Fuel injector having an internal filter
This is a continuation of application Ser. No. 07/847,145 filed on Mar. 5, 1992 now abandoned. 
    
    
     THE FIELD OF THE INVENTION 
     This invention relates to electromechanical actuated fuel injectors of the type used in the fuel systems of spark-ignited internal combustion engines. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     It is known to provide such a fuel injector with an external filter means disposed to filter the fuel as it approaches the fuel injector&#39;s inlet. While such a filter is suitable for preventing particulate material in fuel from entering the fuel injector, it is incapable of filtering particulate material that may originate internally of the fuel injector either on account of processes used to manufacture and assemble the fuel injector or on account of usage. 
     The present invention relates to an improvement that enables a filter to be disposed internally of the fuel injector between the inlet and the internal valve means so that particulate material having an internal origin may also be prevented from reaching the valve means. 
     Although it is known to provide certain mechanical fuel injectors with flow geometries intended to filter particulate material of external origin, insofar as the applicant is aware the issue of filtering particulate material that originates internally of an electromechanical actuated gasoline, or flex fuel, fuel injector has not been successfully addressed. Such fuel injectors are typically manufactured in special environments using special processes to eliminate sources of contamination inside the finished product. Particulate material can originate within such a fuel injector due to manufacturing processes and/or from inadequate cleaning of component parts prior to assembly. Internal particulate material can originate from any assembly tooling, gauging, or air borne matter which becomes trapped inside the fuel injector prior to assembly of the external filter at the fuel injector inlet. Elimination of sources of internal contamination has historically been controlled only through special manufacturing processes, special techniques, and parts inspection. 
     The present invention is not intended to eliminate the need to maintain certain process controls used to avoid the inclusion of particulate material in the finished fuel injector. The invention is, however, intended to possibly minimize the intensity of inspection that may be required of the fuel injector and its component parts during assembly and thus more efficiently satisfy requirements against internal contamination. 
     Briefly, the present invention comprises in a general way the incorporation of an internal filter element in close proximity to the fuel injector&#39;s valve means. Thus, any particulate material greater than a certain size and originating internally of the fuel injector either after assembly or during use of the fuel injector will be prevented from reaching the internal valve means and thus possibly interfering with the proper functioning of the fuel injector. The preferred embodiment of the invention comprises for the filtering element an electroformed metal filter screen element. A preferred embodiment of the invention applied to a particular fuel injector will be disclosed and in this embodiment the arrangement is especially advantageous because of the manner in which the filter element is associated with the individual component parts of that particular fuel injector. Principles of the invention are, however, applicable to embodiments of gasoline, or flex fuel, fuel injectors other than the particular embodiment that is disclosed herein. 
     Further features, advantages and benefits of the invention, along with those already mentioned, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings illustrate a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal view having portions broken away of an electromechanical actuated gasoline, or flex fuel, fuel injector containing a filter element according to principles of the present invention. 
     FIG. 2 is an enlarged view in circle 2 of FIG. 1. 
     FIG. 3 is a view looking in the direction of arrow 3 in FIG. 2. 
     FIG. 4 is an enlarged view of a portion of FIG. 3. 
     FIG. 5 is an enlarged view of a portion of FIG. 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an electromechanical actuated fuel injector 10 which has an inlet 11 at one longitudinal end and a nozzle 12 at the opposite longitudinal end. The injection of fuel from nozzle 12 is controlled by the selective energization and de-energization of an electromagnetic coil 14. Details of the nozzle end of the fuel injector can be seen in FIG. 2. 
     Mounted on the nozzle end are a guide member 16, a seat member 18, a thin disc orifice member 20, and a split stream flow director member 22. Extending through guide member 16 is a central circular guide hole 24 for accurately guiding a circular cylindrical needle 26 for longitudinal reciprocal motion with respect to a seat 28 that is centrally formed in seat member 18. Needle 26 is reciprocated in response to the energization and de-energization of coil 14. Guide member 16 is joined to seat member 18 such that hole 24 is longitudinally aligned with seat 28. Needle 26 has a rounded tip end shown seated on seat 28 when coil 14 is de-energized to close a central circular hole 30 that extends from the bottom of seat 28 through seat member 18. When coil 14 is energized, needle 26 is displaced upwardly to unseat its rounded tip end from seat 28 so as to open hole 30. When the coil is again de-energized, the needle moves downwardly to reseat its rounded tip end on seat 28 to thereby once again close hole 30. Thus the needle and seat constitute the internal valve means of the fuel injector. 
