Abstract:
An engine fuel injector ( 10 ) having a fuel inlet tube ( 12 ) and a biasing spring ( 56 ) loading a solenoid actuated injection valve ( 50 ) within the injector ( 10 ) is provided with a calibration assembly ( 58 ) combining the calibration member ( 74 ) or tube with an internally mounted fuel inlet filter ( 76 ). The calibration member ( 74 ) may include a body ( 78 ) with an enlarged end ( 88 ) that is interference fitted within the fuel inlet tube ( 12 ) and an opposite stepped in end ( 80 ) forming a seat ( 82 ) which is engaged by the biasing spring ( 56 ). The fuel filter ( 76 ) has an enlarged annular base ( 92 ) fixed within the enlarged end ( 88 ) of the calibration member ( 74 ) and having an associated filter screen ( 98 ) or element through which fuel passing through the calibration member is filtered for passage through the injector ( 10 ). The filter screen ( 98 ) may extend completely within the calibration member ( 74 ), or alternatively, can project outward from the enlarged end ( 86 ) of the calibration member ( 74 ) into the inlet end ( 86 ) of the fuel inlet tube ( 12 ). Advantages in the ease of calibration, reduced assembly costs and improved filtration of fuel are provided.

Description:
TECHNICAL FIELD 
     This invention relates to engine fuel injectors, particularly of the solenoid actuated top feed type, and more particularly to an injector having an inlet fuel filter mounted within a frictionally retained valve spring calibration tube. 
     BACKGROUND OF THE INVENTION 
     It is known in the art to provide an engine top feed fuel injector with a fuel inlet filter mounted within the fuel inlet tube. It is further known to provide a calibration tube which is slidable within the inlet tube for adjusting the force on a solenoid actuated fuel inlet valve and to propose a fuel filter mounted on the outer end of the calibration tube. 
     In this proposal, the calibration tube is adjusted by a tool which engages the closed outer end of the filter and forces it down with the tube until the desired valve spring force is achieved. The calibration tube is then fixed to the inlet tube by any suitable means to hold the calibration tube in place. The friction force of the tube by itself is inadequate to maintain the set calibration tube position since adjustment of the tube by applying a force to the filter body requires that the sliding force of the calibration tube be limited to an amount which the plastic body of the filter is able to withstand, preferably not more than about two pounds. Also, the low force sliding fit of the calibration tube in the fuel inlet tube allows fuel carrying contaminant particles up to 100 microns in diameter to bypass the filter by passing through clearance spaces between the tubes. It is accordingly desired to provide a calibration tube mounted inlet filter which overcomes the problems of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention provides a fuel injector having a fuel tube at the inlet end and an injection valve at the discharge end of the injector, the valve including a valve element reciprocable against and away from a valve seat. A biasing spring operatively engages the valve element, optionally through a solenoid-actuated armature, and a calibration member or tube is adjustable within the injector to establish a set force of the valve biasing spring. 
     A fuel filter is mounted within the calibration member, preferably in a manner to allow direct engagement of a calibration tool with the outer end of the calibration member for adjusting the spring force. The fuel filter is preferably mounted in the calibration tube with an interference fit that is adequate to maintain the set position by friction between the members without requiring an additional securing step. Optionally, the calibrating tool may engage a base or mounting portion of the filter body snap fitted or otherwise mounted in a calibration tube. In any case, a force adequate to provide the desired interference fit may be applied to the calibration tube without passing through the complete filter body. Preferably, the interference fit is also sufficient to prevent the bypassing of fuel past the calibration tube and around the filter so as to prevent particles larger than the filter is designed to remove from remaining in the fuel stream. Thus, the filter and the interference fit may be selected to capture particles greater than about 30 microns in diameter. 
