Patent Description:
Certain electric machines, such as electric generators and motors, typically employ a combination of a rotor and a stator to convert rotational energy into electrical energy and vice versa. The electrical machines may include slotted cores (e.g., magnetic cores) having electrical conductors (e.g., coil windings) disposed in slots thereof; the cores and the electrical conductors may be electrically insulated from one another to prevent grounding of the conductors to the core. For example, insulation materials, such as polymer films and insulation papers can be used as slot liners and/or ground wall insulation to provide electrical insulation between the coil windings and the slotted core in the electric machine. However, materials with good dielectric properties often exhibit poor thermal conductivity, which hinders the dissipation of heat from the stator and/or rotor. This poor heat dissipation may result in a reduction in one or both of power generating efficiency and power density, which are the desired performance parameters of an electrical machine.

Furthermore, typical methods of forming components of an electrical machine, such as, stator assembly or coil windings involve multiple steps and multiple parts that are assembled together. Use of multiple steps and multiple parts results in cumbersome manufacturing processes, and may also affect the machine's end performance and reliability. Documents <CIT>, <CIT> and <CIT> disclose methods according to the state of the art.

Accordingly, there remains a need for improved methods of manufacturing and insulating the components of the electrical machines.

In one aspect, the disclosure relates to a method of forming an electrically insulating coating on a component of an electrical machine. The component of the electrical machine is an additively-manufactured stator component or a rotor component. The method includes coating a surface of the component with a ceramic material including a nitride, via an electrophoretic process, to form a first coating. The method further includes contacting the first coating deposited by the electrophoretic process with a thermoset resin to form a second coating; and curing the second coating to form the electrically insulating coating including the ceramic material dispersed in a polymer matrix.

In another aspect, the disclosure relates to a method of forming a coating on a component of an electrical machine. The method includes coating a surface of the component with a ceramic material, via an electrophoretic process, to form a first coating. The method further includes contacting the first coating deposited by the electrophoretic process with a polymeric material to form a second coating; and post-processing the second coating to form the coating including the ceramic material dispersed in a polymer matrix.

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings, wherein:.

In the following specification and the claims, which follow, reference will be made to a number of terms, which shall be defined to have the following meanings. The singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. As used herein, the term "or" is not meant to be exclusive and refers to at least one of the referenced components being present and includes instances in which a combination of the referenced components may be present, unless the context clearly dictates otherwise.

Accordingly, a value solidified by a term or terms, such as "about", and "substantially" is not to be limited to the precise value specified. In some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Similarly, "free" may be used in combination with a term, and may include an insubstantial number, or trace amounts, while still being considered free of the solidified term. The terms "disposed inside" or "disposed in" refer to configurations in which at least portion of a component is disposed inside or within a portion of another component, and does not necessarily connotate that the entirety of the component needs to be disposed within another component. For example, the counter electrode may be completely disposed inside the stator/rotor core or may be partially disposed inside the stator/rotor core. Similarly, a portion of the stator/rotor coil may be disposed in the stator/rotor slots and another portion may be disposed outside the stator/rotor slots.

A method of forming a coating on a component of an electrical machine is presented. The method includes coating a surface of the component with a ceramic material, via an electrophoretic process, to form a first coating. The method further includes contacting the first coating deposited by the electrophoretic process with a thermoset resin to form a second coating. The method furthermore includes heat-treating the second coating to form the coating including the ceramic material dispersed in a polymer matrix.

Non-limiting examples of suitable electrical machines include a motor, a generator, a transformer, a toroid, an inductor, and combinations thereof. In certain embodiments, an electric machine refers to an electric motor that converts electric power to mechanical power or to an electric generator that converts mechanical power to electric power. In general, the electric machine includes a rotor, a stator, and windings. It may be noted that the term "windings" typically refers to electrically insulated conductors wound into a coil. However, in the present disclosure, the terms "stator coil" and "rotor coil" are used herein for "stator windings" and "rotor windings", irrespective of the method employed to form the windings. For example, the terms "stator coil" or "stator windings" are used herein for additively manufactured windings as well, even though these windings may not be manufactured using the conventional winding methods. Therefore, the term "stator coil" refers to stator windings and the term "rotor coil" refers to rotor windings, independent of the method used for fabricating the windings.

<FIG> is a perspective view of an embodiment of an electric machine <NUM> (e.g., electric generator <NUM>) coupled to an engine <NUM> (e.g., an engine of an automobile or an aircraft). While the illustrated electric machine <NUM> is an electric generator, it may be appreciated that the methods discussed herein are applicable to other electric machines, such as electric motors. In the illustrated embodiment, the electric generator <NUM> may be described relative to an axial direction <NUM>, a radial direction <NUM>, and a circumferential direction or an annular direction <NUM>. The electric generator <NUM> includes a rotor assembly <NUM> and a stator assembly <NUM>, which may be concentrically aligned about the axial direction <NUM> of the electric machine <NUM>. The rotor assembly <NUM> is configured to rotate in the circumferential direction <NUM> relative to the stator assembly <NUM>. The rotational energy (e.g., the relative rotation between the rotor assembly <NUM> and the stator assembly <NUM>) is converted to electrical current in armature or power generation coil within the stator or rotor assembly, depending on the design of the generator <NUM>.

