Abstract:
A device that corrects with ease and high precision any deviation of the fuel flow rate due to variation in the constituent components of a carburetor, and to improve the exhaust condition and operability of an engine. A carburetor in which the delivery channel  23  and the suction channel  20  of a fuel pump  15  are connected with the aid of an escape channel  27 , and in which a portion of the delivery fuel is allowed to escape to the suction side in order to prevent pressure exerted on the fuel valve  10  by the fuel delivered to the constant fuel chamber  5  from the fuel pump  15 , which operates by pressure pulses, from reaching or exceeding a specified level, wherein the escape channel  27  is equipped with a manual control valve  29  for steplessly adjusting the surface area thereof. The quantity of fuel retained in the constant fuel chamber  5  can be adjusted so as to achieve a predetermined fuel flow rate by changing the escape quantity of the delivery fuel and rendering the fuel valve  10  more resistant to opening or less resistant to opening.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to pulse-type diaphragm fuel pump for suppying fuel from a fuel tank to a diaphragm-type or float-type constant fuel chamber of a carburetor.  
         [0002]     There are pulse-type diaphragm fuel pumps in which the diaphragm performs reciprocating displacement motion by pressure pulses generated in the suction manifold or the crankcase in association with the rotation of the engine, commonly by pressure pulses generated in the crankcase, which operate to suction fuel from the fuel tank into the pump chamber at negative pressure, and to deliver fuel from the pump chamber toward the constant fuel chamber of a carburetor at positive pressure. These pumps are widely used as means to supply fuel to the carburetor, which supplies fuel to general-purpose engines.  
         [0003]     The fuel valve, which allows or stops the flow of fuel delivered from the fuel pump into the constant fuel chamber, opens and closes so as to retain a fixed quantity of fuel in the constant fuel chamber in accordance with the up and down movement of the float or the reciprocating displacement motion of the diaphragm. The pressure pulses generated by the crankcase or other means in association with the rotation of the engine are repetitions of negative pressure and positive pressure, and the mean pressure thereof increases in association with an increase in the rotational speed of the engine and is at its greatest at full speed.  
         [0004]     In a range of high speed rotation, drawbacks are demonstrated in that the delivery fuel pressure becomes greater than the specified pressure that works on the fuel valve. As a result, the valve is forcefully opened, fuel from the constant fuel chamber is supplied in excess, and the air-fuel mixture is made rich, causing output to be lost and exhaust conditions to be worsened. To address this drawback, the delivery fuel pressure is adjusted to remain equal to or less than a specified pressure for the fuel valve by allowing a portion of the delivery fuel to escape to a low pressure region on the suction side.  
         [0005]      FIGS. 3 and 4  are diagrams that show conventionally known delivery fuel pressure adjustment means.  FIG. 3  is a variation in which a diaphragm-type carburetor and a pulse-type diaphragm fuel pump are integrally configured.  FIG. 4  is a variation in which a float-type carburetor and a pulse-type diaphragm fuel pump are separately configured.  
         [0006]     First, with reference to  FIG. 3 , fuel pump  51  comprises a pulse chamber  53  and a pump chamber  54  facing each other across a diaphragm  52 ; a suction channel  55  having a suction chamber  56  and a suction valve  57 , for introducing fuel from a fuel tank into the pump chamber  54 ; and a delivery channel  58  having a delivery valve  59  and a delivery chamber  60 , for guiding fuel pressurized in the pump chamber  54  to a constant fuel chamber  61 . The exit portion to the constant fuel chamber  61  of the delivery channel  58  is opened and closed by a fuel valve  63  that operates in accordance with the reciprocating displacement motion of the diaphragm  62 .  
         [0007]     The delivery chamber  60  formed on the exit side of the delivery valve  59 , and the suction chamber  56  formed on the entrance side of the suction valve  57  are connected by way of an escape channel  64  having a throttle  65  for limiting the fuel escape quantity.  
         [0008]     The escape channel  64  constantly links the suction side and the delivery side of the fuel pump  51 . This delivery fuel pressure adjustment means is therefore configured so that the fuel escape quantity is increased by the difference in pressure between the delivery side and the suction side when there is an increase in the delivery fuel pressure. As a result, a pressure equal to or greater than a specified pressure is prevented from being exerted on the fuel valve  63 .  
