Abstract:
A push button air primer is provided for a carburetor used with a small internal combustion engine. The carburetor includes a primer chamber having a piston scalingly and slidably movable therein, with a return spring biasing the piston outwardly of the carburetor. The piston is depressible by an operator such that, upon initial depression of the piston, a portion of the piston slides past a plurality of vent holes in the wall of the primer chamber to block communication between the primer chamber and an internal vent passage within the carburetor which leads to the carburetor throat and thence to the atmosphere. Thereafter, further depression of the piston reduces the volume of the primer chamber and forces a quantity of air from the primer chamber into the fuel bowl of the carburetor, thereby pressurizing the air space in the carburetor to force a quantity of liquid fuel into the throat of the carburetor to aid in engine starting.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to carburetors for small internal combustion engines of the type used with lawn mowers, lawn tractors, sport vehicles, and other small working implements.  
           [0003]    2. Description of the Related Art  
           [0004]    Small internal combustion engines typically include a carburetor for providing an air/fuel combustion mixture to the engine. One type of carburetor commonly used in small engines includes a fuel bowl for storing fuel and a throat with a venturi region. Intake air is drawn through the throat to generate a reduced pressure in the venturi region, drawing fuel from the fuel bowl into the throat where the fuel mixes with the intake air to form the combustion mixture.  
           [0005]    In order to start the engine, the carburetor must be primed so that an enriched air-fuel mixture is initially supplied to the engine. Typically, the air space in the fuel bowl is pressurized to force an amount of priming fuel from the fuel bowl directly into the throat to provide an enriched air/fuel mixture for engine starting.  
           [0006]    One primer system includes a resilient primer bulb or bellows that, when manually depressed, increases the pressure in the fuel bowl, causing an amount of priming fuel to flow from the fuel bowl through a nozzle into the carburetor throat. In some of these systems, the primer bulb also serves as a check valve to seal off an internal vent passage within the carburetor, such that air within the primer bulb is directed only into the fuel bowl.  
           [0007]    However, if the operator does not depress the primer bulb completely, the resulting pressure in the fuel bowl may be inadequate to cause a sufficient amount of fuel to flow into the throat. In addition, the primer bulb is most effective as a check valve when it is depressed directly inwardly toward the carburetor along a straight line. If the operator depresses the bulb at an angle, the bulb may not effectively seal off the internal vent passage, allowing air to leak into the internal vent passage such that the fuel bowl is not pressurized sufficiently to provide priming fuel to the carburetor throat in an amount effective for engine starting.  
           [0008]    A number of other primer systems use a primer bulb to introduce liquid fuel directly into the carburetor throat. In these systems, fuel is drawn into the primer bulb when the primer bulb is depressed and then released. When the primer bulb is depressed again, the fuel contained in the primer bulb is forced from the primer bulb into the throat. This system poses similar disadvantages. If the primer bulb is not depressed completely, the fuel injected from the primer bulb to the throat may be insufficient to start the engine.  
           [0009]    It is desired to provide a primer system for small engine carburetors that is an improvement over the foregoing.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention provides a push button air primer for a carburetor used with a small internal combustion engine. The carburetor includes a primer chamber having a piston sealingly and slidably movable therein, with a return spring biasing the piston outwardly of the carburetor. The piston is depressible by an operator such that, upon initial depression of the piston, a portion of the piston slides past a plurality of vent holes in the wall of the primer chamber to block communication between the primer chamber and an internal vent passage within the carburetor which leads to the carburetor throat and thence to the atmosphere. Thereafter, further depression of the piston reduces the volume of the primer chamber and forces a quantity of air from the primer chamber into the fuel bowl of the carburetor, thereby pressurizing the air space in the carburetor to force a quantity of liquid fuel into the throat of the carburetor to aid in engine starting.  