The rotor assembly <NUM> includes a rotor core <NUM> that has end faces <NUM>. The rotor core <NUM> includes a bore <NUM>. The rotor assembly is mounted on a shaft <NUM> such that the rotor core <NUM> rotates together with the shaft <NUM>. The stator assembly <NUM> includes a stator core <NUM> having end faces <NUM>. Further, the rotor assembly <NUM> and the stator assembly <NUM> generally both include coil windings, which are illustrated and discussed below with respect to <FIG>. In certain embodiments, the rotor assembly <NUM> includes field windings that generate a magnetic field, and the stator assembly <NUM> includes armature or power generation windings that generate electrical power as the rotor assembly <NUM> rotates. In other embodiments, the stator assembly <NUM> may include field windings, and rotor assembly <NUM> may include the armature or power generation windings. As illustrated in <FIG>, and discussed below, at least a portion of the rotor core <NUM>, the stator core, <NUM>, the rotor coil <NUM>, and the stator coil <NUM> may be coated with a coating <NUM>. In the embodiment illustrated in <FIG>, the coating <NUM> is illustrated as being in contact with both the rotor core <NUM> and the stator core <NUM>. However, embodiments wherein the coating <NUM> is in contact with only one of the rotor core <NUM> or the stator core <NUM> are also envisaged within the scope of the disclosure. Similarly, embodiments wherein the coating <NUM> is in contact with only one of the rotor coil <NUM> and the stator coil <NUM> are also envisaged within the scope of the disclosure. Further, the coating <NUM> may be coated on the entire surface or only a portion of the surface of the rotor core <NUM>, the stator core <NUM>, the rotor coil <NUM>, or the stator coil <NUM>.

<FIG> is a front view of the stator assembly <NUM> and the rotor assembly <NUM> of the embodiment of the generator <NUM>, illustrated in <FIG>. The stator assembly <NUM> may include the stator core <NUM> having the end faces <NUM>, an axially extending bore <NUM> (e.g., extending in the axial direction <NUM>), and a plurality of slots or stator slots <NUM> that extend radially (e.g., in radial directions <NUM>) away from the bore <NUM>, and extend axially (e.g., in the axial direction <NUM>) through the stator core <NUM>. The stator core <NUM> may be formed from a series of laminations (e.g., laminated steel) or may take on other suitable forms, e.g., a unitary structure manufactured using an additive manufacturing technique. The illustrated stator assembly <NUM> includes stator coil (also referred to as stator windings) <NUM> having portions extending axially through the stator slots <NUM>. The rotor assembly <NUM> is disposed within the bore <NUM> and extends axially along the bore <NUM>. The illustrated rotor assembly <NUM> includes the rotor core <NUM> and a plurality of rotor slots <NUM> that extend radially (e.g., in radial directions <NUM>) toward the shaft <NUM>, and extend axially (e.g., in the axial direction <NUM>) through the rotor core <NUM>. There is typically a gap <NUM> (e.g., an air gap) present between the rotor assembly <NUM> and the stator core <NUM>. The illustrated rotor assembly <NUM> includes rotor coil (also referred to as rotor windings) <NUM> having portions extending axially through the slots <NUM>. The rotor coil <NUM> may be either a field coil or a power generation coil, depending on the electrical machine arrangement. In some embodiments, the coating <NUM> may be selectively coated onto portions of the surfaces of the rotor core, <NUM>, the rotor coil <NUM>, the stator core <NUM>, the stator coil <NUM>, or combinations thereof. The different alternative configurations of the coated portions of the electrical machine <NUM> are further described herein with reference to <FIG>.

<FIG> illustrates embodiments in which the coating <NUM> is selectively coated onto portions of the surfaces of one or both of the stator core <NUM> and the stator coil <NUM>. In some embodiments, the coating <NUM> may coated on at least a portion of the surfaces of the slots <NUM> of the stator core <NUM>. In some embodiments, the coating <NUM> may be additionally coated on at least a portion of the end faces <NUM> of the stator core <NUM>. In some embodiments, the coating <NUM> may be additionally or alternatively coated on at least a portion of the stator coil <NUM>. In certain embodiments, the coating <NUM> provides electrical insulation between the stator coil <NUM> and the stator core <NUM>. In some such embodiments, the coating <NUM> may also dissipate heat from the stator assembly <NUM>. As described in detail later, the coating <NUM> may be coated on the surfaces, either before the assembly of the stator core <NUM> and the stator coil <NUM> to form the stator assembly <NUM>, or after the assembly of the stator core and the stator coil <NUM>.

