Patent Publication Number: US-7717092-B2

Title: Fuel system with air venting and fuel anti-drainback

Description:
FIELD 
   A fuel system if an engine is provided with means to vent air that accumulates within a fuel filter of the fuel system and provide anti-drainback of clean fuel back into the fuel filter when the engine is turned off. The means to vent air and provide anti-drainback are integrated into a signal piece, non-biased piston valve. 
   BACKGROUND 
     FIG. 1  provides a schematic illustration of a fuel system  10  in a diesel engine. The fuel system  10  is shown to include a fuel tank  12 , a low pressure fuel pump  14  pumping fuel from the tank  12 , a fuel filter  16  that filters the fuel from the pump  14 , and a high pressure fuel pump  18  that increases the fuel pressure and feeds the fuel to a fuel reservoir  20 . From the fuel reservoir  20 , the fuel is distributed to a number of fuel injectors  22  where the fuel is injected and combusted in the engine. 
   During operation of a diesel engine, air can accumulate within the fuel system, for example within the fuel filter. In addition, air can enter the fuel system as a result of changing the fuel filter. Regardless of how air enters the fuel system, it is desirable to provide means to vent the air from the fuel system because air can interfere with the smooth and continuous delivery of fuel to the engine, decease engine performance and possibly lead to engine damage. 
   A number of means to vent air from a fuel system have been provided in the past. One such means includes a vent line that connects to the flow line connecting the low pressure pump to the fuel filter, the venting line connecting to the fuel tank so that air is vented into the fuel tank. Another known method is to provide an air vent mechanism on or near the fuel filter. Manually operated mechanical venting valves and venting screws associated with the fuel filter have been often used. These mechanisms can be difficult for a person to actuate, and can lead to fuel spills if they are not actuated properly. To avoid these difficulties, automatic venting has become more common. One automatic venting method is to provide a small orifice in the fuel filter that allows air to flow out of the fuel filter and back to the fuel tank through a vent line. 
     FIGS. 2A-C  illustrate another version of a known automatic venting mechanism  24  associated with a fuel filter. The mechanism  24  is disposed adjacent to, but downstream from, the fuel filter to receive clean fuel via an inlet port  26 . A clean fuel exit port  28  leads to the engine and an air vent passage  30  connected to the fuel tank is provided for air venting. A valve mechanism is provided for controlling the flow of air and fuel through the mechanism  24 . The valve mechanism includes an inner valve  32  and an outer valve  34  which cooperate together to control the flow. 
   The valves  32 ,  34  are actuated by fluid pressure generated by the upstream fuel pump, or in the absence of fuel pump pressure, by gravity.  FIG. 2A  shows the valves  32 ,  34  in a position when the engine is turned off, where the valves  32  and  34  are at their lowermost positions with the valve  32  blocking the inlet port  26  and the valve  34  blocking the exit port  28  in an effort to prevent backflow of clean fuel from the exit port  28  back through the inlet port  26 . Upon starting of the engine, pressure generated by the fuel pump acts on the lower end of the valve  32 , thereby lifting the valve  32  upward as shown in  FIG. 2B . In this position, air is able to flow past a gap between the valve  32  and the inside of the valve  34  in which the valve  32  is disposed, through a hole in the top of the valve  34 , and out the air vent passage  30  back to the fuel tank.  FIG. 2C  illustrates the positions of the valves  32 ,  34  in a topmost position once the air is vented and liquid fuel starts flowing. The fuel acts on the ends of the valves  32 ,  34  to lift the valves  32 ,  34  upward. The top of the valve  32  is lifted up to close the hole through the top of the valve  34  and prevent further venting. The valve  34  is lifted upward until a reduced diameter section thereof intersects the exit port  28 . Fuel can then flow past the valve  34  between the side of the valve  34  and the interior of the valve housing to the exit port  28 . 
