Patent Publication Number: US-2013249120-A1

Title: Carburetor fuel filter

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a fuel filter element for use with a carburetor. 
     BACKGROUND 
     Carburetors for use with combustion engines sometimes include on-board fuel filtration that works in conjunction with one or more other types of filtration along a fuel path from a fuel storage tank to the engine. Such on-board filtration may include a filter element that is assembled with and provided as part of the carburetor assembly. Though fuel is often filtered prior to reaching the carburetor, on-board filtration can provide an additional safeguard against particles in the fuel that could adversely affect the operation of jets, orifices, valves or other components in the carburetor if left in the fuel. 
     SUMMARY 
     In accordance with one embodiment, a carburetor is provided that includes a fuel inlet and a metering system. The metering system includes a metering valve arranged downstream from the fuel inlet. The carburetor also includes a non-metallic filter element supported in a fuel passage of the carburetor. 
     In accordance with another embodiment, a method of making a carburetor is provided. The method includes the steps of providing a substantially flat fuel filter and pressing the fuel filter into a fuel passage opening of the carburetor. The flat fuel filter is sized to have an interference fit with the fuel passage opening, and the fuel filter is substantially not plastically deformed by the interference fit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of preferred embodiments and best mode will be set forth with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional schematic view of a carburetor with a fuel filter in a fuel passage, according to one embodiment; and 
         FIG. 2  is a cross-sectional view of a portion of the carburetor of  FIG. 1 , showing a fuel filter being cut from a sheet of material so that it is aligned with the fuel passage. 
     
    
    
     DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS 
     As described below, a fuel filter for use as part of a carburetor may include a filter element made from a non-metallic material, such as a woven or non-woven polymeric material. While generally described in conjunction with the figures as a filter located between an on-board fuel pump and a metering valve, it should be recognized that the filter may be located anywhere along a fuel passage or passages of the carburetor, with or without a fuel pump. It is noted that the figures are not to scale, with certain features exaggerated and others minimized or not shown. 
     Referring in more detail to the drawings,  FIG. 1  is a cross-sectional schematic view of a carburetor  10  with an on-board fuel filter, according to one embodiment. The carburetor  10  includes a fuel inlet  12 , a fuel pump  14 , a metering system  16 , and an air passage  18  arranged along a fuel flow path between a fuel storage tank or other fuel source and a combustion engine (not shown). A fuel filter  20  is located between the fuel pump  14  and the metering system  16  in the illustrated example. The carburetor  10  receives fuel at fuel inlet  12  from the fuel storage tank or other source, which may or may not be a pressurized source. In this embodiment, the fuel pump  14  provides a pressure differential that causes fuel to flow from the fuel source to the carburetor  10 . Fuel pump  14  also provides fuel to the metering system  16  for metered fuel delivery to the air passage  18 . 
     The fuel pump  14  in this example is a diaphragm fuel pump, including a fuel chamber  22  and a pulse chamber  24 , separated by a diaphragm  26 . Alternating high and low pressure pulses are provided at the pulse chamber  24  via connection to an engine crankcase or other source. Diaphragm  26  moves back and forth (up and down in  FIG. 1 ) accordingly in response to the pressure pulses. A subatmospheric pressure pulse in chamber  24  causes the diaphragm  26  to move in a direction (shown as a dashed line) that increases the volume of the fuel chamber  22 , causing fuel to flow into the fuel chamber  22  from fuel inlet  12  through inlet check valve  28  and closing outlet check valve  30 . A superatmospheric pressure pulse in chamber  24  causes the diaphragm  26  to move in an opposite direction that decreases the volume of the fuel chamber  22 , causing fuel to flow into fuel passage  32  from fuel chamber  22  through outlet check valve  30  and closing inlet valve  28 . Fuel passage  32  is thereby supplies with fuel for use by the metering system  16 , which includes a metering valve  34  and a metering diaphragm  36  that work together to provide metered doses of fuel from fuel passage  32  to the air passage  18  for mixing and delivery to an engine. 