<FIG> illustrates embodiments in which the coating <NUM> is selectively coated onto portions of the surfaces of one or both of the rotor core <NUM> and the rotor coil <NUM>. In some embodiments, the coating <NUM> may coated on at least a portion of the surfaces of the slots <NUM> of the rotor core <NUM>. In some embodiments, the coating <NUM> may be additionally coated on at least a portion of the end faces <NUM> of the rotor core <NUM>. In some embodiments, the coating <NUM> may be additionally or alternatively coated on at least a portion of the rotor coil <NUM>. In certain embodiments, the coating <NUM> provides electrical insulation between the rotor coil <NUM> and the rotor core <NUM>. In some such embodiments, the coating <NUM> may also dissipate heat from the rotor assembly <NUM>. As described in detail later, the coating <NUM> may be coated on the surfaces, either before the assembly of the rotor core <NUM> and the rotor coil <NUM>, or after the assembly of the rotor core <NUM> and the rotor coil <NUM>.

In some embodiments, a method of forming an electrically insulating coating on a component of an electrical machine is presented. In such embodiments, the coating <NUM>, as described herein earlier, is electrically insulating. The term "electrically insulating coating" as used herein refers to a coating capable of providing electrical insulation between the stator/rotor slots and the stator/rotor windings. The electrically insulating coating may be characterized by a volume electric resistivity equal to or greater than <NUM><NUM> ohm centimeters, in some embodiments. In some such embodiments, the coating <NUM> may be further thermally conductive.

The component of the electrical machine may be manufactured using any suitable method, such as, for example, including the steps of winding, enameling, lamination and the like. In certain embodiments, the component of the electrical machine is an additively-manufactured stator component or a rotor component.

The term "additively-manufactured component" as used herein refers to a component formed using an additive manufacturing technique. "Additive manufacturing" is a term used herein to describe a process which involves layer-by-layer construction or additive fabrication (as opposed to material removal as with conventional machining processes). Such processes may also be referred to as "rapid manufacturing processes". The additive manufacturing process forms net or near-net shape structures through sequentially and repeatedly depositing and joining material layers. As used herein the term "near-net shape" means that the additively manufactured structure is formed very close to the final shape of the structure, not requiring significant traditional mechanical finishing techniques, such as machining or grinding following the additive manufacturing process. In certain embodiments, suitable additive manufacturing processes include, but are not limited to, the processes known to those of ordinary skill in the art as direct metal laser melting (DMLM), direct metal laser sintering (DMLS), direct metal laser deposition (DMLD), laser engineered net shaping (LENS), selective laser sintering (SLS), selective laser melting (SLM), electron beam melting (EBM), fused deposition modeling (FDM), binder jet technology, or combinations thereof These methods may employ, for example, and without limitation, all forms of electromagnetic radiation, heating, sintering, melting, curing, binding, consolidating, pressing, embedding, and combinations thereof.

The additively manufactured component may be further characterized as having a unitary structure. The term "unitary structure" as used herein refers to a structure wherein all of the structural features of such structure are integral with each other. As used herein, the term "integral" means that the different geometric and structural features that define the unitary structure are formed together as features of a single, continuous, undivided structure, as opposed to previously formed or otherwise manufactured components that are assembled together or otherwise joined or affixed together using one or more of various joining means to yield a final assembled product. Thus, the different structural or geometric features of the unitary structure are not attached to or affixed to each other, e.g., bolted to, welded to, brazed to, bonded to, or the like.

The additive manufacturing processes may be used on suitable materials (for example, metal-based materials) to form the components of the electrical machine. These materials may be used in these methods and systems in a variety of forms as appropriate for a given material and method or, including for example without limitation, liquids, solids, powders, sheets, foils, tapes, filaments, pellets, liquids, slurries, wires, atomized, pastes, and combinations of these forms.

Conventionally, stator and rotor assemblies are assembled using multiple, sequential steps and components. For example, conventionally, stator assemblies are assembled by sequentially inserting slot liner insulation, windings, and wedges into each stator slot, which can be a cumbersome and time-consuming process. This multistep process may further lead to one or more of poor copper winding dimensional tolerance, low copper fill factor, or insulation damage due to severe mechanical stresses during manufacturing and assembly, thereby affecting the robustness and reliability of the insulation. In accordance with some of the embodiments described herein, the electrical machine components may be precisely printed and assembled, using additive manufacturing techniques, and thus the methods describe herein may reduce or eliminate some of the assembly steps such as enameling, winding, laminating, and the like.

Further, the methods and coatings, in accordance with some of the embodiments described herein address the noted shortcomings in conventional coatings and related deposition methods, at least in part, through depositing coatings via an electrophoretic process on components of the electrical machines using a two-step process. This is in contrast to typical electrophoretic processes that employ a single step to deposit a filler/particle and polymer matrix. As noted earlier, the method includes coating a surface of the component with a ceramic material, via an electrophoretic process, to form a first coating. In some embodiments, the method includes coating a surface of the component with a ceramic material including a nitride, via an electrophoretic process, to form the first coating.

