Patent Application
20120085835
The present disclosure relates generally to fuel injectors, and more particularly to a needle valve member for a fuel injector that includes a frustoconical guide segment.
Almost all fuel injectors include an injector body that defines one or more nozzle outlets, and includes a needle valve member that moves between positions to open and close the nozzle outlets. The needle valve member is typically guided within the fuel injector via a relatively tight diametrical clearance between a cylindrical guide segment of the needle valve member and a cylindrical guide bore disposed within the fuel injector body. The needle valve member includes an opening hydraulic surface that is exposed to fluid pressure in a nozzle chamber, and a spring is utilized to bias the needle valve member downward toward a closed position. In some fuel injectors, the needle valve member includes a closing hydraulic surface exposed to fluid pressure in a needle control chamber. In these instances, an electronically controlled valve is moved to fluidly connect and disconnect the needle control chamber from a low pressure passage in order to change pressures on the closing hydraulic surface of the needle valve member to facilitate movement of the needle valve member for injection events. These fuel injectors can be considered to include a direct operated check.
Over the years, engineers have continued to seek ways to inject fuel into the combustion space of a compression ignition engine in a manner that reduces the production of undesirable emissions, including but not limited to, NOx, particulate matter and unburned hydrocarbons. In general, these goals are improved by operating the fuel injector in a way that the needle valve member lifts toward an open position at a slower rate than it is moved toward a closed position. Thus, abrupt closure of the nozzle outlets is generally preferred, and a less than abrupt opening of the nozzle outlets has found favor. In this regard, many efforts have been made to improve this aspect of control including changes and refinements to electrical actuators, their associated valves, adding orifices to alter pressure change rates, changing area ratios of hydraulic features and many more considerations in a continuing effort to eek out incremental improvements in performance. Nevertheless, easily implemented improvements remain problematic and elusive.
The present disclosure is directed to one or more of the problems set forth above.
In one aspect, a fuel injector includes an injector body with a tip component that defines at least one nozzle outlet, and has disposed therein a needle control chamber separated from a nozzle chamber by a frustoconical bore that tapers inward in a direction of the tip component. A needle valve member is positioned in the injector body, and includes an opening hydraulic surface exposed to fluid pressure in the nozzle chamber, and a closing hydraulic surface exposed to fluid pressure in the needle control chamber. The needle valve member is movable between a first position at which the nozzle outlet is blocked from the nozzle chamber, and a second position at which the nozzle outlet is open to the nozzle chamber. A frustoconical segment of the needle valve member is positioned in the frustoconical bore and has a narrowing taper in the direction of the tip component.
An injection event is initiated by the fuel injector by moving the needle valve member from a closed position toward an open position by reducing pressure on the closing hydraulic surface. An end of an injection event is initiated by moving the needle valve member from the open position toward the closed position by increasing pressure on the closing hydraulic surface.
In another aspect, a needle valve member for a fuel injector includes a frustoconical segment positioned between a closing hydraulic surface and a tip. The frustoconical segment narrows in a direction of the tip. An enlarged spring support shoulder is positioned between the tip and the frustoconical segment. An annular valve surface is positioned between the tip and the enlarged spring support shoulder. An opening hydraulic surface is positioned between the annular valve surface and the frustoconical segment.
Referring to
The injector body 11 includes a tip component 30, a spacer 31, a high pressure containment sleeve 32 and a guide component 33 that are held clamped together by a casing 34. Tip component 30 defines the nozzle outlets 12. Together, tip component 30, spacer 31, pressure containment sleeve 32 and guide component 33 define a nozzle chamber 21 that is fluidly connected to common rail inlet 13 by a nozzle supply passage 28. The common rail inlet 13 includes a conical seat 26 for receiving a conventional spherically ended quill (not shown) to facilitate fluid communication with a common rail (not shown).
A needle valve member 40 is positioned in injector body 11, and movable between a closed position as shown, and an upward open position. When in the closed position, an annular valve surface 49 contacts a seat 38 to block fluid communication between nozzle chamber 21 and sac 29. An opening hydraulic surface(s) 41 is positioned between annular valve surface 49 and a frustoconical segment 43. In the illustrated embodiment, the opening hydraulic surface 41 is partly located contiguous with annular valve surface 49 and partly located where the diameter grows to meet the small diameter end 46. An enlarged spring support 48 may be positioned between tip 47 and frustoconical segment 43. The annular valve surface 49 is positioned between the tip 47 and the enlarged spring shoulder 48. An enlarged guide portion 44 is positioned between the annular valve surface 49 and the enlarged spring support shoulder 48. As shown in
Nozzle chamber 21 is separated from a needle control chamber 20 by a frustoconical bore 23 defined by guide component 33 as best shown in
Needle control chamber 20 is defined by guide segment 33, an orifice disk 36 (
Those skilled in the art will appreciate that the action associated with the movement of needle valve member 40 is closely related to the effective area of closing hydraulic surface 42, the pressure in needle control chamber 20, the effective area of opening hydraulic surface(s) 41, the pressure in nozzle chamber 21 and the biasing force from spring 60. In almost all fuel injectors, the needle valve member is typically guided in its movement by a cylindrical guide segment received in a cylindrical bore, rather than the frustoconical segment received in a frustoconical bore as per the present disclosure. In all cases of the present disclosure, the frustoconical segment 43 of needle valve member 40 includes a large end diameter 45 that tapers inward in the direction of tip 47 down to a small end diameter 46. The effective opening hydraulic area is closely related to the difference between the small end diameter d and the seating diameter 51. In all cases of the present disclosure, the large end diameter 45 is greater than the small end diameter 46, which in turn is greater than the seating diameter 51.
