Patent Application
20130285776
The present invention relates generally to coiled-wire devices and, more particularly, to electromagnetic coil assemblies including braided lead wires brazed to other electrical connectors, as well as to methods for the production of electromagnetic coil assemblies.
Magnetic sensors (e.g., linear and variable differential transducers), motors, and actuators (e.g., solenoids) include one or more electromagnetic coils, which are commonly produced utilizing a fine gauge magnet wire; e.g., a magnet wire having a gauge from about 30 to 38 American Wire Gauge. In certain cases, the electromagnetic coils are embedded within a body of dielectric material (e.g., a potting compound) to provide position holding and electrical insulation between neighboring turns of the coils and thereby improve the overall durability and reliability of the coiled-wire device. The opposing ends of a magnet wire may project through the dielectric body to enable electrical connection between an external circuit and the electromagnetic coil embedded within the dielectric body. In many conventional, low temperature applications, the electromagnetic coil is embedded within an organic dielectric material, such as a relatively soft rubber or silicone, that has a certain amount of flexibility, elasticity, or compressibility. As a result, a limited amount of movement of the magnet wire at point at which the wire enters or exits the dielectric body is permitted, which reduces the mechanical stress applied to the magnet wire during assembly of the coiled-wire device. However, in instances wherein the electromagnetic coil is potted within a material or medium that is highly rigid, such as a hard plastic and certain inorganic materials, the magnet wire is effectively fixed or anchored in place at the wire's entry point into or exit point from the dielectric body. As the external segment of the magnet wire is subjected to unavoidable bending, pulling, and twisting forces during assembly, significant mechanical stress concentrations may occur at the wire's entry or exit point from the dielectric body. The fine gauge magnet wire may consequently mechanically fatigue and work harden at this interface during the assembly process. Work hardening of the fine gauge magnet wire may result in breakage of the wire during assembly or the creation of a high resistance “hot spot” within the wire accelerating open circuit failure of the coiled wire device. Such issues are especially problematic when the coiled magnet wire is fabricated from a metal prone to work hardening and mechanical fatigue, such as aluminum.
It would thus be desirable to provide embodiments of an electromagnetic coil assembly including a fine gauge coiled magnet wire, which is at least partly embedded within a body of dielectric material and which is effectively isolated from mechanical stress during manufacture of the coil assembly. Ideally, embodiments of such an electromagnetic coil assembly would provide redundancy in the electrical coupling to the potted coil (or coils) to improve the overall durability and reliability of the electromagnetic coil assembly. It would still further be desirable to provide embodiments of such an electromagnetic coil assembly capable of providing continuous, reliable operation in high temperature applications (e.g., applications characterized by temperatures exceeding 260° C.), such as high temperature avionic applications. Finally, it would be desirable to provide embodiments of a method for manufacturing such an electromagnetic coil assembly. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying Drawings and the foregoing Background.
Embodiments of a method for the manufacture of an electromagnetic coil assembly are provided. In one embodiment, the method for manufacturing an electromagnetic coil assembly includes the steps of providing a braided aluminum lead wire having a first end portion and a second end portion, brazing the first end portion of the braided aluminum lead wire to a first electrically-conductive interconnect member, and winding a magnet wire into an electromagnetic coil. The second end portion of the braided aluminum lead wire is joined to the magnet wire after the step of brazing.
In a further embodiment, the method for manufacturing an electromagnetic coil assembly includes the step of producing a braided aluminum lead wire having an anodized intermediate portion, a non-anodized first end portion, and a non-anodized second end portion. The non-anodized first end portion of the braided aluminum lead wire is electrically coupled to a magnet wire, and the non-anodized second end portion of the braided aluminum lead wire is joined to an electrically-conductive interconnect member.
