Electric machine cooling and stabilization system and method

Abstract

To relate to cooling and stabilization of a permanent magnet (PM) electric machine.SOLUTION: An electric machine has: a rotor; a stator 32; and a housing supporting the rotor and the stator. The stator includes: a plurality of radially positioned electromagnets; and a stator encapsulant 96 for encapsulating the electromagnets. The housing includes: a peripheral part; a first end plate located on one end of the peripheral part; and a second end plate located on the other end of the peripheral part. The stator encapsulant is thermally connected with the first end plate and the second end plate.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] Copyright Notice

[0001] A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner does not object to the facsimile reproduction of the patent document or the patent disclosure as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights.

[0002]

[0002] This disclosure relates generally to methods, systems, and apparatus for cooling and stabilizing electric machines, such as electric motors or generators, and more specifically to cooling and stabilizing permanent magnet (PM) electric machines. [Background technology]

[0003]

[0003] Electrical machines used in commercial and industrial applications are often required to operate at 100% of their power rating over a typical useful life of 60,000 hours. Thus, motors or other electrical machines used in commercial or industrial environments must be both reliable and versatile. Machine reliability and life can be compromised by a number of factors, including, but not limited to: 1) high temperature operation leading to heat-induced component failures; 2) vibration, heat, friction, out-of-balance operation, contamination, improper material selection, or other causes of mechanically induced component failures; or 3) insulation failures caused by heat, improper material selection, or other causes leading to electrical shorts or opens.

[0004]

[0004] Electric machines often include a mechanical cooling system, such as a fan and cowling configured to direct air to cooling fins cast into the housing of the machine. Many such devices are classified as Totally Enclosed Fan-Cooled (TEFC). TEFC motors suffer from inherently low efficiency because a portion of the total power output from the motor must spin the cooling fan, and is therefore unavailable as power output. For example, a TEFC motor mounted on a conveyor belt must operate both the cooling fan and the conveyor belt, and therefore a portion of the motor's power output required to spin the fan is unavailable to the conveyor belt. The fan and cowling devices of TEFC machines are susceptible to damage and present a safety risk in a typical industrial environment. Furthermore, because TEFC machines drive the cooling fan on one side of the motor shaft, it is impossible or difficult to mount two downstream machines to one TEFC motor.

[0005]

[0005] Conventional electric machines are typically built to be robust and durable by implementing the machine with large, heavy components that can increase the cost and weight of the machine, which are necessary to facilitate stable, long-term operation.

[0006]

[0006] Other electric machines that are directly vented to facilitate cooling and therefore have partially open housings can suffer from moisture and particulate ingress that can cause degradation of mechanical components and degradation and premature failure of wiring insulation or electrical connections. Totally enclosed, naturally cooled (TENV) electric machines present unique cooling challenges because TENV equipment has no direct ventilation or external fans to move air to external cooling fins.

[0007]

[0007] The embodiments disclosed herein are designed to minimize one or more of the problems discussed above. Summary of the Invention [Means for solving the problem]

[0008]

[0008] The embodiments disclosed herein include an apparatus and method for cooling an electric machine. Other embodiments include elements that provide improved robustness and durability to the electric machine. As used herein, the type of device referred to as an electric machine includes both generators and motors. The particular embodiment described herein is a permanent magnet motor having a radial flux configuration. Many of the disclosed methods and devices are also applicable to axial flux machines, transverse flux machines, and linear machines, for heat transfer purposes or in part for robustness purposes. Certain methods and devices may be applicable to non-rotating torque motors, transformers, or inductors. Although a number of specific embodiments are shown with respect to permanent magnet motors, the disclosure and claims are not limited to any particular device configuration and are applicable to any type of electric machine.

[0009] Certain electric machine embodiments disclosed herein minimize heat generation caused by eddy currents in permanent magnets, rotor back assemblies, electromagnetic cores, or other structures. Additionally, methods and apparatus are disclosed for removing heat from the electric machine by conduction, convection, and radiation utilizing various thermal paths through the internal cavities and components or subsystems of the machine.

[0010]

[0010] An embodiment disclosed herein is an electric machine having a rotor, a stator, and a housing. The rotor includes a shaft defining a longitudinal axis. The shaft is surrounded by a rotor back assembly (also called a back iron assembly). The rotor further includes a series of radially mounted permanent magnets disposed about the rotor back assembly. The stator of the machine includes a plurality of electromagnets disposed radially about the rotor, defining an air gap between the outer surfaces of the rotor permanent magnets and the inner surfaces of the stator electromagnets.

[0011] The rotor and the stator are supported by and housed within a housing. In a particular embodiment, the housing is a totally enclosed, naturally cooled (TENV) housing. In one embodiment, the stator and the housing define a substantially cylindrical rotor cavity inside the air gap bounded by an end plate or similar structure of the housing. When the rotor is placed in the rotor cavity, the rotor cavity may be further divided into a first and a second cavity. Specifically, the first cavity is between the rotor and the housing at one end of the rotor and adjacent the end plate of the housing. The second cavity is between the rotor and the housing at the other end of the rotor and adjacent the other end plate. The end plate of the housing may be a separate plate attached to a peripheral portion of the housing, or the one end plate and the periphery of the housing may be a single or together formed housing element, cast, machined, or otherwise.

[0012]

[0012] The first and second cavities are connected through an air gap. In addition, one or more ventilation channels may be provided through the rotor back assembly extending from the first cavity to the second cavity. The first and second cavities, the air gap, and the ventilation channels thus define a fluid circuit around the outside of and through the back iron of the rotor. Additionally, the rotor may include an internal fan extending into either the first or second cavity. The internal fan is part of or connected to the rotor and is configured to create a low pressure in either the air gap or the ventilation channel and a high pressure in the other of the air gap and the ventilation channel. Thus, as the rotor rotates, air or other fluid, such as an air-oil mixture, circulates through the fluid circuit from one cavity through the air gap to the other cavity and back through the ventilation channel to the original cavity. In this way, heat generated in the rotor during operation can be transferred to the air or other fluid flowing through the fluid circuit to cool the rotor.

[0013]

[0013] The rotor fan may be a separate structure or may be a rotor fan blade formed on the outer surface of the rotor back assembly. Additionally, the rotor back assembly, the fan blade, or the fan may be treated to enhance the radiation of heat to the fluid circuit and thus to the first cavity or the second cavity. Suitable surface treatments include, but are not limited to, surface roughening or surface anodization.

[0014]

[0014] During operation of an electric machine, heat is generated in the rotor primarily due to magnetically induced eddy currents in the permanent magnets and magnetically induced eddy currents and hysteresis in the rotor back assembly. In certain embodiments, heat generation in the rotor can be reduced by implementing both the permanent magnets and the rotor back assembly in a series of laminations. Structural support and favorable heat transfer properties can be provided by coupling the permanent magnets to the rotor back assembly with a retaining band that surrounds the outer surface of the magnets facing the air gap.

[0015]

[0015] The heat transfer from the rotor to the fluid circuit, and subsequently from the first and second cavities to the housing of the machine, can be facilitated by various heat transfer structures. One type of heat transfer structure is attached to the rotor facing either the first or second cavity. Another type of heat transfer structure can be attached to the housing, typically at the end plate, facing the first and / or second cavity. Any of these heat transfer structures can include a series of pins, fins, pin / fin combinations, or other structures to increase surface area and turbulence, thus facilitating effective heat transfer to or from the attached rotor or housing structure. Additionally, the heat transfer structures can be fabricated from materials such as aluminum or copper that have relatively high thermal conductivity. The heat transfer structures can be textured, colored, surface treated, or otherwise fabricated to effectively transfer heat to or from the fluid circuit.

[0016]

[0016] Additional heat can be carried away from the permanent magnets by incorporating a thermally conductive filler or sealant in the gaps between adjacent permanent magnets. The thermally conductive sealant can be a polymer, such as an epoxy, and can have additives suspended within the polymer matrix to increase the thermal conductivity of the rotor sealant above the inherent thermal conductivity of the polymer, epoxy, or other rotor sealant. The thermally conductive sealant functions to conduct heat from the sides of the permanent magnets to the first and second cavities during rotor operation. A heat transfer structure attached to the rotor can be in thermal contact with areas of the thermally conductive sealant to facilitate heat exchange with the fluid circuit.

[0017]

[0017] The thermally conductive seals in the gaps between adjacent permanent magnets also provide structural rigidity and robustness to the rotor. The seals serve to further secure the permanent magnets to the rotor back assembly and prevent slippage of the magnets around the rotor under load. In some embodiments, the rotor back assembly may define a fastening surface between adjacent permanent magnets that serves to further securely fasten the seals to the rotor back assembly. The fastening surface may be a groove, protrusion, keyway, or the like formed in or extending from the rotor back assembly.

[0018]

[0018] A portion of the heat generated in the permanent magnet or rotor back assembly can be conducted to the shaft and from there to a device that drives the electric machine or is driven by the electric machine. The shaft of the machine is typically made of steel or other high strength alloys that may not have a very high thermal conductivity. The thermal conductivity of the machine shaft can be improved by providing the shaft with a thermally conductive shaft core made of a material, such as copper, that has a different composition than the rest of the shaft and has a higher thermal conductivity.

[0019]

[0019] In certain embodiments, it is also possible to transfer heat from the housing to the shaft. The shaft is typically supported by bearings at both ends of the rotor. The bearings are supported by the housing. In some embodiments, parts of the bearing structure, such as the bearing seals, can be made from a material with high thermal conductivity, such as copper. The bearing flanges or other housing elements that support the bearings can also be made from a material with high thermal conductivity. In such embodiments, a thermally conductive shaft core can be fabricated to extend around the shaft where the shaft and the bearings are in contact.

[0020] In certain embodiments, it may be advantageous to seal the housing. For example, a TENV motor may be sealed to prevent internal contamination. In such embodiments, the bearings may be accessible from outside the housing so that they can be easily removed or replaced without opening the housing.

[0021]

[0021] An embodiment of the electric machine further includes a stator having a plurality of radially arranged electromagnets. In some embodiments, the stator is sealed such that the stator seal is in thermal contact with a housing structure, such as a housing end plate. In some embodiments, the entire peripheral portion of the housing is in thermal contact with the stator or the stator seal. In one embodiment, the housing includes a peripheral portion and a first end plate and a second end plate. The end plates may be separate structures or may be manufactured together with the peripheral portion of the housing. The stator seal contacts the first end plate and the second end plate such that a bounded cylindrical rotor cavity is defined by a central region of the first end plate, a central region of the second end plate, and the inner stator surface. In some embodiments, there is substantially no air gap extending from the inner stator surface, the central region of the first end plate, and the central region of the second end plate toward the peripheral portion.

[0022]

[0022] The stator encapsulant provides device robustness and heat transfer from the stator to the housing. The thermal conductivity of the encapsulant can be improved by incorporating an additive therein to increase the thermal conductivity of the encapsulant. For example, the encapsulant can be a dielectric material such as a polymer or epoxy, and the additive can be boron nitride, silicon carbide, silicon, aluminum oxide, aluminum powder, copper powder, metal oxides, ceramics, graphene, substantially spherical particles, or a combination of these or similar materials.

[0023]

[0023] Heat transfer between the stator and the housing and the robustness of the entire machine can be improved by fitting the stator closely to the periphery of the housing. Heat transfer between the stator and the periphery of the housing can be further improved by filling the gap between the periphery of the stator and the housing with a thermally conductive lubricant or sealant.

[0024]

[0024] Heat transfer from the rotor cavity defined by the stator and housing can be enhanced by providing one or more heat transfer structures in thermal contact with a central region of the housing or end plate. The heat transfer structures can include pins, fins, pin / fin combinations, or other structures extending into the rotor cavity to increase surface area, increase turbulence, or otherwise enhance heat transfer from the rotor cavity. Additionally, any heat transfer structures can be colored, anodized, or have a surface treatment designed to promote effective heat transfer.

