Patent Publication Number: US-6655603-B2

Title: Reverse flow valve for fuel injectors

Description:
RELATION TO OTHER PATENT APPLICATION 
     This application is a continuation of application Ser. No. 10/029,411, filed Dec. 20, 2001, which is now abandoned. 
    
    
     TECHNICAL FIELD 
     This invention relates generally to fuel injectors, and more specifically to reverse flow check valves within fuel injectors. 
     BACKGROUND 
     Occasionally, an injector nozzle of a fuel injector will become leaky, and after an injection event, allow hot combustion gases from the engine cylinder to leak past the nozzle outlet and travel upwards into the nozzle supply passage of the fuel injector. If the gases are permitted to continue to travel upwards and reach the fuel pressurization chamber, the fuel injector will inject less than a predicted amount of fuel, and can eventually be unable to pressurize fuel and inject it into the engine cylinder. 
     Typically, gases have been blocked from the fuel pressurization chamber by reverse flow check valve assemblies having a variety of structures. One example of such a check valve assembly is shown in co-owned U.S. Pat. No. 5,287,838 issued to Wells on Feb. 22, 1994. The function of the check valve assembly is to permit communication of high pressure fuel from the fuel pressurization chamber to the nozzle outlet of the fuel injector during an injection phase, but to prevent communication (i.e., reverse flow) of engine cylinder combustion gas from the nozzle to the fuel pressurization chamber at the end of an injection event and during a non-injection phase if the nozzle of the fuel injector becomes leaky. 
     Referring to FIG. 1, there is shown a partial sectioned side diagrammatic view of a fuel injector  10  according to the above identified patent. The fuel injector  10  consists of an injector body  11  that includes a barrel  33  separated from a stop component  42  by a relatively thin plate  50 . A plunger  13  is movably positioned along a centerline  12  within the injector body  11 . The plunger  13 , the barrel  33  and the plate  50  define a fuel pressurization chamber  14  that is fluidly connected to a fuel tank (not shown) via a fuel supply line  30 . When the plunger  13  is driven downward, it advances along the centerline  12  in order to pressurize fuel delivered from the fuel tank (not shown) via the fuel supply line  30 . A check valve  32  is positioned within the fuel supply line  30 . The check valve  32  is in its closed position in which it blocks fluid communication between the fuel pressurization chamber  14  and the fuel supply line  30  when the plunger  13  is advancing downward and increasing the pressure within the fuel pressurization chamber  14 . When the plunger  13  is returning to its upward position, the pressure within the pressurization chamber  14  decreases such that the check valve  32  opens and low pressure fuel within the fuel supply line  30  can flow past the check valve  32  and into the fuel pressurization chamber  14 . 
     The injector body  11  defines a nozzle supply passage  15 , a nozzle outlet  17 , and a guide bore  54 . A needle valve is positioned in the injector body  11  and has a needle valve member  20  that is movable between a first position, in which the nozzle outlet  17  is open, and a second position, in which the nozzle outlet  17  is closed. The needle valve member  20  has an opening hydraulic surface  21  that is exposed to fluid pressure within the nozzle supply passage  15 , but is biased toward a closed position by a compressed spring  22 . When the needle valve member  20  is in its open position, a stop surface of the needle valve member  20  is in contact with the stop component  42 , and the nozzle outlet  17  is opened to allow pressurized fuel to be injected into the engine cylinder (not shown). 
     The fuel pressurization chamber  14  is fluidly connected to the nozzle outlet  17  via the nozzle supply passage  15 , which includes the guide bore  54 . Positioned within the guide bore  54 , there is a reverse flow check valve assembly that includes a reverse flow check  52 , the plate  50 , and the stop component  42 . The reverse flow check  52  is preferably a flat circular plate and defines a flow passage  53 . The flow passage  53  is preferably cylindrical and centrally positioned within the reverse flow check  52  and is fluidly connected to the nozzle supply passage  15 . The plate  50 , which is preferably flat, is positioned between the barrel  33  and the stop component  42  and defines a pair of kidney-shaped or crescent-shaped holes  51 , which are fluidly connected to the fuel pressurization chamber  14 . The flow passage  53  of the reverse flow check  52  is radially inwardly spaced from the kidney holes  51  of the plate  50  and is arranged so that the nozzle supply passage  15  is blocked from the pressurization chamber  14  when the reverse flow check  52  and the plate  50  are in contact. The reverse flow check  52  is movable between an open position and closed position. When in its open position, as shown, the reverse flow check  52  is in contact with the stop component  42 , and the fuel pressurization chamber  14  is fluidly connected to the nozzle supply passage  15  via the kidney holes  51  of the plate  50  and the flow passage  53  of the reverse flow check  52 . 