   The mechanism  24  illustrated in  FIGS. 2A-C  uses two valves  32 ,  34  that cooperate together in an effort to achieve air venting and prevent backflow of clean fuel. Since two valves are used, the mechanism is somewhat complicated, and the operation of one or both of the valves  32 ,  34  could be impaired as a result of particulate mater or other contamination accumulating on or in the valves. In addition, the fuel must flow through a relatively narrow opening between the outside of the valve  34  and the interior of the valve housing to reach the exit port  28 . This reduces the amount of fuel that can reach the exit port and increases the pressure requirements for the fuel pump for pumping the fuel. Further, an increased differential pressure from filter inlet to outlet will effectively decrease the service interval (i.e. longevity) of the filter. 
   An improved automatic venting means in a fuel filter system would be beneficial that permits automatic venting and prevents drainback of clean liquid fuel. 
   SUMMARY 
   An air venting assembly in a fuel system of an engine is provided with means to vent air that accumulates within a fuel filter of the fuel system and provide anti-drainback of clean fuel back toward the fuel filter when the engine is turned off. In one embodiment, the means to vent air and provide anti-drainback are integrated into a single piece, non-biased piston valve. In an alternative embodiment, the piston valve is biased to a closed position by a biasing member, such as a spring. 
   The fuel system includes a filter assembly that has a fuel filter, and the air venting assembly adjacent the filter assembly. The air venting assembly includes a stationary housing that has a clean fuel inlet having a first valve seat, a clean fuel outlet, and an air vent passage generally parallel to the clean fuel inlet and generally perpendicular to the clean fuel outlet, with the air vent passage having a second valve seat. A single piece piston valve is slidably disposed within the air vent passage and is movable relative thereto to: a first position in sealing engagement with the first valve seat; a second position in sealing engagement with the second valve seat; and intermediate positions between the first position and the second position. 
   In the first position of the piston valve, fuel flow from the clean fuel outlet through the clean fuel inlet is restricted, and preferably substantially prevented. In the second position, air flow through the air vent passage is restricted, and clean fuel is able to flow to the clean fuel outlet. The piston valve also has intermediate positions between the first position and the second position at which air can flow through the air vent passage. 
   The piston valve has a terminal end that faces toward the clean fuel inlet, and when the piston valve is at the second position, the terminal end surface of the piston valve is positioned between the valve seat and a surface of the clean fuel outlet that intersects the clean fuel inlet. This construction increases the flow are a for the fuel from the clean fuel inlet to the clean fuel outlet, thereby reducing the pressure requirements for the fuel pump and extending fuel filter life. 
   The piston valve preferably has one elastomeric seal, or a plurality of elastomeric seals, for sealing. The use of an elastomeric seal minimizes leakage of fuel from the air venting assembly during filter changes. However, in certain embodiments, the piston valve is devoid of any elastomeric seal, instead relying on material to material, for example metal, sealing. When an elastomeric seal is used, the seal is preferably supported in a manner to prevent damage to the seal particularly at the second position when the fuel pressure is high. The seal support can be provided by an enlarged shoulder adjacent the elastomeric seal. 
   In one embodiment, the air venting occurs back to the fuel tank of the fuel system. In an alternative embodiment, the air venting occurs to atmosphere. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of a fuel system in a diesel engine. 
       FIGS. 2A-C  illustrate a known automatic venting mechanism. 
       FIG. 3  is a perspective view of a portion of a fuel system with a fuel filter assembly and an air venting assembly incorporating the inventive concepts. 
       FIG. 4  is a sectional view of a portion of the air venting assembly in  FIG. 3  with the piston valve in a vent position. 
       FIG. 5  is a view similar to  FIG. 4  with the piston valve in a full-up position to restrict air venting. 
       FIG. 6  is a view similar to  FIG. 4  with the piston valve in a full-down position to provide anti-drainback of clean liquid fuel back to the fuel filter. 
       FIG. 7  is a section view of a portion of an air venting assembly illustrating an alternative embodiment of a piston valve. 
       FIG. 8  is a view of another alternative embodiment of an air venting assembly that vents to atmosphere. 
       FIG. 9  is a view of another alternative embodiment of an air venting assembly. 
       FIG. 10  is a view of yet another alternative embodiment of an air venting assembly. 
       FIG. 11  is a view of yet another alternative embodiment of an air venting assembly. 
       FIG. 12  is a cross-sectional view of a piston valve. 
       FIG. 13  is a view of yet another alternative embodiment of an air venting assembly. 
