Winding slot vapor chambers and heat tubes with end cap heat sinks for electric machines

Abstract

Electric machine (78, 210, 310) comprising: a housing (302); a stator assembly (216, 316) with a stator core (246, 320) attached to the housing (302) and an electromagnetic stator winding (214A, 214B, 214C, 326) mounted in a stator slot (321) of the stator core (246, 320); a rotor assembly (218, 318) with a rotor core (248, 322) rotatably attached to the housing (302) adjacent to the stator assembly (216, 316), and an electromagnetic rotor winding (234, 328) mounted in a rotor slot (323) of the rotor core (248, 322) and configured to be magnetically connected to the stator winding (214A, 214C ... 214B, 214C, 326) fits together;a heat pipe (340) mounted in the rotor slot (323) next to the rotor winding (234, 328) and projecting axially from an axial end of the rotor core (248, 322), wherein the heat pipe (340) is configured to passively draw thermal energy from the rotor winding (234, 328) and carry the thermal energy out of the rotor core (248, 322); further comprising a rotor end cap (350, 352) attached to the axial end of the rotor core (248, 322) and bearing against a longitudinal end of the heat pipe (340) to absorb the thermal energy transferred from the rotor core (248, 322); wherein the rotor end cap (350, 352) has a heat pipe cavity (351, 353) extending into an axial surface of the rotor end cap (350, 352) is embedded and in which the longitudinal end of the heat pipe (340) is embedded;wherein the rotor end cap (350, 352) has a plurality of end cap ribs (354, 356) projecting away from the rotor core (248, 322) and configured to dissipate the extracted heat energy transferred from the rotor core (248, 322) and absorbed by the rotor end cap (350, 352).

Description

introduction The present disclosure relates generally to electrical machines. More specifically, aspects of this disclosure relate to thermal management systems for regulating the operating temperatures of separately excited motor assemblies (SEMs). Today's production vehicles, such as the modern automobile, are originally equipped with a powertrain that propels the vehicle and supplies its onboard electronics. In automotive applications, for example, the powertrain typically consists of a primary drive motor that transmits the drive torque to the vehicle's drive system (e.g., differential, axles, cam modules, wheels, etc.) via an automatic or manual transmission. Historically, automobiles were powered by internal combustion engines (ICEs) due to their easy availability, relatively low weight, and overall efficiency. These engines include compression-ignition (CI) diesel engines, spark-ignition (SI) gasoline engines, two-, four-, and six-stroke engines, and rotary engines, to name just a few.Hybrid electric and fully electric vehicles (collectively referred to as "electrically powered vehicles"), on the other hand, use alternative energy sources to power the vehicle, thus minimizing or eliminating dependence on a fossil fuel-based engine for traction. A full-electric vehicle (FEV) – colloquially referred to as an "electric car" – is a vehicle configuration with an electric drive system in which the internal combustion engine and its associated peripheral powertrain components are completely eliminated, and instead a rechargeable energy storage system (RESS) and a traction motor are used to propel the vehicle. The engine assembly, fuel supply system, and exhaust system of a combustion engine vehicle are replaced in a battery-powered FEV by one or more traction motors, rechargeable battery cells, and cooling and charging equipment. Hybrid-electric vehicle (HEV) powertrains, on the other hand, utilize multiple traction sources to propel the vehicle, typically employing an internal combustion engine in conjunction with a battery- or fuel cell-powered traction motor.Since electric vehicles are able to draw their power from sources other than the engine, HEV engines can be switched off completely or partially while the vehicle is driven by the electric motor(s). US 5,140,204 A describes heat tubes for cooling the pole windings of salient-pole machines. The heat tubes have predetermined configurations and are positioned within the wedges and wedge supports to hold the rotor field windings in place. They efficiently collect the heat generated along the length of the rotor field windings and the rotor surface and transport it to the rotor ends, where it is transferred to a cooling medium such as a gas or a spray liquid. The heat is transferred to a volatile fluid, causing the fluid to transition from a liquid phase to a vapor phase. The vapor then flows at high velocity to a condenser section located beyond the axial length of the rotor field windings, where the heat is transferred from the volatile fluid to the