CROSS REFERENCE TO RELATED APPLICATION [0001] The present application claims priority to U.S. Provisional Application No.

62/909,850, filed on October 3, 2019, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

[0002] This disclosure relates generally to systems and assemblies involving an electric motor with enhanced thermal characteristics and improved heat transfer to the surrounding environment of the electric motor.

BACKGROUND

[0003] An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor’s magnetic field and electric current in wire windings to generate force in the form of rotation of a shaft. Electric motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or rectifiers, or by alternating current (AC) sources, such as a power grid, inverters or electrical generators.

[0004] The torque and power generated at the shaft of the motor are limited by how much current or electric power is input through the wire windings. Increasing current beyond a certain limit can increase the temperature of the wire windings and cause damage to the wires and the electric motor.

[0005] It may thus be desirable to have an electric motor with enhanced thermal characteristics to enable improved heat transfer from the wire windings, thereby reducing the temperature of the wire windings for a given current input, preventing damage to the motor, and enabling an increase in the current limit. It is with respect to these and other considerations that the disclosure made herein is presented.

SUMMARY

[0006] The present disclosure describes implementations that relate to an electric motor with enhanced thermal characteristics.

[0007] In a first example implementation, the present disclosure describes a stator of an electric motor. The stator comprises: (i) a lamination stack; (ii) a slot formed in the lamination stack; (iii) a slot liner disposed in the slot and configured to be electrically- insulating; (iv) a thermally-conductive gap filler disposed in a gap between the slot liner and the lamination stack; and (v) wire windings disposed in the slot.

[0008] In a second example implementation, the present disclosure describes an assembly of an electric motor. The assembly includes a stator having an open annular space. The stator comprises: (i) a lamination stack comprising a plurality of segments disposed adjacent to each other in a radial array; (ii) a plurality of slots formed between adjacent segments of the plurality of segments of the lamination stack; (iii) respective slot liners disposed in the plurality of slots and configured to be electrically-insulating; (iv) a thermally-conductive gap filler disposed in respective gaps between the respective slot liners and the plurality of segments of the lamination stack; and (v) wire windings disposed in the plurality of slots. The assembly further includes a rotor disposed in the open annular space of the stator and comprising: a steel core, and a plurality of magnets disposed in a respective radial array about the steel core.

[0009] In a third example implementation, the present disclosure describes a method. The method includes: (i) providing a segment of a lamination stack of a stator of an electric motor, wherein the segment of the lamination stack comprises a slot; (ii) providing a slot liner formed of an electrically-insulating material; (iii) applying a thermally-conductive gap filler to an exterior surface of the slot liner; (iv) inserting the slot liner with the thermally- conductive gap filler applied thereto into the slot of the segment of the lamination stack, such that the thermally-conductive gap filler is disposed between the exterior surface of the slot liner and the segment; and (v) winding a wire about the segment such that the slot liner and the thermally-conductive gap filler are disposed between the wire and the segment.

[0010] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, implementations, and features described above, further aspects, implementations, and features will become apparent by reference to the figures and the following detailed description.

BRIEF DESCRIPTION OF THE FIGURES

[0011] The novel features believed characteristic of the illustrative examples are set forth in the appended claims. The illustrative examples, however, as well as a preferred mode of use, further objectives and descriptions thereof, will best be understood by reference to the following detailed description of an illustrative example of the present disclosure when read in conjunction with the accompanying Figures.

[0012] Figure 1 illustrates a perspective view of an electric motor, in accordance with an example implementation.

[0013] Figure 2 illustrates a perspective view of a stator and a rotor mounted within the stator, in accordance with an example implementation.

[0014] Figure 3 illustrates a perspective view of a lamination stack of a stator, in accordance with an example implementation.

[0015] Figure 4 illustrates an exploded view of insulation slot liners disposed in respective slots of a lamination stack, in accordance with an example implementation.

[0016] Figure 5 illustrates a perspective view of an individual slot liner, in accordance with an example implementation.

[0017] Figure 6 illustrates components associated with a segment of a lamination stack prior to assembly and winding wires of a stator, in accordance with an example implementation.

[0018] Figure 7 illustrates a segment of a lamination stack after assembly of its components and winding a wire, in accordance with an example implementation.

