Patent Publication Number: US-7210441-B1

Title: Priming and purging system and method for an internal combustion engine

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to fuel systems for small internal combustion engines, and more particularly to fuel priming and vapor purging systems and methods for small internal combustion engines. 
     BACKGROUND OF THE INVENTION 
     Small internal combustion engines often have a manually operated purge pump in fluid communication with a carburetor to allow fuel vapor and stale liquid fuel to be purged from the carburetor, or a prime pump to prime the carburetor with a shot of liquid fuel to facilitate starting the engine. The pumps have a manually actuated bulb and are generally attached directly to the carburetor, or located remotely from the carburetor. The purge pump is actuated to a depressed state, thereby causing liquid fuel and fuel vapor within the bulb to be directed through a downstream fuel line to a fuel tank. The purge pump is then returned to a non-depressed state, thereby drawing liquid fuel and any fuel vapor into the bulb through an upstream fuel line. The purging is generally repeated as necessary to ensure that the fuel vapor is purged from the upstream fuel line. The prime pump bulb is similarly actuated to a depressed state, however, rather than directing the flow into the fuel tank, the flow is typically directed into an air-fuel mixing passage of the carburetor to prime the carburetor. 
     Sometimes users mistake the purge pump for a prime pump and limit the number of actuations of the pump out of fear of “flooding” the engine. As a result, the carburetor may not be fully purged of fuel vapor prior to initiating a starting procedure for the engine, thus, making starting the engine difficult. Similarly, sometimes users mistake the prime pump for a purge pump and actuate the prime pump in excess, thereby causing the engine to be “flooded.” As a result, starting the engine is made more difficult, rather than being made easier. 
     SUMMARY OF THE INVENTION 
     A priming and purging system for an internal combustion engine having a diaphragm carburetor. The carburetor has a pump chamber in operable communication with a crankcase of the engine and a metering chamber downstream from the pump chamber for regulating at least in part the flow of liquid fuel into an air-fuel mixing passage of the carburetor. The priming and purging system includes a pump having an inlet in fluid communication with the metering chamber and an outlet. The outlet of the pump communicates with both the engine and the fuel tank. The pump is manually actuatable to draw liquid fuel and gaseous phase air, fuel vapor and/or fuel bubbles through the inlet of the pump from the metering chamber, and also to pump liquid fuel and gaseous phase through the pump to the fuel tank and dispense priming liquid fuel to a portion of the engine such as the mixing passage of the carburetor, intake manifold, or crankcase of a two-stroke engine for admission to the combustion chamber. 
     Preferably, the fluid flows to the engine and the fuel tank through check valves which preferably open at different pressures with the flow to the tank beginning at a lower pressure than the pressure at which flow to the fuel engine begins. 
     Another aspect of the invention provides a method of purging gaseous phase presence from a liquid fuel metering chamber of a diaphragm carburetor for an internal combustion engine and dispensing a priming shot of liquid fuel into a portion of the engine to facilitate starting the engine. The method includes providing a carburetor having a pump chamber operable in response to pressure pulses from a crankcase of the engine and being in fluid communication with a metering chamber downstream therefrom. The metering chamber has a flexible diaphragm movable in response to pressure differential between atmospheric pressure and engine-intake-induced negative pressure in the air-fuel mixing passage to pump liquid fuel from the metering chamber into the air-fuel mixing passage to form an air-fuel mixture for operating the engine. Further, providing a pump having an inlet in fluid communication with the metering chamber and an outlet communicating with a portion of the engine and a fuel tank. The pump is arranged for manual actuation to draw the gaseous phase and liquid fuel through the inlet from the metering chamber and to pump the gaseous phase and liquid fuel through the outlet of the pump and to the fuel tank and priming liquid fuel into a portion of the engine. 
     The priming and purging system facilitates starting the internal combustion engine by inhibiting the gaseous phase and stale liquid fuel within the metering chamber from reaching the air-fuel mixing passage of the carburetor, while also providing a priming shot of liquid fuel to a portion of the engine. 
