Patent Application
20080217421
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.
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.
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.
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.
The present disclosure is directed to overcoming one or more of the problems set forth above.
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.
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.
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.
Referring to
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.
Referring now to
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
Referring now to
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.
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.
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.
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.
