Abstract:
Methods of operating a diaphragm type carburetor to facilitate the atomization of fuel in the diaphragm-type carburetor are disclosed. Particularly, methods of operating a diaphragm-type carburetor having a check valve installed in a fuel passage leading from a constant-fuel chamber to a main nozzle, and an air bleed passage connected at a position on the downstream side of the check valve are disclosed. Moreover, techniques for operating a diaphragm-type carburetor having a main nozzle including nozzle openings facing downstream with respect to the engine intake air flow are also disclosed, wherein the nozzle openings are located in a tubular member cutting across a central axial line of the venturi so that the tubular member bridges the neck of the venturi.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/080,765 filed May 18, 1998, now U.S. Pat. No. 6,086,054. 
    
    
     FIELD OF THE INVENTION 
     The present invention concerns a diaphragm type carburetor which is used to supply fuel mainly to all-purpose two-cycle engines. 
     BACKGROUND OF THE INVENTION 
     In most all-purpose two-cycle engines used as sources of motive power in small vehicles and portable machinery for agriculture and forestry, etc., fuel is supplied by means of a diaphragm type carburetor equipped with a constant-fuel chamber. The constant-fuel chamber is generally separated from the atmosphere by a diaphragm which adjusts the fuel to a constant pressure. 
     A diaphragm type carburetor is also equipped with a diaphragm type fuel pump driven by pulse pressure generated in the crankcase of the engine. Fuel from the fuel tank is introduced into the constant-fuel chamber by this fuel pump, and is drawn into the air intake passage and supplied to the engine from this constant-fuel chamber. Such a carburetor is ordinarily equipped with a manual starting pump which feeds an extra amount of fuel out into the air intake passage or introduces a specified amount of fuel into the constant-fuel chamber prior to the starting of the engine. The operation of the manual starting pump improves the starting characteristics of the engine at low temperatures. 
     In diaphragm type carburetors, it has long been known to regulate the fuel flow rate by the installation of a main jet in the fuel passage leading from the constant-fuel chamber to the main nozzle, or by the promotion of fuel atomization and limiting of the fuel flow rate by the introduction of bleed air into the fuel in the fuel passage. An example of those techniques is disclosed in Japanese Patent Application Kokoku No. Sho 46-10565. 
     Prevention of the flow of air into the constant-fuel chamber from the main nozzle during engine deceleration by the installation of a check valve in the main nozzle or fuel passage has long been known in diaphragm type carburetors. An example of this technique can be found in U.S. Pat. No. 3,404,872 or Japanese Patent Application Kokai No. Sho 55-69748. 
     All-purpose two-cycle engines equipped with diaphragm type carburetors generally have a single cylinder, so that the air flowing through the air intake passage undergoes a pulse motion. It is known from experience that the supply of fuel from a main nozzle opening into the narrowest part of the venturi of the air intake passage is generally greater in the case of a single-cylinder engine in which the air flow is intermittent than in the case of a multi-cylinder engine in which the air flow is continuous. Accordingly, diaphragm type carburetors for use in all-purpose two-cycle engines are constructed so that the air flow velocity in the narrowest part of the venturi is lower than in a carburetor meant for use in multi-cylinder engines. 
     The main nozzles of diaphragm type carburetors proposed in the past have a nozzle opening at the tip end of the main nozzle. The nozzle configurations of current designs have a nozzle opening at a point which is in the same plane as or protruding slightly from the wall surface of the narrowest part of the venturi. As a result, the fuel which is sucked out by a low-velocity air flow, and thus by a low venturi negative pressure, tends to flow along the wall surfaces, so that sufficient atomization is difficult to achieve even if bleed air is introduced. This leads to uneven engine revolution and insufficient engine output. Especially in carburetors in which a check valve is installed in the main nozzle, poor atomization is achieved because this check valve hinders the atomization of the fuel, resulting in poor combustion when the fuel is first sucked out. 
     The present invention is intended to provide a diaphragm type carburetor which solves the aforementioned problem of difficult fuel atomization encountered in conventional diaphragm type carburetors, so that an appropriate amount of fuel can be sufficiently atomized and supplied to the engine at all times. 
