Stator tooth and winding conductor design for electric machines

Abstract

A motor having optimized stator tooth geometry and multi-gauge stator conductors, methods of manufacturing / using such a motor, and a motor vehicle equipped with such a motor are presented. The motor includes a housing, a rotor assembly rotatably attached to the housing, and a stator assembly coaxial with the rotor assembly and spaced apart from the rotor assembly by an air gap. The rotor assembly includes one or more magnets mounted to a rotor core. The stator assembly includes a stator core having a plurality of axially elongated, circumferentially spaced apart stator slots, a plurality of radially aligned stator teeth interleaved between and separating the slots, and a plurality of electromagnetic windings wound through the slots. Each stator tooth has an elongated tooth body having a tooth head at a radially end of a tooth root, the tooth root attached to a cylindrical hub of the stator core. The tooth head has an axial cross-section with a trapezoidal tooth crown integral with a rectangular tooth tip.

Description

Technical Field

[0001] This disclosure generally relates to electric motors. More specifically, aspects of this disclosure relate to multiphase AC permanent magnet motors having a hairpin winding stator architecture for reducing AC winding losses. Background Technology

[0002] Modern motor vehicles, such as modern cars, were initially equipped with a powertrain that operated to propel the vehicle and provide power to its onboard electronics. For example, in automotive applications, a vehicle powertrain is typically represented by a prime mover, which transmits drive torque to the vehicle's final drive system (e.g., differential, axles, steering modules, wheels, etc.) via an automatic or manual transmission. Historically, automobiles have been powered by reciprocating piston internal combustion engine (ICE) components due to their availability, relatively low cost, light weight, and overall efficiency. As some non-limiting examples, such engines include compression ignition (CI) diesel engines, spark ignition (SI) gasoline engines, two-stroke, four-stroke, and six-stroke architectures, and rotary engines. Hybrid electric vehicles and fully electric vehicles (collectively referred to as "electrically driven vehicles"), on the other hand, utilize alternative power sources to propel the vehicle, thus minimizing or eliminating reliance on fossil fuel-based engines for traction power.

[0003] A fully electric vehicle (FEV) (commonly known as an "electric vehicle") is an electrically driven vehicle configuration that completely omits the internal combustion engine and associated peripheral components of the powertrain system, instead relying on a rechargeable energy storage system (RESS) and a traction electric motor for vehicle propulsion. The engine components, fuel supply system, and exhaust system of an ICE-based vehicle are replaced by one or more traction electric motors, a traction battery pack, and battery cooling and charging hardware in a battery-based FEV. Conversely, a hybrid electric vehicle (HEV) uses multiple traction power sources to propel the vehicle, most typically combining battery-powered or fuel cell-powered traction electric motors to operate the internal combustion engine components. Because hybrid electric vehicles can obtain power from sources other than the engine, the HEV engine can be completely or partially shut off when the vehicle is propelled by one or more electric motors.

[0004] There are three main types of motors used for traction motors in modern electric vehicle powertrains: brushless direct current (BLDC) permanent magnet (PM) motors, brushless asynchronous alternating current (AC) motors, and multiphase synchronous ACPM motors. Permanent magnet motors possess many operating characteristics that make them more attractive for vehicle propulsion applications compared to their available counterparts, including high efficiency, high torque, high power density, and a long constant power operating range. A traction motor is a motor that uses a stator with multiphase electromagnetic windings and a rotatable rotor to convert electrical energy into rotational mechanical energy. These multiphase electromagnetic windings are, for example, conductive "hairpin"-shaped bars, and the rotatable rotor carries engineered magnets, such as surface-mounted or internally mounted permanent magnets. Permanent magnet motors can be classified as DC or AC, rotating or linear, and radial or axial flux. In radial flux PM motor designs, the magnetic bearing rotor can be coaxially nested inside the stator or can surround the stator. Alternatively, PM motors can employ an axial flux arrangement, where the stator and rotor face a coaxial disk. The rotation of the rotor is affected by a magnetic field generated by the current passing through the stator windings and interacts with the magnetic field generated by the magnets carried by the rotor.

[0005] Traditional stator assemblies can be manufactured using a stator core formed from thin iron disks stacked and laminated together to form a cylinder. Each disk has several openings that, when aligned with the openings of adjacent disks, form stator slots extending axially through the length of the stator core. Conductive elements, such as metal rods, bars, or wires, are wound around the stator core and pass through these stator slots. A single stator slot can accommodate several individual conductors arranged radially adjacent to each other relative to the stator core in a manner forming concentric loops of conductors. For radial flux ACPM motors, the rotor can be surrounded by the stator, with an air gap separating the stator assembly from the rotor assembly. The radially innermost ends separating the stator slots are stator teeth that project toward the outer diameter (OD) periphery of the rotor assembly. The stator teeth cause the magnetic flux generated by the stator windings to pass directly through the air gap to the rotor and to electromagnetically link with magnets located in the slots of the rotor core before completing its return path to the stator assembly. Summary of the Invention

[0006] This paper presents an electric motor with optimized stator tooth geometry and multi-specification stator conductors, methods for manufacturing such a motor, methods for operating such a motor, and a motor vehicle equipped with a brushless ACPM motor having improved tooth tip and inner conductor design to reduce AC winding losses. For example, motor efficiency and maximum motor torque output are typically suppressed by excessive AC winding losses caused by the ohmic resistance of the stator windings to the current. Winding losses—also outdatedly referred to as “copper losses” (regardless of conductor material)—lead to the undesirable dissipation of electrical energy as heat, especially during high-speed motor operation. The motor may suffer additional losses due to the AC proximity effect, which causes the stator conductors closest to the air gap to be cut by rotor flux at high operating speeds. This paper presents optimized stator slot and tooth geometries that maintain the stator conductors, especially those closest to the air gap, at a predetermined minimum radial distance from the rotor. Each tooth can have an elongated, base-like geometry terminating at a distal end with a trapezoidal head and an overall rectangular tooth tip facing the rotor core. With this architecture, the closest stator conductors maintain a minimal spacing from the rotor assembly, a spacing that is a function of the air gap size between the stator and rotor. As a further option, the stator conductor closest to the air gap, or the conductor furthest from the air gap, is thinner than the stator conductor furthest from the air gap. For example, the two or four conductors closest to the rotor can have a square cross-section with a cross-sectional area approximately half that of the conductor furthest from the rotor, and each conductor can have a rectangular cross-section.

