Patent Publication Number: US-6708959-B1

Title: Carburetor valve assembly

Description:
FIELD OF THE INVENTION 
     This invention relates generally to carburetors and more particularly to a throttle valve assembly for a carburetor. 
     BACKGROUND OF THE INVENTION 
     Current throttle valves for carburetors have a metallic cam plate fastened tot to a metal shaft extending into the carburetor body and upon which a valve head is fixed to control the flow of air through the carburetor in response to rotation of the valve head. The cam plate is engageable with one or more stops on the carburetor body to limit rotation of the throttle valve assembly between idle and wide open throttle positions. The cam plate, shaft and valve head are machined and plated stamped parts. The cam plate is attached to the shaft with either a threaded fastener or by swaging over a portion of the shaft extending through the cam plate. The valve head may be a disc, such as in a butterfly-type valve arrangement, with the disc attached to the shaft with a threaded fastener. The machined or stamped components are relatively expensive to produce. Further, the use of threaded fasteners to connect the valve head to the shaft, and the cam plate to the shaft or the swaging of the shaft onto the cam plate greatly increases the cost, difficulty, time and labor required to assemble the throttle valve assembly. 
     Some carburetors have choke valves which may be closed to restrict the flow of air through the carburetor to facilitate starting of an associated engine. The choke valve may have a metal shaft extending into the carburetor body and a metal valve disc attached thereto by a threaded fastener which is received in and rotatable in the fuel and air mixing passage of the carburetor. The valve disc is rotated between a closed position substantially restricting air flow past the valve disc and an open position permitting a substantially unrestricted flow of air through the fuel and air mixing passage. Some choke valves have a plastic one-piece shaft with an integral handle which may be grasped by a user and rotated to move the choke valve between its open and closed positions. The valve disc may be press-fit into a slot formed through the shaft. 
     SUMMARY OF THE INVENTION 
     A carburetor with a throttle valve assembly having a plastic cam body connected to a plastic shaft which extends into the carburetor body and a valve head received in a slot formed through the plastic shaft. Desirably, the valve assembly eliminates the use of threaded fasteners and the need to swage or otherwise deform any of the components to connect them together. Desirably, the shaft and cam body are constructed and arranged to prevent relative rotation between them. This permits accurate location of the cam body on the shaft and facilitates calibration of the throttle valve assembly between its idle and wide open throttle positions. Further, the characteristics of the throttle valve assembly can be changed by simply providing a cam body having a different shape or construction with the shaft or valve head being the same for a wide range of carburetors. Still further, the slot in the shaft is preferably longer than the diameter of the valve head so that the valve head may shift axially on the shaft so that it is self-centering within the fuel and air mixing passage. The valve head can preferably also shift laterally relative to the shaft. This greatly facilitates assembly and manufacture of the throttle valve assembly by greatly increasing the tolerances with respect to the location of the valve head on the valve shaft and of the slot receiving the valve head. 
     Objects, features and advantages of this invention include providing a valve assembly which utilizes a plastic cam body connected to a plastic shaft, permits different cam bodies to be used with the same shaft and valve disc for different carburetors, self-centers and assures smooth movement of the valve disc within the fuel and air mixing passage, is lightweight and inexpensive to manufacture and assemble, eliminates the use of machined or stamped metal components for at least the shaft and cam body, eliminates the use of threaded fasteners or mechanical deformation such as swaging to connect components together, has improved corrosion resistant characteristics, reduces the time and cost to assemble the throttle valve assembly into a carburetor, is reliable, durable, rugged and in service has a long, useful life. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiment and best mode, appended claims and accompanying drawings in which: 
     FIG. 1 is an end view of a carburetor having a throttle valve assembly according to the present invention; 
     FIG. 2 is a side view of the carburetor of FIG. 1; 
     FIG. 3 is a cross-sectional view taken generally along lines  3 — 3  of FIG. 2; 
     FIG. 4 is an enlarged fragmentary sectional view taken generally along line  4 — 4  of FIG. 3; 
     FIG. 5 is a side view illustrating a throttle cam body connected to a throttle shaft; 
     FIG. 6 is an end view of the cam body and shaft; 
     FIG. 7 is an enlarged end view of the cam body; 
     FIG. 8 is a cross sectional view of the cam body taken generally along line  8 — 8  of FIG. 7; 
     FIG. 9 is a fragmentary sectional view taken generally along line  9 — 9  of FIG. 7; 
