Abstract:
The present invention relates to high speed control valves which are especially applicable for use in fuel injection systems. Producing a valve with a quick response time within acceptable packaging constraints and with a structure that allows the valve to be mass produced with consistent performance between valves is extremely problematic. By moving flow restrictions within the valve away from the valve seats, flow forces on the valve member can be reduced, while possibly also permitting a reduction in the necessary travel distance of the valve member to improve response time and other performance characteristics. The valve is particularly applicable in controlling hydraulic pressure applied to the closing hydraulic surface of a direct control needle valve in a fuel injector.

Description:
TECHNICAL FIELD 
   The present invention relates generally to high speed liquid valves with a small flow volume, and more particularly to a three way control valve for use in an electro-hydraulic actuator, such as a portion of a fuel injector. 
   BACKGROUND 
   Electro-hydraulic actuators, such as those used in conjunction with fuel injectors having a direct control needle valve, rely upon relatively small and fast valves in order to control fuel injection characteristics. In one class of fuel injection systems, a direct control needle valve opens and closes the nozzle outlet of the fuel injector. The direct control needle valve is controlled hydraulically via a relatively high speed needle control valve that has the ability to apply either low pressure or high pressure to a closing hydraulic surface associated with the direct control needle valve. One such direct control needle valve and accompanying needle control valve is disclosed in co-owned U.S. Pat. No. 5,669,355 to Gibson et al. That reference teaches a fuel injector that includes a needle control valve with the ability to apply high pressure or low pressure oil to a closing hydraulic surface of a direct control needle valve. When high pressure is applied to the closing hydraulic surface, the needle valve stays in, or moves toward, its closed position to end the spray of fuel. When low pressure is applied to the closing hydraulic surface, and the fuel is at injection pressure levels, the needle valve will stay in, or move toward, its open position to allow fuel to spray out of the nozzle outlets of the fuel injector. In order to accomplish various goals, such as reducing undesirable emissions from an engine, engineers are constantly seeking ways of improving performance of direct control needle valves, especially by addressing problems associated with needle control valves. 
   One of the problems that could be addressed in improving a needle control valve is to reduce response time. This problem can then be broken down into seeking ways to reduce the valve member&#39;s travel distance, increasing the travel speed and/or acceleration of the valve member, decreasing the influence of fluid flow forces on valve member movement, and other issues known in the art. In addition, it is desirable to employ strategies that hasten the rate at which pressure changes can occur within the needle control chamber that applies the hydraulic force to the closing hydraulic surface of the needle valve member. These problems are further compounded by issues relating to an available space envelope for the valve, and maybe more importantly the ability to address all of these problems with a structure that allows for the valve to be mass produced with consistent behavior from one valve to another. Still another problem that could be addressed relates to efficiency. For instance, reducing leakage through the valve can make a difference in the overall viability of a given valve. 
   The present invention is directed to one or more of the problems set forth above. 
   SUMMARY OF THE INVENTION 
   In one aspect, a three way control valve includes a valve body with a first passage, a second passage, a third passage, a first seat and a second seat. A valve member is at least partially positioned in the valve body and movable between the first seat and the second seat. The first passage is open to the third passage across the first seat when the valve member is in contact with the second seat. One of the first passage and the third passage has a flow restriction relative to the flow area across the first seat. The second passage is open to the third passage across the second seat when the valve member is in contact with the first seat. One of the second passage and the third passage has a second flow restriction relative to a flow area across the second seat. 
   In another aspect, an electro-hydraulic actuator includes a three way control valve with a closed control pressure volume, with a control passage a high pressure passage fluidly connected to a source of high pressure liquid, and a low pressure passage fluidly connected to a low pressure liquid reservoir. The three way control valve includes a valve member trapped to move between a high pressure seat and a low pressure seat. A movable piston with a control hydraulic surface is exposed to fluid pressure in the control pressure volume. An electrical actuator is operably coupled to the valve member. The low pressure passage is open to the control passage across the low pressure seat when the valve member is in contact with the high pressure seat. One of the low pressure passage and the control passage has a first flow restriction relative to a flow area across the low pressure seat. The high pressure passage is open to the control passage across the high pressure seat when the valve member is in contact with the low pressure seat. One of the high pressure passage and the control passage has a second flow restriction relative to a flow area across the high pressure seat. 