[0007] At least some of the disclosed concepts offer additional benefits, including stator tooth and winding conductor designs that reduce copper losses and proximity effects. For example, moving the innermost conductor away from the air gap reduces any resulting proximity effects, while the designed tapered tooth geometry helps reduce stator flux leakage through the tooth tips, and thus contributes to enhanced motor torque performance. By increasing the distance between the innermost conductor layer and the rotor while reducing the size of the inner conductor layer, the proposed stator slot design improves vehicle range, fuel economy, and thermal management of electric vehicles, particularly at high operating speeds (e.g., 10,000 RPM and higher) and during demanding drive cycles.

[0008] This disclosure relates to various aspects of electric motors, such as electric motors, generators, transformers, inductors, power meters, converters, etc. For example, an electric motor includes a protective housing, a rotor assembly rotatably attached to the housing, and a stator assembly coaxial with the rotor assembly and separated from it by an air gap. The rotor assembly includes a rotor core, with one or more magnets mounted on or within the rotor core. Additionally, the stator assembly includes a stator core having a plurality of axially elongated, circumferentially spaced stator slots and a plurality of radially aligned stator teeth, the stator teeth being staggered between and separating the slots. A plurality of electromagnetic windings are wound through the stator slots. Each of these stator teeth has an elongated tooth body with a tooth head at a radial end of the tooth neck. Each tooth head has an axial cross-section having a trapezoidal crown integral with a rectangular tooth tip.

[0009] Another aspect of this disclosure relates to an electrically driven vehicle having a multiphase brushless ACPM traction motor with features designed to reduce winding losses and proximity effects. As used herein, the terms "vehicle" and "motor vehicle" are used interchangeably and synonymously to include any relevant vehicle platform, such as buses (ICE, HEV, FEV, fuel cell, fully and partially autonomous, etc.), commercial vehicles, industrial vehicles, tracked vehicles, off-road vehicles and all-terrain vehicles (ATVs), motorcycles, agricultural equipment, boats, aircraft, etc. In the examples, the electrically driven vehicle includes a body with multiple drive wheels, a passenger compartment, and other standard original equipment. The traction motor operates alone (e.g., for FEV applications) or in combination with an internal combustion engine assembly (e.g., for HEV applications) to drive one or more drive wheels, thereby propelling the vehicle.

[0010] Continuing the discussion of the above example, the traction motor includes a motor housing, a rotor assembly rotatably attached to the motor housing, and a stator assembly concentric with the rotor assembly and spaced apart from the rotor assembly by an air gap. The rotor assembly includes: a cylindrical rotor core defining a plurality of rotor slots therethrough; a rotor shaft attached to the rotor core and projecting axially from the rotor core; and a plurality of permanent magnets nested within the rotor slots of the rotor core. Similarly, the stator assembly includes a cylindrical stator core defining a plurality of circumferentially spaced stator slots therein. A plurality of radially aligned stator teeth separate the stator slots; an electromagnetic winding is wound through each of the stator slots. Each stator tooth has an elongated tooth body with a tooth head at a radial end of the tooth body. Each tooth head has an axial cross-section with a trapezoidal crown integral with a rectangular tooth tip.

[0011] This disclosure also relates to system control logic and computer-readable media (CRM) for operating or manufacturing any of the disclosed stator assemblies, motors, and / or vehicles. In one example, a method for assembling a motor is proposed. This representative method includes, in any order and with any combination of the options and features disclosed above and below: receiving a housing of the motor; rotatably attaching a rotor assembly to the housing, the rotor assembly including a rotor core and magnets mounted to the rotor core; and mounting a stator assembly coaxial with and spaced apart from the rotor assembly by an air gap, the stator assembly including a stator core defining a plurality of circumferentially spaced stator slots, a plurality of radially aligned stator teeth spaced apart from the stator slots, and a plurality of electromagnetic windings located in the stator slots, each of the stator teeth having an elongated tooth body, the elongated tooth body having a tooth head at a radial end of the tooth body, the tooth head having an axial cross section having a trapezoidal tooth crown integral with a rectangular tooth tip.

[0012] For any of the disclosed vehicles, methods, and motors, the trapezoidal crown of each stator tooth can have an isosceles trapezoidal shape, having a narrow edge, a wide edge parallel to the narrow edge and wider than the narrow edge, and a pair of angled edges that are inclined to and connect the wide and narrow edges. The narrow edge of the trapezoidal crown can be closest to and face the air gap. In this case, the opposite ends of the wide edge of the trapezoidal crown can have rounded corners. Similarly, the opposite ends of the narrow edge of the trapezoidal crown can intersect with the rounded corners of the rectangular tooth tips of adjacent stator teeth. The neck and head of each stator tooth can be integrally formed as a single, monolithic structure.

[0013] For any disclosed vehicle, method, and motor, the stator core may include a hollow cylindrical hub, wherein stator teeth project radially inward from the inner diameter (ID) surface of the cylindrical hub. In this case, each tooth body may include a neck portion for attaching the tooth head to the cylindrical hub. The portion of the neck portion immediately adjacent to and abutting the tooth head has a neck width, while the trapezoidal tooth crown may have a narrow edge with a corresponding width and a wide edge with a corresponding width wider than the narrow edge. The widths of both the wide and narrow edges may be approximately equal to or wider than the neck width. Alternatively, the rectangular tip of each tooth head may have a tip width wider than the neck width, the narrow edge width, and the wide edge width.

[0014] For any of the disclosed vehicle, method, and motor, a corresponding subset of the electromagnetic winding may be wound through each of the stator slots, such that the electromagnetic winding of each subset closest to the rotor assembly is positioned on the trapezoidal crown of the adjacent stator tooth. In this case, the nearest winding is spaced from the rotor assembly by at least a minimum spacing distance. D S Minimum interval distance DS equal( Z / A g ),in A g Z is the air gap distance, and Z is a constant ranging from approximately 1.2 to approximately 2.0.

[0015] For any of the disclosed vehicles, methods, and motors, multiple electromagnetic windings may be wound through each stator slot to define a radial stack of windings therein. The windings of the radial winding stack closest to the rotor assembly may be smaller than the windings of the radial winding stack furthest from the rotor assembly. In this case, the nearest winding may have a corresponding radius / thickness that is approximately half the corresponding radius / thickness of the farthest winding. Furthermore, the farthest winding may have a rectangular axial cross-section, while the nearest winding may have a square axial cross-section. Alternatively, the nearest winding may comprise a plurality of mutually parallel inner windings adjacent to each other, and the farthest winding may comprise a plurality of mutually parallel outer windings adjacent to each other and radially spaced apart from the inner windings.