[0019] Figure 8 illustrates a partial cross-sectional view of a segment of a lamination stack, in accordance with an example implementation. [0020] Figure 9 illustrates placing thermally-conductive gap filler in portions of gaps between a slot liner and segment of a lamination stack and between a cooling tube and the segment of the lamination stack, in accordance with an example implementation.

[0021] Figure 10 illustrates placing thermally-conductive gap filler throughout interfaces between a slot liner and a segment of a lamination stack and between a cooling tube and the segment of the lamination stack, in accordance with an example implementation.

[0022] Figure 11 is a flowchart of a method for assembling a stator or an electric motor, in accordance with an example implementation.

DETAILED DESCRIPTION

[0023] The torque and power generated at a shaft of an electric motor can be limited by how much current or electric power is input through the wire windings of the electric motor. Increasing current beyond a certain limit can cause damage to the wires and motor.

[0024] Within examples, disclosed herein are systems and assemblies that relate to an electric motor with enhanced thermal and heat transfer characteristics. Particularly, the disclosed systems using thermally-conductive gap filler between wire winding insulation liners and the lamination stack of the electric motor. The thermally-conductive gap filler can also be placed between cooling tubes of the electric motor and the lamination stack channels through which the cooling tubes are disposed. The thermally-conductive gap filler can enhance heat transfer from the wire windings of the electric motor.

[0025] Improved heat transfer can enable increasing the current limit of the electric motor, and therefore enable producing higher torque and power for the same electric motor. Improved heat transfer can also enable running the electric motor at a cooler temperature for a given torque output, thereby improving efficiency of the electric motor.

[0026] Figure 1 illustrates a perspective view of an electric motor 100, in accordance with an example implementation. The electric motor 100 includes a stator 102. The stator 102 is configured to generate a magnetic field. Particularly, as described below, the stator 102 can include wire windings wrapped about a lamination stack, and when electric current is provided through the wire windings, a magnetic field is generated. The stator 102 can also include a mounting location 103 to enable mounting the electric motor 100 to a machine or device that utilizes the electric motor 100.

[0027] The electric motor 100 further includes a rotor 104. The stator 102 can have an open annular space in which the rotor 104 is disposed. The rotor 104 can have magnets mounted thereto that can interact with the magnetic field generated by the stator 102 in order to rotate and produce torque. The rotor 104 can rotate relative to the stator 102 by being mounted to the stator 102 via a bearing 106, for example.

[0028] A shaft 108 can be coupled to the rotor 104, and the shaft 108 is configured to transmit the torque generated by the rotor 104, e.g., to a gear box or a component of a machine to rotate such component. The electric motor 100 can include another mounting location 109 to further facilitate mounting the electric motor 100 to the machine that utilizes the generated torque and resulting rotary motion of the shaft 108.

[0029] The electric motor 100 can include other components such as feedback device 110 (e.g., sensor) that provides sensor information indicative of the position of the rotor 104 to an electronic controller of the electric motor 100. The electronic controller can then energize the wire windings of the stator 102 at the appropriate time to achieve a desired torque.

[0030] Cables 112 can be used to provide electric current to the wire windings of the stator 102. The cables 112 can also be used to transmit electric signals generated by the feedback device 110 to indicate position of the rotor 104 to an amplifier.

[0031] Figure 2 illustrates a perspective view of an assembly 200 of the stator 102 and the rotor 104 mounted within the stator 102, in accordance with an example implementation. The stator 102 can have a steel core. The stator 102 can include a lamination stack. The lamination stack can be made as a single piece (e.g., unitary construction) or can comprise multiple segments as described in below with respect to Figure 3.

[0032] Electric wires are wound through segments of the lamination stack. For example, Figure 2 illustrates individual coils (bundles of wires), such as coil 201, wound through the segments of the stator 102. The coils are separated from each other to prevent electric shorts from occurring. When electric current is provided through the wires, the coils can operate as electromagnets and generate a magnetic field.

[0033] The rotor 104 can also have a steel core. The rotor 104 can further have multiple magnets (e.g., permanent magnets), such as magnet 202, disposed in a radial or circumferential array about the steel core of the rotor 104.

[0034] The electric current provided to the coils of the stator 102 can be provided in a particular sequence to the individual coils of the respective segments of the stator 102. As such, the magnetic field generated by the coils of the stator can effectively be moving or changing in a circular manner around the stator 102. The magnetic field interacts with the magnets of the rotor 104, and such interaction of the magnetic field with the magnets causes the rotor 104 (and the shaft 108 coupled thereto) to rotate.

