Abstract:
A valve body of an on-off valve that minimizes the deviation of opening and closing characteristics of a valve member made of an elastic polymer material and provided in a valve body of the on-off valve due to expansion caused by the fluid handled thereby and that maintains the specified opening and closing operation. A base portion of the valve member made with an elastic polymer material is inserted in an attachment hole of a valve element of a valve body with space constituted by a small-diameter-hole portion left at the hole bottom. A constricted-diameter portion formed in a tip opening of the attachment hole is embedded in the valve member to secure the base portion of the valve member. Axial elongation due to swelling of the valve member is distributed as forward elongation and rearward elongation sandwiching the site of securing by the constricted-diameter portion, which minimizes the axial elongation of a tip portion with a valve face and curtails deviation from the settings for on-off timing.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to a valve body of an on-off valve that works in concert with a valve seat to open and close a fluid passage by operating in a direction perpendicular to the closed face of the valve body and, in particular, relates to a valve body suited to control fluid flow of liquid fuel supplied to an engine that causes the swelling of a valve member forming a valve face.  
         BACKGROUND OF THE INVENTION  
         [0002]    Valve bodies of on-off valves that control liquid fuel supplied to automobile engines and general-purpose engines include on-off valves that work in concert with a valve seat to open and close a fluid passage by causing the valve body to operate in a direction perpendicular to the closed face. In addition to being durable, these valves are required to be highly fluid tight and dimensionally precise in order to maintain engine performance.  
           [0003]    A typical on-off valve that controls liquid fuel supplied to an engine is an inlet valve located at the inlet portion of a fixed fuel chamber to control liquid fuel sent from a fuel pump to a float-type or diaphragm-type fixed fuel chamber of an carburetor. The valve body thereof moves linearly in compliance with a lever that rotates in accordance with the rising or falling of the float or the displacement of the diaphragm, controlling the flow of the liquid fuel in concert with a valve seat provided in a fuel passage.  
           [0004]    There are carburetors and, in particular, carburetors for small-exhaust-volume general-purpose engines handle liquid fuel at extremely low flow rates. In such cases a minor deviation in the fuel flow rate greatly affects engine performance. As a result, the fuel passage must be completely closed when the inlet valve is closed and must faithfully open in response to movement of the float or diaphragm, i.e. a drop in fuel in the fixed fuel chamber. As such, the portion forming the valve face for the valve seat of the valve body is made of an elastic polymer material with excellent oil resistance, such as fluororubber, and is made to be both durable and fluid tight with consideration going to minimizing swelling.  
           [0005]    FIGS.  4 (A) and (B) illustrate valve bodies currently used in an inlet valve of a diaphragm-type fixed-fuel chamber. The valve body shown in FIG. 4(A) comprises an injection hole  52  at the tip portion of a metal round-axle valve element  51  with axial grooves. A base portion  54  of a valve member  53  made of fluororubber fills the injection hole  52 , and a forward-protruding tip portion  55  is given a conical shape. In FIG. 4(B), a short axle  58  and a conical head  59  protrude in a unitary manner from the tip of a metal round-axle valve element  57  with axial grooves similar to that noted above. A conical valve member  60  made of fluororubber is firmly joined to the head  59 .  
           [0006]    In each of the valve bodies mentioned above, the valve members  53 ,  60  are formed with injection molding using a metal die that forms a conical valve face. The portion to become the valve face is then polished to provide the prescribed conical shape of the apex. Extensive manufacturing equipment is required as a result.  
           [0007]    In addition, a variety of liquid fuels such as a fuel blended to meet exhaust gas regulations or a fuel used for inspection and adjustment during the manufacture of the carburetor in addition to gasoline and ethanol-blended gasoline, which are widely known liquid fuels, flow over the periphery of the valve body for an extended period of time. The valve members  53 ,  60 , as a result, make contact with the variety of liquid fuels for an extended period of time and unavoidably swell.  
           [0008]    FIGS.  5 (A) and (B) illustrate the conditions in the system before and after swelling when the valve body of FIG. 4(A) is used as the inlet valve of the diaphragm-type fixed fuel chamber. A base portion of the round axle unit  51  is attached to the tip of a lever  66  rotatably supported by a pin  65 . The valve member  53  is brought into tight contact with a valve seat  68  and closes a fuel passage  69  under the spring force of a valve-closing spring  67  that acts on the lever  66 . The base portion of the lever  66  and the central portion of the diaphragm  70  are, as shown in FIG. 5(A), adjusted so as to have a slight gap “a”.  