The electrophoretic process employed in accordance with some embodiments of the disclosure is further described herein with reference to <FIG>. The electrophoretic process may involve submerging the component <NUM> of the electrical machine <NUM> (shown in <FIG>) into a container <NUM> that holds a coating composition <NUM>, and applying an electrical current through the coating composition <NUM>. Typically, the component <NUM> to be coated serves as one of the electrodes (e.g., anode or cathode), and one or more suitable counter-electrodes are used to complete the circuit. For example, in <FIG>, a single counter electrode <NUM> is illustrated that completes the circuit. There are two principles types of electrophoretic processes, anodic and cathodic. In the anodic electrophoretic process, negatively charged materials in the coating composition <NUM> are deposited on a positively charged workpiece, while in the cathodic process, positively charged materials in the coating composition <NUM> are deposited on a negatively charged workpiece. The component <NUM> in <FIG>, in accordance with some embodiments of disclosure, can be at least one of the stator core <NUM>, the rotor core <NUM>, the stator coil <NUM>, and the rotor coil <NUM>, as described herein earlier.

In some embodiments, the coating composition <NUM> includes a ceramic material in a suitable solvent. In some embodiments, the ceramic material is a thermally conductive ceramic material. The term "thermally conductive ceramic material" refers to a ceramic material having a thermal conductivity greater than <NUM> W/mK. Non-limiting examples of a suitable thermally conductive ceramic material include aluminum nitride, boron nitride, diamond, aluminum oxide, or combinations thereof. In certain embodiments, the ceramic material includes a nitride. Non-limiting examples of a suitable nitride includes aluminum nitride, boron nitride, or a combination thereof.

The ceramic material may be in any suitable form, such as particles, nanotubes (e.g., nanotubes of single and/or multiple walls, nanotubes of different chirality), nanofibers, nanowires, nanowhiskers, irregular shapes, etc. The sizes (e.g., diameter, length, width, characteristic length, aspect ratio) of the ceramic material may also be in any suitable range, from nanometer range to micrometer range. Non-limiting examples of suitable solvents include acetylacetone, ethanol, isopropylalchol, or combinations thereof. In certain embodiments, the coating composition <NUM> is the form of a slurry.

One or both of the size and the concentration (e.g., volume percentage) of the ceramic material in the coating composition <NUM> may be tuned to increase the thermal conductivity of the coating <NUM> and/or control the morphology of the coating <NUM>. Further, the stability of the coating composition <NUM> containing the ceramic material may be modified by changing the colloidal chemistry to form a stable coating <NUM> and/or to improve the morphology of the coating <NUM>. In some embodiments, parameters, such as pH (e.g., potential of hydrogen) level and/or zeta potential (e.g., electrokinetic potential in colloidal dispersions) may be modified to change the charging behavior of the ionized groups to form a stable coating <NUM>, for example by employing a charging agent. In some embodiments, suitable solvents, surfactants, and/or additives may be used to form a stable coating <NUM>. In some embodiments, the viscosity of the coating composition <NUM> may be modified to form a stable coating and/or to improve the morphology of the coating <NUM>. In some embodiments, suitable adhesion promoters may be added to the coating composition <NUM> to improve the adhesion of the ceramic particles on the surface of the component <NUM>.

In certain embodiments, the electrophoretic process includes contacting the surface of the component <NUM> with a coating composition <NUM> including the ceramic material and a charging agent. Non-limiting examples of a suitable charging agent include iodine, polyethyleneimine, alkoxysilylalkyl-modified polyethyleneimine, silsesquioxane, or combinations thereof. Non-limiting example of an alkoxylsiylalkyl-modified polyethylene amine includes trimethoxysilylpropyl-modified polyethyleneimine (TMSP-PEI), commercially available from Gelest Inc. Morisville, PA, USA. Non-limiting example of a silisequioxane includes aminoethylamino/vinyl/silsesquioxane in aqueous solution, commercially available from Gelest Inc. Morisville, PA, USA. In some embodiments, the charging agent may include one or more functional groups that may further function as adhesion promoters. The amount of the ceramic material in the coating composition <NUM> may be in a range from about <NUM>/mL to about <NUM>/mL. In certain embodiments, the amount of the ceramic material in the coating composition <NUM> may be in a range from about <NUM>/mL to about <NUM>/mL. The coating composition <NUM> may be further characterized by the amount of the charging agent with respect to the ceramic material. In some embodiments, the amount of the charging agent with respect to the ceramic material is in a range from about <NUM>µL/g to about <NUM>µL/g. In some embodiments, the thickness of the first coating may be varied by controlling the amount of the ceramic material in the coating composition <NUM>. Further, the stability and/or the morphology of the coating may be controlled by adding the charging agent in the coating composition <NUM>. In certain embodiments, greater than <NUM>µL/g of the charging agent (e.g., PEI) may be added to the coating composition to preclude formation of dry cracks in the first coating.

Before the electrophoretic process, the component <NUM> may be prepared to make the component <NUM> more suitable for the coating process. In some embodiments, the preparation includes applying one or more masks (e.g., masking tape) on the component <NUM> to be coated before submerging the component <NUM> to be coated into the coating composition <NUM>. For example, before submerging the stator core <NUM> into the coating composition <NUM>, if only the surfaces of the stator slots <NUM> are to be coated, one or more masks may be applied to the stator core <NUM> to cover other surfaces that are not to be coated, such that these surfaces are not in contact with the coating composition <NUM>. In some embodiments, the preparation may also include any suitable cleaning processes to clean the component <NUM> to be coated or applying a suitable pre-coating, such as a primer coating, to the component <NUM> to be coated. A primer coating may allow for improved adhesion between the ceramic material and the surface of the component <NUM> to be coated.