[0035] Figure 3 illustrates a perspective view of a lamination stack 300 of the stator 102, in accordance with an example implementation. As illustrated in Figure 3, the lamination stack 300 is generally donut-shaped and has an open annular space 302 in which the rotor 104 can be disposed. The lamination stack 300 comprises laminated electrical steel sheets. Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance or other desirable electrical properties.

[0036] The lamination stack 300 can be made of silicon steel, also known as electrical steel, which comprises steel with silicon added to it. Adding silicon to steel increases its electrical resistance, improves the ability of magnetic fields to penetrate it, and reduces the steel’s hysteresis loss. The lamination stack 300 represents the core of the stator 102 and is laminated and insulated in order to reduce induced circulating currents and associated heat as electric current is modulated through the wire windings of the stator 102. [0037] In an example, the lamination stack 300 can be made as a single piece or single component that is not segmented. For instance, the lamination stack 300 can have teeth similar to a gear, and the slots or spaces between the teeth can be configured to receive wires therethrough.

[0038] In another example, the lamination stack 300 includes multiple segments, such as segment 304, segment 306, and segment 308, disposed adjacent to teach other in a radial array and interface with each. The segments are generally formed or shaped as I-beams that have C-shaped side channels or slots on each side thereof. Thus, when two adjacent segments interface with each other, a slot is formed therebetween and comprises the C- shaped channels or respective slots of the two adjacent segments. For example, a slot 310 is formed between the segment 304 and the segment 306, and a slot 312 is formed between the segment 306 and the segment 308. Although the description below refers to a multiple segment construction of the lamination stack 300, it should be understood that similar description would apply to a lamination stack made of having unitary construction and made as a single component that is not segmented. Such a component can have holes, channels, or slots similar to the slots 310, 312 made therein to receive the slot liners described below.

[0039] Each of the slots 310, 312 comprises one slot (partial slot) formed in one segment of the lamination stack 300 and a second slot (partial slot) formed in an adjacent segment of the lamination stack 300. The term “slot” is used herein to refer to a complete slot such as the slot 310 or the slot 312 and is also used to refer to an individual slot or partial slot (a C- shaped channel) of a segment of the lamination stack. Wires are wound through the slots of the lamination stack 300 in wire bundles or coils such as the coil 201 shown in Figure 2.

[0040] As electric current is provided through the wires, the temperature of the wires increases and heat is generated. The heat can be referred to as winding losses. The rising temperature of the wires can cause damage and limit performance of the electric motor 100 as described below.

[0041] In examples, to cool the lamination stack 300 and the wires disposed therein, the lamination stack 300 can be liquid-cooled. As shown in Figure 3, each of the segments can have channels disposed therein that are semi-circular in shape. For instance, the segment 304 has a semi-circular channel 314 disposed longitudinally across an exterior peripheral surface of the segment 304. A tube can be disposed through the semi-circular channel 314, and cooling fluid can be provided through such tube, thereby absorbing some of the heat generated by the wires and cooling the lamination stack 300 and the wires disposed therein.

[0042] The coils of the stator 102 are energized individually as mentioned above to generate a moving or changing magnetic field. As such, it is desirable to electrically insulate the wires of the coils from the lamination stack 300 to prevent shorting or electric connections between wires of two adjacent coils. To isolate the wires from the segments of the lamination stack 300, insulation liners can be disposed in the slots of the lamination stack 300 to operate as electric insulators. For example, paper liners can be used as insulation liners.

[0043] Figure 4 illustrate an exploded view of insulation slot liners disposed in respective slots of the lamination stack 300, and Figure 5 illustrates a perspective view of an individual slot liner 500, in accordance with an example implementation. The slots of the lamination stack 300 can receive therein the respective insulation papers slot liners shown in a radial array in Figure 4. For example, insulation paper slot liner 400 can be inserted in the slot 310, and insulation paper slot liner 402 can be inserted in the slot 312. In an example, an insulation paper slot liner can be composed of two individual slot liners, each slot liner of the two individual slot liners can have a U-shape or C-shape, such that when the meet at their lateral edges, a slot or channel is formed therebetween through which the wires of coils of the stator 102 are disposed. [0044] Figure 5 illustrates an example of such a slot liner 500. The slot liner 500 can have a first side portion 502, a second side portion 504, and a connecting portion 506 that couples or connects the side portion 502 to the side portion 504. With this configuration, the slot liner 500 forms a channel (e.g., C-shaped channel) therein.