     Some of the objects, features and advantages of the invention include providing a priming and purging system and method that automatically purges gaseous phase and stale liquid fuel from a carburetor while priming the engine at the same time, reduces the number of steps to start an engine, improves the ease in starting an engine, maintains a supply of liquid fuel adjacent an air-fuel mixing passage of a carburetor, is relatively simple in design and manufacture, is economical in manufacture, and has a long useful life in service. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects, features and advantages of this invention will be apparent in view of the following detailed description of the presently preferred embodiments and best mode, appended claims and accompanying drawings, in which: 
         FIG. 1  is a schematic view of a priming and purging system according to some presently preferred embodiments of the invention; 
         FIG. 2  is a cross-sectional view of a carburetor with a priming and purging pump system of a presently preferred embodiment of the invention shown schematically arranged in fluid communication with one of an air-fuel mixing passage of the carburetor, an intake manifold of an engine, and a crankcase of a two-stroke engine; 
         FIG. 3  is a partial cross-sectional view of a priming and purging pump system of another presently preferred embodiment of the invention shown schematically arranged in fluid communication with a fuel tank and a carburetor; 
         FIG. 4  is a perspective view of a one-way valve constructed according to one presently preferred embodiment of the invention; and 
         FIG. 5  is a partial cross sectional view of a carburetor constructed according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS 
     Referring in more detail to the drawings,  FIG. 1  illustrates a priming and purging system  10  of an internal combustion engine  11  arranged according to some presently preferred embodiments of the invention. The system  10  is in fluid communication with a carburetor  12  and a fuel tank  14 , and can be arranged in fluid communication with other portions of the engine  11 , such as, by way of example and without limitation, an intake manifold  24  and a crankcase  26  of a two-stroke engine. The system  10  includes a start pump  16  that is manually actuatable to draw or purge gaseous phase, referred to hereafter as fuel vapor, and stale liquid fuel from the carburetor  12  via a fuel passage  18  upstream of the start pump  16  and preferably to direct the fuel vapor and liquid fuel away from the pump  16  via another fuel passage, referred to hereafter as a first fuel passage  20 , downstream of the start pump  16 . The first fuel passage  20  preferably diverges into a pair of fuel passages, referred to hereafter as a second fuel passage  22  and a third fuel passage  23 . To facilitate purging the carburetor  12 , the third fuel passage  23  preferably communicates with the fuel tank  14  to dispense fuel vapor and liquid fuel into the fuel tank  14 . While at the same time the pump  16  purges the carburetor  12 , it also directs a priming shot of liquid fuel through the second fuel passage  22 , downstream of the start pump  16 , to a portion of the engine  11 , and shown here as at least one of the carburetor  12 , the intake manifold  24 , and the crankcase  26  of the engine  11 . Accordingly, the system  10  ensures that the carburetor  12  receives fresh, liquid fuel that preferably is essentially free of fuel vapor while starting the engine  11 , and also ensures that the engine  11  is primed with liquid fuel, thereby improving the ease with which the engine  11  is started. 
     As shown in  FIG. 2 , the carburetor  12  is represented here as a diaphragm carburetor  12  having an intake or air-fuel mixing passage  28  with a butterfly-type throttle valve  30  received at least in part in the mixing passage  28  for movement between idle and wide open positions. The carburetor  12  is shown here, by way of example and without limitation, as having a choke valve  32  received at least in part in the mixing passage  28  upstream of the throttle valve  30  for movement between a closed position to facilitate cold starts, and an open position during normal operation of the engine  11 . The carburetor  12  preferably supports a fuel pump  33  having a pressure chamber  34  communicating with the crankcase  26  of the engine  11  via a passage  36  to receive pulsating pressure therefrom. A resiliently flexible diaphragm  38  of the fuel pump  33  separates the pressure chamber  34  from a pump chamber  40  which communicates with the fuel tank  14  via a fuel passage  42 . As the pump diaphragm  38  is flexed or reciprocated by the pulsating pressure from the crankcase  26 , a check valve  44  allows liquid fuel to flow to the pump chamber  40  and prevents the reverse flow of liquid fuel from the pump chamber  40  back toward the fuel tank  14 . 
     A fuel passage  46  communicates the pump chamber  40  with a fuel metering chamber  48  downstream of the pump chamber  40 , with the metering chamber  48  preferably being defined in a lower portion of the carburetor  12 . The fuel passage  46  preferably has a one-way check valve  50  between the pump chamber  40  and the metering chamber  48  to facilitate regulating the flow of liquid fuel therebetween. The check valve  50  closes when the pump diaphragm  38  draws fuel from the fuel tank  14 , and opens when the pump diaphragm  38  pushes the fuel into the metering chamber  48 , as is known. To further regulate the flow of liquid fuel through the passage  46  and into the metering chamber  48 , preferably a pivotally supported fuel inlet valve  52  movable between open and closed positions is interposed between the pump chamber  40  and the metering chamber  48 , and preferably between the check valve  50  and the metering chamber  48 . 
