Patent Publication Number: US-6217008-B1

Title: Diaphragm-type carburetor

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a diaphragm-type carburetor, and in particular, to an improvement in a diaphragm-type carburetor including a constant-pressure fuel chamber having an outlet bore communicating with a lower end of a fuel nozzle through a fuel jet and a check valve, a fuel pump incorporated in a fuel passage which communicates between an inlet bore in the constant-pressure fuel chamber and a fuel tank for providing fuel for the constant-pressure fuel chamber in response to a pulsation pressure in a pulsation pressure generating source, and a fuel introduction control valve for controlling the introduction of the fuel into the constant-pressure fuel chamber by opening or closing the inlet bore in the constant-pressure fuel chamber. The fuel introduction control valve is provided with a cylindrical valve seat member mounted on an upper wall of the constant-pressure fuel chamber and having the inlet bore in its upper end, and a valve member lifted and lowered within the valve seat member to open and close the inlet bore. 
     2. Description of the Related Art 
     A diaphragm-type carburetor is already known, as disclosed, for example, in Japanese Patent Application Laid-Open No. 1-151758. 
     In such a carburetor, fuel delivered to a constant-pressure fuel chamber by operation of a diaphragm pump is often converted into a large amount of fuel vapor by a pressure pulsation received from the diaphragm pump, heat or vibration received from an engine or the like. When a large amount of fuel vapor is introduced all at one time into the constant-pressure fuel chamber and ejected from the fuel nozzle, the fuel-air ratio of the fuel-air mixture is extremely reduced, thereby causing misoperation of the engine. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a diaphragm-type carburetor of the above-described type, wherein when fuel vapor is generated in the fuel discharged from the diaphragm pump, a large amount of fuel vapor can be prevented from being ejected all at one time from the fuel nozzle by finely dividing the fuel vapor and introducing it along with the fuel, thereby substantially suppressing the variation in fuel-air ratio of a fuel-air mixture. 
     To achieve the above object, according to a first aspect and feature of the present invention, there is provided a diaphragm-type carburetor comprising a constant-pressure fuel chamber having an outlet bore communicating with a lower end of a fuel nozzle through a fuel jet and a check valve, a fuel pump incorporated in a fuel passage for permitting communication between an inlet bore in the constant-pressure fuel chamber and a fuel tank. The pump pumps fuel into the constant-pressure fuel chamber in response to a pulsation pressure in a pulsation pressure generating source, and a fuel introduction control valve for controlling the introduction of the fuel into the constant-pressure fuel chamber by opening and closing the inlet bore in the constant-pressure fuel chamber. The fuel introduction control valve has a cylindrical valve seat member mounted on an upper wall of the constant-pressure fuel chamber and has the inlet bore at the upper end thereof. A valve member is raised and lowered within the valve seat member to open and close the inlet bore, wherein a fuel vapor treating chamber is provided in the fuel passages for finely dividing fuel vapor at a location before the inlet bore. 
     With the above arrangement, when fuel vapor is generated in the fuel discharged from the fuel pump, the fuel vapor is finely divided in the fuel vapor treating chamber and passes through the inlet bore in the valve seat member along with the fuel into the constant-pressure fuel chamber. Therefore, the finely divided fuel vapor passes smoothly into the fuel nozzle along with the fuel without stagnating in the constant-pressure fuel chamber. Thus, the amount of fuel vapor ejected from the fuel nozzle per unit time is relatively small, whereby the reduction in fuel-air ratio of a fuel-air mixture can be suppressed to a small level to ensure the normal operation of the engine. 
     According to a second aspect and feature of the present invention, a porous element having a large number of pores is placed in the fuel vapor treating chamber. 
     With the above arrangement, the fuel vapor can be finely divided by a simple structure, wherein the porous element is placed in the fuel vapor treating chamber, and thus, it is possible to provide a diaphragm-type carburetor at a lower cost. 
     The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a vertical sectional front view of a diaphragm-type carburetor of the present invention. 
     FIG. 2 is a sectional view taken along a line  2 — 2  in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring first to FIG. 1, a diaphragm-type carburetor C is mounted in a hand-held type engine carried on a portable working machine adapted to be used in all-direction attitudes, such as a mowing-off machine. A carburetor body  1  of the carburetor C includes a horizontal intake passage  2  connected to an intake port (not shown) of the engine, and a bottomed cylindrical valve guide bore  3  extending in a vertical direction perpendicular to the intake passage  2 . A rotary-type throttle valve  4  is rotatably and slidably received in the valve guide bore  3 , and a cap  5  for closing the valve guide bore  3 , is secured to the carburetor body  1 . A spring  6  is mounted under compression between the throttle valve  4  and the cap  5  for biasing the throttle valve  4  toward a bottom of the valve guide bore  3 . The throttle valve  4  has a throttle bore  9  provided so that the area of communication with the intake passage  2  is increased in response to the rotation of the throttle valve  4  in an opening-degree increasing direction. 