           [0009]    When the volume of fuel in a fixed fuel chamber  71  drops, the diaphragm  70  is displaced toward the fixed fuel chamber  71  and rotates the lever  66  clockwise as shown in the drawing to cause the valve member  53  to separate from the valve seat  68 , whereupon fuel is introduced into the fixed fuel chamber  71 . When the volume of fuel in the fixed fuel chamber  71  rises, the diaphragm  70  is displaced in the opposite direction to that previously mentioned, and the lever  66  rotates counterclockwise, seating the valve member  53  on the valve seat  68 . Therefore, in order for a fixed volume of fuel to be accurately provided to the fixed fuel chamber  71  and fuel to be supplied to the engine at an accurate flow rate, the gap “a” and the load characteristics of the valve-closing spring  67  must be appropriately set, and the gap “a” must be precisely adjusted.  
           [0010]    But swelling of the valve member  53  appears as elongation in the axial direction. When the swelling of the valve member  53  shown in FIG. 5(B) results in elongation to the extent of “c” in the axial direction in comparison to the valve member  53  in FIG. 5(A) prior to swelling, the elongation “c” separates the base portion of the lever  66  from the diaphragm  70  by the lever ratio of L2:L1, which widens the gap “a to b” and compresses the valve-closing spring  67 , changing its load characteristics. Therefore, the fuel passage  69  is closed to the extent of dramatically decreasing the volume of fuel in the fixed fuel chamber  71  compared to that before swelling. The fuel passage  69  is closed when a volume of fuel less than that supplied before swelling is introduced, which causes the flow rate of fuel supplied to the engine to drop and thereby negatively affects engine performance and the condition of the exhaust.  
           [0011]    This phenomenon also occurs with the valve body shown in FIG. 4 (B). However, the impact due to swelling is larger with the valve body shown in FIG. 4(A), in which the axial length of the valve member  53  is longer than that of the valve member  60  in FIG. 4(B).  
           [0012]    Thus, it is desirable to provide a valve body for resolving the problems associated with prior-art valve bodies comprising a valve member made of an elastic polymer material such as fluororubber and located at the tip of a valve element—i.e., manufacturing can be problematic and tend to require extensive equipment to form the valve member such as metal dies for injection molding, and thus high costs are therefore unavoidable, and axial elongation due to the swelling of the valve member directly impacts the fuel flow rate—, that can be easily manufactured without the use of a metal die and that greatly reduces the negative effect of swelling on performance during the control of the flow rate of fuel.  
         SUMMARY OF THE INVENTION  
         [0013]    In the present invention, a base portion of a valve member is inserted and fastened in a hole provided at a tip portion of a valve element with space remaining at the hole bottom, and a valve face is formed on a tip portion of the valve member, which protrudes from the front of the attachment hole, in order to reduce the negative influence of swelling on control performance associated with the valve body of on-off valves comprising on the tip of the valve element a valve member made of a polymer material that forms a valve face for a valve seat.  
           [0014]    The axial elongation due to swelling when the valve member swells is divided into elongation toward the hole-bottom space of the base portion and elongation toward the front of the tip portion. The elongation of the tip portion as a result is less than the entire elongation, which reduces the deviation from the settings for on-off timing and thereby results in the reduction of the negative effects caused by swelling.  
           [0015]    In addition, the present invention, in order to solve the above mentioned manufacturing-equipment-specific problem associated with the valve body of an on-off valve comprising a valve member made with an elastic polymer material that forms a valve face for the valve seat at the tip of a valve element made of metal or hard synthetic resin, involves manufacturing the valve body under a process comprising the steps of preparing a valve element comprising an attachment hole that opens to a tip face on a tip portion and an elastic member made of a polymer material inserted into the attachment hole with virtually no gap or inserting the elastic member in the attachment hole so that space remains at the hole bottom and the elastic member protrudes forward; securing the elastic member to the valve element by constricting the diameter of at least the tip opening of the attachment hole; and forming by machining a prescribed valve face of the elastic member that protrudes forward from the attachment hole.  
           [0016]    In other words, the objective of manufacturing a valve body that reduces the negative effects due to swelling can be achieved using simple manufacturing equipment without dies in which an elastic member to become the valve member is inserted in the attachment hole and compressed to secure it, and the protruding portion is machined away.  
           [0017]    Other aspects 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  
       [0018]    [0018]FIG. 1 is a partially cutaway plan view showing one embodiment of the valve body of the invention.  
         [0019]    [0019]FIG. 2 is a partially cutaway plan view showing a different embodiment of the valve body of the invention.  
         [0020]    [0020]FIG. 3(A), (B), (C) and (D) are process diagrams illustrating an embodiment of a method for manufacturing the valve body of the invention.  
         [0021]    FIGS.  4 (A) and (B) are partially cutaway plan views illustrating different examples of the prior art.  