     The metering chamber  48  is defined in part by one side of a diaphragm  54 , and an atmospheric chamber  56  is defined on the opposite side of the diaphragm  54 . As is known, the diaphragm  54  flexes or moves in response to a pressure differential across it to control movement of the fuel inlet valve  52  between its open and closed positions. When the pressure in the metering chamber  48  is less than the pressure in the atmospheric chamber  56 , the diaphragm  54  moves or flexes upwardly and moves the fuel inlet valve  52  to its open position. When the pressure in the metering chamber  48  is equal to or greater than the pressure in the atmospheric chamber  56 , the fuel inlet valve  52  remains in its closed position, and may be biased to its closed position by a spring  58 , as is known. 
     The metering chamber  48  is in fluid communication with the throttle bore or air-fuel mixing passage  28  via a main fuel passage  60 , which is regulated in part by a high speed needle valve  62  and a low speed or idle fuel passage  64 , regulated in part by a low speed needle valve  66 . The liquid fuel is dispensed into the air-fuel mixing passage  28  through the main fuel passage  60  and the idle fuel passage  64  at a desired flow rate, depending on the relative positions of the needle valves  62 ,  66 , the relative positions of the throttle and choke valves  30 ,  32  and the relative pressures between the air-fuel mixing passage  28  and the metering chamber  48 , as is known. 
     The metering chamber  48  is preferably in direct fluid communication with the manual pump  16  via the fuel passage  18  upstream of the pump  16 , wherein the pump  16  can be carried by the carburetor  12 , or, as shown in  FIG. 3 , can be carried remotely from a carburetor  12 ′ which has essentially the same construction as carburetor  12 . As such, the fuel passage  18  can span a short or relatively long distance, as necessary, depending on the proximity of the pump  16  to the carburetor  12 ,  112 . 
     The pump  16 , by way of example and without limitation, can be a diaphragm pump, a positive displacement piston-type pump, or as shown in  FIGS. 2 and 3 , a bulb-type pump having an inlet  71  in fluid communication with the metering chamber  48  via the fluid passage  18  and an outlet  73  in fluid communication with the first fuel passage  20 . The pump  16  has a resilient dome shaped bulb  68  sealed about its periphery to a housing  70  to define a pump chamber  72 . The chamber  72  encapsulates the fuel passage  18  from the metering chamber  48  and the first fuel passage  20  flowing downstream from the pump  16 . The pump  16  includes a one-way valve, represented here by way of example and without limitation, as an umbrella shaped valve  74 , overlying the fuel passage  18  from the metering chamber  48 . The valve  74  allows a flow of fuel vapor and liquid fuel from the metering chamber  48  into the pump chamber  72  while preventing a reverse flow from the pump chamber  72  toward the metering chamber  48 . The pump  16  includes another one-way valve, represented here by way of example and without limitation, as a duck bill-shaped valve  76  received in an inlet of the first fuel passage  20  and preferably constructed integrally and as one piece with the umbrella valve  74 . The valve  76  allows a flow of fuel vapor and liquid fuel from the pump chamber  72  into the first fuel passage  20  while preventing a reverse flow from the first fuel passage  20  into the pump chamber  72 . 
     The first fuel passage  20  is preferably connected in fluid communication to the second and third fuel passages  22 ,  23  via a T-shaped connector  82 . The connector has an inlet  83  arranged for a sealed connection to the first fuel passage  20  and a pair of outlets  84 ,  85  arranged for a sealed connection to the second and third fuel passages  22 ,  23 , respectively. 
     The second and third fuel passages  22 ,  23  are in fluid communication with the engine  11  and the fuel tank  14 , respectively, and preferably have first and second one-way check valves  86 ,  88  therein, respectively, to regulate the flow rate of the liquid fuel through the fuel passage  22 ,  23 . As best shown in  FIG. 4 , the check valves  86 ,  88  are represented here, by way of example and without limitation, as spring biased check valves that ordinarily remain closed until acted on by a pressure great enough to overcome a biasing force imparted by a coil spring  90 . The spring has one end  91  in engagement with an end wall  92  of the check valve, and another end  93  in engagement with a ball  94  within the check valve. The ball  94  is yieldably biased into sealed engagement with a valve seat  95 , wherein the valve seat is represented here, for example, as being press-fit into a body of the check valves  86 ,  88 . 
