Abstract:
A solenoid actuator is provided having an armature assembly with a separate joined shunt side bearing consisting of a non-magnetic or slightly magnetic material. The material of the shunt side bearing prevents significant amounts of magnetic flux transferring through the lower bearing area of the armature assembly in the radial direction.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to solenoid actuators. 
       BACKGROUND OF THE INVENTION 
       [0002]    Most solenoid actuators have a ferromagnetic casing. The casing encircles a coil which is typically wrapped in a polymeric bobbin. Within the coil is a core assembly or core. An armature (or armature assembly), slides within the core (or core assembly). The armature is moved via flux transfer as current is run through the coil. The flux loop is completed by flux transfer from the casing to the core to the armature and back through the core to the casing. Armature translation is accomplished by transfer of flux from the upper section of the core (sometimes referred to as the flux return or flux tube) through the armature to the lower section of the core (shunt end or shunt). For this reason, there is a thin section of the core in between the upper and lower sections (commonly referred to as the flux choke) to reduce the amount of flux directly transferring from the upper to lower core. 
         [0003]    While flux is intended to travel from the upper to lower core through the armature, it is desirable for this flux path to be more axially oriented than radially oriented in the lower section of the core (shunt end). Radial flux transfer in this portion of the assembly leads to higher magnetic side loading of the armature and thus higher frictional forces. It is desirable that the armature be designed to reduce the relative amount of side loading of the armature within the core. 
         [0004]    In order to guide the armature through the core and minimize armature misalignment, it is desirable to maximize the bearing length. With a continuous steel armature, as the bearing length is increased, the lower section of the bearing goes deeper into the shunt, causing higher side loading. Even when the steel armature or core bearing surface is plated or coated in some way, side loads remain high. It is desirable to decouple the lower bearing from the magnetic portion of the armature. 
       SUMMARY OF THE INVENTION 
       [0005]    To make manifest the above noted and other desires, a revelation of the present invention is brought forth. In a preferred embodiment the present invention endows a freedom of a solenoid actuator with an armature assembly including a base magnetic material portion with a separate shunt side bearing portion attached to a base magnetic material portion. The shunt side bearing consists of a non-magnetic or slightly magnetic material to prevent significant amounts of flux from transferring through a lower bearing area of the armature assembly in the radial direction. The nonmagnetic or semi-magnetic material can be joined to a base magnetic material portion of the armature assembly in any number of ways including but not limited to press fitting, attachment to an intermediate pin, sintering, gluing, molding, brazing, etc. In the case of coated armatures, the shunt side bearing can be coated or plated along with or separately from the base armature material. 
         [0006]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0008]      FIG. 1  is a sectional view of a normally low control pressure solenoid actuator according to the present invention; and 
           [0009]      FIG. 2  is a sectional view of an armature assembly in an alternate preferred embodiment solenoid actuator according to the present invention. 
           [0010]      FIG. 3  is a sectional view of an alternate preferred embodiment armature assembly according to the present invention. 
           [0011]      FIG. 4  is a sectional view of another alternate preferred embodiment armature assembly according to the present invention. 
           [0012]      FIG. 5  is a schematic view of a prior art armature assembly. 
           [0013]      FIG. 6  is a graphic display of radial side forces in armature assemblies. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0015]    Referring to  FIG. 1 , a solenoid actuator  7  according to the present invention is provided. The solenoid actuator  7  has a ferromagnetic can or casing  10 . The casing includes a lower housing  12 . The lower housing has a generally vertical portion  14  joined to an end cap  16 . The end cap  16  has a central opening  18 . The lower housing  12  is press fit into an upper housing  20 . Positioned within the casing  10  is a coil  26 . The coil  26  is typically fabricated from a non-magnetic material such as copper. The coil  26  is wrapped on an outer diameter of a polymeric bobbin  28 . Encircled by the coil  26  is core  30 . The core  30  has an upper portion providing a flux return herein referred to as the flux tube  32 . The core  30  has another portion referred to as the shunt  34 . Separating the flux tube  32  from the shunt  34  is a flux choke  36  which is generated by the narrowing of the core. The core  30  is magnetically connected with the casing  10 . In  FIG. 1 , the flux tube  32  and shunt  34  are integral, however in other embodiments (not shown) the flux choke  36  can be provided by an axial gap separation of the flux tube  32  and shunt  34 . 