[0025]

[0025] Thermal energy transferred to the housing can be removed from the electric machine by conduction, convection, or radiation. Heat transfer from the housing can be enhanced by providing the housing with fins, external heat transfer structures, black anodization, or other means. Additionally, the housing can include feet fabricated from a material with high thermal conductivity, such as aluminum. Heat can be transferred from the feet to a mounting surface, such as a factory floor, shelf, or other equipment. Heat transfer from the feet to the mounting surface can be enhanced by providing an interface between the feet and the mounting surface with high thermal conductivity, such as thermal paste or copper.

[0026]

[0026] An embodiment of the stator includes radially arranged electromagnets. In a particular embodiment, each electromagnet includes a core having a stack of laminations defining a tooth portion and a yoke portion. An insulating bobbin may be provided that surrounds a portion of the teeth of each lamination. A conductive winding then surrounds a portion of the bobbin. In one embodiment, each lamination in the lamination stack is held against the adjacent lamination by pressure only from the bobbin, without the use of screws, welds, pins, crimp joints, adhesives, or other fastening means.

[0027]

[0027] In some embodiments, heat transfer from the electromagnetic core can be enhanced by providing a heat transfer layer in thermal contact with one or both of the flat surfaces defined by the core laminae. The heat transfer layer can be any material that has a higher thermal conductivity than the magnet steel used to manufacture the laminae. Exemplary heat transfer materials include, but are not limited to, metals such as copper, nickel, or silver, or materials such as graphene. The heat transfer material must be in thermal contact with the associated laminae, i.e., capable of directly transferring heat from the laminae to the heat transfer material. The thermal contact can be physical contact. Alternatively, the thermal contact can occur through an intervening material such as thermal paste. In some examples, the heat transfer material can be deposited, plated, coated, or otherwise permanently bonded to the laminae.

[0028]

[0028] Additionally, the electromagnetic core typically includes a dielectric layer between the laminae. In one embodiment, the laminae have a dielectric layer applied to or in contact with one flat surface and a heat transfer layer in thermal contact with the other flat surface. In this embodiment, the interface between adjacent laminae will include the dielectric layer from one laminae and the heat transfer layer from the other laminae.

[0029]

[0029] The arcuate yoke portions defined by the lamination of laminations may, in certain embodiments, define tongue and opposing groove structures configured to mate with one another. Thus, a stator may be assembled from multiple electromagnets by engaging the tongue structure of a first electromagnet with the groove structure of an adjacent electromagnet, etc., until the stator is complete. In certain embodiments, the yoke portions of the multiple electromagnets are directly supported by shoulder structures extending from the housing or housing end plates, which provide mechanical rigidity and a direct thermal path from the stator to the housing.

[0030]

[0030] Other embodiments include a method for cooling a rotor of an electric machine, a method for cooling a stator of an electric machine, a method for cooling an electric machine, a method for manufacturing an electric machine, a method for stabilizing an electric machine, and a method for manufacturing an electromagnet for an electric machine.

[0031] A further understanding of the nature and advantages of certain embodiments can be realized by reference to the remaining portions of this specification and the drawings, in which like reference numerals are used to refer to like components. In some cases, a supplemental label is combined with a reference numeral to refer to one of several similar components. When referring to a reference numeral without specifying the supplemental label present, it is intended to refer to all of such several similar components. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a perspective view of a totally enclosed, naturally cooled (TENV) permanent magnet (PM) motor, which is a typical electric machine. [Diagram 2] FIG. 2 is a cross-sectional perspective view of the motor of FIG. 1. [Diagram 3] FIG. 2 is a shaft end (SE) perspective view of the rotor showing permanent magnets and other structure. [Figure 4] FIG. 4 is a perspective view of the shaft other end (OSE) of the rotor of FIG. 3. [Diagram 5]FIG. 13 is a perspective view of the shaft other end (OSE) of another rotor embodiment. [Figure 6] FIG. 4 is a SE perspective view of the rotor of FIG. 3, showing the retention band around the rotor structure. [Figure 7] FIG. 7 is an OSE perspective view of the rotor of FIG. [Figure 8] FIG. 2 is a side cross-sectional view of the motor of FIG. 1. [Figure 9] FIG. 9 is an enlarged view of a portion of the motor of FIG. 8, showing the forced fluid circuit. [Figure 10] FIG. 2 is a perspective view of a portion of the housing and stator of the motor of FIG. 1. [Figure 11] FIG. 2 is a perspective view of a portion of the housing and stator of the motor of FIG. 1, showing the stator seals. [Figure 12] FIG. 2 is a cross-sectional perspective view of the motor of FIG. 1 with the rotor removed. [Figure 13] FIG. 2 is a perspective view of a portion of the housing and stator of the motor of FIG. 1 with selected portions of the electromagnets removed. [Figure 14A] FIG. 2 is a perspective view of an electromagnet structure. [Figure 14B] FIG. 14B is an exploded perspective view of the electromagnet structure of FIG. 14A. [Figure 15A] FIG. 1 is a schematic diagram showing a layered EM lamella structure. [Figure 15B] FIG. 1 is a schematic diagram showing another layered EM lamella structure. [Figure 15C] FIG. 1 is a schematic diagram showing another layered EM lamella structure. [Figure 16] FIG. 2 is a cross-sectional side view of the motor of FIG. 1 showing details at the interface between the housing and the stator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033]

[0051] overview Certain embodiments disclosed herein are electric machines designed to provide relatively maintenance-free, robust, long-term, and efficient operation in commercial, transportation, or industrial environments. As used herein, the type of equipment referred to as "electric machine" includes both generators and electric motors. Certain embodiments described herein are permanent magnet motors having a radial flux configuration. Many of the disclosed methods and apparatus are also applicable to improving the overall robustness and thermal performance of axial flux, transverse flux, and linear machines. Certain methods may also be applicable to the thermal management or stability of non-rotating torque motors, transformers, or inductors. Although a number of specific embodiments are illustrated herein with respect to totally enclosed, naturally cooled (TENV) permanent magnet motors, the disclosure and claims are not limited to any particular equipment configuration and are applicable to any type of electric machine.

[0034]

[0052] Electrical machines generate heat during operation. If not properly dissipated, heat can significantly shorten the life of the machine. Continuous operation at high temperatures can affect the physical properties of many machine components, including but not limited to electrical insulation, electrical contacts, sealing materials, magnets, etc. Excessive heat can cause these components to first soften at high temperatures and then become increasingly brittle, affecting the performance of the device and leading to premature failure. Thus, two keys to designing robust electrical machines are to reduce heat generation during operation of the machine and to increase heat dissipation from the machine. Many of the methods and devices described herein provide one or both of reduced heat generation and effective heat dissipation from the machine during operation. The disclosed techniques and structures are collectively referred to as thermal management methods or thermal management devices.

[0035]

[0053] Some methods and apparatus for providing advantageous thermal management also generally increase the mechanical stability of the machine, thus making it more robust and durable. Other methods and apparatus described herein improve the stability and robustness of the machine without adversely affecting its thermal properties.

[0036]

[0054] Certain TENV machines disclosed herein feature an overall device configuration designed to improve thermal management and machine robustness. For example, a representative TENV machine, permanent magnet motor 10 of FIG. 1, can have a pancake geometry with concentrated electromagnet windings, maximized slot fill factor, oversized surface mounted permanent magnets, and other devices to provide enhanced thermal management and overall machine robustness as detailed herein. Certain embodiments of the disclosed permanent magnet TENV motor 10 use less than half the copper and electrical steel compared to an induction motor of the same power rating.

[0037]

[0055] Additionally, some disclosed embodiments utilize active yet passive cooling: multiple thermal paths are designed into the machine to provide heat transfer from the internal structure to the outer housing where it can be dissipated by natural convection into the surrounding air, by radiation to surrounding objects, by conduction to the machine's mounting surface, and / or by conduction through the drive shaft to the driven device (e.g., a fan, pump, conveyor belt, wheel, or other device).

[0038]

[0056] FIG. 1 is a perspective view of the exterior of a representative electric machine, a permanent magnet TENV motor 10. FIG. 2 is a perspective cut-away view of motor 10 showing certain internal elements. Motor 10 includes a housing 12 that encloses and supports the internal components and a shaft 14 connected to a rotor 16. Housing 12 may be connected to or include a variety of support structures that may be provided or modified as needed. For example, the housing may be connected to feet 18, lifting eyes 20, a C-face, a flange face, or other support or mounting structure that facilitates placement and mounting of motor 10 in an operating environment.

[0039]

[0057] As shown in FIG. 2, the shaft 14 is connected to the rotor 16 to define a longitudinal shaft axis 22 about which the shaft 14 and rotor 16 rotate during operation of the motor 10. Alternatively, if the electric machine is a generator, an external torque applied to the shaft 14 can rotate the rotor about the shaft axis 22. The shaft 14 and rotor 16 are supported by bearings 24 and 26 mounted in bearing flanges 28 and 30. The embodiment shown in FIGS. 1 and 2 features the shaft 14 extending through the housing 12 from only one side of the rotor 16. Alternative embodiments can include the shaft 14 extending through the housing 12 from both sides of the rotor 16. Such alternative embodiments, which are not feasible in TEFC machines due to cooling fans, can advantageously drive two downstream machines at once, one mounted on each end of the shaft 14. In embodiments featuring a shaft 14 extending from only one side of the rotor 16, the ends of the motor 10 may be referred to for convenience as the shaft end "SE" and the shaft other end "OSE." Accordingly, elements such as the bearing 24 and flange 28 may be referred to herein as the SE bearing 24 and the SE bearing flange 28, respectively. However, it is important to note that the present disclosure expressly encompasses electric machines having a shaft 14 extending from one side of the housing 12, a shaft 14 extending from both sides of the housing 12, or a shaft 14 that does not extend from the housing 12 at all.

[0040]

[0058] The rotor 16 is substantially surrounded by a stator 32. As will be described in detail herein, the rotor 16 includes an array of permanent magnets 34 disposed about and spaced from the shaft axis 22. The permanent magnets 34 are supported by a rotor back assembly 36, sometimes referred to as a back-iron assembly because it is typically constructed of a magnetic material such as steel or other types of steel / iron alloys. The rotor back assembly 36 is mechanically joined to the shaft 14 or is manufactured together with the shaft.

[0041]

[0059] The stator 32 includes a series of electromagnets 38 that surround the rotor 16, with the electromagnets 38 and permanent magnets 34 separated from each other by an air gap 40. In simplest terms, motor operation occurs when an alternating current is applied to the windings 42 of the electromagnets 38, changing the magnetic field created by the stator 32. Magnetic forces between the permanent magnets 34 and the electromagnets 38 in the changing magnetic field cause the rotor 16 to rotate relative to the stator 32. Torque can therefore be transmitted to any device attached to the shaft 14, as is typical in a motor. In an alternative generator configuration, the shaft 14 can be rotated by an external torque source to create a changing magnetic field by the permanent magnets 34. The changing magnetic field can then induce an alternating current in the windings 42, thereby generating electricity.