     The fuel filter  20  is located along the fuel flow path from the fuel source to the engine. In the illustrated embodiment, it is located along the fuel flow path between the fuel inlet  12  and the metering valve  34 , the metering valve  34  being located downstream from the fuel inlet  12 . More particularly, the fuel filter  20  is located in fuel passage  32  between the fuel chamber  22  of the fuel pump  14  and the metering valve  34 . As used herein, a fuel passage is any port, conduit, line, opening, aperture, recess, or other element along which fuel flows on its way from the fuel source to the engine. The illustrated carburetor  10  includes a number of fuel passages, including fuel inlet  12 , fuel chamber  22 , fuel passage  32 , and several other undesignated fuel passages such as those associated with the metering system  16 . Some fuel passages include a plurality of smaller passages. For example, as is apparent from  FIG. 1 , the pump chamber  22  and the fuel passage  32  each include portions formed in both first and second carburetor bodies  38 ,  40 . 
     The illustrated fuel filter  20  and fuel passage  32  together form an interference fit—i.e., the width or diameter of fuel filter  20  is slightly larger than the fuel passage  32  before assembly. Thus the fuel filter  20  may be substantially flat prior to assembly and assume a slightly curved shape after assembly, as shown. The fuel filter  20  includes a filter element  42 . In one embodiment, the fuel filter  20  consists essentially of the filter element  42 . In other embodiments, the fuel filter  20  may include additional elements such as a housing, frame, another feature that supports the filter element  42  in the particular fuel passage, or some other element that provides additional functionality to the fuel filter  20 . As used herein, a filter element is a component with opposite surfaces through which fluid can flow from one surface to the other and is characterized by its ability to remove unwanted or unnecessary components from the fluid, such as particles larger than a certain size or chemical components. In one embodiment, the filter element  42  is a mechanical filter element, meaning that it removes particles larger than a certain size from the fluid that passes therethrough. For example, a mechanical filter element with a plurality of 35 micron holes or pores formed therethrough may remove particles larger than 35 microns from the fluid passing through the filter element. 
     In one embodiment, the fuel filter  20  includes a non-metallic filter element  42 . As used herein, a non-metallic filter element is a filter element in which metal is not a majority constituent. For example, the filter element  42  may be a polymeric filter element. A polymeric filter element may be constructed from any suitable polymeric material, such as a semi-crystalline plastic. Semi-crystalline plastics may provide exceptional solvent resistance properties, which are useful along a fuel flow path that subjects the filter element  42  to solvents such as gasoline, ethanol, or other hydrocarbon fuels. Some non-limiting examples of suitable polymeric materials include certain polyamides, polyesters, fluoropolymers, polyacetals, polyethylenes, or alloys or copolymers thereof. Some more specific examples include nylon 6,6, polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), polyethylene terephthalate (PET) (e.g., Mylar by Dupont), polyoxymethylene (POM), low-density polyethylene (LDPE), or ethylene vinyl alcohol (EVOH). Polymeric materials may optionally include fillers or modifiers such as colorants, stabilizers, reinforcements, electrical conductors, etc. 
     The filter element  42  may be a woven material or a non-woven material. For example, one particular example of a suitable filter element  42  is a filter element constructed from a woven nylon 6,6 material. It has been found that a woven nylon 6,6 filter element with a nominal 35 micron rating allows about the same flow rate of fuel therethrough as a woven stainless steel filter with a nominal 44 micron rating installed in the same size fuel passage. Thus it is possible in some cases to achieve better fuel filtration with a non-metallic filter element than with a metal filter element. This may be due, at least in part, to the ability to weave smaller polymeric fibers together to form the filter element material than is possible with certain metal fibers. In other words, the facial area of a polymeric filter element may include less solid material between flow openings than a metal filter element with the same size flow openings. Of course, other factors may play a role. 
     In another embodiment, the filter element  42  is formed from a non-woven material. For example, the filter element may be cut or otherwise formed from a film or other sheet stock material by piercing holes or forming pores of the desired size through the material while in sheet form. Laser cutting, machining, punching, calendaring, or another suitable technique may be used to form such holes or pores through the material. Some techniques, such as laser cutting, may be useful to enable changes in the size, number, or pattern of the holes or pores without the expense and complication of new tooling, for example. 