     Prior to an injection event, the plunger  13  is driven downward by a hydraulic intensifier piston or a tappet along a centerline  12  of the fuel injector  10  toward its downward position. This greatly increases the pressure within the upper portion of the nozzle supply passage  15  which includes the fuel pressurization chamber  14  and the lower portion of the nozzle supply passage  15 . The increased pressure within the fuel pressurization chamber  14  will also close the check valve  32 , blocking fluid communication between the fuel pressurization chamber  14  and the fuel tank (not shown) via the fuel supply line  30 . The reverse flow check  52  will be in its first, or open, position, and in contact with the stop component  42 . Thus, the pressurized fuel will flow from the fuel pressurization chamber  14  through kidney holes  51  within the plate  50  and through the flow passage  53  of the reverse flow check  52  to the lower portion of the nozzle supply passage  15 . Thus, during an injection event, the fuel pressurization chamber  14  is fluid connected to the lower portion of the nozzle supply passage  15 . 
     Shortly before the desired amount of pressurized fuel is injected into the engine cylinder via the nozzle outlet  17  of the fuel injector  10 , the plunger  13  will stop moving downward, resulting in a fuel pressure drop to below valve closing pressure. This causes the needle valve member  20  to move to its closed position under the action of spring  22 . Towards the end of the movement of the needle valve member  20  to its closed position, there is a reverse flow of pressurized fuel within the lower portion of the nozzle supply passage  15 . The reverse flow of fuel will lift the reverse flow check  52  out of contact with the stop component  42 . The reverse flow check  52  will be lifted upward until it is in contact with the plate  50  and, thus, in its second, or closed, position. Due to the positioning and placement of the kidney holes  51  of the plate  50  and the flow passage  53  of the reverse flow check  52 , fluid communication between the fuel pressurization chamber  14  and the nozzle supply passage  15  will be blocked. Gas ingestion can occur over a brief instant as the needle valve member  20  is not yet closed while fuel pressure has dropped below cylinder pressure. If any engine cylinder combustion gases enter through the nozzle outlet  17  into the lower portion of the nozzle supply passage  15 , they will be blocked from fluid communication with the fuel pressurization chamber  14  when the reverse flow check  52  is in its closed position. Thus, the prior injector prevents gas from being trapped within the fuel pressurization chamber  14  by utilizing the reverse flow check  52 , the plate  51 , and the stop component  42 . 
     The hydraulic pressure acting on the plunger  13  is then reduced allowing the plunger  13  to retract along the centerline  12  to its upward position under the action of its biasing spring  16 . As the plunger  13  retracts, the pressure within the fuel pressurization chamber  14  preferably will lessen such that fuel from the fuel tank (not shown) can be drawn into the fuel pressurization chamber  14  via the fuel supply line  30  past the check valve  32 . The injection process can once again begin. 
     Although these reverse flow check valve assemblies have performed well, there is room for improvement. For instance, the reverse flow check valve assemblies limit combustion gases from leaking into the fuel pressurization chamber  14  through the nozzle outlet  17  by blocking fluid communication between the lower portion of the nozzle supply passage  15  and the fuel pressurization chamber  14  toward the end of an injection event. However, the reverse check valve assemblies do not prevent all gases ingested through the nozzle outlet  17  from traveling to the fuel pressurization chamber  14 . Because the reverse flow check  52  remains in the closed position only for a limited time when the reverse flow of fuel is hydraulically displacing it, there is the possibility that combustion gases can leak past the nozzle outlet  17  after the hydraulic pressure caused by the reverse flow of fuel within the nozzle supply passage has subsided. This can occur due to excessive wear on the needle valve seat. Further, the reverse control valve assembly cannot prevent gases from leaking into the fuel pressurization chambers  14  by other means than gas ingestion through the nozzle outlet  17 . Theoretically, gas trapping may occur if t hot combustion gases leak past seals on the outer surface of the fuel injector  10  and travel upward along the outer surface of the fuel injector  10  until they reach the area in the engine head where the fuel supply line  30  exists. The gases then mix with the low pressure fuel and are delivered to the fuel pressurization chamber  14 . 
