Abstract:
A carburetor with a single fuel system that is capable of ensuring stable engine operation and lower fuel consumption. The fuel system comprises an electrical fuel control C that, in addition to mechanically coordinating the fuel flow rate with air intake by way of a metering needle  22  that operates in coordination with the throttle valve  3,  opens and closes opening/closing valve  30  and cuts off and delivers fuel to the air intake passage  2  so as to maintain a required target rotational speed with little fuel consumption in a specific region of the degrees of opening of the throttle valve  3.  Stable operation with minimal fluctuations in the rotational speed is ensured by cutting off the fuel when the rotational speed rises above the target rotational speed, and delivering the fuel when the rotational speed falls below the target rotational speed.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a carburetor for application in supplying fuel to general purpose engines, and more particularly to a carburetor that is capable of allowing stable engine operation while achieving lower fuel consumption.  
         BACKGROUND OF THE INVENTION  
         [0002]    The following devices are well known as carburetors that supply fuel to two-cycle or four-cycle general purpose engines: fixed-venturi carburetors that comprise a butterfly-type throttle valve and two fuel systems composed of a main system and a speed-reducing system as shown in Japanese Patent Application Laid-open No. 55-69748, and other publications; variable-venturi carburetors that comprise a cylindrical sliding throttle valve and a single fuel system in which the fuel delivery quantity is made variable by way of a metering needle as shown in Japanese Utility Model Publication No. 49-17682, and other publications; and carburetors that comprise a cylindrical rotating throttle valve and a single fuel system in which the fuel delivery quantity is made variable by way of a metering needle as shown in Japanese Patent Application Laid-open No. 58-101253, and other publications.  
           [0003]    Because a carburetor comprising a sliding throttle valve or rotating throttle valve is configured with a single fuel system, it has advantages in that the fuel passage structure is simple in comparison with one comprising a main system and a speed-reducing system, and the fuel consumption from low speeds to high speeds is smooth. In common practice, carburetors comprising a single fuel system and a sliding-type or rotating-type throttle valve have a diaphragm-type constant fuel chamber.  
           [0004]    When an engine to which fuel is supplied by the carburetor described above is operated, and particularly when the constant fuel chamber is a diaphragm type, the diaphragm may malfunction, the fuel may leak, and other problems may be brought about by engine vibration and the discharge of residual air from the constant fuel chamber, in addition to atmospheric temperature, pressure, fuel temperature, and other external conditions, and because of these factors, marked fluctuations in rotational speed of the engine cannot be avoided even at rated load operation. Marked fluctuations in the rotational speed of the engine result are an impediment in terms of achieving a smooth operation during outdoor work when using a lawn mower or the like, and also result in an increase of toxic substances in the exhaust.  
           [0005]    Conversely, a lean mixture in a narrow air-fuel ratio range is required in order to operate an engine with good stability while reducing fuel consumption. Any inconsistencies in the fuel delivery quantity caused by variation in component precision (inherent in the carburetor itself) during manufacture, in addition to discharge of residual air, fuel leaking, and other above-described phenomena that occur during service, make it difficult to maintain a lean mixture in a narrow air-fuel ratio range.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention was developed to solve the above-described problems and is aimed at allowing stable operation in an engine while realizing lower fuel consumption for a carburetor with a single fuel system that delivers fuel from a constant fuel chamber to an air intake passage.  
           [0007]    To solve the above-mentioned problems, the present invention includes providing a fuel system comprising maximum flow regulating means for fuel delivered to the air intake passage; mechanical fuel control means for adjusting the quantity of fuel delivered to the air intake passage in accordance with the degree of opening of the throttle valve; and electrical fuel control means for delivering and cutting off the delivery of fuel to the air intake passage so as to achieve a required target rotational speed of the engine in a specific region of the degrees of opening of the throttle valve.  