cooling medium. DE 10 2022 122 605 A1 describes an electric machine comprising a stator and a rotor, the rotor including a shaft that is at least partially hollow for guiding oil and at least one rotor lamination stack in which at least one magnet or at least one winding is arranged. At least one heat pipe or at least one heat conductor is arranged in the rotor lamination stack, which has an evaporator section located inside the rotor and at least one capacitor section projecting from the rotor. Several radial bores are arranged in the shaft such that oil exits the rotating shaft through the radial bores and is guided, at least by centrifugal force, directly or indirectly to the at least one capacitor section for cooling the rotor. DE 102 58 778 A1 describes an electric machine with a stator and a rotor, which have heat sources to be cooled, in particular windings, laminated cores, winding heads, wherein cooling is carried out by heat pipes. US Patent 2022 / 0239197A1 describes a cooling structure for an electric motor. The cooling structure comprises a shaft, a rotor located on the outer circumference of the shaft, a stator located on the outer circumference of the rotor, a magnet held by the rotor, a coolant passage formed on the inner surface of the magnet in a radial direction along the shaft, and a heat pipe located between the coolant passage and the magnet. The heat pipe comprises a first tubular section extending radially along the shaft from one side of the coolant passage to one side of the magnet, and a second tubular section connecting to one end of the first tubular section on the magnet side and extending axially along the shaft. DE 20 52 839 A describes an arrangement for cooling the rotor cage of electric asynchronous machines, wherein the cage bars and the short-circuit rings of the asynchronous machine are integrally designed as heat tubes. Description The invention is defined by the claims. A traction motor is an electric machine that converts electrical energy into mechanical rotational energy to propel a vehicle, such as FEVs and HEVs. Many traction motors contain a fixed stator carrying multiphase electromagnetic windings, such as copper hairpin or I-pin rods, and a rotating rotor carrying an arranged pattern of magnets, such as core-mounted permanent magnets (PM) or electromagnetic armature windings, such as core-mounted copper coils. Traction motors can be categorized as alternating current (AC) or direct current (DC), brushed or brushless, rotary or linear, and radial or axial flux. In internal rotor designs with radial flux, the rotor can be nested coaxially within the stator, while in rotary designs with axial flux, the rotor and stator can lie side by side as opposing, coaxial plates.The rotational excitation of the rotor assembly can be achieved by a magnetic field generated by the current flow through multi-phase AC stator windings; this magnetic field emitted by the stator interacts with a counter-magnetic field generated by permanent magnets or DC armature coils located in the rotor. The rotor assemblies of many modern traction motors consist of a rotor core made of thin ferromagnetic disks stacked and laminated together to form a cylindrical body. Each rotor disk has several openings which, when aligned with the openings of adjacent disks, form rotor slots extending axially along the length of the rotor core. Permanent magnet or electrically excited magnetic elements, such as PM rods or copper coils, are inserted into these rotor slots and attached to the rotor core. Unlike permanent magnet motors, where the rotor assembly carries internal or surface-mounted magnets, a separately excited motor (SEM) is generally characterized by armature windings in the rotor that interact electromagnetically with field windings in the stator to convert electrical energy into mechanical energy.The rotor core can be mounted on a motor shaft to output the drive-generating motor torque produced by the motor or to introduce the power-generating regenerative torque received by the motor. During operation of a traction motor, the internal electrical and electromagnetic hardware can generate a considerable amount of heat, for example, due to winding, friction, and hysteresis losses. An integrated motor cooling system can be used to prevent undesirable overheating conditions in the motor. Active thermal management (ATM) systems, for example, use a dedicated controller or special control module to regulate the operation of a cooling circuit that circulates coolant through the heat-generating motor components. In indirect liquid cooling systems, a heat-transferring coolant circulates through a network of internal channels and pipes within the motor housing. In contrast, direct liquid cooling—or “liquid immersion cooling”—uses a heat-transferring coolant directly against