Further provided are embodiments of an electromagnetic coil assembly. In an embodiment, the electromagnetic coil assembly includes a coiled aluminum magnet wire, an aluminum braided lead wire having a first end portion crimped to the coiled aluminum magnet wire and having a second end portion, and an electrically-conductive pin brazed to the second end portion of the aluminum braided lead wire.
At least one example of the present invention will hereinafter be described in conjunction with the following figures, wherein like numerals denote like elements, and:
The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding Background or the following Detailed Description. As appearing herein, the term “aluminum” encompasses materials consisting essentially of pure aluminum, as well as aluminum-based alloys containing aluminum as a primary constituent in addition to any number of secondary metallic or non-metallic constituents. This terminology also applies to other metals named herein; e.g., the term “nickel” encompasses pure and near pure nickel, as well as nickel-based alloys containing nickel as a primary constituent.
The following describes embodiments of electromagnetic coil assemblies including electromagnetic coils at least partially embedded, and preferably wholly encapsulated within, an electrically-insulative medium (referred to herein as a “body of a dielectric material” or, more simply, a “dielectric body”). As described in the foregoing section entitled “BACKGROUND,” the electromagnetic coils are commonly produced utilizing fine gauge magnet wires, such as magnet wires having gauges ranging from about 30 to about 38 American Wire Gauge (“AWG”). While the electromagnetic coil assembly can easily be designed such that the opposing ends of a given magnet wire project through the dielectric body to provide electrical connection to the potted coil, in instances wherein the dielectric body is relatively rigid, the magnet wire may be subject to unavoidable mechanical stresses concentrated at the wire's entry point into or exit point from the dielectric as the wire is manipulated during manufacture. In view of its relatively fine gauge, the magnet wire is generally unable to withstand significant mechanical stress without fatiguing, work hardening, and potentially snapping or otherwise breaking Work hardening and mechanical fatigue is especially problematic when the fine gauge magnet wire is fabricated from a metal, such as aluminum, prone to such issues.
To overcome the above-noted limitations, embodiments of the electromagnetic coil assemblies described herein employ braided lead wires, which terminate within the dielectric body and provide a convenient means of electrical connection to the coiled magnet wire or wires embedded therein. As will be described in more detail below, each braided lead wire assumes the form of a plurality of interwoven filaments or single-strand conductors, which are interwoven into an elongated ribbon, tube, or the like having an extremely high flexibility and mechanical strength. As a result, and in contrast to fine gauge single strand magnet wires, the braided lead wires are able to withstand significant and repeated mechanical stress without experiencing mechanical fatigue and work hardening. Furthermore, as each braided lead wire is comprised of numerous interwoven filaments, the braided lead wires provide added redundancy in the electrical connection to the potted coil or coils thereby improving the overall durability and reliability of the electromagnetic coil assembly. Additional description of electromagnetic coil assemblies employing braided lead wires is further provided in co-pending U.S. application Ser. No. 13/276,064, entitled “ELECTROMAGNETIC COIL ASSEMBLIES HAVING BRAIDED LEAD WIRES AND METHODS FOR THE MANUFACTURE THEREOF,” filed Oct. 18, 2011, and bearing a common assignee with the Instant Application.