           [0008]    The maximum flow regulating means is commonly a fixed jet; the mechanical fuel control means is a device comprising a metering needle in which the surface area of the fuel passage opening is variable; and the electrical fuel control means is an apparatus comprising an electromagnetically driven opening/closing valve for opening and closing the fuel passage. To achieve the object of the present invention, it is preferable that these be arranged in the order of electrical fuel control means, maximum flow regulating means, and mechanical fuel control means in the direction from the constant fuel chamber to the air intake passage; and, in particular, that the electrical fuel control means be disposed in a location proximate to the constant fuel chamber.  
           [0009]    The maximum flow regulating means and mechanical fuel control means described above serve to deliver fuel to the air intake passage in accordance with the engine inlet air quantity, and set the basic flow rate of the fuel. The electrical fuel control means serves to open and close the fuel passage so as to maintain a required target rotational speed in a specific region of the degrees of opening of the throttle valve, and maintains the engine rotation with fuel delivered on the downstream side thereof when closed, opens the fuel passage when the rotational speed of the engine decreases to the target rotational speed or less, and closes the fuel passage again when the rotational speed is restored to the target rotational speed. Adopting this approach allows fuel consumption to be reduced and stable operation to be achieved without marked fluctuations in the rotational speed.  
           [0010]    Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a longitudinal section showing the first embodiment of the present invention.  
         [0012]    [0012]FIG. 2 is a longitudinal section showing the second embodiment of the present invention.  
         [0013]    [0013]FIG. 3 is a layout drawing showing an embodiment of the electrical control circuit.  
         [0014]    [0014]FIG. 4 is a flow chart of electrical control.  
         [0015]    [0015]FIG. 5 is a diagram of fuel consumption curve versus rotational speed of the engine.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    Describing the preferred embodiments with reference to the diagrams, FIG. 1 is a diagram showing an embodiment wherein the present invention has been applied to a carburetor comprising a butterfly-type throttle valve and a diaphragm-type constant fuel chamber. A cylindrical valve disc  4  of the throttle valve  3  is disposed in the air intake passage  2  that is formed completely through the main body  1 , and a throttle valve lever  7  that is turned by the valve-closing spring  6  or accelerator operation by the driver is fastened to one end of the valve stem  5  that runs completely through the main body  1 . A constant fuel chamber  9  that comprises a depression and is separated from the atmosphere by the diaphragm  8  is further disposed on one surface of the main body  1 . The constant fuel chamber  9 , as is well known, holds a fixed quantity of fuel by cutting off or allowing fuel delivered from a fuel pump (not shown) to flow in accordance with the displacement of the diaphragm  8 , as is well known.  
         [0017]    The fuel system  11  for delivering fuel from the constant fuel chamber  9  to the air intake passage  2  has a check valve  12  that prevents air from flowing into the constant fuel chamber  9  during priming, a fixed jet  13  (which is the maximum flow regulating means A for the fuel), a nozzle body  14 , and a fuel port  18 . The check valve  12  is disposed aside and facing the constant fuel chamber  9 . The fixed jet  13  and the nozzle body  14  are fitted adjacent each other so as to be air- and fluid-tight in a mounting hole  20 , which is formed parallel to the valve stem  5  in the portion between the constant fuel chamber  9  and the throttle valve  3  of the main body  1 . The nozzle body  14  has a through-hole  15  that passes completely through the front and back and is connected to the jet hole exit of the fixed jet  13 , and has one or a plurality of slit-shaped nozzle openings  16  in the peripheral side wall. The nozzle opening  16  is connected to the fuel port  18  which opens on the downstream side of the throttle valve  3  of the air intake passage  2  by way of a toroidal chamber  17 .  
         [0018]    The path that reaches the fuel port  18  by way of the jet hole of the fixed jet  13  from the above-described check valve  12 , the through-hole  15  of the nozzle body  14 , the nozzle opening  16 , and the toroidal chamber  17  constitute a fuel passage  19 . The fixed jet  13  is disposed in a location adjacent to the check valve  12 .  