With continued reference to <FIG>, the method may include submerging the component <NUM> to be coated as one of the electrodes (e.g., anode or cathode) in the coating composition <NUM>, and submerging a counter electrode <NUM> to set up a complete electrical circuit, followed by application of direct electrical current through the coating composition <NUM> using the electrodes <NUM>, <NUM>. Parameters that affect the electrophoretic process can be controlled to achieve the desired qualities for the coating <NUM>. These parameters may include, for example, applied voltage, coating temperature, coating time, coating or deposition rate, etc. These parameters may affect the deposition kinetics to change the quality or characteristics of the coating <NUM> (e.g., thickness, morphology, uniformity, surface coverage, etc.). In some embodiments, the electrophoretic process may include applying an electric field in a range from about <NUM> Volts/mm to about <NUM> Volts/mm. In some embodiments, the thickness of the first coating may be varied by controlling the electric field applied.

After deposition of the ceramic material on the component <NUM>, the coated component may be post-processed. Post-processing the coated component <NUM> may include rinsing the component <NUM> to remove excess coating composition <NUM> from the component <NUM>. In certain embodiments, if one or more masks (e.g., masking tape) were applied to the coated components, the masks may be removed after the electrophoretic process.

As mentioned earlier, after the electrophoretic process, and any post-processing steps, the component <NUM> includes a first coating of a ceramic material deposited on a surface of the component <NUM>. In some embodiments, the first coating includes a nitride (e.g., aluminum nitride or boron nitride) deposited on the surface of the component <NUM>. In some embodiments, the first coating may include an interconnected network of ceramic particles and a packing density of the ceramic particles in the first coating may be greater than <NUM> volume %. In some embodiments, the packing density may be greater than <NUM> volume %. The first coating may further include voids or gaps between the ceramic particles, and these voids or gaps may be at least partially filled by impregnating a polymeric material in these voids or gaps.

In some embodiments, the deposited ceramic material may be subjected to one or more heat treatment steps before contacting the first coating with the polymeric material (described herein later). By heat treating the deposited ceramic material, partial or complete sintering of the ceramic material may be achieved, which may provide improved mechanical integrity of the deposited first coating during subsequent contacting impregnation steps. Further, partial or completely sintered ceramic material may result in improved thermal conductivity of the coating <NUM>.

The method further includes contacting the first coating deposited by the electrophoretic process with a polymeric material to form a second coating. A polymeric material may include a thermoplastic material or a thermoset resin. In some embodiments, the polymeric material includes a thermoplastic selected from the group consisting of polyetheretherketone (PEEK), polyetherketone (PEK), polyetherketoneketone (PEKK), perfluoroalkoxy alkane (PFA), polytetrafluoroethylene (PTFE), polyethersulfone (PES), and combinations thereof. In some embodiments, the polymeric material includes a thermoset resin selected from the group consisting of epoxy, siloxane, polyester, polyurethane, cyanate ester, polyimide, polyamide, polyamideimide, polyesterimide, polyvinyl ester, and combinations thereof.

In some embodiments, the method further includes contacting the first coating deposited by the electrophoretic process with a thermoset resin to form the second coating. Non-limiting examples of suitable thermoset resin include an epoxy, a siloxane, polyester, polyurethane, cyanate ester, polyimide, polyamide, polyamideimide, polyesterimide, polyvinyl ester, or combinations thereof. In certain embodiments, the thermoset resin includes epoxy, silicone, or a combination thereof.

The first coating may be contacted with the polymeric material using any suitable technique, such as, for example an immersion process or a vacuum pressure impregnating process. The technique as well as the conditions used for the contacting step may depend, at least in part, on the characteristics of the polymeric material. For example, for a low viscosity polymeric material, such as, epoxy or silicone, an immersion process or a vacuum pressure impregnation process may be employed. However, for high-viscosity thermoplastic materials, high pressure impregnation may be employed, for example by using an autoclave. The method further includes impregnating the polymeric material (e.g., a thermoset resin) into a plurality of voids present in the first coating deposited by the electrophoretic process on the surface of the component <NUM>, thereby forming the second coating.

Subsequently, the method further includes post-processing the second coating to form the coating <NUM> including the ceramic material dispersed in a polymer matrix. Post-processing of the second coating may include melting or curing the polymeric material in the second coating. Post-processing may include subjecting the second coating to any suitable treatment such that one or more of partial curing of the polymeric material, complete curing of the polymeric material, partial melting of the polymeric material, and complete melting of the polymeric material is achieved. The melting or curing of the polymeric material in the second coating may be achieved using any suitable treatments by heat, ultraviolet (UV) light, infrared (IR) light, plasma and/or electron beam energy.

In certain embodiments, the method includes curing the thermoset resin in second coating to form the electrically insulating coating <NUM> including the ceramic material dispersed in a polymer matrix. In some embodiments, the curing step may include suitable treatments by heat, ultraviolet (UV) light, infrared (IR) light, and/or electron beam energy to crosslink the deposited thermoset resin. Additionally, heat treatment or curing process may substantially reduce or eliminate the gaps, voids, and/or fractures in the as-deposited second coating to form a continuous, conformal coating on the component <NUM>, in some embodiments.