In embodiments wherein electromagnetic coil assembly 10 is incorporated into a sensor, such as an LVDT, bobbin 12 is preferably fabricated from a non-ferromagnetic material, such as aluminum, a non-ferromagnetic 300 series stainless steel, or a ceramic. However, in embodiments wherein assembly 10 is incorporated into a solenoid, a motor, or the like, either a ferromagnetic or non-ferromagnetic material may be utilized. Furthermore, in embodiments wherein bobbin 12 is fabricated from an electrically-conductive material, an insulative coating or shell 44 (shown in
As previously indicated, coiled magnet wire 26 may be formed from a magnet wire having a relatively fine gauge; e.g., by way of non-limiting example, a gauge of about 30 to about 38 AWG, inclusive. However, embodiments of the present invention are also advantageously utilized when the coiled magnet wire is of a larger wire gauge (e.g., about 20 to 28 AWG) and could chip or otherwise damage the surrounding dielectric material during manipulation if allowed to pass from the interior to the exterior of dielectric body 24. Thus, in preferred embodiments, the gauge of coiled magnet wire 26 may range from about 20 to about 38 AWG. Coiled magnet wire 26 may be fabricated from any suitable metal or metals including, but not limited to, copper, aluminum, nickel, and silver. Coiled magnet wire 26 may or may not be plated. When electromagnetic coil assembly 10 is designed for usage within a high temperature environment, coiled magnet wire 26 is preferably fabricated from aluminum, silver, nickel, or clad-copper (e.g., nickel-clad copper). Advantageously, both aluminum and silver wire provide excellent conductivity enabling the dimensions and overall weight of assembly 10 to be reduced, which is especially desirable in the context of avionic applications. Relative to silver wire, aluminum wire is less costly and can be anodized to provide additional electrical insulation between neighboring turns of coiled magnet wire 26 and bobbin 12 and thereby reduce the likelihood of shorting and breakdown voltage during operation of assembly 10. By comparison, silver wire is more costly than aluminum wire, but is also more conductive, has a higher mechanical strength, has increased temperature capabilities, and is less prone to work hardening. The foregoing notwithstanding, coiled magnet wire 26 is preferably fabricated from aluminum wire and, more preferably, from anodized aluminum wire.
In low temperature applications, dielectric body 24 may be formed from an organic material, such as a hard plastic. In high temperature applications, however, dielectric body 24 is fabricated from inorganic materials and will typically be substantially devoid of organic matter. In such cases, dielectric body 24 is preferably formed from a ceramic medium or material; i.e., an inorganic and non-metallic material, whether crystalline or amorphous. Furthermore, in embodiments wherein coiled magnet wire 26 is produced utilizing anodized aluminum wire, dielectric body 24 is preferably formed from a material having a coefficient of thermal expansion (“CTE”) approaching that of aluminum (approximately 23 parts per million per degree Celsius), but preferably not exceeding the CTE of aluminum, to minimize the mechanical stress applied to the anodized aluminum wire during thermal cycling. Thus, in embodiments wherein coiled magnet wire 26 is produced from anodized aluminum wire, dielectric body 24 is preferably formed to have a CTE exceeding approximately 10 parts per million per degree Celsius (“ppm per ° C.”) and, more preferably, a CTE between approximately 16 and approximately 23 ppm per ° C. Suitable materials include inorganic cements, and certain low melt glasses (i.e., glasses or glass mixtures having a melting point less than the melting point of anodized aluminum wire), such as leaded borosilicate glasses. As a still more specific example, dielectric body 24 may be produced from a water-activated, silicate-based cement, such as the sealing cement bearing Product No. 33S and commercially available from the SAUEREISEN® Cements Company, Inc., headquartered in Pittsburgh, Pa.
Dielectric body 24 can be formed in a variety of different manners. In preferred embodiments, dielectric body 24 is formed utilizing a wet-winding process. During wet-winding, the magnet wire is wound around bobbin 12 while a dielectric material is applied over the wire's outer surface in a wet or flowable state to form a viscous coating thereon. The phrase “wet-state,” as appearing herein, denotes a ceramic or other inorganic material carried by (e.g., dissolved within) or containing a sufficient quantity of liquid to be applied over the magnet wire in real-time during the wet winding process by brushing, spraying, or similar technique. For example, in the wet-state, the ceramic material may assume the form of a pre-cure (e.g., water-activated) cement or a plurality of ceramic (e.g., low melt glass) particles dissolved in a solvent, such as a high molecular weight alcohol, to form a slurry or paste. The selected dielectric material may be continually applied over the full width of the magnet wire to the entry point of the coil such that the puddle of liquid is formed through which the existing wire coils continually pass. The magnet wire may be slowly turned during application of the dielectric material by, for example, a rotating apparatus or wire winding machine, and a relatively thick layer of the dielectric material may be continually brushed onto the wire's surface to ensure that a sufficient quantity of the material is present to fill the space between neighboring turns and multiple layers of coiled magnet wire 26. In large scale production, application of the selected dielectric material to the magnet wire may be performed utilizing a pad, brush, or automated dispenser, which dispenses a controlled amount of the dielectric material over the wire during winding.