[0016] The present invention also includes the following solutions:

[0017] Option 1. An electric motor, comprising:

[0018] case;

[0019] A rotor assembly rotatably attached to the housing, the rotor assembly including a rotor core and a magnet mounted to the rotor core; and

[0020] A stator assembly, coaxial with and spaced apart from the rotor assembly by an air gap, includes a stator core, a plurality of radially aligned stator teeth, and a plurality of electromagnetic windings. The stator core defines a plurality of circumferentially spaced stator slots, the plurality of radially aligned stator teeth space the stator slots, and the plurality of electromagnetic windings are located in the stator slots. Each stator tooth has an elongated tooth body, the elongated tooth body having a tooth head at its radial end, the tooth head having an axial cross-section having a trapezoidal tooth crown integral with a rectangular tooth tip.

[0021] Option 2. The motor according to Option 1, wherein the trapezoidal tooth crown has an isosceles trapezoidal shape, the isosceles trapezoidal shape has a narrow edge, a wide edge that is parallel to the narrow edge and wider than the narrow edge, and a pair of angled edges that are inclined to the wide edge and the narrow edge and connect the wide edge and the narrow edge, the narrow edge facing the air gap.

[0022] Option 3. The motor according to Option 2, wherein the opposite ends of the wide edge of the trapezoidal tooth crown include rounded corners.

[0023] Option 4. The motor according to Option 2, wherein the opposite ends of the narrow edges of the trapezoidal tooth crown intersect with the rounded corners of the adjacent rectangular tooth tips.

[0024] Option 5. The motor according to Option 1, wherein the stator core includes a cylindrical hub, the stator teeth protruding radially inward from the inner diameter surface of the cylindrical hub, and each of the teeth includes a tooth head attaching to a tooth neck of the cylindrical hub.

[0025] Option 6. The motor according to Option 5, wherein the portion of the tooth neck adjacent to the tooth head has a neck width, and wherein the trapezoidal tooth crown has an isosceles trapezoidal shape, the isosceles trapezoidal shape has a narrow edge parallel to the wide edge, the narrow edge and the wide edge have a narrow edge width and a wide edge width respectively, and both the narrow edge width and the wide edge width are wider than the neck width.

[0026] Option 7. The motor according to Option 6, wherein the rectangular tooth tip has a tip width that is wider than the neck width, the narrow edge width, and the wide edge width.

[0027] Option 8. The motor according to Option 1, wherein a corresponding subset of the electromagnetic winding is wound through each of the stator slots, and wherein the nearest winding in the subset of the electromagnetic winding that is closest to the rotor assembly is disposed on the trapezoidal crown of the adjacent stator tooth in the stator teeth.

[0028] Option 9. The motor according to Option 8, wherein the nearest winding is spaced apart from the rotor assembly by at least a minimum spacing distance. D S And wherein, the minimum interval distance D S = (Z / A g ) ,in, A g Z is the air gap distance of the air gap, and Z is a constant from about 1.2 to about 2.0.

[0029] Option 10. The motor according to Option 1, wherein a plurality of electromagnetic windings in the electromagnetic windings are wound through each of the stator slots to define a radial winding stack therein, and wherein the nearest winding in the radial winding stack closest to the rotor assembly is smaller than the farthest winding in the radial winding stack farthest from the rotor assembly.

[0030] Option 11. The motor according to Option 10, wherein the nearest winding has a first radius or thickness, the first radius or thickness being approximately half the second radius or thickness of the farthest winding.

[0031] Option 12. The motor according to Option 11, wherein the farthest winding has a rectangular axial cross-section and the nearest winding has a square axial cross-section.

[0032] Option 13. The motor according to Option 11, wherein the nearest winding comprises a plurality of mutually parallel inner windings that are adjacent to each other, and wherein the farthest winding comprises a plurality of mutually parallel outer windings that are adjacent to each other and radially spaced from the inner windings.

[0033] Option 14. The motor according to Option 1, wherein each of the stator teeth includes a neck tooth integrally formed as a single piece with the tooth head.

[0034] Option 15. A motor vehicle, comprising:

[0035] Body;

[0036] Multiple drive wheels, which are mounted to the vehicle body; and

[0037] A traction motor, mounted to the vehicle body and operable to drive one or more of the drive wheels to propel the motor vehicle, the traction motor comprising:

[0038] Motor housing;

[0039] A rotor assembly rotatably attached to the motor housing, the rotor assembly including a cylindrical rotor core, a rotor shaft, and a plurality of permanent magnets, the cylindrical rotor core defining a plurality of rotor slots therethrough, the rotor shaft being attached to the rotor core and projecting axially from the rotor core, the plurality of permanent magnets being nested within the rotor slots of the rotor core; and

[0040] A stator assembly, concentric with and spaced apart from the rotor assembly by an air gap, includes a cylindrical stator core defining a plurality of circumferentially spaced stator slots, a plurality of radially aligned stator teeth separating the stator slots, and a plurality of electromagnetic windings wound through each of the stator slots. Each of the stator teeth has an elongated tooth body with a tooth head at a radial end of the tooth body. The tooth head has an axial cross-section with a trapezoidal crown integral with a rectangular tooth tip.

[0041] Option 16. A method for assembling an electric motor, the method comprising:

[0042] Receive the housing of the motor;

[0043] A rotor assembly is rotatably attached to the housing, the rotor assembly including a rotor core and a magnet mounted to the rotor core; and

[0044] A stator assembly is mounted coaxially with and spaced apart from the rotor assembly by an air gap. The stator assembly includes a stator core defining a plurality of circumferentially spaced stator slots, a plurality of radially aligned stator teeth that space the stator slots, and a plurality of electromagnetic windings located in the stator slots. Each of the stator teeth has an elongated tooth body with a tooth head at a radial end of the tooth body. The tooth head has an axial cross section with a trapezoidal crown integral with a rectangular tooth tip.

[0045] Option 17. The method according to Option 16, wherein the trapezoidal crown has an isosceles trapezoidal shape, the isosceles trapezoidal shape has a narrow edge parallel to the wide edge, the narrow edge facing the air gap.

[0046] Option 18. The method according to Option 17, wherein the stator core includes a cylindrical hub, the stator teeth protruding radially inward from the cylindrical hub, each of the teeth including a tooth neck attaching the tooth head to the cylindrical hub, and wherein the portion of the tooth neck adjacent to the tooth head has a neck width, the narrow edge and the wide edge have a narrow edge width and a wide edge width, respectively, both the narrow edge width and the wide edge width being wider than the neck width.