     SUMMARY OF THE INVENTION 
     A first embodiment of the present invention comprises a main jet used for fuel regulation and a check valve used to prevent back flow installed in a fuel passage leading from a constant-fuel chamber to a main nozzle, wherein the main nozzle included nozzle openings formed in the circumferential surface of a tubular member. The tubular member of the device extends through the central axial line of a venturi in a direction which cuts across the narrowest part of the venturi. 
     Thus, when a cross-bar type main nozzle of the type used in the multiple venturis of carburetors used in multi-cylinder engines (as known from Japanese Patent Application Kokai No. Sho 58-20956, etc.) is applied to the single venturi of a diaphragm type carburetor, the fuel is sucked out into the air flowing through the venturi so that there is no formation of a wall surface flow and the fuel is more fully atomized. Furthermore, the check valve installed in the fuel passage closes during engine deceleration so that fuel is held on the main nozzle side; accordingly, an appropriate amount of fuel will always be supplied to the engine without delay at the time of the next acceleration. 
     In a second embodiment of the present invention, the device is configured so that a main jet used for fuel regulation and a check valve used to prevent back flow are installed in a fuel passage leading from a constant-fuel chamber to a main nozzle. The main nozzle has a construction in which nozzle openings are formed in the circumferential surface of a tubular member, wherein the tubular member is substantially perpendicular to the valve shaft of a throttle valve. The tubular member extends through the central axial line of a venturi in a direction which cuts obliquely across the venturi along the pivoting track of the outer circumferential edge of the throttle valve. The nozzle openings are preferably installed in positions on the upstream side of the pivoting track. 
     In this second embodiment, in addition to the functions obtained using the first means, the negative pressure acting on the nozzle openings is controlled in accordance with the degree of opening of the throttle valve. The response and stability of the fuel sucking action are thus improved and a more appropriate fuel supply during acceleration and transition from low-speed fuel to high-speed fuel is assured. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal sectional view which illustrates one working configuration of the present invention. 
     FIG. 2 is a longitudinal sectional view which illustrates another working configuration of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Working configurations of the present invention will be described with reference to the attached figures. In FIGS. 1 and 2, a constant-fuel chamber  5  is installed on one side surface of a carburetor main body  1  equipped with an air intake passage  4  which has a venturi  2  and a throttle valve  3 . This constant-fuel chamber  5  has a structure which is well known in the art and is described in Japanese Patent Application Kokai No. Sho 55-69748, etc. The constant-fuel chamber  5  is separated by a diaphragm  6  from an atmosphere chamber  8  located inside a diaphragm cover  7  and may be engaged with a lever (not shown) that is caused to contact the center of the diaphragm  6  by the force of a spring. The fuel that is fed from the fuel pump is controlled in accordance with the displacement of the diaphragm  6 , so that a prescribed amount of fuel is held at a constant pressure. 
     The fuel pump is a diaphragm type fuel pump (not shown) which is well known in the prior art and is further described in Japanese Patent Application Kokai No. Sho 55-69748. This fuel pump is installed on the outside surface of the diaphragm cover  7 , or on the side surface of the carburetor main body  1  located on the opposite side from the constant-fuel chamber  5 . The diaphragm is operated by pulse pressure generated in the crankcase of the engine, so that fuel from the fuel tank is pressurized by suction and fed into the constant-fuel chamber  5 . 
     In the working configuration shown in FIG. 1, the fuel in the constant-fuel chamber  5  passes through a main jet  12  into a fuel passage  11 . The fuel is sucked through the fuel passage and out into the air intake passage  4  from a main nozzle  23  which is preferably installed in the narrowest part of the venturi  2 . The main jet  12  comprises a fixed throttle which is exposed to the constant-fuel chamber  5  and fastened in place by being screwed into the carburetor main body  1 . 