the motor housing.: liquid immersion cooling (LIC) - parts of the engine are sprayed, sprinkled or immersed in a directly conductive, dielectric cooling fluid. This paper presents electrical machines with heat pipes and / or vapor chambers embedded in the winding slots and cooling elements integrated into the end cap, methods for manufacturing and operating such machines, and vehicles equipped with such machines. As a non-limiting example, a novel, separately excited motor design is described in which heat is dissipated from the rotor-supported windings by integrating heat pipes and / or vapor chambers into each rotor pole and anchoring the pipes / chambers in the winding bundles. The extracted heat can be transferred axially to the opposite axial ends of the rotor core and conducted into the larger heat sinks of the rotor end caps. The rotor end caps can be equipped with axial pin fins that dissipate the transferred heat into an internal coolant volume of the drive unit (DU) housing.Spray cooling can be used to dissipate heat from the pin fins and simultaneously transport the thermal energy out of the DU casing. Each heat pipe / vapor chamber can be embedded in an axial rotor slot and surrounded by the rotor windings. The axially projecting pin fins can be integrated into the rotor end caps to efficiently dissipate heat to the DU casing volume. End cap spray cooling and / or splash cooling can be used to increase the thermal conductivity of the end caps, thereby facilitating heat dissipation from the rotor windings. Among the associated advantages of at least some disclosed concepts are SEM architectures with reduced winding temperatures (e.g., at worst-case operating points, WCOP), resulting in improved motor efficiency and extended motor power limits (i.e., compared to similar IPM designs). Unlike complex shaft-fed ATM cooling concepts, which add significant cost, complexity, and points of failure to the system, the disclosed SEM designs use sealed heat pipes / vapor chambers and end-cap heat sinks to dissipate heat quickly and efficiently from the motor windings. Further advantages include SEM systems that eliminate the need for rare earth (RE) and heavy rare earth (HRE) materials, which are susceptible to price fluctuations and raw material shortages.In contrast to many conventional SEM solutions that operate with lower rotor field peak currents and limit the rotor field peaks to reduce motor temperatures, the disclosed SEM systems use both active and passive cooling functions to dissipate heat caused by copper losses from the windings, thus extending the SEM peak power limits. Aspects of this disclosure relate to vapor chambers and / or heat tubes embedded in winding slots for cooling the electromagnetic rotor and / or stator windings of electrical machines such as motors, generators, transformers, chokes, dynamometers, converters, etc. According to the invention, an electric machine comprises a protective outer casing, a stator assembly fixed to the casing, and a rotor assembly rotatably mounted on the casing adjacent to the stator assembly. The stator assembly comprises a stator core with at least one stator slot and at least one electromagnetic stator winding mounted in the stator slot(s). Similarly, the rotor assembly comprises a rotor core with at least one rotor slot and at least one electromagnetic rotor winding mounted in the rotor slot(s). At least one heat pipe is mounted in one, some, or all of the rotor slots adjacent to the rotor winding(s). The heat pipe(s) project axially from one or both opposite axial ends of the rotor core. Each heat pipe passively extracts heat energy from the rotor winding(s) and conducts the extracted heat energy out of the rotor core.The electric machine further comprises a rotor end cap, which is attached to the axial end of the rotor core and rests against a longitudinal end of the heat tube to absorb the thermal energy transferred from the rotor core. The rotor end cap has a heat tube cavity recessed into an axial surface of the rotor end cap, in which the longitudinal end of the heat tube is embedded. The rotor end cap has a plurality of end cap fins projecting away from the rotor core and configured to dissipate the extracted thermal energy transferred from the rotor core and absorbed by the rotor end cap. Other aspects of this disclosure relate to electric vehicles powered by SEM-type traction motors cooled by vapor chambers and / or heat pipes embedded in winding slots. As used herein, the terms "vehicle" and "motor vehicle" may be used interchangeably and synonymously to refer to any relevant vehicle platform, such as passenger vehicles (ICE, HEV, FEV, fuel cell, fully and partially autonomous vehicles, etc.), commercial vehicles, industrial vehicles, tracked vehicles, off-road vehicles, motorcycles, agricultural