Cavitation erosion reduction strategy for a valve member and fuel injector using the same

Abstract

A valve member (25, 125) for a fuel injector control valve comprising a unitary metal body with a threaded bore therethrough concentric with a cylindrical outer surface (42); wherein the cylindrical outer surface (42) has a composite ring (26); wherein a portion of the composite ring (26) is defined by an annular valve surface (43); wherein the composite ring (26) is located in a small diameter segment (46) of the cylindrical outer surface (42); wherein an additional ring is defined by a large diameter segment (47) of the cylindrical outer surface (42); wherein the composite ring (26) has a small ring (45) which opens into a large ring (44); wherein a center of the small ring (45) is offset with respect to a center of the large ring (44); and wherein the small ring (45) has a U-shaped cross-section.

Description

Technical area

[0001] The present disclosure relates generally to a strategy for reducing cavitation erosion in a fuel injector, and more particularly to a valve member of a fuel injector employing the strategy for reducing cavitation erosion. background

[0002] Most fuel injectors include one or more electronically controlled valves that open and close various fuel passageways to facilitate the control of fuel injection events. One class of such fuel injectors is typically referred to as a mechanically actuated, electronically controlled unit injector (MEUI), which uses an electronically controlled valve to precisely control the timing at which fuel is pressurized within the fuel injector. Specifically, a rotating cam periodically advances a plunger to pressurize fuel in a fuel pressurization chamber, but the pressure does not increase until a spill valve is closed.When a spill valve is closed during a tappet stroke, fuel pressure rises rapidly, followed by a nozzle outlet opening event to execute an injection event. A spill valve for such an injector is shown, for example, in commonly assigned U.S. Patent 6,349,920. Later developments 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 compression event achieved by the spill valve.

[0003] The phenomenon known as cavitation can sometimes occur in unexpected locations within a fuel injector. Furthermore, cavitation damage to the various internal surfaces that define the fuel passageways through the fuel injector is much more likely to lead to fuel injector failure than simple wear and tear. The common location where fuel injectors experience cavitation damage is at the valve members. The collapse of cavitation bubbles can eventually erode an annular surface on the valve member and can affect its operation, the operation of the fuel injector, and the operation of the engine. Cavitation erosion is also undesirable because it creates small metal particles that can cause pitting and seizure in moving parts of a fuel system.

[0004] Unfortunately, modeling fluid systems to predict the occurrence of cavitation, as well as the potential damage magnitudes and their respective locations due to cavitation, has proven extremely difficult. Thus, a computer-aided design strategy to avoid certain cavitation damage problems is not realistic, as the modeling tools available to simulate various different design forms and evaluate them for potential cavitation damage are not capable of accurately and reliably predicting certain cavitation damage problems. Thus, engineers are sometimes left with no choice but to simply use trial and error with various design alternatives to address considerations related to potential cavitation damage.

[0005] Documents US 4 653 455 A, FR 2 817 296 A1, DE 103 51 680 A1, and AT 500 302 A2 relate to valves with a valve member and an annular valve surface or a valve seat. These valve surfaces can have both straight and curved cross-sections or profiles. Furthermore, DE 10 2005 048 226 A1 describes a method for measuring the surface shape and quality of a valve member. In particular, the method provides for measuring the surface profile over both a first and a second distance to obtain first and second groups of data points.

[0006] The present disclosure is directed to overcoming one or more of the problems outlined above. The present invention is particularly directed to reducing or even preventing cavitation damage in fuel injection devices. The object of the present invention is achieved by a valve member according to claim 1 and by a fuel injection device according to claim 3. The subclaims relate to preferred embodiments of the invention.

[0007] The following describes a fuel injector having an injector body with a fuel passage disposed therein, partially defined by an annular valve seat. An electronically controlled valve includes a valve member having 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 composite ring defined by the valve member.