     FIG. 10 is a side view of the throttle shaft; 
     FIG. 11 is an end view of the throttle shaft; 
     FIG. 12 is an enlarged fragmentary view of an end portion of the throttle shaft; 
     FIG. 13 is an enlarged fragmentary cross-sectional view illustrating the connection between the throttle shaft and cam body; 
     FIG. 14 is a plan view of a valve disc; and 
     FIG. 15 is a side view of the valve disc of FIG.  14 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring in more detail to the drawings, FIGS. 1-3 illustrate a carburetor  10  having a throttle valve assembly  12  including a valve head  14  rotatably carried by a shaft  16  within a fuel and air mixing passage  18  of the carburetor  10  to control fluid flow therethrough. Rotation of the throttle valve assembly  12  is typically accomplished by a Boden cable and wire assembly (not shown) which is attached to and drives a throttle cam body  20  connected to the shaft  16  for rotation therewith. The throttle valve assembly  12  rotates from an idle position as shown in FIG. 1, substantially preventing fluid (namely, air) flow through the fuel and air mixing passage  18 , and a wide open throttle position permitting a substantially unrestricted flow of fluid through the fuel and air mixing passage  18 . In general, as shown in FIG. 3, fuel is discharged into the fuel and air mixing passage  18  from a fuel metering chamber  22  which receives fuel through a diaphragm actuated inlet valve  24  which selectively communicates the fuel metering chamber  22  with a diaphragm-type fuel pump  26  which draws fuel from a fuel tank for delivery to the fuel metering chamber  22 . Fuel discharged from the fuel metering chamber  22  into the fulel and air mixing passage  18  is mixed with air flowing therethrough and is delivered to the engine in proportion to the engine&#39;s fuel demand to support engine operation over a wide range of operating conditions. The construction and operation of the fuel metering chamber  22 , valve  24 , fuel pump  26 , and related components may be as disclosed is U.S. Pat. No. 4,752,420, the disclosure of which is incorporated herein by reference in its entirety. 
     The throttle valve assembly  12  has the shaft  16  which extends through a bore  28  through a body  30  of the carburetor  10  at a right angle to and intersecting the fuel and air mixing passage  18 . A split ring retainer  32  cooperates with a groove  34  at a first end  36  of the shaft  16  projecting from the carburetor body  30  to retain the shaft  16  within the body  30 . As best shown in FIGS. 5,  6  and  10 - 12 , the shaft  16  is generally cylindrical with a second end  38  constructed to be disposed within a complementary recess or passage  40  in the cam body  20 . Adjacent the second end, a pair of flat sides  42 ,  44  are formed on opposite sides of the shaft  16 . A groove  46  is formed at least in part around the shaft  16  inboard of its second end  38  and within the area of the flat sides  42 ,  44 . An elongate slot  48  formed through the shaft  16  between its ends  36 ,  38  is constructed to receive the valve head  14  therein to connect them together. The shaft  16  is preferably formed of a plastic or polymeric material and may be readily molded such as by an injection molding or other molding process. 
     As best shown in FIGS. 6-9, the cam body  20  has a generally tubular barrel portion  50  having a non-circular recess or passage  40  in which the second end  38  of the shaft  16  is pressed to connect the cam body  20  and shaft  16  together. At least a portion of the passage  40  is defined by at least two and preferably four flat surfaces or shoulders  52  which, in assembly, bear on and engage the flat sides  42 ,  44  of the shaft  16  to prevent relative rotation between the shaft  16  and cam body  20 . A plate portion  54  of the cam body  20  extends outwardly from the barrel portion  50  and defines two stop surfaces  56 ,  58  engageable with associated stops  60 ,  62  carried by the carburetor body  30  to limit rotation of the throttle valve assembly  12 . Preferably, at least one of the stops  60  of the carburetor body  30  is adjustable and as shown, is defined by a conical end of a screw  66  which may be advanced or retracted relative to the carburetor body  30  to change the location of engagement between the cam body stop  56  and the carburetor body stop  60  defined by the end of the screw  66 . Accordingly, the circumferential spacing between the stops  56 ,  58  of the cam body  20  as well the location of the stops  60 ,  62  on the carburetor body  30  determines the amount of rotation of the throttle valve assembly  12  between its idle and wide open throttle positions. Desirably, a spring  68  which bears on the cam body  20  yieldably biases the throttle valve assembly  12  to its idle position as shown in FIGS. 1-3. One or more holes  70  are preferably provided through the plate  54  spaced from the barrel portion  50  to facilitate connection with the wire of the Boden wire cable assembly (not shown) which drives the throttle valve assembly  12  for rotation. A hole  71  may receive one finger or end of the spring  68  which yieldably biases the throttle valve assembly  12  to its idle position. 