As noted above, dielectric body 24 can be fabricated from a mixture of at least a low melt glass and a particulate filler material. Low melt glasses having coefficients of thermal expansion exceeding approximately 10 ppm per ° C. include, but are not limited to, leaded borosilicates glasses. Commercially available leaded borosilicate glasses include 5635, 5642, and 5650 series glasses having processing temperatures ranging from approximately 350° C. to approximately 550° C. and available from KOARTAN™ Microelectronic Interconnect Materials, Inc., headquartered in Randolph, N.J. The low melt glass is conveniently applied as a paste or slurry, which may be formulated from ground particles of the low melt glass, the particulate filler material, a solvent, and a binder. In a preferred embodiment, the solvent is a high molecular weight alcohol resistant to evaporation at room temperature, such as alpha-terpineol or TEXINOL®; and the binder is ethyl cellulose, an acrylic, or similar material. It is desirable to include a particulate filler material in the embodiments wherein the electrically-insulative, inorganic material comprises a low melt glass to prevent relevant movement and physical contact between neighboring coils of the anodized aluminum wire during coiling and firing processes. Although the filler material may comprise any particulate material suitable for this purpose (e.g., zirconium or aluminum powder), binder materials having particles generally characterized by thin, sheet-like shapes (commonly referred to as “platelets” or “laminae”) have been found to better maintain relative positioning between neighboring coils as such particles are less likely to dislodge from between two adjacent turns or layers of the wire's cured outer surface than are spherical particles. Examples of suitable binder materials having thin, sheet-like particles include mica and vermiculite. As indicated above, the low melt glass may be applied to the magnet wire by brushing immediately prior to the location at which the wire is coiled around the support structure.
After performance of the above-described wet-winding process, the green state dielectric material is cured to transform dielectric body 24 into a solid state. As appearing herein, the term “curing” denotes exposing the wet-state, dielectric material to process conditions (e.g., temperatures) sufficient to transform the material into a solid dielectric medium or body, whether by chemical reaction or by melting of particles. The term “curing” is thus defined to include firing of, for example, low melt glasses. In most cases, curing of the chosen dielectric material will involve thermal cycling over a relatively wide temperature range, which will typically entail exposure to elevated temperatures well exceeding room temperatures (e.g., about 20-25° C.), but less than the melting point of the magnet wire (e.g., in the case of anodized aluminum wire, approximately 660° C.). However, in embodiments wherein the chosen dielectric material is an inorganic cement curable at or near room temperature, curing may be performed, at least in part, at correspondingly low temperatures. For example, if the chosen dielectric material is an inorganic cement, partial curing may be performed at a first temperature slightly above room temperature (e.g., at approximately 82° C.) to drive out moisture before further curing is performed at higher temperatures exceeding the boiling point of water. In preferred embodiments, curing is performed at temperatures up to the expected operating temperatures of electromagnetic coil assembly 10, which may approach or exceed approximately 315° C. In embodiments wherein coiled magnet wire 26 is produced utilizing anodized aluminum wire, it is also preferred that the curing temperature exceeds the annealing temperature of aluminum (e.g., approximately 340° C. to 415° C., depending upon wire composition) to relieve any mechanical stress within the aluminum wire created during the coiling and crimping process described below. High temperature curing may also form aluminum oxide over any exposed areas of the anodized aluminum wire created by abrasion during winding to further reduces the likelihood of shorting.