         [0016]    Slidably mounted in the core  30  is an armature assembly  40 . The armature is fabricated from at least two separate components fabricated from different types of material. The first component is a base fabricated from a base magnetic material. In the example shown, the base material is low carbon steel. The base material  42  has an axial bore  44  axially extending there through to allow hydraulic oil to be on both sides of the armature  40 . The armature assembly  40  in its extreme retracted position abuts a magnetic stop  46  provided in the housing  20 . The armature assembly  40  also has a joined bearing adjacent to the flux choke  36  or hereinafter referred to as the shunt side bearing  50 . The shunt side bearing  50  is fabricated from a material having significantly less magnetic permeability of at least fifty percent less of that of the magnetic carbon steel material. The shunt side bearing  50  can be fabricated from a polymeric material, copper, aluminum, stainless steel, zinc, ceramic materials and/or alloys or composites thereof. The shunt side bearing  50  can be attached to the armature base material  42  by one or more of the following methods including an interference fit, sintering, adhesive connection, molded connection, brazing and/or bonding. In many applications, the shunt side bearing will be attached to an axial face of the base magnetic material  42 . The shunt side bearing  50  need not cover the entire face of the armature assembly  40 , but it is preferred that it have a radial width or thickness of at least 350 microns and an axial length of 200 microns adjacent the shunt side bearing. Connected with the armature  40  is a transported member  60 . The shunt side bearing  50  can be first joined to the transported member  60  and then connected (to the armature base material) by the transported member  60  being fixably connected with a base material  42  of the armature. The solenoid actuator  7  also has a stop  62  to limit travel of the armature. Directly adjacent to the shunt side bearing  50  the base material  42  has a reduced diameter axial wedge shaped section  64  to further ensure contact of the shunt side bearing  50 . The reduced diameter axial wedge shaped section  64  minimizes radial flux transfer and maximizes axial flux transfer for this portion of the armature. (Note: In  FIG. 1  the radial width of section  64  is exaggerated for clarity of illustration.) The above noted feature allows for customization of the force versus current versus axial position characteristics of the solenoid actuator. 
         [0017]    In operation the solenoid  7  in its typical rest position has the armature assembly  40  abutted with the stop  46  by virtue of a biasing spring not shown or by virtue of a spring bias provided against the transported member  60  by an apparatus not shown. When the coil  26  is actuated, magnetic flux travels through the casing to the flux tube core into the armature assembly  40  out through the face  66  of the base material and then into the shunt  34 . This causes a downward force on the armature causing the armature to slide downward as shown in  FIG. 1  thrusting the transported member  60  forward. Lateral force on the shunt side bearing  50  is virtually eliminated. 
         [0018]    Optionally if desired both the shunt side bearing  50  and the armature base material  42  can have their outer perimeter coated with a light coating of a nickel or other non-magnetic alloy to facilitate the sliding movement of the armature within the core  30 . 
         [0019]    Referring to  FIG. 2  an alternate preferred embodiment armature according to the present is provided with a base material  142  with a press fit shunt side bearing  150 . Shunt side bearing  150  can be fabricated from the various materials noted for shunt side bearing  50 . 
         [0020]      FIG. 3  illustrates an armature assembly according to the present invention wherein the shunt side bearing  250  has an inner core that press fits with an axial bore  244  to attach with a base magnetic material  242 . Similar to shunt side bearing  50 , shunt side bearing  250  covers a majority of the axial face of the base magnetic material  242 . 
         [0021]      FIG. 4  illustrates an armature assembly wherein the base magnetic material has an integrated rear bearing. A shunt side non-magnetic material bearing  30  has a diameter essentially equal to that of the base magnetic material. 
         [0022]      FIG. 6  illustrates the reduction in radial force experienced in the shunt side bearing  50  of  FIG. 1 , see line  27  versus the higher radial force experienced by the shunt side bearing of  FIG. 5 . (Note: the shunt side bearing of  FIG. 5  is exaggerated in dimension for clarity of illustration.) 
         [0023]    While the invention is shown in  FIGS. 1-4  as only a solenoid motor or actuator assembly, it can be combined with various pin, spool or other components to achieve any number of solenoid powered mechanical or valve functions. 
         [0024]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.