In some embodiments, the component <NUM> is the stator core <NUM> and the stator coil <NUM> (illustrated earlier in <FIG>). In some such instances, the method incudes separately coating a surface of the stator core <NUM> and the stator coil <NUM> by using the electrophoretic process, and assembling a coated stator core and a coated stator coil to form a stator assembly <NUM>. For example, the method may include loading the stator coil <NUM> into the slots <NUM> of the stator core <NUM>, wherein both are coated with the coating <NUM>.

In some embodiments, the component <NUM> is the stator core <NUM> and the stator coil <NUM> (illustrated earlier in <FIG>), wherein the stator coil <NUM> is disposed in the stator core <NUM> to form a stator assembly <NUM>. In some such instances, the method incudes simultaneously coating the surfaces of the stator core <NUM> and the stator coil <NUM> with the coating. In such instances, the surfaces of the stator core <NUM> and the stator coil <NUM> may be electrophoretically coated with the ceramic material by contacting the stator assembly <NUM> with a coating composition <NUM>, thereby forming the first coating. The coated stator assembly may be then contacted with a polymeric material to form a second coating, which may be post-processed (e.g., cured) to form the coating <NUM>, such as, an electrically insulating coating.

The coating <NUM> deposited on the component <NUM> of the electrical machine <NUM> may be further characterized by functional characteristics. For example, in some embodiments, the coating <NUM> may be substantially continuous and substantially uniform (e.g., uniform in terms of composition, thickness, etc.). The dielectric breakdown strength of the coating <NUM> may be affected by the coating thickness and/or uniformity. In particular, the dielectric breakdown strength may increase by increasing the coating <NUM> thickness and/or uniformity. In some embodiments, the coating <NUM> may have a thickness in a range of about <NUM> millimeters (mm) to about <NUM>. In some embodiments, the coating <NUM> may have a thickness in a range of about <NUM> to about <NUM>.

In some embodiments, the coating <NUM> may be substantially conformal, meaning it is continuous and conforms to the contours (e.g., surface features, including troughs, channels, edges, corners, and surface irregularities) of the coated component. Further, the coating <NUM> may be substantially free of voids and cracks. As set forth above, these morphological characteristics, as well as the thickness of the coating <NUM>, may be controlled by modifying the parameters of electrophoretic process.

In addition, the coating <NUM> includes a substantial amount of the ceramic material. An amount of the thermally ceramic material in the electrically insulating coating <NUM> may be in a range from about <NUM> volume percent to about <NUM> volume percent. In some embodiments, an amount of the ceramic material in the electrically insulating coating <NUM> may be in a range from about <NUM> volume percent to about <NUM> volume percent.

In some embodiments, the thermal conductivity of the coating <NUM> may be greater than <NUM> W/mK. In some embodiments, the thermal conductivity of the coating <NUM> may be greater than <NUM> W/mK. The improved thermal conductivity may be achieved based at least in part on the distribution, packing, and/or content of the ceramic material within the coating <NUM>.

A component of an electrical machine including a surface coated with a coating using the methods describe herein is also presented. In some embodiments, the component has a unitary structure, and the component includes a stator core, a rotor core, a stator coil, a rotor coil, or combinations thereof. The coating includes a ceramic material dispersed in a polymer matrix. <FIG> described herein earlier illustrate the different components of the electrical machine <NUM> coated with the coating <NUM>. An electrical motor including the component coated with coating <NUM> is also presented.

In accordance with some embodiments of the present disclosure, the coating <NUM> may be advantageously both thermally conductive and electrically insulating. Further, the coating <NUM> may be designed to be conformally deposited onto at least portions of a stator core and/or rotor core of an electrical machine to electrically isolate the stator core and/or rotor core from their respective windings. Further, the embodiments described herein may reduce or eliminate the need for additional components such as enamel coating, slot liners, wedges, and the like. In accordance with some embodiments of the present disclosure, the coating <NUM> and the methods of depositing the coating <NUM>, may enable the manufacture of electric machines with improved heat dissipation, as well as improved robustness to electrical shorts because of thermal cycling fatigue.

The examples that follow are merely illustrative, and should not be construed to be any sort of limitation on the scope of the claimed invention. Unless specified otherwise, all ingredients are commercially available from common chemical suppliers.

Metal coupons were used as the substrates for electrophoretic deposition (EPD) of aluminum nitride (A1N) or boron nitride (BN). Metal coupons used were copper (Cu), aluminum (Al), steel alloy, and Hiperco <NUM>™ magnetic material. Cu and Al are representative examples of materials used in stator/rotor windings while Hiperco <NUM>™ is a representative example of a magnetic material used as stator/rotor core. The coupons were cut to size (<NUM>"x3"). Copper coupons are roughened with a sand paper after cutting, other material coupons are used as is. To remove cutting oil and grease from the surface, the coupons were sonicated in acetone for <NUM>, followed by sonication in propanol for <NUM>, and N<NUM> dry-blow with visual inspection and hand cleaning of the residuals. A <NUM>% solution in ethanol of either Chemlok® <NUM> or Chemlok® AP-<NUM> adhesive was used to prime the surface after cleaning. Primer was applied to the coupon surface using dip coating. After the surface preparation, the coupons were weighed followed by application of back-protection tape (Kapton) and EPD coating process. Unless, otherwise mentioned below, the aluminum nitride or boron nitride particles were either employed as is or after milling.