[0047] Option 19. The method according to Option 16, wherein a corresponding subset of the electromagnetic winding is wound through each of the stator slots, the nearest winding in the subset of windings closest to the rotor assembly is disposed on the trapezoidal crown of the adjacent stator tooth in the stator teeth, and wherein the nearest winding is at least a minimum spacing distance from the rotor assembly. D S And wherein, the minimum interval distance D S = (Z / A g ) ,in, A g Z is the air gap distance of the air gap, and Z is a constant of about 1.2 to 2.0.

[0048] Option 20. The method according to Option 16, wherein a plurality of electromagnetic windings in the electromagnetic windings are wound through each of the stator slots to define a radial winding stack in the stator slots, and wherein the nearest winding in the radial winding stack that is closest to the rotor assembly is smaller than the farthest winding in the radial winding stack that is farthest from the rotor assembly.

[0049] This summary is not intended to represent every embodiment or aspect of this disclosure. Rather, it provides only examples of some novel concepts and features set forth herein. The foregoing features and advantages, as well as other features and accompanying advantages, will become apparent when taken in conjunction with the accompanying drawings from the following detailed description of the illustrated examples and representative modes for implementing this disclosure. Furthermore, this disclosure expressly includes any and all combinations and sub-combinations of the elements and features presented above and below. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of a representative electric motor vehicle with a hybrid electric powertrain according to aspects of this disclosure, which employs an internal combustion engine and an electric motor / generator unit (MGU).

[0051] Figure 2 This is an end view of a representative AC permanent magnet (ACPM) motor employing a hairpin winding stator according to various aspects of this disclosure.

[0052] Figure 3 For example, it is used according to aspects of this disclosure. Figure 1 MGU or Figure 2 An enlarged view of a portion of a representative stator assembly of an ACPM motor, which features optimized stator tooth geometry and multi-specification stator conductors to provide reduced proximity effects and AC winding losses.

[0053] Figure 4 yes Figure 3 An enlarged illustration of a subset of the stator teeth.

[0054] This disclosure may have various modifications and alternatives, and some representative embodiments are illustrated by way of example in the accompanying drawings and will be described in detail herein. However, it should be understood that the novel aspects of this disclosure are not limited to the specific forms shown in the drawings listed above. Rather, this disclosure will cover all modifications, equivalents, combinations, sub-combinations, substitutions, groupings, and alternatives that fall within the scope of this disclosure, for example, as covered by the appended claims. Detailed Implementation

[0055] This disclosure allows for numerous different forms of embodiments. Representative embodiments of this disclosure are shown in the accompanying drawings and will be described in detail herein. It should be understood that these embodiments are provided as examples of the principles disclosed and not as limitations on the broad aspects of this disclosure. In this regard, elements and limitations described, for example, in the abstract, introduction (including the technical field and background), summary of the invention, and detailed description sections but not expressly set forth in the claims should not be incorporated, alone or jointly, by implication, inference, or otherwise into the claims.

[0056] For the purposes of this specific embodiment, unless specifically waived: the singular includes the plural, and vice versa; the words “and” or “or” should be both connective and disjoint; the words “any” and “all” should both mean “any and all”; and the words “including,” “contains,” “comprising,” “having,” etc., should each mean “including but not limited to.” Furthermore, approximate words, such as, for example, “about,” “almost,” “substantially,” “largely,” “approximately,” etc., may each be used herein in the sense of, for example, “in,” “nearly,” or “within 0-5% of,” or “within acceptable manufacturing tolerances,” or any logical combination thereof. Finally, directional adjectives and adverbs, such as front, back, inside, outside, right, left, vertical, horizontal, up, down, front, back, left, right, etc., may be relative to the motor vehicle, such as the forward driving direction of the motor vehicle when the vehicle is operatively oriented on a level driving surface.

[0057] Referring now to the accompanying drawings, in which the same reference numerals denote the same features in all views. Figure 1 A schematic diagram of a representative automobile is shown, generally designated 10, and depicted herein as a passenger vehicle with a parallel dual-clutch (P2) hybrid electric powertrain for the purposes of discussion. The automobile 10 shown (also referred to herein simply as a “motor vehicle” or “vehicle”) is merely an exemplary application that can practice the novel aspects of this disclosure. Similarly, the implementation of the inventive concept in a hybrid electric powertrain should also be understood as a representative implementation of the novel concept disclosed herein. Therefore, it will be understood that aspects of this disclosure can be applied to other powertrain architectures, can be incorporated into any logically related type of motor vehicle, and can be used for both automotive and non-automotive applications, etc. Finally, only selected components of the motor vehicle and motor have been shown and will be described in more detail herein. However, the vehicles and apparatus discussed below may include numerous additional and alternative features, as well as other available peripheral components and hardware, for performing the various methods and functions of this disclosure.

[0058] Figure 1The diagram illustrates a representative vehicle powertrain system with a prime mover and an electric motor / generator unit (MGU) 14. The prime mover is represented herein by a restartable internal combustion engine (ICE) assembly 12. The MGU is driven to the drive shaft 15 of the final drive system 11 via a multi-speed automatic transmission 16. The ICE assembly 12 typically transmits power to the input side of the transmission 16 via torque through the engine crankshaft 13. Engine torque is first transmitted via the engine crankshaft 13, which serves as the engine torque output component, to rotate the engine-driven torsional damper assembly 26, and simultaneously via the torsional damper assembly 26 to the engine disconnector 28. When operatively engaged, the engine disconnector 28 transmits the torque received from the ICE assembly 12 to the input structure of the torque converter (TC) assembly 18 via the damper 26. As the name suggests, the engine disconnector 28 can be selectively disconnected to operatively separate the ICE assembly 12 from the electric motor 14, the torque converter (TC) assembly 18, and the transmission 16.

[0059] In order to promote Figure 1 In the hybrid vehicle 10, the transmission 16 is adapted to receive, selectively manipulate, and distribute traction power output from the internal combustion engine (ICE) assembly 12 and the electric motor 14 to the vehicle's final drive system 11. The final drive system 11 is represented herein by a drive shaft 15, a rear differential 22, and a pair of rear drive wheels 20. Figure 1 The powertrain 16 and torque converter (TC) assembly 18 may share a common transmission oil pan or "sump" 32 for supplying hydraulic fluid. A common transmission pump 34 provides sufficient hydraulic pressure to selectively actuate the transmission 16, the torque converter (TC) assembly 18, and, in some embodiments, the hydraulic actuation elements of the engine disconnect device 28.