   In still another aspect, a method of operating a three way control valve includes a step of fluidly connecting a first passage to a third passage across a first valve seat at least in part by positioning a valve member in contact with a second seat. Liquid flow from the third passage to the first passage is restricted at least in part by locating a first flow restriction in one of the first passage and the control passage, wherein the first flow restriction is restrictive relative to a flow area across the first seat. The second passage is fluidly connected to the third passage across an second seat at least in part by moving the valve member into contact with the first seat. Liquid flow from the second passage to the third passage is restricted at least in part by locating a second flow restriction in one of the second passage and the control passage, wherein the second flow restriction is restrictive relative to a flow area across the second seat. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectioned side diagrammatic view of a fuel injector according to one aspect of the present invention; 
       FIG. 2  is a sectioned side diagrammatic view of an electro-hydraulic actuator portion of the fuel injector shown in  FIG. 1 ; 
       FIG. 3  is an isometric view of a solenoid stator assembly according to an aspect of the present invention; 
       FIG. 4  is a top diagrammatic view of a three way valve portion of the electro-hydraulic actuator shown in  FIG. 2 ; 
       FIG. 5  is a sectioned side diagrammatic view of the three way valve shown in  FIG. 4  as viewed along section lines  5 — 5 ; 
       FIG. 6  is a side diagrammatic view of the valve member for the three way valve of  FIGS. 4 and 5 ; 
       FIG. 7  is a sectioned side diagrammatic view of the three way valve according to another aspect of the invention; and 
       FIG. 8  is a sectioned side diagrammatic view of a three way valve according to still another aspect of the invention. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a fuel injector  10  includes a direct control needle valve  11  that is operably coupled to an electro-hydraulic actuator  12 . Electro-hydraulic actuator  12  includes a three way valve  14  that is operably coupled to an electrical actuator  16 . Fuel injector  10  is connected to a source of high pressure fuel  18  via a fuel supply line  19 , and connected to a low pressure fuel reservoir  20  via a fuel transfer passage  21 . Those skilled in the art will recognize that the source of high pressure fuel  18  can come from a common rail, a fuel pressurization chamber within a unit injector or any other means known in the art for pressurizing fuel to injection levels. In addition, the injector body  22  includes at least one nozzle outlet  23 . 
   Within fuel injector  10 , fuel arriving from high pressure fuel source  18  travels through an unobstructed nozzle supply passage  24  to arrive at a nozzle chamber  25 , which is shown blocked from fluid communication with nozzle outlet  23  by a needle portion  30  of direct control needle valve  11 . Needle portion  30  includes an opening hydraulic surface  34  exposed to fluid pressure in nozzle chamber  25 . Direct control needle valve  11  is normally biased downward to its closed position, as shown, by the action of a biasing spring  35  acting on a lift spacer  31 , which is in contact with a top surface of needle portion  30 . Direct control needle valve  11  also includes a piston portion  32  with a closing hydraulic surface  33  exposed to fluid pressure in a needle control chamber  37 . Opening hydraulic surface  34  is in opposition to closing hydraulic surface  33 . When three way valve  14  is in a first position, needle control chamber  37  is fluidly connected to source of high pressure fuel  18  via a high pressure passage  40  that connects at one end into nozzle supply passage  24 . When valve  14  is at its second position, needle control chamber  37  is fluidly connected to low pressure reservoir  20  via a low pressure passage  41 . Three way valve  14  is moved between its first position and its second position by energizing and deenergizing electrical actuator  16 . When high pressure exists in needle control chamber  37 , direct control needle valve  11  will stay in, or move toward, its downward closed position, as shown. When needle control chamber  37  is connected to low pressure, direct control needle valve  11  will lift to its upward open position if fuel pressure acting on opening hydraulic surface  34  is above a valve opening pressure, which is preferably determined by a biaser, such as the preload of biasing spring  35 . In practice, the valve opening pressure of direct control needle valve  11  is adjusted by choosing a VOP spacer  36  of an appropriate thickness. In addition, the lift distance of direct control needle valve  11  is controlled by choosing an appropriate thickness for lift spacer  31 . Those skilled in the art will appreciate that in the disclosed embodiment, needle control chamber is a closed volume. 