     As best shown in FIGS. 8 and 9, to retain the cam body  20  on the shaft  16  and prevent their inadvertent separation, the cam body  20  has at least one and preferably a plurality of barbs or tabs  72  extending radially inwardly from an inner wall  74  of the barrel  50  into the passage  40 . In assembly, the cam body  20  is pressed onto the shaft  16  until the tabs  72  pass over the second end  38  of the shaft  16  and are received within the groove  46  adjacent to the second end  38  to retain the cam body  20  on the shaft  16  with an interference fit. The cam body  20  is preferably formed of a plastic or polymeric material and may be molded separately from the shaft  16  to permit different cam bodies to be used with the same shafts for different carburetor applications. Alternatively, the shaft  16  and cam body  20  may be integrally formed together in one piece to eliminate the need for the structures preventing relative rotation between the shaft  16  and cam body  20  and the structures retaining the them together. 
     As best shown in FIGS. 4,  14  and  15 , the valve head  14  is preferably a generally flat circular plate or disc which may be formed of a metallic or polymeric material. The valve head  14  has a plurality of raised, inclined retainer tabs  80 ,  81  preferably integrally formed therewith. Desirably, as shown in FIG. 15, the tabs  80 ,  81  are laterally spaced from the center of the valve head  14  and have ramps  82  leading to opposing stop surfaces  84  constructed to bear on the throttle shaft  16  to retain the valve head  14  in the slot  48  of the shaft  16 . In assembly, the valve head  14  is pressed or pushed into the shaft  16  until the tab or tabs  80  on one side of the valve head  14  are forced through the slot  48  and the shaft  16  is received between the opposed laterally spaced tabs  80 ,  81 . Desirably, due to the inclined or ramp surfaces  82  of the tabs  80 ,  81  it is relatively easy to push the valve head  14  into the slot  48  in shaft  16 . However, it is difficult to remove the valve head  14  from the shaft  16  due to the abrupt stop surfaces  84  which oppose such movement of the valve head  14 . Accordingly, inadvertent separation of the valve head  14  and shaft  16  is prevented. 
     Desirably, the valve head  14  is slidably carried by the shaft  16  so that it is self-centering within the fuel and air mixing passage  18 . To accomplish this, the slot  48  formed in the shaft  16  preferably has a length greater than the diameter of the valve head  14  to permit shifting of the valve head  14  axially relative to the shaft  16 . The slot also has a length at least equal to and preferably greater than the diameter of the fuel and air mixing passage  18  with the slot  48  spanning the entire fuel and air mixing passage  18  so that the valve-head  14  is self-centering therein. Further, to permit lateral shifting of the valve head  14  relative to the shaft  16  and thereby further enable the valve head  14  to center itself in passage  18 , the distance between the stop surfaces  84  of the opposed laterally spaced tabs  80 ,  81  is preferably greater than the outer diameter of the shaft  16 . In this manner, the tolerances of the valve head  14  and shaft  16  are greatly increased to facilitate their manufacture and assembly both with respect to each other and their assembly into the carburetor  10 . 
     The shaft  16 , cam body  20  and valve head  14  may be formed from any suitable polymeric material with currently preferred materials including, without limitation, acetal copolymers such as those sold under the trademarks Delrin 500 and Celcon M-90. The valve head  14  may also be formed of brass or other metal. Desirably, the throttle valve assembly  12  can be assembled without the use of any fasteners, adhesives or the like. Further, the use of machined, stamped or other costly to manufacture components can be at least substantially reduced, and preferably eliminated. Still further, the valve head  14  and shaft  16  can be used with a wide range of cam bodies  20  to increase the versatility of the throttle valve assembly  12  for a wide range of carburetors  10  and engine applications. Accordingly, the cost to manufacture and assemble the throttle valve assembly  12  itself as well as to install the throttle valve assembly  12  into a carburetor  10  is significantly reduced. The polymeric materials are also cheaper and have greater resistance to corrosion than their metal counterparts.