[0008] Further described is a valve member for a fuel injector control valve having a unitary metal body with a threaded bore therethrough concentric with a cylindrical outer surface. A composite ring is defined by the cylindrical outer surface. A portion of the composite ring is also defined by an annular valve surface that is a portion of the cylindrical outer surface. Short description of the drawings Fig. 1 is a cross-sectional schematic view of a fuel injector according to one aspect of the present disclosure; Fig. 2 is an enlarged partial view of the spill valve portion of the fuel injector of the Fig. 1; Fig. 3 is a sectional side view of the valve member for the overflow valve portion of the Fig. 2; Fig. 4 is a sectional side view of a valve member susceptible to cavitation damage; Fig. 5 is an enlarged view of the assembled ring portion of the valve member of the Fig. 3; and Fig. 6 is an enlarged view of the cavitation damage region of the valve member susceptible to cavitation damage. Detailed description

[0009] With reference to Fig. 1, the fuel injector 10 includes an injector body 11 defining a nozzle outlet 12 and a fuel inlet / return port 13. A cam-driven plunger 15 is positioned to move into the injector body 11 to displace fuel into the fuel passage 18 disposed within the injector body 11. A fuel spill passage 20 is disposed within the injector body 11 and extends between the fuel passage 18 and the supply / return port 13. An electronically controlled spill valve 22 includes a valve member 25 with an annular valve surface 43 ( Fig. 2) which moves into and out of contact with an annular valve seat 29 to close and open the overflow passage 20. The valve member 25 has a threaded bore 40 extending therethrough that is concentric with the annular valve surface 43. A solenoid armature 23 is attached to the valve member 25 via a threaded fastener 24 that is fitted into the threads 40 of the valve member 25 by means of an external thread set 40. When the plunger 15 is driven downward to pressurize fuel in the fuel pressurization chamber 17, the fuel may initially be displaced back through the supply / return port 13 via the overflow passage 20.When the electronically controlled valve 22 is energized to move the annular valve surface 43 into contact with the annular valve seat 29, the spill passage 20 is closed and the fuel pressure in the chamber 17 and hence in the nozzle chamber 19 rapidly rises to injection pressure levels.

[0010] The fuel injector 10 also includes an electronic needle control valve 30 that fluidly connects or disconnects a needle control chamber 33 from the fuel passage 18. This electronic needle control valve 30 includes a solenoid that is separate from the electronically controlled spill valve 22. During an injection event, the needle control chamber 33 is fluidly connected to the fuel passage 18, and the pressure on the hydraulic closure surface 34 of the directly controlled needle valve 32 is high, and the nozzle 12 is held closed.When the electronic needle control valve 30 is moved to close this fluid connection, the pressure in the needle control chamber 33 drops via a fluid connection (not shown) to the supply / return port 13, allowing the directly controlled needle valve 32 to lift to open the nozzle outlet 12, provided that the fuel pressure in the nozzle chamber 19 is sufficient to overcome a needle biasing spring in a manner well known in the art.

[0011] Fig. 2 shows the valve member 25 in its downwardly closed position where the annular valve surface 43 is in contact with the annular valve seat 29 to close the spill passage 20. When the solenoid is de-energized, a biasing spring 36 acts on the armature 23 to urge the valve member 25 upwardly to open the annular valve seat 29. When this occurs, the spill passage 20 is fluidly connected to the supply / return port 13 via the composite ring 26, the armature chamber 28, and the low pressure passage 27. The composite ring 26 is defined by the valve member 25, which is preferably a unitary metal body. In the context of the present disclosure, composite ring means a smaller volume ring that opens into a larger volume ring.Thus, an injection event is typically initiated during a downward movement of the plunger 15 by energizing the electronically controlled spill valve 22 to close the annular valve seat 29. The fuel injection event is then begun by moving the electronic needle control valve 30 to a position that relieves the pressure in the needle control chamber 33. An injection event can be terminated either by repressurizing the needle control chamber 33 or by relieving the fuel pressure in the nozzle chamber 19 by reopening the spill control valve 22.

[0012] Now with reference to the Fig. 4 and Fig. 6, a valve member 125 according to a first embodiment comprises a single large ring 126 which is partially defined by the annular valve surface 143. Although this design performs well with regard to cavitation, there is always room for improvement. After many hours of operation, which include many injection cycles, it is possible that cavitation, which may occur around the valve member 125, may begin to erode the ring 126 at a location 110 (which is on the low pressure side of the circuit) according to a pattern 111. It is believed that the cavitation bubbles that occur around the valve member 125 develop shortly after the annular valve seat 29 closes. It is believed that when this occurs, the moment orthe momentum of the fluid overflowing through the spill passage 20 has a water hammer effect in that a vacuum develops adjacent the valve seat 29, and flow conditions cause at least a portion of the cavitation bubbles adjacent the valve member 125 to collapse at location 110. It is possible that over time, the continued collapse of the cavitation bubbles may begin to erode the valve member 125. If the erosion were to continue over time, the erosion would eventually break through into the threaded bore 40, ultimately resulting in the electronically controlled spill valve being less able to fully close the spill passage 20 to allow fuel pressure to develop in the fuel injector. As a result, that injector may be unable to inject fuel, and the associated engine cylinder may become cold.can no longer ignite.

