Patent Abstract:
Because of the relatively high pressures experienced within fuel injectors, several internal components can undergo substantial deformation each time fuel is pressurized to injection levels. In some instances, such as when a solenoid operated control valve is positioned near a distortion region, the internal distortion can cause a fuel injector to behave with less predictability, and can undermine consistency from one fuel injector to another, since distortion levels and affects therefrom are likely to vary substantially from one injector to another. In order to desensitize fuel injector performance to this internal distortion, a deflection cavity is disposed within the fuel injector between the distortion region and the needle valve of the fuel injector. This strategy finds particular applicability to needle control valves disposed deep within fuel injectors in order to control fluid pressure on a closing hydraulic surface of a direct control needle valve, which opens and closes the nozzle outlets.

Full Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to desensitizing fuel injector performance to internal component distortion, and more particularly to a solenoid carrier assembly that includes a deflection cavity to desensitize solenoid armature air gap to distortion in the fuel injector component stack.  
         BACKGROUND  
         [0002]    Engineers are constantly seeking ways to improve fuel injector performance in order to accomplish various goals, such as reducing undesirable engine exhaust emissions. One strategy that has been adopted in this regard is the use of a hydraulic direct control needle valve to open and close the nozzle outlets of the fuel injector. In such fuel injectors, a needle control valve is moveable between positions that either expose a closing hydraulic surface on a needle valve member to high pressure or low pressure. While this innovation has greatly improved the ability to electronically control fuel injection characteristics, there remains room for improvement.  
           [0003]    One area in need of potential improvement relates to the response time of the direct control needle valve to an electrically actuated needle control valve. Among other things, the response time can be improved if the volume of the needle control chamber, which applies either high or low pressure to the closing hydraulic surface of the needle valve, can be reduced. One strategy for accomplishing this goal is to locate the needle control valve and its associated electrical actuator deep inside the fuel injector in close proximity to the direct control needle valve. Another potential strategy for reducing response time is to reduce the travel distance of the needle control valve member, which acts as a pressure switch in exposing the closing hydraulic surface of the direct control needle valve to either high pressure or low pressure. While these two strategies appear to have promise, their implementation can potentially introduce new problems.  
           [0004]    In one class of directly controlled fuel injectors, a solenoid is the chosen type of electrical actuator to control movement of the needle control valve. In order for these relatively small fast moving electrically actuated valves to behave predictably, the armature air gap should be known in order to produce predictable results. In order for the valve to perform in a manner consistent with other valves produced in mass production, the air gap should be uniform among valves in order to insure consistent performance in one fuel injector compared to another. These issues are further complicated by the fact that the armature air gap should be relatively small in order to extract the maximum performance from the interaction between the solenoid coil and stator relative to the armature. Furthermore, because the needle control valve wants to be located in close proximity to the direct control needle valve, it might have to be located under a distortion region within the fuel injector, which relates to the area underneath a plunger within a fuel injector. In other words, each time a plunger reciprocates within a fuel injector, fuel is raised to extremely high injection pressure levels. In turn, these pressure forces cause some measurable amount of distortion within the fuel injector. While these distortions are relatively small in magnitude, they can approach a magnitude that is on the same order as an armature air gap tolerance. Thus, in some situations it is possible for component distortion within a fuel injector to cyclically alter the needle control valve&#39;s armature air gap to the point that it briefly distorts the armature air gap out of acceptable geometrical tolerances. As such, the predictability of performance is undermined, and the variability in distortion from one fuel injector to another undermines the ability to mass produce valves that behave consistently between different fuel injectors.  
           [0005]    Another potential problem introduced by locating an electrically actuated needle control valve in close proximity to the direct control needle valve relates to packaging considerations. In other words, the act of locating the needle control valve deep within the fuel injector further pressures packaging considerations that insure that all of the various fuel injector performance functions and structure can be packaged in an available envelope of space.  