[0042]

[0060] Heat generation in electrical machines When the motor 10 or other electric machine operates, heat is generated in both the rotor 16 and the stator 32. The primary causes of heat generated in the rotor 16 are eddy current losses in the permanent magnets 34, as well as eddy current or hysteresis losses in the rotor back assembly 36. The primary causes of heat generated in the stator 32 include resistance in the windings 42, as well as eddy current / hysteresis losses in the associated electromagnet core 44. In addition, drag, also referred to as windage, is created as the rotor 16 rotates within the motor 10. The windage losses generate additional heat. Friction at the surfaces of the bearings 24 and 26 also generates heat inside the housing 12. As mentioned above, certain types of electric machines are described as fully enclosed and non-vented "TENV" machines or motors. TENV motors provide certain advantages, including but not limited to reduced maintenance requirements, because the internal motor elements are substantially sealed against contamination from outside. However, to avoid premature component failure, heat generated within the sealed TENV machine must be dissipated without external fans to circulate air throughout the housing and without any openings for direct ventilation.

[0043]

[0061] The disclosed apparatus and methods for facilitating thermal management in electric machines and thus improving overall machine robustness can be categorized as either (a) methods and structures for minimizing heat generation or (b) methods and structures for facilitating machine cooling after heat generation. Some thermal management techniques described herein include rejection of heat by the rotor 16, stator 32, and / or housing 12. Several alternative thermal management strategies are described herein. The various methods and apparatus can be combined with each other in any manner, scaled or scaled, or partially implemented, as needed to achieve individual thermal mitigation goals.

[0044]

[0062] Rotor structure for electrical machines As mentioned above, heat generation during operation of an electric machine is unavoidable, but can in some cases be mitigated. The primary sources of heat generation in the rotor 16 are magnetically induced eddy currents in the permanent magnets 34 and magnetically induced eddy currents or hysteresis losses in the rotor back assembly 36. The extent of each type of magnetic eddy current and the resulting heat generation can be reduced by implementing the permanent magnets 34 and rotor back assembly 36 as laminated structures.

[0045]

[0063] For example, Figures 3-5 are perspective views of two alternative embodiments of rotor 16. The first embodiment of rotor 16 shown in Figures 3 and 4 is the rotor 16 from Figure 2. This rotor 16 features a shaft 14 extending from only one side. An alternative embodiment includes a shaft 14 extending from both sides of rotor 16. The rotor embodiment of Figures 3 and 4 is shown in the SE perspective view of Figure 3 and the OSE perspective view of Figure 4. The alternative rotor 16 of Figure 5 can be realized in a single shaft configuration or a dual shaft configuration. Each rotor 16 features a rotor back assembly 36 mechanically joined around a portion of shaft 14. Permanent magnets 34 are mounted around and in contact with rotor back 36 such that the permanent magnets 34 are radially disposed around shaft 14, but spaced from shaft 14.

[0046]

[0064] The permanent magnet 34 may be fabricated from any number of laminations 44. The laminations 44 are fabricated from a permanent magnet material, which may be, for example, a rare earth magnet material such as neodymium-iron-boron magnet material, samarium-cobalt magnet material, alnico magnet, or a conventional magnet material such as ferrite ceramic. In one exemplary embodiment, as shown in FIG. 5, the permanent magnet 34 of the rotor 16 has 24 laminations 46. Each lamination 46 is a relatively thin, flat portion of permanent magnet material, and multiple laminations are stacked on top of each other such that the plane defined by the interface between adjacent laminations is generally perpendicular to the shaft axis 22. Alternative embodiments of the permanent magnet 34 can include any number of laminae 46, for example, the permanent magnet 34 can include 2, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, or even more laminae 46 to reduce the degree of magnetically induced eddy currents and heat generation. Optionally, each laminae 46 within the permanent magnet 34 can be separated from adjacent laminae 46 by an insulator, such as lacquer, varnish, paper, or other relatively thin insulating material.

[0047]

[0065] Relatively high performance rare earth magnet materials may be selected for the permanent magnets 34 of the rotor 16. Rare earth magnets have higher remanence and much higher coercivity and energy product than other types of permanent magnets. Thus, rare earth permanent magnets 34 can increase the efficiency of the machine, but if rare earth permanent magnets 34 are utilized, steps must be taken to promote overall machine robustness and stability.

[0048]

[0066] Specifically, rare earth magnets can demagnetize if they get too hot, and their magnetic properties do not recover when the magnet cools down. Therefore, a rare earth magnet 34 must be selected that has a temperature rating higher than the maximum temperature of the permanent magnet 34 expected in thermally stable operation at full rated power. For example, if the high temperature expected for the permanent magnet 34 in the selected design is 130°C, it is recommended to use a rare earth magnet 34 with a temperature rating of at least 35% higher (per UH rating), e.g., up to 180°C, to provide margin in operation.

[0049]

[0067] Rare earth permanent magnets can also be demagnetized by excessive magnetic flux caused by high currents in the stator windings 42. Therefore, selected embodiments of the motor 10 utilize permanent magnets 34 with a shape that produces a large permeance coefficient to increase resistance to flux-induced demagnetization. For example, as shown in Figures 3 and 4, the motor 10 can include a rotor 12 having rare earth permanent magnets 34 with a radial thickness dimension w measured along a radial line extending outward from the shaft axis that is eight or more times the width of the magnetic air gap 40 measured along the same radial line. Using rare earth permanent magnets 34 with a large permeance coefficient allows the motor to be operated at conditions far beyond its nominal rating without fear of demagnetization. Some of these conditions include operation at peak torque, operation over a wider speed range using field weakening, or a combination of both.

[0050]

[0068] The rotor back assembly 36 may also be constructed from multiple laminations of steel, iron, another iron alloy, or another suitable rotor back assembly material. In one exemplary embodiment shown in FIG. 5, the rotor back assembly 36 includes six laminations 50. Each lamination 50 is a relatively thin, flat, annular portion of rotor back material. The laminations are stacked together with a plane defined by the interface between adjacent laminations 50 generally perpendicular to the shaft axis 22. Alternative embodiments of the rotor back assembly 36 may include any number of laminations 50, for example, the rotor back 36 may include 2, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, or even more laminations 50 to minimize the degree of magnetic eddy currents, hysteresis losses, and heat generation within the rotor back assembly 36. Optionally, each lamination 50 in the rotor back assembly 36 may be separated from adjacent laminations 50 by an insulator, such as lacquer, varnish, paper, or other relatively thin insulating material.

[0051]

[0069] During operation, the rotor 16 rotates at high speeds and is exposed to changing magnetic flux. Therefore, it is important to ensure a secure attachment of the permanent magnets 34 to the rotor back assembly 36. Optionally, an adhesive may be used to attach the permanent magnets to the rotor back assembly 36. In certain embodiments, as shown in FIGS. 6 and 7, the rotor 16 includes a retaining band 52 that goes around the periphery of the rotor 16 facing the air gap 40 and the stator 32. The retaining band 52 may be prestressed to secure the permanent magnets 34 and adjacent structures during operation. Additionally, the retaining band 52 may be specifically configured to minimize drag as the rotor 16 rotates, thereby minimizing windage heat generation.

[0052]

[0070] In certain embodiments, the retaining band 52 is made from a magnetic material, such as steel or a graphene composite. In such embodiments, the band may be realized from a number of separate bands to minimize the generation of eddy currents in the band 52. Additionally, the band may be impregnated with a heat transfer material or otherwise treated to promote heat transfer from the permanent magnets 34 to the outer surface of the band 52 and the air gap 40. Alternatively, the entire retaining band 52 may be made from a material selected to have good heat transfer properties, such as copper or aluminum, for example. Alternatively, the entire band 52 may be made from a carbon fiber mat or filaments that can be prestressed, does not generate eddy currents, and also has a relatively high thermal conductivity.

[0053]

[0071] Rotor cooling method and device While heat generation in the rotor of an electric machine during operation can be reduced using the techniques described above, some heat generation is unavoidable. Accordingly, several apparatus and methods for cooling the rotor of an electric machine are disclosed herein. It is important to note that the rotor 16, particularly in a TENV machine such as the motor 10, is substantially or completely contained within the machine housing 12 and surrounded by the stator 32. Thus, cooling the rotor 12 often requires heat transfer to another motor structure prior to dissipating the heat from the motor 10. In certain instances, the rotor cooling methods and apparatus described herein operate in conjunction with methods and apparatus for cooling other portions of the motor 10, the stator 32, and / or the housing 12.

[0054]

[0072] A. Rotor forced flow circuit FIG. 8 is a side cross-sectional view of the motor 10 shown in FIG. 2. FIG. 9 is an enlarged view of the rotor 16, housing 12, and a portion of the stator 32 shown in FIG. 8. In operation, the rotor 16 must be able to rotate freely inside the stator 32 and housing 12. Thus, the rotor 16, stator 32, and housing 12 cooperate to define a particular cavity in which the rotor 16 operates. For example, the housing 12 of FIGS. 1 and 2 and 8 and 9 includes a peripheral portion 54 that surrounds the stator 32 and thus the shaft axis 22. The peripheral portion 54 of the housing 12 is substantially closed, except for one or more enclosed shaft openings, by a first end plate 56 and an opposing end plate 58 at each end of the peripheral portion 54. Thus, the peripheral portion 54, the first end plate 56, and the opposing end plate 58 define an overall pancake shape of the motor 10. The peripheral portion 54, the first end plate 56, and the second end plate 58 may be separate structures that are joined together to form the housing 12. Alternatively, the peripheral portion 54 and one of the end plates 56, 58 or other housing structures may be cast, machined, or otherwise formed as a single piece, with the peripheral portion 54 and the end plate 56 or 58 serving to define different regions of a single housing structure.

[0055]

[0073] 10 and 11, the portion of the stator 32 facing the air gap 40 and the end plates 56, 58 define a substantially cylindrical rotor cavity 60. Certain embodiments of the motor 10 include apparatus designed to force air to circulate between various distinct regions of the generally cylindrical rotor cavity 60, as described below.

[0056]

[0074] Specifically, the open space between one end 62 of the rotor 16 and the adjacent portion of the housing 12 defines a substantially annular first cavity 64 within the cylindrical rotor cavity 60. Similarly, the open space between an opposite end 66 of the rotor 16 and the adjacent portion of the housing 12 defines a substantially annular second cavity 68 within the cylindrical rotor cavity 60. Additionally, a relatively thin air gap 40 extends between the outer periphery of the rotor 16 and the inwardly facing surface of the stator 32 to complete the cylindrical rotor cavity 60. As best shown in FIGS. 8 and 9 , air, air / oil mixtures, other gases, liquids, or mixed fluids may be circulated through the air gap 40 from one cavity 64, 68 to the other cavity 64, 68 by providing the rotor 16 with an internal fan surface, such as an internal fan 70, and one or more ventilation channels 72 through the stator 32.

[0057]

[0075] Specifically, a series of vent channels 72 may be provided through the rotor back assembly 36, as best shown in Figures 3 and 4. In the illustrated embodiment, each vent channel 72 defines a portion of an arc around the shaft axis 22 and defines an opening that extends through each lamination 50 of the rotor back assembly 36. Other shapes and configurations of vent channels 72 are within the scope of the present disclosure, provided that each vent channel 72 has an opening that is in fluid communication with the first cavity 64 and the second cavity 68.

[0058]

[0076] The first cavity 64, the second cavity 68, the air gap 40, and each ventilation channel 72 cooperate to define an internal forced fluid circuit 74 that partially surrounds and extends through the rotor 16. Air, other fluid, or a mixture of air and oil as described below, may be circulated through the internal forced fluid circuit 74 by an internal fan 70. The fan 70 may be part of, attached to, or driven by the rotor 16 and may circulate air or other fluid in the internal forced fluid circuit 74. Specifically, the fan 70 includes a plurality of fan blades 76 configured to create a zone of relatively low pressure in the air gap 40 and a zone of relatively high pressure in the second cavity 68 toward the shaft 14 when the rotor 16 rotates in a clockwise direction as viewed in FIG. 4 .

