Abstract:
Particularly in the fuel injector art, two components may define a high pressure space that is sealed against leakage via a planar sealing land between the two components. If a leak develops in the planar contact area between the two components, it can act to wedge the two components apart, which tends to exacerbate the leakage problem, and so on. Since some leakage between the two components is almost inevitable for a variety of reasons known in the art, a strategy that arrests the leak before it can produce the component separating wedge affect would be beneficial. This can be accomplished by positioning a leak arrest volume, which may be vented, around a majority of the perimeter of the high pressure space. The usage of a leak arrest volume finds particular application in fuel injectors, especially a class of common rail fuel injectors that are maintained at high pressure during prolonged periods between injection events.

Description:
TECHNICAL FIELD 
   The present invention relates generally to limiting leakage between components that define a high pressure space, and more particularly to implementation of a leak arrest volume around a planar sealing land between two components. 
   BACKGROUND 
   In many devices, such as fuel injectors, a plurality of components are positioned in contact with one another to define a high pressure space. These components are clamped together in an effort to prevent leakage through the planar sealing land between the components. In the case of fuel injectors, these components can be charged with sealing against leakage in the face of relatively high pressures, which can be on the order of 200 MPa or greater. Engineers have observed that when a leak develops between adjacent components, at such high pressures, it can sometimes act as a wedge to separate the two components creating an even larger leak path. In other words, as the leak penetrates the sealing land between the components, it remains at a relatively high pressure pushing the two components apart, which creates an even larger leak area. This action can cause even further component separation, resulting in even more leakage. 
   In the case of fuel injectors, this type of leakage is undesirable for several reasons. First, any leaked fuel that was at one time pressurized, arguably results in a waste of energy, since the fuel was pressurized from engine power but not injected into the same. In addition, leakage can undermine the ability to accurately predict the performance of a fuel injector. For instance, if fuel is being leaked that was expected to be injected, the fuel injector may be injecting less fuel than it should. In some fuel injectors, leakage can also reduce injection pressure. In addition, leakage can be a source of variable performance among a plurality of fuel injectors in a given engine. For instance, if each fuel injector exhibits substantially different leakage rates, that can cause differing fuel injector performance. In other words, the plurality of fuel injectors could be injecting different amounts of fuel based upon an identical set of control signals. 
   One previous strategy for dealing with sealing against leakage between fuel injector components with a planar interface, is to reduce the area of the planar surface so that more of the clamping load is concentrated in a smaller area. This strategy, for instance, is illustrated in co-owned U.S. Pat. No. 5,897,058, invented by Coldren et al. While such a strategy can be effective in many applications, other factors, such as spatial limitation features, can reduce the applicability of such a strategy. For instance, in some situations there may be so many fluid passageways, dow alignment bores and/or fastener bores that an implementation of a reduced sealing land area strategy can cause other undesirable effects, such as component distortion that may lead to even more leakage. 
   The present invention is directed to one or more of the problems set forth above. 
   SUMMARY OF THE INVENTION 
   In one aspect, a component sub-assembly includes a first component with a planar surface in contact with a planar surface of a second component. The first and second components define a high pressure space that passes through the planar surfaces at a perimeter. The first and second component define at least one leak arrest volume that is distributed to surround at least a majority of the perimeter. 
   In another aspect, a fuel injector includes a plurality of stacked components that include a first component and a second component in contact with one another in a plane. The first and second components define high pressure space that passes through the plane at a perimeter. The first and second components define at least one leak arrest volume that is distributed to surround at least a majority of the perimeter. 
   In still another aspect, a method of limiting leakage between components includes a step of placing a planar surface of a first component in contact with a planar surface of the second component to define a high pressure space with a perimeter. At least one leak arrest volume is defined between the first and second components. The leak arrest volume is distributed to surround at least a majority of the perimeter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectioned side diagrammatic view of the 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 a top view of a valve lift spacer from the fuel injector of  FIG. 1 ; and 
       FIG. 4  is a bottom view of the valve lift spacer of FIG.  3 . 