           [0006]    One potential strategy for desensitizing injector performance to geometrical distortions taking place within the fuel injector is to employ a two way valve as the needle control valve instead of a three way valve. In the case of a two way valve such as that shown in Heavy Duty Diesel Engines—The Potential of Injection Rate Shaping for Optimizing Emissions and Fuel Consumption”, presented by Messrs. Bernd Mahr, Manfred Dürnholz, Wilhelm Polach, and Hermann Grieshaber, Robert Bosch GmbH, Stuttgart, Germany, at the 21st International Engine Symposium, May 4-5, 2000, Vienna, Austria. The control valve member merely moves into and out of contact with a single seat, rather than moving between two seats as in the case of a three way valve. While such a two way valve strategy can potential assist in desensitizing fuel injector performance to component distortion, it necessarily suffers from other draw backs rendering it less than desirable. For instance, a two way valve strategy inherently results in substantial wastage of high pressure fuel since the fuel injector is controlled by opening its high pressure fuel passage directly to a low pressure drain during injection events. Even when flow restrictions are placed in the control passageways, the amount of fuel spilling leakage can be so substantial as to undermine the overall efficiency of the fuel injection system.  
           [0007]    The present invention is directed to one or more of the problems set forth above.  
         SUMMARY OF THE INVENTION  
         [0008]    In one aspect, a solenoid carrier assembly includes a carrier with a top surface separated from a bottom surface by a side surface. A stator assembly is attached to the carrier and includes an exposed bottom surface. A deflection cavity is disposed in the carrier between the top surface of the carrier and the stator assembly.  
           [0009]    In another aspect, a fuel injector includes a plurality of stacked components, which include a solenoid carrier assembly positioned between a barrel and a needle valve. The solenoid carrier assembly includes a deflection cavity disposed in the solenoid carrier assembly between its top surface and a stator assembly. The deflection cavity is located underneath a plunger bore disposed in the barrel.  
           [0010]    In still another aspect, a method of desensitizing armature air gap to component distortion in a fuel injector includes a step of assembling a stator assembly to a carrier, which has a distortion region. The distortion region is separated from a portion of a top surface of the stator assembly with a deflection cavity. The bottom surface of the carrier and the bottom surface of the stator assembly are made flush.  
           [0011]    In another aspect, a carrier assembly includes a stator assembly attached to a carrier. The carrier includes a ball valve seat. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a front sectioned diagrammatic view of a fuel injector according to the present invention;  
         [0013]    [0013]FIG. 2 is a sectioned side diagrammatic view of the fuel injector of FIG. 1;  
         [0014]    [0014]FIG. 3 is a sectioned side view of the needle control valve assembly from the fuel injector of FIGS. 1 and 2;  
         [0015]    [0015]FIG. 4 is an isometric view of a stator assembly according to one aspect of the present invention;  
         [0016]    [0016]FIG. 5 is a top view of the stator assembly of FIG. 4;  
         [0017]    [0017]FIG. 6 is a sectioned view of the stator assembly of FIG. 5 as viewed along section line A-A;  
         [0018]    [0018]FIG. 7 is a sectioned view of the stator assembly of FIG. 5 as viewed along section line B-B; and  
         [0019]    [0019]FIG. 8 is a bottom view of the stator assembly of FIGS. 4 and 5. 
     
    
     DETAILED DESCRIPTION  
       [0020]    Referring to FIGS. 1 and 2, a fuel injector  14  includes an injector body  21  that can be thought of as including an upper portion  26  and a lower portion  28 . Fuel injector  14  can also be thought of as being divided between fuel pressurization assembly  27  and a direct control nozzle assembly  29 . In the fuel injector  14  illustrated, fuel pressurization assembly  27  is located in upper portion  26 , whereas direct control nozzle assembly  27  is located in lower portion  28 . Although the fuel injector  14  shows the fuel pressurization assembly  27  and the direct control nozzle assembly  29  joined into a unit injector  14 , those skilled in the art will appreciate that those respective assemblies could be located in separate bodies connected to one another with appropriate plumbing. The fuel pressurization assembly  27  includes a pressure intensifier  30  and a flow control valve  34 , which is operably coupled to an electrical actuator  32 . Direct control nozzle assembly  29  includes a needle control valve assembly  36  that is operably coupled to an electrical actuator  38 , which is located in and attached to lower portion  28 . In addition, a direct control needle valve  39  is controlled in its opening and closing by needle control valve assembly  36 , and hence electrical actuator  38 . Pressurized oil enters injector body  21  through its top surface at actuation fluid inlet  20 , and used low pressure oil is recirculated back to a sump (not shown) via an actuation fluid drain  22 . Fuel is circulated among the lower portions  28  of fuel injectors  14  via fuel inlet  24 .  
