TECHNICAL FIELD 
     The present application relates to internal combustion engine valve control. More particularly, the present application relates to independent needle valve control in a hydraulically actuated, intensified fuel injector. 
     BACKGROUND AND PRIOR ART 
     Referring to the prior art drawings,  FIG. 1  shows a prior art fuel injector  50 . The prior art injector  50  is substantially as described in U.S. Pat. No. 5,460,329 to Sturman. A fuel injector having certain similar features may be found in U.S. Pat. No. 5,682,858 to Chen et al. The fuel injector  50  is typically mounted to an engine block and injects a controlled pressurized volume of fuel into a combustion chamber (not shown). The injector  50  is typically used to inject diesel fuel into a compression ignition engine, although it is to be understood that the injector could also be used in a spark ignition engine or any other system that requires the injection of a fluid. 
     The fuel injector  50  has an injector housing  52  that is typically constructed from a plurality of individual parts. The housing  52  includes an outer casing  54  that contains block members  56 ,  58 , and  60 . The outer casing  54  has a fuel port  64  that is coupled to a fuel pressure chamber  66  by a fuel passage  68 . A first check valve  70  is located within fuel passage  68  to prevent a reverse flow of fuel from the pressure chamber  66  to the fuel port  64 . The pressure chamber  66  is coupled to a nozzle chamber  304  and to a nozzle  72  by means of fuel passage  74 . A second check valve  76  is located within the fuel passage  74  to prevent a reverse flow of fuel from the nozzle  72  and the nozzle chamber  304  to the pressure chamber  66 . 
     The flow of fuel through the nozzle  72  is controlled by a needle valve  78  that is biased into a closed position by spring  80  located within a spring chamber  81 . The needle valve  78  has a shoulder  82  in the nozzle chamber  304  above the location where the passage  74  enters the nozzle  78 . When fuel flows in the passage  74 , the pressure of the fuel applies a force on the shoulder  82  in the nozzle chamber  304 . The shoulder force acts to overcome the bias of spring  80  and lifts the needle valve  78  away from the nozzle  72 , allowing fuel to be discharged from the injector  50 . 
     A passage  83  may be provided between the spring chamber  81  and the fuel passage  68  to drain any fuel that leaks into the chamber  81 . The drain passage  83  prevents the build up of a hydrostatic pressure within the chamber  81  which could create a counteractive force on the needle valve  78  and degrade the performance of the injector  50 . 
     The volume of the pressure chamber  66  is defined in part by an intensifier piston  84 . The intensifier piston  84  extends through a bore  86  of block  60  and into a first intensifier chamber  88  located within an upper valve block  90 . The piston  84  includes a shaft member  92  which has a shoulder  94  that is attached to a head member  96 . The shoulder  94  is retained in position by clamp  98  that fits within a corresponding groove  100  in the head member  96 . The head member  96  has a cavity which defines a second intensifier chamber  102 . 
     The first intensifier chamber  88  is in fluid communication with a first intensifier passage  104  that extends through block  90 . Likewise, the second intensifier chamber  102  is in fluid communication with a second intensifier passage  106 . 
     The block  90  also has a supply working passage  108  that is in fluid communication with a supply working port  110 . The supply working port  110  is typically coupled to a system that supplies a working fluid which is used to control the movement of the intensifier piston  84 . The working fluid is typically a hydraulic fluid, preferably engine lubricating oil, that circulates in a closed system separate from fuel. Alternatively the fuel could also be used as the working fluid. Both the outer body  54  and block  90  have a number of outer grooves  112  which typically retain O-rings (not shown) that seal the injector  10  against the engine block. Additionally, block  62  and outer shelf  54  may be sealed to block  90  by O-ring  114 . 
     Block  60  has a passage  116  that is in fluid communication with the fuel port  64 . The passage  116  allows any fuel that leaks from the pressure chamber  66  between the block  62  and piston  84  to be drained back into the fuel port  64 . The passage  116  prevents fuel from leaking into the first intensifier chamber  88 . 
     The flow of working fluid (preferably engine lubricating oil) into the intensifier chambers  88  and  102  can be controlled by a four-way solenoid control valve  118 . The control valve  118  has a spool  120  that moves within a valve housing  122 . The valve housing  122  has openings connected to the passages  104 ,  106  and  108  and a drain port  124 . The spool  120  has an inner chamber  126  and a pair of spool ports that can be coupled to the drain ports  124 . The spool  120  also has an outer groove  132 . The ends of the spool  120  have openings  134  which provide fluid communication between the inner chamber  126  and the valve chamber  134  of the housing  122 . The openings  134  maintain the hydrostatic balance of the spool  120 . 