           [0011]    More specifically, in one embodiment, a carburetor is provided including a carburetor body having a fuel bowl storing a quantity of fuel, as well as a throat extending through the carburetor body, and a main fuel jet communicating the fuel bowl with the throat. The carburetor includes a primer chamber in communication with the fuel bowl, the primer chamber defined by an annular sleeve inserted within an annular wall of the carburetor body. An outer chamber is defined between the annular sleeve and the annular wall of the carburetor, the outer chamber in communication with an internal vent passage of the carburetor and thence to the atmosphere via the carburetor throat. The annular sleeve includes a plurality of vent holes which are spaced radially therearound with respect to the longitudinal axis of the primer assembly, the vent holes communicating the primer chamber with the outer chamber and the internal vent passage.  
           [0012]    A piston is sealingly and slidably disposed within the primer chamber, and is biased outwardly of the carburetor toward a proximal end of the primer chamber by a return spring to a position in which the piston is disposed outwardly of the vent holes in the sleeve. A retaining assembly limits the outward extent of travel of the piston within the primer chamber. Upon initial depression of the piston against the bias force of the return spring toward a distal end of the primer chamber, an outer sealing portion of the piston slides past the vent holes, thereby blocking communication between the primer chamber and the outer chamber and internal vent passage. Thereafter, continued depression of the piston inwardly toward the carburetor forces air within the primer chamber into the fuel bowl of the carburetor, thereby pressurizing the air space in the fuel bowl and forcing a quantity of liquid priming fuel into the throat of the carburetor to aid in engine starting.  
           [0013]    Advantageously, the piston is confined for slidable movement within the primer chamber along the longitudinal axis of the primer chamber. Specifically, the piston and annular sleeve of the primer chamber are made of substantially rigid components in close fitting engagement with one another, such that the sliding relationship therebetween restricts movement of the piston along the longitudinal axis of the primer chamber, reducing the potential for operator error during the priming operation. Thus, regardless of the particular direction from which the piston is depressed, the piston moves only along the longitudinal axis of the primer chamber to initially block the vent holes thereof, and subsequently to force air from the primer chamber into the fuel bowl.  
           [0014]    In one form thereof, the present invention provides a carburetor, including a carburetor body having a throat therethrough; a fuel bowl containing a quantity of fuel, the fuel bowl in communication with the throat; an internal vent passage in communication with the throat; and a primer assembly, including a primer chamber in communication with the internal vent passage through at least one vent hole disposed at a proximal end of the primer chamber, the primer chamber also in communication with the fuel bowl at a distal end of the primer chamber; and a piston slidable within the primer chamber, whereby initial travel of the piston closes the at least one vent hole, and further travel of the piston displaces air from the primer chamber into the fuel bowl.  
           [0015]    In another form thereof, the present invention provides a carburetor, including a carburetor body having a throat; a fuel bowl containing a quantity of fuel and an air space above the quantity of fuel, the fuel bowl in communication with the throat; and a primer assembly, including a primer chamber in communication with the fuel bowl air space; vent means for communicating the primer chamber with the throat; and piston means for closing the vent means and forcing air from the primer chamber into the fuel bowl air space. In a further form thereof, the present invention provides a method of priming a carburetor for starting an internal combustion engine, including the steps of depressing a piston assembly within a primer chamber in a direction from a proximal end to a distal end of the primer chamber to thereby move a portion of the piston assembly beyond a vent in the primer chamber to block communication between the primer chamber and an internal vent of the carburetor; and continuing depression of the piston assembly to force air within the primer chamber into a fuel bowl of the carburetor to pressurize the fuel bowl and thereby convey fuel from the pressurized fuel bowl to a throat of the carburetor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:  
         [0017]    [0017]FIG. 1 is a perspective view of a lawnmower including a small internal combustion engine having a carburetor with a primer assembly in accordance with the present invention;  
         [0018]    [0018]FIG. 2 is a sectional view of the carburetor of FIG. 1, including a primer assembly in accordance with the present invention;  
         [0019]    [0019]FIG. 3 is an enlarged fragmentary view of a portion of the carburetor of FIG. 2, showing the piston of the primer assembly in a first position;  
         [0020]    [0020]FIG. 4 is a enlarged fragmentary view of a portion of the carburetor of FIG. 2, showing the piston of the primer assembly in a second position; and  
         [0021]    [0021]FIG. 5 is an exploded view of the carburetor of FIG. 2, showing the components of the primer assembly. 