         [0021]    Pressure intensifier  30  includes a stepped top intensifier piston  42  and a plunger  44 , which is preferably a free floating plunger. Intensifier piston  42  is biased to its retracted position, as shown, by a return spring  43 . The stepped top of intensifier piston  42  allows the initial movement rate, and hence possibly the initial injection rate, to be lower than that possible when the stepped top clears its counter bore. Return spring  43  is positioned in a piston return cavity  46 , which is vented directly to the area underneath the engine&#39;s valve cover via an unobstructed vent passage  47 . Piston  42  and plunger  44  move in barrel  31 , which is located near the top of the component stack  19 . Free floating plunger  44  is biased into contact with the underside of intensifier piston  42  via low pressure fuel acting on one end in fuel pressurization chamber  50 . Plunger  44  preferably has a convex end in contact with the underside of intensifier piston  42  to lessen the effects of a possible misalignment. In addition, plunger  44  is preferably symmetrical about three orthogonal axes such that fuel injector  14  can be more easily assembled by inserting either end of plunger  44  into the plunger bore located within injector body  21 . When intensifier piston  30  is undergoing its downward pumping stroke, fuel within fuel pressurization chamber  50  is raised to injection pressure levels. Any fuel that migrates up the side of plunger  44  is preferably channeled back for recirculation via a plunger vent annulus and a vent passage  52 . Pressure intensifier  30  is driven downward when flow control valve  32  connects actuation fluid passages  40 / 41  to high pressure actuation fluid inlet  20 . Between injection events, flow control valve  34  connects actuation fluid passages  40 / 41  to low pressure drain  22  allowing the intensifier  30  to retract toward its retracted position, as shown, via the action of return spring  33  and fuel pressure acting on the underside of plunger  44 . Thus, when pressure intensifier  30  is retracting, fresh fuel is pushed into fuel pressurization chamber  50  past check valve  53  via fuel inlet  24 . Check valve  53  includes carrier  102  having a ball valve seat  113  that is a distance away from top surface  103  that ball valve member  116  is below top surface  103 .  
         [0022]    A flow control valve  34  includes an electrical actuator  32 , which in the illustrated embodiment is a solenoid, but could equally be any other suitable electrical actuator known in the art including, but not limited to, piezos, voice coils, etc. Flow control valve  34  includes a valve body that includes separate passages connected to actuation fluid inlet  20 , actuation fluid drain  22  and actuation fluid passages  40 / 41 , respectively. Flow control valve  34  includes a spool valve member biased via a biasing spring to a first position that fluidly connects actuation fluid passage  40 / 41  to actuation fluid drain  22 . When electrical actuator  32  is energized, a spool valve member moves away from the coil toward a second position. At this energized position, the spool valve member closes the fluid connection between actuation fluid passage  40 / 41  and drain  22 , and opens high pressure inlet  20  to actuation fluid passages  40 / 41 .  
         [0023]    When pressure intensifier  30  is driven downward, high pressure fuel in fuel pressurization chamber  50  can flow via nozzle supply passage  67  to the nozzle chamber  65 , and out of nozzle outlets  64  if direct control needle valve  39  is in an open position. A portion of nozzle supply passage  67  extends between top surface  103  and bottom surface  104  of carrier  102 . A reverse flow valve member  117  is positioned in nozzle supply passage  67  adjacent top surface  103 , and acts to reduce penetration of combustion gases into fuel pressurization chamber  50 . When direct control needle valve  39  is in its closed position as shown, nozzle chamber  65  is blocked from fluid communication with nozzle outlets  64 . Direct control needle valve  39  includes a needle valve member made up of a needle portion  72  separated from a piston portion  69  by a lift spacer  66 . Thus, the needle valve member in this embodiment is made up of several components for ease of manufacturability and assembly, but could also be manufactured from a single solid piece. The needle valve member includes an opening hydraulic surface  63  exposed to fluid pressure in nozzle chamber  65  and a closing hydraulic surface  61  exposed to fluid pressure in a needle control chamber  60 . The thickness of lift spacer  66  preferably determines the maximum opening travel distance of direct control needle valve  39 . The direct control needle valve  39  is biased toward its downward closed position, as shown, by a biasing spring  62  that is compressed between lift spacer  66  and a VOP (valve opening pressure) spacer  68 . Thus, the valve opening pressure of the direct control valve  39  can be trimmed at time of manufacture by choosing an appropriate thickness for VOP spacer  68 .  
