Precision Ground Armature Assembly For Solenoid Actuator And Fuel Injector Using Same

Abstract

A solenoid actuator includes a hard guide piece and a soft flux piece. The hard guide piece has a stop surface ground to create a final air gap distance between the soft flux piece and a stator assembly when the stop surface on the guide piece is in contact with the stator assembly. The final air gap is set by grinding the stop surface on the guide piece so that the distance between the stop surface on the guide piece and a top surface on the soft flux piece along an axis of the guide bore is equal to the final air gap. The step of grinding the armature assembly may be done after attaching the guide piece and the flux piece together. In an exemplary embodiment, the step of grinding the stop surface and associated guide surface(s) are performed in a single chucking.

What is claimed is: 
     
         1 . A fuel injector comprising:
 an armature assembly including a flux piece attached to a guide piece which includes a stop surface;   the guide piece being slidably movable from a first position where the guide piece is out of contact with a valve member and the stop surface on the guide piece is in contact with a stator assembly, and a second position where the guide piece is in contact with the valve member and the stop surface on the guide piece is out of contact with the stator assembly.   
     
     
         2 . The fuel injector of  claim 1  wherein:
 the valve member moves a valve travel distance between a first stop and a second stop; 
 the armature assembly moves an armature travel distance between the first position and the second position; 
 the armature travel distance being greater than the valve travel distance. 
 
     
     
         3 . The fuel injector of  claim 1  further including:
 a first spring operatively positioned to bias the armature assembly towards the second position; 
 a second spring operatively positioned to bias the valve member towards the second stop. 
 
     
     
         4 . The fuel injector of  claim 3  wherein:
 the first spring has a first preload; 
 the second spring has a second preload; 
 the first preload being greater than the second preload. 
 
     
     
         5 . The fuel injector of  claim 3  wherein energizing the stator assembly pulls the armature assembly towards the first position against the bias of the first spring. 
     
     
         6 . The fuel injector of  claim 1  wherein energizing the stator assembly operatively moves the armature assembly and the valve member. 
     
     
         7 . The fuel injector of  claim 1  wherein:
 the armature assembly being guided via an interaction between the guide piece and a guide sleeve of the stator assembly; 
 the guide piece having a first guide surface separated from a second guide surface by a reduced diameter section; and 
 an air gap being defined by a distance between a surface on the flux piece and the stop surface along an axis of a guide bore defined by the guide sleeve. 
 
     
     
         8 . A fuel injector comprising:
 solenoid actuator assembly, which includes an armature assembly and a stator assembly, mounted in an injector body;   the armature assembly including a flux piece attached to a guide piece;   the stator assembly includes an inner pole piece with an inner wall in contact with a guide sleeve defining a guide bore;   the guide piece being slidably received in the guide bore, and having a stop surface movable between a first position in contact with the stator assembly and a second position out of contact with the stator assembly; and   an air gap being defined between a bottom surface on the stator assembly and a top surface on the flux piece when the guide piece is in the first position.   
     
     
         9 . The fuel injector of  claim 8  wherein a distance between the top surface on the flux piece and the stop surface along an axis of the guide bore equals the air gap. 
     
     
         10 . The fuel injector of  claim 8  wherein the flux piece is welded to the guide piece. 
     
     
         11 . The fuel injector of  claim 8  wherein the flux piece is press fitted onto the guide piece. 
     
     
         12 . The fuel injector of  claim 8  wherein the air gap is about 0.05 mm. 
     
     
         13 . The fuel injector of  claim 8  wherein the armature assembly is guided via an interaction between the guide piece and the guide sleeve of the stator assembly. 
     
     
         14 . The fuel injector of  claim 13  wherein the guide piece includes a first guide surface separated from a second guide surface by a reduced diameter section; and
 a valve member unattached to, but in contact with, the guide piece. 
 
     
     
         15 . The fuel injector of  claim 8  wherein the bottom surface, which is partially defined by the guide sleeve and the inner pole piece, is planar. 
     
     
         16 . The fuel injector of  claim 8  including a first spring that biases the armature assembly away from the stator assembly; and
 a second spring that biases the armature assembly toward the stator assembly. 
 
     
     
         17 . The fuel injector of  claim 8  wherein the stator assembly includes a coil positioned in a cavity defined by the inner pole piece and an outer pole piece. 
     
     
         18 . The fuel injector of  claim 8  including a valve member out of contact with armature assembly at the first position, but the valve member being in contact with the armature assembly at the second position. 
     
     
         19 . The fuel injector of  claim 8  including a valve member that moves a valve travel distance between a first stop and a second stop;
 the armature assembly moves an armature travel distance between the first position and the second position; and 
 the armature travel distance is greater than the valve travel distance. 
 
     
     
         20 . A fuel injector comprising:
 solenoid actuator assembly, which includes an armature assembly and a stator assembly, mounted in an injector body;   the armature assembly including a flux piece attached to a guide piece;   the stator assembly having a planar bottom surface;   the guide piece having a stop surface movable between a first position in contact with planar bottom surface of the stator assembly and a second position out of contact with the stator assembly;   the flux piece being out of contact with the stator assembly at both the first position and the second position, the flux piece being separated from the planar bottom surface of the stator assembly by an air gap at the first position; and   a distance between a top surface on the flux piece and the stop surface of the guide piece along an axis of the guide piece equals the air gap.