   Referring to  FIG. 2 , electro-hydraulic actuator  12  is shown apart from the fuel injector of  FIG. 1 . In addition,  FIGS. 3–6  show the stator assembly, three way valve assembly and valve member respectively, that make up portions of electro-hydraulic actuator  12 . Three way control valve  14  is preferably positioned in close proximity to piston portion  32  so that the volume of needle control chamber  37  is made relatively small. Those skilled in the art will appreciate that pressure changes in needle control chamber  37  can be hastened by reducing its volume. This issue is addressed by actuator  12  in at least two ways. First, three way valve  14  is positioned in close proximity to the closing hydraulic surface  33  of piston portion  32 . In addition, needle control chamber  37  is preferably designed to be defined at least in part by volume reducing surface features. Thus, those skilled in the art will recognize that some measurable amount of improved performance can be achieved by paying attention to what surface features which define needle control chamber, can be changed in order to reduce the volume of needle control chamber  37  without otherwise undermining performance. In most instance, it will be desirable to make any flow areas associated with needle control chamber  37  less restrictive than the flow areas associated with high pressure passage  40 , low pressure passage  41 , or the flow areas across seats  50  and  51 . When valve member  42  is in contact with lower seat  51 , as shown, needle control chamber  37  is fluidly connected across high pressure seat  50  to nozzle supply passage  24  via high pressure passage  40 . When valve member  42  is lifted upward into contact with high pressure seat  50 , needle control chamber  37  is fluidly connected to a low pressure area that surrounds actuator  12  across low pressure seat  51  via low pressure passage  41 . Thus, valve member  42  can be thought of as being trapped between upper seat  50  and lower seat  51 . Seats  50  and  51  can also be referred to as first and second seats, or vice versa. In order to reduce the influence of hydraulic forces on opposite ends of valve member  42 , a vent passage  83  vents armature cavity  82  to low pressure, and a vent passage  81  connects vented chamber  80  to low pressure. 
   Valve member  42  is preferably operably coupled in a known manner to the moveable portion of an electrical actuator. In the illustrated embodiment, valve member  42  is attached to an armature  62  via a nut  63  that is threaded onto one end of valve member  42 . In particular, an armature washer  63  rests upon an annular shoulder  58  ( FIG. 6 ), upon which armature  62  is supported. Next, a nut washer  64  is placed in contact with the other side of armature  62  followed by a spacer  65 , against which nut  66  bears. Armature  62  and hence valve member  42  are biased downward to close low pressure seat  51  by a suitable biaser, such as biasing spring  67 . Those skilled in the art will appreciate that a hydraulically biaser could be an alternative to the mechanical bias shown. In addition, while electrical actuator  16  has been shown as a solenoid, those skilled in the art will appreciate that any other suitable electrical actuator, such as a piezo (disks and/or a bender) or a voice coil could be substituted in its place. A stator assembly  17  includes a stator  61 , a coil  60  and preferably includes a female/male electrical socket connector  69 . Stator assembly  17  is preferably positioned within a carrier assembly  70  such that there respective bottom surfaces lie in a common plane. By doing so, a solenoid spacer  71  having an appropriate thickness can be chosen to provide a desired air gap between armature  62  and stator  61 . Thus, solenoid spacer  71  is preferably a categorized part that comes in variety of slightly different thicknesses that allow different valves to perform similarly by choosing an appropriate thickness to provide uniformity in the armature air gap from one actuator to another. 
   In order to aid in concentrically aligning upper seat  50  with lower seat  51  along common centerline  38 , valve member  42  includes an upper guide portion  54  with a close diametrical clearance (i.e. a guide clearance) with an upper guide bore  55  located in upper seat component  43 . In addition, valve member  42  also preferably includes a lower guide portion  56  having a relatively close diametrical clearance with a lower guide bore  57  located in lower seat component  45 . Thus, these guide regions tend to aid in concentrically aligning upper and lower seats  50  and  51  during the assembly of three way valve  15  ( FIG. 5 ) as well as substantially fluidly isolating needle control chamber  37  from vented chamber  80  and/or armature cavity  82 , regardless of the position of valve member  42 . Because it is difficult to be certain, before assembly, the depth into seats  50  and  51  that valve member  42  will penetrate before coming in contact in closing that particular seat, three way valve  15  preferably employs a valve lift spacer  44  that is also a category part, and is preferably categorized in a plurality of different thickness groups. Thus, the distance that valve member  42  travels between upper and lower seats  50  and  51  is adjustable by choosing an appropriate thickness for valve lift spacer  44 . 