[0059]

[0077] This pressure differential circulates air or other fluid from the second cavity 68 through the vent channel 72 and into the first cavity 64. At the same time, air or other fluid is forced to circulate from the first cavity 64 through the air gap 40 and into the second cavity 68, completing the forced fluid circuit 74. Alternate fan configurations or rotation directions can circulate the air or other fluid in the opposite direction.

[0060]

[0078] In the embodiment of FIG. 4, the fan 70 extends into the second cavity 68. In other embodiments, the fan 70 may extend into the first cavity 64, or separate fans may extend into both cavities 64 and 68. In certain embodiments, the fan 70 and / or fan blades 76 are separate structures attached to or driven by the rotor 16. In other embodiments, the fan 70 may comprise a plurality of fan blades 76 formed in the rotor back assembly 36, formed on a portion of the shaft 14, or otherwise attached to the rotor 16. In any embodiment, the fan 70 circulates air or other fluid around and through the rotor 16 as the rotor rotates, completing a forced fluid circuit 74.

[0061]

[0079] The air or other fluid circulating within the forced fluid circuit 74 is heated by the heat generated within the rotor 16 as described above, and therefore cools the rotor 16. The heated fluid can transfer this heat to another structure to ultimately cool the motor 10. Various structures that facilitate heat transfer from the rotor 16 to the forced fluid circuit 74 and further from the forced fluid circuit 74 are described below. Additionally, various structures associated with the rotor can have surface treatments designed to facilitate efficient heat transfer from the rotor 16 to the forced fluid circuit 74. For example, any rotor structure, such as, but not limited to, the fan 70, the fan blades 76, the shaft 14, the rotor back assembly 36, the retaining band 52, or other structures, can be roughened to increase surface area or treated, for example with black anodizing, to facilitate heat transfer between the rotor and the forced fluid circuit 74.

[0062]

[0080] Heat transfer from the rotor 16 to the forced fluid circuit 74, or from the forced fluid circuit 74 to other motor structures such as the housing 12, and ultimately from the motor 10, may be facilitated by supplemental heat transfer structures. For example, as shown in FIG. 5, the rotor back assembly 36 or another rotor structure may be in thermal contact with one or more heat transfer structures, such as the SE heat transfer structure 78 and the OSE heat transfer structure 80 shown in FIGS. 5, 8, and 9. As defined herein, "thermal contact" means contact between two or more structures such that thermal energy can flow from one structure to another. Structures that are in direct thermal contact with each other are also in physical contact with each other. Alternatively, thermal contact may occur through an intervening material such as thermal paste. The SE heat transfer structure 78 and the OSE heat transfer structure 80 are merely representative of any number of types or configurations of heat transfer structures that may be attached to, formed on, or otherwise in thermal contact with the rotor 12. In either case, the rotor heat transfer structure 78 or 80 contacts the rotor on one side and extends into either the first cavity 64 or the second cavity 68 to facilitate heat transfer between the rotor 16 and the forced fluid circuit 74.

[0063]

[0081] Other heat transfer structures can be bonded to or formed in thermal contact with the housing 12 to facilitate heat transfer from the forced fluid circuit 74 to the housing 12 and then from the motor 10 by thermal radiation, conduction, or convection. For example, as shown in Figures 2, 8, 9, and 10, one, two, or more heat transfer structures can be attached to the housing 12 that extend toward the rotor 12 into the first cavity 64 or the second cavity 68. In a representative example shown in the figures, but not limited to, the motor 10 includes an SE housing heat transfer structure 82 and an OSE housing heat transfer structure 84 that extend into the first cavity 64 and the second cavity 68, respectively. Each of the heat transfer structures 82, 84 is shown as being substantially annular, although other shapes and configurations are within the scope of the present disclosure.

[0064]

[0082] The SE housing heat transfer structure 82 and the OSE housing heat transfer structure 84 are merely representative of any number of heat transfer structure types or configurations that may be attached to, formed in, or otherwise in thermal contact with the housing 12. In either case, the housing heat transfer structure 82 or 84 contacts the housing 12 on one side and extends into either the first cavity 64 or the second cavity 68 to facilitate heat transfer from the forced fluid circuit 74 to the housing 12.

[0065]

[0083] In some of the illustrated embodiments, the heat transfer structures 78, 80, 82, or 84 may be formed with a number of pins, fins, pin / fin combinations 86, or other structures designed to increase surface area and turbulence. The pins / fins 86 extend away from the housing 12 or stator 32 into the adjacent cavity 64 or 68. The heat transfer structures 78, 80, 82, or 84 may be roughened to increase surface area or treated, for example by black anodizing, to facilitate heat transfer to or from the heat transfer structures and the forced fluid circuit 74. Additionally, one or more of the heat transfer structures 78, 80, 82, or 84 may be fabricated from materials such as copper or aluminum that have high thermal conductivity. The heat transfer structures 78, 80, 82, or 84 may be bonded to adjacent rotor or housing structures using a heat transfer paste or other interface that promotes effective heat transfer from the heat transfer structures 78, 80, 82, or 84 to or from the forced fluid circuit 74.

[0066]

[0084] B. Sealing and Stabilizing the Rotor In certain embodiments, adjacent permanent magnets 34 are separated by a gap 88, as shown, for example, in FIG. 5. Additional heat transfer from the rotor 16, particularly from the sides of each permanent magnet 34, can be provided by filling all or a portion of the gap 88 with a thermally conductive rotor sealant 90. As described in more detail below, the thermally conductive sealant 90 also reduces windage losses and provides mechanical stability to the rotor 16. Representative examples of thermally conductive rotor sealants 90 include, but are not limited to, epoxies, synthetic polymers, polyesters, polyurethanes, silicones, or other plastics or flowable or moldable materials suitable for filling the gap 88. Thermal management can be improved by providing additives to the thermally conductive rotor sealant 90 to increase the thermal conductivity of the sealant above the inherent thermal conductivity of the unmodified sealant. Exemplary additives for increasing thermal conductivity include, but are not limited to, suspended particles of boron nitride, silicon carbide, silica, aluminum oxide, aluminum, copper, other metals, other metal oxides, ceramics, graphene, etc. The thermal conductivity of encapsulant 90 can be further increased if the suspended particles are spherical, have radially oriented fibers, or have other shapes or orientations designed to promote heat conduction.

[0067]

[0085] Alternatively, certain portions or regions of the thermally conductive rotor seal 90 may be fabricated from a material having a relatively high thermal transmittance. For example, the gap 88 may be filled with an epoxy or other polymer constrained within a metal shell 92, such as a copper or aluminum shell, where the shell has a higher thermal conductivity than the polymer. In another embodiment, the gap 88 may be filled with an epoxy or other polymer that surrounds a higher thermal conductivity core, such as an aluminum or copper core, that contacts the permanent magnets 34, rotor back assembly 36, and / or forced fluid circuit 74 through the seal. In any embodiment, the thermally conductive rotor seal should have a glass transition temperature and maximum operating temperature significantly higher than the expected motor operating temperatures.

[0068]

[0086] Additionally, the thermally conductive rotor seal 90 provides mechanical strength to the rotor 12, thus helping to improve the overall robustness of the motor 10. For example, the thermally conductive rotor seal 90 may contact and / or be bonded to the rotor back assembly 36 between adjacent permanent magnets 34 to mechanically secure the permanent magnets 34 and prevent the permanent magnets 34 from slipping circumferentially around the rotor back assembly 36 under heavy loads. The bond between the thermally conductive rotor seal 90 and the rotor back assembly 36 may be mechanically strengthened by providing slots 94, grooves, keyways, roughened surfaces, holes, protrusions, or other structures in the rotor back assembly 36 at the interface between the rotor back assembly 36 and the surface of the thermally conductive rotor seal 90.

[0069]

[0087] As best shown in Figures 3 and 4, the thermally conductive rotor seal 90 may be in contact with one or more rotor-side auxiliary heat transfer structures at one or both ends. The particular embodiment of Figures 3 and 4 includes a series of SE heat transfer elements 78 in thermal contact with the thermally conductive rotor seal 90 and extending into the first cavity 64. Additionally, the embodiment of Figures 3 and 4 includes a series of OSE heat transfer elements 80 in thermal contact with the other end of the thermally conductive rotor seal 90 and extending into the second cavity 68.

[0070]

[0088] Heat transfer structures 78 and 80 are merely representative of any number of heat transfer structures that may be attached to, formed on, or otherwise in thermal contact with one or other end of thermally conductive rotor seal 90. In either case, heat transfer structures 78, 80 extend into either first cavity 64 or second cavity 68 to facilitate heat transfer between rotor 16 and forced-fluid circuit 74.

[0071]

[0089] In another embodiment, one or more of the heat transfer structures 78, 80, 82, or 84 may be configured to function as a fan 70. For example, the pin / fin combinations 86 of the heat transfer structures 78 of FIG. 5 may be angled or otherwise configured to create a pressure gradient that causes circulation of fluid through the forced fluid circuit 74.

[0072]

[0090] C. Heat transfer oil In certain embodiments, the efficiency of heat transfer within the motor 10 can be improved by utilizing a heat transfer fluid in combination with or in place of air. For example, a quantity of transformer oil or another heat transfer fluid can be added to the first cavity 64 and / or the second cavity 68. When the motor is not running, oil pools at the bottom of each cavity 64, 68, filling, for example, the bottom quarter of the air gap 40. As the rotor 16 rotates, the permanent magnets 34 are successively submerged in the oil bath, allowing heat to be removed from all exposed surfaces of the permanent magnets 34 and the retaining bands 52.

[0073]

[0091] As will be described in more detail below, a stator sealant may be added between the stator 32 and the housing 12, in part to ensure that oil added to the internal cavities 64, 68 pools in contact with the rotor 16. See, for example, stator sealant 96 in FIG. 11. Sufficient oil may be added to the cavities 64, 68 to cover the air gap 40 and / or the sunken portions of one or more of the heat transfer structures 78, 80, 82, 84 or other heat transfer structures. The cavities 64, 68 and the air gap 40 are interconnected regions of the rotor cavity 60. Thus, heat transfer fluid added to one cavity flows to the other cavity. The amount of oil or other heat transfer fluid added to the cavities 64, 68 may be 50% or less of the total volume of the cavities 64 and 68, 25% or less of the total volume of the cavities 64 and 68, or any other suitable volume.

[0074]

[0092] When the rotor 16 rotates at relatively high speeds, the movement of the rotor 16 and / or heat transfer structures 78, 80 can splash and atomize the oil or other heat transfer fluid, improving the thermal performance of the forced-fluid circuit 74. The retaining bands 52 may be fitted with a perforated coating or thin mesh surface to ensure turbulence and low drag as the rotor 16 moves through the oil bath.

[0075]

[0093] D. Dissipating heat from the rotor back assembly Generally, as described above, the rotor back assembly 36 conducts heat from the edges of the permanent magnets 34 that face the shaft axis 22, and also generates some heat due to eddy currents and hysteresis losses in the rotor back assembly 36 itself. Heat conducted to or generated within the rotor back assembly 36 may be conducted radially to the ventilation channels 72. Alternatively, heat conducted to or generated within the rotor back assembly 36 may be conducted axially to the SE heat transfer structure 78, the OSE heat transfer structure 80, other heat transfer structures, or the fan 70, from where it may be transferred to the forced-fluid circuit 74. Surfaces of the rotor back assembly 36 that face the cavities 64, 68 may be structured, textured, anodized, or otherwise treated to enhance the transfer of heat from the rotor 16 to the forced-fluid circuit 74, the stator 32, the housing 12, or other structures that may dissipate the heat to the environment.

