Abstract:
A system and method is provided for automatically priming a fuel system by bleeding/purging air or vapor therefrom. The system includes a bleed valve configured to automatically move between three positions in response to the pressure of the fuel in the system. When fuel pressure is in a first pressure range, the bleed valve automatically moves to a first-closed position for preventing fuel from draining to the fuel tank and thereby drawing air into the fuel system. When the fuel pressure moves to a second, higher pressure range, the bleed valve automatically moves to an open position for bleeding air out of the fuel system and into the tank, thereby priming the fuel system. When the fuel pressure moves to a third, still higher pressure range, the bleed valve automatically moves to a second-closed position so as to not interfere with the regulation of the pressure regulating valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Patent Application No. 60/949,455, filed Jul. 12, 2007, which is incorporated by reference. 

   TECHNICAL FIELD 
   This patent disclosure relates generally to a system and method for priming a fuel system and, more particularly, to a system and method for automatically priming a fuel system. 
   BACKGROUND 
   A typical fuel system for use with an internal combustion engine may include a liquid pump, a tank, a filter, a regulating valve, and fuel injectors, and a series of conduits that interconnect these components. The tank is located downstream from the liquid pump, whereas the filter, the regulating valve, and injectors are located upstream. The liquid pump has an inlet and an outlet and draws fuel from the tank into its inlet and discharges fuel from its outlet to the other components of the system. 
   Air or vapor can enter these fuel systems, causing the liquid pump to dry out and lose pressure. This pressure loss may render the pump unable to overcome restriction created by the resistance of the filter, the regulating valve, and the injectors. Thus, the pump becomes unable to pump fuel to the injectors. This may cause the engine to stall, operate inefficiently, or fail to start. When this occurs, the fuel system must be primed. Priming purges/bleeds air from the system, thereby rewetting the pump so that it can pump fuel through the filter and to the injectors. 
   Some known systems include hand pumps for pushing air out of the system and thereby priming the engine. Although these pumps can be effective, an operator does not always have the time or the strength to pump the number of strokes necessary for properly priming the engine. Additionally, it is often difficult to generate enough pressure with these pumps to open the regulator valve, which may be necessary for pushing air to the tank. 
   Other known systems include a bypass passage around the pressure regulating valve and/or the cylinder head. This bypass passage includes a restriction orifice that allows air to pass without restriction, but is relatively restrictive to liquid flow. Such a system is shown in portions of U.S. Pat. No. 6,701,900 to Millar et. al. entitled “Quick Priming Fuel System and Common Passageway Housing for Same.” These systems, however, have shortcomings. For example, restriction orifices do not work well in fuel systems where the cylinder head is elevated above the rest of the fuel system. This is because most air introduced in the system rises past the restriction orifice, without entering the orifice, and this air continues rising until it reaches the cylinder head. Eventually, this risen air must pass through the cylinder head. The restriction orifice can also disadvantageously compete with the regulating valve. Because the restriction orifice is always open, it affects the fuel pressure when the regulating valve opens for regulating the fuel pressure. The restriction orifice can also allow fuel to drain back to tank when the engine is turned off. If there exists an opening to atmosphere at any point in the system, e.g., a tiny hole in a hose, the system will suck in air through that opening for filling the volume vacated by the drained fuel. 
   Another known system for priming is to utilize a manual valve in a bypass passage around a pressure regulator and/or the cylinder head. The manual valve is typically opened when the engine is off and is being primed via a hand priming pump. The manual valve is open to allow air to bleed out of the fuel system, and the system is primed when fuel is expelled from the valve. Upon noticing the appearance of fuel, the operator then closes the manual valve and cranks the engine to start in a conventional manner. 
   Other systems for priming utilize an open-close valve in a bypass passage around a pressure regulator and/or the cylinder head. This type of valve is open when the fuel pressure is between zero and a low pressure, e.g., the valve is open between 0 and 30 psi, for bleeding air to tank and thereby facilitating priming. The valve closes and remains closed once the fuel pressure rises above the low pressure threshold, e.g., the valve is closed when the fuel pressure is above 5 psi. This system of using an open-close valve is disadvantageous because the valve is open when the engine is off. This allows fuel to drain back to tank, possibly causing the system to suck in air. 
   The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the present disclosure nor to limit or expand the prior art discussed. Thus, the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use within the present disclosure, nor is it intended to indicate that any element is essential in implementing the present disclosure. 