   In order to reduce the influence of fluid flow forces on the movement of valve member  42 , high pressure passage  40  and low pressure passage  41  preferably include flow restrictions that are restrictive relative to a flow area across respective seats  50  and  51 . While these flow restrictions could be located in upper seat component  43  and/or lower seat component  45 , they are preferably located in valve lift spacer  44  as shown in  FIG. 2 . In particular, the flow characteristics through high pressure passage  40  can be relatively tightly controlled by including a cylindrical segment  47  having a predetermined length and flow area. Furthermore, cylindrical segment  47  is relatively restrictive to flow relative to that across upper seat  50 . Those skilled in the art will appreciate that it is easier to control and consistently machine a flow characteristic via a cylindrical segment as opposed to attempting to consistently control a flow area between stationary seat component and moveable valve member  42 . Likewise, low pressure passage  41  preferably includes a cylindrical segment  48  that is located in valve lift spacer  44 . In order to differentiate the rate at which pressure changes can occur in needle control chamber  37 , cylindrical segment  48  preferably has a different flow area relative to cylindrical segment  47 . This feature is present in the illustrated example as a strategy by which the opening rate of the direct control needle valve is slowed relative to the closure rate of the same. In other words, when direct control needle valve  11  lifts toward its open position, fluid is displaced from needle control chamber  37  through the flow restriction defined by cylindrical segment  48 . When direct control needle valve  11  is closed, high pressure fluid flows into needle control chamber  37  from high pressure passage  40  through the flow restriction defined by cylindrical segment  47 . Since cylindrical segment  48  has a smaller flow area than cylindrical segment  47 , in the illustrated embodiment, the opening rate of direct control needle valve  11  can be made slower than its closure rate, which is often desired. 
   In order to accommodate for the possibility of a slight angular misalignment between the centerline of valve member  42  and the respective centerlines of upper and lower seats  50  and  51 , valve member  42  preferably includes spherical valve surfaces  52  and  53 , which have a common center as shown in  FIG. 6 . Those skilled in the art will appreciate that spherical valve seats  52  and  53  can contact and close valve seats  50  and  51  even in the event of some minor angular misalignment between valve member  42  and its respective seats. In order to insure that the respective passageways, such as nozzle supply passage  24 , provide the proper fluid connection as shown in  FIG. 2 , the stationary components of three way valve  15  preferably include dowel bores  86  and  87  ( FIG. 4 ), which are present to prevent the valve from being misassembled. In order to hold three way valve  15  together, it preferably includes a plurality of fasteners  46  that are threadably received in fastener bores  49  located in upper seat component  43 . Nevertheless, those skilled in the art will appreciate that numerous other strategies could be employed for clamping three way valve  15  together. 
   Although piston  32  could be located in a common body as lower seat component  45 , it is preferably separated from the same by a relatively thin separator  75  and housed in its own piston guide body  76 , as shown in  FIGS. 1 and 2 . 
   Referring now to  FIG. 7 , a three way valve  114  according to another aspect of the present invention is similar to the three way valve previously described except that cylinder passage segments  147  and  148  have been relocated. In particular, like the earlier embodiment, three way valve  114  includes an upper seat component  143  separated from a lower seat component  145  by a valve lift spacer that determines the travel distance of valve member  42  between high pressure seat  150  and low pressure seat  151 . When valve member  42  is in contact with low pressure seat  151 , control passage  39  is fluidly connected to high pressure passage  140  across high pressure seat  150 . When valve member  42  is in its upward position closing high pressure seat  150 , needle control passage  139  is fluidly connected to low pressure passage  141  across low pressure seat  151 . When fluid flows from high pressure passage  140  into control pressure passage  139 , cylindrical passage segment  147  restricts fluid flow to needle control chamber  37  ( FIG. 1 ). As in the previous aspect, cylindrical passage segment  147  is restrictive relative to flow across high pressure seat  150 . 
   When needle valve member  42  is in its upward position closing high pressure seat  150 , fluid can flow from needle control chamber  37  ( FIG. 1 ) into low pressure passage  141  across low pressure seat  151 . In this case, low pressure passage  141  includes a cylindrical passage segment  148 , which performs in much the similar manner as the cylindrical segment  48  described in the earlier three way valve  14 . In other words, cylindrical passage segment  148  is restrictive to flow relative to a flow area across low pressure seat  151 . It should be noted that both cylindrical passage segment  147  and cylindrical passage segment  148  have been relocated from the valve lift spacer of the three way valve  14  described earlier to the needle stop plate  175 , which need not be a category part. Thus, the issues involving valve lift spacer  144  being a category part can be separated from the need to closely control the flow areas through cylindrical passage segments  147  and  148 . The three way valve  114  could be substituted in place of the valve  14  shown in the earlier Figures. Three way valve  114  may also exhibit an advantage over the three way valve  14  described earlier. In particular, it may be subject to lower amounts of leakage. In particular, leakage of high pressure fuel into low pressure passage  141  along the top and bottom surfaces of valve lift spacer  144  is believed to be reduced by relocating low pressure passage  141  into lower seat component  145  and plate stop component  175 . 