         [0009]     Second, with reference to  FIG. 4 , fuel pump  71  comprises a pulse chamber  73  and a pump chamber  74  facing each other across a diaphragm  72 ; a suction channel  75  having a suction chamber  76  and a suction valve  77 , for introducing fuel from a fuel tank into the pump chamber  74 ; and a delivery channel  78  having a delivery valve  79  and a delivery chamber  80 , for guiding fuel pressurized in the pump chamber  74  to a constant fuel chamber  81 . The exit portion to the constant fuel chamber  81  of the delivery channel  78  is opened and closed by a fuel valve  83  that operates in accordance with the up and down movement of a float  82 .  
         [0010]     The delivery chamber  80  formed on the exit side of the delivery valve  79 , and the suction chamber  76  formed on the entrance side of the suction valve  77  are connected by way of an escape channel  84 , and a piston-type escape valve  85  for opening and closing the escape channel  84  is provided.  
         [0011]     The escape valve  85  in the delivery fuel pressure adjustment means that comprises the escape channel  84  and escape valve  85  is opened by pressure when the delivery fuel pressure becomes equal to or greater than a set value. As a result, a pressure equal to or greater than a specified amount is prevented from being exerted on the fuel valve  83  by opening the escape channel  84  and allowing a portion of the delivery fuel to escape to the suction side.  
         [0012]     In common practice, there are variations in all components of a carburetor that cannot be avoided in the production process. In particular, variations in the components related to the fuel flow rate and disposed in the fuel passage that reaches the suction channel from the constant fuel chamber varies the fuel flow rate supplied to the engine and directly affects the exhaust condition. It is well known that precise control of the fuel flow rate is required in order to meet emission regulations, and more-precise control is particularly required for carburetors that handle a small quantity of fuel, such as carburetors for general-purpose engines.  
         [0013]     Nevertheless, in the conventional delivery fuel pressure adjusting means described above, the fuel level of the constant fuel chambers  61  and  81  is held constant by limiting the fuel pressure exerted on the fuel valves  63  and  83  to a pressure equal to or less than that set in advance by the valve-closing spring load of the escape valve  85  or the diameter of the throttle  65 . As a result, variability in the fuel flow rate created by variation in the constituent components of the fuel passage, which reaches the suction channel from the constant fuel chambers  61  and  81 , cannot be corrected, and it is impossible to precisely control the fuel flow rate so as to meet emission regulations.  
       SUMMARY OF THE INVENTION  
       [0014]     The present invention provides a solution to the above-described drawbacks in a conventional delivery fuel pressure adjusting means composed of a throttle or a throttle valve in the escape channel in which variability in the fuel flow rate due to variation in the constituent components of the carburetor cannot be corrected to meet emission regulations. An object thereof is to provide a pulse-type diaphragm fuel pump comprising a delivery fuel pressure adjusting means that is capable of arbitrarily adjusting the delivery fuel pressure exerted on the fuel valve so as to solve the variability of the fuel flow rate created by variation in the constituent components of the carburetor, making it possible to set the fuel flow rate supplied to the engine to an accurate flow that meets emission regulations, and hence to allow the engine to operate in a stable manner.  
         [0015]     The present invention provides a solution to such problems by providing a pulse-type diaphragm fuel pump for a carburetor comprising a pulse chamber and a pump chamber facing each other across a diaphragm, a suction channel having a suction valve for introducing fuel from a fuel tank into the pump chamber, and a delivery channel having a delivery valve, for guiding fuel pressurized in the pump chamber to a constant fuel chamber in the carburetor; wherein the exit side of the delivery valve of the delivery channel and the entrance side of the suction valve of the suction channel are connected by an escape channel for allowing a portion of the delivery fuel to escape to the suction side, wherein a manual control valve for steplessly adjusting the escape surface area of the escape channel is provided. Alternatively, a throttle for limiting the fuel escape quantity to an amount less than the maximum throughflow of the control valve to the return channel is additionally provided to such a control valve.  
         [0016]     When the fuel flow rate changes to one that is less than a predetermined quantity due to the variation in constituent components of carburetors, the quantity of fuel retained in the constant fuel chamber can be increased and the fuel flow rate to the suction channel enhanced by decreasing the degree of opening of the control valve to reduce the fuel escape quantity, increase the pressure exerted on the fuel valve, and facilitate opening. When the fuel flow rate conversely changes to one that is greater than a predetermined quantity, the quantity of fuel retained in the constant fuel chamber can be decreased and the fuel flow rate to the suction channel enhanced by increasing the degree of opening of the control valve to increase the fuel escape quantity, reduce the pressure exerted on the fuel valve, and impede opening.  
