Abstract:
A mechanically actuated electronically controlled unit injector includes an electronically controlled spill valve to precisely control timing of fuel pressurization within a fuel pressurization chamber. Cavitation bubbles may be generated in the region of the valve seat when the spill valve member is closed to raise fuel pressure in the fuel injector. This cavitation can cause erosion on the spill valve member and the surrounding injector body. In order to preempt cavitation damage, the valve member may be modified to include a compound annulus that includes a small annulus that corresponds to an identified cavitation damage pattern. Although the generation of cavitation bubbles may continue after such a strategy, cavitation erosion, and the associated liberation of metallic particles into the fuel system can be reduced, and maybe eliminated, by the preemptive cavitation reduction strategy.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to a cavitation erosion reduction strategy in a fuel injector, and more particularly to a valve member of a fuel injector incorporating the cavitation erosion reduction strategy. 
       BACKGROUND 
       [0002]    Most fuel injectors include one or more electronically controlled valves that open and close various fuel passageways to facilitate control over fuel injection events. One class of such fuel injectors is typically identified as a mechanically actuated, electronically controlled unit injector (MEUI) which utilize an electronically controlled valve to precisely control a timing at which fuel in the fuel injector becomes pressurized. In particular, a rotating cam periodically advances a plunger to pressurize fuel in a fuel pressurization chamber, but pressure does not rise until a spill valve is closed. If a spill valve is closed during a plunger stroke, fuel pressure quickly rises followed by opening of a nozzle outlet to perform an injection event. A spill valve for such an injector is shown, for example in co-owned U.S. Pat. No. 6,349,920. Later evolutions of the MEUI fuel injector added a second electronically controlled valve to control the opening and closing of the nozzle outlet somewhat independently of the fuel pressurization event accomplished through the spill valve. 
         [0003]    The phenomenon known as cavitation can sometimes arise at unexpected locations within a fuel injector. Furthermore, cavitation damage can in some cases potentially lead to premature fuel injector failure rather than simple wear and tear on the various inner surfaces defining the fuel passageways through the fuel injector. One common location where fuel injectors receive cavitation damage is on the valve members. The collapse of cavitation bubbles may eventually erode an annular surface on the valve member and may affect its operation, the operation of the fuel injector, and the operation of the engine. Cavitation erosion is also undesirable because it produces small metallic particles that can cause scuffing and seizure in moving parts of a fuel system. 
         [0004]    Unfortunately, modeling fluid systems to predict the occurrence of cavitation, as well as potential magnitudes of damage and their respective locations due to cavitation has proven to be extremely difficult. Thus, a computer aided design strategy for avoiding some cavitation damage problems is not realistic as the modeling tools available to simulate various different design shapes and evaluate the same for potential cavitation damage are not capable of accurately and reliably predicting some cavitation damage problems. Thus, engineers are sometimes left with exploiting simple trial and error in various design alternatives in order to address potential cavitation damage issues. 
         [0005]    The present disclosure is directed to overcoming one or more of the problems set forth above. 
       SUMMARY OF THE INVENTION  
       [0006]    In one aspect, a fuel injector includes an injector body with a fuel passage disposed therein that is partly defined by an annular valve seat. An electronically controlled valve includes a valve member with an annular valve surface that moves into and out of contact with the annular valve seat to close and open the fuel passage, respectively. The annular valve surface defines a portion of the compound annulus defined by the valve member. 
         [0007]    In another aspect, a valve member for a fuel injector control valve comprises a unitary metallic body with a threaded bore therethrough concentric with a cylindrical outer surface. A compound annulus is defined by the cylindrical outer surface. A portion of the compound annulus is also defined by an annular valve surface, which is a portion of the cylindrical outer surface. 
