Abstract:
The present invention relates to engines having common rail fuel injection systems. In traditional common rail fuel injection systems, each fuel injector utilized by the fuel system includes its own solenoid. These individual solenoids must cooperate to ensure that the proper amount of fuel is being injected from each injector at the proper time. Having individual solenoids requires a multiple number of moving electrical components. In contrast to the traditional common rail fuel injection system, the fuel injection system of the present invention includes fuel injectors that are controlled in operation by a common electronic actuator that is positioned remote from the fuel injectors. Therefore, the present invention reduces the number of moving electrical components in the fuel injection system by reducing the need for individual solenoids for each fuel injector.

Description:
RELATION TO PRIOR APPLICATION  
       [0001]    This application is a division of U.S. patent application Ser. No. 09/740,533, and entitled FUEL INJECTION SYSTEM WITH COMMON ACTUATION DEVICE AND ENGINE USING SAME, now U.S. Pat. No. ______. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This invention relates generally to engines, and more particularly to common rail fuel injection systems that use a common electrical actuator(s) to control multiple fuel injectors.  
         BACKGROUND  
         [0003]    Common rail fuel injection systems are becoming more widespread for use with diesel engines. One example of such a fuel injection system is shown and described in U.S. Pat. No. 5,133,645, which issued to Crowley et al. on Jul. 28, 1992. Crowley et al. includes an electronic control module and an electronic distribution unit which control a plurality of high pressure fuel supply pumps and fuel injectors. As with other traditional common rail fuel injection systems, each of the fuel injectors included in the Crowley et al. fuel injection system includes its own individual electrical actuator. In this and other common rail fuel injection systems, the individual electrical actuators must cooperate to ensure that the proper amount of fuel is injected from each injector at the proper time. While the Crowley fuel injection system has performed adequately, there is room for improvement. For instance, if the number of electrical actuators, or solenoids, could be reduced, this could benefit the fuel injection system in a number of ways. First, because the number of parts has been reduced, there are less parts that can fail during system operation and hinder system performance. Additionally, injector performance variability might be reduced. Any reduction in the number of moving and/or electrical components should improve system robustness.  
           [0004]    The present invention is directed to overcoming one or more of the problems as set forth above.  
         SUMMARY OF THE INVENTION  
         [0005]    In one aspect of the present invention, a fuel injector comprises an injector body with a needle control chamber disposed therein. A direct control needle valve is at least partially positioned in the injector body and includes a closing hydraulic surface exposed to fluid pressure in the needle control chamber. The fuel injector also comprises an unobstructed high pressure passage extending between the needle control chamber and outside the injector body. Also, the fuel injector comprises an unobstructed low pressure passage extending between the needle control chamber and outside the injector body.  
           [0006]    In another aspect of the present invention a method of injecting fuel comprises the steps of opening a nozzle outlet of a fuel injector at least in part by relieving pressure on a closing hydraulic surface of a direct control needle valve. Restricting fuel flow to the nozzle outlet at least in part by positioning a flow restriction valve member in a first position. Unrestricting fuel flow to the nozzle outlet at least in part by positioning said flow restriction valve member in a second position. Finally, closing the nozzle outlet at least in part by increasing pressure on the closing hydraulic surface of the direct control needle valve.  
           [0007]    In yet another aspect of the present invention, a fuel injection system comprises a high pressure fuel rail and a low pressure fuel drain. Also, the fuel injection system comprises a plurality of fuel injectors that each include a direct control needle valve and a common electrical actuator coupled to the plurality of fuel injectors. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a schematic representation of a fuel injection system according to one embodiment of the present invention;  
         [0009]    [0009]FIG. 2 is a sectioned diagrammatic representation of a fluid switch for use with the fuel injection system of FIG. 1;  
         [0010]    [0010]FIG. 3 is a sectioned diagrammatic representation of a fuel injector for use with the fuel injection system of FIG. 1;  
         [0011]    [0011]FIG. 4 is a schematic representation of a fuel injection system according to another embodiment of the present invention;  
         [0012]    [0012]FIG. 5 is a sectioned diagrammatic representation of a fuel injector for use with the fuel injection system of FIG. 4;  
         [0013]    [0013]FIG. 6 is a schematic representation of a fuel injection system according to yet another embodiment of the present invention;  
         [0014]    [0014]FIG. 7 is a sectioned diagrammatic representation of a fuel injector for use with the fuel injection system of FIG. 6;  
         [0015]    [0015]FIGS. 8 a - f  are graphs of pressure release switch position, pressure release actuator current, pressure release valve position, net force on the needle, needle position and injection rate, respectively, versus time for the fuel injector of FIG. 3 for one injection cycle;  
         [0016]    [0016]FIGS. 9 a - h  are graphs of pressure release switch position, pressure release actuator current, pressure release valve position, net force on the needle, flow area to the nozzle, injection rate, rate shaping actuator current and rate shaping valve position, respectively, versus time for the fuel injector of FIG. 5 for one injection cycle;  
         [0017]    [0017]FIGS. 10 a - i  are graphs of pressure release switch position, pressure release actuator current, net force on the needle, flow area to the nozzle, injection rate, rate shaping valve position, pressure build-up actuator current, pressure build-up valve position and pressure build-up switch position, respectively, versus time for the fuel injector of FIG. 7 for one injection cycle; and  
         [0018]    [0018]FIG. 11 is a graphical representation of total fuel consumption versus time for the fuel injection systems of FIGS. 1, 4 and  6 . 