[0076]

[0094] The apparatus and methods disclosed herein, including but not limited to the ventilation channels 72, heat transfer structures 78, 80, and thermally conductive rotor seals 90, ensure that the rotor back assembly 36 is relatively cooler than the permanent magnets 34 during motor operation. This temperature gradient causes heat to flow from the permanent magnets 34, to the rotor back assembly 36, and out of the motor through the shaft 14, the forced fluid circuit 74, and the housing 12, or other exhaust paths described herein.

[0077]

[0095] E. Shaft heat dissipation Another path for heat transfer from the rotor utilizes the shaft 14. The shaft 14 is rigidly connected to the rotor back assembly 36, usually by metal-to-metal contact. Thus, heat from the permanent magnets 34, the rotor back assembly 36, or other rotor structures can be conducted to the shaft 14. The dissipation of heat through the shaft 14 can be improved by providing the shaft 14 with a relatively highly thermally conductive core 98, or other shaft structure made of a material having a relatively high thermal conductivity, such as aluminum or copper, when compared to the surrounding steel shaft material. The shaft 14 is connected to the body of the driven equipment, such as a fan, pump, drive roller, or material processing machine. Thus, the shaft 14, especially if provided with a thermally conductive core 98, can conduct heat to the driven machine where it can be dissipated by convection, conduction, or radiation.

[0078]

[0096] Method and apparatus for cooling a stator The primary sources of heat generation in the stator 32 are magnetically induced eddy currents in the metal core 44 of the electromagnets 38 and resistive losses in the windings 42. The amount of heat generated in the stator 32 can be reduced by maximizing the wire gauge of the windings 42 to maximize slot fill factor and reduce AC resistive losses. Additionally, rectangular wire can be used in the windings 42 to increase slot fill factor and reduce resistive losses. Magnetically induced eddy currents in the steel electromagnet cores 44 can be minimized by fabricating each core from electrically insulated sheet metal, as described in more detail below.

[0079]

[0097] Several devices and methods are disclosed for cooling the stator of an electric machine and dissipating heat from the machine. It is important to note that the stator 32, particularly in a TENV machine, is completely enclosed within the housing 12 of the machine. Thus, cooling the stator 32 often requires transferring heat to another motor structure, such as the housing 12 or shaft 14, prior to dissipating heat from the motor 10. In certain instances, the stator cooling methods and devices described herein work in conjunction with methods and devices for cooling other portions of the motor 10, rotor 16, and / or housing 12. The various thermal management methods and devices can be combined, scaled, or partially implemented in any manner to achieve desired thermal management and machine durability goals.

[0080]

[0098] A. Structure of an electromagnet As shown in Figures 10, 13, and 14, the stator 32 of a typical electric machine includes a number of electromagnets 38 arranged radially around the shaft axis of a machine, such as the motor 10. As best seen in Figure 14A and exploded view Figure 14B, the electromagnet 38 includes a core 44 of a magnetic metal, typically a steel alloy. Magnetically induced eddy currents can be reduced by fabricating the core 44 from a stack of relatively thin laminations 46 of similar or identical shapes. The particular lamination shape shown in Figure 15 includes a tooth portion 100 and a yoke portion 102. When a number of laminations 46 are stacked to form the electromagnet core 44, the tooth portion 100 directly or indirectly supports the windings 42, while the yoke portion 102 provides structure to the stator 32, a heat transfer path to the exterior of the stator 32, and additional magnetic core mass.

[0081]

[0099] In order to reduce magnetically induced eddy currents in the core 44, electrical insulation must be provided between adjacent laminations 46. Thus, both flat sides of each lamination 46 may be covered with lacquer, epoxy, plastic, insulating paint, paper, or another dielectric layer or coating to provide electrical insulation between adjacent laminations 46 when multiple laminations are stacked to produce the electromagnetic core 44. Traditional lamination insulation methods also tend to thermally insulate each lamination, limiting the flow of heat generated in either the core 44 or the surrounding windings 42.

[0082]

[0100] The magnetic steel alloys used for the core laminations 46 typically have a relatively low thermal conductivity. The thermal performance of the electromagnetic core 44, and therefore the electric machine, can be improved by coating or otherwise combining the magnetic steel laminations 46 with a material that has a relatively higher thermal conductivity than the magnet steel. For example, a portion or the entire outer surface of the steel laminations 46 can be coated, plated, deposited, or otherwise combined with a relatively thin heat transfer layer 104 of a metal such as nickel, nickel silver, copper, or aluminum, graphene, or other material that has a higher thermal conductivity than the interior of the steel laminations. An electrical insulation layer 106 can be added on the heat transfer layer 104 to minimize eddy currents when the laminations 46 are stacked into an operational configuration. In certain embodiments, one layer can function as both an insulator and a heat transfer layer, provided that the material selected is a dielectric material and has a higher thermal conductivity than the magnetic steel used for the laminations. For example, a variety of graphene oxides can function as a single layer that provides both improved heat transfer and electrical insulation.

[0083]

[0101] An example of a layered sheet configuration having a higher thermal conductivity than a simple insulated steel sheet is shown in Figure 15A. In this embodiment, a steel sheet 46 is first coated with a heat transfer layer 104 that has a higher thermal conductivity than the steel of the underlying sheet 46. The heat transfer layer 104 can then be coated or otherwise combined with a dielectric insulation layer 106.

[0084]

[0102] Alternatively, as shown in Figure 15B, only one flat surface of the sheet 46 can be coated or otherwise insulated with a dielectric insulating layer 106. The other flat surface of the sheet 46 can be coated, contacted, bonded, plated or otherwise associated with a heat transfer layer 104 of a material selected to facilitate heat transfer from the electromagnetic core 44. If the core 44 is fabricated from multiple sheets 46 prepared in this manner, the heat transfer layer 104 need not provide electrical insulation because the dielectric insulating layer 106 of immediately adjacent sheets 46 will electrically insulate both sheets from each other, so long as each sheet is oriented in the same direction as shown in Figure 15B.

[0085]

[0103] The heat transfer layer 104 may be, for example, a metal having a significantly higher thermal conductivity than the steel disposed on the lamina 46. Exemplary metals having a higher thermal conductivity than steel include, but are not limited to, copper, nickel, gold, silver, or aluminum. Other materials, such as graphene or graphing oxide, may be deposited on the lamina 46 as the heat transfer layer 104. Combinations of the above materials may also be used. For example, as shown in FIG. 15C, the core 44 may be fabricated by stacking an inner steel lamina 46 having a dielectric coating 106 deposited or otherwise combined on one surface of the lamina 46 and a metal 104a, such as nickel silver, coated on the other surface, followed by a graphene layer 104b. When this pattern is repeated throughout the stack, each lamina 46 is insulated from the next lamina, yet each lamina is also in contact with one or more heat conductive transfer layers 104 that provide for the evacuation of heat from the core 44.

[0086]

[0104] The laminated laminations 46 that form the electromagnetic core 44 must be held together during assembly and operation and insulated from the windings 42. Conventional electromagnetic cores are often held together by adhesives, lacquers, screws, bolts, pins, crimped surfaces, other fasteners, welded joints, or other means. Insulation can be provided by supplemental structures such as adhesives or lacquers, tape or paper, or simply the insulation of the windings. The embodiments of the present disclosure can be realized by any of the assembly and insulation techniques described above. Alternatively, as shown in FIG. 14, the laminations of laminations 46 and the lamination coatings 104, 106 can be pressed tightly together by a dielectric bobbin 108 that surrounds the top, bottom, and sides of the teeth 100 of each lamination 46 within the core 44 to provide a core 44 with superior thermal properties. The dielectric bobbin 108 can be manufactured by injection molding, for example, from plastic, nylon, or similar material. Utilizing the bobbin 108 as a means of pressing the sheets together facilitates the use of a heat transfer layer 104 that may be compromised using other sheet attachment methods such as, but not limited to, adhesives or lacquers between the respective faces of the sheets, bolts or screws passing through adjacent sheets, welded joints located along one or more sides of the stack of sheets, mechanical crimp connections between sheets, notches, or other fastening methods.

[0087]

[0105] Specifically, the bobbin 108 ensures a constant, evenly distributed pressure across the teeth 100 of each lamination 46 within the electromagnetic core 44. The evenly distributed pressure minimizes gaps between the laminations 46 or layers 104, 106, thus facilitating heat transfer from each lamination 46 to the associated heat transfer layer 104. Additionally, using the bobbin 108 to compress the laminations 46 and associated layers 104, 106 together to form the core 44 avoids the possibility of bolts, screws, crimps, welds, or other mechanical fasteners causing short circuits between one or more laminations 46, thus compromising the electromagnetic properties of the core 44. In certain embodiments, the bobbin 108 is the only structure holding adjacent laminations together.

[0088]

[0106] 14, the bobbin 108 supports the windings 42. Certain portions of the windings 42 extend through the slots between adjacent electromagnetic cores 44. Other portions of the windings 42 are end turns 109 that span adjacent slots across each electromagnetic core 44.

[0089]

[0107] As shown in FIG. 14, the yoke portion 102 of each lamination may be formed into opposing male and female dovetails, tongue and groove, or other mating structures 110 and 112. Thus, as best shown in FIG. 13, when a series of electromagnets 38 are assembled into a stator, the adjacent male and female tongue 110 and groove 112 structures provide mechanical support to the stator 32. Additionally, the tapered shape of each tooth 100, bobbin 108, and winding 42 creates a concentrated winding coil that tapers into the shape of the slot, resulting in a high slot fill factor. A high slot fill factor results in reduced electrical resistance, thus reducing losses and reducing heat generation.

[0090]

[0108] B. Stator / Housing Interface The stacked outwardly facing surfaces of the multiple yoke sections 102 define an outer surface 114 of the stator 32. As shown in FIG. 13, the outer stator surface 114 fits snugly inside the peripheral portion 54 of the housing 12. Heat can flow within each core 44 to the outer stator surface 114, particularly when the heat transfer layer 104 is provided on or between the laminations 46 as described above. The transfer of heat from the outer stator surface 114 to the peripheral portion 54 of the housing 12, and then to the external environment, can be facilitated by providing a thermally conductive lubricant between the outer stator surface 114 and the inner surface 116 of the peripheral portion 54 of the housing 12. Exemplary thermally conductive lubricants include, but are not limited to, thermal grease, graphene, or boron nitride powder.

[0091]

[0109] Careful bonding of the stator 32 to the housing 12 also further enhances the robustness and thermal performance of the overall machine. For example, as shown in Figures 12, 13, and 16, one or more end plates 56, 58 may define a lip and shoulder structure on the end plate 56, 58 that contacts the yoke portion 102. The lip / shoulder structure 120 engages the yoke portion 102 of each electromagnetic core 44 to space each electromagnetic core 44 somewhat from the remainder of the end plate 56, 58. The lip / shoulder structure 120 thus creates a pocket in the end plate to provide clearance for the end turns 109 of the windings 42. The height of the lip / shoulder structure 120 (labeled (h) in Figure 16) may be selected to reduce the distance from the end turns 109 to the end plate 56, 58 to facilitate heat transfer. As described in more detail below, the remaining gap may be filled with a thermally conductive sealant or other structure or material to enhance heat transfer. Additionally, the height h of the lip / shoulder structure 120 may be increased as necessary to minimize the formation of magnetically disturbed currents in the end plates 56, 58.

[0092]

[0110] Further mechanical robustness can be achieved by providing an engagement structure 122 on the exterior surface 114 of the selected electromagnet core 44. The housing 12 can include a mating engagement structure 124 opposite the engagement structure 122. The engagement structures 122 and 124 can be of any shape or size configured to mechanically engage the exterior surface 114 of the stator 32 with the interior surface 116 of the housing 12, thus preventing rotation or other movement of the stator 32 under load. The particular embodiment of the engagement structures 122, 124 shown in FIG. 13 includes a rounded slot formed in the electromagnet core 44 and a corresponding rounded slot formed in the peripheral portion 54 of the housing 12. Each slot can be engaged with a pin for receiving the stator 32 into the housing 12. The tight fit of the exterior surface 114 of the stator 32 with the interior surface 116 of the housing 12 provides further robustness by stiffening the case and protecting the electromagnet 38 from shock, vibration, or other forces.