         [0019]    A guide hole  21  is disposed on the same central axial line as the mounting hole  20  on the reverse side of the fixed hole  13  of the nozzle body  14 . A holding member  23  in the form of a hollow shaft is fitted in the guide hole  21  wherein a metering needle  22  is held so as to protrude at the end so as to allow movement in the axial direction. The metering needle  22  is inserted in the through-hole  15  of the nozzle body  14  and the base is threadably fitted into the holding member  23 , so as to allow the protruding length from the end to be adjustable, and operates so as to change the aperture surface area of the nozzle opening  16 .  
         [0020]    The holding member  23  is fitted into the guide groove  25  formed by extending the diaphragm cover  10 , and is attached to the guide member  24  which moves in a linear manner. The guide member  24  holds a contact piece  26  comprising a steel ball in a freely rotatable manner. Conversely, a cam  27  is fastened to the end portion of the valve stem  5  on the reverse side of the throttle valve lever  7 . The contact piece  26  is kept in constant contact with this cam  27  by way of the spring force of a pushing spring  28 .  
         [0021]    In the idle position of the throttle valve  3 , the contact piece  26  makes contact with the lowest portion of the cam  27  causing the insertion of the metering needle  22  into the through-hole  15  deeper, which minimizes the aperture surface area of the nozzle opening  16 . In the fully open position of the throttle valve  3 , the contact piece  26  makes contact with the highest portion of the cam  27  causing the insertion of the metering needle  22  into the through-hole  15  more shallow, which maximizes the aperture surface area of the nozzle opening  16 . In other words, the metering needle  22  steplessly changes the aperture surface area of the nozzle opening  16  in accordance with the degree of opening of the throttle valve  3 , delivers fuel to the air intake passage  2  at a flow rate corresponding to the inlet air quantity of the engine, and sets the basic flow rate of the fuel in cooperation with the fixed jet  13 .  
         [0022]    The above-described nozzle  14 , metering needle  22 , holding member  23 , guide member  24 , cam  27 , and pushing spring  28  therefore constitute the mechanical fuel control means B for adjusting the fuel delivery quantity to the air intake passage  2  in accordance with the degree of opening of the throttle valve  3 .  
         [0023]    The valve element  31  of the opening/closing valve  30  with the fixed jet  13  serving as the valve seat is subsequently inserted into the mounting hole  20  from the aperture end side. The opening/closing valve  30  is electromagnetically driven, and an actuator  32  thereof is configured such that the connector  32 B fastened to and extending into the coil case  32 A is attached to the main body  1  by being screwed into the mounting hole  20 . The valve element  31  is attached to the end of a movable iron core (plunger)  33 . The entrance of the jet hole of the fixed jet  13  is closed when the coil is nonconductive, and open when the coil is conductive. Fuel from the constant fuel chamber  9  is delivered to the nozzle body  14  by way of the check valve  12 , the interior of the connector  32 B, and the fixed jet  13 .  
         [0024]    A signal generator  35  is disposed on the surface of the main body  1  on the side on which the throttle valve lever  7  is positioned. The signal generator  35  comprises a fixed contact point  37 A in the form of a flat spring, a movable contact point  38 A mounted within the container  36 , and a push pin  39  held in a linearly movable fashion in the wall of the container  36  so as to bend the moveable contact point  38 A with the application of pressure and cause contact with the fixed contact point  37 A. When these contact points  37 A and  38 A make contact, a signal sent by the energizing is transmitted from the terminals  37 B and  38 B to the control circuit  43  of the actuator  32 . The push pin  39  is caused to move by the throttle valve lever  7 , and in the present embodiment, the throttle valve lever  7  is configured so as to push the push pin  39  and send a signal when the throttle valve  3  is half open or in a range of degrees of opening that is slightly greater.  
         [0025]    The electrical control circuit comprises an engine rotational speed sensor  41 , a rotational speed discriminating circuit  42 , a control circuit  43  for the actuator  32 , a signal generator  35 , and an ignition kill switch  44  shown in FIG. 3; and along with the opening/closing valve  30 , these constitute the electrical fuel control means C for cutting off and delivering fuel to the air intake passage  2 . The rotational speed can be set in any rotational speed range by manual input to the rotational speed circuit  42 , and it is possible to set a plurality of rotational speed ranges.  