[0045] When two slot liners similar to the slot liner 500 are disposed next to each other such that the respective edges of the side portions of the slot liners interface with each other (i.e., the connecting portions do not interface with each, but are rather disposed opposite each other with the respective C-channels disposed therebetween), an insulation paper slot liner of the insulation paper slot liners shown in Figure 4 is formed. The slot liners (e.g., the slot liner 500) can be inserted individually in the slots of the respective segments of the lamination stack 300.

[0046] In another example, the insulation paper slot liners 400, 402 can be made as a single rectangular-shaped liner, rather than two individual slot liners. In still another example, rather than having separate insulation paper slot liners like the insulation paper slot liners 400, 402, the slots liners of the entire lamination stack 300 can be made as a single component that goes all around to line the respective slots of the lamination stack 300.

[0047] Figure 6 illustrates components associated with a segment 600 of the lamination stack 300 prior to assembly and winding wires of the stator 102, in accordance with an example implementation. The segment 600 can represent any of the segments of the lamination stack 300 (e.g., any of the segments 304, 306, 308).

[0048] As mentioned above, the segments of the lamination stack 300 are generally formed or shaped as I-beams that have C-shaped channels on each side thereof. The segment 600 can have a first slot or first channel 602 and a second slot or second channel 604. A first slot liner

606 can be disposed in the first channel 602, and similarly, a second slot liner 608 can be disposed in the second channel 604. The slot liners 606, 608 can also be C-shaped to conform to shape of the channels 602, 604 of the segment 600. When wires are wound about the segment 600, the slot liners 606, 608 insulate the wires from sides of the segment 600 (i.e., the surfaces of the channels 602, 604).

[0049] The slot liners 606, 608 do not extend to the ends of the segment 600 and might not isolate end surfaces of the segment 600 from end-turns of the wires as the wires wrap around the ends of the segment 600. To insulate end-turns of the wires, a first end-turn insulator 610 can be inserted at a first end of the segment 600, and a second end-turn insulator 612 can be inserted at a second end of the segment 600 prior to winding the wire.

[0050] Figure 7 illustrates the segment 600 after assembly of its components and winding a wire 700, in accordance with an example implementation. As depicted in Figure 7, the slot liners, such as the slot liner 606, are positioned in their respective channels of the segment 600, and the end-turn insulators 610, 612 are also inserted at the respective ends of the segment 600. The wire 700 can then be wound about the segment 600 to form a coil associated with the segment 600.

[0051] With this configuration, the wire 700 is electrically insulated from the segment 600, and therefore when the multiple segments of the lamination stack 300 are assembled in a radial array to form the lamination stack 300, their respective coils are electrically-insulated from each other. Further, wires can be coated with an electrically-insulating material (e.g., a synthetic polymer such as nylon polyamide) so as to isolate the individual wires of a given segment from each other and prevent electrical shorting.

[0052] Once inserted in the channels 602, 604, the exterior surfaces of the slot liners 606, 608 can interface with interior surface of the segment 600 of the lamination stack 300. However, gaps can separate the exterior surface of the slot liners 606, 608 and the interior surface of the segment 600.

[0053] Figure 8 illustrates a partial cross-sectional view of the segment 600, in accordance with an example implementation. As depicted in Figure 8, when the slot liner 606 is inserted in the channel 602 of the segment 600, a gap 800 can separate exterior surfaces of the side portions (e.g., the side portions 502, 504) and the connecting portion (e.g., the connecting portion 506) from the interior surfaces of the channel 602 of the segment 600 in which the slot liner 606 is disposed.

[0054] As mentioned above with respect to Figure 3, each of the segments of the lamination stack 300 can have a semi-circular channel disposed therein to receive a cooling tube therethrough. For example, the segment 600 can receive a cooling tube 802 as depicted in Figure 8. Another gap 804 can separate the cooling tube 802 from the interior surface of the segment 600 that bounds the semi-circular channel in which the cooling tube 802 is disposed.