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is a cross-sectional view through an engine fuel injector of the top feed type shown as mounted within an engine cylinder head and connected within the cup of an engine fuel supply system; 
     FIG. 2 is a cross-sectional view of a preferred embodiment of valve spring calibration tube having an internally mounted fuel filter according to the invention, as shown in FIG. 1; 
     FIG. 3, is a cross-sectional view of an alternative embodiment of calibration tube with an internally mounted fuel filter wherein the body of the filter extends out through the inlet end of the calibration tube; 
     FIG. 4 is still another embodiment of calibration tube with an internally mounted fuel filter, wherein the filter body is insert molded within the tube and the body also extends out through the inlet end of the calibration tube; and 
     FIG. 5 is a cross-sectional view of yet another embodiment of calibration tube with an internally mounted filter, wherein the filter body has a base that is snap fitted into the inlet of the tube and the body extends outward from the inlet end of the tube which is shown as mounted within an injector assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1 of the drawings in detail, numeral  10  generally indicates a solenoid actuated fuel injector which is similar to that disclosed in copending U.S. patent application Ser. No. 09/320,501, filed May 26, 1999, but includes modifications in accordance with the present invention. 
     Injector  10  includes a continuous fuel tube  12  which is centered on a central axis  14  and encloses a continuous fuel passage  15  through the injector from an inlet end  16  of the tube to a discharge end  18 . Preferably, the fuel tube  12  has no openings except at the inlet and outlet ends and defines a continuous imperforate passage in which fuel is conducted and kept separate from all the components of the injector that are mounted externally of the fuel tube. These include a coil assembly  20  having a solenoid coil  22  extending around and closely adjacent to the fuel tube  12 . A magnetic coil body or strap  24  surrounds the coil  22  and has upper and lower portions  26 ,  28  fixed to the outer surface of the tube  12 . 
     A support member or cover  30  is formed as a two-piece tubular member that is assembled over the tube and surrounds the body  24 . The cover includes a slot  32  for receiving a retainer clip, not shown, that holds the injector inlet end within a cup  34  of an associated fuel rail, not shown. The cover also provides a backup surface for constraining a seal ring  36  of a conventional O-ring type. A push-on seal retainer  38  is frictionally or otherwise retained on the inlet end  16  of the fuel tube  12  to form with the other parts an annular groove in which the seal ring  36  is retained. A lower end of the cover  30  also backs up an O-ring seal  40  retained by a lower seal retainer  42  on an expanded diameter portion  44  at the lower end of the fuel tube  12 . 
     Within the fuel tube  12 , a tubular magnetic pole  46  is fixed in engagement with the interior surface of the fuel tube  12 . The pole  46  extends from adjacent the upper end  26  of the magnetic body  24  to a position within the axial extent of the coil  22 . An injection valve  50  is reciprocable within the tube  12  and includes a ball end  52  connected with a hollow armature  54  that slides within the tube  12 . A biasing spring  56  engages an upper end of the armature  54  and is compressed with a predetermined force by a calibration assembly  58  best shown in FIG.  2  and to be subsequently further described. 
     Within the expanded portion  44  of the fuel tube  12 , a valve seat  60  and a lower guide  62  are retained by crimped over portions of the tube outlet end  18  which engage a seat washer  64 . The lower guide  62  is a disc which guides the ball end  52  of the injection valve and includes openings  66  that allow fuel flow through the guide to a conical surface  68  of the valve seat against which the ball end  52  seats in the valve closed position. A central discharge opening of the valve seat  60  connects with a multi-hole spray director  70  held in a recess of the valve seat by a retainer  72 . 
     To properly control the speed and efficiency of valve action in the injector, it is important that the valve stroke be set a desired predetermined value. This may be accomplished by providing for adjusting the position of the valve seat. However, in the present embodiment, the valve stroke is preferably set by making the magnetic pole  46  axially adjustable within the fuel tube  12  to establish the desired clearance between the pole  46  and the valve armature  54  in the valve closed position. This is done by sliding the pole inside the tube to obtain the proper clearance, after which the pole may be fixed within the tube by the friction developed from an interference fit or by crimping or otherwise securing the tube to the pole in the adjusted position. 
     In accordance with the invention, the calibration assembly  58  shown in FIGS. 1 and 2 is substantially modified from the generally straight calibration tube disclosed in the previously mentioned U.S. patent application Ser. No. 09/320,501 and which is known in injectors of this type. In the present invention, the calibration tube and separately mounted filter of the previously mentioned U.S. patent application Ser. No. 09/320,501 are replaced by the calibration assembly  58  which includes a preferably metal calibration tube or member  74  in which a fuel intake filter  76  is mounted. The calibration member  74  includes a generally tubular body  78  sized to be telescopically received within the magnetic pole  46  of the injector. At its lower end  80 , body  78  is stepped into a smaller diameter forming an annular seat  82  against which the biasing valve spring  56  is seated and an annular extending spring guide  84  which extends into spring  56  for guiding the upper end thereof. 