[0060] The internal combustion engine (ICE) assembly 12 operates to propel the vehicle 10 independently of the traction electric motor 14, for example in an "engine-only" operating mode, or in cooperation with the electric motor 14, for example in a "vehicle start" or "electric motor boost" operating mode. Figure 1 In the example shown, the internal combustion engine (ICE) component 12 can be any available or later-developed engine, such as a compression-ignition diesel engine or a spark-ignition gasoline or flexible fuel engine, which is readily adapted to typically provide its available power output in revolutions per minute (RPM). Although in Figure 1 Although not explicitly described, it should be understood that the final drive system 11 can adopt any available configuration, including front-wheel drive (FWD) layout, rear-wheel drive (RWD) layout, four-wheel drive (4WD) layout, all-wheel drive (AWD) layout, six-by-four (6×4) layout, etc.

[0061] Figure 1 Also shown is an electric motor / generator unit (“motor”) 14, operably connected via a rotor shaft, motor support hub, or belt (collectively referred to as motor output member 29) to a hydraulic torque converter (TC) assembly 18. The torque converter (TC) assembly 18, in turn, drivesly connects the motor 14 to the input shaft 17 of a transmission 16. The motor / generator unit 14 comprises an annular stator assembly 21 surrounding and concentric with a cylindrical rotor assembly 23. Electricity is supplied to the stator assembly 21 via a high-voltage electrical system comprising electrical conductors / cables 27 passing through the motor housing via a suitable sealed and insulated feedthrough (not shown). Conversely, electricity can be supplied from the motor / generator unit 14 to an onboard traction battery pack 30, for example, through regenerative braking. The operation of any of the powertrain components shown can be controlled by an onboard or remote vehicle controller or a network of controllers and devices. Figure 1 The programmable electronic control unit (ECU) 25 is represented in the middle.

[0062] The powertrain 16 may use a differential gear assembly 24 to achieve selectively variable torque and speed ratios between the input shaft 17 and the output shaft 19 of the transmission, respectively. One form of differential gear assembly is a planetary gear assembly, which offers the advantages of compactness and different torque and speed ratios between the components of the planetary gear assembly. Conventionally, hydraulically actuated torque-building devices, such as clutches and brakes, can selectively engage to actuate the aforementioned gear elements for establishing the desired forward and reverse speed ratios between the input shaft 17 and the output shaft 19 of the transmission. Although conceived as a 6-speed or 8-speed automatic transmission, the powertrain 16 may optionally employ other functionally suitable configurations, including continuously variable transmission (CVT) architectures, automatic manual transmissions, etc.

[0063] Figure 1The hydraulic torque converter (TC) assembly 18 operates as a fluid coupler for operatively connecting the internal combustion engine (ICE) assembly 12 and the electric motor 14 to the internal planetary gear assembly 24 of the power transmission 16. A bladed impeller 36 facing a bladed turbine 38 is disposed within the internal fluid chamber of the torque converter (TC) assembly 18. The impeller 36 and turbine 38 are juxtaposed in series power flow fluid communication, with a TC stator (not shown) positioned between the impeller 36 and turbine 38 to selectively alter the fluid flow between them. Torque from the engine torque output member (engine crankshaft 13) and the electric motor output member 29, transmitted to the transmission 16 via the torque converter (TC) assembly 18, can be excited by the agitation of a hydraulic fluid, such as transmission fluid, within the internal fluid chamber of the TC caused by the rotation of the impeller and turbine blades 36, 38. To protect these components, the torque converter (TC) assembly 18 is configured with a TC pump housing, which is primarily defined by a transmission-side pump housing 40 fixedly attached to the engine-side pump cover 42, thereby forming a working hydraulic fluid chamber between the transmission-side pump housing and the engine-side pump cover.

[0064] Figure 2 An example of a motor 114 is shown, which employs a magnetic material to exchange electromagnetic forces with conductive windings to convert electrical energy into mechanical energy, and vice versa. Motor 114 has a multiphase, hairpin-wound stator assembly 116 nested within the motor and surrounding a synchronous reluctance rotor assembly 118 with PM bearings. While similar applications are possible in both automotive and non-automotive settings, Figure 2 The motor 114 is particularly suitable for use in hybrid electric powertrains as a traction motor (e.g., an internal combustion engine (ICE) assembly 12) that has an engine (e.g., an internal combustion engine (ICE) assembly 12). Figure 1 The motor 114 can operate in at least engine-start mode, regenerative charging mode, and torque-assisted mode. The motor 114 can be designed to achieve: relatively high efficiency, such as at least about 85% efficiency over a calibrated output power and speed range; relatively high power density (e.g., greater than about 1500 watts / liter) and torque density (e.g., greater than about 5 Nm / liter); a relatively wide peak power range (e.g., about 4 to 6 kilowatts or greater); a maximum speed of at least about 18,000 rpm; reduced mass and inertia (e.g., for rapid dynamic response to user output demands); and suitability for a relatively small package size. The motor 114 can employ numerous alternative motor architectures to meet similar and alternative operating parameters.

[0065] Continue to refer to Figure 2The stator assembly 116 is coaxial with and surrounds the rotor assembly 118, while maintaining a small air gap 115 between them. According to the example shown, the air gap 115 may be no less than about 0.2 mm and no more than about 1.0 mm, for example, in order to maximize power output and minimize the number of permanent magnets 120 carried by the rotor assembly 118 to provide the desired power output. Figure 2 Representative stator assembly 116 and rotor assembly 118 are concentrically aligned about the longitudinal central axis A of motor 114. Both assemblies are depicted as truncated straight cylinders with a generally annular shape. Stator assembly 116 has a hollow stator core 126 with a central hole 122 in which the rotor assembly 118 is nested. Rotor assembly 118 has a hollow rotor core 128, which is, for example, keyed, splined, welded to the motor shaft, etc. (e.g., Figure 1 The motor output component 29). It should be understood that the protective housing (in Figure 1 (Schematally shown) The rotor and rotor output shaft of the motor 114 can be rotatably supported around the outer periphery of the stator assembly 116.

[0066] Figure 2 The rotor assembly 118 is manufactured having a rotor core or body 128 for supporting a plurality of permanent magnets 120 (24 PM in the illustrated example) circumferentially spaced around a central bore 124. Specifically, the rotor core 128 is stamped, precision-machined, and assembled with a plurality of rotor slots 130 arranged in radially spaced blocking layers (e.g., four different blocking layers). A first blocking layer 130A of the slot 130 may be positioned closest to the inner periphery of the rotor core 128, while a fourth blocking layer 130D of the slot 130 may be positioned furthest from the inner periphery of the rotor body than the other blocking layers. A second blocking layer 130B may be radially inserted between the first and third blocking layers 130A, 130C, while a third blocking layer 130C may be radially inserted between the second and fourth blocking layers 130B, 130D. In at least some embodiments, only selected blocking layers (e.g., first and third blocking layers 130A, 130C) may accommodate the magnet 120, while other selected blocking layers (e.g., second and fourth blocking layers 130B, 130D) do not accommodate the magnet 120 and thus serve as magnetic flux barriers. In other embodiments, only one or all of the blocking layers may include slots in which permanent magnets are stored. The rotor core 128 may be made of a metal disc-shaped laminate comprising a high-grade steel material, the laminations being stacked and bonded together to keep high-speed rotational stress within predetermined limits.

