Patent Application
20080169366
The present disclosure relates generally to solenoid actuated valves, and more particularly to a method of joining a valve member to an armature via an intervening nut.
Fuel Injectors typically utilize one or more electronically controlled valves to control fuel injection quantity and timing independent of engine crank angle. In some instances, the electronically controlled valve takes on a typical structure that utilizes a relatively hard non-magnetic valve member that is attached by some means to a relatively soft magnetic armature. When a solenoid coil is energized, the armature is drawn toward the coil, and the valve member is moved toward or away from a valve seat. Because of many factors including the high number of impact cycles, the presence of liquid around the armature, acceleration from the coil and inertia factors, making a robust attachment strategy between the armature and the valve member to survive this hostile environment over many millions of actuation cycles, and do so at a reasonable cost, can be somewhat problematic.
Besides the repeated accelerations and decelerations encountered by these electronically controlled valves, other problems have been associated with consistently manufacturing large quantities of valves with relatively small air gaps that allow for relatively short valve travel distances. Those skilled in the art recognize that short travel distances are often desirable since they correlate closely to quick valve response times. Thus, insuring good perpendicularity between the armature and the valve member can allow for tighter tolerances and reduced air gap distances, and a corresponding decrease in valve response time.
In one previous valve assembly structure that addressed these problems, the valve member included an annular shoulder upon which a spacer would be supported. An armature having a guide clearance with the valve member sits atop the spacer with a relatively tight guide clearance. The perpendicular plane of the shoulder and the tight guide clearance supposedly insure good perpendicularity. Atop the armature is another spacer followed by a threaded nut that would hold the two spacers and armature securely against the shoulder of the valve member. While such a solution provides adequate long term robustness to withstand the repeated accelerations and decelerations, relying upon interactions between supposedly perpendicular surfaces on the components themselves to insure perpendicular geometry, especially at edges of the armature remote from the valve member centerline can be more problematic.
Another potential solution, which is taught in co-owned U.S. patent application Ser. No. 11/073,571, filed Mar. 8, 2005, teaches the idea of using an orientation neutral interface between the armature and the valve member, utilizing a fixture to arrange the pieces with good perpendicularity, and then welding the armature directly to the valve member. While such a strategy probably improves upon the perpendicularity issues of the previously discussed strategy, the welded joint between the armature and the valve member may not be as robust as the usage of a nut and spacers. An orientation neutral interface might be one in which the valve member includes an annular raised rounded portion upon which the armature can be press fit in a variety of orientations (plus or minus a fraction of a degree) to allow for setting in a fixture to achieve relatively near perfect perpendicularity. This alternative also has the undesirable feature of having to leave a portion of the valve member less heat treat hardened in order to make it “weldable.” While this strategy has shown promise, a valve member with a relatively small diameter reduces the amount of weld interface available, which may not provide as robust an attachment as other strategies.
The present disclosure is directed toward one or more of the problems set forth above.
In one aspect, a valve assembly includes a valve body having a contact surface defining a stacking plane. A valve member with a shoulder stop and a set of external threads is received in the valve body. A nut is threadably attached to the set of external threads at a first diameter with the nut in contact with the shoulder stop. An armature is affixed to the nut at a second, larger diameter, and has a surface defining an air gap plane parallel separated from the stacking plane by an air gap distance.
In another aspect, a fuel injector includes an injector body with a stack of components that include a valve body of a valve assembly in contact between a coil component and a needle control component at first and second stacking planes, respectively, that are parallel to each other. The valve assembly includes a valve member with a set of external threads and a shoulder stop. A nut is threadably attached to the set of external threads at a first diameter and in contact with the shoulder stop. An armature is affixed to the nut at a second, larger diameter, and has a surface defining an air gap plane parallel separated from the first stacking plane by an air gap.
In still another aspect, a method of assembling a valve for a fuel injector includes inserting a threaded end of a valve member through a guide bore of a valve body. A nut is threaded onto the threaded end of the valve member until the nut contacts a shoulder stop on the valve member. A surface of an armature that defines an air gap plane if positioned in parallel with, and at an air gap distance from, a stacking plane defined by a contact surface of the valve body. The armature is fit onto the outer surface of the nut with an interference fit, and then the armature is affixed to the nut via a weld.
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In addition to the coil 34 associated with spill valve 30, coil component 37 includes a second coil 53 associated with needle control valve assembly 40. In that instance, coil component 37 is in contact with valve assembly component 38 at a stacking plane 61. Valve assembly 40 includes a valve member 50 in sliding guide contact with valve assembly component 38 at a guide bore 36. In order to improve performance, valve member 50 may be hardened, especially at its valving surfaces. This hardening may render portions, or all, of valve member 50 “unweldable” and non magnetic. A nut 51 is attached to valve member 50, and an armature 52 is affixed to nut 51 such that an air gap plane 64 is created between armature 52 and the underside or stacking plane 61 of coil component 37. The material of the armature may be soft, weldable and magnetic relative to the valve member 50. There is no direct contact between armature 52 and valve member 50. The valve assembly component 38 is in contact with needle control component 39 at a stacking plane 60. The upper surface or stacking plane 60 of needle control component 39 defines a flat seat 58. Valve member 50 is trapped to move between flat seat 58 and a conical seat 59. In other alternative embodiments one of the seats could be a simple stop surface, and the conical seat could be substituted for the flat seat, and vice versa. When in contact with conical seat 59, the pressure control chamber 44 (
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The assembly of needle control valve assembly 40 is initiated by inserting the threaded end 71 of valve member 50 through guide bore 56. Next, nut 51 is threaded onto valve member 50 until it contacts shoulder stop 70. Meanwhile, an armature 52 is placed on and in contact with elevated air gap plane support surface 98. Next, the nut is advanced into cylindrical bore 57 (
Since the nut 51 presents a larger diameter weld with respect to armature 52 than if the armature were welded directly to valve member 50, a substantially strengthened attachment can be created. In addition, not only is there a larger weld, but some of the repeated acceleration and decelerations applied to armature 52 and valve member 50 may be absorbed by the threaded attachment between nut 52 and valve member 50. In addition, by utilizing an orientation neutral interface 75 between the nut 51 and armature 52, the perpendicularity between the air gap plane 64 of the armature 52 and the centerline 55 of the valve member 50 can be set with great precision, especially when utilizing a fixture as shown. In addition, this attachment strategy results in a reduction of parts associated with a previous strategy that utilized two spacers, and allows for a more precise setting of the air gap plane to valve member centerline perpendicularity. Thus, the attachment strategy taught produces a robust attachment that has a higher level of orientation precision, and this all is accomplished with a reduced number of parts, and an associated reduction in cost. In addition, because of the larger diameter weld location afforded by nut 52, the disclosed attachment strategy represents a substantially more robust attachment than if the armature were simply welded directly to the valve member at a relatively smaller diameter. In addition, the strategy of the present disclosure also allows for less special care being taken in heat treat hardening of valve member 50, since no welds will be made to the valve member, and the armature is separated and out of contact with the valve member via the intervening nut 51. In addition, the material utilized for the nut can be chosen without compromise for improved welding strength, which further allows for a robust connection.
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. Although the valve assembly of the present disclosure has been shown in the context of a cam driven fuel injector, those skilled in the art will appreciate that the valve assembly could be utilized in other fuel injectors, including hydraulically actuated, or common rail fuel injectors, and could find potential application in many valving applications outside the fuel injector arena where repeated accelerations and decelerations can fatigue a connection strategy between a relatively soft magnetic armature and a relatively hard non-magnetic valve member.