         [0022]    FIGS.  5 (A) and (B) illustrate the differences in opening and closing characteristics before and after swelling. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0023]    Embodiments of the invention will be discussed in reference to the drawings. FIG. 1 illustrates an embodiment in which the invention is applied to a valve element  1  used in an inlet valve of a diaphragm-type fixed fuel chamber of a carburetor. A valve element  1  comprises a surface made with a metal, generally aluminum, to which is applied a non-electrolyte nickel plating. The valve element  1  has a round axle form that can be inserted into the opening portion of the fuel passage to the fixed fuel chamber with almost no gap. The valve element  1  includes on its outer circumference thereof a communicating portion  2  with a plurality of axial grooves  3  that introduce a liquid fuel that passes through the valve seat to the fixed fuel chamber. On the base of the valve element  1  is an integrally formed latching portion  4  comprising a neck portion and a head unit for attaching to a tip of a lever that rotates in conformity to the displacement of the diaphragm. Protruding from the tip of the valve element  1  is a tubular portion  5 . The tubular portion  5  has an outer diameter almost equivalent to the bottoms of the axial grooves  3 .  
         [0024]    The inner portion of the tubular portion  5  forms an attachment hole  6  that opens to the tip, and a small-diameter hole portion  7  extends through a step bore portion  8  in the inner end.  
         [0025]    In the attachment hole  6  is a short, cylindrical base portion  13  of a valve member  12 . The valve member  12  is preferably made of an elastic polymer material such as a fluorine resin, Nylon, polypropylene, NBR, or fluororubber but generally fluororubber that is inserted in an almost fluid tight manner superimposed on the stepped bore portion  8 . The tip portion of the tubular portion  5 , i.e., the cylindrical wall of the tip opening of the attachment hole  6 , is compressed by constriction and the compressed diameter portion  10  thereby formed is embedded in the valve member  12  to secure the valve member  12 . A tip portion  14  of the valve member  12  protruding forward from the attachment hole  6  is formed into a conical shape with a specified apex, and the outer circumference thereof forms a valve face  15  for a valve seat.  
         [0026]    When this valve body opens or closes the fuel passage, the swelling of the valve member  12  due to the liquid fuel over time cannot be avoided. The valve member  12  in this embodiment in particular is longer in the axial direction than in diameter, so elongation in the axial direction due to swelling cannot be ignored. However, in this embodiment, as is shown in FIG. 1, the valve member  12  is secured by a compressed diameter portion  10  located nearer the tip than the middle area. Sandwiching the securing location, the conical tip portion  14  on the tip side of the valve member  12  elongates forward, while the cylindrical base portion  13  on the base side of the valve member  12  elongates rearward, entering into the hollow small-diameter hole portion  7  of the valve element  1 .  
         [0027]    In this manner, the axial elongation due to swelling is elongation to the front and elongation toward the rear sandwiching the compressed diameter portion  10 . Because the forward portion of the valve member  12  forward of the compressed diameter portion  10  is axially shorter than the rearward portion thereof, the elongation of the tip portion  14  is very small, which drastically reduces the negative effects on open-shut performance as illustrated in FIGS.  5  (A) and (B).  
         [0028]    [0028]FIG. 2 shows a different embodiment of the valve body-the fundamental construction of the valve element  1  and the valve member  12  is identical to that shown in FIG. 1, with the exception in this embodiment of toothing  9  comprising a female helix or an annular toothing pattern provided on the circumference of the attachment hole  6 . The toothing  9 , which is provided in the compressed diameter portion  11  by compressing the tip portion of the tubular portion  5 , is deeply embedded into the base portion  13  to fasten the valve member  12  even more securely.  
         [0029]    As shown in the embodiments in FIGS. 1 and 2, the compressed diameter portions  10 ,  11  may be formed over a wide range toward the base from the tip of the tubular portion  5  and not limited to a narrow region of the tip of the tubular portion  5  to fasten the valve member  12  even more securely. However, in an embodiment in which the valve member  12  is secured over a narrow region, the ratio of rearward elongation can be increased and the elongation of the tip portion  14  that directly affects performance of an on-off valve can be made very small.  
         [0030]    Moreover, this embodiment does not prohibit the use of an adhesive, and an adhesive can be coated on the outer circumference of a portion of the base portion  13  of the valve member  12  into which the compressed diameter portion  10 ,  11  is embedded to increase the degree of fastening. If this is to be done, the application of the adhesive is very simple, so the valve body can be manufactured without requiring a complicated step. Moreover, securing with the adhesive alone without the combined use of the compressed diameter portions  10 ,  11  and the adhesive is also possible. In this case, the adhesive can be applied to the outer circumference of the base portion  13  located in the tip opening of the attachment hole  6  to perform fastening.  