     The valve spool  120  is moved between the first position shown in prior art  FIG. 1 and a  second opposed position, by a first solenoid  138  and a second solenoid  140 . The solenoids  138  and  140  are typically coupled to an external controller (not shown) which controls the operation of the injector. When the first solenoid  138  is energized, the spool  120  is pulled to the first position, wherein the first groove  132  allows the working fluid to flow from the supply working passage  108  into the first intensifier chamber  88 , and the fluid flows from the second intensifier chamber  102  into the inner chamber  126  and out the drain port  124 . When the second solenoid  140  is energized the spool  120  is pulled to the second position, wherein the first groove  132  provides fluid communication between the supply working passage  108  and the second intensifier chamber  102 , and between the first intensifier chamber  88  and the drain part  124 . 
     The groove  132  and passages  128  are preferably constructed so that the initial port is closed before the final port is opened. For example, when the spool  120  moves from the first position to the second position, the portion of the spool adjacent to the groove  132  initially blocks the first passage  104  before the passage  128  provides fluid communication between the first passage  104  and the drain port  124 . Delaying the exposure of the ports reduces the pressure surges in the system and provides an injector which has predictable firing points on the fuel injection curve. 
     The spool  120  typically engages a pair of bearing surfaces  142  in the valve housing  122 . Both the spool  120  and the housing  122  are preferably constructed from a magnetic material such as a hardened  52100  or  440   c  steel, so that the hysteresis of the material will maintain the spool  120  in either the first or second position. The hysteresis allows the solenoids  138 ,  140  to be de-energized after the spool  120  is pulled into position. In this respect the control valve  118  operates in a digital manner, wherein the spool  120  is moved by a defined power pulse that is provided to the appropriate solenoid  138 , 140 . Operating the valve  118  in a digital manner reduces the heat generated by the coils and increases the reliability and life of the injector  50 . 
     In operation, the first solenoid  138  is energized and pulls the spool  120  to the first position, so that the working fluid flows from the supply port  110  into the first intensifier chamber  88  and from the second intensifier chamber  102  into the drain port  124 . The flow of working fluid into the intensifier chamber  88  moves the piston  84  and increases the volume of chamber  66 . The increase in the chamber  66  volume decreases the chamber pressure and draws fuel into the chamber  66  from the fuel port  64 . Power to the first solenoid  138  is terminated when the spool  120  reaches the first position. 
     When the chamber  66  is filled with fuel, the second solenoid  140  is energized to pull the spool  120  into the second position. Power to the second solenoid  140  is terminated when the spool  120  reaches the second position. The movement of the spool  120  allows working fluid to flow into the second intensifier chamber  102  from the supply port  110  and from the first intensifier chamber  88  into the drain port  124 . 
     The head  96  of the intensifier piston  96  has an area much larger than the end of the piston  84 , so that the pressure of the working fluid generates a force that pushes the intensifier piston  84  and reduces the volume of the pressure chamber  66 . The stroking cycle of the intensifier piston  84  increases the pressure of the fuel within the pressure chamber  66  and, by means of passage  74 , in the nozzle chamber  304 . The pressurized fuel acts on shoulder  82  in the nozzle chamber  304  to open the needle valve  78  and fuel is then discharged from the injector  50  through the nozzle  72 . The fuel is typically introduced to the injector at a pressure between 1000-2000 psi. In the preferred embodiment, the piston has a head to end ratio of approximately 10:1, wherein the pressure of the fuel discharged by the injector is between 10,000-20,000 psi. 
     The HEUI injector  50  described above is commonly referred to as the G2 injector. The G2 injector  50  uses a fast digital spool valve  120  to control multiple injection events. During its operation, every component inside of the injector  50  (spool valve  120 , intensifier piston  84 , and needle valve  78 ) has to open/close multiple times to either trigger the injection or stop the injection during the injection event. The digital spool valve  120  has to handle large flow capacity to supply actuation liquid to the intensifier piston  78 . The spool valve  120  size is relatively big and the response of a large spool valve  120  is therefore limited. 
     The intensifier  84  is also relatively large in mass. Therefore reversing the motion of the intensifier  84  to achieve pilot injection operation is inefficient. Once committed to compression of fuel for injection, it is much more efficient to maintain the intensifier  84  motion in the compressing stroke throughout the duration of the injection event. 
