Solenoid with non-magnetic front bearing

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.

FIELD OF THE INVENTION

The present invention relates to solenoid actuators.

BACKGROUND OF THE INVENTION

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.

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.

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

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1, a solenoid actuator7according to the present invention is provided. The solenoid actuator7has a ferromagnetic can or casing10. The casing includes a lower housing12(as shown inFIG. 1). The lower housing has a generally vertical portion14joined to an end cap16. The end cap16has a central opening18. The lower housing12is press fit into an upper housing20. Positioned within the casing10is a coil26. The coil26is typically fabricated from a non-magnetic material such as copper. The coil26is wrapped on an outer diameter of a polymeric bobbin28. Encircled by the coil26is core30. The core30has an upper portion providing a flux return herein referred to as the flux tube32. The core30has another portion referred to as the shunt34. Separating the flux tube32from the shunt34is a flux choke36which is generated by the narrowing of the core. The core30is magnetically connected with the casing10. InFIG. 1, the flux tube32and shunt34are integral, however in other embodiments (not shown) the flux choke36can be provided by an axial gap separation of the flux tube32and shunt34.

Slidably mounted in the core30is an armature assembly40. 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 material42has an axial bore44axially extending there through to allow hydraulic oil to be on both sides of the armature40. The armature assembly40in its extreme retracted position abuts a magnetic stop46provided in the housing20. The armature assembly40also has joined thereto a bearing adjacent to the flux choke36or hereinafter referred to as the shunt side bearing50. The shunt side bearing50is 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 bearing50can be fabricated from a polymeric material, copper, aluminum, stainless steel, zinc, ceramic materials and/or alloys or composites thereof. The shunt side bearing50can be attached to the armature base material42by 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 material42. The shunt side bearing50need not cover the entire face of the armature assembly40, 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 armature40is a transported member60. The shunt side bearing50can be first joined to the transported member60and then connected (to the armature base material) by the transported member60being fixably connected with a base material42of the armature. The solenoid actuator7also has a stop62to limit travel of the armature. Directly adjacent to the shunt side bearing50the base material42has a reduced diameter axial wedge shaped section64to further ensure contact of the shunt side bearing50. The reduced diameter axial wedge shaped section64minimizes radial flux transfer and maximizes axial flux transfer for this portion of the armature. (Note: InFIG. 1the radial width of section64is 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.

In operation the solenoid7in its typical rest position has the armature assembly40abutted with the stop46by virtue of a biasing spring not shown or by virtue of a spring bias provided against the transported member60by an apparatus not shown. When the coil26is actuated, magnetic flux travels through the casing to the flux tube core into the armature assembly40out through the face66of the base material and then into the shunt34. This causes a downward force on the armature causing the armature to slide downward as shown inFIG. 1thrusting the transported member60forward. Lateral force on the shunt side bearing50is virtually eliminated.

Optionally if desired both the shunt side bearing50and the armature base material42can 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 core30.

Referring toFIG. 2an alternate preferred embodiment armature according to the present is provided with a base material142with a press fit shunt side bearing150. Shunt side bearing150can be fabricated from the various materials noted for shunt side bearing50.

FIG. 3illustrates an armature assembly according to the present invention wherein the shunt side bearing250has an inner core that press fits with an axial bore244to attach with a base magnetic material242. Similar to shunt side bearing50, shunt side bearing250covers a majority of the axial face of the base magnetic material242.

FIG. 4illustrates an armature assembly wherein the base magnetic material has an integrated rear bearing. A shunt side non-magnetic material bearing30has a diameter essentially equal to that of the base magnetic material.

FIG. 6illustrates the reduction in radial force experienced in the shunt side bearing50ofFIG. 1, see line27versus the higher radial force experienced by the shunt side bearing ofFIG. 5. (Note: the shunt side bearing ofFIG. 5is exaggerated in dimension for clarity of illustration.)

While the invention is shown inFIGS. 1-4as 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.