In embodiments wherein dielectric body 24 is formed from a material susceptible to water intake, such as a porous inorganic cement, it is desirable to prevent the ingress of water into body 24. As will be described more fully below, electromagnetic coil assembly 10 may further include a housing or container, such as a generally cylindrical canister, in which bobbin 12, dielectric body 24, and coiled magnet wire 26 are hermetically sealed. In such cases, the ingress of moisture into the hermetically-sealed container and the subsequent wicking of moisture into dielectric body 24 is unlikely. However, if additional moisture protection is desired, a liquid sealant may be applied over an outer surface of dielectric body 24 to encapsulate body 24, as indicated in
To provide electrical connection to the electromagnetic coil embedded within dielectric inorganic body 24, braided lead wires are joined to opposing ends of coiled magnet wire 26. In the exemplary embodiment illustrated in
Braided lead wire 36 is mechanically and electrically joined to a first segment or end of coiled magnet wire 26 by way of a first joint 40 (
To facilitate connection to a given braided lead wire, the coiled magnet wire is preferably inserted or threaded into the braided lead wire prior to formation of the wire-to-wire joint. In embodiments wherein the braided lead wire is a flat woven ribbon (commonly referred to as a “flat braid”), the fine gauge magnet wire may be inserted through the sidewall of the interwoven filaments and, perhaps, woven into the braided lead wire by repeatedly threading the magnet wire through the lead wire's filaments in an undulating-type pattern. Alternatively, in embodiments wherein the braided lead is an interwoven tube (commonly referred to as a “hollow braid”), an end portion of the coiled magnet wire may be inserted into the central opening of the tube or woven into the braided lead wire in the previously-described manner. For example, as shown in
As noted above, joints 40 and 42 may be formed by any suitable combination of soldering (e.g., brazing), crimping, twisting, or the like. In preferred embodiments, joints 40 and 42 are formed by soldering and/or crimping. For example, and as indicated in
In addition to or in lieu of crimping, end portion 50 of braided lead wire 38 may be joined to end portion 48 of coiled magnet wire 26 by soldering. In this case, solder material, preferably along with flux, may be applied to joint 40 and heated to cause the solder material to flow into solder joint 40 to mechanically and electrically join magnet wire 26 and lead wire 38. A braze stop-off material is advantageously impregnated into or otherwise applied to braided lead wire 38 adjacent the location at which braided lead wire 38 is soldered to coiled magnet wire 26 (represented in
In certain embodiments, such as when the coiled magnet wire 26 is fabricated from an oxidized aluminum wire, it may be desirable to remove oxides from the outer surface of magnet wire 26 and/or from the outer surface of braided lead wire 38 prior to crimping and/or brazing/soldering. This can be accomplished by polishing the wire or wires utilizing, for example, an abrasive paper or a commercially-available tapered cone abrasive dielectric stripper typically used for fine AWG wire preparation. Alternatively, in the case of oxidized aluminum wire, the wire may be treated with a suitable etchant, such as sodium hydroxide (NAOH) or other caustic chemical, to remove the wire's outer alumina shell at the location of crimping and/or soldering. Advantageously, such a liquid etchant can be easily applied to localized areas of the magnet wire and/or braided lead wire utilizing a cotton swab, a cloth, or the like. When applied to the wire's outer surface, the liquid etchant penetrates the relatively porous oxide shell and etches away the outer annular surface of the underlying aluminum core thereby undercutting the outer alumina shell, which then flakes or falls away to expose the underlying core.