     The throttle valve  4  has a valve stem  4   a  extending through the cap  5 , and an operating arm  7  is secured to the valve stem  4   a  by a sleeve  8  fitted in a hollow in the valve stem  4   a.    
     A boss  10  is provided in the bottom of the valve guide bore  3  to protrude into the throttle bore  9 , and a fuel nozzle  11  is mounted to the boss  10  and rises in the throttle bore  9 . A needle valve  12 , threadedly mounted in the sleeve  8 , is inserted into the fuel nozzle  11 . 
     An annular slant  7   a  is formed on a lower surface of the operating arm  7  and the operating arm  7  is supported by a ball  13  mounted on an upper surface of the cap  5 . When the operating arm  7  is rotated in a direction to open the throttle valve  4 , it is pushed up by the ball  13 , and with this pushing, the throttle valve  4  is displaced upwards along with the needle valve  12  against the biasing force of the spring  6 , thereby increasing the opening degree of the fuel nozzle  11 . 
     A stopper bolt  14  is threadedly mounted in the cap  5  for regulation of advancing and retracting movement, and is adapted to abut against the operating arm  7  to define an idle opening degree of the throttle valve  4 . 
     A pressure plate  15 , a resilient packing  16  and a bottom plate  17  are coupled to a lower surface of the carburetor body  1  in a sequentially superposed manner. A fuel pipe  21  connected to a fuel tank T is connected to a joint  22  which projects from a lower surface of one side of the bottom plate  17 . An upstream fuel passage  23   a  in carburetor body  1  is connected to the joint  22 , and a pump chamber  29  in a diaphragm-type fuel pump  24  in bottom plate  17 . A downstream fuel passage  23   b  is provided in the carburetor body  1  and connected to the pump chamber  29 , and a constant-pressure fuel chamber  26  is provided in the bottom plate  17  and is connected to the downstream fuel passage  23   b.    
     The diaphragm-type fuel pump  24  has a diaphragm  27  which is formed by a portion of packing  16 . An operating chamber  28  and the pump  29  chamber faced by upper and lower surfaces of the diaphragm  27 , are formed on the carburetor body  1  and the bottom plate  17 , respectively. An intake valve  30  utilizing a portion of the packing  16 , and a fuel filter  31  located upstream of the intake valve  30 , are mounted in the upstream fuel passage  23   a,  and a discharge valve  32  likewise utilizing a portion of the packing  16 , is mounted in the downstream fuel passage  23   b.  The operating chamber  28  communicates with a pulsation pressure generating source P, e.g., the inside of a crank chamber or an intake pipe through a conduit  34 . 
     As shown in FIGS. 1 and 2, a fuel introduction control valve  35  is mounted in the constant-pressure fuel chamber  26  for controlling the introduction of fuel from the downstream fuel passage  23   b  into the constant-pressure fuel chamber  26 . The fuel introduction control valve  35  is comprised of a cylindrical valve seat member  37  mounted on the bottom plate  17  on one side of the constant-pressure fuel chamber  26 , so that an inlet bore  36  in an upper end wall faces the downstream fuel passage  23   b.  A valve member  38  is vertically movably received in the valve seat member  37  to open and close the inlet bore  36 , and an operating lever  40  which is swingably carried on a support shaft  39 , is supported on the bottom plate  17  with one end engaged with a lower end of the valve member  38 . A valve spring  41  biases the operating lever  40  in a direction to close the valve member  38 , and a diaphragm  42  is mounted on a lower surface of the bottom plate  17  so as to form a bottom surface of the constant-pressure fuel chamber  26 . A urging element  42   a  is mounted at a central portion of the diaphragm  42  to abut against the other end of the operating lever  40  for movement away from such other end. The diaphragm  42  has a peripheral edge fastened to the bottom plate  17  along with a cover  43  which covers the diaphragm  42 . The cover  43  is provided with an air vent  44  for applying atmospheric pressure to a lower surface of the diaphragm  42 . 
     A fuel vapor treating chamber  51  is provided in the downstream fuel passage  23   b  at a location short of the inlet bore  36  of the valve seat member  37 , and a porous element  52  having a large number of pores is placed in the fuel vapor treating chamber  51 . The porous element  52  is formed of a material having a resistance to gasoline, such as a foamed resin having open cells or a sintered material. 