     Guide member 16 has a number of through-holes 32 spaced outwardly of hole 24 to allow fuel to pass through the guide member. There are six such circular through-holes uniformly circumferentially spaced around the guide member. An elastomeric O-ring 34 is disposed in a groove around seat member 18 to seal between the seat member and the wall of the fuel injector nozzle end. Thin disc orifice member 20 comprises two circular orifices 36,38 that perform fuel splitting and metering functions. Split stream flow director member 22 comprises two holes 46,48 arranged to deflect flow streams from orifices 36,38. This much of the fuel injector that has been mentioned under this Description of the Preferred Embodiment is like that disclosed in the applicant&#39;s commonly assigned U.S. Pat. No. 5,016,819. The fuel flow passage 39 through the injector extends longitudinally from inlet 11 to nozzle 12. 
     The present invention comprises the inclusion of a filter screen element 50, which is disposed on the upstream face of guide member 16. Details of filter screen element 50 can be seen in FIGS. 3-5. Filter screen element 50 has a circular annular shape comprising a circular inside diameter and a circular outside diameter. It is also flat, having a uniform thickness. The filter screen element comprises an annular filtering zone 52 that is disposed between an inner annular imperforate zone 54 and an outer annular imperforate zone 56. The filter screen element is secured in assembly on the fuel injector by the outer margin of zone 56 being sandwiched by guide member 16 directly against an internal shoulder 58 of the fuel injector nozzle end which face the direction toward which fuel is injected. Filtering zone 52 overlies the six circular through-holes 32 in guide member 16 so that fuel passing through through-holes 32 is first filtered by the filter element. Because of the fuel pressure, it is actually unnecessary for the inner margin of the filter element&#39;s inner zone 54 to be joined to the corresponding inner margin of member 16, but actual attachment could be performed if desired. With the injector flowing fuel, the minimal pressure drop across the filter element is sufficient to maintain the filter element in place against member 16 even though the only mechanical attachment is by means of the sandwiching force acting to sandwich the outer margin of the filter element between shoulder 58 and member 16. The diameter of through-hole 24 is selected to provide a very close running clearance fit of member 16 to the outside diameter (O.D.) of needle 26. The size of this clearance presents to the fluid a very high resistance flow path that is in parallel with the much less restrictive flow path through the series combination of perforate zone 52 and through-holes 32. As a result there is essentially no flow through the extremely small annular clearance that exists between needle 26 and through-hole 24. Moreover, the diametral clearance between needle 26 and through-hole 24 is much less than the size of the diameter of each individual through-hole in perforate zone 52. In view of these features, particulate material that is intended to be filtered by the filter element is prevented from by-passing perforate zone 52, without the necessity of attaching the inner margin of filter screen element to member 16 and without the need for extremely close control of the filter screen element&#39;s I.D. Therefore essentially all the flow to the internal valve means is through the through-holes 32, and that flow is filtered by the filter screen element. 
     Because the filter screen element is disposed in close proximity to, but upstream of, the internal valve means, it is capable of filtering particulate material that is introduced into the fuel injector at any point upstream of the filter whether the particulate material is introduced with fuel entering inlet 11 or originates internally of the fuel injector. 
     The particular filter element is non-woven stainless steel having a generally uniform thickness throughout. It is fabricated by known electroforming (electroplating) technology. The representative filter element comprises a thickness in the range from about 50 microns to about 100 microns. The filtering zone 52 is perforate and comprises a multitude of through-holes 60 which are arranged in a desired pattern to provide a suitable open area. In the illustrated embodiment shown enlarged in FIGS. 4 and 5, the pattern is a hexagon one such that each hole is equally distant from its immediately adjacent ones. Each through-hole has an area substantially equivalent to that of a 50 micron diameter circle. The open area is from about 15% to about 30% of the total annular area of zone 52. 
     A filter element of this character is provided with suitable backup support by virtue of the fact that it is disposed against the upstream face of member 16. The holes in member 16 are neither sufficiently large nor sufficiently spaced closely together to deprive the filtering zone 52 of adequate backup support, and thus it is kept substantially flat throughout. The parts 50, 16, 18, 20, and 22 are assembled into the fuel injector via its nozzle end whose edge is thereafter crimped to capture the parts in assembly. 
     The electroforming processing produces holes that are substantially circular in transverse cross-section but these holes may be endowed with a very slight taper. Because of this, it is preferred that the filter element be disposed in the fuel injector such that the taper narrows in the flow direction. Moreover, the total net flow area through the filtering zone 52 overlying the underlying holes in member 16 is such that the inclusion of the filter element imposes negligible pressure drop. This is important because the inclusion of the filter should not impair the proper metering functions that are provided by the fuel injector. 
     While a presently preferred embodiment of the invention has been illustrated and described, it is to be appreciated that principles of the invention may be embodied in other ways that are equivalent to the following claims.