[0093]

[0111] C. Stator sealing and stabilization Further heat transfer from portions of the stator 32 or other mechanical structure, as well as improved stator robustness, can be provided by a thermally conductive stator seal, heat transfer structure, or potting material. For example, certain embodiments can include a thermally conductive stator seal 96 that seals most of the stator structure. In the particular embodiment of FIG. 11, the thermally conductive stator seal 96 seals the entire electromagnet assembly 38 except for the outer stator surface 114 and the air gap-facing inner surface 126 of some or all of the magnetic cores 44. Additionally, the thermally conductive stator seal 96 directly contacts one or both housing end plates 56, 58 or other housing structure, providing a direct thermal path from the stator 32 to the housing 12.

[0094]

[0112] Alternative structures may be used in place of or in combination with the full or partial stator seal. These alternative structures are within the scope of this disclosure. For example, heat transfer from the stator may be provided by a separate thermal contact structure, such as a thermally conductive compressible or compliant solid material, disposed in contact with some portion of the stator 32 and the housing 12, or disposed between a portion of the stator seal 96 and the housing 12. The thermal contact structure may be substantially solid, or may have a honeycomb structure, a wave washer structure, or the like. The thermal contact structure may be made of thermally conductive felt, foam, metal, coated metal, compliant epoxy, composites such as silicone-based pads with alumina fillers, or any other suitable thermally conductive compound, material, or combination of materials.

[0095]

[0113] In addition to thermal management, embodiments in which the gap between the stator 32 and the housing 12 is partially or substantially filled with the stator seal 96, such as those in which the stator seal 96 substantially fills a peripheral portion of the housing 12, provide structural benefits. Encapsulating the electromagnet 38 with the stator seal 96 physically prevents contamination of the electromagnet 38 with moisture or particulate matter. Such contamination can cause insulation degradation and ultimately shorts between adjacent wires. Additionally, the dielectric seal 96 provides additional protection against manufacturing defects in the insulation of the wires. Thus, the seal 96 can provide redundant protection against shorts between the windings and supplement the insulation of the windings 42. In certain embodiments, the seal 96 also seals the electrical connections of the coil phases, thus providing additional protection against phase-to-phase shorts as well as manufacturing defects in the wiring or electrical connections.

[0096]

[0114] Additionally, the encapsulant 96 also reduces vibration of the wiring in the stator 32. Vibrations can reduce the integrity and lifespan of the windings 42. Thus, the stator encapsulant 96 provides improved thermal management and increased robustness of the machine. Various sensors 85, such as, but not limited to, one or more thermal and vibration sensors, can be embedded in the stator encapsulant 96 to detect increased temperature or increased vibration of the stator or rotor. The sensors 85 can be wired, wireless, Internet of Things (IoT), or other types of monitoring sensors, or another suitable type of sensor. By monitoring the operation of the electric machine with one or more sensors, degradation of the machine's performance can be detected remotely and preventative measures can be taken.

[0097]

[0115] In one embodiment, the stator seal 96 includes a relatively rigid outer portion that surrounds the entire stator structure and contacts the housing as described below. However, as shown in FIG. 10, there are relatively small spaces between the windings 42 of adjacent electromagnets 38, and therefore it may be advantageous to fill the interior of the stator 32 with a relatively flowable interior potting material. Any type of stator seal 96 having any suitable viscosity can be treated to have a high thermal conductivity that facilitates the transfer of heat from the stator 32 to the housing 12, as described in more detail below.

[0098]

[0116] 1 and 2 and 8-13 includes a peripheral portion 54 that surrounds the stator 32. Heat transfer from the stator 32 to the housing 12 can be enhanced by having a stator seal 96 in physical contact with one or both of the end plates 56 and 58. In the particular embodiment of FIG. 8, the stator seal 96 contacts the entire annular inner surface of each of the end plates 56 and 58.

[0099]

[0117] The housing 12 may include a separate peripheral portion 54, a separate first end plate 56, and a separate second end plate 58 that are joined together to form the housing 12. However, it is important to note that the housing may be formed by other methods. For example, in other embodiments, the peripheral portion 54 and one of the end plates 56, 58 may be cast, machined, or otherwise formed as a single piece. Thus, in some embodiments, the end plates and the peripheral portion may be an integrated structure. In such embodiments, the stator seal 96 may be in direct or indirect thermal contact with the end plate areas of the integrated housing structure.

[0100]

[0118] 11 , the stator seals 96 and the inner surface 126 of certain electromagnet cores 44 define a substantially cylindrical inner stator surface 128 that faces the air gap 40, with each end of the inner stator surface 128 bounded by central portions of the first and second end plates 56 and 58. The end plates and the inner stator surface 128 collectively define a closed cylindrical rotor cavity 60. In certain embodiments, the motor 10 includes minimal air gaps between any stator structure and the housing that are not filled with the stator seals 96.

[0101]

[0119] Thus, the stator seal 96, in conjunction with the thermally conductive lubricant in contact with the outer surface of the stator 114 and the inner surface 116 of the peripheral portion of the housing, places all surfaces of the stator 32, except for the inner stator surface 128 potentially located in the air gap 40, in direct thermal contact with one or more portions of the housing 12.

[0102]

[0120] The thermal conductivity of the stator seal 96 can be enhanced by including certain materials in the seal matrix. These materials can be included whether the seal is a substantially rigid exterior seal or a relatively flowable interior potting material. For example, the stator seal 96 can be a dielectric material that is applied in a liquid state to fill substantially all voids outside the rotor cavity 60. In certain embodiments, the material applied as a liquid is fully cured or partially cured into a generally rigid stator seal 96. Exemplary dielectric materials suitable for thermally enhancing the stator seal include, but are not limited to, suspended particles of boron nitride, silicon carbide, silica, aluminum oxide, aluminum, copper, other metals, other metal oxides, ceramics, graphene, and the like. The thermal conductivity of the seal 96 can be further enhanced if the suspended particles are spherical, have radially oriented fibers, or have other shapes or orientations designed to promote heat transfer.

[0103]

[0121] Alternatively, instead of or in conjunction with the use of suspended particles, larger scale structures can be incorporated into the stator seal 96 to increase the thermal conductivity of the seal. For example, a solid component such as a metal or ceramic ring that has a higher thermal conductivity than the seal can be embedded into the seal to create a composite that has a higher thermal conductivity than the seal alone.

[0104]

[0122] As mentioned above, the rotor-facing electromagnetic core face 126 and the inner surface of the stator seal 96 are exposed to the air gap 40. These structures, together with the end plates 56, 58, define an enclosed rotor cavity 60. Heat transferred from the stator 32 to the rotor cavity 60 has not yet been exhausted from the machine. Additionally, the rotor 16 of the machine operates within the rotor cavity 60, adding additional heat to this space. Heat can be transferred from the rotor cavity 60 through the housing end plates 56, 58 to the outside environment. Heat transfer from the rotor cavity 60 to the end plates can be enhanced by fabricating a central region of one or both end plates 56, 58 with or in contact with one or more heat transfer structures that extend into the rotor cavity 60.

[0105]

[0123] For example, as shown in Figures 2, 8, and 10-13, a central portion of each end plate 56, 58 can be in thermal contact with a heat transfer structure 82 and 84, respectively. The configurations of heat transfer structures 82 and 84 are representative of any number of types or configurations of heat transfer structures that can be attached to, formed on, or otherwise in thermal contact with the end plates 56, 58. In each case, the heat transfer structure 82 or 84 contacts the end plate on one side and extends into the rotor cavity 60 on the opposite side.

[0106]

[0124] The heat transfer structure 82 or 84 may be formed with a number of pins, fins, pin / fin combinations 86, or other structures designed to increase surface area and promote heat transfer. The pin fins 86 extend away from the end plates 56, 58 into the rotor cavity 60. Additionally, the inner surface of the heat transfer structure 82 or 84 may be roughened to increase surface area or treated, for example, by black anodizing, to promote heat transfer. Additionally, the heat transfer structure 82 or 84 may be fabricated from materials such as copper or aluminum that have high thermal conductivity. The heat transfer structure 82 or 84 may be bonded to the end plates 56, 58 or other housing structures using a heat transfer paste or another method that promotes effective heat transfer. Although each of the heat transfer structures 82, 84 is illustrated as being substantially annular, other shapes and configurations are within the scope of the present disclosure.

[0107]

[0125] Heat removal from the housing The evacuation of heat from the housing 12 to the external environment can be enhanced by providing the housing with feet 18 or other structure that enhances the transfer of heat from the housing to a building floor, a building wall, a mounting bracket, a machine component, or other external structure to which the motor 10 is attached. The evacuation of heat through the feet 18 can be enhanced by fabricating the feet from a material having a high thermal conductivity, such as, for example, aluminum, copper, a thermally transparent composite, or the like. Additionally, the interface 130 between the feet 18 and the external structure can be in contact with or covered with a material that enhances the transfer of thermal energy from the feet 18 to the external structure. For example, the interface 130 can be covered with a thermally conductive paste or other material that has a higher thermal conductivity than the feet 18, such as copper.

[0108]

[0126] Further heat removal from the housing can be facilitated by providing fins, pins, or other heat transfer structures on the exterior portion of the housing 12. Portions of the housing 12 can be roughened to increase surface area or treated, for example, with black anodization or thermally conductive paint, to facilitate heat transfer. Additionally, the housing 12 can be fabricated from a material such as aluminum that has a relatively high thermal conductivity.

[0109]

[0127] Heat removal from the stator through the shaft As mentioned above, one path for carrying heat away from the rotor 16 utilizes the shaft 14. Additionally, heat conducted from the stator 32 to the housing end plates 56, 58 or other motor structures may be conducted to the shaft 14. The dissipation of heat through the shaft 14 may be enhanced by providing the shaft 14 with a thermally conductive core 98 or other shaft structure made of a material having a relatively high thermal conductivity, such as aluminum or copper. The shaft 14 is connected to the body of the equipment being driven by the shaft 14, such as a fan, pump, drive roller, or material processing machine. The shaft 14, particularly if provided with a thermally conductive core 94, may thus conduct heat to the driven equipment where it may be dissipated by convection, conduction, or radiation.

[0110]

[0128] Additionally, the shaft 14 is supported by bearings 24, 26 supported by bearing flanges 28, 30. Heat transfer from the housing 12 to the shaft 14 can be enhanced by implementing a portion of one or more of the bearings 24, 26 and / or bearing flanges 28, 30 from a material having a relatively high thermal conductivity, such as, for example, copper or aluminum. In one particular embodiment, the bearings 24, 26 include bearing seals 132, 134 fabricated from copper to enhance heat transfer from the housing 12 to the shaft 14. The bearing flanges 28, 30 can also be fabricated from copper or other materials having a relatively high thermal transmittance. Additionally, the thermally conductive core 98 can extend laterally to or near the shaft surface in the area where the shaft 14 contacts the bearings 24 and / or 26 or the bearing seals 132, 134.

[0111]

[0129] In certain embodiments, the peripheral portions of the housing 54, the first end plate 56, and the second end plate 58 can be manufactured together, welded together, or otherwise manufactured to prevent ingress into the housing. Thus, the bearing flanges 28, 30, or another housing structure, can support a bearing cartridge with bearings 24, 26 that can be replaced from outside the housing. Thus, the bearings 24, 26, which experience faster mechanical wear compared to other moving parts of the motor 10, can be replaced without accessing the interior of the housing 12, thus improving overall machine robustness.