   Referring now to  FIG. 8 , a three way valve  214  according to still another aspect of the present invention is similar to those previously described, except that flow to and from needle control chamber  237  is restricted relative to flow areas across high pressure seat  250  and low pressure seat  251  via an orifice plate  260  located in needle control passage  239 . Like the earlier versions, valve member  42  is trapped to move between a high pressure seat  250  located in an upper seat component  243  and a lower seat component  251  located in lower seat component  245 . When valve member  42  is in contact closing low pressure seat  251 , high pressure passage  240  is fluidly connected to needle control chamber  237  past high pressure seat  250  and through cylindrical passage segments  247  and  248 . In this embodiment, the total flow area through cylindrical segments  247  and  248  is restrictive relative to a flow area across high pressure seat  250 , so that this version of the three way valve behaves in much the same manner as the previously described embodiments. When valve member  42  is in its upward position closing high pressure seat  250 , fluid can flow from needle control chamber  237  into low pressure passage  241  past low pressure seat  251 . However, this fluid flow lifts orifice plate  260  up into contact with flat seat  261  to close cylindrical passage segment  247 . Thus, after orifice plate  260  lifts up into contact with flat seat  261 , flow of fluid from needle control chamber  237  is restricted only to cylindrical passage segment  248 , which is restrictive relative to a flow area across low pressure seat  251 . When in its lower position, orifice plate  260  rests atop needle stop  275 . This embodiment differs from the previous embodiments in that it does not include a valve lift spacer. Instead, the surfaces that include high pressure seat  250  and low pressure seat  251  are preferably contoured in a way that the valve travel distance can be controlled to an acceptable tolerance. Alternatively, one of the upper seat component  243  and the lower seat component  245  could be a category part. In still another alternative, each upper seat component  243  could be matched with a separate lower seat component  245  that provides for an acceptable valve travel distance. All three valves according to the present invention could perform in much of a similar manner. 
   INDUSTRIAL APPLICABILITY 
   The present invention finds potential application in any valve whose performance characteristics must be relatively tightly controlled while at the same time providing a structure that permits mass production and consistent performance from one valve to another. In addition, the present invention preferably finds particular application in the case of high speed valves that are required to accommodate relatively low flow volumes, such as pressure control valves employed in fuel injection systems. 
   When fuel injector  10  is in operation, electro-hydraulic actuator  12  works in conjunction with direct control needle valve  11  to control both timing and quantity of each injection event. Each injection event is initialized by raising fuel pressure in high pressure source  18  to injection levels. In some systems, this is accomplished by maintaining a common rail at some desired pressure. Alternatively, source  18  can be a fuel pressurization chamber within a unit injector which is pressurized when a plunger is driven downward, which is usually accomplished with a cam or a hydraulic force. Because valve member  42  is biased downward to close low pressure seat  51 , direct control needle valve  11  will stay in its downward closed position due to the high pressure force acting on closing hydraulic surface  33  of piston portion  32 . Shortly before the timing at which the injection event is desired to start, electrical actuator  16  is preferably energized by supplying an excessive current to coil  60 . Because the speed at which electrical actuator  16  operates is related to the current level supplied to coil  60 , one preferably supplies the maximum available current, which can be substantially higher than an amount of current necessary to cause the armature to move against the action of the spring bias. When sufficient magnetic flux builds, armature  62  and valve member  42  are pulled upwards until spherical valve surface  52  contacts upper or high pressure seat  50 ,  150 ,  250 . When this occurs, needle control chamber  37  is fluidly connected to low pressure fuel reservoir  20  via low pressure passage  41 ,  141 ,  241 . In order for direct control needle valve  11  to lift to its upward open position, fluid must be displaced from needle control chamber  37  toward low pressure reservoir  20 . The rate at which direct control needle valve  11  opens is slowed by restricting this flow through cylindrical segment  48 ,  148 ,  248 . This aids in allowing fuel injector  10  to produce some rate shaping. Shortly before the desired end of an injection event, current to electrical actuator  16  is reduced or terminated to a level that allows spring  67  to push armature  62  and valve member  42  downward until spherical seat  53  comes in contact with low pressure seat  51 ,  151 ,  251 . When this occurs, high pressure fluid originating in nozzle supply passage  24  flows through high pressure passage  40 ,  140 ,  240  past high pressure seat  50 ,  150 ,  250  and into needle control chamber  37 . The rate at which pressure builds in needle control chamber  37  and hence the response time from when current is terminated until direct control needle valve  11  moves toward its closed position can be influenced by appropriately sizing cylindrical segment  47 ,  147 , or the combined flow area of cylindrical segments  247  and  248 . 