     A check valve  14  is installed at an intermediate point in the fuel passage  11 . This check valve  14  consists of a cylindrical main valve body  15  which is fastened in place by being press-fitted into a mounting hole  13  formed in the carburetor main body  1  and opening into the constant-fuel chamber  5 . An annular groove  16  is formed on the outside circumferential surface of the main valve body  15  so that the groove communicates with the portion of the fuel passage  11  that is located on the side of the main jet  12 . A valve chamber  17  is formed in the front portion of the main valve body  15  facing the venturi  2  and a valve passage  18  communicates with the annular groove  16  and opens into the valve chamber  17 . Inside the valve chamber  17  is a plate-form valve body  19 , and a stopper  20  is installed on the end surface of the valve chamber  17 . The circumferential edge of the stopper  20  is fastened to the main valve body  15 . 
     When the pressure in the portion of the fuel passage  11  located on the side of main nozzle  23  is lower than the pressure in the constant-fuel chamber  5 , the valve body  19  contacts the stopper  20  and opens the valve passage  18 , so that fuel may enter the valve passage  18 . The flow rate of this fuel is regulated by the orifice  12   a  of the main jet  12  and is fed into the main nozzle  23 . When the aforementioned pressure relationship is reversed, the valve body  19  closes the valve passage  18 , so that the flow of fuel on the downstream side (as well as the flow of air) into the constant-fuel chamber  5  is prevented. In cases where a starting pump is installed so that fuel is introduced into the constant-fuel chamber  5  by suction, the check valve  19  closes the valve passage  18  so that air is prevented from being sucked in, making it possible to introduce the prescribed amount of starting fuel without hindrance. 
     An air bleed passage  21  is connected to the fuel passage  11  at a position located on the downstream side of the check valve  14 . Bleed air is metered by a bleed jet  22  located in passage  21  which is then admixed with the fuel, thus promoting atomization and limiting the fuel flow rate. Even if the main jet  12  is formed with a large diameter orifice, the fuel flow rate is appropriately regulated and the working of the main jet  12  is accordingly facilitated. 
     In addition to air from the main nozzle  23 , the air which has entered the fuel passage  11  from the air bleed passage  21  is also prevented from flowing into the constant-fuel chamber  5  by the check valve  14 . 
     The check valve  14  is installed so that the check valve  14  faces the narrowest portion of the venturi  2 , and so that the valve  14  is oriented perpendicular to the central axial line of the venturi  2 . A tubular member  24  is installed in front of the tip end of the check valve  14  so as to communicate with the fuel passage  11 . Preferably, the check valve  14  and tubular member  24  are positioned on the same central axial line, and the tubular member  24  is installed so that it cuts across the central axial line of the venturi  2  and bridges the narrowest portion of the venturi  2 . Nozzle openings  25  which open in the downstream direction of the engine intake air flow are formed in the circumferential surface of the tubular member  24 . 
     Together, the tubular member  24  and nozzle openings  25  constitute a main nozzle  23 . Two nozzle openings  25  are formed in the portion of the tubular member  24  located on the upstream side of the pivoting position in the region on the downstream side of the valve shaft  3   a  of the throttle valve  3 , wherein the valve shaft  3   a  is installed perpendicular to the tubular member  24 . More specifically, the nozzle openings  25  are located on the tip side of the tubular member  24  with respect to the central axial line of the venturi  2  (in the configuration shown in the figures). Accordingly, a portion of the fuel sucked out of the nozzle openings  25  passes through the gap between the wall of the air intake passage  4  and the throttle valve  3  and is fed to the engine. Another portion of the fuel collides with the throttle valve  3 , so that almost all of the fuel flows downstream without being blocked by the valve shaft  3   a , and is fed to the engine. Thus, the required amount of fuel can be smoothly supplied to the engine. 
     In addition, the number of nozzle openings  25  is not limited to two; it would also be possible to form a single nozzle opening or three or more nozzle openings. Such nozzle openings may be formed in the base end side of the tubular member  24  with respect to the central axial line of the venturi  2 . 