         [0031]    [0031]FIG. 3 shows an embodiment for manufacturing the valve member and body shown in FIG. 1. In FIG. 3(A), the valve element  1  and an elastic member  17  are readied. The valve element  1  is made of metal, and, as illustrated in FIG. 1, comprises a round-axle communicating portion  2  with a plurality of axial grooves  3  on the outer circumference, a latching portion  4  provided in a unitary manner on the base thereof and a tubular portion  5  protruding from the tip. An attachment hole  6  and a small-diameter hole portion  7  on the inner end thereof are located in the interior of the tubular portion  5 . The elastic member  17  is made of an elastic polymer, has a diameter equivalent to or slightly smaller than the diameter of the attachment hole  6 , and is a cylindrical unit longer than the depth of the attachment hole  6 .  
         [0032]    First, the elastic member  17  is inserted into the attachment hole  6  and as is shown in FIG. 3(B), is joined with the valve element  1  so that the base surface overlaps with the stepped bore portion  8  that is the inner end of the attachment hole  6 . Alternatively, the elastic member  17  could be inserted to a certain depth while leaving part of the inner end of the attachment hole  6  unfilled using a valve element  1  having an attachment hole  6  lacking a small-diameter hole portion  7  on the inner end thereof. However, according to this embodiment, the elastic member  17  is fastened at a certain depth so a tip portion of a constant length can always be made to protrude forward, which advantageously allows the formation of a valve face  15 , which will be discussed later, to be performed precisely.  
         [0033]    Next, as is shown in FIG. 3(C), the wall of the tip portion of the tubular portion  5 , i.e., the tip portion of the attachment hole  6 , is crimped using a crimping tool  21  to compress it to form a compressed diameter portion  10  and embed it into the elastic member  17 . Through this step, the base side of the elastic member  17  is secured in the attachment hole  6 , and the tip side thereof is secured in a state protruding from the front of the valve element  1 .  
         [0034]    And as shown in FIG. 3(D), the portion of the elastic member  17  protruding from the front of the valve element  1  is given a conical shape of a prescribed apex using a cutting tool  22  that uses a grinding stone and polishing paper for grinding and polishing in combination or separately.  
         [0035]    Through the above steps, a valve member  12  is formed from an elastic polymer member comprising a base portion  13 , which is secured into the attachment hole  6 , and a conical tip portion  14  with an outer circumference that forms the valve face  15  for a valve seat.  
         [0036]    The above-mentioned manufacturing process is an embodiment involving a valve element  1  made of metal, but it is not limited to metal, and the invention can also appropriately use a hard synthetic resin. A valve body in which the valve element  1  made with a hard synthetic resin is manufactured by, for example, giving it the same shape and construction as that shown in FIG. 3(A), inserting the elastic member  17  in the attachment hole  6  to bring about the condition shown in FIG. 3(B), applying heat from electrical resistance or high-frequency vibration to the tip portion of the tubular portion  5  to cause it to contract under heat, thereby forming a contracted portion  10  that is embedded in the elastic member  17 , and using the cutting tool  22  shown in FIG. 3(D) to form the prescribed valve face  15 .  
         [0037]    The elastic member  17  can be secured in the valve element  1  using an adhesive. The adhesive is applied to the outer circumference of the elastic member  17  located at the opening of the tip of the attachment hole  6  to secure the elastic member to the valve element  1  in concert with the constricted diameter portion  10  or using the adhesive alone without constricting the tubular portion  5 .  
         [0038]    The long elastic member  17  can be attached to the valve element  1  by first readying a long elastic member, and, after inserting it into the attachment hole  6 , cutting it off at a spot where it protrudes out for a certain length and then repeating this process in order. However, readying elastic members that have already been cut to the prescribed length allows them to be inserted efficiently to a plurality of valve elements  1  or insertion to be performed either with manual insertion or automatically using a dedicated assembling machine. This advantageously adds options to the list of manufacturing means.  
         [0039]    Moreover, the elastic member  17  is not limited to a cylindrically shaped object. Also useful is an elastic member  17  made with a valve face comprising a surface that is conically or spherically formed to correspond to the seat surface of the valve seat, which comprises a planar surface perpendicular to the direction of valve movement, or a valve face of any of a variety of other shapes that provides a shape suitable for formation with minimal grinding or polishing, such as providing the portion to become the base portion  13  upon insertion into the attachment hole  6  with a cylindrical shape and making the portion protruding forward a conical, spherical, or trapezoidal shape.  
         [0040]    As has been discussed, according to the present invention, the axial elongation due to swelling of the valve member made of an elastic polymer material is both forward and rearward such that the elongation of the portion that forms the valve face for the valve seat is small, the change in opening and closing characteristics due to swelling is minimized, deviation from the settings for on-off timing are minimized, and opening and closing actions are performed within a tolerable range that allows the fluid flow rate to be controlled in a stable manner.  
         [0041]    While the invention is susceptible to various modifications and alternative forms, a specific example thereof has been shown in the drawings and is herein described in detail. It should be understood, however, that the invention is not to be limited to the particular form 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.