[0055] When electric current is provided through the wires (e.g., the wire 700) of the electric motor 100, heat is generated and temperatures of the components of the electric motor 100 can rise. The heat generated from the wire or coils of the electric motor 100 can be referred to as winding losses and can be determined based on the magnitude of the electric current (7) and electric resistance ( R ) of the wire. Particularly, the winding losses can be determined as I ² R.

[0056] Further, the heat generated (the winding losses) can be transferred to the surrounding environment of the electric motor 100 at a particular heat transfer rate (q) that is based on temperature of the wire f/w ). ambient temperature (7a), and winding-to-ambient thermal resistance ( Rthwa ). Particularly, the heat transfer can be determined by the following equation: Winding Losses

(1)

[0057] For a given ambient temperature Ta, electric resistance P, and winding-to-ambient thermal resistance Rthwa, equation (1) indicates that the winding temperature Tw is proportional to the square of the electric current (7 ² ). During operation of the electric motor 100, if the winding temperature Tw exceeds a threshold level, damage to the electric motor 100 can occur. For example, the coating of the wires (e.g., polyamide coating) can be damaged, thereby causing the individual wires of a coil or winding to touch each other and electric short to occur.

[0058] To prevent damage to the electric motor 100, the magnitude of the electric current (7) is limited so as to prevent the winding losses from exceeding a particular level that would cause the winding temperature Tw to exceed a threshold level. However, limiting the magnitude of the electric current (I) can also limit the magnitude of the torque that the electric motor 100 can produce. In particular, the torque (7) that the electric motor 100 produces can be determined as T = K _t I, where Kt is the motor torque constant and is based on a constant multiplied by a length of the stator 102 and the number of turns of the wire. The power (P) generated by the electric motor 100 can be determined as P = Tw = K _t Ia>, where w is the rotational speed of the rotor 104 or the shaft 108 coupled thereto.

[0059] As such, limiting the magnitude of the electric current 7 also limits the torque T and power P that the electric motor 100 can generate. Further, at a particular power level, the amount of heat generated can affect efficiency of the electric motor 100 (e.g., the ratio of the power P produced by the electric motor 100 divided by the electric power provided to the electric motor 100). Running the electric motor 100 at a lower winding temperature Tw for a particular power output P can increase efficiency of the electric motor 100. [0060] The slot liners discussed above (e.g., the slot liners 500, 606, 608) are configured to be electrically-insulating, but might not be thermally -conductive and may thus cause a higher thermal resistance to, and may impede, heat transfer from the wires to the environment. In other words, the slot liners being not configured to be made of a thermally-conductive material may increase Rthwa. Further, if there is a gap (e.g., the gap 800) between a slot liner and the segment of the lamination stack, the gaps can be filled with air, which may further increase Rthwa.

[0061] One way to enable the electric motor 100 to receive higher magnitudes of electric current (I) without damaging its components involves reducing the winding-to-ambient thermal resistance {Rthwa). Based on equation (1) above, reducing Rthwa can maintain the winding temperature Tw at a particular level for a higher magnitudes of electric current (I), which enables the electric motor 100 to produce higher torque (7) and power (P) without damaging its components. Alternatively, the same current level (I) can be used and the electric motor 100 can generate the same torque (7) and power (P) while reducing the winding temperature Tw, thereby increasing efficiency of the electric motor 100.

[0062] In an example, reducing the winding-to-ambient thermal resistance {Rthwa) can be achieved by placing a thermally-conductive gap filler in the gaps between the slot liners (e.g., the slot liner 606) and the lamination stack 300 (e.g., in the gap 800). Additionally or alternatively, a thermally-conductive gap filler can be placed in the gap between the cooling tubes (e.g., the cooling tube 802) and the lamination stacks 300 (e.g., in the gap 804). Such a thermally-conductive gap filler can reduce thermal resistance (resistance to heat flow from the windings to the lamination stack 300 and then to the environment), thus reducing Rthwa.

[0063] In examples, the thermally-conductive gap filler can be placed in, or can line, a portion of the respective gap (e.g., the gap 800 and/or the gap 804). In other examples, the thermally-conductive gap filler can be used to fill the entire interface between the slot liners and the lamination stack 300 and the interface between the cooling tubes and the lamination stack 300.