     
    
     DETAILED DESCRIPTION  
       [0019]    Referring now to FIG. 1, there is shown an engine  10  including a common rail fuel injection system  11  according to the present invention. Fuel injection system  11  is positioned within an engine housing  12  and includes a low pressure fuel drain, which is preferably a fuel tank  13 , that is in fluid communication with a high pressure fuel rail  16 . A high pressure pump  15  is positioned between fuel tank  13  and high pressure fuel rail  16 , and is supplied with fuel from fuel tank  13  by a gear pump  14 . High pressure fuel rail  16  includes a plurality of outlets  17  that are in fluid communication with an equal number of fuel injectors  60  via high pressure fuel supply lines  18 .  
         [0020]    Each fuel injector  60  includes an injector body  61  that defines a nozzle outlet  99  that can spray fuel into a combustion chamber of engine  10 . Each fuel injector  60  also defines a pressure release drain  62  for reduction of internal pressure to allow injection to take place. A pressure release switch  20  is in fluid communication with each pressure release drain  62  via a series of drain passages  21 . Cam  19  of pressure release switch  20  is driven by a crank and preferably rotates at one half the speed of the engine. Referring in addition to FIG. 2, there is shown a sectioned view of a preferred version of pressure release switch  20 . Included in pressure release switch  20  are a number of spring biased valve members  23 , equal to the number of fuel injectors  60  included in fuel injection system  11 . Each valve member  23  is biased toward a first, or left, position by a biasing spring  25  and includes a contact surface  24 , which is preferably a convex surface. As cam  19  rotates, a contact platform  22  is rotated which comes in contact with contact surface  24  of valve member  23 . Contact platform  22  preferably includes sloped sides such that contact surface  24  can move smoothly over contact platform  22 , to allow valve member  23  to make a smooth transition to its second, or right, position. When valve member  23  is in its biased, first position, an annulus  26 , included on valve member  23  is out of fluid communication with drain passage  21  and a main passage  29 , as illustrated in FIG. 2 by valve member  23   b . However, when valve member  23  is in its second position, such as valve member  23   a , annulus  26  is open to main passage  29  and drain passage  21  via drain passage  28 .  
         [0021]    When annulus  26  is open to drain passage  28  for a particular fuel injector  60 , that fuel injector  60  is capable of being connected to fuel tank  13  via main passage  29 . Therefore, only one fuel injector  60  can be connected to fuel tank  13 , at a time, depending on the position of cam  19  in relation to pressure release switch  20 . However, fuel injector  60  is not connected to fuel tank  13  via main passage  29  until a pressure release electronic actuator  32  is activated by an electronic control module  33 . Pressure release electronic actuator  32  is attached to a pressure release electronic control valve  31  that is positioned remote from fuel injectors  60 . Pressure release electronic actuator  32  is preferably a two position control valve. Pressure release electronic control valve  31  is moved from a biased, closed position to an open position when pressure release electronic actuator  32  is activated. While pressure release electronic actuator  32  is preferably a solenoid, it should be appreciated that other actuators, such as a piezoelectric actuator, could be substituted.  
         [0022]    Referring in addition to FIG. 3, there is shown a fuel injector  60  for use with fuel injection system  11 . Fuel injector  60  includes an injector body  61  that defines a nozzle outlet  99 , pressure release drain  62  and a high pressure fuel inlet  63 . Pressure release drain  62 , which is connected to drain passage  21 , can fluidly connect a needle control chamber  88  with fuel tank  13 , via a drain passage  70 , when pressure release electronic actuator  32  is activated and pressure release electronic control valve  31  and pressure release switch  20  are appropriately positioned. High pressure fuel inlet  63  fluidly connects fuel injector  60  to high pressure fuel rail  16  via high pressure fuel supply line  18 . A high pressure fuel passage  71  is defined by injector body  61  and includes a needle control passage  73  and a nozzle supply passage  93  which fluidly connect high pressure fuel inlet  63  to needle control chamber  88  and a nozzle chamber  97  respectively.  