         [0024]    A needle control chamber  60  is fluidly connected to either low pressure fuel inlet  24  or to nozzle supply passage  67  depending upon the positioning of needle control valve assembly  36 . When needle control chamber  60  is fluidly connected to nozzle supply passage  67 , direct control needle valve  39  will remain in, or move toward, its closed position, as shown, under the action of fluid pressure forces on closing hydraulic surface  61  and the spring force from biasing spring  62 . When needle control chamber  60  is fluidly connected to fuel inlet  24 , while nozzle passage  67  and hence nozzle chamber  65  are above a valve opening pressure, the fluid forces acting on opening hydraulic surface  63  are sufficient to lift the direct control needle valve  39  upward towards its open position against the action of biasing spring  62  to open nozzle outlets  64 .  
         [0025]    Referring in addition to FIGS. 3 and 4, the inner workings of needle control valve  36  are illustrated. Valve assembly  36  includes a carrier assembly  74  which defines a portion of nozzle supply passage  67 , a connection passage  70 , a low pressure passage  71  and a needle control passage  59 . The valve assembly  36  is a two position three way valve that includes a needle control valve member  89  that is moveable between contact with a high pressure seat  94  and a low pressure seat  95 . Depending upon the position of valve member  89 , needle control passage  59 , which is fluidly connected to needle control chamber  60  (FIGS. 1 and 2), is fluidly connected to nozzle supply passage  67  via connection passage  70  or to fuel inlet  24  via low pressure passage  71 . Needle control valve assembly  36  includes a second electrical actuator  38  which in the illustrated embodiment is a stator assembly  37 , but could also be another type of electrical actuator, such as a piezo, a voice coil, etc. The stator assembly  37  includes a stator  90 , a coil  92  and a pair of female electrical socket connectors  57  that are electrically connected to coil  92 . Stator assembly  37  is attached to carrier  102  to produce a carrier assembly  74 . The female electrical socket connection  57 , which could instead be male, opens through top surface  103  and permits an electrical extension  56  to mate with stator assembly  37  within injector body  21  while providing exposed terminals for insulated conductors  55  outside of upper portion  26 . As illustrated, the socket connection is preferably oriented at a small angle, greater than zero, with respect to centerline  18 . Valve member  89  is biased downward to close low pressure seat  95  by a biasing spring  91  via an armature  93  that is attached to valve member  89 . When coil  81  is energized, armature  93  is lifted upward causing valve member  89  to open low pressure seat  95  and close high pressure seat  94 . Because the flow area is past seats  94  and  95  effect the performance of the fuel injector  14 , such as by effecting the opening and/or closing rate of direct control valve  29 , flow restrictions  96  and  97  are included. In particular, flow restriction  96 , which is preferably manufactured in a valve lift spacer  78  as a flow area that is restrictive relative to the flow area past seat  94 . Likewise, flow restriction orifice  97  preferably has a flow area that is restricted relative to the flow past low pressure seat  95 . Because these respective orifices  96  and  97  are based upon simple bore diameters rather than a clearance area between two separate moving parts, the performance between respective fuel injectors can be made more uniform. Furthermore, because these features are machined in a single valve lift spacer  78 , the manufacturability and assembly of needle control valve assembly  36  can be improved.  
         [0026]    Referring in addition to FIGS.  5 - 8 , carrier assembly  74  includes a stator assembly  37  attached to a carrier  102 . Stator assembly  37  is preferably attached to carrier  102  by including adhesive along the cylindrical side bore that makes up cavity  106 . Stator assembly  37  is preferably advanced into cavity  106  until a peripheral raised portion  101  comes in contact with an internal surface  107  of carrier  102 . With this construction, a deflection cavity  100  is created between internal surface  107  and a majority of the top surface of stator assembly  37 . This deflection cavity is located directly beneath a deflection region  54  in carrier  102 , which itself is located underneath fuel pressurization chamber  50 , which forms a portion of the plunger bore (FIG. 2). When fuel is pressurized in fuel pressurization chamber  50 , distortion region  54  is highly stressed and deforms in the direction of fuel injector tip along centerline  18 . Preferably, the height of raised portion(s)  101  is preferably substantially larger than the expected deformation of region  54 . Raised portion  101  is preferably a flat topped ridge arranged in circular pattern. Those skilled in the art will recognize that raised portion  101  could be located on surface  107  of carrier  102 . In this way, any distortion in distortion region  54  changes the shape of deflection cavity  100  without causing substantial deformations to occur in stator assembly  37 . This in turn prevents the distortion occurring above from substantially altering the air gap  79  that exists between armature  93  and the bottom surface  111  of stator assembly  37 .  
