Patent Application
20130248612
The present disclosure relates generally to stopping an armature of a solenoid actuator, and more specifically to a fuel injector with an armature assembly that includes a soft magnetic armature and a hard non-magnetic stop piece.
One class of fuel injectors for common rail compression ignition engines include a single solenoid actuator to relieve and apply pressure to a closing hydraulic surface of a direct control needle valve. Fuel injection events are typically initiated by energizing the solenoid, and opening a valve responsive to movement of an armature assembly toward a stator. Injection events are ended by de-energizing the solenoid to allow the valve to reclose to resume pressure on the closing hydraulic surface of the direct control needle valve. Performance advantages have been observed by providing a solenoid actuator with the ability to precisely control injection sequences that include short dwell times separating substantial injection quantities from precisely controlled small injection quantities.
In an effort to improve performance in limited spatial envelopes, engineers have adopted a variety of materials to accommodate the various needs of a complete solenoid actuator. For instance, a highly magnetic but extremely fragile compound, which is sometimes referred to as somaloy, is attractive for use in stators for solenoid assemblies. Other components, such as the piece that links a soft magnetic armature to the valve member, might include a relatively hard non-magnetic high impact material. Although utilization of various materials for different components of solenoid actuator have incrementally improved performance, new problems continue to occur, and old problems endure making design changes to improve precise, consistent and robust performance elusive.
The present disclosure is directed toward improving upon solenoid actuators for fuel injectors.
In one aspect, a fuel injector includes an injector body that defines a fuel inlet and a plurality of nozzle outlets, and includes a stop surface. A direct control needle valve has a closing hydraulic surface positioned in a needle control chamber. A solenoid actuator has an armature assembly that moves as a unit with respect to a stator between an initial air gap position and a final air gap position, such that the armature assembly is always out of contact with the stator. The armature assembly includes a soft magnetic armature and a hard non-magnetic stop piece, which is located further from the stator than the armature. The stop piece is in contact with the stop surface at the final air gap position, but is out of contact with the stop surface at the initial air gap position.
In another aspect, a solenoid actuator includes an actuator body with a stop surface. A stator is mounted to the actuator body and has a centerline. An armature assembly moves between an initial air gap position and a final air gap position. The armature assembly includes a soft magnetic armature and a hard non-magnetic stop piece that are each attached to a pin at a small radius from the centerline. The stop piece is in contact with the stop surface at a large radius from the centerline when at the final air gap position, but is out of contact with the stop surface at the initial air gap position.
In still another aspect, a method of injecting fuel includes starting an injection event by energizing a solenoid actuator, and ending the injection event by de-energizing the solenoid actuator. The energizing step includes moving an armature assembly toward a stator. The stator is protected from impact damage by maintaining the armature assembly out of contact with the stator. Residual magnetism in the armature assembly is reduced by stopping the armature assembly outside of a magnetic flux circuit through the stator and soft magnetic armature of the armature assembly, when the solenoid actuator is energized.
Referring to
Solenoid actuator 30 includes an armature assembly 31 that moves as a unit with respect to a stator 32 between an initial air gap position and a final air gap position, such that the armature assembly 31 is always out of contact with stator 32. Armature assembly 31 and stator 32 are positioned in an actuator body 12, which is merely a subset of the components that make up injector body 11. Stator assembly 32 is typical in that it includes a coil winding, which may be surrounded by soft delicate, but highly magnetic material, sometimes referred to somaloy. The somaloy may be partially or fully enclosed by a magnetic metallic alloy with sufficient strength to support stator 32 under the expected clamping forces that exist to hold fuel injector 10 together. Although not necessary, stator 32 may be ground or otherwise manufactured to include a planar bottom surface 38. Armature assembly 31 includes a soft magnetic armature 35 and a hard non-magnetic stop piece 36 that may both be mounted to move as a unit with pin 37. The non-magnetic stop piece 36 is located further from the stator than the armature 35 so that the armature assembly 31 can be stopped outside of a magnetic flux circuit 55 through the stator 32 and the soft magnetic armature 35, when solenoid actuator 30 is energized. Preferably, the upper surface of soft magnetic armature 35 is planar and parallel to the bottom planar surface 38 of stator 32. Soft magnetic armature 35 may be made from powdered metal with good magnetic properties, but too soft to undergo repeated impacts. On the other hand, hard non-magnetic stop piece 36 may be a suitable steel alloy (e.g. stainless steel) that is hard to undergo repeated impacts, but that same hardness may undermine the ability of the stop piece 36 to be a good carrier of magnetic flux. Armature 35 and stop piece 36 may be attached to pin 37 in any suitable manner, such as for instance welding.