         [0008]    In still another aspect, a method of reducing cavitation erosion in a fuel system includes operating a fuel injector over a sufficient number of injection cycles to detect cavitation damage in a valve member of an electronically controlled valve of the fuel injector. A cavitation damage pattern is identified on the valve member. A new valve member is formed identical to the valve member in a region corresponding to the cavitation damage pattern, except the new valve member defines an additional annulus corresponding to the cavitation damage pattern. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a side sectioned diagrammatic view of a fuel injector according to one aspect of the present disclosure; 
           [0010]      FIG. 2  is an enlarged partial view of the spill valve portion of the fuel injector of  FIG. 1 ; 
           [0011]      FIG. 3  is a sectioned side elevational view of the valve member for the spill valve portion of  FIG. 2 ; 
           [0012]      FIG. 4  is a sectioned side view of a cavitation damage prone valve member; 
           [0013]      FIG. 5  is an enlarged view of the compound annulus portion of the valve member of  FIG. 3 ; and 
           [0014]      FIG. 6  is an enlarged view of the cavitation damage region of the cavitation damage prone valve member. 
       
    
    
     DETAILED DESCRIPTION  
       [0015]    Referring to  FIG. 1 , fuel injector  10  includes an injector body  11  that defines a nozzle outlet  12  and a fuel inlet/return opening  13 . A cam driven plunger  15  is positioned to move in the injector body  11  to displace fuel into fuel passage  18 , which is disposed in injector body  11 . A fuel spill passage  20  is disposed in injector body  11  and extends between fuel passage  18  and supply/return opening  13 . An electronically controlled spill valve  22  includes a valve member  25  with an annular valve surface  43  ( FIG. 2 ) that moves into and out of contact with an annular valve seat  29  to close and open spill passage  20 . The valve member  25  includes a threaded bore  40  extending therethrough that is concentric with the annular valve surface  43 . A solenoid armature  23  is attached to valve member  25  via a threaded fastener  24  that is mated to threads  40  of valve member  25  via a set of external threads  41 . Thus, when plunger  15  is being driven downward to pressurize fuel in fuel pressurization chamber  17 , the fuel may be initially displaced back through supply/return opening  13  via spill passage  20 . When electronically controlled valve  22  is energized to move annular valve surface  43  into contact with annular valve seat  29 , spill passage  20  becomes closed, and fuel pressure in chamber  17 , and hence nozzle chamber  19 , quickly rises to injection pressure levels. 
         [0016]    Fuel injector  10  also includes an electronic needle control valve  30  that fluidly connects or disconnects a needle control chamber  33  to fuel passage  18 . This electronic needle control valve  30  includes a solenoid separate from the electronically controlled spill valve  22 . During an injection event, needle control chamber  33  is fluidly connected to fuel passage  18 , pressure on closing hydraulic surface  34  of direct control needle valve  32  is high and the nozzle  12  is maintained closed. When electronic needle control valve  30  is moved to close that fluid connection, pressure in needle control chamber  33  drops via a fluid connection (not shown) to supply/return opening  13 , allowing direct control needle valve  32  to lift to open nozzle outlet  12 , provided fuel pressure in nozzle chamber  19  is sufficient to overcome a needle biasing spring in a manner well known in the art. 
         [0017]      FIG. 2  shows valve member  25  in its downward closed position where annular valve surface  43  is in contact with annular valve seat  29  to close spill passage  20 . When the solenoid is de-energized, a biasing spring  36  acts on armature  23  to push valve member  25  upward to open annular valve seat  29 . When this occurs, spill passage  20  is fluidly connected to supply/return opening  13  via compound annulus  26 , armature chamber  28  and low pressure passage  27 . Compound annulus  26  is defined by valve member  25 , which is preferably a unitary metallic body. In the context of the present disclosure, a compound annulus means a smaller volume annulus that opens into a larger volume annulus. Thus, an injection event is typically initiated during downward movement of plunger  15  by energizing electronically controlled spill valve  22  to close annular valve seat  29 . The fuel injection event is then commenced by moving electronic needle control valve  30  to a position that relieves pressure in needle control chamber  33 . An injection event may be ended either by repressurizing needle control chamber  33 , or by relieving fuel pressure in nozzle chamber  19  by reopening spill control valve  22 . 