     Reversing of the motion of the spool valve  120  and the intensifier piston  84  results in the injection event no longer being a single shot injection, but effectively multiple short independent injection events during the injection event. Both the motion of the spool valve  120  and the intensifier piston  84  must be reversed in the duration between the pre-injection and the actual injection and reversed again to effect the “actual” injection. With such relatively massive devices as the spool valve  120  and the intensifier piston  84 , this is highly inefficient. 
     It is believed that pilot or split injection should be injection interruptions effected during a single shot injection, e.g., with no motion reversal of either the spool valve  120  or the intensifier piston  84 , but with control of the needle valve  78  opening and closing motions. As indicated above, the intensifier piston  84  has relatively large mass hence it is difficult or slow to reverse its motion. 
     A responsive injection system should avoid reverse motion of the intensifier  84  and, preferably, of the spool valve  120 . Therefore, there is a need in the industry to utilize a mechanism to efficiently control the needle valve  78  independent of intensifier piston  84  and its controller. 
     SUMMARY OF THE INVENTION 
     The present invention substantially meets the needs of the industry. Control of the needle valve multiple times during an injection event is achieved by a device that permits the spool valve to cycle only a single time, open at the initiation of the injection event and close after the termination of the injection event, and the intensifier piston to maintain a continuous compressing stroke during the injection event. 
     The present invention is a hydraulically actuated, intensified fuel injector includes a controller achieving a desired injection control strategy by selectively independently porting actuating fluid to and venting actuating fluid from an intensifier piston to control the compressive stroke of the intensifier piston and selectively independently porting actuating fluid to and venting actuating fluid from a needle valve to control the opening and closing of the needle valve during the injection event. The present invention is further a method of control. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a prior art fuel injector; 
         FIG. 2  is a sectional view of the dual control valve of the present invention with both valves on the off position; 
         FIG. 3  is a sectional view of the dual control valve of the present invention with both valves on the on position; and 
         FIG. 4  is a sectional view of a fuel injector incorporating the dual control valve of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is related to the dual control valve, shown generally at  500  in the  FIGS. 2 and 3 , and the application of the dual control valve  500  to a fuel injection system in FIG.  4 . 
     Referring to  FIGS. 2 and 3 , the dual control valve  500  has two major components, pressure control valve  502  and timing control valve  504 . The pressure control valve  502  and timing control valve  504  of the control valve  500  each include a dedicated respective control coil  506 ,  508  and cap assemblies  510 ,  512 , respective return springs  514 ,  516 . The pressure control valve  502  includes a single balanced spool valve  518 . The timing control valve  504  is comprised of a half spool valve  520  (The timing control valve  504  may also be a poppet valve). Both valves  502 ,  504  are depicted being on the same longitudinal axis and in this configuration may be installed from both ends in a bore  522  defined in a common housing  524 . It should be noted that the valves  502 ,  504  need not be in the depicted coaxial disposition. 
     Both valves  502 , 504  are never in contact with each other and accordingly the valves  502 ,  504  can be operated independently without interference. Both valves  502 ,  504  are electronically energized to the on position of FIG.  3  and returned by the respective return spring  514 ,  516  to the off position of FIG.  2 . Both spool valves  502 ,  504  have a respective large disk plate  524 ,  526  at one end (air gap side  528 ,  530 ) to provide a large magnetic force to provide for actuation of the respective spool valves  502 ,  504 . The disk plates  524 ,  526  also provide a stop function to the respective spool valves  502 ,  504  when the respective disk plate  524 ,  526  has reached (is seated on) either the respective valve housing stop  532 ,  534  or the respective end cap stop  536 ,  538 . Actuating fluid forms from the high pressure rail  542  as controlled by the valves  502 ,  504 . Actuating fluid is vented via vents  537 ,  539  as controlled by the valves  502 ,  504 . 
     The large balanced spool valve  518  is functionally similar to the prior art control valve  120 , described above. Spool valve  518  is a flow symmetric valve. Actuating fluid flow therefore goes into both the left and right sides of the lands  540  (flows fully around the lands  540 , thereby equalizing the forces generated on both sides of the lands  540 ) when the spool valve  518  is in the open and flow is from rail  542  (see  FIG. 3 ) or closed position and flow is vented through vents  537  (see FIG.  2 ). The symmetric flow pattern around the lands  540  allows the spool valve  518  to move with very little or negligible flow force, hence the spool valve  518  provides for more efficient use of magnetic force and has a faster valve response. Symmetric flow around the lands  540  provides for a relatively greater flow area and therefore has the advantage of a smaller valve stroke necessary to achieve the required porting of fluid. 