         [0027]    Other features that help maintain air gap  79  include a desirability in having the bottom surface  111  of stator assembly  37  about flush with the bottom surface  104  of carrier  102 . When this feature is combined with an air gap spacer  75  that contacts both bottom surfaces  104  and  111  as shown in FIG. 3, the compressive forces acting on raised portion  101  are transmitted downward along the peripheral portion of stator assembly  37  to the air gap spacer  75 , and from there downward in the component stack  19  (FIG. 2).  
         [0028]    In order to conserve space and reduce part count, carrier assembly  74  preferably includes other functional features, such as plumbing passages, so that it provides more functionality than merely acting as a support for the stator assembly  37 . In particular, carrier  102  includes a top surface  103  separated from a bottom surface  104  by a circumferential side surface  105 . Side surface  105  includes a pair of annular ridges  114  and  115 , between which fuel supply passage  112  opens. The clearance between ridges  114  and  115  with the inner surface of the casing component shown in FIGS. 1 and 2 provide for an edge filter  51  for fuel entering fuel injector  14  through fuel inlet  24  on its way to fuel pressurization chamber  50 . In order to prevent the back flow of fuel through fuel supply passage  112 , it includes a check valve  53  that seats in a conical valve seat  113 . Apart from this plumbing, carrier assembly  74  includes a portion of nozzle supply passage  67 , which extends between top surface  103  and bottom surface  104 .  
       INDUSTRIAL APPLICABILITY  
       [0029]    Each engine cycle can be broken into an intake stroke, a compression stroke, a power stroke and an exhaust stroke. During each engine cycle, each fuel injector  14  has the ability to inject up to five or more discrete shots per engine cycle. While a majority of these injection events will take place at or near the transition from the compression to power strokes, injection events can take place at any timing during the engine cycle to produce any desirable effect. For instance, an additional small injection event elsewhere in the engine cycle might be useful in reducing undesirable emissions. During each engine cycle, a number of basic steps are performed to inject fuel, and each of those acts is performed at a timing and in a number to produce a variety of fuel injection sequences, which include one or more injection events.  
         [0030]    Among the steps performed at least once each engine cycle in each portion of the injection system (e.g., fuel injector) for each engine cylinder is the step of positioning a needle control valve  36  in a position that fluidly connects the needle control chamber  60  to the fuel pressurization chamber  50 , and fluidly blocks the needle control chamber  60  to the low pressure passage  71 . In the illustrated embodiment, that is accomplished by biasing the needle control valve member  89  into contact to close low pressure seat  95  by a spring  91 . The valve member  89  could be biased in the other direction and operate in a manner opposite to that described with regard to the illustrated embodiment. In the illustrated embodiment, the previously described act is performed by a three way valve. With this configuration, the pressurization chamber  50  is only briefly connected to the fuel inlet  24  when the needle control valve member  89  is moving between low pressure seat  95  and the high pressure seat  94 . Between injection events when pressure in fuel pressurization chamber  50  is relatively low, very little leakage occurs past needle control valve assembly  36 . In addition, little leakage occurs during each injection event since the respective high pressure seat  94  is closed. When the needle control chamber  60  is fluidly connected to the fuel pressurization chamber  50  and blocked from the low pressure passage  71 , no fuel injection takes place. In other words, when that occurs, direct control needle valve  39  is preferably held in or moved toward its downward closed position, as shown.  
         [0031]    Another act that is performed at least once during each engine cycle includes increasing fuel pressure within the fuel pressurization chamber at least in part by moving the flow control valve  34  to a first position. The first position described is preferably the position at which valve  34  opens actuation fluid inlet  20  to actuation fluid passage  40 / 41 . When this step is performed, high pressure actuation fluid bears down onto the intensifier piston  42 , which compresses fuel in fuel pressurization chamber  50  to injection levels.  