         [0018]    Referring now to  FIGS. 4 and 6 , a valve member  125  according to a first embodiment includes a single large annulus  126  that is defined in part by annular valve surface  143 . Although this design performs well with regard to cavitation, there is always room for improvement. After many hours of operation involving many injection cycles, it is possible that cavitation that may occur around valve member  125  may begin to erode annulus  126  at location  110  (which is on the low pressure side of the circuit) according to pattern  111 . The cavitation bubbles that occur around valve member  125  are believed to develop shortly after the closing of annular valve seat  29 . When this occurs, the momentum of the fluid spilling through spill passage  20  is believed to have a water hammer effect, in that a vacuum develops adjacent to valve seat  29 , and flow conditions cause at least some of the cavitation bubbles to collapse adjacent to the valve member  125  at location  110 . Over time, it is possible that the continuous collapsing of the cavitation bubbles may begin to erode valve member  125 . If the erosion were to continue over time, the erosion could eventually break through into threaded bore  40  leaving the electronic control spill valve less able to completely close spill passage  20  to allow fuel pressure to develop in the fuel injector. As a result, that injector could be unable to inject fuel and the associated engine cylinder might go cold. 
         [0019]    In order to both minimize the amount of debris set loose in the fuel system due to cavitation erosion and to minimize the likelihood of cavitation erosion in the first place, the present disclosure contemplates a rather counterintuitive solution. In particular, the present disclosure teaches that by adding an annulus, such as annulus  45  in the vicinity of, and with a magnitude (shape and volume) associated with the potential cavitation erosion pattern  111  illustrated in  FIG. 6 , cavitation erosion may be reduced, and potentially actually avoided. In other words, it is believed that by preemptively removing material that might otherwise be eventually eroded via cavitation, flow patterns around the valve member may change such that either the cavitation bubbles no longer are generated, or that they collapse at a location away from the valve member to minimize the likelihood of erosion in the relevant locations or cause any erosion that may occur to occur on a less critical surface within the fuel injector  10 . Thus, based on conventional wisdom, which might suggest that the preemptive addition of an annulus corresponding to a potential cavitation erosion pattern  111  might actually hasten cavitation erosion, the cavitation erosion minimization strategy disclosed in the present disclosure actually provides a surprising result. Other potential solutions, such as lengthening annulus  26  or changing the contours of the same, may also be possible, but are believed to be less successful at reducing the likelihood of cavitation erosion. Factors that may influence the degree of minimization of the likelihood of cavitation erosion may include the location and size of the additional small annulus  45 . Since no reliable modeling tools for predicting the likelihood of cavitation erosion in relatively complex fluid flow environment of a spill valve of a fuel injector is known to exist, some experimentation in finding a solution may be necessary. The present disclosure teaches that a good place to start in finding an alternative shape to a valve member to minimize the likelihood of cavitation erosion in a particular area is to actually preemptively add an annulus  45  (remove material relative to a previous design of the valve member) corresponding to a potential cavitation erosion pattern  111 . Thus, in a valve member according to a second embodiment of the present disclosure, the valve member  25  includes a compound annulus  26  with a small annulus  45  that opens into a large annulus  44 . 
         [0020]    Referring now to  FIGS. 3 and 5 , valve member  25  according to the second embodiment includes a symmetrical cylindrical outer surface extending along its length with various contours that include a large diameter segment  47  adjacent a small diameter segment  46 . Compound annulus  26  is located in small diameter segment  46 , and annular valve surface  43  is located at the transition from small diameter segment  46  to large diameter segment  47 . An additional annulus  48  is located in the large diameter segment  47 , which is longer than the small diameter segment  46 . As best shown in  FIG. 5 , the small annulus  45  is offset a distance d from the center of large annulus  26 , but not so far that the small annulus  45  shares a common wall segment with the surface defining annular valve surface  43 . According to one exemplary embodiment, the small annulus  45  has a U shaped cross section, which may be semicircular, having proportions as illustrated in  FIG. 5 . However, those skilled in the art will appreciate that the location, shape and size of small annulus  45  could be varied to achieve satisfactory results. 