   SUMMARY OF THE DISCLOSURE 
   In one aspect, a system and method is provided for automatically priming a fuel system by bleeding/purging air or vapor therefrom. In the described system, a bleed valve automatically moves between three positions in response to the pressure of the fuel in the system. When fuel pressure is in a first pressure range, the bleed valve automatically moves to a first-closed position for preventing fuel from draining to the fuel tank and thereby sucking air into the fuel system. When the fuel pressure is in a second, higher pressure range, the bleed valve automatically moves to an open position for bleeding air out of the fuel system and into the tank, thereby priming the fuel system. When the fuel pressure is in a third, still higher pressure range, the bleed valve automatically moves to a second-closed position so as to not interfere with the regulation of the pressure regulating valve. 
   Additional and alternative features and aspects of the disclosed system and method will be appreciated from the following description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of a fuel system according to an embodiment of the present disclosure; 
       FIG. 2  is a schematic illustration of a fuel filter assembly, according to an embodiment of the present disclosure, for use in the fuel system of  FIG. 1 ; 
       FIG. 3  is a front view of an automatic bleed valve, according to an embodiment the present disclosure, for use in the fuel filter assembly of  FIG. 2 ; 
       FIG. 4  is a side cross-sectional view of the automatic bleed valve of  FIG. 3  in a closed position; 
       FIG. 5  is a side cross-sectional view of the automatic bleed valve of  FIG. 3  in an open position; 
       FIG. 6  is a side cross-sectional view of the automatic bleed valve of  FIG. 3  in a closed position; 
       FIG. 7  is a side cross-sectional view of another embodiment of the automatic bleed valve in a closed position; 
       FIG. 8  is a side cross-sectional view of the automatic bleed valve of  FIG. 7  in an open position; and 
       FIG. 9  is a side cross-sectional view of the automatic bleed valve of  FIG. 7  in a closed position. 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a schematic view of a fuel system  10  for providing fuel to an internal combustion engine. The system  10  includes a fuel tank  12 , a primary filter  14 , a liquid pump  16 , a secondary filter assembly  18 , and cylinder head  20 . The pump  16  draws fuel from the tank  12  into passage  22  and across the primary filter  14 . Because the primary filter  14  can include a fine filter media, for example 120 micron or finer, the fuel pressure decreases as the fuel is drawn through the filter media. This pressure decrease can be significant enough to cause the fuel pressure to drop below the saturation pressure of fuel. When this occurs, entrained air escapes from the fuel and creates air bubbles in the filter  14 . This is one way that has been discovered in which air can enter the fuel system  10 . The air bubbles remain in the filter  14  during normal operation of the fuel system  10 , i.e. when the engine is running. However, when the system  10  is not in operation, i.e., when the engine is off, the air bubbles may migrate through passage  24  and into the pump  16 . Also, while the system  10  and the engine are not in operation, atmospheric air may enter the fuel system  10 . For example, atmospheric air can enter the system  10  during a filter change or through a cracked line or a leaky connection. This atmospheric air may also migrate to the pump  16 . 
   Air entering the pump  16  while the engine is off reduces the viscosity of the fuel in the pump  16 . In this condition, when an engine start is attempted, internal leakage may occur in the pump  16  because its gears cannot effectively pump the reduced-viscosity fuel. If the internal leakage rate exceeds the output rate of the pump  16 , then the pump  16  cannot provide flow to the system  10 . Accordingly, the engine will fail to start because the pump  16  is incapable of performing its intended function of pumping fuel through passage  26  to the secondary filter assembly  18 , and through passage  28  to the cylinder head  20 , where fuel injectors  30  are mounted. Also, if air enters the pump  16 , then the system loses pressure and the engine may start but stall soon thereafter. This occurs when there is enough fuel in the system for starting the engine, but the pump  16 , which is contaminated with air, is unable to provide flow of additional fuel to the system for continued operation of the engine. 
   Referring to  FIG. 2 , the secondary filter assembly  18  is shown having a bypass passage  32 . Passage  32  includes an automatic bleed valve  34  or a first valve for priming the fuel system  10  by opening and closing access to a drain passage  36 . When the automatic bleed valve  34  is open, fuel and air can bypass the passage  28 , which leads to the cylinder head  20 , and flow back to tank  12  though drain passage  36 . This reduces restriction on the pump  16 , and enables the pump  16  to create flow and self-prime. 