         [0017]     In other words, by adjusting the degree of opening of the control valve, the delivery fuel pressure exerted on the fuel valve can be steplessly changed, variability of the fuel flow rate due to variation in the constituent components of a carburetor can be corrected, and a predetermined flow rate of fuel can be accurately supplied, with the result that the objective of meeting emission regulations and consequently making the operability of the engine stable can be achieved.  
         [0018]     In a carburetor wherein a throttle, in addition to a control valve, is provided to the escape channel, the delivery fuel pressure exerted on the fuel valve does not reach or fall below a fixed value even if the control valve is completely opened, and the minimum fuel flow rate required by the engine can be held to a range which allows the objectives of the present invention to be achieved. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a longitudinal section showing an embodiment of the present invention.  
         [0020]      FIG. 2  is an enlarged view of the principal components of  FIG. 1 .  
         [0021]      FIG. 3  is a schematic longitudinal section showing a conventional embodiment.  
         [0022]      FIG. 4  is a schematic longitudinal section showing another conventional embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]      FIGS. 1 and 2  show an embodiment in which the present invention is integrally incorporated into a diaphragm-type carburetor. A diaphragm  3  and a diaphragm cover  4  are overlaid on the lower surface of a main body  1 . A suction channel  2  having a venturi tube and throttle valve is laterally formed completely through the main body  1 . The internal space of a diaphragm cover  4  and the cavity of the main body  1  facing each other across a diaphragm  3  form a constant fuel chamber  5  and a back pressure chamber  6  connected to the atmosphere.  
         [0024]     A lever  8  supported in a freely rotatable manner by a pin  7  is mounted inside the constant fuel chamber  5 . One end of this lever  8  is held in constant contact with the center portion of the diaphragm  3  by a spring  9 , and the fuel valve  10  is attached to the other end. The valve element  11  of the fuel valve  10  is needle-shaped or conically shaped, and is seated in a valve seat  12 , which is disposed on the exit end of the constant fuel chamber  5  of the delivery channel  23  of the fuel pump  15  described hereinafter, by a valve closing force exerted by the spring  9 .  
         [0025]     When the quantity of fuel retained in the constant fuel chamber  5  decreases, the diaphragm  3  displaces in the direction of the constant fuel chamber  5  and pushes the lever  8  upward to cause rotation, the valve element  11  separates from the valve seat  12 , and fuel delivered by the fuel pump  15  is introduced to the constant fuel chamber  5 . When the quantity of fuel retained increases and the diaphragm  3  displaces toward the back pressure chamber  6 , the spring  9  pushes the lever  8  to cause rotation, the valve element  11  is seated in the valve seat  12 , and the delivery channel  23  is closed.  
         [0026]     The diaphragm  16  and the pump cover  17  are overlaid on the upper surface, which is on the opposite side of the constant fuel chamber  5  of the main body  1 . The internal space of the pump cover  17  and the cavity of the main body  1  face each other across a diaphragm  16  forming a pump chamber  18  and pulse chamber  19  connected to the crankcase. A suction channel  20  and a delivery channel  23  are connected to the pump chamber  18 . The diaphragm  16 , pump chamber  18 , pulse chamber  19 , suction channel  20 , and delivery channel  23  constitute the fuel pump  15 .  
         [0027]     The suction channel  20  has a suction chamber  21  opened on the upper surface of the main body  1 , as well as a flap-shaped suction valve  22  formed by providing an incision in the diaphragm  16  that covers the upper surface of the opening thereof, and an entrance end connected to the fuel tank. The delivery channel  23  has a delivery chamber  24  opened on the upper surface of the main body  1 , as well as a flap-shaped delivery valve  25  formed by providing an incision in the diaphragm  16  that covers the upper surface where the valve opens, and the above-described valve seat  12  is disposed at the exit end. The suction chamber  21  and the delivery chamber  24  smooth the pulse of the fuel and aid in increasing the suction and delivery efficiency, but are not necessarily required.  