         [0026]    [0026]FIG. 2 is a diagram showing an embodiment wherein the present invention has been applied to a rotating throttle-type carburetor, and a cylindrical throttle valve  53  having a throttle through-hole  54  disposed perpendicular to the air intake passage  52  of a main body  51 . A metering needle  72  is attached to this throttle valve  53  so as to allow the protruding length into the throttle through-hole  54  to be adjustable. The metering needle  72  is inserted in a nozzle body  64  that protrudes from the opposite side into the throttle through-hole  54  so that the aperture surface area of the nozzle opening  66  can be varied.  
         [0027]    The constant fuel chamber  59  is separated from the atmosphere side by a diaphragm  58 . The fuel system  61  for delivering fuel from the constant fuel chamber  59  to the air intake passage  52  has a check valve  62 , a fixed jet  13  (which is maximum flow regulating means A for the fuel), and a nozzle body  64 . The path that starts at the check valve  62 , passes through the jet hole of the fixed jet  13 , and reaches the nozzle opening  66 , constitutes a fuel passage  69 . The fixed jet  13  is disposed in a location adjacent to the check valve  62 .  
         [0028]    A throttle valve lever  57  is fastened to a valve stem  55  that passes completely through a main body cover  60  from the throttle valve  53  and extends to the exterior. The throttle valve  63  is moved in the axial direction by a cam mechanism (not shown) while rotated by a return spring  56  or the accelerator operation by the driver, and the air flow is controlled by the throttle through-hole  54  and fuel flow control by the metering needle  72  in the same manner as a conventional rotating throttle-type carburetor.  
         [0029]    The above-described metering needle  72  and the nozzle body  64  constitute mechanical fuel control means B for adjusting the quantity of fuel delivered to the air intake passage  52  in accordance with the degree of opening of the throttle valve  53 .  
         [0030]    The valve element  31  of the opening/closing valve  30  with the fixed jet  13  serving as the valve seat is subsequently inserted from the aperture end side into a mounting hole  70 , into which the fixed jet  13  is fitted. An actuator  32  for electromagnetically driving the opening/closing valve  30  is attached to the main body  51 . A signal generator  35  operated by the throttle lever  57  is disposed in the main body cover  60 . Because the structure and function of the opening/closing valve  30 , the actuator  32 , and the signal generator  35  are the same as described for the embodiment of FIG. 1, redundant description has been omitted.  
         [0031]    In the present embodiment, an electrical control circuit comprising the equipment shown in FIG. 3 is provided. The circuit and the opening/closing valve  30  constitute the electrical fuel control means C for cutting off and delivering fuel to the air intake passage  52 .  
         [0032]    Here, an example of fuel control by the electrical fuel control means C in the above-described two embodiments is described with reference to FIGS. 4 and 5. The curve F of fuel consumption versus rotational speed of the engine depicted in FIG. 5 shows the fuel consumption at a constant load by the mechanical fuel control means B.  
         [0033]    The driver initially operates the opening/closing valve  30 , sets the rotational speed of the engine range, which controls the air-fuel ratio, and provides input to the rotational speed discriminating circuit  42 . This rotational speed range is the range in which machinery equipped with an engine commonly operates at normal operational speed. The throttle valve levers  7  and  57  are made so as to cause the signal generator  35  to operate at a degree of opening position of the throttle valves  3  and  53  which provides air intake corresponding to this range of rotational speed.  
         [0034]    The engine is subsequently operated under air-fuel ratio control by way of the mechanical fuel control means B, and when the rotational speed of the engine sensor  41  determines that the detected rotational speed of the engine A 1  has reached the rotational speed range set in advance by the rotational speed discriminating circuit  42 , the throttle levers  7  and  57  actuate the signal generator  35  concurrently therewith, and a command signal that causes electrical fuel control to be performed is transmitted to the control circuit  43  of the actuator  32 .  