         [0023]    A direct control needle valve  90  is movably positioned in injector body  61  and includes a piston portion  91  and a needle portion  95 . Needle valve  90  is movable between a downward position in which nozzle outlet  99  is closed and an upward position in which nozzle outlet  99  is open. Needle valve  90  is biased toward its downward position by a biasing spring  94 . Needle valve  90  includes an opening hydraulic surface  96  that is exposed to fluid pressure within nozzle chamber  97 . A closing hydraulic surface  92  of needle valve  90  is included on piston portion  91  and is exposed to fluid pressure within needle control chamber  88 . A small diameter portion  79  included on needle control passage  73  limits the amount of high pressure fuel that can flow into needle control chamber  88  above piston portion  91 . Small diameter portion  79  is sized to communicate pressure while simultaneously limiting flow volume therethrough. Piston portion  91  and needle control chamber  88  are preferably sized such that a match clearance exits between piston portion  91  and injector body  61 . Preferably, this will prevent fuel from flowing around piston portion  91  toward biasing spring  94 . However, because some fuel could migrate downward toward biasing spring  94  during the movement of needle valve  90 , injector body  61  preferably defines a drain passage  72  that fluidly connects needle control chamber  88  to a drain  68  to vent any fuel that flows below piston portion  91  from fuel injector  60 .  
         [0024]    When pressure release drain  62  is blocked from fluid communication with fuel tank  13 , high pressure fuel can act on both closing hydraulic surface  92  and opening hydraulic surface  96 . Closing hydraulic surface  92  and opening hydraulic surface  96  are preferably sized such that needle valve  90  will remain in its downward, biased position to close nozzle outlet  99  when pressure release drain  62  is blocked from fuel tank  13 . When pressure release drain  62  is open to fuel tank  13  via drain passage  21 , high pressure fuel in needle control chamber  88  can flow out of fuel injector  60  through drain passage  70 . In other words, when pressure release drain  62  is open to fuel tank  13 , high pressure fuel rail  16  is fluidly connected to fuel tank  13  via needle control chamber  88  and drain passages  70 ,  21 . However, recall that small diameter portion  79  of needle control passage  73  limits flow volume into needle control chamber  88 . When needle control chamber  88  is fluidly connected to fuel tank  13 , fuel pressure acting on opening hydraulic surface  96  is sufficient to overcome the downward bias exerted by biasing spring  94  and needle valve  90  can be moved toward its upward position to open nozzle outlet  99 .  
         [0025]    Referring to FIGS. 4 and 5, there is shown a common rail fuel injection system  100  and fuel injector  160  according to an alternate embodiment of the present invention. Fuel injection system  100  and fuel injector  160  are similar to fuel injection system  11  and fuel injector  60 , respectively. Therefore, like reference numerals have been used to denote like components, and a repeated description of like components will not be provided. With minor modification, fuel injection system  100  could be incorporated into engine  10  to make a complete engine. In addition to the fuel injection system components shown and described in the FIG. 1 embodiment, fuel injection system  100  includes a rate shaping electronic control valve  140  that is operably connected to electronic control module  33  and includes a rate shaping electronic actuator  142 , which is preferably a two position solenoid, but could be another electronic actuator, such as a piezoelectric actuator. Rate shaping electronic control valve  140  is preferably a two position control valve and is positioned remote from each fuel injector  160  fluidly between high pressure fuel rail  16  and a rate shaping fuel inlet  164  of each fuel injector  160 . When rate shaping electronic actuator  142  is activated by electronic control module  33 , rate shaping electronic control valve  140  is moved from a biased, closed position toward an open position. When rate shaping electronic control valve  140  is in its open position, rate shaping fluid inlet  164  is fluidly connected to high pressure fuel rail  16  via a high pressure fluid passage  143 . When rate shaping electronic control valve  140  is in this position, high pressure fuel can flow into a rate shaping fluid passageway  174 , defined by injector body  161 , via rate shaping fluid inlet  164  to change the position of a flow restriction valve member  180  that is movably positioned in injector body  161 .  
         [0026]    High pressure fuel flowing into rate shaping fluid passageway  174  can act on flow restriction valve member  180 . Flow restriction valve member  180  is preferably any suitable valve member, such as a spool valve member, and includes a hydraulic surface  181  that is exposed to fluid pressure in rate shaping fluid passageway  174 . Flow restriction valve member  180  is movable between an upward, retracted position and a downward, advanced position and is biased toward its upward position by a biasing spring  183 . When flow restriction valve member  180  is in its retracted position, an annulus  182  included on flow restriction valve member  180  allows for unrestricted flow of fuel from high pressure fuel inlet  63  into nozzle supply passage  93 . When flow restriction valve member  180  is in its advanced position, annulus  182  partially blocks high pressure fuel inlet  63  from nozzle supply passage  93 , as illustrated in FIG. 5, to create a flow restriction  185  relative to nozzle outlet  99 .  