     Occasionally, hot combustion gases are ingested through the injector tip and/or enter via the fuel supply are trapped within the fuel pressurization chamber  14  and the nozzle supply passage  15  by the check valve  32  and the direct needle control valve member  20 . The trapped gas creates pressure within the fuel pressurization chamber  14  sufficient to prohibit the check valve  32  from rising off its seat and allowing low pressure fuel into the fuel pressurization chamber  14 . Thus, the fuel pressurization chamber  14  is blocked from fluid communication with the fuel supply line  30  by the check valve  32 . The pressure caused by the trapped gas acting on the opening hydraulic surface  21  within the nozzle supply passage  15  is sometimes not great enough to overcome the biasing spring  22  of the needle valve member  20 . Thus, the nozzle supply passage  15 , is blocked from fluid communication with the nozzle outlet  17 . When this gas trapping occurs, the plunger  13  will advance downward to pressurize the fuel, but there will be little or no fuel within the fuel pressurization chamber  14  because the fuel pressurization chamber  14  is blocked from the fuel supply line  30  by the closed check valve  32 . The gas can never reach a high enough pressure to open the needle valve member  20  and the gas pressure never drops low enough to allow the check valve  32  to lift to its open position to allow fuel into the fuel pressurization chamber  14 . Thus, the plunger  13  reciprocates up and down but nothing happens with the fuel injector  10 . In these cases, the fuel injector  10  needs a means for re-priming itself. 
     Also, during assembly of new fuel injectors  10 , gases, other than engine cylinder gases, can be trapped within the empty space within the fuel pressurization chambers  14 . If the gas trapping occurs in a new fuel injector  10 , the fuel injector  10  is unable to prime itself and inject fuel into the engine cylinder. If the gas trapping occurs during operation of a fuel injector  10 , the fuel injector  10  is unable to re-prime itself by pushing the gases out of the nozzle outlet  17 . In either situation, once gases are in the fuel pressurization chamber  14 , the pressure within the nozzle supply passage  15  will be insufficient to open the nozzle outlet  17  and the pressure within the fuel pressurization chamber  14  will be too great for the check valve  32  to open. Thus, because the fuel injector  10  has no way of pushing the gas pressure out of the fuel pressurization chamber  14 , the plunger  13  will reciprocate up and down and nothing will happen within the fuel injector  10 . 
     Moreover, the plate  50  used as a stop for the reverse flow check  52  is subject to fretting, and the thin plate decreases the available height of the stop component  42  which in return increases the risk of oil to fuel transfer. 
     The present invention is directed to overcoming one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a fuel injector comprises an injector body that defines a nozzle supply passage and a nozzle outlet. Within the injector body is positioned a reverse flow valve member that has an opening hydraulic surface exposed to fluid pressure in an upper portion of the nozzle supply passage. The reverse flow valve member is moveable between a closed position in which the nozzle supply passage is blocked and an open position in which the nozzle supply passage is open. The reverse flow valve member is biased toward the closed positioned by a compressed spring. 
     In another aspect, a fuel injector includes an injector body defining a nozzle outlet. The injector body also includes a barrel that is in contact with a stop component. A movable plunger is at least partially positioned in the barrel. A reverse flow valve member is trapped between the barrel and the stop component, and is movable between a first position and a second position. The plunger, the reverse flow valve member, and the injector body define a nozzle supply passage that includes a fuel pressurization chamber. When the reverse flow valve member is in the second position, the nozzle supply passage is fluidly connected to a lower portion of the nozzle supply passage. A compressed spring is operably positioned in the injector body to bias the reverse flow valve member toward the first position, in which the fuel pressurization chamber is blocked from the lower portion of the nozzle supply passage. 