       INDUSTRIAL APPLICABILITY 
       [0021]    The teachings of the present disclosure are directed toward making a valve member that reduces the likelihood of erosion caused by cavitation. The present disclosure finds potential application in any fuel injector that exhibits, or is likely to exhibit, cavitation erosion on an outer surface of a valve member. The present disclosure finds specific application in reducing the likelihood of cavitation erosion on a spill valve member of a mechanically actuated electronically controlled unit injector. Thus, the present disclosure is also directed to reducing the likelihood of introducing metallic debris in a fuel system, which can cause scuffing and seizures of moving parts. The present disclosure recognizes that issues relating to cavitation erosion are often difficult to predict with currently available modeling tools, and thus are most often discovered after a fuel injector has been put into production and has performed over many hours and possibly millions of injector cycles. Thus, the present disclosure may also relate to a case where a fuel injector has been operated for a sufficient number of injection cycles to detect cavitation erosion on a valve member of an electronic controlled valve of a fuel injector. Once the occurrence of cavitation erosion is noticed, a cavitation erosion pattern  111  on the valve member  125  can be identified. For instance, this can be accomplished by operating a plurality of fuel injectors over a sufficient number of hours to reveal an expected magnitude and variation in the cavitation erosion pattern among the valve members for the plurality of fuel injectors. An alternative valve member design may be made that is substantially identical to the previous design valve member in a region corresponding to the cavitation erosion pattern or likely cavitation erosion pattern, except the new valve member defines an additional annulus corresponding to the cavitation erosion pattern. The term “corresponding” in this case refers to the notion that the additional annulus is located where the cavitation erosion pattern is identified or likely, and the size and shape of the additional annulus may be related to an average cavitation erosion observed over some period of time. In other words, adding an additional annulus that is too small, or too large, may not have an impact on the likelihood of cavitation erosion or the actual cavitation erosion experienced. In addition, mislocating the added small annulus may also lead to a situation where there is little or no affect on the likelihood of cavitation erosion or on the experience cavitation erosion. 
         [0022]    Once a cavitation erosion pattern  111  has been identified, the present disclosure would suggest that a first attempt at finding a solution would be to form new valve members having an additional annulus with different combinations of cross sectional shape, volume and location at the cavitation erosion location  110 . Then, new fuel injectors with the new valve member should be operated on the order of a number of hours corresponding to when the cavitation erosion started or was likely to start on the previous version of the valve members. Those skilled in the art will recognize that conditions more favorable to cavitation can be created by elevating the fluid temperature. This can hasten the iteration process in finding a suitable design alternative. The new valve members would then be sorted according to a cavitation erosion criteria. For instance, some of the new valve members may show no evidence of cavitation erosion, some may show frosting as to some limited cavitation erosion and others may show cavitation erosion more severe even than the unmodified previous design valve members. Utilizing this technique, in one or two or more iterations as needed, should allow one to arrive at an additional annulus shape, location and volume that sufficiently reduces the cavitation erosion issue such that one could expect the valve member to exhibit over a performance lifetime on the order of that expected from the other components of the fuel injector. In other words, a fuel injector with a modified or new valve member with an added annulus could expect to have an extended life relative to the earlier version, which could mean that during a remanufacturing process, the valve would not have to be replaced when other parts of fuel injector would. 
         [0023]    In the specific case where the cavitation erosion occurs or has the potential to occur in an already existing annulus, the present disclosure teaches that the additional small annulus  45  may added to open into the large annulus  44  to result in a compound annulus  26  that substantially reduces or eliminates the likelihood of cavitation erosion. While the disclosed cavitation reduction strategy may not lead to the elimination of cavitation bubbles, the strategy may result in a changing of flow patterns in the effected region to result in cavitation bubbles being collapsed at a location where some erosion is more acceptable or collapse at a location that does not, or is less likely to, produce cavitation erosion. In the case of the present disclosure, a U-shaped small annulus  45  having a semicircular cross section may be added at a location corresponding to a potential cavitation erosion pattern  111  at a location offset from the center of the large annulus  44 . 
         [0024]    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 of the invention can be obtained from a study of the drawings, the disclosure and the appended claims.