In embodiment wherein braided lead wires 36 and 38 are fabricated from aluminum, additional improvements in breakdown voltage of electromagnetic coil assembly 10 (
Anodization of braided lead wires 36 and 38 may entail a cleaning step, a caustic etch step, and an electrolytic process. During the electrolytic process, the braided lead wires may serve as the anode and a lead electrode may serve the cathode in a sulfuric acid solution. Aluminum metal on the outer surface of the wire is oxidized resulting in the formation of a thin (usually approximately 5 micron thick) insulating layer of alumina (Al2O3) ceramic. It is preferred to prevent the formation of an alumina shell over the end portions of the braided lead wires where electrical connections are made as bare aluminum wire will crimp and/or braze more readily. Thus, to prevent the formation of an alumina shell thereof, the end regions of the braided lead wires can be masked prior to the anodization process. Masking can be accomplished physically (e.g., by taping-over the braid lead wire end portions) or by coating with suitable resists. Alternatively, the entire wire bundle can be anodized, and the alumina shell formed over the braided lead wire ends can be chemically removed; e.g., in one embodiment, the end portions of the braided lead wires may be dipped in or otherwise exposed to caustic solution, such as a NaOH solution. In the present context, the end portions of a wire bundle or braided lead wire that are not covered, by an outer alumina shell, at least in substantial part, are considered “non-anodized,” whether such end portions were not anodized during the anodization process (e.g., due to masking in the above-described manner) or such end portions were originally anodized and the outer alumina shell was subsequently removed therefrom (e.g., by treatment in a caustic solution of the type described above). Testing has shown that, by forming an insulating layer of alumina over the braided lead wires through such an anodization process, the breakdown potential of embodiments of electromagnetic coil assembly 10 (
After connection of coiled magnet wire 26 to braided lead wires 36 and 38, and after formation of dielectric body 24 (
After assembly in the above described manner, electromagnetic coil assembly 10 may be integrated into a coiled-wire device. In the illustrated example wherein electromagnetic coil assembly 10 includes a single wire coil, assembly 10 may be included within a solenoid. In alternative embodiments wherein electromagnetic coil assembly 10 is fabricated to include primary and secondary wire coils, assembly 10 may be integrated into a linear variable differential transducer or other sensor. Due at least in part to the inorganic composition of potted dielectric body 24, electromagnetic coil assembly 10 is well-suited for usage within avionic applications and other high temperature applications.
Feedthrough connector 80 can assume the form of any assembly or device, which enables two or more wires, pins, or other electrical conductors to extend from a point external to coil assembly housing 70 to a point internal to housing 70 without compromising the sealed environment thereof. For example, feedthrough connector 80 can comprise a plurality of electrically-conductive pins, which extend through a glass body, a ceramic body, or other electrically-insulative structure mounted through housing 70. In the exemplary embodiment illustrated in
Metal tube 86, and the feedthrough wires 84 contained therein, extend through an opening provided in end cap 90 of chimney structure 82 to allow electrical connection to braided lead wires 36 and 38 and, therefore, to opposing end segments of coiled magnet wire 26 (
Feedthrough wires 84 may be non-insulated or bare metal wires fabricated from one or more metals or alloys; e.g., in one implementation, feedthrough wires 84 are stainless steel-clad copper wires. In embodiments wherein feedthrough wires 84 are non-insulated, wires 84 can short if permitted to contact each other or the interior surface of elongated metal tube 86. The breakdown voltage of external feedthrough connector 80 may also be undesirably reduced if feedthrough wires 84 are allowed to enter into close proximity. While generally not a concern within metal tube 86 due to the tightly-packed composition of dielectric packing 88, undesired convergence and possible contact of feedthrough wires 84 can be problematic if wires 84 are not adequately routed when emerging from the terminal ends of feedthrough connector 80. Thus, a specialized interconnect structure may be disposed within coil assembly housing 70 to maintain or increase the lateral spacing of wires 84, and thus prevent the undesired convergence of feedthrough wires 84. When emerging from the inner terminal end of feedthrough connector 80. In addition, such an interconnect structure also provides a useful interface for electrically coupling braided lead wires 36 and 38 to their respective feedthrough wires 84 in embodiments wherein lead wires 36 and 38 and feedthrough wires 84 are fabricated from disparate materials. An example of such an interconnect structure is described below in conjunction with