[0067] Figure 2The stator assembly 116 is manufactured having a stator core or body 126 having a plurality of radially aligned, axially elongated, and circumferentially spaced stator slots 132 (e.g., a total of 60 slots in the illustrated example). Each stator slot 132 extends longitudinally through the stator core 126 parallel to the axis of rotation A of the motor 114. The stator slots 132 accommodate complementary leads of conductive multiphase stator windings 134. The stator windings 134—also referred to herein as “hairpin windings”—can be grouped into different groups, each group capable of carrying the same number of current-carrying phases, such as three, five, six, or seven phases. Furthermore, the stator windings 134 may extend axially beyond the longitudinal ends of the stator core 126. The ratio of the outer diameter of the stator core 126 to its axial length may be not less than 1.5 and not greater than 3.5, for example, to meet the packaging space constraints of the desired application of the motor 114, such as… Figure 1 The vehicle's powertrain.

[0068] For ease of manufacture and to increase cost savings, it may be desirable for all permanent magnets 120 to share the same rectangular polyhedral shape. However, any one or more or all PM bodies can take on a multitude of shapes and sizes, including other polyhedral magnets, toroidal (ring-shaped) magnets, bread-block-shaped magnets, curved tile-shaped magnets, etc. In a non-limiting example, each permanent magnet 120 may have a thickness of approximately 1.5 mm to 2.5 mm to fit within a slot 130 with complementary dimensions. The total mass of the magnet material used in the motor 114 (i.e., the mass of all magnets 120) may be approximately 150 grams to approximately 250 grams. The permanent magnets 120 of the motor 114 may all be made of the same material, such as neodymium iron boron (NdFeB); alternatively, the magnets 120 may be made of different materials, such as any combination of samarium cobalt (SmCo), alnico (AlNiCo), or rare earth magnet materials.

[0069] Similar to Figure 2 The permanent magnet 120 may ideally allow all multiphase stator windings 134 to share the same construction, including material composition, manufacturing method, and final geometry. Each stator winding 134 may be made of a monolithic strip conductor formed into a U-shaped geometry defined by a pair of hairpin-shaped feet protruding from opposite ends of a hairpin crown. The monolithic strip conductor of the hairpin may have a rectangular cross-section, a square cross-section, a circular cross-section, or any other suitable shape. The hairpin feet are inserted into slots 132 of the stator core 126, with each foot extending through a different stator slot 132, such that the hairpin crown (or “end turn”) extends over several of the stator slots 132 (e.g., each crown may extend across three or more slots). These hairpin windings 134 may be inserted in a “staggered” or “interleaved” pattern relative to adjacent hairpins. Any given stator slot 132 may include multiple hairpin feet (e.g., in…) Figure 2(Four are shown in the example shown). Once all the hairpin stator windings 134 are inserted into the slots 132 of the stator core 126, the ends of the hairpin leads extending from the longitudinal end of the stator core 126 are bent. Then, each winding 134 is electrically connected.

[0070] During operation of the motor 114, such as in regenerative charging mode, the rotor assembly 118 rotates via the rotor output shaft, while the stator assembly 116 remains relatively stationary. In this way, the permanent magnet 120 moves through the multiphase stator winding 134; the magnetic field emitted by the permanent magnet 120 induces a current in the winding 134 through electromagnetic induction. This induced current can be used to power a load (e.g., for...). Figure 1 (The traction battery pack 30 is recharged). Conversely, during operation of the motor 114, such as in engine start mode, EV motor drive mode, or torque assist mode, current is supplied to the stator windings 134 through a suitable power source (e.g., the traction battery pack 30). The supplied current through the multiphase stator windings 134 generates a magnetic field at the stator teeth 136. The magnetic field output from the stator teeth 136 interacts with the permanent magnets 120 in the rotor assembly 118, causing the rotor core 128 and the attached shaft to rotate in unison to generate rotational driving force.

[0071] Next, turn to Figure 3 and Figure 4 An example of a motor 214 with a stator assembly 216 is shown, which has optimized stator tooth geometry and variable-sized conductor layers, for example, to reduce AC winding losses and proximity effects. Although the appearance differs, it is conceivable that the above reference... Figure 1 Traction motor / generator unit 14 and Figure 2 Any features and selections described in the multiphase ACPM motor 114 can be combined individually or in any combination with Figure 3 and Figure 4 In the radial flux motor 214, and vice versa. As a non-restrictive overlap point, the hairpin-wound stator assembly 216 is coaxially aligned with the magnet-supported rotor assembly 218 and separated by an air gap 215. Similar to Figure 2 Stator assembly 116, Figure 3 The stator assembly 216 comprises a flux-permeable cylindrical stator core 226 having a plurality of circumferentially spaced stator slots 232, the stator slots being radially aligned with and extending axially through the core 226. A plurality of electromagnetic conductors or windings 234 are wound through these stator slots 232, which may have the properties of hairpin windings 134, coil windings, or other similar suitable electrical conductors. Figure 3 Motor 214 and its Figure 1 and Figure 2Exemplary demarcation points between the corresponding elements (such as their tooth heads, stator slots, and conductor layer designs) will be described in detail below.

[0072] Elongated stator teeth 236 intersect and separate the stator core slots 232, these stator teeth being circumferentially spaced from each other and radially aligned relative to the stator core 226. These stator teeth 236 can be seen from the cylindrical hub portion of the stator core 226 (…). Figure 2 The inner diameter (ID) surface of the stator teeth 238 protrudes radially inward and is equidistantly spaced around the rotor assembly 218. For design simplicity and ease of manufacture, it may be desirable that all stator teeth 236 be substantially identical in structure (within acceptable manufacturing tolerances). Each flux-transmitting stator tooth 236 is formed with a stator tooth body 221, which consists of a tooth neck 223 and a tooth head 225, as shown in the figure. Figure 4 The best visible part is the tooth neck 223. The outermost radial end of the tooth neck 223 is integrally or otherwise attached to the ID surface of the cylindrical hub, while the innermost radial end of the tooth neck 223 is integrally or otherwise attached to the tooth head 225. The cylindrical hub 138 is a rigid annular structure that defines the body and circumferential periphery of the stator core 226. Consistent with the example shown, the tooth neck 223, tooth head 225, and cylindrical hub are integrally formed to define a single-piece integral structure. For a laminated stator structure, the teeth are multi-piece segments laminated together, and each laminated tooth neck 223, head 225, and hub portion is integrally formed with each other.