equipment, watercraft, aircraft, e-bikes, etc. By way of example, a motor vehicle comprises a vehicle body with a passenger compartment, multiple wheels mounted to the vehicle body (e.g., via corner modules coupled to a unibody or body-on-frame chassis), and other standard original equipment.For electric vehicle applications, the vehicle is equipped with a rechargeable energy storage system (RESS) (e.g., traction battery pack) and an electrified powertrain that uses one or more motor / generator units (MGUs) which operate alone (e.g., for FEV powertrains) or in conjunction with an internal combustion engine assembly (e.g., for HEV powertrains) to selectively drive one or more of the road wheels and thereby propel the vehicle. Continuing the discussion so far, the traction motor comprises a protective and insulating motor housing, a stator assembly rigidly mounted within the motor housing, and a rotor assembly rotatably mounted within the motor housing adjacent to the stator assembly. The stator assembly includes an annular stator core with a series of circumferentially spaced stator slots in which several electromagnetic stator windings (e.g., copper hairpin winding bars) are mounted. Conversely, the rotor assembly comprises a cylindrical rotor core located within and circumscribed by the annular stator core. The rotor core has a series of circumferentially spaced rotor slots in which several electromagnetic rotor windings (e.g., copper winding coils) are mounted.A single or a set of heat tubes is mounted in each rotor slot alongside the rotor windings in that slot and projects axially from one or both axial ends of the rotor core. Each heat tube comprises a sealed container containing a working fluid that changes its phase between liquid and gas in order to extract thermal energy from the rotor windings and transfer the extracted thermal energy to the outside through the axial end(s) of the rotor core. Aspects of this disclosure also relate to manufacturing processes, computer-readable media, and control logic for manufacturing or using any of the disclosed winding cooling systems, electric machines, and / or motor vehicles. An example presents a method for assembling an electric machine. This representative method comprises, in any order and in any combination with any of the options and features disclosed above and below, receiving a housing of the electric machine; attaching a stator assembly to the housing, the stator assembly comprising a stator core and an electromagnetic stator winding mounted in a stator slot of the stator core;Attaching a rotor assembly to the housing such that the rotor assembly is adjacent to and rotatable with respect to the stator assembly, the rotor assembly comprising a rotor core and an electromagnetic rotor winding mounted in a rotor slot of the rotor core; and placing a heat tube in the rotor slot such that the heat tube is adjacent to the rotor winding and projects axially from an axial end of the rotor core, the heat tube being configured to passively draw thermal energy from the rotor winding and carry the thermal energy out of the rotor core. In all disclosed vehicles, processes, and electrical machines, the rotor assembly may contain a bundle of rotor windings mounted in the rotor slot. In this case, the heat pipe may comprise multiple heat pipes mounted in the rotor slot and embedded within the bundle of rotor windings. Alternatively, the heat pipes may be stacked in a given rotor slot in a straight line extending radially around the rotor core. In this case, the heat pipes may be arranged parallel to each other and radially spaced. In multi-slot and bundle configurations, the electrical machine may contain multiple stacks of heat pipes arranged at equal intervals around the rotor core, with each heat pipe stack oriented at an oblique angle to its adjacent heat pipe stacks. In all disclosed vehicles, processes, and electrical machines, each heat pipe can contain a sealed, thermally conductive container (e.g., a copper or aluminum tube) containing a working fluid (e.g., water, acetone, methanol, or ammonia). The working fluid changes phases between liquid and gas to extract heat from the rotor winding(s) and conduct the extracted heat to the outside through one or both axial ends of the rotor core. Inside the heat pipe container is a wick structure (e.g., a grooved, sintered, or sieve-type wick) that rests against and may cover an inner surface of the container. The wick structure transports the liquid working fluid, e.g., by capillary action, to the center of the container. An elongated vapor channel may extend longitudinally through the center of the wick structure.The vapor channel directs the working fluid, which has evaporated into a gas, to the opposite axial ends of the sealed container; when the working fluid condenses into