Patent Publication Number: US-2013248612-A1

Title: Solenoid Actuator And Fuel Injector Using Same

Description:
TECHNICAL FIELD 
     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. 
     BACKGROUND 
     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. 
     SUMMARY 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front sectioned view of a fuel injector according to the present disclosure; 
         FIG. 2  is an enlarged front sectioned view of the solenoid actuator portion of the fuel injector of  FIG. 1 ; 
         FIG. 3  is a front sectioned view of an armature assembly according to another embodiment of the present disclosure; 
         FIG. 4  is a sectioned perspective view of the armature assembly of  FIG. 3 ; 
         FIG. 5  is a top view of an armature stop spacer according to the embodiment of  FIG. 3 ; and 
         FIG. 6  is a top view of the armature assembly of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1 and 2 , a fuel injector  10  includes an injector body  11  that defines a fuel inlet  13 , a plurality of nozzle outlets  14  and a drain outlet  18 . The term “injector body” is intended to encompass those components of fuel injector  10  that are fixed in position at all times. Thus, the injector body  11  includes multiple, but not all, of the components that make up fuel injector  10 . Fuel injector  10  is illustrated as a common rail fuel injector for use in compression ignition engines, but could be a different type of fuel injector for a different type of engine. The common rail nature of fuel injector  10  is evidenced by fuel inlet  13  having a conical shaped seat to receive a quill for supplying high pressure from a common rail (not shown). Nozzle outlets  14  are opened and closed with a direct control needle valve  27  by relieving and applying pressure to a closing hydraulic surface  28  that is positioned in a needle control chamber  21 . Fuel injector  10  may include a single solenoid actuator  30  that controls movement of a control valve member  25  with respect to a flat valve seat  22 . When solenoid actuator  30  is de-energized, a biasing spring  48  causes a pin  37  to push control valve member  25  downward into contact with a flat seat  22 . When solenoid actuator  30  is energized, pin  37  moves upward along centerline  19  to allow control valve member  25  to move out of contact with flat seat  22  to fluidly connect needle control chamber  21  to low pressure drain outlet  18 . When this occurs, pressure acting on closing hydraulic surface  28  drops, and the direct control needle valve  27  lifts to an open position responsive to continuous high fuel pressure on opening hydraulic surface  26  to commence an injection event. 
     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  FIG. 2 , the soft magnetic armature  35  has a perimeter surface  40 , which may be circular, surrounded by, but spaced from, an inner surface  41  of annular stop spacer  16 . The separation between perimeter surface  40  and inner surface  41  might have a minimum distance that is greater than the separation distance between the armature  35  and stator  32  at the initial and final air gap positions. This spacing may help to encourage magnetic flux path  55  to stay in the stator  32  and soft magnetic armature  35  without substantial portions of the magnetic flux arcing over through annular spacer  16 . Also shown in  FIG. 2 , the stop piece  36  has a perimeter surface  42  surrounded by, but spaced from, the annular air gap spacer  17 . It should be pointed out that the soft magnetic armature  35  and the hard non-magnetic stop piece  36  may be attached to pin  37  at a relatively small radius  51 , but stop surface  20  contacts stop piece  36  at a relatively large radius  52  from centerline  19 . Those skilled in the art will appreciate that the one or both of the stop piece  36  and the annular stop spacer  16  may be coated at the contact surface with a layer of hardening material to further allow for repeated impacts without undermining performance of fuel injector  10 . 
     Referring now in addition to  FIGS. 3-6 , an alternative embodiment of an armature assembly  131  includes different features that may assist in the manufacturability of fuel injector  10 . Like the earlier embodiment, armature assembly  131  includes a soft magnetic armature  135  and a hard non-magnetic stop piece  136  that are attached to a pin  137  that is guided in a guide bore  129  of a guide piece  115 . This embodiment differs in that the armature  135  may have a perimeter surface  140  that has a non-circular shape that may be received through an inner surface of annular stop spacer  116 . In particular, and in one specific example, annular stop spacer  116  may define a hexagonal inner surface just larger than a hexagonal perimeter surface  140  of armature  135 . In this way, the armature assembly  131  may be fitted into guide piece  115  during the assembly of fuel injector  10 . Thereafter, annular stop spacer  116  would be maneuvered from above past and over soft magnetic armature  135  to a position resting on a shoulder top surface of guide piece  115 . Thereafter, the two components could be rotated out of phase, as best shown in  FIG. 6 . Next, the appropriate height air gap spacer  117  would be positioned atop stop spacer  116 . Thereafter, the stator  32  would be clamped down into contact with an upper planar surface of annular air gap spacer  117 . This embodiment differs in that the perimeter surface  140  of the soft magnetic armature  135  has a minimum spacing distance separating it from the inner surface  141  of the air gap spacer  117 , whereas the earlier embodiment showed this spacing between the armature  135  and the stop spacer  116 . This embodiment also differs in that the perimeter surface  142  of the stop piece  136  is separated at some minimum distance from an inner wall of guide piece  115 . These spacings might be chosen to encourage the magnetic flux circuit  55  ( FIG. 1 ) to stay between stator  32  and armature  135  rather than arcing over through one of the air gap spacers  17 ,  117  or stop spacers  16 ,  116 . The embodiment of  FIGS. 3-6  also differs in that the stop piece  136  and the annular air gap spacer  117  are located on opposite sides of the annular stop spacer  116  along centerline  19  of pin  137 . 
     INDUSTRIAL APPLICABILITY 
     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&#39;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.