     
    
       [0022]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention any manner.  
       DETAILED DESCRIPTION  
       [0023]    Referring to FIG. 1, lawnmower  10  is shown, including deck  12  having wheels  14 , and handle  16  attached to deck  12 . Additionally, lawnmower  14  includes internal combustion engine  18  mounted to deck  12 , wherein the power take-off (“PTO”) end of the engine crankshaft (not shown) is disposed vertically, and extends beneath deck  12  for driving connection to a blade (not shown). Engine  18  may be of any suitable type, such as a side valve or L-head engine, an overhead valve (“OHV”) engine, or an overhead cam (“OHC”) engine, for example. In particular, engine  18  may be a small single or twin-cylinder engine such as those disclosed in U.S. Pat. Nos. 6,276,234; 6,279,522; 6,295,959; and 6,499,453, each assigned to the assignee of the present invention, the disclosures of which are incorporated herein by reference.  
         [0024]    Engine  18  additionally includes carburetor  20  attached thereto for supplying an air/fuel mixture to engine  18  via intake pipe  22  attached to intake port  24  of cylinder  26  of engine  18 . Carburetor  20 , as shown in FIG. 2, includes primer assembly  30 , described in further detail below, for priming carburetor  20  to aid in starting engine  18 . Although primer assembly  30  and carburetor  20  are shown in connection with engine  18  of lawnmower  10 , it should be understood that primer assembly  30  may generally be used with a carburetors of any small internal combustion engine of the type used with lawnmowers, lawn tractors, sport vehicles, or other small working implements.  
         [0025]    Referring to FIG. 2, carburetor  20  generally includes carburetor body  32  and fuel bowl  34  attached to carburetor body  32 . Carburetor  20  includes many features similar to the carburetor disclosed in U.S. Pat. No. 6,152,431, assigned to the assignee of the present invention, the disclosure of which is expressly incorporated herein by reference. Carburetor body  32  includes throat  36  therethrough, having a venturi portion (not shown) disposed proximate main fuel jet  38 , which extends from fuel bowl  34  into throat  36  to supply fuel to throat  36  in response to vacuum created at venturi portion of throat  36  during running of engine  18 . Fuel bowl  34  includes a quantity of fuel therein, and also includes float  40  which floats on the fuel  42  within fuel bowl  34  and periodically actuates a valve (not shown) for metering a supply of fuel into fuel bowl  34  from a separate fuel tank (not shown). Air space  44  is defined within fuel bowl  34  above the fuel  42  therewithin, and is vented to the atmosphere via internal vent passage  46  which is connected to throat  36 .  
         [0026]    Referring additionally to FIG. 5, carburetor body  32  includes annular wall  48  projecting therefrom, which forms a recess or chamber  50  in carburetor body  32 . Fuel bowl vent passage  52  communicates recess  50  with fuel bowl  34 , and internal vent passage  46  communicates recess  50  with throat  36  and thereby to the atmosphere. Carburetor  20  additionally includes extended prime well  53 , the operation of which is described in detail in the above-incorporated U.S. Pat. No. 6,152,431.  
         [0027]    Referring to FIG. 5, the components of primer assembly  30  are shown, generally including sleeve  54 , O-ring  56 , return spring  58 , piston  60 , retaining ring  62 , and lock ring  64 , wherein the foregoing components are aligned along longitudinal axis L 1 -L 1  of primer assembly  30 . Sleeve  54  is annular in overall shape, and is made from metal or from a rigid or semi-rigid plastic material, for example, such as Celcon® M90, available from Ticona Inc., 90 Morris Ave., Summit, N.J. 07901. (Celcon® is a registered trademark of Celanese Corp., 522 5th Ave., New York, N.Y. 10036).  