   

   DETAILED DESCRIPTION 
   The inventive concepts will be described herein with respect to a fuel system in a diesel engine and venting air and vapors from, and anti-drainback of, diesel fuel. However, the inventive concepts could also be used for venting and anti-drainback of other fuels in other types of engines, for example gasoline engines, and for other liquids, for example lubricating oil. 
   With reference to  FIG. 3 , a portion of a fuel system with a fuel filter assembly  50  and an air venting assembly  52  that incorporate the inventive concepts are illustrated. The fuel filter assembly  50  and air venting assembly  52  are used within a fuel system, such as the system illustrated in  FIG. 1 , so that the fuel filter assembly and air vent assembly receive fuel from the low pressure pump and direct the fuel to the high pressure pump.  FIG. 3  schematically illustrates the filter assembly  50 , which can be a spin-on filter assembly of a type known in the art which is designed to be threaded into engagement with the air venting assembly  52 . The construction and operation of spin-on filter assemblies is well known in the art, and is not further described herein. The inventive concepts described herein would be used with other types of filter assemblies as well, for example top load filter assemblies. 
   The top of the filter assembly  50  includes a neck  54  that engages with a neck  56  on the air venting assembly  52  (shown in  FIG. 4 ) when the filter assembly  50  is secured to the air venting assembly, to form a fuel flow path from the filter assembly to the air venting assembly. The filter in the filter assembly  50  can be designed for outside-in flow or fuel, with fuel exiting the filter assembly through the central axis of the filter assembly. However, other flow path configurations could be used. 
   With reference to  FIGS. 3 and 4 , the air venting assembly  52  includes a housing  58  hat during use is stationary within the fuel system and is illustrated as being located vertically above the filter assembly  50 . The housing  58  includes the neck  56 , a clean fuel inlet  60  through which clean fuel enters the air venting assembly  52  from the fuel filter assembly,  50 , a clean fuel outlet  62  connected to the high pressure pump through which clean fuel exists the housing  58 , and an air vent passage  64  for venting air. 
   As shown in  FIG. 4 , the clean fuel inlet  60  is generally vertical and is on-center with the central axis of the fuel filter assembly  50 . The clean fuel outlet  62  extends through the housing  58  generally perpendicular to the central axis of the inlet  60 . The outlet  62 , which is generally circular in cross-section, includes a bottom surface  66  that intersects the inlet  60 . The vent passage  64  is generally parallel to the axis of the inlet  60 , preferably coaxial with the inlet  60 , and generally perpendicular to the outlet  62 . 
   The housing  58  includes a banjo fitting  68  disposed at the top thereof, and a hollow fitting  70  extends down through the fitting  68  and is threaded into the housing  58 . Washers  72 ,  74  are disposed between the fitting  68  and the housing, and between the fitting  70  and the fitting  68  to provide sealing. The fitting  68  includes a flow passage  76  extending at a right angle to the axis of the fitting  70 , the passage  76  being connected to the fuel tank by a suitable conduit. Holes  78  in the fitting  70  connect the hollow, interior of the fitting  70  with the flow passage  76 . 
   As illustrated in  FIG. 4 , the air vent passage  64  is defined by the hollow interior of the fitting  70  and extends upward from the top of the outlet  62 . The vent passage  64  connects to the passage  76  via the holes  78 . As a result, air passing upwardly through the vent passage  64  enters the passage  76  and is directed back to the fuel tank. 
   A single piece piston valve  80  is slidably disposed in the vent passage  64  and extends down into the outlet  62 . The valve  80  is movable to a first or full-down position, shown in  FIG. 6 , a second or full-up position, shown in  FIG. 5 , and intermediate positions between the first position and the second position (one such intermediate position being shown in  FIG. 4 ). The valve  80  is not biased by a spring or any resilient member. Instead, movement of the valve  80  between the first position, second position and the intermediate positions is automatically controlled by the pressure of fluid (e.g. air, vapor, liquid and mixtures thereof) coming from the filter assembly  50  through the inlet  60 . If desires, a biasing member, such as a spring  200  shown in  FIG. 13 , could be used to bias the valve  80  to the first position. The biasing force of such a biasing member would be chosen based on the fluid pressure that is present as fluid exists the filter assembly ad enter the inlet  60 . A biasing member would be required in embodiments where the venting assembly  52  is positioned in a location relative to the filter assembly  50  such that the valve  80  and vent passage  64  are not oriented vertically, in which case gravity may not be able to return the valve  80  to the first position upon shutting off of the engine. In that case, the biasing member would be used to bias the valve to the first position upon engine shut off. The biasing member could act on the end of the valve  80  (i.e. the end opposite the terminal end), and be disposed between the end and the interior of the fitting  70 . 