[0064] Figure 9 illustrates placing thermally-conductive gap filler in portions of the gap 800 and the gap 804, in accordance with an example implementation. As depicted in Figure 9, thermally-conductive gap filler 900 (illustrated by a dashed line) can be placed in a portion between the connecting portion (e.g., vertical portion) of the slot liner 606 and the interior surface of the segment 600 of the lamination stack 300. A respective thermally-conductive gap filler 902 (illustrated by a curved dashed line) can also be placed in a portion of the gap 804 between a respective exterior surface of the cooling tube 802 and the interior surface of the semi-circular channel of the segment 600 in which the cooling tube 802 is disposed.

[0065] In examples, the thermally-conductive gap filler 900, 902 can be placed in the segment 600 of the lamination stack 300 prior to insertion of the slot liner 606 and the cooling tube 802. Alternatively, the thermally-conductive gap filler 900, 902 can be applied to exterior surfaces of the slot liner 606 and the cooling tube 802 prior to their insertion in their respective channels of the lamination stack 300.

[0066] Figure 10 illustrates placing thermally-conductive gap filler throughout interfaces between the slot liner 606 and the segment 600 and between the cooling tube 802 and the segment 600, in accordance with an example implementation. As depicted in Figure 10, thermally-conductive gap filler 1000 (illustrated by a dashed line) can be placed throughout the gap 800 between, or disposed along, the side portions and the connecting portion of the slot liner 606 and the interior surface of the segment 600 that bounds the channel in which the slot liner 606 is disposed. Thermally-conductive gap filler 1002 (illustrated by a curved dashed line) can also be placed throughout the gap 804 between the cooling tube 802 and the interior surface of the semi-circular channel of the segment 600 in which the cooling tube 802 is disposed. [0067] Figures 9-10 illustrate a partial cross-section depicting one side or one half of the segment 600 and using thermally-conductive gap fillers with respect to a portion of the segment 600. It should be understood, however, that the thermally-conductive gap fillers can be used on the other side of the segment 600 and can be used with all or some of the other segments of the lamination stack 300. Further, as mentioned above, the thermally-conductive gap filler can be placed in the segments of the lamination stack 300 prior to insertion of the slot liner 606 and the cooling tube 802, or alternatively, the thermally-conductive gap filler can be applied to the slot liners (e.g., applied to the side portions 502, 504 and the connecting portion 506 of the slot liner 500) and the cooling tubes (e.g., the cooling tube 802) prior to their insertion in their respective channels.

[0068] Different types of thermally-conductive fillers can be used. For example, the thermally conductive filler can take the form of a paste comprising a mineral oil with thermally-conductive solid particles (e.g., metallic material) suspended therein. In other examples, the thermally conductive filler can take the form of a thermally-conductive pad comprising a silicone polymer that is combined with a thermal medium (e.g., ceramic).

[0069] In an example, the thermally-conductive gap filler can include silicone grease or wax filled with a thermally-conductive material such as aluminum oxide. Such silicon grease can take the form of a semi-liquid or solid material at normal room temperature, and may liquefy or soften at elevated temperatures to flow and better conform to any irregularities of the interface surfaces between the slot liners and the segments of the laminations stack 300 or between the cooling tubes and the lamination stack 300. In some examples, the silicon greases or waxes can be provided in the form of a film. To provide such a film, a substrate, web, or other carrier can be provided.

[0070] In another example, the thermally-conductive gap fillers can include a cured, sheet- like material. Such materials can be compounded as containing one or more thermally- conductive particulate fillers dispersed within a polymeric binder, and may be provided in the form of cured sheets, tapes, pads, or films. Example binder materials include silicones, urethanes, thermoplastic rubbers, and other elastomers, with example fillers including aluminum oxide, magnesium oxide, zinc oxide, boron nitride, and aluminum nitride.

[0071] In another example, the thermally-conductive gap fillers can include a cured, form- stable, sheet-like, thermally-conductive material for transferring thermal energy from the wire windings and the lamination stack 300 to the environment. Such material can be formed of a urethane binder, a curing agent, and one or more thermally-conductive fillers. The fillers, which may include aluminum oxide, aluminum nitride, boron nitride, magnesium oxide, or zinc oxide, can range in particle size from about 1-50 microns or can comprise nanoparticles, for example.