   In order to produce fuel injectors  10  that behave consistently, the present invention preferably includes a structure for three way valve  15  that alleviates some of the problems that have plagued past valves. By including flow restrictions (cylindrical segments  47 ,  147 ,  247  and  48 ,  148 ,  248 ) away from valve seats  50 ,  150 ,  250  and  51 ,  151 ,  251 , respectively fluid flow forces that can interfere with movement of the valve member  42  are reduced since the pressure differentials often associated with valves are moved away from the valve seats. Furthermore, by locating these flow restrictions in the valve lift spacer  44  ( FIGS. 1–5 ), stop plate  175  ( FIG. 7 ) or orifice plate  260  ( FIG. 8 ), the flow restrictions can be more easily manufactured, and permits valve opening and closing pressure control to be set somewhat independently. This same strategy allows more consistency in performance among valves since their performance is desensitized from the flow areas across the respective seats of the valves which will likely be different from one valve to another due at least in part to the fact that each component has geometrical tolerances that render them realistically manufacturable. Because the cylindrical segments formed in the valve lift spacers can be made with great consistency, the behavior of the respective valves can be made more consistent. 
   Another feature of the three way valve  15  of the present invention that can provide for more consistent performance includes the use of a valve lift spacer as a category part. In other words, in order for consistency to be maintained, the valve travel distance from one valve to another should be made as consistent as possible. In the case of the present valve, this is accomplished by choosing a valve lift spacer for each individual valve with a thickness that results in a relatively uniform travel distance from one valve to another. In other words, each valve should have relatively uniform travel distances, but this is accomplished by employing valve lift spacers of a variety of thicknesses in each of the different valves. In the case of the present invention, the valve travel distance is preferably on the order of about 30 microns, or between 25 and 35 microns. In any event, the strategy of the present invention can be employed to reliably produce valves with consistent lifts less than about 50 microns. This is accomplished by grouping valve lift spacers in a plurality of different thickness groups. Preferably, each of these groups contain valve lift spacers of a specific predetermined thickness plus or minus about three microns. 
   Another strategy employed by the present invention in order to improve response time includes defining the needle control chamber, which is referred to in the claims as the “third passage”, at least in part with volume reducing features. Ordinarily, this will be accomplished by paying attention to machining the various components that make up needle control chamber  37  in order to reduce its volume. By reducing its volume, it can respond to pressure changes more quickly. For instance, in the present invention, this strategy is employed, for example, by making the vertical portion of needle control chamber  37  only extend a portion of the way into valve lift spacer  44 . Thus, the top surface of this segment could be considered a volume reducing surface feature. 
   Those skilled in the art will appreciate that leakage through the valve, especially during fuel injection events, is generally undesirable. Fluid leakage is generally reduced by relying upon a three way valve as in the present invention instead of a two way valve that relies upon leakage to produce its pressure changes as in some other known needle control strategies. In addition, the embodiments of  FIGS. 7 and 8  seek to further reduce potential leakage through the three way valve by moving the low pressure passage away from the valve. Those skilled in the art will appreciate that the pressure differentials in the three way valve can be extremely high during a fuel injection event. This pressure acts to push the upper seat component away from the lower seat component, and fluid will tend to migrate in the area especially on the upper and lower surfaces of the valve lift spacer. By locating the low pressure passage away from this area, these embodiments may exhibit better performance with regard to reducing leakage. Reducing leakage can generally improve the reliability and predictability of the fuel injection quantity. Since a fuel injection quantity is often defined by the control valve on time duration, any fuel that leaks past the valve can necessarily reduce the amount of fuel actually injected below a predicted amount. 
   Those skilled in the art will appreciate that that various modifications could be made to the illustrated embodiment without departing from the intended scope of the present invention. For instance, the third passage (needle control chamber  37 ) need not necessarily be a closed volume in another application of the present invention. Thus, those skilled in the art will appreciate the other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.