   The valve  80  has a longitudinal axis that is parallel to the vent passage  64  and the inlet  60 , and includes a guide section  82  and a valve head section  84 . The guide section  82  is sized to slide in the vent passage  64  as the valve  80  moves up and down. At the same time the guide section  82  is sized to provide a gap between the outer circumference of the guide section and the interior of the fitting  70  to allow fluid (e.g. air, vapor, liquid) to flow between the guide section  82  and the interior of the fitting  70 . Instead of sizing the guide section  82  to provide a gap, the guide section  82  and/or the interior of the fitting  70  could be provided with channels or flats to facilitate the flow of fluid through the vent passage  64  during venting.  FIG. 12  illustrates the guide section  82  with flats  250  and channels  255 . The flats  250  and channels  255  can be used separately or together as shown, and the number of channels or flats will vary depending upon the gas flow requirements past the guide section  82 . 
   The valve head section  84  has a shoulder  86  that has a diameter greater than the diameter of the guide section  82 , and a terminal end  88  positioned on the side of the shoulder  86  opposite from the guide section  82  and that faces the inlet  60 . The terminal end  88  is sized so a as to fit within the inlet  60 . 
   A first seal  90  and a second seal  92 , for example elastomeric o-ring seals, are disposed on opposite sides of the shoulder  86 . The first seal  90  is disposed in a circumferential channel  94  formed around the guide section  82  while the second seal  92  is disposed in a circumferential channel  96  formed around the terminal end  88 . 
   As shown in  FIG. 6 , the seal  92  is designed to seat against a first valve seat  98  formed at the upper end of the inlet  60  when the valve  80  moves to the first position. Similarly, as shown in  FIG. 5 , the seal  90  is designed to seat against a second valve seat  100  formed at the end of the fitting  68 . As best seen in  FIG. 4 , both of the valve seats  98 ,  10  have a double chamfer configuration with a first chamfer section  102  angled from approximately 40-50 degrees, more preferably 45 degrees, relative to a vertical axis, and a second chamfer section  104  angled from approximately 15-25 degrees, more permeably 20 degrees, from vertical. The valve seat  98  further includes a generally vertical section  106 . The first chamfer sections  102  provide an angled surface that is suitable for sealing engagement with the seals  90 ,  92 , while the second chamfer sections  104  help to guide the valve head section  84  to the first and second positions. 
     FIG. 6  illustrates the first position of the valve  80  which is achieved when the engine is not operating and the fuel pump is not generating pressure on the filter side of the vent assembly  52 . As a result, gravity causes the valve  80  to move down to the first position into sealing engagement with the valve seat  98 . In the first position, the sealing engagement between the seal  92  and the valve seat  98  is sufficient to substantially prevent the flow of fuel from the outlet  62  back through the inlet  60 . This keeps fuel in the outlet  62  and downstream portions of the fuel system to aid in starting the engine. In addition, this prevents fuel leakage from the venting assembly through the inlet  60  when the filter assembly  50  is removed during a filter change. 
   Upon cranking and starting of the engine, the pressure created by the fuel pump acts on the valve  80  and the valve  80  is lifted upward from the valve seat  98 , as shown in  FIG. 4 . Air, vapor and small amounts of liquid fuel can thus flow from the filter assembly  50  and into the venting assembly  52  through the inlet  60  past the valve head section  84 , as indicated by the arrow in  FIG. 1 . Air and vapor can then flow into the vent passage  64  through the gap between the guide section  82  and the fitting  70  and into the passage  76  for routing back to the fuel tank. 