     In still another aspect, gas ingestion in a fuel injector is reduced by moving a reverse flow valve member at least in part with a spring to a position that blocks a downstream portion of a nozzle supply passage to an upstream portion of the nozzle supply passage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial sectioned side diagrammatic view of a fuel injector according to the prior art; 
     FIG. 2 is a partial sectioned side diagrammatic view of a fuel injector according to the preferred embodiment of the present invention; 
     FIG. 3 is an enlarged view of the reverse flow valve member positioned within the fuel injector of FIG. 2; 
     FIG. 4 is a top view of the reverse flow valve member shown in FIG.  3  and FIG. 2; 
     FIG. 5 is a partial sectioned side diagrammatic view of a reverse flow valve member positioned within a fuel injector according to an alternative embodiment of the present invention; 
     FIG. 6 is a top view of the reverse flow valve member shown in FIG. 5; 
     FIG. 7 is a partial sectioned side diagrammatic view of a reverse flow valve member positioned within a fuel injector according to a second alternative embodiment of the present invention; and 
     FIG. 8 is a front view of the reverse flow valve member shown in FIG.  7 . 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 2, there is shown a partial sectioned side diagrammatic view through a fuel injector  110  according to the present invention. The fuel injector  110  includes an injector body  111  that includes a barrel  133  and a stop component  142 . Features of fuel injector  110  that are identical to those described with respect to fuel injector  10  of FIG. 1 have identical numbering. A plunger  13  is movably positioned along a centerline  12  within the injector body  111 . While the plunger  13 , the barrel  33  and a thin plate  50  define a pressurization chamber  14  according to the prior art as illustrated in FIG. 1, the injector body  111 , the plunger  13 , and a reverse flow valve member  160  define a nozzle supply passage  115  that includes a fuel pressurization chamber  114  according to the present invention as illustrated in FIG.  2 . The fuel pressurization chamber  114  is fluidly connected to a fuel tank (not shown) via a fuel supply line  130 . When plunger  13  is hydraulically-activated, it advances downward along the centerline  12  in order to pressurize fuel delivered from the fuel tank (not shown) via the fuel supply line  130 . A check valve  32  is positioned within the fuel supply line  130 . The check valve  32  is in its closed position in which it blocks fluid communication between the fuel pressurization chamber  114  and the fuel supply line  130  when the plunger  13  is advancing downward and increasing the pressure within the pressurization chamber  114 . When the plunger  13  is returning to its upward position, the pressure within the pressurization chamber  114  decreases such that the check valve  32  opens and low pressure fuel within the fuel supply line  130  can flow past the check valve  32  and into the pressurization chamber  114 . 
     The injector body  111  defines a nozzle outlet  17  and a nozzle supply passage  115 , which includes a guide bore  154 . A direct control needle valve is positioned in the injector body  11  and has a direct control needle valve member  20  that is movable between a first position, in which the nozzle outlet  17  is open, and a second position, in which the nozzle outlet  17  is closed. When the direct control needle valve member  20  is in the second, or open, position, the direct control needle valve member  20  is in contact with the stop component  142 . The direct control needle valve member  20  has an opening hydraulic surface  21  that is exposed to fluid pressure within the nozzle supply passage  115  and a closing hydraulic surface  23  that is exposed to fluid pressure within a needle control chamber  24 . A pressure communication passage  25  is in fluid communication with the needle control chamber  24  and controls fluid pressure within the same. The closing hydraulic surface  23  and the opening hydraulic surface  21  are preferably sized such that even when a valve opening pressure is attained in the nozzle supply passage  115 , the direct control needle valve member  20  will not lift open when the needle control chamber  24  is fluidly connected to a source of high pressure actuation fluid. However, it should be appreciated that the relative sizes of the closing hydraulic surface  23  and the opening hydraulic surface  21  should be such that when the closing hydraulic surface  23  is exposed to low pressure in the needle control chamber  24 , the high pressure fuel acting on the opening hydraulic surface  21  should be sufficient to move the direct control needle valve member  20  upward against the force of its biasing spring  22  to open the nozzle outlet  17 . Those skilled in the art should appreciate that while direct control needle valve is the preferred method of controlling the nozzle outlet  17 , a nozzle outlet valve solely controlled by the biasing spring  22  and the hydraulic pressure within the nozzle supply passage  115  may also be used in the present invention. 