   In addition to passage  32  and the automatic bleed valve  34 , the secondary filter assembly  18  includes an inlet  40 , a secondary fuel filter  44 , an outlet  46  to the cylinder head, a return inlet  48  from the cylinder head, a pressure regulating valve  50  or a second valve, and an outlet  52  to the fuel tank. The assembly  18  further includes a passage  54  that extends between secondary filter  44  and outlet  46  to the cylinder head. In the illustrated embodiment, as shown in  FIG. 2 , passage  32  is an internal passageway formed in the filter base  18 . One end of passage  32  is connected between the secondary filter  44  and outlet  46 , while the other end is connected between regulating valve  50  and outlet  52 . Accordingly, passage  32  enables fuel to bypass the pressure regulating valve  50 . 
   It should be appreciated that one end of passage  32  can be connected anywhere between the pump  16  and the pressure regulating valve  50 , while the other end can be connected anywhere between the pressure regulating valve  50  and the fuel tank  12 . For example, one end of passage  32  can be connected between the second filter  44  and outlet  46 , or between outlet  46  and inlet  48 , or between inlet  48  and valve  50 , while the other end can be connected anywhere between valve  50  and the tank  12 . These embodiments, like the embodiment of  FIG. 2 , enable fuel to bypass the pressure regulating valve  50  and flow to the lower pressure area created when the bleed valve  34  opens bypass passage  32 . 
   It should also be appreciated that passage  32  can be an external passage. For example, as illustrated by the phantom lines in  FIG. 2 , the passage  32 ′ is an external passage having the automatic bleed valve  34  connected thereto. 
   Fuel enters the filter assembly  18  at either inlet  40  or  48 . Inlet  40  receives fuel from tank  12 . This fuel is pumped by the pump  16  from tank  12  and through passage  26 . Once in the filter assembly  18 , this fuel from tank travels to the secondary fuel filter  44  for additional filtering and then, if the bleed valve  34  is closed, passes through outlet  46  to the cylinder head. However, if the bleed valve  34  is open, this fuel from tank returns to tank via outlet  52 . Inlet  48  receives return fuel from the cylinder head  20 . This return fuel, which is excess fuel, passes from the cylinder head  20  through return passage  58  and then, if the pressure regulating valve  50  is open, exits the filter assembly via outlet  52  to tank. 
   The bleed valve  34  and the regulating valve  50  open and close in response to fuel pressure, and when either valve  34  or  50  is open, fuel returns to tank  12  via drainage passage  36 . The bleed valve  34  opens in lower pressure ranges, while the pressure regulating valve  50  opens in higher pressure ranges. For example, in an embodiment, when the fuel pressure is in a first pressure range, e.g., between 0 psi and about 5 psi, the bleed valve  34  and the regulating valve  50  are both closed and no fuel exits through outlet  52  for draining back to tank  12 . However, when the fuel pressure is in a second, higher pressure range, e.g., between about 5 psi and about 30 psi, the bleed valve  34  is open and the regulating valve  50  is closed. Accordingly, in this second pressure range, fuel can pass through the bleed valve  34  and outlet  52  for draining back to tank  12 . When the fuel pressure is in a third, still higher pressure range, e.g., about 30 psi to about 60 psi, the bleed valve  34  and the regulating valve  50  are both closed and no fuel exits through outlet  52 . When the fuel pressure exceeds the outer limit of the third pressure range, e.g., greater than about 60 psi, the regulating valve  50  is open and the bleed valve  34  is closed. In this case, fuel can pass through the regulating valve  50  and outlet  52  for draining to tank  12 . 
   The regulating valve  50  opens and closes for keeping the fuel pressure of the system  10  at an ideal operating pressure. In an embodiment, the ideal operating pressure may be about 60 psi. To keep the fuel pressure at 60 psi, the regulating valve  50  remains closed when the fuel pressure is at or below 60 psi and opens when the fuel pressure exceeds 60 psi. When the regulating valve  50  is open, the fuel pressure remains relatively constant or decreases because fuel can bypass the cylinder head  20  and drain back to the tank  12 . The valve  50  will find a balance between opened and closed to maintain fuel pressure near 60 psi. Accordingly, the regulating valve  50  opens and closes for maintaining the fuel pressure of the system  10  at an ideal or pre-established operating pressure. 