         [0028]    Sleeve  54  includes outer surface  66 , inner surface  68 , base wall  70  at one end thereof, and flange  72  at an end thereof opposite base wall  70 . Flange  72  includes an annular recess  74  in which O-ring  56  is received. Sleeve  54  also includes a plurality of vent holes  76  which are spaced radially around sleeve  54  with respect to longitudinal axis L 1 -L 1 . As may be seen in FIG. 5, vent holes  76  are disposed in annular orientation radially around longitudinal axis L 1 -L 1 , and are positioned adjacent flange  72  of sleeve  54 .  
         [0029]    Return spring  58  is made from a suitable metal, and is shown herein as a helically coiled spring including first end  78  and second end  80 .  
         [0030]    Piston  60  is made from a substantially rigid plastic material such as Celcon® M90, available from Ticona Inc., 90 Morris Ave., Summit, N.J. 07901. (Celcon® is a registered trademark of Celanese Corp., 522 5th Ave., New York, N.Y. 10036). Piston  60  includes button portion  82  and flange portion  84  having annular recess  86  (FIGS. 3 and 4) therein for receipt of second end  90  of return spring  58 , as discussed below. Flange portion  84  of piston includes outer sealing surface  88 , which may include a lip formed from a material which is more resilient that the material from which the remainder of piston is made. Piston  60  is dimensioned to be closely received within sleeve  54 , such that sealing surface  88  of piston  60  engages and slidably seals against inner surface  68  of sleeve  54  when piston  60  is inserted within sleeve  54 .  
         [0031]    Retaining ring  62  is made of a heavy gauge metal, for example, or from a rigid plastic material, and includes opening  90 . Lock ring  64  is also made of a heavy gauge metal or from a rigid plastic material, and includes a plurality of locking tabs  92  spaced therearound.  
         [0032]    Referring to FIGS. 3-5, primer assembly  30  is assembled by inserting sleeve  54  within recess  50  of carburetor  20  until base wall  70  of sleeve  54  abuts carburetor body  32 . O-ring  56  is placed within annular recess  74  of flange  72  of sleeve  54 , and return spring  58  is inserted within sleeve  54 . Thereafter, piston  60  is inserted closely within sleeve  54 , with first end  78  of return spring  62  abutting base wall  70  of sleeve  54 , and second end  80  of return spring  62  received within annular recess  86  of flange  84  of piston  60 . Retaining ring  62  is inserted over button portion  82  of piston  60 , with button portion  82  closely received through opening  90  of retaining ring  62 . The side of retaining ring  62  which faces piston abuts O-ring  56  to seal retaining ring  62  with flange  72  of sleeve  54 . Finally, locking ring  64  is inserted within annular wall  48  of carburetor  20  and pressed therewithin, bending locking tabs  94  against annular wall  48  of carburetor  20  to capture the foregoing components of primer assembly  30  within recess  50  of carburetor  20 .  
         [0033]    Referring to FIG. 3, return spring  58  is held under compression between base wall  70  of sleeve  54  and flange portion of piston  60 , and flange portion of piston  60  is in turn captured between second end  80  of return spring  58  and retaining ring  62 , which limits outward travel of piston  60  along longitudinal axis L 1 -L 1  in a direction away from carburetor  20 . In the position of FIG. 3, button portion  82  of piston  60  projects outwardly of annular wall  48  of carburetor  20  such that same is accessible for depressing piston  60  to prime carburetor  20 , as described in further detail below.  
         [0034]    Primer chamber  94  is defined interiorly within sleeve  54  between base wall  70  thereof and piston  60 , and includes proximal end  94   a  positioned outwardly with respect to carburetor  20 , and distal end  94   b  positioned inwardly with respect to carburetor  20 . Outer chamber  96  is a substantially annular space defined between annular wall  48  of carburetor  20  and outer surface  66  of sleeve  54 . Outer chamber  96  is in communication with throat  36  of carburetor  20  via internal vent passage  46 , and primer chamber  94  is in communication with outer chamber  96  through vent holes  76  in sleeve  54 . Primer chamber  94  is also in communication with fuel bowl  34  of carburetor  20  through fuel bowl vent passage  52 .  