         [0027]    Flow restriction  185  reduces the amount of high pressure fuel that is flowing into nozzle chamber  97 , thus reducing the fuel pressure exerted on opening hydraulic surface  96 . Therefore, when flow restriction valve member  180  is in its advanced position, fuel injector  160  will inject fuel at a lower pressure than it will when flow restriction valve member  180  is in its retracted position. While the size of annulus  182  can be varied to alter injection pressure when flow restriction valve member  180  is in its advanced position, it should be appreciated that annulus  182  could be sized so large that flow restriction  185  has little or no effect on the pressure of fuel flowing into nozzle chamber  97 . Similarly, annulus  182  could be sized small enough that fuel pressure in nozzle chamber  97  cannot be sustained above a valve opening pressure. Therefore, annulus  182  should be sized such that a valve opening pressure can be sustained when flow restriction  185  is present in nozzle supply passage  93 , while still achieving the desired, lower injection pressure.  
         [0028]    Note that unlike pressure release electronic control valve  31 , rate shaping electronic control valve  140  is not prevented from affecting conditions within all fuel injectors  160 . This is because rate shaping electronic control valve  140  is not separated from the injectors by a switch, such as pressure release switch  20 . It should be appreciated that this should not effect fuel injection, or which fuel injector is injecting fuel, because pressure introduced into non-injecting fuel injectors  160  as a result of the position of rate shaping electronic control valve  140  merely changes the position of flow restriction valve member  180 . In other words, the pressure forces acting on closing hydraulic surface  92  and opening hydraulic surface  96  are unaffected by the movement of rate shaping electronic control valve  140 . Therefore, movement of rate shaping electronic control valve  140  to its open position should not cause a non-injecting fuel injector to inject fuel at an undesirable time. It should be appreciated, however, that a switch could be included to allow rate shaping electronic control valve  140  to connect only the injecting fuel injector  160  to high pressure fuel rail  16  during the injection event without departing from the spirit of the present invention.  
         [0029]    Referring to FIGS. 6 and 7, there is shown a common rail fuel injection system  200  and fuel injector  260  according to yet another embodiment of the present invention. This embodiment of the present invention is the preferred mode for carrying out the invention, as it provides an even greater control over the injection event than the previous embodiments. Fuel injection system  200  is similar to fuel injection systems  11  and  100  and fuel injector  260  shares several common features with fuel injectors  60  and  160 . Therefore, like numerals have been used to denote like components. With minor modification, fuel injection system  200  could be incorporated into engine  10  to create a complete engine. Because fuel injection system  200  and fuel injector  260  share common features with the previously disclosed embodiments, a repeated description of like components has not been provided.  
         [0030]    In addition to the features shown and described for fuel injection system  100 , fuel injection system  200  includes a pressure build-up switch  250  which is positioned fluidly between the rail outlet  17  of high pressure fuel rail  16  and each high pressure fuel inlet  265  of the fuel injectors  260 . Pressure build-up switch  250  allows selective fluid communication between nozzle chamber  88  of a fuel injector  260  and high pressure fuel rail  16  via high pressure supply lines  253 . Pressure build-up switch  250  is preferably similar to pressure release switch  20  in both form and function. However, while pressure release switch  20  can connect one fuel injector  260  to fuel tank  13  via drain passage  21  and main passage  29  to begin an injection event, pressure build-up switch  250  can connect a high pressure fuel inlet  265  of one fuel injector  260  to high pressure fuel rail  16  to end an injection event. A pressure build-up electronic control valve  251  controls fuel flow between high pressure fuel rail  16  and fuel injectors  260  via pressure build-up switch  250 . Pressure build-up electronic control valve  251  is positioned remote from fuel injectors  260  and includes a pressure build-up electronic actuator  252 . Pressure build-up electronic control valve  251  is preferably a two position control valve and is biased to a closed position. When pressure build-up electronic actuator  252  is activated by electronic control module  33 , pressure build-up electronic control valve  251  is moved to an open position. As with pressure release electronic actuator  32  and rate shaping electronic actuator  142 , pressure build-up electronic actuator  252  is preferably a solenoid, however, other electronic actuators, such as a piezoelectric actuator, could be substituted.  
         [0031]    Referring in addition to FIG. 7, unlike fuel injectors  60  and  160 , high pressure fuel passage  71  of fuel injector  260  does not include branch passages that open into both needle control chamber  88  and nozzle chamber  97 . Instead, high pressure fuel passage  71  includes only nozzle supply passage  93  which opens into nozzle chamber  97 . Injector body  261  defines a high pressure fuel passage  276  that fluidly connects high pressure fuel rail  16  to needle control chamber  88 , via high pressure fuel inlet  265 . Because high pressure fuel is entering needle control chamber  88  and nozzle chamber  97  from separate fuel inlets, it is possible to close needle control chamber  88  from high pressure fuel rail  16  without affecting fuel flow to nozzle chamber  97  or otherwise affecting injector performance. Recall that with the fuel injectors  60 ,  160  of the previous embodiments, needle control chamber  88  was continuously open to high pressure fuel rail  16  via high pressure fuel passage  71 . However, in this embodiment of the present invention, pressure build-up switch  250  and pressure build-up electronic control valve  251  can be positioned and activated such that the needle control chamber  88  of a particular fuel injector  260  is closed from high pressure fuel rail  16  prior to opening needle control chamber  88  to fuel tank  13 .  