[0112]

[0130] method Other embodiments include, but are not limited to, a method for cooling a rotor of an electric machine, a method for cooling a stator of an electric machine, a method for cooling an electric machine, a method for manufacturing an electric machine or a component of an electric machine, a method for stabilizing an electric machine, and a method for manufacturing an electromagnet for an electric machine. Various methods will be apparent to those skilled in the art based entirely on the apparatus disclosed herein.

[0113]

[0131] An exemplary method includes a method for cooling a rotor 16 or an electric machine 10 having a rotor 16 and a stator 32. The method includes rotating the rotor 16 relative to the stator 32 to drive an internal fan 70. The internal fan 70 circulates a fluid, such as air or an air-oil mixture, in a fluid circuit 74 between a first cavity 64 and a second cavity 68 adjacent the rotor 16 to cool the rotor 16. Heat transferred to the fluid circuit 74 may then be transferred to the machine housing 12 and then carried away from the machine 10.

[0114]

[0132] Another representative embodiment is a method of cooling the stator 32 or electric machine 10 by thermally contacting the stator 32 and a housing region 12 of the machine, such as the first end plate 56 or the second end plate 58, with a stator sealant 96. The thermal conductivity of the stator sealant 96 can be enhanced by mixing an additive into the sealant 96 to increase the thermal conductivity. In this manner, heat generated in the stator 32 can be conducted from the stator 32 through the sealant 96 to the housing 12.

[0115]

[0133] Another representative embodiment is a method of manufacturing a stator 32 or electric machine 10 having a plurality of electromagnets 38 with electromagnet cores 44. The plurality of electromagnet cores 44 may be formed to include a stack of laminations 46 defining tooth portions 100 and yoke portions 102. Each yoke portion may also define a tongue structure 110 and an opposing groove structure 112. The electromagnets 38 may be assembled into a stator 32 by mating the tongue and groove structures 110 of each electromagnet 38 with the corresponding tongue and groove structures 110 of an adjacent electromagnet 38. After the electromagnets are so assembled, the stator 32 may be encapsulated with a thermally conductive encapsulant 96.

[0116]

[0134] Another representative embodiment is a method of stabilizing an electric machine 10. The method includes stabilizing the rotor 16 with thermally conductive dielectric rotor seals 90 in contact with the adjacent permanent magnets 34 and stator 32 with thermally conductive dielectric stator seals 96 in contact with the adjacent electromagnets 38.

[0117]

[0135] Various modifications and additions can be made to the above-described embodiments without departing from the scope of the present invention. For example, although the above-described embodiments refer to particular features, the scope of the present invention also includes embodiments having different combinations of features and embodiments that do not include all of the features described above.

[0118]

[0136] Additionally, although the steps of the methods and processes described herein have been described in a particular order for ease of description, various steps can be rearranged, added, and / or omitted according to various embodiments, unless otherwise clear from the context. Additionally, steps described with respect to one method or process can be incorporated into other methods or processes described, and similarly, system components described according to a particular structural architecture and / or described with respect to one system can be organized into other structural architectures and / or incorporated into other systems described. Thus, while various embodiments have been described with or without particular features for ease of description and to illustrate exemplary aspects of those embodiments, various components and / or features described herein with respect to a particular embodiment can be substituted, added, and / or subtracted from other described embodiments, unless otherwise clear from the context. Thus, although several exemplary embodiments have been described above, it will be understood that the invention is intended to encompass all modifications and equivalents falling within the scope of the following claims.

Claims

1. a rotor comprising a shaft defining a longitudinal shaft axis, a rotor back assembly surrounding a portion of the shaft, and a plurality of permanent magnets radially disposed about the rotor back assembly; a stator including a plurality of electromagnets arranged radially around the rotor; a housing supporting the rotor and the stator; Equipped with The rotor, the stator, and a portion of the housing are a first cavity between the rotor and the housing at one end of the rotor; a second cavity between the housing and the other end of the rotor; an air gap extending between the rotor and the stator from the first cavity to the second cavity; a ventilation channel extending through the rotor back assembly from the first cavity to the second cavity; The following is set forth: a rotor fan extending into one of the first cavity and the second cavity and circulating fluid between the first cavity and the second cavity through the ventilation channel and the air gap as the rotor rotates relative to the stator.

2. The electric machine of claim 1 , wherein the rotor fan comprises a plurality of fan blades formed on an outer surface of the rotor back assembly.

3. The electric machine of claim 2 , wherein at least one of the rotor back assembly and the plurality of fan blades comprises a surface treatment to enhance radiation of heat into the first cavity or the second cavity.

4. The electric machine of claim 2 , wherein the rotor back assembly comprises a plurality of laminations.

5. The electric machine of claim 1 , wherein at least one of the plurality of permanent magnets comprises a plurality of permanent magnet laminations.

6. The electric machine of claim 1 , further comprising a retaining band surrounding an outer surface facing the air gap of each of the plurality of permanent magnets.

7. a first heat transfer structure in thermal contact with the housing and extending into the first cavity; The electric machine of claim 1 further comprising:

8. a second heat transfer structure in thermal contact with the housing and extending into the second cavity. The electric machine of claim 7 further comprising:

9. The electric machine of claim 1 , wherein the rotor comprises a third heat transfer structure extending into the first cavity.

10. The electric machine of claim 9 , wherein the rotor comprises a fourth heat transfer structure extending into the second cavity.

11. The rotor is A gap between adjacent permanent magnets; a thermally conductive material filling the gaps between adjacent permanent magnets; Further equipped with The electric machine of claim 10 , wherein the third heat transfer structure is in thermal communication with a first end of the thermally conductive material.

12. The electric machine of claim 11 , wherein the fourth heat transfer structure is in thermal communication with a second end of the thermally conductive material.

13. The electric machine of claim 1 , wherein the fluid comprises air and another heat transfer fluid other than air.

14. The electric machine of claim 1 , further comprising a thermally conductive shaft core, the shaft core comprising a thermally conductive material having a different composition than a portion of the shaft surrounding the shaft core.

15. a rotor comprising a shaft defining a longitudinal shaft axis, a rotor back assembly surrounding a portion of the shaft, and a plurality of permanent magnets radially disposed about the rotor back assembly; a stator including a plurality of electromagnets arranged radially around the rotor; a housing supporting the rotor and the stator; Equipped with The rotor, the stator, and a portion of the housing are a first cavity between the rotor and the housing; a second cavity between the housing and the other end of the rotor; The following is set forth:

1. An electric machine comprising: an electric motor including a first cavity and a second cavity, the electric motor including a first cavity and a second cavity, the first cavity being spaced apart from the first cavity and the second cavity being spaced apart from the second cavity, the second ...

16. The electric machine of claim 15 , wherein the additive comprises one or more of boron nitride, silicon carbide, aluminum powder, aluminum oxide powder, copper powder, and graphene.

17. a heat transfer structure in thermal communication with the thermally conductive material and with at least one of the first cavity and the second cavity; The electric machine of claim 15 further comprising:

18. a shaft defining a longitudinal shaft axis, the shaft comprising a thermally conductive shaft core, the shaft core including a thermally conductive material having a different composition than a portion of the shaft surrounding the shaft core; a rotor back assembly surrounding a portion of the shaft; a plurality of permanent magnets arranged radially around the rotor back assembly; A rotor for an electric machine comprising:

19. a rotor fan including a plurality of fan blades formed on an outer surface of the rotor back assembly; one or more ventilation channels extending through said rotor back assembly; The rotor of claim 18 further comprising:

20. The rotor of claim 18 , wherein the rotor back assembly comprises a plurality of laminations.

21. The rotor of claim 18 , wherein at least one of the plurality of permanent magnets comprises a plurality of permanent magnet laminations.

22. A gap between adjacent permanent magnets; a thermally conductive material that fills the gap between the adjacent permanent magnets and includes a polymer doped with an additive to enhance thermal conductivity; The rotor of claim 18 further comprising:

23. The rotor of claim 22 , wherein the additive comprises one or more of boron nitride, silicon carbide, aluminum powder, aluminum oxide powder, copper powder, and graphene.

24. a heat transfer structure in thermal communication with the thermally conductive material; The rotor of claim 22 further comprising:

25. 1. A method of cooling a rotor, comprising: The rotor, the stator, and the housing support a rotor and a stator, the rotor, the stator, and the housing include: a first cavity between the rotor and the housing at one end of the rotor; a second cavity between the rotor and the housing at the other end of the rotor; an air gap extending between the rotor and the stator from the first cavity to the second cavity; a ventilation channel extending through a rotor back assembly from the first cavity to the second cavity; providing an electric machine, the electric machine defining rotating the rotor relative to the stator to drive an internal fan; circulating a fluid between the first cavity and the second cavity through the ventilation channel and the air gap with the fan upon rotation of the rotor; A method comprising:

26. providing a first heat transfer structure in thermal contact with the housing and extending into one of the first cavity and the second cavity; transferring heat from the fluid circulated by the fan between the first cavity and the second cavity to the first heat transfer structure; transferring heat from the first heat transfer structure to the housing; 26. The method of claim 25, further comprising:

27. providing a second heat transfer structure in thermal contact with the rotor and extending into one of the first cavity and the second cavity; transferring heat from the rotor to the second heat transfer structure; transferring heat from the second heat transfer structure to the fluid circulated by the fan between the first cavity and the second cavity; 27. The method of claim 26, further comprising:

28. providing the rotor with a plurality of permanent magnets radially arranged about the rotor back assembly, the permanent magnets being separated by gaps between adjacent permanent magnets; filling a portion of the gap between adjacent permanent magnets with a thermally conductive material including a polymer doped with an additive to enhance thermal conductivity; 26. The method of claim 25, further comprising:

29. 30. The rotor of claim 28, wherein the additive comprises one or more of boron nitride, silicon carbide, aluminum powder, aluminum oxide powder, copper powder, and graphene.

30. A rotor; a stator including a plurality of radially arranged electromagnets and a stator sealant that seals the electromagnets; a housing supporting the rotor and the stator; Equipped with The housing includes: The surrounding area and a first end plate located at one end of the peripheral portion; a second end plate located at the other end of the peripheral portion; and Equipped with The stator seal is in thermal contact with the first end plate and the second end plate.

31. 31. The electric machine of claim 30, wherein the stator seal contacts the first end plate and the second end plate such that a central region of the first end plate, a central region of the second end plate, and an inner stator surface define an enclosed cylindrical rotor cavity substantially free of voids extending from the inner stator surface, the central region of the first end plate, and the central region of the second end plate toward the peripheral portion.

32. The electric machine of claim 30 , wherein the first end plate and the peripheral portion comprise an integrated housing unit.

33. The electric machine of claim 30 , wherein the stator seal includes a dielectric material and an additive to increase the thermal conductivity of the seal.

34. 34. The electric machine of claim 33, wherein the dielectric material comprises a polymer and the additive comprises one or more of boron nitride, silicon carbide, silicon, aluminum oxide, aluminum powder, copper powder, metal oxides, ceramics, graphene, and substantially spherical particles.

35. The electric machine of claim 30 , wherein an interface between an inner surface of the peripheral portion of the housing and an outer stator surface includes a thermally conductive lubricant.

36. a first heat transfer structure in thermal contact with one of the central region of the first end plate and the central region of the second end plate; Further equipped with The electric machine of claim 30 , wherein the first heat transfer structure extends into the rotor cavity.

37. a second heat transfer structure in thermal contact with the other of the central region of the first end plate and the central region of the second end plate. Further equipped with The electric machine of claim 36 , wherein the second heat transfer structure extends into the rotor cavity.