     At its upper end  86 , the calibration member body  78  has a diametrically enlarged or expanded portion  88  which is sized to be an interference fit within the injector fuel tube  12  where it is received toward the inlet end of the injector. Fuel filter  76  includes a plastic frame  90  having an enlarged annular base  92  connected by two or more longitudinal ribs  94  with a solid cap  96 , forming a plurality of spaced windows through which fuel may pass. A tubular filter screen  98  is molded into the plastic frame  90  and extends between the base  92  and cap  96  alongside the ribs  94 . The screen  98  covers all the windows and requires fuel passing therethrough to pass through the filter screen to screen out solid particles of a desired size. In the present instance, particles carried in the fuel that are greater than 30 microns are separated out by the filter screen  98 . 
     In this preferred embodiment, the filter  76  has its base  92  fitted tightly within the enlarged portion  88  of the calibration member body  78 , the upper end  86  of which is crimped or rolled over at  100  to mount the filter tightly within the calibration member  74 . The filter is mounted so that the filter screen  98  and end cap  96  extend downward within the body  78  of the calibration member  74 . The design allows sufficient clearance around the outside diameter of the filter to allow the free flow of fuel into the upper end  86  of the calibration member and through the filter screen  98  and the interior of the body  78 , passing out through the lower end  80  of the calibration member  74 . 
     As shown in FIG. 1, the calibration assembly  58  is inserted into the fuel tube  12  with the enlarged portion  88  at its upper end forced into the inlet end of the fuel tube  12 . The parts are sized for an interference fit forming a sufficient restriction to prevent any significant bypassing of fuel around the fuel filter within the calibration tube. The interference fit is also adequate to prevent the passage of particles around the filter which are greater than 30 microns which the filter is designed to remove from the fuel passing therethrough. The lower end  80  of the calibration member  74  is positioned with its annular seat  82  against the biasing spring  56  and with the spring guide  84  extending inside the upper end of the spring. 
     In order to calibrate the biasing spring to obtain the proper spring force against the injection valve  50 , a calibrating tool  102  is used as shown in phantom in FIG.  1 . During assembly of the injector, before insertion into the fuel rail cup  34 , the tool  102  is inserted through the inlet end of the fuel tube  12  into engagement with the crimped over portion  100  of the calibration assembly  58  and a force, which can be as much as 40 to 80 pounds, is exerted which is adequate to slide the calibration tube downward against the spring until the desired spring force or fuel flow for the injector is reached. The calibrating tool  102  is then removed and the calibration assembly  58  is retained in fixed position within the injector by the substantial interference fit between the enlarged portion  88  of the calibration member  74  and the interior of the fuel tube  12 . If desired, the body  78  of the calibration member could also be fitted with sufficient force into the tubular magnetic pole  46  to supplement the securing force applied to the calibration member within the fuel tube  12 . 
     The improved assembly  58  of the calibration member  74  and fuel filter  76  and its interference mounting within the fuel tube  12  provides significant advantages in simplification and cost during the assembly of the fuel injector  10 . Because the calibration assembly  58  is designed to allow calibration of the valve spring force with the filter in place, the fuel filter may be installed in the injector in an earlier stage of assembly of the injector than in injectors wherein the fuel filter is mounted separately at the inlet of the fuel tube. This allows the fuel filter to prevent contamination of the interior of the calibration tube and the valve member ball end  52  and armature within the fuel passage during assembly steps of the injector after insertion of the calibration assembly and during the calibration process itself. 
     In addition, the interference fit of the calibration assembly  58  within the fuel tube  12  prevents substantial bypassing of fuel around the fuel filter and positively precludes particles larger than that removed by the fuel filter from entering the fuel stream below the fuel filter within the injector tube. The interference fit also is sufficient to hold the calibration member  74  in position after calibration without requiring an additional step, such as crimping or welding, to hold the tube in place after the calibration process is completed. These advantages simplify the process of assembly and provide a significant reduction of cost in the assembly process. 