[0013] In order to minimize the amount of debris released into the fuel system due to cavitation erosion, and primarily to simultaneously minimize the likelihood of cavitation erosion, the present invention contemplates a rather counterintuitive approach. In particular, the present disclosure teaches that by adding a ring, such as ring 45, in the vicinity of the potential cavitation erosion pattern 111 and having a size (shape and volume) associated with the potential cavitation erosion pattern 111, as shown in Fig. 6, cavitation erosion can be reduced and possibly even avoided. In other words, it is believed that by preemptively removing material that might otherwise eventually be eroded by cavitation, flow patterns around the valve member can be altered such that either the cavitation bubbles are no longer generated, or they collapse at a location remote from the valve member to minimize the likelihood of erosion at the relevant locations, or to cause any erosion that may occur to occur at a less critical surface within the fuel injector 10.Thus, based on conventional wisdom that might suggest that the precautionary addition of a ring corresponding to a potential cavitation erosion pattern 111 might actually accelerate cavitation erosion, the cavitation erosion minimization strategy disclosed in the present disclosure actually provides a surprising result. Other possible solutions, such as lengthening the ring 26 or altering its contours, may also be possible, but are believed to be less successful in reducing the likelihood of cavitation erosion. Factors that may influence the extent to which the likelihood of cavitation erosion is minimized include the location and size of the additional small ring 45.Since no reliable modeling tools exist to predict the likelihood of cavitation erosion in a relatively complex fluid flow environment of a fuel injector spill valve, some experimentation may be necessary to find a solution. The present disclosure teaches that a good starting point in finding an alternative shape for a valve member to reduce the likelihood of cavitation erosion in a particular area is to preemptively add a ring 45 corresponding to a potential cavitation erosion pattern 111 (remove material relative to a previous valve member design). Thus, in a valve member according to a second embodiment of the present disclosure, the valve member 25 includes a composite ring 26 with a small ring 45 opening into a large ring 44.

[0014] Now with reference to the Fig. 3 and Fig. 5, the valve member 25 according to the second embodiment has a symmetrical cylindrical outer surface extending along its length with various contours including a large diameter segment 47 adjacent to a small diameter segment 46. The composite ring 26 is located in the small diameter segment 46, and the annular valve surface 43 is located at the transition from the small diameter segment 46 to the large diameter segment 47. An additional ring 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 ring 45 is offset by a distance d from the center of the large ring 26, but not so far that the small ring 45 shares a common wall segment with the surface defining the annular valve surface 43. According to an exemplary embodiment, the small ring 45 has a U-shaped cross-section, which may be semicircular, with proportions as shown in Fig. 5. However, one skilled in the art will recognize that the position, shape, and size of the small ring 45 could be varied to achieve satisfactory results. Industrial applicability

[0015] The teachings of the present disclosure are directed to producing a valve member that reduces the likelihood of erosion caused by cavitation. The present disclosure has potential application to any fuel injector that exhibits, or is likely to exhibit, cavitation erosion on an outer surface of a valve member. The present disclosure has particular application to reducing the likelihood of cavitation erosion in a spill valve of a mechanically actuated, electronically controlled unit injector. Thus, the present disclosure is also directed to reducing the likelihood of introducing metallic debris into a fuel system, which can also cause galling and pitting of moving parts.The present disclosure recognizes that cavitation erosion considerations 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 operated for many hours and potentially millions of injector cycles. Thus, the present disclosure may also address 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 electronically controlled valve of a fuel injector. Once the occurrence of cavitation erosion is noted, the cavitation erosion pattern 111 on the valve member 125 may be identified.This can be achieved, for example, by operating a plurality of fuel injectors for a sufficient number of hours to demonstrate an expected magnitude and variation of the cavitation erosion pattern among the valve members for the plurality of fuel injectors. An alternative valve member design can be made that is substantially identical to the valve member of the previous design in a region corresponding to the cavitation erosion pattern or the likely cavitation erosion pattern, except that the new valve member defines an additional annulus corresponding to the cavitation erosion pattern.The term "corresponding" in this case refers to the note that the additional ring is located where the cavitation erosion pattern is identified or likely, and the size and shape of the additional ring may be related to the average cavitation erosion observed over a certain period of time. In other words, adding an additional ring that is too small or too large may have no effect on the probability of cavitation erosion or the actual cavitation erosion that occurs. In addition, incorrectly placing the added small ring may also lead to a situation where there is little or no effect on the probability of cavitation erosion or on the occurrence of cavitation erosion.