         [0032]    Returning to fuel injector  260 , a flow restriction valve member  280  is movably positioned in injector body  261  and includes an internal passage  282  that can introduce a flow restriction  285  into nozzle supply passage  93 . Flow restriction valve member  280  is preferably any suitable valve member, such as a spool valve member and is biased to fully open high pressure fuel passage  71  to nozzle supply passage  93  by a biasing spring  283 . When rate shaping inlet  164  is fluidly connected to high pressure fuel rail  16 , flow restriction valve member  280  moves against the bias of spring  283  to a position in which flow restriction  285  is introduced into nozzle supply passage  93 . While flow restriction valve member  280  is preferably sized to prevent fluid flow into the area surrounding biasing spring  283 , injector body  261  also defines a drain  267  and a drain passage  277  that can vent any fuel that has migrated into the area surrounding biasing spring  283  from fuel injector  260 . Additionally, it should be appreciated that internal passage  282  is preferably sized and positioned such that a valve opening pressure can be reached in nozzle chamber  97  when flow restriction  285  is present in nozzle supply passage  93  while allowing for the desired reduction in injection pressure.  
         [0033]    Industrial Applicability  
         [0034]    Referring to the FIGS.  1 - 3  embodiment of the present invention and in addition to the FIGS. 8 a - f  graphs of pressure release switch position, pressure release actuator current, pressure release valve position, net force on the needle, needle position and injection rate, respectively, versus time. Prior to an injection event, high pressure in needle control chamber  88  prevails and high pressure fuel is acting on both opening hydraulic surface  96  and closing hydraulic surface  92  of needle valve  90  such that needle valve  90  is in a downward position closing nozzle outlet  99 , as illustrated in FIG. 8 d . Cam  19  rotates such that a first valve member  23  moves over contact platform  22  to allow pressure release switch  20  to enable a first fuel injector  60  to be fluidly connected to fuel tank  13  via drain passage  21 , as illustrated at 1 in FIG. 8 a . Fuel injection from the first fuel injector  60  begins when pressure release electronic actuator  32  is activated by electronic control module  33  to move pressure release electronic control valve  31  to its open position as illustrated at 3 and 8 in FIGS. 8 b - c , respectively.  
         [0035]    When pressure release electronic actuator  32  is activated, the fuel injector  60  enabled by pressure release switch  20  becomes fluidly connected to fuel tank  13  via pressure release drain  62  and drain passage  21 . However, pressure release electronic actuator  32  need not pull current for the entire injection event, and instead can be reduced to a hold level, as illustrated at 4 in FIG. 8 b . High pressure fuel within needle control chamber  88  can flow out of fuel injector  60  via drain passage  70 , thus reducing the pressure acting on closing hydraulic surface  92  of needle valve  90 , as illustrated at 12 in FIG. 8 d . Because high pressure fuel is still flowing into nozzle chamber  97 , fuel pressure acting on opening hydraulic surface  96  exceeds a valve opening pressure and needle valve  90  moves to its upward position opening nozzle outlet  99  and allowing fuel to spray into combustion chamber  19 , as illustrated at 16 in FIG. 8 e . The corresponding increase in injection rate toward the maximum is illustrated at 20 in FIG. 8 f.    
         [0036]    As illustrated in FIG. 8, it is possible to create a split injection, such as when the engine is operating under idle operating conditions. Note that the injection characteristics for rated operating conditions have been graphed as solid lines while those for idle operating conditions have been graphed as dashed line. For instance, when current to pressure release electronic actuator  32  is ended, pressure release electronic control valve  31  closes briefly, as illustrated at 6 and 10 in FIGS. 8 b - c , respectively. When pressure release electronic control valve  31  is closed, pressure can increase in needle control chamber  88  to a sufficient level to close needle valve  90 . When pressure release electronic actuator  32  is re-activated (at 7 in FIG. 8 b ), pressure release electronic control valve  31  is reopened (at 11 in FIG. 8 c ). Pressure in needle control chamber  88  can again be vented, and needle valve  90  can reopen due to the fuel force exerted on opening hydraulic surface  96 . The net force on the needle valve and this movement of the needle valve during the injection event has been illustrated at 14 and 15, and 18 and 19 in FIGS. 8 d - e , respectively. In addition, the injection rate, and in particular the split injection created by the movement of needle valve  90  has been graphed at 22 and 23 in FIG. 8 f.    
         [0037]    The injection event of a particular fuel injector  60  is ended when pressure release electronic actuator  32  is deactivated, thus blocking needle control chamber  88  from communication with fuel tank  13  (at 5 in FIG. 8 b ). Pressure release electronic control valve  31  is now moved to its closed position, as illustrated at 9 in FIG. 8 c . While high pressure fuel can no longer flow from needle control chamber  88 , needle control chamber  88  is still exposed to high pressure in high pressure fuel rail  16  via first branch passage  73  and high pressure fuel inlet  63 . Pressure acting on closing hydraulic surface  92  of needle valve  90  once again begins to build and subsequently, and the high fuel pressure acting on opening hydraulic surface  96  is no longer sufficient to hold needle valve  90  in its upward, open position. Needle valve  90  is returned to its downward position under the action of biasing spring  94  to close nozzle outlet  99  and the injection event is ended, as illustrated at 13, 17 and 21 in FIGS. 8 d - f.    