Injector body 11 includes a guide piece 15 that defines a guide bore 29 that receives pin 37. Thus, pin 37 undergoes a guide interaction with guide piece 15 to ensure that armature assembly 31 moves along centerline 19 between its initial and final air gap positions with respect to stator 32. When armature assembly 31 moves upward due to the energization of solenoid actuator 30, its movement is arrested when stop piece 36 comes in contact with a stop surface 20, which is located on a planar bottom of an annular stop spacer 16. Stop spacer 16 is stacked in contact with an annular air gap spacer 17, and both annular spacers 16 and 17 should be considered portions of the injector body 11 (or actuator body 12, for purposes of the present disclosure). Although not necessary, the annular air gap spacer 17 and annular stop spacer 16 may be clamped between the bottom planar surface 38 of stator 32 and a top surface of guide piece 15. Both of the annular spacers 16 and 17 have planar top and bottom surfaces separated by a wall of a relatively uniform thickness. The planar top and bottom surfaces are separated by a spacer distance. In terms of manufacturing, the annular stop spacer 16 may have a fixed spacer size, but the air gap spacer 17 may be a category part of various heights so that tolerance stack ups can be overcome by selecting an appropriate height spacer. This allows different fuel injectors to have different height spacers, but relatively uniform distances associated with the initial and final air gaps separating armature 35 from stator 32. This of course allows different fuel injectors 10 to respond more consistently with each other to the same control signals.
Although not necessary, fuel injector 10 may be equipped with an over travel spring 49, which is relatively weak relative to biasing spring 48. Over travel spring 49 allows the armature assembly 31 to continue downward travel after solenoid actuator 30 has been de-energized and control valve member 25 has come into contact with flat valve seat 22. This feature may serve to inhibit valve bouncing that could undermine settling times and/or lead to undesirable secondary injection events.
As best shown in
Referring now in addition to
The solenoid actuator of the present disclosure could find potential in applications that require short movement distances, fast action and short settling times. The solenoid actuator finds specific applicability in fuel injectors, and even more specific application in common rail fuel injectors to control relieving and applying pressure to a closing hydraulic surface of a direct control needle valve. The present disclosure is specifically applicable when the solenoid actuator utilizes relatively soft delicate, but highly magnetic materials that are not well suited to undergo repeated impacts during the operation of fuel injector 10. Thus, the present disclosure finds specific applicability when there is a desire to maintain the armature assembly out of contact with the stator throughout movement of the armature assembly from its initial air gap position to its final air gap position.
When fuel injector 10 is being operated, an injection event may be started by energizing solenoid actuator 30. The injection event may be ended by de-energizing solenoid actuator 30. When solenoid actuator 30 is energized, the armature assembly 31, 131 moves toward stator 32. The stator 32, and maybe armature 35, 135, are protected from impact damage by maintaining the armature assembly 31, 131 out of contact with the stator 32 at all times. In addition, inducement of residual magnetism in the armature assembly 31, 131 may be reduced by stopping the armature assembly 31, 131 outside of the magnetic flux circuit 55 through the stator 32 and a soft magnetic armature 35, 135 of the armature assembly 31, 131 when the solenoid actuator 30 is energized. As stated earlier, the armature assembly 31, 131 moves from the initial air gap position to the final air gap position responsive to energizing the solenoid actuator 30. In addition, pressure on the closing hydraulic surface 28 direct control needle valve 27 is relieved responsive to the armature assembly 31, 131 moving away from the initial air gap position. The armature assembly 31, 131 is stopped by contacting the stop piece 36, 136 with a stop surface 20, 120 of the injector body 11. Pressure on the closing hydraulic surface 28 is resumed responsive to de-energizing solenoid actuator 30 so that biasing spring 48 can act on pin 37, 137 to push control valve member 25 back downward into contact to close flat valve seat 22. When this is done, the fluid connection between the needle control chamber 21 and the drain outlet 18 is blocked.
The present disclosure presents a strategy for reducing impact damage to the soft magnetic components of a solenoid actuator. In addition, the disclosed strategy reduces inducement of residual magnetism in the armature assembly, which could otherwise make the armature assembly's movement back toward its initial air gap position sluggish following de-energization of the solenoid actuator.
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.