Electrically-conductive pin 104 includes first and second end portions 114 and 116, which are referred to herein as “inner and outer pin terminals 114 and 116” in view of their relative proximity to potted electromagnetic coil 22 (
A more detailed discussion will now be provided of preferred manners by which braided lead wires 36 and 38 can be electrically and mechanically joined to inner pin terminals 116 and 120 of electrically-conductive pins 104 and 106, respectively, or other electrical connectors or conductors. As previously noted, braided lead wires 36 and 38 are advantageously fabricated from aluminum to facilitate crimping to coiled magnet wire 26 (
In contrast to crimping, soldering or brazing does not require the application of deformation forces to the wire-to-wire or pin-to-wire interface, which can cause the above-noted issues with fine gauge aluminum wire. While the terms “soldering” and “brazing” are commonly utilized to denote joining techniques wherein filler materials melt above or below 450° C., such terms are utilized interchangeably herein, as are the terms “solder joint” and “braze joint.” However, brazing of fine gauge aluminum wire also presents certain difficulties. Due to its relatively low melt point and thermal mass, fine gauge aluminum wire can easily be overheated and destroyed during the brazing processing. The likelihood of inadvertently overheating the aluminum wire is especially pronounced when brazing is carried-out in a relatively confined space utilizing, for example, a microtorch. Heating during brazing can also result in formation of oxides along the wires' outer surfaces increasing electrical resistance across the braze joint. As a still further drawback, moisture present at the braze interface can accelerate corrosion and eventual connection failure when aluminum wire is joined to a secondary wire formed from a metal, such as copper, having an electronegative potential that differs significantly as compared to aluminum wire.
In accordance with embodiments of the present invention, braided lead wires 36 and 38 are joined to terminal end portions 116 and 120, respectively, of electrically-conductive pins 104 and 106 by brazing. To overcome the above-noted drawbacks associated with brazing of fine gauge aluminum wire, braided lead wires 36 and 38 are brazed to interconnect pins 104 and 106 prior to connection to opposing end segments of coiled magnet wire 26 (
Exemplary method 130 commences with the production of number of brazed lead wire/connector assemblies and, in one specific example, a number of brazed lead wire/pin assemblies (BLOCK 134,
While it is desirable to form an electrically-insulative oxide shell over the elongated bodies of the braided lead wires, it is generally desirable to prevent the formation of an alumina shell over the terminal end portions of the braided lead wires to facilitate electrical connection by crimping, brazing, or other suitable means. In one embodiment, the end regions of the braided lead wires can be masked prior to the anodization process. Masking can be accomplished physically (e.g., by taping-over the braid lead wire end portions) or by coating the braided wire end portions with a chemical resist. Alternatively, the braided lead wires can be anodized in their entirety, and the portion of the alumina shell formed over the braided lead wire ends can subsequently be removed by, for example, treatment with a caustic solution; e.g., in one embodiment wherein the braided lead wires are anodized in their entirety, the opposing end portions of the braided lead wires may be dipped or wiped with an NaOH solution to remove the oxide coating therefrom. Testing has shown that, by forming an insulating layer of alumina over the braided lead wires through such an anodization process, the breakdown potential of embodiments of electromagnetic coil assembly 10 (
Next, at STEP 136 (
A brazing process is performed to join each braided lead wire to its respective electrically-conductive interconnect member or other conductor (STEP 144,
At this juncture in exemplary method 130, a number of brazed lead wire/pin assemblies have been fabricated. In preferred embodiments, each brazed lead wire/pin assembly is produced by brazing a fine gauge aluminum wire braid to a non-aluminum interconnect pin; however, the risks of overheating of the fine gauge aluminum braid are eliminated by performing the brazing process prior to assembly of the electromagnetic coil assembly and in a highly controlled environment, such as a controlled atmosphere induction furnace. Each brazed lead wire/pin assembly may now be incorporated into an electromagnetic coil assembly to provide connection between the coiled magnet wire and the conductors of the feedthrough connector. For example, as indicated in