         [0038]    After needle valve  90  returns to its downward position to end the injection event for this fuel injector, fuel injection system  11  prepares a subsequent fuel injector  60  for fuel injection. The corresponding valve member  23  within pressure release switch  20  moves off of contact platform  22 , as cam  19  continues to rotate, to prevent pressure release electronic control valve  31  from reopening needle control chamber  88  of that particular fuel injector  60  to fuel tank  13  (at 2 in FIG. 8 a ). Cam  19  continues to rotate and a second valve member  23  moves over contact surface  22  to enable the next fuel injector  60  to be fluidly connected to fuel tank  13  via needle control chamber  88  and drain passage  21 . It should be appreciated that because only one fuel injector  60  is capable of being fluidly connected to fuel tank  13  via drain passage  21 , fuel injection system  11  will have no more than one fuel injector  60  injecting fuel into combustion chamber  19  at any given time.  
         [0039]    Referring now to the FIGS.  4 - 5  embodiment of the present invention and in addition to the graphs of pressure release switch position, pressure release actuator current, pressure release valve position and net force of needle valve  90 , respectively, versus time of FIGS. 9 a - h . Prior to an injection event, high pressure in needle control chamber  88  prevails and high pressure fuel is acting on closing hydraulic surface  92  and opening hydraulic surface  96 , such that needle valve  90  is in its downward, closed position, as illustrated in FIG. 9 d . Rate shaping electronic actuator  142  is preferably de-activated such that rate shaping inlet  164  is not connected to high pressure fuel rail  16 , as illustrated in FIG. 9 g . Low pressure is acting on hydraulic surface  181  and flow restriction valve member  180  is positioned in its upward, biased position, allowing unrestricted flow of fuel from high pressure fuel passage  71  to nozzle supply passage  93 , as illustrated in FIG. 9 h . Cam  19  is rotating at one half the speed of the engine and valve member  23  moves onto contact surface  22  to allow pressure release switch  20  to enable a first fuel injector  60  to be fluidly connected to fuel tank  13  (at 1 in FIG. 9 a ).  
         [0040]    Prior to activation of pressure release electronic actuator  32 , rate shaping electronic actuator  142  is preferably activated, and rate shaping electronic control valve  140  moves to its open position, as illustrated at  17  and  20 , respectively in FIGS. 9 g - h . Rate shaping inlet  164  is now open to high pressure fuel rail  16 , via high pressure fuel passage  143  exposing hydraulic surface  181  of flow restriction valve member  180  to high pressure fuel. Flow restriction valve member  180  then moves toward its advanced position, causing a flow restriction  185  between high pressure fuel passage  71  and nozzle supply passage  93 . Pressure release electronic actuator  32  is now activated to move pressure release electronic control valve  31  to its open position to allow the injection event to begin, as illustrated at 3 and 6 in FIGS. 9 b - e . Corresponding movement of needle valve  90  toward its open position, increase in flow area to nozzle outlet  99  and initial injection rate are illustrated at  8 ,  11  and  14  in FIGS. 9 d - f.    
         [0041]    Operation of fuel injection system  100 , and fuel injector  160 , would be identical to that of fuel injection system  11  and fuel injector  60  if rate shaping electronic actuator  142  was not activated during fuel injection. As with pressure release electronic actuator  32 , rate shaping electronic actuator  142  need not pull current for the duration of the injection event, and can instead be reduced to a hold level as illustrated at 4 and 1) in FIGS. 9 b  and  9   g . At the desired point during the injection event, rate shaping electronic actuator  142  is de-activated and rate shaping electronic control valve  140  moves to its closed position to end fluid communication between rate shaping inlet  164  and high pressure fuel rail  16  (at 19 and 21 in FIGS. 9 g - h ). Flow restriction valve member  180  can now return to its biased, retracted position under the action of biasing spring  183 . As flow restriction valve member  180  retracts, annulus  182  retracts in a corresponding manner such that fuel flow between high pressure fuel passageway  71  and nozzle supply passage  93  is unrestricted. This unrestricted flow into nozzle supply passage  93  increases the amount of fuel flowing into nozzle chamber  97 , therefore increasing the pressure being exerted on opening hydraulic surface  96  and raising the pressure of fuel being injected by fuel injector  160  (at 9, 12 and 15 in FIGS. 9 d - f ). By varying the timing of rate shaping electronic actuator  142 , it should be appreciated that a number of rate shapes, such as boot shapes, can be accomplished with fuel injection system  100 . However, it should also be appreciated that at certain operating conditions it may be undesirable to have front end rate shaping. In these instances, rate shaping electronic actuator need not be activated, such that rate shaping electronic control valve remains in its closed position throughout the injection event.  