   Because the regulating valve  50  does not open until the fuel pressure reaches the pre-determined operating pressure, the pump  16 , suffering from internal leakage caused by the reduced-viscosity fuel, is unable to generate enough flow and increase the fuel pressure enough to open the regulating valve  50 , which would bleed air through passage  36  to tank  12 . Accordingly, the system  10  is unable to prime and the engine will stall or fail to start because the pump  16 , having reduced-viscosity fuel therein, is unable to overcome system restriction and provide flow in the system  10 . However, opening the bleed valve  34  reduces system restriction on the pump  16 , thereby enabling the pump  16  to create flow. This is because when the bleed valve  34  is open, fuel can bypass the pressure regulating valve  50  and the cylinder head  20 , which are high restriction areas having high pressure, and drain to tank  12 , which is a lower restriction area having lower pressure. 
   In the fuel system  10  of the present disclosure, if the pump  16  loses pressure, the fuel pressure in the system will eventually drop below an ideal operating-range. This drop in the fuel pressure of the system will trigger the opening sequence of the bleed valve  34 . Accordingly, the bleed valve  34  will open and reduce restriction on the pump  16 , thus enabling the pump  16  to push the air through passage  36  to the tank  12 . Once the air is expelled from the pump  16  and the rest of the system  10 , the pump  16  is able to create flow and increase the fuel pressure. This increase in fuel pressure will eventually cause the bleed valve  34  to close, enabling the pressure regulating valve  50  to regulate the system  10  during normal operation. 
   The operating sequence of the automatic bleed valve  34  will now be described in more detail. The bleed valve  34  is configured to close and remain closed when the fuel pressure is in the first pressure range. Typically, during this pressure range, the engine is off. The automatic bleed valve  34  is closed when the engine is off to prevent fuel from entering passage  36  and draining to tank  12  because, if fuel does drain to tank, the system  10  may ingest air from the atmosphere to replace the volume vacated by the drained fuel. 
   The bleed valve  34  is further configured to open when the fuel pressure is in the second, higher pressure range, in which air and vapor are often present in the fuel. Accordingly, the bleed valve  34  opens to permit fuel, having air or vapor therein, to bypass the cylinder head  22  and return to the tank  12  via return  36 . This reduces the restriction on the transfer pump  16 , enabling it to flush any air or vapor out of the system  10 . Once the air and vapor are pushed out of the pump  16  and the rest of the system  10 , the pump  16  is able to provide flow and increase the fuel pressure to the third, still higher pressure range. When this occurs, the bleed valve  34  is configured to close and remain closed until the pressure drops to the second pressure range. In other words, the bleed valve  34  is closed when the fuel pressure exceeds the outer limit of the second pressure range. Closing the bleed valve  34  at such pressures prevents the bleed valve  34  from compromising the function of regulating valve  50 . That is, when the fuel pressure rises above the ideal operating pressure, e.g., about 60 psi, the regulating valve  50  opens to reduce the fuel pressure, and if the bleed valve  34  were to open in this pressure range, it would interfere with the regulation of the regulating valve  50 . 
     FIGS. 3-6  illustrate an embodiment of the automatic bleed valve  34 . The bleed valve  34  is in a first-closed position in  FIG. 4 , an open position in  FIG. 5 , and a second-closed position in  FIG. 6 . The illustrated bleed valve  34  includes a valve body  70  having a first end  72  and a second end  74 . An inlet  76  is formed in the first end  72 , and an outlet  78  is formed in a side portion of the valve body  70 . It should be appreciated that other outlets  78  may be formed at various locations in the body  70 . The inlet  76  is in fluid communication with passage  54  of the secondary filter assembly  18 , and the outlet  78  is in fluid communication with drain passage  36 , which leads to the fuel tank  12 . The valve body  70  includes a chamber  80  and a first plunger  82  slidably positioned therein. The first plunger  82  has first and second ends  84 ,  86 , an outer surface  88 , a bore  90 , and a passage  92 . It should be appreciated that the first plunger  82  can have more than one passage  92 . The bore  90  is formed in the first end  84  of the first plunger  82  and is in fluid communication with the inlet  76  of the valve body  70 . The passage  92  extends between the bore  90  and the outer surface  88  of the first plunger  82  and, as shown in  FIG. 5 , when the passage  92  is inline with the outlet  78 , the inlet  76  and the outlet  78  are in fluid communication with each other and the bleed valve  34  is in the open position. On the other hand, as shown in  FIGS. 4 and 6 , when the passage  92  is not inline with the outlet  78 , the bleed valve  34  is in either the first- or second-closed position. 