         [0035]    Normally, the components of primer assembly  30  are disposed as shown in FIGS. 2 and 3, in which return spring  58  biases piston  60  outwardly of carburetor  20  toward proximal end  94   a  of primer chamber  94  and to a position in which flange  84  of piston  60  is in abutment with retaining ring  62  and button portion  82  of piston  60  projects outwardly of carburetor  20  for access, as described above. Additionally, in this position, flange  84  of piston  60  is disposed outwardly of vent holes  76  of sleeve  54 , such that primer chamber  94  is in communication with outer chamber  96  and internal vent passage  46  and thence to the atmosphere via throat  36 , and primer chamber  94  is also in communication with fuel bowl  34  of carburetor  20  through fuel bowl vent passage  52 . In this manner, air space  44  of fuel bowl  34  is at atmospheric pressure when engine  18  is at rest.  
         [0036]    To prime carburetor  20  to aid in starting engine  18 , a user places a finger on button portion  82  of piston  60  and depresses piston  60  inwardly against the bias of return spring  58  toward distal end  94   b  of primer chamber  94 . Alternatively, an actuation mechanism (not shown) may be used to depress piston  60 , wherein the actuation mechanism may be remotely actuated by a user. Piston  60  is constrained to move along longitudinal axis L 1 -L 1  of primer assembly  30  due to the rigidity of piston  60  and sleeve  54 , wherein piston  60  is closely received within sleeve  54  such that outer sealing surface  88  of flange  84  of piston  60  seals against inner surface  68  of sleeve  54 . Further, the receipt of second end  80  of return spring  58  within annular recess  86  of flange  84  of piston  60  distributes the bias force of return spring  58  substantially evenly around flange  84 , which aids in constraining piston  60  for travel along longitudinal axis L 1 -L 1  of primer assembly  30 . Advantageously, regardless of the direction from which button portion  82  of piston  60  is pressed from externally of carburetor  20 , the constrained movement of piston  60  along longitudinal axis L 1 -L 1  of primer assembly  30  facilitates correct operation of primer assembly  30 , as described below.  
         [0037]    During initial movement of piston  60  along the longitudinal axis L 1 -L 1  inwardly toward carburetor  20 , and toward distal end  94   b  of primer chamber  94 , against the bias of return spring  58 , flange  84  of piston  60  clears or passes inwardly beyond vent holes  76  of sleeve  54  to thereby sever or break communication between primer chamber  94  and outer chamber  96 .  
         [0038]    Thereafter, as shown in FIG. 4, further movement of piston  60  along longitudinal axis L 1 -L 1  and against the bias of return spring  58  reduces the volume of primer chamber  94  and forces the air in primer chamber  94  through fuel bowl vent passage  52  into air space  44  of fuel bowl  32  to pressurize air space  44 . Pressurization of air space  44  forces a quantity of liquid fuel  42  upwardly through main fuel jet  38  into throat  36  of carburetor  20  to “wet” throat  36 , thus providing an enriched air/fuel mixture during initial cranking of engine  18  to aid in starting engine  18 .  
         [0039]    Inward movement of piston  60  toward carburetor  20  is eventually limited by the compression of return spring  58 , as shown in FIG. 4. Thereafter, release of piston  60  allows return spring  58  to bias piston  60  outwardly along longitudinal axis L 1 -L 1  in a direction away from carburetor  20 , toward proximal end  94   a  or primer chamber  94 , and back to the initial position shown in FIGS. 2 and 3. When flange  84  of piston  60  passes outwardly of vent holes  76  of sleeve  54 , primer chamber  94  is again communicated with outer chamber  96  to allow atmospheric air from throat  36  of carburetor  20  into primer chamber  94  to equalize the pressure between throat  36  of carburetor  20  and air space  44  of fuel bowl  32 . After engine  18  starts, reduction of pressure in throat  36  of carburetor  20  is communicated through internal vent passage  46 , outer chamber  96 , vent holes  76 , primer chamber  94 , and fuel bowl vent passage  52  to air space  44  of carburetor  20 , such that air space  44  of carburetor  20  is at less than atmospheric pressure during running of engine  18 .  
         [0040]    While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.