     The timing control valve  504  can either be a part of the balanced spool valve, say a half spool valve  520  or a small poppet valve (not shown). The design objective of the timing control valve  504  is to make valve  504  as small as possible in order that the valve  504  have fastest possible response time. A half spool valve  504  has less flow capability than a balanced spool valve, such as spool valve  518 , but has faster response time since it has substantially less mass. 
     It should be noted that in the off position, the pressure control valve  502  is venting actuating fluid to the vents  537  while the timing control valve  504  is porting actuating fluid in from rail  542 . Conversely, in the on position the pressure control valve  502  is porting actuating fluid in and timing control valve  504  is venting. 
     Actuation fluid from the rail  542  is directed to and vented from a different part of the hydraulic system independently both in timing and in duration through the coordination of the independent operation both control valves  502 ,  504 . Following are examples of how the dual control valve  500  is employed to enhance the injection performance. 
     Fuel Injector Application: 
       FIG. 4  shows the application of the present invention to a fuel injection system. The prior art injector of  FIG. 1  has a single two-position 3-way control valve  120 . This single control valve is replaced in the present invention by the two-position 3-way valves  502 ,  504  of the dual control valve  500 . A balanced spool valve  518  of the pressure control valve  502  is always used to control the actuation process of the intensifier piston  84 . The half spool valve  520  of the timing control valve  504  is used to control the timing of the injection and how much fuel is injected through the needle valve  78 . By having two independent control valves  502 ,  504 , the injection pressure generation process through the intensifier piston  84  and the injection timing control process through the needle valve  78  are managed independently. 
     In the injector of  FIG. 4 , an advantageous strategy is to turn the pressure control valve  502  on ahead of turning the timing control valve  504  on. The pressure control valve  502  actuates the intensifier piston  84  and acts to prepare the fuel pressure and get ready for injection (no injection is possible with the timing control valve  504  in the off position). The pressure control valve  502  opens only once during an injection event and stays open throughout the injection event to provide constant injection pressure throughout the entire injection process. This allows the intensifier piston  84  to stay at either a down stroke compression motion or in a hydraulic lock mode with actuation fluid pressure applied to the intensifier piston  84  when the entire fuel injection is stopped as controlled independently by the timing control valve  504 . The pressure control valve  502  is preferably shut off to vent actuating fluid through vents  537  (see  FIG. 2 ) only when the entire fluid injection event, including, for example, pilot, main and post injection, is finished. The pressure control valve  502 , preferably the balance spool valve  518 , is relatively large. The pressure control valve  502  has less flow restriction and the response of the balance spool valve  518  is not as critical as the response of the small half spool valve  520  of the timing control valve  514 . 
     Direct Needle Control 
     In  FIG. 4 , the coil  508  of the half spool valve  520  of the timing control valve is initially at off. Actuation fluid at rail pressure from the rail  542  is ported in and flows around the groove  544 , through the passageway  546  and is in communication with the needle back  548  of the needle actuation piston  550 . The needle actuation piston  550  is big enough to provide sufficient force (the combined force of the return spring  552  and the force generated on the needle back actuation surface  548  by the actuation fluid) to hold down the needle valve  78  and stop the needle valve  78  from opening at all injection pressure levels. In  FIG. 4 , the needle actuation piston  550  is depicted as a separate component from the needle valve  78 , having a shank  554 . The distal end  556  of the shank  554  bears on the upper margin  558  of the needle valve  78 . The needle actuation piston  550  and the needle valve  78  could be formed as an integral component. 
     The return spring  552  bears on the needle back actuation surface  548  and is disposed in the variable volume chamber  553  that is formed in part by the needle back actuation surface  548 . The opposing chamber  555  is also variable and is vented to a substantially ambient pressure actuating fluid reservoir. An additional variable volume chamber  559  is formed in part by the upper margin  558  of the needle valve  78 . The chamber  559  is vented to a substantially ambient pressure fuel reservoir. 
     When the coil  508  of half spool valve  520  is turned on, the valve  520  is shifted to the vent position seated on the end cap stop  538 , as depicted in  FIGS. 3 and 4 , and the needle back  548  is vented to ambient pressure level. The needle valve  78  may then be lifted up (opened) if the nozzle side fuel pressure acting on shoulder surface  82  generates a force that is higher than the minimum cranking pressure of the needle return spring  552  and some small amount of residual pressure acting on the needle back  548 . 