         [0042]    As described for the FIGS.  1 - 3  embodiment of the present invention, fuel injection from fuel injector  160  is ended when current to pressure release electronic actuator  32  is ended and pressure release electronic control valve  31  returns to its closed position, as illustrated at  5  and  7 , respectively, in FIGS. 9 b - c . Needle control chamber  88  is now blocked from fluid communication with fuel tank  13  and pressure within needle control chamber  88  acting on closing hydraulic surface  92  can rise. Because of the size differential between closing hydraulic surface  92  and opening hydraulic surface  96 , the high pressure acting on opening hydraulic surface  96  is no longer sufficient to hold needle valve  90  in its upward position, and needle valve  90  returns to its downward position under the action of biasing spring  94  (at 10 in FIG. 9 d ). Needle valve  90  is moved toward its downward movement by the increased pressure acting on closing hydraulic surface  92 . The corresponding decrease in flow area to nozzle outlet  99  and in injection rate has been illustrated at 13 and 16 in FIGS. 9 e - f , respectively. As with fuel injection system  11 , after needle valve  90  returns to its downward position to end the injection event for this fuel injector  160 , fuel injection system  100  prepares a subsequent fuel injector  160  for fuel injection. Cam  19  continues to rotate and first valve member  23  moves off of contact surface  22  to close pressure release switch  20  from enabling this fuel injector  160  from being fluidly connected to fuel tank  13  via needle control chamber  88  and drain passage  21 , as illustrated at 2 in FIG. 9 a . A second valve member  23  moves over contact surface  22  to enable the needle control chamber of the next fuel injector  160  to be fluidly connected to fuel tank  13 .  
         [0043]    Referring to the FIGS.  6 - 7  embodiment of the present invention and in addition to the FIGS. 10 a - i  graphs of pressure release switch position, pressure release actuator current, net force on the needle, flow area to the nozzle, injection rate, rate shaping valve position, pressure build-up actuator current, pressure build-up valve position and pressure build-up switch position, respectively, versus time. Prior to an injection event, high pressure in needle control chamber  88  prevails, high pressure inlet  63  is open to high pressure fuel rail  16  to expose opening hydraulic surface  96  to high pressure and residual high pressure is acting on closing hydraulic surface  92  such that needle valve  90  is in a downward position closing nozzle outlet  99 . Rate shaping inlet  164  is preferably not connected to high pressure fuel rail  16 , such that low pressure acting on hydraulic surface  281  allows flow restriction valve member  280  to remain in its biased, retracted position, allowing an unrestricted flow path between high pressure fuel passage  71  and nozzle supply passage  93 . Just prior to the initiation of an injection event, pressure build-up switch  250  enables the high pressure fuel inlet  265  of a first fuel injector  260  to be fluidly connected to high pressure fuel rail  16 , as illustrated at 20 in FIG. 10 i . However, because pressure build-up electronic control valve  251  remains in its closed position, as illustrated in FIG. 10 h , high pressure fuel inlet  265  is not opened to high pressure fuel rail  16  at this time. Cam  19  now rotates such that pressure release switch  20  enables a first fuel injector  260  to be fluidly connected to fuel tank  13 , as illustrated at 1 in FIG. 10 a.    
         [0044]    Prior to activation of pressure release electronic control valve  31 , rate shaping electronic actuator  142  is preferably activated to move rate shaping electronic control valve  140  to an open position to fluidly connect rate shaping inlet  164  with high pressure fuel rail  16  (at 14 in FIG. 10 f ). Recall that at certain operating conditions, front end rate shaping may not be desirable. Therefore, it should be appreciated that fuel injection can take place if rate shaping electronic control valve  140  remains in its closed position. With high pressure now acting on hydraulic surface  281 , flow restriction valve member  280  can move toward its advanced position against the action of biasing spring  283 . The corresponding movement of internal passage  282  creates a flow restriction  285  in nozzle supply passage  93  that will create a lower injection pressure at the beginning of the injection event. The injection event is initiated by the brief activation of pressure release electronic actuator  32 , as illustrated at 3 in FIG. 10 b , which fluidly connects pressure release drain  62  to fuel tank  13 . It should be appreciated that pressure release electronic actuator  32  does not need to receive current for the duration of the injection event, as it did for fuel injection systems  11  and  100 , because it only takes a short amount of time to vent the residual pressure in needle control chamber  88 . Also, only a small fixed amount of fuel must be displaced from needle control chamber  88  for fuel injection to proceed. Therefore, pressure release electronic control valve  31  need only be moved to its open position for a relatively short amount of time. Recall that in fuel injection systems  11  and  100 , the needle control chambers  88  of the fuel injectors  60 ,  160  were continuously open to high pressure fuel rail  16 , and as a result, pressure release electronic control valve  31  remained in an open position to allow fuel pressure above needle valve  90  to be vented for the duration of the injection event.  