   While air is present, the viscosity difference between air and liquid is used to keep the valve  80  in an intermediate venting position. However, once the air is purged and liquid begins to flow, enough differential pressure is created to lift the valve upward to the second or full-up position shown in  FIG. 5 . In this position, the seal  90  is in sealing engagement with the valve seat  100  to substantially prevent the flow of fuel through the vent passage  64 , forcing the fuel to flow through the outlet  62 . 
   Upon shutting off of the engine, the fuel flow is stopped, and the valve  80  moves back down to the first position shown in  FIG. 6  as a result of gravity. 
   When in the first and second positions, especially the second position where the fuel pressure acting on the valve  80  is the highest, the position of the shoulder  86  is such that the shoulder  86  supports the seals  90 ,  92  from behind to prevent damage to the seals. 
     FIGS. 7-11  illustrate variations of air venting assemblies that incorporate one or more of the inventive concepts described herein. In  FIGS. 7-11 , parts identical to parts in the venting assembly  52  are referenced by identical reference numbers. 
     FIG. 7  illustrates a variation of an air venting assembly  152  where the assembly  152  includes a piston valve  154  that uses a single elastomeric seal  156 , without a shoulder backing the seal  156 . As with the valve  80 , the valve  154  is movable to a first position (not shown) in sealing engagement with the inlet  60 , a second position (shown in  FIG. 7 ), and intermediate positions therebetween. With this construction, the guide section of the valve  154  is able to move farther up the vent passage  64  compared to the valve  80 , and the size of the valve head section is reduced, thereby reducing obstruction to fuel flowing from the inlet  60  to the outlet  62 . 
     FIG. 8  illustrates a variation of an air venting assembly  252  that vents to atmosphere rather than back to the fuel tank. In this embodiment, the hollow fitting  254  is provided with an aperture  256  at the end thereof, and a membrane  258  is mounted within the end of the fitting  254 . The membrane  258  is constructed to allow flow of air therethrough, but prevent flow of liquid. A suitable material for the membrane is a porous metal available from Mott Corporation of Farmington, Conn. Other materials could be used for the membrane. For example, a plurality of layers of a fuel filter media could be used. 
     FIG. 9  illustrates an air venting assembly  352  with a valve  354  devoid of elastomeric seals. Instead, the valve  354  relies upon material to material sealing between the opposite ends of the valve with the valve seats. In addition, a vent passage  356  is formed by a first portion  358  and a second portion  360  within a hollow fitting  362 . As a result, no portion of the valve  354  slides within the fitting  362 . Instead, movement of the valve  354  is guided by the first portion  358  of the vent passage which is defined by the housing. 
   In the embodiment in  FIG. 9 , when sealing engagement between the ends of the valve and the valve seats occurs, some minimal fluid leakage may occur. At the top end of the valve  354 , leakage at the second position of the valve  354  may actually be desirable in certain circumstances to allow for continual venting of air through the vent passage  356  while the engine is running. The sealing engagement at the second position may actually be designed for “intentional leakage” for this purpose, i.e. although in sealing engagement, a defined amount of air is permitted to leak past the seal. 
     FIG. 10  illustrates an air venting assembly  452  with a valve  454  having elastomeric seals  456  adjacent the ends thereof rather than being positioned adjacent a common end as in the venting assembly  52 . 
     FIG. 11  illustrates an air venting assembly  552  that only provides for air venting; it does not provide anti-drainback of fuel through an inlet back to the fuel filter assembly. The assembly  552  includes a hollow fitting  554 . A cup-shaped valve  556  is slidably disposed within the fitting  554 , with the cup side facing down and its rounded bottom facing upward. A retainer  558 , for example a press-fit retainer or snap-ring, is secured into the end of the fitting to limit downward movement of the valve  556  and prevent the valve  556  from falling from the fitting. A chamfered surface  560  is formed on the interior of the fitting to limit upward movement and define a valve seat for sealing engagement with the rounded end of the valve  556 . 
   When air is present, the valve  556  is lifted upward from the retainer  558 , allowing air to flow into and through a vent passage  562  around the gap between the outer circumference of the valve  556  and the interior of the fitting  554  to an outlet  564  at the upper end of the fitting  554 . This permits rapid removal of air, followed by a choking of liquid flow. 
   The invention may be embodied in other forms without departing from the spirit or novel characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.