The foregoing has thus provided embodiments of an electromagnetic coil assembly wherein flexible, braided lead wires are joined to a coiled magnet wire partially or wholly embedded within a body of dielectric material to provide a convenient and robust electrical connection between an external circuit and the potted electromagnetic coil, while effectively protecting the magnet wire from mechanical stress during assembly that could otherwise fatigue and work harden the magnet wire. As braided lead wires are fabricated from multiple interwoven filaments, braided lead wires also provide redundancy and thus increase the overall reliability of the electromagnetic coil assembly. The usage of flexible braided lead wires can be advantageous in certain low temperature applications wherein the coiled magnet wire is potted within a relatively rigid, organic dielectric, such as a hard plastic; however, the usage of such flexible braided lead wires is particularly advantageous in high temperature applications wherein highly rigid, inorganic materials are utilized, which are capable of maintaining their electrically-insulative properties at temperatures well-above the thresholds at which conventional, organic dielectrics breakdown and decompose. In such embodiments, the electromagnetic coil assembly is well-suited for usage in high temperature coiled-wire devices, such as those utilized in avionic applications. More specifically, and by way of non-limiting example, embodiments of the high temperature electromagnetic coil assembly are well-suited for usage within actuators (e.g., solenoids and motors) and position sensors (e.g., variable differential transformers and two position sensors) deployed onboard aircraft. This notwithstanding, it will be appreciated that embodiments of the electromagnetic coil assembly can be employed in any coiled-wire device, regardless of the particular form assumed by the coiled-wire device or the particular application in which the coiled-wire device is utilized.
The foregoing has also provided embodiments of a method for manufacturing an electromagnetic coil assembly. In one embodiment, the method includes step of pre-brazing a lead wire to a connector pin prior to crimping the opposing end of the lead wire to a magnet wire. In the process, the flow of braze can be precisely controlled by braze stop-off and the braze applied to the aluminum braid and pin in a paste form. The paste is dried then the assembly is heated in a controllable fashion in a furnace to melt the braze. In addition to precise thermal control, furnaces also provide the ability to control the atmospheric environment in which brazing takes place to minimize aluminum oxidation and promote flow. As a still further advantage, the furnace temperature can be precisely controlled to minimize exposure at peak temperature and reduce the formation of undesired intermetallics. After brazing, the flux and braze-stop materials are easily removed by immersing the lead wire/pin assembly in a vessel with solvent, which can be agitated by exposure to ultrasonic energy to promote chemical removal of the flux and braze-stop materials.
In the above-described embodiments, braided lead wires were pre-brazed to elongated pins, such as pins 104 and 106 shown in
In further embodiments, the above-described electromagnetic coil assembly manufacturing process includes the step of producing a braided aluminum lead wire having an anodized intermediate portion, a non-anodized first end portion, and a non-anodized second end portion. The non-anodized first end portion of the braided aluminum lead wire is electrically coupled to a magnet wire, either before or after winding of the magnet wire into one or more electromagnetic coils. The non-anodized second end portion of the braided aluminum lead wire is joined to an electrically-conductive interconnect member. The term “non-anodized,” as appearing herein, denotes a portion of an aluminum wire that is substantially free of an aluminum oxide shell. Thus, an end portion of a braided lead wire that is anodized and then subsequently treated to remove the oxide shell therefrom is considered “non-anodize” in the present context. For example, a braided lead wire having non-anodized end portions and an anodized intermediate portion by anodizing the body of braided lead wire after masking the end portions thereof or, alternatively, by anodizing the braided lead wire in its entirety and subsequently removing the outer alumina shell from the lead wire's end portions by exposure to NaOH or another caustic solution, as generally described above in conjunction with
While multiple exemplary embodiments have been presented in the foregoing Detailed Description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing Detailed Description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set-forth in the appended Claims.