     With reference to  FIG. 2 , a method of making a carburetor including a fuel filter such as those described above is also disclosed. In one embodiment, the method includes providing fuel filter  20  in substantially flat form and sized to have an interference fit with the fuel passage  32  and/or a fuel passage opening  44  of the carburetor. The method further includes pressing the fuel filter  20  through opening  44  and into fuel passage  32  such that the fuel filter  20  is substantially not plastically deformed by the interference fit. In other words, though the filter  20  may assume a more curved shape when subjected to the interference fit, it may substantially return to its flat shape if removed from the fuel passage  32 . Substantial plastic deformation, as used here, refers to generally non-reversible deformation that occurs at the time of installation. Substantial plastic deformation generally results in visible creases, folds, or bends in the material that do not go away after the applied strain is removed. Plastic deformation that may occur during service life due to stress-relaxation or creep is not included in the substantial plastic deformation as used here. 
     By way of example, it has been found that a flat fuel filter  20  consisting of a filter element  42  made from certain polymeric materials can be configured to have an interference fit with the fuel passage  32  sufficient to retain the filter element  42  in the passage  32  at the desired location without permanently deforming the filter element  42 . That is to say that the filter element material has a characteristic elastic region below a critical strain value, and the interference fit is such that the filter element material is subjected to an amount of strain less than the critical strain value. Above the critical strain value, the material plastically deforms and will not return to its original shape. In one particular example, an interference fit of about 0.15-0.41 mm with a round polymeric filter element (diameter=8.20 mm) has been found to sufficiently retain the filter in the desired passage (diameter=7.79-8.05 mm) without substantial plastic deformation so that, if removed just after installation, the filter element returns to its original diameter and can be reinstalled with the expectation of about the same retention force. 
     This characteristic may be useful for a variety of reasons. For example, it may reduce manufacturing scrap by allowing reuse of the filter element  42  if installed crooked or otherwise incorrectly because it retains its flat configuration. If the filter is significantly plastically deformed during installation, filter retention force could be too low to withstand use over time, which may include hot and cold thermal cycling, vibration, or other conditions that tend to dislodge fuel filters. Installing the filter so that its deformation is sufficiently low to maintain the filter material in its elastic region can help ensure retention during such use. Some polymeric filter elements may be bent nearly in half and return to a flat configuration, while a woven metal filter element may be permanently deformed when subjected to the same bending. 
     Additionally, a metal fuel filter configured to have an interference fit sufficient to retain the filter in the fuel passage and also thick enough to avoid plastic deformation during installation may scrape a wall  46  of the fuel passage as its metal edge slides therealong. The carburetor may be particularly sensitive to contaminants that disrupt metering valve operation, and scraping the fuel passage wall  46  during fuel filter installation may introduce fine particles to the components downstream from the filter  20  before the carburetor is ever in use. 
     According to one embodiment, the fuel filter  20  has an edge  48  that is polymeric. The polymeric edge  48  may be provided by providing a polymeric filter element  42  as the fuel filter  20  as shown, or by providing a polymeric housing or frame at the edge  48  with any type of filter element  42 . The polymeric edge  48  thus slides along the passage wall  46  during filter installation, reducing the likelihood of scraping. 
     The method may also include cutting the fuel filter element  42  from a sheet  50  of polymeric material. The sheet  50  may be in strip and/or roll form with filter elements  42  successively and individually cut from the strip by a punch or other tool, or the sheet may be sufficiently wide to cut several fuel filter elements  42  from the strip or sheet at once. In the illustrated embodiment, the filter element  42  is cut from the sheet  50  of material so that the resulting filter element  42  is aligned with the fuel passage opening  44  at the time the filter element  42  is cut from the sheet  50 . The filter element  42  may subsequently be pressed into the fuel passage  32  and is shown in dashed lines at various positions along the passage  32  during installation. In one embodiment, the same tool is used to cut the filter element  42  from the sheet  50  and to press the filter element through the fuel passage opening  44  and into the fuel passage  32 . Such a configuration, in which the finished fuel filter  20  is installed directly from the sheet  50 , may allow for fuel filters to be produced with no handling required between filter production and installation. These illustrative methods may of course include additional steps or may be performed with certain steps omitted. 
     While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.