A slurry formulation was prepared by mixing <NUM> of A1N, <NUM>µL of polyethyleneimine (PEI), and <NUM>µL of <NUM>-aminopropyl trimethoxysilane (3APTS) in <NUM> of ethanol. The cleaned and primed Cu coupon as described earlier was contacted with the slurry prepared above and A1N was electrophoretically deposited on the Cu coupon using an electrode gap of <NUM>, applied voltage of <NUM> Volts and deposition time of <NUM> seconds. The thickness of the AlN coated on the Cu coupon was <NUM>.

The AlN-coated Cu coupon was placed in a vacuum oven, and heat to a temperature of <NUM>. A full vacuum of <NUM> mBar was applied to the coated coupon in the vacuum oven and the coupon was held for <NUM> hour under vacuum. The AlN-coated Cu coupon was lowered into an epoxy resin solution at the speed of <NUM>/min followed by lifting it out of the solution at the speed of <NUM>/min. The epoxy resin-impregnated AlN-coated coupon was heated at a temperature of <NUM> until the resin was fully cured. <FIG> shows the scanning electron micrograph (SEM) image of a coating after the EPD process. A1N constituted about <NUM> volume % of the coating deposited using the EPD process. <FIG> shows the SEM image of the coating after epoxy-resin back fill. As shown in <FIG>, the epoxy resin has infiltrated substantially majority of the voids present in the EPD coating. The average alternating current (AC) breakdown strength of the cured coating was greater than 25kV/mm and the average thermal conductivity measured was greater than <NUM> W/m.

(A) Varying the deposition voltage and AlN concentration, while keeping the PEI/AlN ratio fixed.

Different EPD-coated samples were prepared, as described above in Example <NUM>, by varying the deposition voltage and AlN concentration, while keeping the PEI/AlN ratio fixed. Table <NUM> provides the details of the different slurry compositions employed.

<FIG> shows the weight/area (or thickness of the A1N coating) as a function of the applied field for Samples <NUM>-<NUM> (varying AlN concentration). As shown in <FIG>, for all the three samples, the thickness of the AlN coating was linearly proportional to the applied field. <FIG> shows the thickness of the AlN coating as a function of the AlN concentration using two different deposition voltages (<NUM> Volts and <NUM> Volts). As shown in <FIG>, for both the deposition voltages, the thickness of the A1N coating was linearly proportional to the AlN concentration. (B) Varying the deposition voltage and PEI concentration, while keeping the A1N concentration fixed.

Different EPD-coated samples were prepared, as described above in Example <NUM>, by varying the deposition voltages and PEI concentration, while keeping the AlN concentration fixed. Table <NUM> provides the details of the different slurry compositions employed.

<FIG> shows the thickness of the AlN coating as a function of the PEI/AlN ratio. Therefore, it was observed that the coating thickness is dependent on the AlN concentration rather than the PEI concentration, at the same applied electric field. (C) Effect of increasing the A1N concentration in the slurry.

A slurry was prepared as described in Example <NUM> using <NUM> of AlN, <NUM> of PEI in <NUM> of ethanol. The slurry was electrophoretically coated on a coupon using the EPD process described above in Example <NUM> by varying the voltage that was applied for <NUM> using an electrode gap of <NUM>. The coated film did not show any dry film cracking even at the higher concentrations of AlN in the slurry, when PEI/AlN was above <NUM>µL/g.

A slurry formulation was prepared by mixing <NUM> of A1N and <NUM> of PEI in <NUM> of ethanol. The steel laminate core slots of the statorette were cleaned from any grease followed by rinsing. The cleaned slots were then placed in an etchant solution for about <NUM> seconds. This was followed by distilled water wash and cleanse drying before deposition. The cleaned statorette was then contacted with the slurry prepared above and A1N was electrophoretically deposited on the slots using different electrode configurations.

<FIG> shows an electrode configuration in which a plurality of electrodes was placed in individual slots. The electrode gap using this configuration was <NUM>, deposition voltage was <NUM> Volts and deposition time was <NUM> seconds. <FIG> shows an electrode configuration in which a single electrode was placed in the stator bore. The electrode gap using this configuration was about <NUM>, deposition voltage was <NUM> Volts, and deposition time was <NUM> seconds.