   

   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  and needle control passage  39 . 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 needle control passage  39  and 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 needle control passage  39  and 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  37  is a closed volume. 
   Referring to  FIG. 2 , electro-hydraulic actuator  12  is shown apart from the fuel injector of FIG.  1 . 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 many instances, 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. 
   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 stop plate  75  and housed in its own piston guide body  76 , as shown in  FIGS. 1 and 2 . Leak arrest volume(s) and vent paths could also be used to limit leakage between lower seat component  45 , stop plate  75  and guide body  76 . In such a case, needle control chamber  37  would be the high pressure space of the claims. 
   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  66  that is threaded onto one end of valve member  42 . In particular, an armature washer  63  rests upon an annular shoulder  58 , 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 to better facilitate bringing electrical energy to actuator  16  via conductors (not shown) penetrating down through injector body  22 . Stator assembly  17  is preferably positioned within a carrier assembly  70  such that their 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  14  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  14  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  47  and  48 , respectively, 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. Those skilled in the art will appreciate that spherical valve surfaces  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  14  preferably include dowel bores, which are present to prevent the valve from being misassembled. In order to hold three way valve  14  together, it preferably includes a plurality of fasteners that are threadably received in fastener bores 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  14  together. 
   Referring now in addition to  FIGS. 3 and 4 , valve lift spacer  44  includes leak arrest features to limit leakage between valve lift spacer  44  and upper and lower seat components  43  and  45 . Valve lift spacer  44  includes four fastener bores  46  that allow valve  14  to be assembled. Proper alignment in the assembly of valve  14  is insured via the usage of dowels and dowel bores  90 . Valve lift spacer  44  includes a first side  91  with a first planar surface  101  that creates a sealing land in contact with a second planar surface  102  of side  92  of upper seat component  43 . When together as shown in  FIGS. 1 and 2 , components  43  and  44  could be considered a component sub-assembly  15  that defines a portion of control volume  85 , which can also be considered a high pressure space when fuel pressure in the same is high. High pressure space  85  is bounded by a first perimeter  86 , while the components themselves are bounded by a perimetrical side surface  96 . In addition to control volume  85 , components  43  and  44  also define a portion of nozzle supply passage  24  and high pressure passage  40 , each of which could also be considered a high pressure space according to the present invention. In order to arrest the wedge affect of a potential leak, valve lift spacer  44  also includes a leak arrest volume  98  that encloses first perimeter  86  and is distributed around passages  24  and  40 . Leak arrest volume  98  is vented to the low pressure space adjacent perimetrical side surface  96  inside injector casing via vent passage  88 . 
   Those skilled in the art will appreciate that vent passages  88  may not be desirable in the case of some fuel injectors. For instance, vent passages  88  would likely be desirable for common rail applications in which the fuel injector is maintained at relatively high pressures for the long durations between injection events, but vent passages  88  could be omitted in the case of fuel injectors that are only cyclically at high pressures. Because valve lift spacer  44  is a relatively thin component, leak arrest volume  98  and vent passage(s)  88  can potentially be manufactured via a coining or stamping process at the blank stage. If vent passage(s)  88  are omitted, leak arrest volume  98  should have a sufficiently large volume that its pressure can be maintained below some predetermined level, but that pressure has the ability to decay between injection events when pressure is low. 