[0016] Once a cavitation erosion pattern 111 has been identified, the present disclosure would suggest that a first attempt to find a solution would be to form new valve members with an additional ring having different combinations of cross-sectional shape, volume, and arrangement at the cavitation erosion location 110. Then, new fuel injectors with the new valve member should be operated for a number of hours in order of when cavitation erosion started or was likely to start in the previous version of the valve members. Those skilled in the art will recognize that more favorable conditions for cavitation can be created by increasing the fluid temperature. This can accelerate the iteration process in finding a suitable design alternative. The new valve members would then be sorted according to a cavitation erosion criterion.For example, some of the new valve members may show no sign of cavitation erosion, some may show a hint of cavitation erosion, such as some limited cavitation erosion, and others may even show more severe cavitation erosion than the unmodified valve members with the previous design. Using this technique, in one or two or more iterations as needed, should allow for the creation of an additional annular shape, location, and volume that sufficiently mitigates the cavitation erosion problem so that the valve member can be expected to exhibit a performance life comparable to that expected from other fuel injector components.In other words, a fuel injector with a modified or new valve member with an added ring could be expected to have an extended service life compared to an earlier version, which could mean that during a remanufacturing or retrofitting process, the valve would not need to be replaced when other parts of the fuel injector needed to be replaced.

[0017] In the specific case where cavitation erosion is occurring or has the potential to occur in a pre-existing ring, the present disclosure teaches that the additional small ring 45 can be added so that it opens into the large ring 44 to result in a composite ring 26 that substantially reduces or eliminates the likelihood of cavitation erosion. While the disclosed cavitation reduction strategy may not result in the elimination of cavitation bubbles, the strategy may result in a change in flow patterns in the affected region, causing cavitation bubbles to collapse in a location where some erosion is more acceptable, or in a location that does not produce cavitation erosion or is less likely to produce cavitation erosion.In the case of the present disclosure, a U-shaped small ring 45 with a semicircular cross-section may be added at a location corresponding to a possible cavitation erosion pattern 111, at a location offset from the center of the large ring 44.

[0018] It should be noted that the above description is provided 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 recognize that other aspects of the invention may be obtained from a study of the drawings, the disclosure, and the appended claims.

Claims

[1] A valve member (25, 125) for a fuel injector control valve comprising a unitary metal body having a threaded bore therethrough concentric with a cylindrical outer surface (42); wherein the cylindrical outer surface (42) has a composite ring (26); wherein a portion of the composite ring (26) is defined by an annular valve surface (43); wherein the composite ring (26) is located in a small diameter segment (46) of the cylindrical outer surface (42); wherein an additional ring is defined by a large diameter segment (47) of the cylindrical outer surface (42); wherein the composite ring (26) has a small ring (45) which opens into a large ring (44); wherein a center of the small ring (45) is offset with respect to a center of the large ring (44); and wherein the small ring (45) has a U-shaped cross-section. [2] Valve member (25, 125) according to claim 1, wherein the large diameter segment (47) extends over a greater length than the small diameter segment (46). [3] Fuel injection device comprising: an injector body (11) having a fuel passage (18) disposed therein, partially defined by an annular valve seat (29); an electronically controlled valve comprising a valve member (25, 125) according to claim 1 or 2; wherein the annular valve seat (29) is located at a transition from the small diameter segment (46) to the large diameter segment (47) of the valve member (25, 125), and wherein the valve member (25, 125) is configured to move into and out of contact with the valve seat (29) to open and close the fuel passage (18). [4] The fuel injector of claim 3, wherein the electronically controlled valve is a spill valve, and wherein the fuel passage (18) is a spill passage (20); wherein a plunger (15) is positioned to move within the injector body (11) to displace fuel from a fuel pressure chamber (17) disposed within the injector body (11); and wherein the overflow passage (20) is arranged in the injector body (11) and extends between the fuel pressure chamber (17) and a low-pressure outlet. [5] A fuel injector according to claim 4, wherein the valve member (25, 125) has a threaded bore extending therethrough concentric with the annular valve surface (43); a solenoid armature (23) attached to the valve member (25, 125) via a threaded fastener (24) to mate with the threaded bore.

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