     In the working configuration shown in FIG. 2, a main jet  12  is formed as an integral part of the main valve body  15  of a check valve  14 . The check valve  14  is secured by press-fitting the valve body  15  into a mounting hole  13  which is formed in the carburetor main body  1  and opens into the constant-fuel chamber  5 . An orifice  12   a  of the main jet  12  and a valve passage  18  which is formed in the main valve body  15  are formed on the same central axial line. The fuel in the constant-fuel chamber  5  enters the valve passage  18  with the flow rate of the fuel controlled by the orifice  12   a , after which the fuel passes through a valve chamber  17  and through a fuel passage  11 , where it is sucked out into the air intake passage  4  from a main nozzle  23 . The opening and closing action of the valve body  19  is the same as in the configuration shown in FIG.  1 . Additionally, an air bleed passage (not shown in the figure) may be connected to the fuel passage  11  so that atomization of the fuel is promoted, and so that the flow rate of the fuel is regulated. 
     In its preferred embodiment, the tubular member  24 , is substantially perpendicular to the valve shaft  3   a  of the throttle valve  3 . The tubular member  24  passes through the central axial line of the venturi  2 , and cuts obliquely across the venturi  2  along the pivoting track A of the outside circumferential edge of the throttle valve  3  at the pivoting position in the region on the upstream side of the valve shaft  3   a  of the throttle valve  3 . In other words, this tubular member  24  extends obliquely upstream. The base end portion of the tubular member  24  is fastened by press-fitting it into the carburetor main body  1 , so that the tubular member  24  is installed in a cantilever configuration. 
     In this alternative configuration, the main jet  12 , check valve  14  and fuel passage  11  are positioned on the same central axial line perpendicular to the central axial line of the venturi  2 , at a point slightly downstream from the narrowest part of the venturi  2 . The base end of the tubular member  24  communicates with the fuel passage  11 . 
     Nozzle openings  25  which face downstream with respect to the direction of engine intake air flow are formed in the base end portion, intermediate portion, and tip end portion of the circumferential surface of the tubular member  24 . An idle port  31  and slow ports  32  open in the wall surface of the air intake passage  4  located on the same side of the intake passage  4  as the base end of the tubular member  24 . 
     When the throttle valve  3  begins to open from the idle position, fuel is drawn out from the slow ports  32 . At the time that the outside circumferential edge of the throttle valve  3  passes in front of the slow ports  32 , fuel begins to be sucked out from the nozzle opening  25  located at the base end of the tubular member  24 . As a result, the transition from low-speed fuel to high-speed fuel is accomplished very smoothly. When the throttle valve  3  is opened even further so that the intake air flow rate is increased, the amount of fuel sucked out from the base-end nozzle opening  25  is increased, and fuel begins to be sucked out from the intermediate and tip-end nozzle openings  25 . As the throttle valve  3  approaches the full-open position so that the outside circumferential edge of the throttle valve  3  is positioned beneath the intermediate nozzle opening  25  which is positioned in the vicinity of the narrowest part of the venturi, a large amount of fuel is sucked out from the intermediate nozzle opening  25  so that the fuel required for high output can be supplied to the engine. 
     By appropriately selecting the angle of inclination of the tubular member  24  and distance of the tubular member  24  from the pivoting track, as well as the size and installation positions of the nozzle openings  25 , it is possible to create an air flow corresponding to the opening and closing action of the throttle valve  3  in the vicinity of the nozzle openings  25 , thus causing the necessary stable negative pressure to act so that the response and stability of the sucking action of the fuel are improved, thereby further improving the transition from low-speed fuel to high-speed fuel and the supply of fuel during acceleration. 
     When the tubular members  24  shown in the configurations illustrated in FIGS. 1 and 2 are attached to the carburetor main body  1 , the phase can be varied so that the nozzle openings  25  are positioned in a phase relationship so that the system is not directly affected by blow-back from the engine, and which at the same time allows the fuel to be sucked out in a favorable manner by the intake air flow. Accordingly, the positions in which the nozzle openings  25  are formed are not limited to positions on the underside of the tubular member  24  facing downstream with respect to the intake air flow as shown in the figures. 
     When the present invention is used, as was described above, an appropriate amount of fuel can be easily supplied to the engine after being thoroughly atomized, so that smooth operation is possible. 
     While the above description contains many specifics, these should not be construed as limitations on the scope of the invention, but rather as examples of particular embodiments thereof. Many other variations are possible. Accordingly, the scope of the present invention should be determined not by the embodiments described herein, but by the appended claims the their legal equivalents.