Slight tapers fall within the scope of the present disclosure. However, one could expect the benefits associated with the present disclosure to become more problematic as the taper angle of the frustoconical shape increases due in part to the possibility of new failure modes in the movement of needle valve member 40 as well as the fact that the diametrical clearance 25 between the frustoconical segment 43 and the frustoconical shaped bore 23 increases when the needle valve member 40 moves toward its upward open position. This increase in the diametrical clearance becomes more exacerbated with larger taper angles. In general, predictable and repeatable performance is better achieved when the guide clearance 25 is small so that the fluid communication between nozzle chamber 21 and needle control chamber 20 via the diametrical clearance 25 is small in contributing to pressure changes within needle control chamber 20. When diametrical clearance 25 becomes larger, the potential for fluid flow in the diametrical clearance becomes greater, which can contribute to unpredictable and less control over pressure in needle control chamber 20. Given these considerations, the large end diameter 45 may be up to fifteen percent larger than the small end diameter 46, but that difference is preferably greater than five percent. Although not necessary, the length 24 of frustoconical bore 23 is greater than larger diameter 45. Those skilled in the art will appreciate that longer guide bores 23 tend to help in fluidly isolating needle control chamber from nozzle chamber along the diametrical clearance 25.
Over the years, engineers have observed, in general, lower undesirable emissions can be achieved from a combustion event when the needle valve member movement from its closed position toward its open position is slower than the counterpart movement from the open position toward the closed position. Also in general, the best results are often associated with very abrupt movement of the needle valve member from its open position to its closed position, but a slower opening rate associated with a more gradual increase in injection rate toward the beginning of an injection event is also desirable, again in general. The frustoconical shape of segment 43 of needle valve member 40 in conjunction with the frustoconical bore 43 may tend to improve both of these characteristics relative to a counterpart equivalent fuel injector that includes a typical cylindrical guide segment received in a cylindrical bore. This improvement may be attributable to the net opening hydraulic forces being smaller in the case of the frustoconical features of the present disclosure relative to the counterpart fuel injector with cylindrical features, and the net closing hydraulic force may be larger in the case of the present disclosure relative to a counterpart fuel injector with cylindrical features. The net result being a potentially slower opening of the needle valve member and a more abrupt closure, which may lead to an incremental improvement in reductions in undesirable emissions relative to an equivalent fuel injector with cylindrical features operating under the same pressures with an identical control signal. In addition, the frustoconical features of the present disclosure may afford the opportunity to decrease the minimum controllable fuel injection quantity for the fuel injector relative to its cylindrical feature counterpart.
The present disclosure finds potential application in any fuel injector, but finds particular application in fuel injectors that include a direct operated check. Those skilled in the art will appreciate that a direct operated check refers to fuel injector with a needle valve member having an opening hydraulic surface exposed to fluid pressure in a nozzle chamber, and a closing hydraulic surface exposed to fluid pressure in a needle control chamber, whose pressure can be controlled by an electrical actuator in a known manner. The frustoconical strategy of the present disclosure allows for a potentially incremental improvement in performance of a fuel injector with a small change to the shape of a segment of the needle valve member and its associated guide bore. Thus, the present disclosure offers the possibility of a small incremental improvement in performance without the risks and uncertainties associated with a complete redesign.
When the fuel injector 10 operates, each injection event is initiated by moving needle valve member 40 from a closed position, as shown, toward an open position by reducing pressure on the closing hydraulic surface 42. Injection events are ended by moving the needle valve member from the open position toward the closed position by increasing pressure on the closing hydraulic surface 42. Between consecutive injection events, the pressure in nozzle chamber 21 and needle control chamber 20 may equalize to the pressure in nozzle supply passage 28 (common rail pressure) by the nozzle supply passage's 28 fluid connection to nozzle chamber 21 and to needle control chamber 20 via orifice passage 70. Thus, both the nozzle chamber and the needle control chamber are fluidly connected to the common rail inlet 13 between injection events. Movement of the needle valve member during both opening and closing is guided by an interaction between frustoconical segment 43 and frustoconical bore 23 as well as an interaction between large guide portion 44 with guide wall 35.
Referring now in addition to the graphs of
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 disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