[0073] To help minimize ohmic copper losses in the conductive winding 234, and simultaneously reduce the AC proximity effect experienced by the winding 234 closest to the rotor assembly 218, especially at high operating speeds, the stator tooth tips 225 are designed to minimize stator flux leakage through the tooth tips, while maintaining a design comparable to that of the winding 234 (e.g., Figure 2 Further away from the air gap 215. According to an aspect of the disclosed embodiment, the tooth head 225 may share a common axial cross section—cut along a plane orthogonal to the axis of rotation A—having a trapezoidal crown 227 portion integral with the rectangular tooth tip 229 portion. Figure 4The trapezoidal tooth crown 227 shown has an isosceles trapezoidal shape, with its narrow edge (indicated by hidden line 231) smaller than and parallel to its wide edge (indicated by hidden line 233). The wide edge 233 may define the outermost radial end of the stator tooth 236, while the narrow edge 231 may define the innermost radial end of the trapezoidal tooth crown 227, which is closest to and faces the air gap 215. The opposite ends of the wide edge 233 of the trapezoidal tooth crown 227 may terminate at a fillet 235 (e.g., rounded with a radius of approximately 0.2 mm). Similarly, the opposite ends of the narrow edge 231 may terminate at and intersect with the protruding fillet 237 of the adjacent rectangular tooth tip 229. The shape and size of the rectangular tooth tip 229 may be configured to maintain a narrow stator slot gap 239, which helps to minimize flux leakage through the gap, thereby optimizing torque pulsation.

[0074] In order to provide a stator slot with a roughly uniform circumferential width W SS The stator slot 232, the neck 223 portion of each stator tooth body 221 may have a variable circumferential neck width W that varies along the diameter length of the stator tooth 236. TN In particular, Figure 4 Neck width W TN It gradually tapers, and therefore its dimensions gradually decrease from the outermost radial end to the innermost radial end of the neck 223, resulting in a groove width W. SS Fixed along the diameter length of each stator slot 232. For the optimized tooth geometry, the portion of the tooth neck 223 immediately adjacent to and abutting the tooth head 225 has a neck width W. TN' It extends circumferentially relative to the stator core 226 (e.g., in...). Figure 4 (From left to right). The narrow edge 231 of crown 227 has a corresponding narrow edge width W. NE Furthermore, the wide edge 233 has a wider width than the narrow edge W. NE Width of wide edge W WE The narrow edge width W of crown 227 NE and wide edge width W WE Both can be approximately equal to the neck width W. TN' Or, as shown in the figure, wider than the neck width W TN' Similarly, the cusp width W of the rectangular cusp 229 of the crown TT It can be compared to the width of the neck (W) TN' Narrow edge width W NE and wide edge width W WE Width.

[0075] To minimize the AC proximity effect and any resulting internal resistance to the current flowing through the stator conductors, adjacent stator teeth of the stator core 226 cooperatively hold the electromagnetic winding 234 in its respective stator slots 232, particularly those closest to the air gap 215, at a predetermined minimum radial distance from the rotor assembly 218. Figure 3 In the best visible configuration, for example, each subset of the electromagnetic windings 234 housed in a particular stator slot 232 has the "nearest" winding 234' closest to the air gap 215 and the rotor assembly 218. Each of these windings 234' is positioned abutting against the trapezoidal crown 227 of the adjacent stator tooth 236 and supported on a support shoulder defined by a protruding section of a wide edge 233. The nearest winding 234', and thus all the electromagnetic windings 234 in the stator slot 232, are spaced apart from the rotor assembly 218 by at least a minimum spacing distance. D S The minimum interval distance D S It can be calculated as ( Z / A g ),in A g Z is the air gap distance of 215, and Z is a constant from approximately 1.2 to approximately 2.0. In a non-limiting example, the air gap distance is... A g It can be equal to approximately 0.60 mm to approximately 0.80 mm, or in a specific example, approximately 0.68 mm, making the spacing distance... D S It is equal to approximately 1.5 mm to approximately 3.3 mm, or in a specific example, at least approximately 2.6 mm.

[0076] Continue to refer to Figure 3 and Figure 4 The radial flux motor 214 presented herein has a corresponding subset of electromagnetic windings 234 wound through each of the stator slots 232. According to Figure 3 In a non-limiting example, the leads of eight (8) electromagnetic hairpin windings 234 are wound through each stator slot 232 and arranged in a radially stacked configuration, wherein the winding leads are enclosed parallel to each other and radially spaced apart. One or more of the radially stacked windings 234 closest to the rotor assembly 218 are smaller than one or more of the windings furthest from the rotor assembly 218. Specifically, the four windings 234 closest to the rotor assembly 218 (in...) Figure 3 The windings (commonly referred to as 241) have a first radius / thickness that is approximately equal to the four windings 234 furthest from the rotor assembly 218. Figure 3The central section is collectively represented as half the second radius / thickness of 243. As shown, the four furthest windings 243 each have a rectangular axial cross-section, while the four closest windings 241 each have a square axial cross-section. It should be understood that each stator slot 232 may contain more or fewer than eight electromagnetic windings 234. Furthermore, the windings 234 may employ alternative cross-sectional geometries, including those described above. Figure 2 The ones mentioned in the discussion may include more than or less than four farthest and four nearest windings, and may combine more than two different conductor sizes.

[0077] Various aspects of this disclosure have been described in detail with reference to the illustrated embodiments; however, those skilled in the art will recognize that many modifications can be made thereto without departing from the scope of this disclosure. This disclosure is not limited to the precise construction and composition disclosed herein; any and all modifications, alterations, and variations apparent from the foregoing description are within the scope of this disclosure as defined by the appended claims. Furthermore, the inventive concept explicitly includes any and all combinations and sub-combinations of the foregoing elements and features.