38. The electric machine of claim 37 , wherein at least one of the first heat transfer structure and the second heat transfer structure comprises a plurality of pins or fins.

39. 38. The electric machine of claim 37, wherein at least one of the first heat transfer structure and the second heat transfer structure comprises a surface treatment that facilitates transfer of heat from the rotor cavity.

40. The electric machine of claim 30 , wherein the housing includes one or more thermally conductive feet attached to the peripheral portion.

41. 41. The electric machine of claim 40, wherein the thermally conductive feet comprise a separate heat transfer material disposed between the feet and a mounting surface.

42. an electromagnet comprising a core comprising a stack of laminations defining teeth and a yoke portion, an insulating bobbin surrounding a portion of the teeth of each lamination, and an electrically conductive winding surrounding a portion of the bobbin; 31. The electric machine of claim 30, wherein each lamination in the stack of laminations is held relative to adjacent laminations by the bobbin.

43. 43. The electric machine of claim 42, wherein the yoke portions of a plurality of electromagnets are in direct physical contact with a shoulder structure extending from the first end plate, the shoulder structure supporting each electromagnet a selected distance away from the first end plate such that there is no physical contact between the windings of any electromagnet and the first end plate.

44. Each individual sheet in the stack of sheets is first and second opposing planar surfaces; a heat transfer layer in thermal contact with at least one of the first and second planar surfaces; 44. The electric machine of claim 43, comprising:

45. Each individual sheet in the stack of sheets is first and second opposing planar surfaces; a dielectric layer in physical contact with one of said first and second planar surfaces; a heat transfer layer different from the dielectric layer in thermal contact with the other of the first and second flat surfaces; Equipped with 44. The electric machine of claim 43, wherein an interface between adjacent laminations in the stack of laminations comprises the dielectric layer of one lamination and the heat transfer layer of an adjacent lamination.

46. The electric machine of claim 45 , wherein the heat transfer layer comprises graphene.

47. 44. The electric machine of claim 43, wherein the yoke portion defined by laminations of sheets further defines a tongue and opposing groove structure, the tongue and opposing groove structure mating with a tongue and groove structure of the laminations of an adjacent electromagnet.

48. a shaft extending from the rotor through one or both of the first end plate and the second end plate; a shaft bearing attached to one of the first end plate and the second end plate and supporting the shaft; a bearing seal attached to the shaft bearing; Further equipped with The electric machine of claim 30 , wherein the bearing seal comprises a material having a greater thermal conductivity than the shaft bearing.

49. 49. The electric machine of claim 48, wherein the shaft comprises a thermally conductive shaft core, the core including a thermally conductive material having a different composition than a portion of the shaft surrounding the shaft core.

50. 50. The electric machine of claim 49, wherein the thermally conductive shaft core extends toward an outer surface of the shaft where the shaft contacts the shaft bearing.

51. 1. An electromagnet for an electric machine, comprising: a stack of laminations defining the teeth and yoke portions; an insulating bobbin surrounding a portion of the teeth of each lamination and holding each lamination against its adjacent laminations; a conductive winding surrounding a portion of the bobbin; a sealant for completely sealing the bobbin and the winding; Equipped with The encapsulant includes a dielectric material and an additive for increasing the thermal conductivity of the encapsulant.

52. 52. The electromagnet of claim 51 , wherein the dielectric material comprises a polymer and the additive comprises one or more of boron nitride, silicon carbide, silicon, aluminum powder, copper powder, metal oxides, ceramics, and graphene.

53. Each individual sheet in the stack of sheets is first and second opposing planar surfaces; a heat transfer layer in thermal contact with at least one of the first and second planar surfaces; 52. The electromagnet of claim 51 , comprising:

54. 54. The electromagnet of claim 53, wherein each individual lamination in the stack of laminations further comprises a dielectric layer in physical contact with one of the first and second planar surfaces opposite the heat transfer layer.

55. 1. A method for cooling a stator, comprising: A rotor; a stator including a plurality of radially arranged electromagnets and a stator sealant that seals the electromagnets; a housing supporting the rotor and the stator; Equipped with The housing includes: The surrounding area and a first end plate located at one end of the peripheral portion; a second end plate located at the other end of the peripheral portion; and providing an electric machine comprising: placing the stator seal in thermal contact with the first end plate and the second end plate; conducting heat from the stator encapsulation to the first end plate and the second end plate; A method comprising:

56. placing the stator seal in thermal contact with the first end plate and the second end plate such that a cylindrical rotor cavity is defined by a central region of the first end plate, a central region of the second end plate, and an inner stator surface; providing a heat transfer structure in thermal contact with one of the central region of the first end plate and the central region of the second end plate and extending into the rotor cavity; transferring heat from the rotor cavity to the first end plate or the second end plate through the heat transfer structure; 56. The method of claim 55, further comprising:

57. 1. A method of manufacturing a stator, comprising the steps of: a stack of laminations defining a tooth and a yoke portion, the yoke portion further defining a tongue structure and an opposing groove structure; an insulating bobbin surrounding a portion of the teeth of each lamination and holding each lamination against its adjacent laminations; a conductive winding surrounding a portion of the bobbin; providing a plurality of electromagnet cores, each of the electromagnet cores having: assembling the plurality of electromagnets into a stator by mating the tongue and groove structure of each electromagnet with the corresponding tongue and groove structure of an adjacent electromagnet; encapsulating the assembled stator with a thermally conductive encapsulant; A method comprising:

58. Adding an additive to the encapsulant to increase the thermal conductivity of the encapsulant.

58. The method of claim 57, further comprising:

59. placing a heat transfer layer in thermal contact with at least one flat surface of the selected plate of the selected electromagnet; 58. The method of claim 57, further comprising:

60. a shaft defining a longitudinal shaft axis; a rotor back assembly surrounding a portion of the shaft; a plurality of permanent magnets radially arranged around the rotor back assembly; a first thermally conductive dielectric encapsulant in contact with adjacent permanent magnets; a rotor comprising: a plurality of electromagnets arranged radially around the rotor and separated from an outer surface of the rotor by magnetic air gaps; a second thermally conductive dielectric encapsulant in contact with an adjacent electromagnet; a stator comprising: a housing supporting the rotor and the stator; An electric machine comprising:

61. 61. The electric machine of claim 60, wherein the housing comprises a totally enclosed, naturally cooled (TENV) housing.

62. 61. The electric machine of claim 60, wherein the first thermally conductive dielectric encapsulant contacts the rotor back assembly between adjacent permanent magnets.

63. 63. The electric machine of claim 62, wherein the rotor back assembly defines a fastening surface between adjacent permanent magnets, and the first thermally conductive dielectric encapsulant contacts the fastening surface.

64. 64. The electric machine of claim 63, wherein the fastening surface comprises grooves formed in the rotor back assembly between adjacent permanent magnets.

65. a prestressed retaining band surrounding an outer surface of each of the plurality of permanent magnets facing the air gap; 61. The electric machine of claim 60 further comprising:

66. 61. The electric machine of claim 60, wherein a radial thickness dimension of each of the plurality of permanent magnets measured along a radial line extending radially outward from the shaft axis is greater than or equal to eight times a width of the magnetic air gap measured along the radial line.

67. 61. The electric machine of claim 60, wherein at least one of the first thermally conductive dielectric encapsulant and the second thermally conductive dielectric encapsulant comprises a polymer and an additive to increase the thermal conductivity of the polymer.

68. 61. The electric machine of claim 60, wherein the second thermally conductive dielectric encapsulant comprises a polymer and a heat transfer element embedded in the polymer and having a higher thermal conductivity than the polymer.

69. 61. The electric machine of claim 60, wherein the second thermally conductive dielectric encapsulant is in contact with the housing.

70. 70. The electric machine of claim 69, wherein the second thermally conductive dielectric encapsulant substantially fills a peripheral portion of the housing.

71. one or more sensors embedded in the second thermally conductive dielectric encapsulant 61. The electric machine of claim 60 further comprising:

72. A thermal sensor and a vibration sensor embedded in the second thermally conductive dielectric encapsulant.

61. The electric machine of claim 60 further comprising:

73. a first bearing in contact with the housing supporting the rotor; a second bearing in contact with the housing supporting the other end of the rotor; Further equipped with 61. The electric machine of claim 60, wherein the first bearing and the second bearing are removable from an exterior surface of the housing without opening the housing.

74. a shaft defining a longitudinal shaft axis; a rotor back assembly surrounding a portion of the shaft; a plurality of permanent magnets arranged radially around the rotor back assembly; a first thermally conductive dielectric encapsulant in contact with adjacent permanent magnets; a rotor comprising: a stator including a plurality of electromagnets arranged radially around the rotor and separated from an outer surface of the rotor by a magnetic air gap; Equipped with 11. An electric machine, wherein a radial thickness dimension of each of the plurality of permanent magnets measured along a radial line extending radially outward from the shaft axis is greater than or equal to eight times a width of the magnetic air gap measured along the radial line.

75. a first thermally conductive dielectric encapsulant in contact with adjacent permanent magnets and further in contact with said rotor back assembly; 75. The electric machine of claim 74, further comprising:

76. 1. A method for stabilizing an electric machine, comprising: a shaft defining a longitudinal shaft axis; a rotor back assembly surrounding a portion of the shaft; a plurality of permanent magnets arranged radially around the rotor back assembly; a rotor comprising: a stator including a plurality of electromagnets arranged radially around the rotor and separated from an outer surface of the rotor by a magnetic air gap; providing an electric machine comprising: supporting the stator and the rotor by a housing; stabilizing the rotor by providing a first thermally conductive dielectric encapsulant in contact with adjacent permanent magnets; stabilizing the stator by providing a second thermally conductive dielectric encapsulant in contact with adjacent electromagnets; A method comprising:

77. Enclosing the rotor and stator in a totally enclosed, naturally cooled (TENV) housing.

77. The method of claim 76, further comprising:

78. contacting the first thermally conductive dielectric encapsulant with the rotor back assembly between the adjacent permanent magnets.

77. The method of claim 76, further comprising:

79. providing fastening surfaces on the rotor back assembly between adjacent permanent magnets; attaching the first thermally conductive dielectric encapsulant to the fastening surface; 79. The method of claim 78, further comprising:

80. 80. The method of claim 79, wherein the fastening surface comprises grooves formed in the rotor back assembly between adjacent permanent magnets.

81. encircling an outer surface of each of the plurality of permanent magnets facing the air gap with a prestressed retaining band.

77. The method of claim 76, further comprising:

82. Providing the permanent magnet with a radial thickness dimension measured along a radial line extending radially outward from the shaft axis that is at least eight times greater than a width of the magnetic air gap measured along the radial line.

77. The method of claim 76, further comprising:

83. 77. The method of claim 76, wherein at least one of the first thermally conductive dielectric encapsulant and the second thermally conductive dielectric encapsulant comprises a polymer and a heat transfer element embedded in the polymer and having a higher thermal conductivity than the polymer.

84. Contacting the second thermally conductive dielectric encapsulant with the housing.

77. The method of claim 76, further comprising:

85. Substantially filling a peripheral portion of the housing with the second thermally conductive dielectric encapsulant.

85. The method of claim 84, further comprising:

86. Embedding one or more sensors in the second thermally conductive dielectric encapsulant.

77. The method of claim 76, further comprising:

87. Embedding a thermal sensor and a vibration sensor in the second thermally conductive dielectric encapsulant.

87. The method of claim 86, further comprising:

88. providing a first bearing in contact with the housing supporting the rotor; providing a second bearing in contact with the housing for supporting the other end of the rotor; Further comprising:

77. The method of claim 76, wherein the first bearing and the second bearing are removable from an exterior surface of the housing without opening the housing.

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