     The injector body  111 , the plunger  13 , and a reverse flow valve member  160  define the nozzle supply passage  115 , which includes the fuel pressurization chamber  114 . Although the described fuel injector  110  includes a fuel pressurization chamber  114 , those skilled in the art will appreciate that the present invention could be utilized in a common rail fuel injector in which there is no fuel pressurization chamber. Rather than the plate  50  being positioned between the barrel  33  and the stop component  42  as it is in the fuel injector  10  according to the prior art, a barrel  133  and a stop component  142  are in contact in the fuel injector  110  according to the present invention. It should also be appreciated that, by removing the plate  50 , the height of the stop component  142  can be increased, which should reduce the oil to fuel transfer and prevent fretting that sometimes occurs in plate  50 . Further, by removing the plate  50  from the present invention, the plate breakage that could occur over time is no longer a concern. A reverse flow valve member  160  is positioned within the guide bore  154  and is trapped between the barrel  133  and the stop component  142 . Although it could be positioned at any point along the nozzle supply passage  115 , the reverse flow valve member  160  preferably is positioned as close to the plunger  13  as possible so that the reverse flow valve member  160  can aid in priming a new fuel injector  110  in the event gas is trapped within its fuel pressurization chamber  114  upon assembly. The reverse flow valve member  160  member is movably positioned along a line parallel to and offset a distance, from the centerline  12  of the injector body  111 . The reverse flow valve member  160  is movable between a first position, or closed position, in which the lower portion of the nozzle supply passage  115  is blocked from fluid communication with the fuel pressurization chamber  114 , and a second position, or open position, in which the lower portion of the nozzle supply passage  115  is open to fluid communication with the fuel pressurization chamber  114 . The reverse flow valve member  160  is biased to its first position by a compressed spring  161  operably positioned in the injector body 
     Referring to FIG.  3  and FIG. 4, there is shown an enlarged view and a top view of the reverse flow valve member  160  of FIG. 2, respectively. In the preferred embodiment, the reverse flow valve member  160  has a cupped shape and defines a hollow interior in which a compressed spring  161  is operably positioned to bias the reverse flow valve member  160  toward its upward, closed position. The reverse flow valve member  160  has an opening hydraulic surface  164  exposed to fluid pressure within the fuel pressurization chamber  114  that is part of the upstream portion of the nozzle supply passage  115 . When the plunger  13  advances downward to pressurize fuel within the fuel pressurization chamber  114 , the increased pressure within the fuel pressurization chamber  114  acting on the opening hydraulic surface  164  moves the reverse flow valve member  160  against the action of its compressed spring  161  to its open position in which it is not in contact with a flat valve seat  163  of the barrel  133 . In its open position or its second position, as shown, the reverse flow valve member  160  defines a groove  153  that fluidly connects the fuel pressurization chamber  114  that is included in the upper portion of the nozzle supply passage  115  to the lower portion of the nozzle supply passage  115 . Toward the end of an injection event, the decreased pressure acting on the opening hydraulic surface  164  permits the reverse flow valve member  160  to return in its closed, or first, position, in which the reverse flow valve member  160  is in contact with the flat valve seat  163  of the barrel  133  and, thus, blocks fluid communication between the fuel pressurization chamber  114  and the nozzle supply passage  115 , and vice versa. The size of the groove  153  is preferably selected such that it is large enough to communicate a portion of the required fuel to flow past the reverse flow valve member  160  during an injection event but small enough that there is no leakage between the reverse flow valve member  160  and the valve seat  163  of the barrel  133  during a non injection period. 
     While the prior art solely relied on of the pressure gradient between the fuel pressurization chamber  14  and the lower portion or the nozzle supply passage  15  to control the movement of the reverse flow check  52 , the present invention uses the compressed spring  161  positioned underneath the reverse flow valve member  160  and the pressure within the fuel pressurization chamber  114  to control the movement of the reverse flow valve member  160 . The strength of the compressed spring  161  is great enough that the reverse flow valve member  160  will remain in its first position for a time sufficient to prevent gas ingestion into the fuel pressurization chamber  114  during peak cylinder pressure. However, the strength of the compressed spring  161  is limited such that the reverse flow valve member  160  remains in its second position for a time sufficient to allow pressurized fuel to flow into the nozzle supply passage  115  before the next injection event. The present invention allows for better control over the movement of the reverse flow valve member  160 , which helps prevent fuel leakage into the engine cylinder. In the preferred embodiment, a pin  162  is operably positioned within the guide bore  154  between the reverse flow valve member  160  and the stop component  142 . Because the pin  162  is received in the guide bore  154  and into the stop component  142 , the pin  162  prevents the reverse flow valve member  160  from rotating with respect to the injector body  111 . 
     Referring to FIG.  5  and FIG. 6, there is shown a partial sectioned side diagrammatic view and a front view of a reverse flow valve member  260  according to an alternate embodiment of the present invention, respectively. Similarly as the preferred embodiment of the present invention, the reverse flow valve member  260  is trapped between a stop component  242  and a barrel  233  and is movable between a first position, or a closed position, and a second position, or an open position. The difference between the fuel injector  110  of the preferred embodiment and the fuel injector  210  of the alternate version is the shape of the reverse flow valve members  160 ,  260 . Rather than having a cupped-shape and a hollow interior as does the reverse flow valve member  160  of the preferred embodiment, the reverse flow valve member  260  is a solid disc under which a compressed spring  261  is positioned. Just as in the preferred embodiment, a pin  262  is operably positioned within a guide bore  254  between the reverse flow valve member  260  and the stop component  242  so to prevent the reverse flow valve member  260  from rotating with respect to its injector body  211 . 