[0072] In an example, the thermally-conductive gap fillers can include phase-change materials, which can be self-supporting and form-stable at room temperature for ease of handling. Such phase-change materials can liquefy or otherwise soften at temperatures within the operating temperature range of the electric motor 100 to form a viscous, thixotropic phase, which can better conform to the interface surfaces between the slot liners and the segments of the laminations stack 300 or between the cooling tubes and the lamination stack 300 The phase-change materials, which can be supplied as free-standing films, or as heated screen printed onto a substrate surface, can operate as greases and waxes in conformably flowing within the operating temperature of the electric motor 100 under relatively low clamping pressures of about 5 pounds per square inch (psi).

[0073] In another example, the thermally-conductive gap fillers can include a tape or sheet comprising an inner and outer release liner and an interlayer of a thermal compound. One side of the tape or sheet can be coated with a thin layer of a pressure-sensitive adhesive (PSA) for the application of the material to the heat transfer surfaces between the slot liners and the segments of the laminations stack 300 or between the cooling tubes and the lamination stack 300.

[0074] Other example thermally-conductive gap filler materials can include thermal interface compounds, caulks, form-in-place materials, or encapsulants. These materials can be provided as charged within one or more tubes, containers as one or two-part liquid or otherwise fluent, filled reactive systems, which cure at room or elevated temperatures to be formed-in-place within the gaps (e.g., the gaps 800, 804).

[0075] In another example, the thermally-conductive gap fillers can include a thermally- conductive compound that is dispensable under an applied pressure as issued as a bead or mass from a nozzle or other orifice. The material, which may be charged in a tube, cartridge, or other container, can be dispensed onto a surface of the slot liners or the cooling tubes, which forms a gap (e.g., the gaps 800, 804) with a segment of the lamination stack 300 or directly into the gaps formed between the adjoining surfaces. As applied, the material can form a bead or mass of material “in place.” Within the gap, the formed-in-place bead or mass of the material can operate as an interface material in being conformable to at least partially fill the gaps and to thereby provide a thermally-conductive pathway between the surfaces and reduce the winding-to-ambient thermal resistance ( Rthwa ). In examples, the material can be fully cross-linked or otherwise cured as charged within the tube, cartridge, or other container, or as otherwise supplied. While being of a fluent viscosity, the material can be generally viscoelastic and, as filled, might not exhibit appreciable settling of the metallic filler particles.

[0076] The thermally-conductive compound can be formulated as being fluent under an applied pressure, yet form-stable as applied to a surface or within the gaps, as a blend or admixture of: (i) a polymer gel component; and (ii) a particulate filler component, which can be thermally-conductive particles or a blend thereof. The gel component can be, for example, a thermoplastic gel or a silicone gel which may be an organopolysiloxane. [0077] Gels that can be used for the above-mentioned thermally-conductive compound include systems based on silicones, i.e., polysiloxanes, such as polyorganosiloxane, as well as systems based on other polymers, which may be thermoplastic or thermosetting, such as polyurethanes, polyureas, fluoropolymers, chlorosulfonates, polybutadienes, butyls, neoprenes, nitrites, polyisoprenes, and buna-N, copolymers such as ethylene-propylene (EPR), styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), ethylene-propylene- diene monomer (EPDM), nitrile butadiene (NBR), styrene-ethylene-butadiene (SEB), and styrene-butadiene (SBR), and blends thereof such as ethylene or propylene-EPDM, EPR, or NBR.

[0078] The polymer gel can include fluid-extended polymer system comprising a continuous polymeric phase or network, which can be chemically, e.g., ionically or covalently, or physically cross-linked, and an oil, such as a silicone or other oil, a plasticizer, unreacted monomer, or other fluid extender, which swells or otherwise fills the interstices of the network. The cross-linking density of such network and the proportion of the extender can be controlled to tailor the modulus, i.e., softness, and other properties of the gel. The polymer gel can also encompass materials that alternatively can be classified broadly as pseudogels or gel-like as having viscoelastic properties similar to gels, such has by having a “loose” cross- linking network formed by relatively long cross-link chains, but as, for example, lacking a fluid extender. Example polymer or silicone gels can include soft silicone gels such as “GEL- 8100” by NuSil™.

[0079] The polymer gel component can be rendered thermally-conductive via its loading with a thermally-conductive filler such as: noble and non-noble metals such as nickel, copper, tin, aluminum, and nickel; noble metal-plated noble or non-noble metals such as silver-plated copper, nickel, aluminum, tin, or gold; non noble metal-plated noble and non-noble metals such as nickel-plated copper or silver; and noble or non-noble metal plated non-metals such as silver or nickel-plated graphite, glass, ceramics, plastics, elastomers, or mica; and mixtures thereof.