     FIGS. 3-5 illustrate some alternative embodiments of calibration assemblies which are exemplary of various additional forms that may be utilized within the scope of the invention. In FIG. 3, calibration assembly  104  includes a calibration member  74  and a fuel filter  76 , as in FIG.  2 . However, the fuel filter is reversed in position so that, while its hollow base  92  is still crimped into the enlarged portion  88  of the calibration member body  78 , the filter screen  98  and the supporting ribs  94  and cap  96  extend out through the inlet end or upper end  86  of the calibration member so that fuel flow passes through the filter screen in the opposite direction from the embodiment of FIG.  2 . 
     In spite of the protruding fuel filter, calibration of the force on the biasing spring  56  within the injector may be accomplished in the same manner by a tubular calibration tool, not shown, which extends into engagement with the crimped over portions  100  at the upper end of the calibration member body  78 . In this way, sufficient force can be applied to the calibration assembly  104  as to the previous assembly embodiment  58  to permit the assembly  104  to be retained in the fuel tube by an interference fit. The required force, which may be in the neighborhood of 40-80 pounds would be excessive if it was intended to calibrate the assembly by applying force to the plastic filter cap, or the filter frame would have to be made much stronger at additional cost in order to accept forces of this magnitude. 
     Referring now to FIG. 4, an alternative embodiment of calibration assembly  106  is illustrated. The calibration member  108  is formed with a straight cylindrical lower end but could optionally be formed with the stepped in smaller diameter of the previously described embodiments, if desired. The upper end includes an enlarged portion  110  into which a filter  112  is insert molded. In this process, the calibration member  108  and filter screen  114  are positioned in their proper relationship within plastic molding dies and the plastic frame  116  is molded in place. The frame  116  includes an integral base, spaced ribs and cap, all of which secure the filter screen  114  in place and the insert molding process fixes the frame  116  within the enlarged portion  110  of the calibration member  108 . The resulting assembly  106  is installed in the injector fuel tube  12  and calibrated in the same manner as with the previously described embodiments. 
     Referring now to FIG. 5, a calibration assembly  118  is illustrated having a calibration member  120  and a fuel filter  122 . Member  120  is formed at its lower end with the same configuration as in the embodiments of FIGS. 2 and 3, whereas the upper end  124  is enlarged with a generally cylindrical end portion having an internally raised bead  138  intermediate the ends of the enlarged portion. The accompanying fuel filter  122  includes an outwardly extending annular plastic base  128  connecting at its lower end with wraparound ribs  130  that extend around the lower end of a filter screen  132  and longitudinally upward to a closed outer end cap  134  while providing intermediate support to the filter screen between its ends. The base  128  includes an intermediate annular recess  136  which allows the filter assembly to be snapped into engagement with the upper end  124  of the calibration member  120 . There it is held in place by the inwardly raised bead  138  engaging the annular recess  136  of the filter base  128 . 
     Installation of the assembly  118  into the fuel tube  12  of an associated injector can be accomplished in the same manner as before except that the tubular calibration tool, not shown, is positioned to engage the upper edge  139  of the plastic fuel filter base  128  rather than crimped over metal portions of the calibration member as in the previous embodiments. While calibration member  118  is shown with the fuel filter  122  extending outward from its mounting within the calibration member or tube  120 , as is the case with the embodiments of FIGS. 3 and 4, it should be recognized that the embodiment of FIG. 5 could be designed for installation in the reverse direction with the filter extending into the lower body portion of the calibration member, as in the embodiment of FIG.  2 . The base  128  of the filter frame would still, if properly designed, snap into the enlarged upper end  124  of the calibration member. The filter would then operate in the same manner as described for the embodiment of FIG. 2 except, again, the calibration tool would engage the outer end of the base  128  instead of the calibration member itself. In both instances, however, the inwardly extending filter member has the advantage, if needed, that the injector may be made shorter, where the associated engine application would permit, than would be the case with outwardly extending filter mounting arrangements, such as in FIGS. 3 and 4. 
     The various embodiments of calibration members described herein have been shown with a fuel injector having a continuous fuel tube defining the fuel passing through the injector. However, the invention is also applicable to other forms of top feed fuel injectors which include a fuel inlet tube through which a calibration tube assembly may be inserted. 
     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.