     Referring to FIG.  7  and FIG. 8, there is shown a partial sectioned side diagrammatic view and a front view of a reverse flow valve member  360  according to a second alternate embodiment of the present invention, respectively. The second alternate embodiment works similar to the preferred embodiment of the present invention except for the shape of a reverse control flow valve member  360 , the shape of a valve seat  364  and the interaction between the reverse flow valve member  360  and its injector body  311 . Rather than having a circular shape, the reverse flow valve member  360  is rectangular. Because the reverse flow valve member  360  is solid, a compressed spring  361  is operably positioned below the reverse flow valve member  360  in order to bias the reverse flow valve member  360  to its closed position. Further, a valve seat  363  of a barrel  333  is flat and slanted rather than flat and horizontal like in the other embodiments of the present invention. Because the reverse flow valve member  360  and a guide bore  354  are rectangular, there is no need for a pin to prevent the reverse flow valve member  360  from rotating. 
     INDUSTRIAL APPLICABILITY 
     Referring to FIG. 2, operation of the present invention will be discussed for fuel injectors that pressurize fuel within their injector bodies. It should be appreciated that the present invention can operate in common rail fuel injectors in which the fuel is pressurized outside the body of the fuel injectors. Moreover, it should be appreciated that while different fuel injectors within the engine operate at different stages, the present invention operates in the same manner for each fuel injector and can be applied in an engine with any number of fuel injectors. 
     In the present invention, the plunger  13  is biased to its upward position under the action of its biasing spring  16 . When plunger  13  is in its upward position, the pressure within the upper portion of the nozzle supply passage  115  that includes the fuel pressurization chamber  114  is at relatively low fuel supply pressure and, thus, permits the check valve  32  to open and low pressure fuel to flow from the fuel tank (not shown) to the fuel pressurization chamber  114  via the fuel supply line  130 . When the plunger  13  is in its upward position, the pressure within the lower portion of the nozzle supply passage  115  acting on the opening hydraulic surface  21  of the direct control needle valve member  20  is also low. Thus, the direct control needle valve member  20  will remain in its closed position under the action of its biasing spring  22  and the hydraulic pressure within the direct control chamber  24 , blocking fluid communication between the nozzle outlet  17  and the fuel pressurization chamber  114 . 
     Prior to an injection event, the plunger  13  is driven downward by a hydraulic intensifier piston or a tappet to move along a centerline  12  of the fuel injector  110  toward its downward position. This greatly increases fuel pressure within the upper portion of the nozzle supply passage  115  which includes the fuel pressurization chamber  114  and the lower portion of the nozzle supply passage  115 . The increased pressure within the fuel pressurization chamber  114  will close the check valve  32 , blocking fluid communication between the fuel pressurization chamber  114  and the fuel tank (not shown) via the fuel supply line  130 . The pressurized fuel will act on the opening hydraulic surface  164  of the reverse flow valve member  160  and move the reverse flow valve member  160  downward against the action of the compressed spring  161  to its second, or open, position. The reverse flow valve member  160  will move out of contact with the valve seat  163  of the barrel  133  so that the pressurized fuel can flow through to the lower portion of the nozzle supply passage  115  via the groove  153  defined by the reverse flow valve member  160  when in its second position. The direct control needle valve member  20  remains in its closed position blocking fluid communication between the nozzle outlet  17  and the nozzle supply passage  115  until the pressurized fuel acting on the opening hydraulic surface  21  of the direct control needle valve member  20  reaches a valve opening pressure sufficient to overcome the bias of the biasing spring  22  and the needle control chamber  24  is connected to low pressure via the pressure communication line  25 . When the direct control needle valve member  20  moves to its open position, a stop surface of the nozzle outlet valve member  20  is in contact with the stop component  142 , and the nozzle outlet  17  is opened to allow pressurized fuel to be injected into the engine cylinder (not shown). 