The AlN-coated statorette was placed in a container in an autoclave along with an application of vacuum for <NUM> minutes. Following the application of the vacuum, epoxy resin was allowed to enter the autoclave from the bottom of the container, until the statorette was fully immersed in the epoxy resin. After complete immersion of the statorette in the epoxy resin, the autoclave was held under vacuum for <NUM> minutes, followed by application of <NUM> psi N<NUM> to the autoclave and holding the autoclave under pressure for ~ <NUM> hours. This vacuum and pressure cycle was repeated a few times to ensure that the epoxy resin is fully penetrated into the A1N coating. After taking the statorette out from the autoclave, the excess resin was drained and coating was cured in an oven using the resin curing profile. The uniformity of the coating obtained using the electrode configuration of <FIG> was better than the uniformity of the coating obtained using the electrode configuration of <FIG>.

A slurry formulation was prepared by mixing <NUM> of AlN, <NUM>µL of PEI (<NUM> MW branched, <NUM>% in ethanol) in <NUM> of ethanol. The slip was prepared by ultrasonicating the mixture with small horn in a <NUM> metal beaker with ice bath cooling and no magnetic stirring for <NUM> active sonication time, using an amplitude of <NUM>%. The cleaned and primed Hiperco <NUM>™ coupons, as described earlier, were contacted with the slurry prepared above and AlN was electrophoretically deposited on the coupons using an electrode gap of <NUM>, applied voltage of <NUM> Volts and deposition time of <NUM> seconds.

Hardsil™ (from Gelest) silicone resin for dip coating was prepared by mixing <NUM>% part A with <NUM>% part B, followed by degassing the mixture under house vacuum at room temperature until bubbles were almost gone. The AlN-coated coupons were placed in a vacuum oven, and heated to a temperature of <NUM>. A full vacuum of <NUM> mBar was applied to the coated coupons in the vacuum oven and the coupons were held for <NUM> hour under vacuum. The AlN-coated coupons were lowered into the silicone resin solution at the speed of <NUM>/min followed by lifting them out of the solution at the speed of <NUM>/min. The silicone resin-impregnated AlN-coated coupons were heated at <NUM> for <NUM> hours (<NUM> ramp heating time), and <NUM> for <NUM> hours (<NUM>. ramp heating time). This was followed by heating at <NUM> for <NUM> hours (<NUM>. ramp heating time) and <NUM> hours of cooling to room temperature. The average alternating current (AC) breakdown strength of the cured coating was greater than <NUM> kV/mm.

A slurry formulation was prepared by mixing <NUM> of A1N and <NUM>µL of the charging agent in <NUM> of ethanol. Two different charging agents from Gelest were used: trimethoxysilylpropyl-modified polyethyleneimine (TMSP-PEI) <NUM> wt% in in IPA and aminoethylamino/vinyl/silsesquioxane <NUM> wt% in aqueous solution. The slips were prepared by ultrasonicating the mixture with small horn in a <NUM> metal beaker with ice bath cooling and no magnetic stirring for <NUM> active sonication time, using an amplitude of <NUM>%. The cleaned and primed Cu and Hiperco <NUM>™ coupons, as described earlier, were contacted with the slurry prepared above and A1N was electrophoretically deposited on the coupons using an electrode gap of <NUM>, applied voltage of <NUM> Volts and deposition time of <NUM> seconds. The thickness of the A1N coated on the coupons was about <NUM>.

A slurry formulation was prepared by mixing <NUM> of BN, <NUM>µL of PEI (<NUM> MW branched, <NUM>% in ethanol) in <NUM> of ethanol. The cleaned and primed Cu and steels coupons, as described earlier, were contacted with the slurry prepared above and BN was electrophoretically deposited on the coupons using an electrode gap of <NUM>, applied voltage of <NUM> Volts and deposition time of <NUM> seconds. The thickness of the BN coated on the coupons was about <NUM>.

Hardsil™ (from Gelest) silicone resin for dip coating was prepared by mixing <NUM>% part A with <NUM>% part B, then degassing the mixture under house vacuum at room temperature until bubbles were almost gone. The BN-coated Cu coupons were placed in a vacuum oven, and heated to a temperature of <NUM>. A full vacuum of <NUM> mBar was applied to the coated coupons in the vacuum oven and the coupons were held for <NUM> hour under vacuum. The BN-coated coupons were lowered into the silicone resin solution at the speed of <NUM>/min followed by lifting them out of the solution at the speed of <NUM>/min. The silicone resin-impregnated BN-coated coupons were heated at <NUM> for <NUM> hours (<NUM> ramp heating time), and <NUM> for <NUM> hours (<NUM>. ramp heating time). This was followed by heating at <NUM> for <NUM> hours (<NUM>. ramp heating time) and <NUM> hours of cooling to room temperature. The average alternating current (AC) breakdown strength of the cured coating was greater than <NUM>-<NUM> kV/mm.

Claim 1:
A method of forming a coating (<NUM>) on a component (<NUM>) of an electrical machine (<NUM>), comprising:
coating a surface of the component (<NUM>) with a ceramic material, via an electrophoretic process, to form a first coating;
contacting the first coating deposited by the electrophoretic process with a polymeric material;
impregnating the polymeric material into a plurality of voids present in the first coating to form a second coating; and
curing or melting the polymeric material in the second coating to form the coating (<NUM>) comprising the ceramic material in a polymer matrix; characterised in that
the component (<NUM>) is a stator assembly or a rotor assembly