Claims

1. An electric motor, comprising: case; A rotor assembly rotatably attached to the housing, the rotor assembly including a rotor core and a magnet mounted to the rotor core; as well as A stator assembly, coaxial with and spaced apart from the rotor assembly by an air gap, includes a stator core, a plurality of radially aligned stator teeth, and a plurality of electromagnetic windings. The stator core defines a plurality of circumferentially spaced stator slots, the plurality of radially aligned stator teeth space the stator slots, and the plurality of electromagnetic windings are located in the stator slots. Each stator tooth has an elongated tooth body, the elongated tooth body having a tooth head at a radial end of the tooth body, the tooth head having an axial cross-section having a trapezoidal tooth crown integral with a rectangular tooth tip, wherein the trapezoidal tooth crown has an isosceles trapezoidal shape, the isosceles trapezoidal shape having a narrow edge, a wide edge parallel to the narrow edge and wider than the narrow edge, and a pair of angled edges inclined to the wide edge and the narrow edge and connecting the wide edge and the narrow edge, the narrow edge facing the air gap.

2. The motor according to claim 1, wherein, The rectangular tooth tip is wider than the wide and narrow edges of the trapezoidal tooth crown.

3. The motor according to claim 1, wherein, The opposite ends of the wide edge of the trapezoidal crown include rounded corners.

4. The motor according to claim 1, wherein, The opposite ends of the narrow edge of the trapezoidal crown intersect with the rounded corners of the adjacent rectangular tooth tips.

5. The motor according to claim 1, wherein, The stator core includes a cylindrical hub, and the stator teeth project radially inward from the inner diameter surface of the cylindrical hub, each of the teeth including a tooth head that attaches to the neck of the cylindrical hub.

6. The motor according to claim 5, wherein, The portion of the tooth neck adjacent to the tooth head has a neck width, and wherein the narrow edge and the wide edge of the trapezoidal crown have a narrow edge width and a wide edge width, respectively, both of which are wider than the neck width.

7. The motor according to claim 6, wherein, The rectangular tooth tip has a tip width that is wider than the neck width, the narrow edge width, and the wide edge width.

8. The motor according to claim 1, wherein, The respective subsets of the electromagnetic windings are wound through each of the stator slots, and wherein the nearest winding in the subset of the electromagnetic windings to the rotor assembly is disposed on the trapezoidal crown of the adjacent stator tooth in the stator tooth.

9. The motor according to claim 8, wherein, The nearest winding is spaced apart from the rotor assembly by at least a minimum distance. D S And wherein, the minimum interval distance D S = (Z / A g ) ,in, A g Z is the air gap distance of the air gap, and Z is a constant from 1.2 to 2.

0.

10. The motor according to claim 1, wherein, The plurality of electromagnetic windings in the electromagnetic windings are wound through each of the stator slots to define a radial winding stack therein, wherein the nearest winding in the radial winding stack that is closest to the rotor assembly is smaller than the farthest winding in the radial winding stack that is farthest from the rotor assembly.

11. The motor according to claim 10, wherein, The nearest winding has a first radius or thickness, which is half the second radius or thickness of the farthest winding.

12. The motor according to claim 11, wherein, The farthest winding has a rectangular axial cross-section, and the nearest winding has a square axial cross-section.

13. The motor according to claim 11, wherein, The nearest winding includes a plurality of mutually parallel inner windings that are adjacent to each other, and wherein the farthest winding includes a plurality of mutually parallel outer windings that are adjacent to each other and radially spaced from the inner windings.

14. The motor according to claim 1, wherein, Each of the stator teeth includes a neck that is integrally formed with the tooth head as a single-piece structure.

15. A motor vehicle, comprising: Body; Multiple drive wheels are mounted to the vehicle body; as well as A traction motor, mounted to the vehicle body and operable to drive one or more of the drive wheels to propel the motor vehicle, the traction motor comprising: Motor housing; A rotor assembly rotatably attached to the motor housing, the rotor assembly including a cylindrical rotor core, a rotor shaft, and a plurality of permanent magnets, the cylindrical rotor core defining a plurality of rotor slots therethrough, the rotor shaft being attached to the rotor core and projecting axially from the rotor core, the plurality of permanent magnets being nested within the rotor slots of the rotor core; and A stator assembly, concentric with and spaced apart from the rotor assembly by an air gap, includes a cylindrical stator core defining a plurality of circumferentially spaced stator slots, a plurality of radially aligned stator teeth separating the stator slots, and a plurality of electromagnetic windings wound through each of the stator slots. Each of the stator teeth has an elongated tooth body with a tooth head at a radial end of the tooth body. The tooth head has an axial cross-section with a trapezoidal crown integral with a rectangular tooth tip. The trapezoidal crown has an isosceles trapezoidal shape with a narrow edge parallel to a wide edge facing the air gap.

16. A method for assembling an electric motor, the method comprising: Receive the housing of the motor; The rotor assembly is rotatably attached to the housing, the rotor assembly including a rotor core and a magnet mounted to the rotor core; as well as A stator assembly is mounted coaxially with and spaced apart from the rotor assembly via an air gap. The stator assembly includes a stator core defining a plurality of circumferentially spaced stator slots, a plurality of radially aligned stator teeth that space the stator slots, and a plurality of electromagnetic windings located in the stator slots. Each of the stator teeth has an elongated tooth body with a tooth head at a radial end of the tooth body. The tooth head has an axial cross-section with a trapezoidal crown integral with a rectangular tooth tip. The trapezoidal crown has an isosceles trapezoidal shape with a narrow edge parallel to a wide edge facing the air gap.

17. The method according to claim 16, wherein, The rectangular tooth tip is wider than the wide and narrow edges of the trapezoidal tooth crown.

18. The method according to claim 16, wherein, The stator core includes a cylindrical hub, stator teeth protruding radially inward from the cylindrical hub, each of the teeth including a tooth head attaching to the cylindrical hub, and wherein the portion of the tooth neck adjacent to the tooth head has a neck width, the narrow edge and the wide edge having a narrow edge width and a wide edge width, respectively, both the narrow edge width and the wide edge width being wider than the neck width.

19. The method of claim 16, wherein, A corresponding subset of the electromagnetic windings is wound through each of the stator slots, and the nearest winding in the subset of windings to the rotor assembly is disposed on the trapezoidal crown of the adjacent stator tooth in the stator tooth, wherein the nearest winding is at least a minimum spacing distance from the rotor assembly. D S And wherein, the minimum interval distance D S = (Z / A g ) ,in, A g Z is the air gap distance of the air gap, and Z is a constant from 1.2 to 2.

0.

20. The method of claim 16, wherein, The plurality of electromagnetic windings in the electromagnetic windings are wound through each of the stator slots to define a radial winding stack in the stator slots, wherein the nearest winding in the radial winding stack that is closest to the rotor assembly is smaller than the farthest winding in the radial winding stack that is farthest from the rotor assembly.

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