     Shortly before the desired amount of pressurized fuel is injected into the engine cylinder via the nozzle outlet  17  of the fuel injector  110 , the pressure communication line  25  will connect the needle control chamber  24  with a source of high pressure actuation fluid. The direct control needle valve member  20  will close under the hydraulic force within the needle control chamber  24  and the bias of its spring  22 . In its closed position, the direct control needle valve member  20  is blocking fluid communication between the nozzle outlet  17  and the nozzle supply passage  115 . Those skilled in the art should appreciate that the direct needle control valve is the preferred method for operating the nozzle outlet  17 . The direct needle control valve allows the nozzle outlet  17  to be closed under high pressure within the needle control chamber  24  even when there is high pressure within the nozzle supply passage  115 . Thus, the nozzle outlet  17  can remain blocked despite the pressure within the nozzle supply passage  115 . Although a nozzle outlet valve that is controlled solely by a biasing spring and  4  the pressure within the nozzle supply passage  115  can be used, the timing of the reverse flow valve member  160  can be important. When a nozzle outlet valve is used, if the reverse flow valve member  160  moves too quickly to its closed position, gases will be trapped within the nozzle supply passage  115  causing pressure on the hydraulic surface  21  of the nozzle valve outlet member such that it slows the closing of nozzle outlet  17 . Fuel will be able to leak past the open nozzle outlet  17  and dribble into the engine cylinder causing smoke from the engine. If the reverse flow valve member  160  moves too slowly into its closed position, then the nozzle outlet  17  will close approximately at the same time as the reverse flow valve member  160  moves to its closed position. Thus, if the pressure within the engine cylinder is greater than the pressure within the nozzle supply passage  115  at the time the nozzle outlet  17  closes, some of the combustion gases will enter into the injector tip. 
     The hydraulic pressure acting on the plunger  13  is then reduced allowing the plunger  13  to retract along the centerline  12  to its upward position under the action of its biasing spring  16 , causing the pressure within the fuel pressurization chamber  114  to decrease. The decreased pressure within the fuel pressurization chamber  114  acting on the opening hydraulic surface  164  of the reverse flow valve member  160  will be insufficient to overcome the action of the compressed spring  161 . Thus, the reverse flow valve member  160  will move to its first, or closed position, under the action of the compressed spring  161 . When in the first position, the reverse flow valve member  160  is in contact with a valve seat  163  of the barrel  133  and is blocking fluid communication between the fuel pressurization chamber  114  and the lower portion of the nozzle supply passage  115 . In the event of gas ingestion through the tip of the fuel injector  110 , the gases moving up the lower portion of the nozzle supply passage  115  will be blocked from the fuel pressurization chamber  114  by the reverse flow valve member  160 , which is preferably already in its closed position due to the low pressure within the fuel pressurization chamber  114  acting on its opening hydraulic surface  164 . Thus, the present invention blocks fluid communication between the fuel pressurization chamber  114  and the lower portion of the nozzle supply passage  115  during a non-injection event. This limits gas ingestion due to tip leakage to the relatively small volume below the reverse flow control valve member  160 . 
     Recall that, with the prior art, gases occasionally are trapped within the fuel pressurization chamber  14  and the nozzle supply passage  15  by the check valve  32  and the direct control needle valve member  20 . The trapped gas creates pressure within the fuel pressurization chamber  14  sufficient to prohibit the check valve  32  from rising off its seat and allowing low pressure fuel into the fuel pressurization chamber  14 . Thus, the fuel pressurization chamber  14  is blocked from fluid communication with the fuel supply line  30  by the check valve  32 . The pressure caused by the trapped gas acting on the opening hydraulic surface  21  within the nozzle supply passage  15  is not great enough to open the needle valve member  20 . Thus, the nozzle supply passage  15  is blocked from fluid communication with the nozzle outlet  17 . The plunger  13  will advance downward to pressurize the fuel, but there will be no fuel within the fuel pressurization chamber  14  because the fuel pressurization chamber  14  is blocked from the fuel supply line  30  by the closed check valve  32 . The gas can never reach a high enough pressure to open the direct needle control valve member  20  and the gas pressure never drops low enough to allow the check valve  32  to lift to its open position to allow fuel into the fuel pressurization chamber  14 . The plunger  13  reciprocates up and down but nothing happens with the fuel injector  10 . While this gas trapping exists in the prior art, it is eliminated in the present invention. Because the movement of the reverse flow valve member  160  is controlled by pressure within the fuel pressurization chamber  114 , the pressure caused by gases that travel into the fuel pressurization chamber  114  will act on the opening hydraulic surface  164  and move the reverse flow valve member  160  to its open position. The gases will flow through the groove  153  and into the nozzle supply passage  115 . Thus, even if gases travel into the fuel pressurization chamber  114 , they will not accumulate and be trapped. 