   A first biasing spring  96  is disposed in the chamber  80 , near the second end  74  of the valve body  70 , as shown in  FIG. 5 . The first spring  96  is generally positioned between a top portion  98  of the chamber  80  and the second end  86  of the plunger  82 . This arrangement enables the spring  96  to bias the plunger  82  toward the first end  72  of the valve body  70 . The plunger  82  moves between positions in response to changes in the fuel pressure at the inlet  76 . It should be appreciated that the fuel pressure in passages  54  and  32  is substantially the same as the fuel pressure at the inlet  76 . As fuel pressure at the inlet  76  increases, the spring  96  compresses and the plunger  82  retracts into the chamber  80 , toward the second end  74  of the valve body  70 . Likewise, as fuel pressure at the inlet  76  decreases, the biasing spring  96  relaxes and the plunger  82  moves toward the first end  72  of the valve body  70 . 
   As shown in  FIG. 4 , when fuel pressure at the inlet  76  is in the first pressure range, the first end  84  of the plunger  82  is generally flush with the first end  72  of the valve body  70 , and the spring  96  (not shown in  FIG. 4 ) is generally relaxed. In this condition, the bleed valve  34  is in the first-closed position because the passage  92  is positioned axially below, and out of fluid communication with, the outlet  78 . As shown in  FIG. 5 , when the fuel pressure at the inlet  76  increases to the second pressure range, the first spring  96  is contracted and the first plunger  82  is retracted into the chamber  80 . In this condition, the passage  92  is inline with the outlet  78 , and fluid may flow from the inlet  76  to the outlet  78  by-way-of the passage  92 . Accordingly, the bleed valve is in the open position when fuel pressure at the inlet  76  is in the second pressure range. As shown in  FIG. 6 , when fuel pressure at the inlet  76  increases to the third pressure range and above, the spring  96  is further contracted and the plunger  82  is further retracted into the chamber  80 . In this condition, the bleed valve  34  is in the second-closed position because the passage  92  is positioned axially above, and out of fluid communication with, the outlet  78 . 
   Referring to  FIGS. 7-9 , another embodiment of the bleed valve  34  is shown. The bleed valve  34  is in the first-closed position in  FIG. 7 , the open position in  FIG. 8 , and the second-closed position in  FIG. 9 . In addition to the features of the embodiment illustrated in  FIGS. 3-6 , the bleed valve  34  illustrated in  FIGS. 7-9  includes a second plunger  100  and a second biasing spring  102 . The second plunger  100  and second spring  102  are both located in the bore  90  of the first plunger  82 . The second spring  102  has a small spring constant relative to the first spring  96 . 
   As shown in  FIG. 7 , when the fuel pressure at the inlet  76  is in the first pressure range, both springs  96  and  102  are generally relaxed and both plungers  82  and  100  are generally flush with the second end  72  of the valve body  70 . The bleed valve  34  is in the first-closed position at this pressure because the second plunger  100  closes the inlet  76  and prevents flow to the passage  92 , which is inline with the outlet  78  when the bleed valve  34  is in the first-open position. Because of the relatively small magnitude of its spring constant, the second spring  102  gradually contracts and the second plunger  100  retracts into the bore  90  when the fuel pressure at the inlet  76  increases to the second pressure range. However, the first spring  96 , because of the relatively large magnitude of its spring constant, does not retract and the passage  92  and the outlet  78  remain inline with each other. Accordingly, as shown in  FIG. 8 , when the fuel pressure at the inlet  76  is in the second, higher pressure range, the passage  92  and the outlet  78  remain inline and the second plunger  100  retracts to a position above the passage  92 . This allows fuel to flow from the inlet  76  through the passage  92  and the outlet  78 . As shown in  FIG. 9 , when the fuel pressure at the inlet  76  is in the third, yet higher pressure range, the first spring  96  contracts, causing the first plunger  82  to retract into the chamber  80 , moving the passage  92  to a position axially above, and out of fluid communication with, the outlet  78 . Here, the bleed valve is in the second-closed position and no fluid communication exists between the inlet  76  and the outlet  78 . 
   INDUSTRIAL APPLICABILITY 
   The industrial applicability of the system  10  described herein will be readily appreciated from the foregoing discussion. The system  10  of the present disclosure may be associated with any type of machine engine, such as internal combustion type engines, that operate in various types of host systems. For example, the system  10  may be affiliated with an engine associated with a host system such as a marine vehicle, a land vehicle, and/or an aircraft. Further, the system  10  may be associated with an engine operating in a non-vehicle based host system, such as machines operating within a manufacturing plant or generator sets. Accordingly, it will be appreciated that the system  10  may be associated with any type of host system that includes various types of engines that may operate in different environments. 
   It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. 
   Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. 
   Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.