[0080] Figure 11 is a flowchart of a method 1100 for assembling the stator 102 of the electric motor 100, in accordance with an example implementation.

[0081] The method 1100 may include one or more operations, or actions as illustrated by one or more of blocks 1102-1110. Although the blocks are illustrated in a sequential order, these blocks may also be performed in parallel, and/or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and/or removed based upon the desired implementation. It should be understood that for this and other processes and methods disclosed herein, flowcharts show functionality and operation of one possible implementation of present examples. Alternative implementations are included within the scope of the examples of the present disclosure in which functions may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art.

[0082] At block 1102, the method 1100 includes providing a segment (e.g., the segment 600) of the lamination stack 300 of the stator 102 of the electric motor 100, wherein the segment 600 of the lamination stack comprises a slot (e.g., the channel 602 or the channel 604). The term “providing” as used herein, and for example with regard to the segment of the lamination stack 300 or other components (e.g., the slot liner 606) includes any action to make the segment or any other component available for use, such as supplying the segment or bringing the segment to an apparatus or to a work environment for further processing (e.g., mounting other components, winding a wire, etc.). [0083] At block 1104, the method 1100 includes providing a slot liner (e.g., the slot liner 606) formed of an electrically-insulating material (e.g., insulation paper).

[0084] At block 1106, the method 1100 includes applying a thermally-conductive gap filler (e.g., the thermally-conductive gap filler 900, 1000) to an exterior surface of the slot liner.

[0085] At block 1108, the method 1100 includes inserting the slot liner with the thermally- conductive gap filler applied thereto into the slot of the segment of the lamination stack, such that the thermally-conductive gap filler is disposed between the exterior surface of the slot liner and the segment.

[0086] At block 1110, the method 1100 includes winding a wire (e.g., the wire 700) about the segment such that the slot liner and the thermally-conductive gap filler are disposed between the wire and the segment.

[0087] The method 1100 can further include other steps associated with assembling the stator 102 and the electric motor 100 described above, such as: applying the thermally-conductive gap filler along one or more of the first side portion, the second side portion, or the connecting portion of the slot liner; applying the thermally-conductive gap filler 902, 1002 to the exterior surface of the cooling tube 802; inserting the cooling tube 802 in the semi circular channel disposed on an exterior peripheral surface of the segment 600; mounting the end-turn insulators 610, 612 to the segment 600; etc.

[0088] The detailed description above describes various features and operations of the disclosed systems with reference to the accompanying figures. The illustrative implementations described herein are not meant to be limiting. Certain aspects of the disclosed systems can be arranged and combined in a wide variety of different configurations, all of which are contemplated herein. [0089] Further, unless context suggests otherwise, the features illustrated in each of the figures may be used in combination with one another. Thus, the figures should be generally viewed as component aspects of one or more overall implementations, with the understanding that not all illustrated features are necessary for each implementation.

[0090] Additionally, any enumeration of elements, blocks, or steps in this specification or the claims is for purposes of clarity. Thus, such enumeration should not be interpreted to require or imply that these elements, blocks, or steps adhere to a particular arrangement or are carried out in a particular order.

[0091] Further, devices or systems may be used or configured to perform functions presented in the figures. In some instances, components of the devices and/or systems may be configured to perform the functions such that the components are actually configured and structured (with hardware and/or software) to enable such performance. In other examples, components of the devices and/or systems may be arranged to be adapted to, capable of, or suited for performing the functions, such as when operated in a specific manner.

[0092] By the term “substantially” or “about” it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

[0093] The arrangements described herein are for purposes of example only. As such, those skilled in the art will appreciate that other arrangements and other elements (e.g., machines, interfaces, operations, orders, and groupings of operations, etc.) can be used instead, and some elements may be omitted altogether according to the desired results. Further, many of the elements that are described are functional entities that may be implemented as discrete or distributed components or in conjunction with other components, in any suitable combination and location.

[0094] While various aspects and implementations have been disclosed herein, other aspects and implementations will be apparent to those skilled in the art. The various aspects and implementations disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims, along with the full scope of equivalents to which such claims are entitled. Also, the terminology used herein is for the purpose of describing particular implementations only, and is not intended to be limiting.