         [0028]     When the pressure pulse created in the crankcase in association with the rotation of the engine is introduced into the pulse chamber  19 , the diaphragm  16  when under negative pressure displaces in the direction of the pulse chamber  19 , the pump chamber  18  is placed under negative pressure, the suction valve  22  opens, the fuel sent to the suction channel  20  from the fuel tank is introduced to the pump chamber  18 , the delivery valve  25  closes, and the delivery channel  23  is closed. When the pressure pulse introduced into the pulse chamber  19  is positive, the diaphragm  16  displaces in the direction of the pump chamber  18 , the pump chamber  18  is placed under negative pressure, the delivery valve  25  opens, the fuel pressurized in the pump chamber  18  is introduced to the constant fuel chamber  5  from the delivery channel  23 , the suction valve  22  closes, and the suction channel  20  is closed. Supplying fuel from the fuel tank to the constant fuel chamber  5  with this action is the same as a conventional pulse-type diaphragm fuel pump.  
         [0029]     The delivery chamber  24  positioned at the exit side of the delivery valve  25  of the delivery channel  23 , and the suction chamber  21  positioned at the entrance side of the suction valve  22  of the suction channel  20  are connected by way of an escape channel  27  formed in the main body  1 . The escape channel  27  is configured so that the channel surface area is steplessly adjustable by a control valve  29  disposed partway, and has a throttle  28  comprising a fixed jet on the downstream side thereof.  
         [0030]     The control valve  29  comprises a needle-shaped valve element  35  that protrudes at the leading end of a valve stem  34 , itself extending forward from the leading end of a screw shaft  33  in which a head body  31  with a tool hole  30  has been provided to the base end, and also comprises a valve hole  37  formed in the escape channel  27 . The valve element  35  is fashioned so as to be capable of being inserted and removed from the valve hole  37  by positioning the valve hole  37  on the same center axis line, inserting a screw shaft  33  into an attachment hole  38  having a female screw  39  formed in the main body  1 , and threadably fitting the female screw  39 .  
         [0031]     The region that reaches to the entrance of the valve hole  37  from the leading end portion of the female screw  39 , which is the deep end portion of the attachment hole  38 , forms a valve chamber  40 . The escape channel  27  reaches the suction chamber  21  by way of the valve chamber  40  and valve hole  37  from the delivery chamber  24 . The shoulder portion, which constitutes a transition from the valve stem  34  to the valve element  35 , forms a conical contact surface  36 , and the step portion that constitutes a transition from the valve chamber  40  to the valve hole  37  is a conical seat surface  41  fashioned at the same angle as the contact surface  36 . A seal member  32  comprising an O-ring is mounted on the head body  31 . The seal member  32  adheres to the peripheral surface of the attachment hole  38  and renders the valve chamber  40  air- and fluid-tight while simultaneously working as a detent for the screw shaft  33  by means of the friction force thereof.  
         [0032]     The annular piece  43  is fixed by being press-fitted into an opening portion on the base end of the attachment hole  38 . This annular piece  43  catches on the head body  31  and works to prevent the screw shaft  33  from escaping to the exterior of the main body  1  from the attachment hole  38  when the screw shaft  33  completely slips out from the female screw  39  and is in a free state inside the attachment hole  38 . The annular piece  43  is fixedly fitted in the attachment hole  38  after the screw shaft  33  is turned and the insertion depth in the valve hole  37  of the valve element  35  is adjusted so as to configure the effective surface area of the escape channel  27  to the required surface area. It is, however, possible to insert a tool with a diameter smaller than the inside diameter thereof, to engage to the tool hole  30 , and to make readjustments.  
         [0033]     The fuel system that sends fuel from the constant fuel chamber  5  to the suction channel  2  comprises a main jet, a low-speed jet, a main bleed air jet, a low-speed bleed air jet, a main fuel control needle valve, a low-speed fuel control needle valve, a check valve for preventing back bleed, and a number of other functional components related to the fuel flow rate, and any variation that cannot be avoided in the production of the these components has a noticeable effect on the exhaust condition and engine operability, particularly in a carburetor for a general-purpose engine with a low fuel flow rate.  
         [0034]     On the other hand, the mean pressure of a pressure pulse, which is a repetition of negative pressure and positive pressure introduced to the pulse chamber  19  of the fuel pump  15 , increases as the rotational speed of the engine increases from a low speed to a high speed, and is maximum at full speed. A resulting drawback is that the delivery fuel pressure of the fuel pump  15  also increases in association with the rise in the rotational speed of the engine, and, as a result, the force in the direction of opening the valve exerted on the valve element  11  of the fuel valve  10  increases to forcibly open the valve, the fuel from the constant fuel chamber  5  is increased to a specified quantity or more, the fuel delivery rate to the suction channel  2  is increased, and the air-fuel mixture is made excessively rich.  