     The first and second check valves  86 ,  88  can be arranged to crack or open at a selected or predetermined pressure to regulate the flow of liquid fuel through the respective fuel passages  22 ,  23 , depending on the requirements of the specific engine arrangement. For instance, the pressures at which the check valves  86 ,  88  crack can be changed, such as, for example, by changing the spring rate and/or force characteristics and/or by changing the extent to which the spring is compressed between the valve seat  95  and the end wall  92 . Preferably, but not necessarily, the first check valve  86  is arranged to crack at a different pressure from the second check valve  88 , and more preferably at a pressure that is greater than the pressure required to crack the second check valve  88 . This facilitates stale fuel and any fuel vapor or air being directed toward the fuel tank and fresh liquid fuel being directed to the engine for priming it. By way of example and without limitation, preferably the spring  90  in the first check valve  86  in the second fuel passage  22  is selected to compress and open the valve under a pressure of about 3 psi, whereas the spring  90  in the second check valve  88  is selected to compress and open the valve under a pressure of about 2 psi. 
     To start the engine, whether it is cold or already warmed from use, the pump  16  can be manually actuated by depressing the bulb  68  to purge the carburetor  12  and to prime the engine  11 . When flexing or depressing the bulb  68 , the volume of vapor and/or liquid fuel within the pump chamber  72  is pumped through the first fuel passage  20 , through the connector  82 , and through the second and third fuel passages  22 ,  23 , respectively. As the bulb  68  is released and returns to its relaxed domed shape, a vacuum is drawn in the fuel passage  18 , thereby drawing liquid fuel and any air and fuel vapor from the metering chamber  48  into the pump chamber  72 . The pump  16  can be manually actuated, preferably a prescribed number of times, without flooding the engine  11 . The priming shot(s) of liquid fuel is delivered via the second fuel passage  22  to at least one of the air-fuel mixing passage  28 , intake manifold  24 , and crankcase  26 . To facilitate delivering the fuel shot to the intake manifold  24 , the outlet of the second fuel passage  22  can be angled or inclined to dispense a fine stream of liquid fuel directly into the intake manifold  24 . The second fuel passage  22  could have an outlet dispensing liquid fuel into the air-fuel mixing passage  28 , preferably downstream from the throttle valve  30 , and/or into the intake manifold  24  downstream from the air-fuel mixing passage  28 . The outlet preferably has a diameter of about 0.4–0.5 mm to create a fine stream of liquid fuel, though any suitable diameter could be used, depending on the spray pattern or stream desired. As such, a sufficient amount of liquid fuel is dispensed through the second fuel passage  22  to prime the engine  11 , while ensuring that the engine  11  is not flooded with too much liquid fuel, preferably substantially regardless of the number of times the pump  16  is actuated. The liquid fuel and any gases such as fuel vapor and air flowing through the third fuel passage  23  is preferably dispensed into the fuel tank  14  to purge the carburetor  12 . 
     As shown in  FIG. 5 , another carburetor  212  constructed according to another presently preferred embodiment of the invention has a reservoir  96 , shown here, by way of example and without limitation, generally adjacent the air-fuel mixing passage  28 . An opening or plurality of openings  97 ,  98  are arranged to communicate the reservoir  96  with the air-fuel mixing passage  28 . A piece of porous material  99  is sized for receipt within the reservoir  96  and is preferably maintained in a fixed position, such as through the use of a closure or washer  100  press-fit in an end of the reservoir  96 . The washer  100  has an opening  101  arranged for fluid communication with the second fluid passage  22 , thereby allowing liquid fuel to flow from the second fluid passage  22  into the reservoir  96 . As such, the porous material  99  is able to be wetted or saturated with liquid fuel, thereby providing a supply of liquid fuel adjacent the air-fuel mixing passage  28  to facilitate priming the engine  11 . The material  99  can be any suitable porous material that is compatible with liquid fuel, such as a metallic mesh or Porex®, for example. 
     The embodiments of the starter system  10  discussed above are intended to be illustrative of presently preferred embodiments of the invention, and are not limiting. Various modifications within the spirit and scope of the invention will be readily apparent to those skilled in the art. For example, the pressure at which each check valve  86 ,  88  opens may be varied relative to the fuel pressure produced by the pump  16  and the quantity of fuel needed to prime a particular engine.