   Referring now to  FIG. 4 , valve lift spacer  44  also includes a third planar surface  103  of a third side  93  in contact with a fourth planar surface  104  of a fourth side  94  of lower seat component  45 . These two components also define a portion of control volume  85  that is bounded at the sealing land by second perimeter  87 . Like the opposite side of valve lift spacer  44 , third side  93  includes a leak arrest volume  99  that is distributed to enclose second perimeter  87  and distributed to surround the other high pressure spaces defined by nozzle supply passage  24  and high pressure passage  40 . In this embodiment, leak arrest volume  99  is vented to the low pressure space adjacent perimetrical side surface  96  via vent passage(s)  89 . Those skilled in the art will appreciate that the leak arrest volumes are defined by the side surfaces of the two components so as to arrest any leakage that could develop in the sealing lands between the high pressure spaces and the leak arrest volume. Although the leak arrest volumes are shown as being defined by a planar surface of one component covering a groove in an opposing component, those skilled in the art will appreciate that the grooves could be formed in both components in order to form the leak arrest volume(s) of the present invention. 
   INDUSTRIAL APPLICABILITY 
   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 that 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 . When this occurs, needle control chamber  37  is fluidly connected to low pressure fuel reservoir  20  via low pressure passage  41 . 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 valve surface  53  comes in contact with low pressure seat  51 . When this occurs, high pressure fluid originating in nozzle supply passage  24  flows through high pressure passage  40  past high pressure seat  50  and into needle control chamber  37 . The high pressure force on piston  32  moves needle valve member  30  toward its closed position. 
   Like many fuel injectors, fuel injector  10  includes a plurality of stacked components  13  that need to be sealed against leakage at their various planar sealing land contact surfaces. In those areas where a potential leak could cause a component separation wedging affect, the present invention finds potential applicability. For instance,  FIGS. 1 and 2  show valve lift spacer  44  and stop plate  75  as including leak arrest volumes that are distributed to surround high pressure spaces  37 ,  85 ,  40  and  24 . If the application is a common rail fuel injector, these leak arrest volumes are preferably vented (such as by vent passages  88 ) to a low pressure space via an appropriate vent paths as described earlier. In the case of cyclic pressure fuel injectors, such as cam or hydraulically driven fuel injectors, vent paths could be omitted by making the leak arrest volume large enough to have the capacity to increase in pressure during an injection event below some pre-determined pressure, while also having the ability to have that pressure decay between injection events. Those skilled in the art might also find is desirable to include leak arrest volumes and vent paths between other components that seal against leakage of nozzle supply passage  24 . In the illustrated embodiment, the leak arrest volumes and vent paths are preferably stamped or coined into valve lift spacer  44  and stop component  75 . By including vent paths, the size of leak arrest volumes in the vent passages can be relatively loosely controlled since the volume of these spaces need not be tightly controlled. After being stamped, the planar surfaces of these components can be ground in a conventional manner. 
   The leak arrest volume should be distributed to sufficiently surround the high pressure perimeter that a wedging affect caused by a leak is prevented from causing substantial component separation which could lead to an even larger leakage. Although the leak arrest volumes preferably enclose the high pressure space in which they are sealing against leakage, they need not necessarily do so. For instance, passages  24  and  40  are not completely enclosed by leak arrest volume  98 , but the leak arrest volume  98  is distributed to surround a majority of a perimeter around these passages. 
   The present invention is potentially advantageous in that leakage that exists between components can be limited by arresting a wedging affect that could cause even larger amounts of leakage. Those skilled in the art will appreciate that leakage is very undesirable in that it contributes to a number of undesirable affects, including energy wastage, altered injection amounts and variability among fuel injectors, among other potential problems. By appropriately locating leak arrest volumes according to the present invention, any leakage that does start to occur between components is prevented from substantially exacerbating into a large leak by connecting the leak to a low pressure space long before it reaches the perimetrical outer side surface that surrounds the two components. Alternatively, if the high pressure space is near the outer side surface of the components ( FIG. 3 , passage  24 ), then it may not be desirable to insert a leak arrest volume between the higher pressure space and the outer side surface of the component(s). 
   Although the present invention has been illustrated in the context of a fuel injector, those skilled in the art will appreciate that the concept of the present invention could find potential application in any component sub-assembly that includes a planar sealing land that is intended to prevent leakage from a high pressure space within the components. 
   It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. Thus, those skilled in the art will appreciate that other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.