         [0035]     This drawback is not consistent, and the fuel flow rate may change to become smaller or greater than the standard predetermined flow rate due to variation in the components of the fuel system that extends to the suction channel  2  from the constant fuel chamber  5 . In view of the above, it is apparent that the variation in the fuel flow rate can be corrected by increasing the quantity of fuel retained in the constant fuel chamber  5  and raising the fuel flow rate in a fuel system whose fuel flow rate tends to decrease, and reducing the quantity of fuel retained in the constant fuel chamber  5  and lowering the fuel flow rate in a fuel system whose fuel flow rate tends to increase. Constantly delivering a predetermined flow rate of fuel to the suction channel  2  is preferable from the aspect of exhaust management and engine operating performance.  
         [0036]     According to the present embodiment, the channel surface area of the escape channel  27  can be steplessly adjusted from a state wherein the valve element  35  is completely removed from the valve hole  37  and the control valve  29  is completely open, to a state wherein the contact surface  36  is seated in the seat surface  41  and wherein the valve is completely closed. The valve is completely closed by way of a state wherein the screw shaft  33  is rotated and advanced by manually operating a tool, the valve body  35  is inserted in the valve hole  37 , and the effective surface area of the valve hole  37  is gradually reduced, and then a state wherein the contact surface  36  approaches the seat surface  41 , and the interval between these gradually grows smaller.  
         [0037]     For a fuel system in which the fuel flow rate delivered to the suction channel  2  from the constant fuel chamber  5  tends to become smaller than a standard predetermined flow rate, the insertion depth in the valve hole  37  of the valve element  35  is therefore increased, the fuel escape quantity which flows from the delivery chamber  24  toward the suction chamber  21  through the escape channel  27  by means of a pressure difference between these is reduced, the amount of reduction in the delivery fuel pressure is made smaller, and the fuel valve  10  is allowed to open more easily. The above approach allows the fuel valve  10  to open more easily at an engine rotational speed that is lower than the standard valve-opening timing, and the required fuel in the range of high-speed rotation in particular can be accurately supplied.  
         [0038]     For a fuel system in which the fuel flow rate tends to become greater than a standard predetermined flow rate, the insertion depth in the valve hole  37  of the valve element  35  is reduced, the fuel escape quantity that flows through the escape channel  27  is increased, the amount of reduction in the delivery fuel pressure is increased, and the fuel valve  10  is rendered more difficult to open. With the above approach, the fuel valve  10  is rendered resistant to opening until the rotational speed of the engine is higher than the standard valve-opening timing, the fuel flow rate delivered to the suction channel  2  is reduced, and the drawback whereby the air-fuel mixture in a range of high speed rotation is made excessively rich is overcome.  
         [0039]     The control valve  29  is capable of steplessly having its degree of opening adjusted by manual operation, so any deviation of the fuel flow rate can be corrected in accordance with the variations of individual fuel systems for carburetors, and the fuel flow rate can also be easily controlled with high precision in carburetors for general-purpose engines that handle small quantities of fuel.  
         [0040]     At this point, when the throttle valve  29  is opened a certain degree of opening or greater, the throttle  28  in the escape channel  27  does not allow the fuel escape quantity to increase above this degree of opening. By limiting the quantity to a level below the fuel throughflow when the control valve  29  is completely open, it is possible to prevent the air-fuel mixture from being made overly thin and the exhaust condition and engine operational performance from being adversely affected even if the fuel flow rate delivered to the constant fuel chamber  5  is reduced when the control valve  29  is mistakenly opened completely. The throttle  28  is not limited to the downstream side from the control valve  29  of the escape channel  27 , but may also be disposed in the upstream side.  
         [0041]     The attachment hole  38  for mounting the control valve  29  was formed inside the main body  1 , but it may be formed on the exterior of the main body  1 , on the pump cover  17 , or in another location, depending on the arrangement of the suction channel  20  and the delivery channel  23 , or the location of the fuel pump  15 .  
         [0042]     According to the present invention, the channel surface area of the escape channel for allowing a portion of the delivery fuel to escape to the low pressure region of suction side can be steplessly adjusted by a manual control valve so that the delivery fuel pressure from the fuel pump exerted on the fuel valve that controls the introduction of fuel to the constant fuel chamber does not increase beyond a specified pressure, wherein variability in the fuel flow rate to the suction channel caused by variation in the constituent parts of the carburetor can easily be corrected with high precision, a predetermined flow rate of fuel can be accurately supplied to the engine, and excellent exhaust conditions and operability can be achieved, as described above.