         [0035]    The fuel consumption by the mechanical fuel control means B when the signal generator  35  operates is shown by P on the curve F, and the flow rate of fuel required by the engine at this time is shown by the curve F 1 . In the present embodiment, the rotational speed of the engine corresponding to the point P is designated as the target rotational speed X, and the fuel consumption Q that is below curve F but still allows the target rotational speed X to be obtained is set on the curve F 1 .  
         [0036]    When the rotational speed of the engine A 1  is higher than the target rotational speed X, the control circuit  43  demagnetizes the actuator  32  and closes the opening/closing valve  30 , and the fuel passages  19  and  69  are shut off. Adopting this approach allows the fuel remaining on the downstream side of the opening/closing valve  30  of the fuel passages  19  and  69  to be delivered and the engine rotation to be maintained. When the remaining fuel becomes a small quantity or is completely delivered, the rotational speed of the engine A 1  decreases, and when the rotational speed of the engine is less than the target rotational speed X, the control circuit  43  magnetizes the actuator  32  and opens the opening/closing valve  30 , restarting fuel supply. The above approach allows the opening/closing valve  30  to be closed again when rotational speed of the engine A 1  rises and exceeds the target rotational speed X. The fuel consumption resulting from these actions is shown by the P-Q-R line.  
         [0037]    Repeating the above operations allows the rotational speed of the engine to be maintained at a target rotational speed with little fuel consumption within a preset rotational speed range. By opening and closing the opening/closing valve  30  in a small margin of rising and declining rotational speed, stable operation is made possible without marked fluctuations of rotational speed.  
         [0038]    Fuel consumption can be automatically caused to converge at point Q by the control actions described above even if there is variation in the fuel flow rate due to variability in external conditions, service conditions, structural component precision, assembly, and other conditions.  
         [0039]    When the throttle valves  3  and  53  are opened wide by the operation of the accelerator, the signal generator  35  ceases sending command signals, the system returns from fuel control by the electrical fuel control means C to fuel control by mechanical fuel control means B, and the throttle valves  3  and  53  are fully opened.  
         [0040]    In the present embodiment, the control circuit  43  opens and closes the opening/closing valve  30  regardless of the signal generator  35  so that the rotational speed of the engine A 2  when the throttle valve is fully open is set as the fully open target rotational speed Y on the engine-required fuel curve F 2  when the throttle valve is fully open. In this case, when the rotational speed of the engine A 2  exceeds the fully open target rotational speed Y by a certain range or more and the opening/closing valve  30  is opened, the load is reduced and the required fuel can be supplied even if the engine is at a high rotational speed.  
         [0041]    In the present embodiment, a low speed target rotational speed Z, which is set to a significantly lower value than the rated idle rotational speed or the rotational speed of the engine from cranking at engine start, is input and set into the rotational speed discriminating circuit  42 . When the rotational speed of the engine A 3  is below this level, the opening/closing valve  30  is closed, and when above this level, the opening/closing valve  30  is opened. The fuel consumption at this time is shown by the line S-T-U. In this case, the rotational speed discriminating circuit  42  issues a command signal whereby the actuator  32  is operated by the control circuit  43  on the basis of the ON signal of the ignition kill switch  44 . As described above, by not supplying fuel until the rotational speed of the engine A 3  rises above the low speed target rotational speed Z that has been set to a very low value, needless fuel flow is prevented when cranking fails, and engine stalling due to an overly rich mixture and an increase of fuel consumption can be avoided.  
         [0042]    As described above, fuel consumption can be lowered and the engine can be stably operated in accordance with the present invention, in which mechanical fuel control and electrical fuel control are used jointly, and fuel is cut off and delivered so as to achieve a required target rotational speed by electrical control in a specific region of the degrees of opening of the throttle valve.  
         [0043]    While the invention is susceptible to various modifications, and alternative forms, specific examples thereof have been shown in the drawings and are herein described in detail. It should be understood, however, that the invention is not to be limited to the particular forms or methods disclosed, but to the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the appended claims.