     A fuel well  45  is defined in the bottom plate  17  and is located above the other end of the constant-pressure fuel chamber  26 . The fuel well  45  communicates at its lower portion with the constant-pressure fuel chamber  26  through an outlet bore  47  and at its upper portion with a lower end of the fuel nozzle  11  through a check valve  48  and a fuel jet  49 . 
     Further, a bypass passage  50  is provided in the bottom plate  17  and passes above the constant-pressure fuel chamber  26  to permit the lower end of the valve seat member  37  to communicate with the fuel well  45 . 
     The operation of the embodiment will be described below. 
     When the engine is operated, a pulsation pressure in the pulsation pressure generating source P is applied to the operating chamber  28  in the fuel pump  24  to vibrate the diaphragm  27 . When the diaphragm  27  is flexed toward the operating chamber  28 , the pump chamber  29  is increased in volume, thereby pumping fuel in the fuel tank T through the intake valve  30  and the upstream fuel passage  23   a.  When the diaphragm  27  is flexed toward the pump chamber  29 , the pump chamber  29  is reduced in volume, thereby delivering the fuel therein toward the downstream fuel passage  23   b  through the discharge valve  32 . 
     In this case, if the fuel in the constant-pressure fuel chamber  26  does not reach a defined amount, the diaphragm  42  is displaced upwards under the action of the atmospheric pressure to swing the operating lever  40  in a clockwise direction as viewed in FIG. 1 against the biasing force of the valve spring  41 , thereby pulling down the valve member  38  to open the inlet bore  36 . Therefore, the fuel in the downstream fuel passage  23   b  is introduced into the constant-pressure fuel chamber  26 . When the fuel introduced into the constant-pressure fuel chamber  26  reaches the defined amount, the diaphragm  42  is lowered to pull the urging element  42   a  away from the operating lever  40 . Then, the operating lever  40  pushes up the valve member  38  by the action of the biasing force of the valve spring  41 , thereby closing the inlet bore  36 . Thus, the introduction of the fuel into the constant-pressure fuel chamber  26  is stopped. In this manner, the defined amount of fuel is constantly stored in the constant-pressure fuel chamber  26  during operation of the engine and passes through the outlet bore  47  to fill the fuel well  45 . 
     On the other hand, in the intake passage  2  and the throttle bore  9 , a negative pressure is produced around the fuel nozzle  11 . The fuel in the fuel well  45  rises sequentially in the check valve  48 , the fuel jet  49  and the fuel nozzle  11  and ejected into the throttle bore  9  by the action of such negative pressure. The ejected fuel is drawn into the engine, while being mixed with air passed through the intake passage  2  and the throttle bore  9  to produce a fuel-air mixture. The amount of fuel-air mixture into the engine is regulated by increasing or decreasing the opening degree of the throttle valve  4 . 
     When the fuel delivered from the fuel pump  24  into the downstream fuel passage  23   b  is subjected to a pressure pulsation caused by the vibration of the diaphragm, heat or vibration from the engine or the like, thereby generating fuel vapor, the fuel vapor is finely divided along with the fuel by the large number of pores in the porous element  52  in the fuel vapor treating chamber  51  and then introduced through the inlet bore  36  in the valve seat member  37 , along with the fuel, into the constant-pressure fuel chamber  26 . Therefore, the finely divided fuel vapor passes smoothly from the outlet  47  into the fuel well  45  along with the fuel without stagnating in the constant-pressure fuel chamber. 
     Particularly, in the illustrated embodiment, the lower end of the valve seat member  37  communicates with the fuel well  45  through the bypass passage  50  extending above the constant-pressure fuel chamber  26 . Therefore, when the fuel vapor passes through the valve seat member  37 , it immediately rises up in the bypass passage  50  to enter the fuel well  45 . Thus, the fuel vapor is ejected from the fuel nozzle  11  along with the fuel in the fuel well  45 . Therefore, the amount of fuel vapor ejected per unit time from the fuel nozzle  11  is very small and the fuel-air ratio of the fuel-air mixture varies only slightly and hence, the normal operation of the engine can be ensured. 
     The construction for finely dividing the fuel vapor at the location short of the inlet bore  36  in the valve seat member  37  is a simple construction wherein the porous element  52  is placed in the fuel vapor treating chamber  51 , leading to a very small increase in cost. 
     Although the embodiment of the present invention has been described in detail, it will be understood that the present invention is not limited to the above-described embodiment, and various modifications in design may be made without departing from the spirit and scope of the invention defined in claims. For example, the throttle valve  4  may be constructed into a butterfly type.