         [0045]    Once residual pressure within needle control chamber  88  has been vented, the high fuel pressure acting on opening hydraulic surface  96  can exceed a valve opening pressure defined by biasing spring  94 . Needle valve  90  then moves to its upward, open position to commence fuel spray from nozzle outlet  99 , as illustrated at 5 in FIG. 10 c . Note, however, that flow area to nozzle outlet  90  increases only to a restricted amount due to flow restriction  185 , as illustrated at 8 in FIG. 10 d . The corresponding initial injection rate has been illustrated at 11 in FIG. 10 e . Pressure release electronic actuator  142  is then deactivated (at 4 in FIG. 10( b )) to return electronic control valve  31  to its closed position to block needle control chamber  88  from fluid communication with fuel tank  13 . Operation of fuel injector  260  and fuel injection system  200  progresses in a similar manner as that described for fuel injector  160  and fuel injection system  100 , until just prior to the end of the injection event. At that time, pressure build-up electronic actuator  252  is activated briefly to move pressure build-up electronic control valve  251  to its open position, as illustrated at 16 and 18, respectively, in FIGS. 10 g - h . High pressure fuel inlet  265  is once again fluidly connected to high pressure fuel rail  16  and high pressure fuel flows into needle control chamber  88  via high pressure fuel supply line  253 . Because closing hydraulic surface  92  is again exposed to high pressure within nozzle chamber  88 , needle valve  90  is moved to its downward, closed position to close nozzle outlet  99  and end the injection event, as illustrated at 7 in FIG. 10 c . The corresponding decrease in flow area to nozzle outlet  99  and injection rate has been illustrated at 10 and 13, respectively, in FIGS. 10 d - e.    
         [0046]    After needle valve  90  moves to its downward position to end fuel injection from fuel injector  250 , fuel injection system  200  prepares a subsequent fuel injector  260  to begin injection. Cam  19 , which has been rotating throughout the previous injection event, rotates such that valve member  23  within pressure release switch  20 , corresponding to the previously injecting fuel injector  260 , moves off contact platform  22 , and valve member  23  corresponding to the fuel injector that is about to inject moves on to platform  22  (at 2 in FIG. 10 a ). Preferably, at about the same time, the contact platform within pressure build-up switch  250  is rotated such that the valve member  23  corresponding to the previously injecting fuel injector  260  returns to its biased position, and the valve member  23  for the fuel injector  260  about to inject moves onto the contact platform (at 21 in FIG. 10 i ). The subsequent fuel injector  260  can now inject fuel in the manner described above.  
         [0047]    Referring now to FIG. 11, total fuel consumption for fuel injection systems  11 ,  100  and  200  have been graphed versus time for both idle operating conditions, at 1, and for rated operating conditions, at 2. Note that the total amount of fuel consumed by fuel injection system  200 , graphed as a solid line, is substantially less than that used by fuel injection systems  11  and  100 , where these systems are represented by dashed and dotted lines, respectively. This result should be expected because pressure build-up switch  250  and pressure build-up electronic control valve  251  allow each fuel injector to be blocked from fluid communication with high pressure rail  16  prior to being fluidly connected to fuel tank  13 . Therefore, in fuel injection system  200 , high pressure fuel rail  16  is preferably not fluidly connected to fuel tank  13  at any time during the injection event. It should be appreciated that the total fuel consumed by fuel injection system  200  is still higher than the total fuel injected because an amount of fuel from high pressure fuel rail  16  is not injected, but instead acts on needle valve  90  within needle control chamber  88 .  
         [0048]    The fuel injection systems of the present invention have a number of advantages over prior art systems. Because the electronic control valves used in the present invention are located remote from the individual fuel injectors, the number of electronic control valves used in the fuel injection system can be reduced. For instance, because nozzle chamber  97  is always fluidly connected to high pressure fuel rail  16 , injection can begin at full pressure. This is unlike those systems where the needle valve opens at a valve opening pressure that is well below a maximum injection pressure. With regard to fuel injection system  11 , only one electronic control valve is used to control the injection of each fuel injector, instead of utilization of as many electronic control valves as the number of fuel injectors. In addition, fuel injection systems  100  and  200  allow for flexible rate shaping of the injection event. Further, because fuel injection system  200  has the ability to block fluid communication between the high pressure fuel rail and the fuel drain during an injection event, fuel injection system  200  consumes, and therefore wastes, less fuel than prior art fuel injection systems of this nature.  
         [0049]    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. For instance, while the present invention does not include a switch between the pressure build-up electronic control valve and the fuel injectors, it should be appreciated that such a switch could be utilized. Further, while the fuel injection systems of the present invention include electronic control valves that are preferably solenoids, it should be appreciated that other suitable actuators, such as a piezoelectric actuator, could be substituted. Thus, those skilled in the art will appreciate that other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.