         [0032]    Another act that is performed at least once each engine cycle, and in some cases many times per engine cycle, includes moving the needle control valve  36  to a second position that fluidly connects the needle control chamber  60  to the low pressure passage  71 , and fluidly blocks the needle control chamber  60  to the fuel pressurization chamber  50 . This act is accomplished at least in part by supplying electrical energy to direct control nozzle assembly  29 . In the illustrated example, that includes supplying electrical energy to terminals  55  located outside the upper portion of fuel injector  14 , and channeling that electricity via electrical socket connection  57  to electrical actuator  32  located in the lower portion  28  of the injector body  21 . When this occurs, needle control valve member  89  is lifted to close high pressure seat  94  such that needle control chamber  60  is fluidly connected to low pressure passage  71 . If fuel pressure in nozzle chamber  65  is above a valve opening pressure, the direct control needle valve  39  will move to, or stay in, an open position that fluidly connects fuel pressurization chamber  50  to nozzle outlet  64  via nozzle supply passage  67 . If fuel pressure is below a valve opening pressure, the direct control needle valve  39  will move toward, or stay in, its biased closed position due to the action of biasing spring  62  being the dominant force.  
         [0033]    Another step that occurs at least once each engine cycle includes decreasing fuel pressure in the fuel pressurization chamber  50  at least in part by moving a flow control valve  34  to a position that fluidly connects the actuation fluid passage  40 / 41  to the actuation fluid drain  22 . In the illustrated embodiments, this is the act that allows the fuel injector  14  to reset itself for a subsequent injection sequence. When this step occurs, intensifier piston  42  and plunger  44  will retract upward toward their retracted positions as shown, under the respective actions of return spring  43  and fuel pressure in fuel pressurization chamber  50 . In the illustrated embodiment, this act is accomplished by ending electrical energy to actuator  32  in order to allow flow control valve  34  to return to its biased position that opens actuation fluid drain  22 .  
         [0034]    Referring now to FIG. 3, the needle control valve assembly portion of the component stack  19  is constructed by first trapping valve member  89  between an upper seat component  76  and a lower seat component  77 , which are separated by a valve lift spacer  78  having a nominal thickness. Next, the valve travel distance is measured. If its travel distance deviates more than a predetermined amount from a predetermined desired travel distance, a valve lift spacer  78  having a slightly different thickness is chosen in order to cause valve member  89  to have the desired predetermined travel distance. Next, armature  93  is attached to one end of valve member  89 . Next, an armature air gap spacer  75  is positioned atop upper seat component  76 . A biasing spring  91  is placed on top of armature  93 . Finally, a carrier assembly  74  is positioned on top of air gap spacer  75  such that the bottom surfaces  111  and  104  of stator assembly  37  and carrier  102 , respectively, are in contact with the top surface of air gap spacer  75 . At this point, air gap  79  is measured, if the measured air gap deviates from a predetermined air gap by greater than an acceptable tolerance, an air gap spacer  75  having a different thickness is substituted in place. This substituted air gap spacer should be chosen to have a thickness that results in an air gap  79  having a predetermined magnitude. Thus, when manufacturing a large number of valves, air gap spacer  75  can be provided in a range of thicknesses in order to insure that all of the manufactured valves can be made to have consistently sized air gaps  79 .  
         [0035]    Carrier assembly  74  is manufactured by first machining the various passageways  67  and  112  therethrough. In addition, cavity  106  is machined in a conventional manner. Next, a stator assembly  37  is preferably glued to the cylindrical surface that defines a portion of cavity  106  until raised portion  101  comes into contact with the undersurface  107  of carrier  102 . Some care should be taken to prevent an excessive amount of adhesive from finding its way into deflection cavity  100  during this attachment process. After stator assembly  37  is attached to carrier  102 , their bottom surfaces  104  and  111  are ground to be flush with one another and parallel to top surface  103 .  
         [0036]    During an injection event, the downward movement of pressure intensifier  30  causes fuel pressure in pressurization chamber  50  to rise dramatically. This pressure in turn causes a downward distorting force on carrier assembly  74  in distortion region  54 . Preferably, the height of raised portion(s)  101  is preferably larger than the expected deformation of distortion region  54  into deflection cavity  100 . In this way, the distortion is not carried through to stator  90  in a way that could substantially alter air gap  79 . In the illustrated embodiment, raised portion  101  has a height on the order of about 100 microns, and the expected distortion of distortion region  54  is less than 100 microns across the complete operating range of fuel injector  14 .  
         [0037]    Those skilled in the art will appreciate that various modifications could be made to the illustrated embodiment without departing from the intended scope 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.

Technology Classification (CPC): 5