     The needle valve  78  is closed at all times that the timing control valve  504  is turned off (rail pressure being ported in), as depicted in  FIG. 2 , the disc plate  526  being seated against the valve housing stop  534 . This is true without regard to the disposition of the pressure control valve  502 . If the pressure control valve  502  is open, as depicted in  FIG. 3 , closing the timing control valve  504  acts to close the needle valve  78 , thereby putting the intensifier piston  84  into a state of hydraulic lock. This hydraulic lock is evidenced by the actuating fluid ported in by the pressure control valve  502  generating a force on the intensifier piston  84  and, with the needle valve  78  closed, no fuel is being injected so that the high pressure passage  74  is sealed off. Without injection occurring, a certain volume of fuel is trapped in the high pressure passage  74  and that trapped volume prevents the intensifier piston  84  from continuing its actuating compressive stroke. 
     There are several ways to operate the injection process as noted below. 
     (1) Prebuild Pressure. 
     As noted above, the pressure control valve  502  is turned on substantially prior to turning on the timing control valve  504 . This ports high pressure actuating fluid to bear on the intensifier piston  84 . The intensifier piston  84  is initially in a state of hydraulic lock since the timing control valve  504  is off and high pressure actuating fluid is bearing on the needle back  548  holding the needle valve  78  closed. The intensifier chamber  102  and plunger chamber  66  pressure are prebuilt and are ready to use. The fuel in the plunger chamber  66  is being pressurized but is not flowing due to the needle valve  78  being held in a closed disposition by the pressure on the needle back  548  caused by the actuating fluid ported through the timing control valve  504 , the timing control valve  504  being in the off position as depicted in FIG.  2 . 
     The timing control valve  504  is then turned on, as depicted in  FIG. 3 , to trigger the fuel delivery. The rail  542  to the timing control valve  504  is sealed off and the actuating fluid acting on the needle back  548  is vented to ambient via vent  539 . The high pressure fuel from the plunger chamber  66  acting on the shoulder surface  82  of the needle valve  78  causes the needle valve  78  to open, resulting in the injection of pressurized fuel. 
     The timing control valve  504  can be turned on and off multiple times during an injection event to cause multiple independent injections and multiple dwell periods (during which no injection occurs), such as pilot, main and post injections. The pressure control valve  502  stays on during the entire injection event until the very end, continuously porting actuating fluid to the intensifier piston  84 . The intensifier piston  84  goes though multiple downward compression and hydraulic lock states during an injection event as described immediately above. 
     (2) Slow Ramped Injection. 
     It may be desirable to have the initial portion of the rate of injection ramp up relatively slowly to the full rate of injection. This is possible with the dual control valve  500  of the present invention by turning on the timing control valve  504  prior to the pressure generation process. Turning on the timing control valve  504  results in the needle back  548  being vented to ambient through vent  539 . In this condition, the spring preload of the return spring  552  stops the needle valve from lifting (opening) under pressurization until the force generated on the shoulder surface  82  by the rising fuel press exceeds the spring preload. 
     The pressure control valve  502  may then turned on to relatively gradually build up the actuating fluid pressure in the intensifier chamber  102  and thereby to gradually build up the fuel pressure in the plunger chamber  66 . As soon as the fuel pressure acting on the shoulder surface  82  generates a force exceeding the needle return spring  552  preload force level, the needle valve  78  opens and injection starts gradually and ramps up over time to the full rate of injection. End of injection is always controlled by closing the needle valve  78  through turning the timing valve  504  off before the pressure control valve  502  is turned off. Turning the pressure control valve  502  off allows the intensifier piston  84  to return to its initial disposition ready for the succeeding injection event. This valve sequence provides for the full injection pressure being available for injection (since the intensifier piston  84  is still in its compression stroke) until injection is terminated by closing the needle valve  78  by turning the timing valve  504  off. 
     It will be obvious to those skilled in the art that other embodiments in addition to the ones described herein are indicated to be within the scope and breadth of the present application. Accordingly, the applicant intends to be limited only by the claims appended hereto.
A hydraulically actuated, intensified fuel injector includes a controller achieving a desired injection control strategy by selectively independently porting actuating fluid to and venting actuating fluid from an intensifier piston to control the compressive stroke of the intensifier piston and selectively independently porting actuating fluid to and venting actuating fluid from a needle valve to control the opening and closing of the needle valve during the injection event. A method of control is further included.