     If gases, other than combustion gases, become trapped within the fuel pressurization chamber  114  of a new fuel injector during assembly, the present invention also includes a priming feature that pushes the gas through the fuel injector  110  and out the nozzle outlet  17 . The pressure caused by the gases will act on the opening hydraulic surface  164  of the reverse flow valve member  160  causing the reverse flow valve member  160  to move downward against the action of the compressed spring  161  and open fluid communication between the fuel pressurization chamber  114  and the lower portion of the nozzle supply passage  115 . When the plunger  13  advances, it will push the gases through the groove  153  and into the lower portion of the nozzle supply passage  115 . If there is still gas within the fuel pressurization chamber  114  sufficient to keep the check valve  32  in its closed position when the plunger  13  retracts to its upward position, fuel will not flow into the fuel pressurization chamber  114  from the fuel tank (not shown). However, the plunger  13  will again be hydraulically activated to move downwards against the action of its biasing spring  16  and increase the pressure within the fuel pressurization chamber  114 . The gases will again act on the opening hydraulic surface  164  of the reverse flow control valve member  160  and open fluid communication between the fuel pressurization chamber  114  and the lower portion of the nozzle supply passage  115 . The gases will once again be pushed through the groove  153  and into the nozzle supply passage  115 . The reciprocating plunger  13  will continue pushing the gases out of the fuel pressurization chamber  114  into the lower portion of the nozzle supply passage  115  until the pressure within the fuel pressurization chamber  114  is low enough to allow the check valve  32  to open. Fuel can then flow from the fuel tank (not shown) to the fuel pressurization chamber  114  via the fuel supply line  130  past the check valve. As fuel flows in, repeated plunger movements will eventually achieve needle valve opening pressure allowing the compressed gas and the fuel to exit via the nozzle outlet  17 . Thus, the present invention not only prevents gas trapping within the fuel pressurization chamber  114  by blocking fluid communication between the lower portion of the nozzle supply passage  115  and the fuel pressurization chamber  114 , the present invention also allows fuel injector  110  to prime itself if gas trapping does occur within the fuel pressurization chamber  114 . 
     Referring to FIGS. 5 through 8, there is shown sectioned side diagrammatic illustrations and top views of the reverse flow valve members  260 ,  360  according to the two alternate versions of the present invention. The reverse flow valve member  260 ,  360  according to the alternate versions of the present invention perform in the same manner as the reverse flow valve member  160  according to the preferred embodiment of the present invention. The difference between the three embodiments are the shapes of the reverse flow valve members  160 ,  260 ,  360  and the shape of the valve seats  163 ,  263 ,  363 . For a discussion on these differences, see the Detailed Discussion section of this Application. 
     Both the prior art and the present invention limit the trapping of combustion gases within the fuel pressurization chambers  14 ,  114  by blocking fluid communication between the nozzle supply passage  15 ,  115  and the fuel pressurization chamber  114 . However, unlike the prior art, in the event that gases, other than combustion gasses, are trapped within the fuel pressurization chamber  114  of a new fuel injector  110 , the present invention can prime itself by pushing the gases out of the fuel pressurization chamber  114  and decreasing the pressure such that the check valve  32  can lift and allow fuel to flow into the fuel pressurization chamber  114 . Also, this priming feature will eliminate the need for the fuel injector  110  to re-prime itself because any gas that travels into the fuel pressurization chamber  114  should eventually be pushed out of the chamber  114  by the downward strokes of the plunger  13 . Moreover, unlike the prior art in which the reverse flow check  52  may not stay closed during the entire non-injection event, the reverse flow control valve member  160  of the present invention will remain closed during the entire non-injection event. Therefore, the present invention does not just reduce, but prevents, gas trapping in the fuel pressurization chamber  114  caused by gas ingestion in the injector tip. Any gases that are ingested through the tip of the fuel injector  110  will always remain in the portion of the nozzle supply passage  115  below the reverse flow valve member  160 . The present invention removes the plate  50  from between the stop component  142  and the barrel  133 . Thus, the seal between the stop component  142  and the barrel  133  is improved and should reduce oil to fuel transfer. Moreover, the removal of the plate  50  eliminates the potential for excessive wear and plate breakage over time. 
     It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.