickly, and fuel immediately is returned to a predetermined negative pressure. Further, fuel in fixed fuel chamber  8  is drawn into pump chamber  26  when throttle valve  5  is closed. Nevertheless, because the negative pressure within fixed fuel chamber  8  increases so as to substantially open the inlet valve at this time, a significant amount of fuel is fed from the fuel pump, and fuel immediately is returned to the predetermined negative pressure when an increase of the volumetric capacity of pump chamber  26  is finished. In other words, in accordance with the present embodiment, it is possible not only to properly supply the accelerated fuel required during acceleration and with a good response, the amount of fuel delivered is reduced or the fuel is not delivered because the negative pressure in fixed fuel chamber  8  increases during deceleration, so that a fuel cutting effect during deceleration can be obtained. Further, because fixed fuel chamber  8  immediately is returned to the predetermined negative pressure when the acceleration and the deceleration are finished, it is possible to stably maintain engine operation thereafter. 
   Next, if the fuel is introduced to a newly manufactured carburetor or after the carburetor has not been used for a substantial period of time, the air frequently remains within pump chamber  26 . Further, when the engine ceases operation, fuel vapor may be generated within pump chamber  26  due to engine heat. If the engine is operated in a state in which the air and the fuel vapor remain within the pump chamber  26 , the air and the fuel vapor are discharged little by little so as to enter into fixed fuel chamber  8 . Further, when the air and the fuel vapor create the pumping effect for extruding fuel within pump chamber  26  due to the vibration of the engine and the machine, the extruded fuel enters into fixed fuel chamber  8 . Accordingly, the flow rate of fuel flow delivered to intake passages during the steady operation is not disrupted so as to dilute the air-fuel mixture, and the fuel flow rate is not altered irregularly so as to destabilize the air fuel ratio, thereby stabilizing engine operation during the steady operation and preventing the harmful material content in the exhaust gas from increasing. 
   Because accelerated fuel passage  29  is provided independently from main fuel passage  10 , pump chamber  26  is not affected by the influence of the negative pressure pulsation of venturi tube  4 . 
   Although embodiments of the present invention have been described in detail herein, the scope of the invention is not limited thereto. It will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the invention. Accordingly, the embodiments disclosed herein are only exemplary. It is to be understood that the scope of the invention is not to be limited thereby, but is to be determined by the claims which follow.