a liquid, the vapor channel directs the liquid into the wick structure. In all disclosed vehicles, processes, and electrical machines, a left-hand (first) rotor end cap can be attached to one axial end of the rotor core, and a right-hand (second) rotor end cap can be attached to the opposite axial end of the rotor core. Each end cap abuts a longitudinal end of the heat tube(s) to absorb the heat energy dissipated from the rotor core. The rotor end cap can be an annular, plate-like structure containing one or more heat tube cavities, each of which is recessed into an inwardly facing axial surface of the rotor end cap and fits into the longitudinal end of the heat tube. Each rotor end cap can be manufactured with a set of end cap ribs projecting axially from the rotor core; these end cap ribs dissipate the extracted heat energy transferred from the rotor core and absorbed by the rotor end cap.An optional active thermal management system can spray or inject a dielectric coolant onto the end cap fins and, if desired, pump the heated coolant away from the rotor assembly. In all disclosed vehicles, processes, and electrical machines, the rotor assembly may have a series of circumferentially spaced rotor slots, each extending axially through the rotor core and having open terminal ends. In this case, a group of rotor windings may be wound through and secured in each rotor slot. A single heat tube or a group of heat tubes may be secured in each of the rotor slots, for example, by extending through the center of the grouped rotor windings in that slot. The heat tubes may be arranged in discrete stacks of tubes spaced circumferentially around the rotor core, embedded within the rotor windings, and each located in one of the rotor slots. The above summary does not represent every embodiment or aspect of the present disclosure. Rather, the preceding summary merely provides an overview of some of the novel concepts and features set forth herein. The features and advantages mentioned above, as well as other features and associated advantages of this disclosure, will be readily apparent from the following detailed description of illustrated examples and representative modes of implementation of the disclosure when considered in conjunction with the accompanying drawings and the attached claims. Furthermore, this disclosure expressly includes all combinations and subcombinations of the elements and features described above and below. Brief description of the drawings Fig. 1 is a partially schematic side view of a representative motor vehicle with a rechargeable traction battery pack, a high-voltage electrical system, and an SEM-based electrified powertrain with which the aspects of this disclosure can be put into practice. Fig. 2 is a schematic single-line diagram showing a representative SEM drive system with which the aspects of this disclosure can be put into practice. Fig. 3 is a side sectional view of a representative electric machine with heat tubes embedded in the winding slots and heat sinks integrated into the end cap according to the aspects of this disclosure. Fig. 4 is an end view of the rotor assembly of the representative electric machine of Fig. 3, with the rotor end caps removed to better see the heat tubes embedded in the winding slots, which are embedded in the rotor-supported electromagnetic windings. The present disclosure is suitable for various modifications and alternative forms, and some representative embodiments of the disclosure are illustrated by way of example in the drawings and are described here in detail. It should be understood, however, that the novel aspects of this disclosure are not limited to the particular forms illustrated in the drawings listed above. Rather, this disclosure encompasses all modifications, equivalents, combinations, permutations, groupings, and alternatives that fall within the scope of this disclosure, such as those covered, for example, by the attached claims. Detailed description This disclosure can be realized in many different forms. Representative embodiments of the disclosure are shown in the drawings and are described in detail here, with the understanding that these embodiments serve as examples of the disclosed principles and not as limitations of the general aspects of the disclosure. Therefore, elements and limitations described, for example, in the sections "Summary," "Introduction," "Description," "Brief Description of Drawings," and "Detailed Description," but not expressly set forth in the claims, should not be considered as being included in the claims, either individually or collectively, by implication, by conclusion, or otherwise. Furthermore, the use of "first," "second," "third," etc., serves no purpose other than to provide a general basis for the disclosure.The terms used in the description or in the claims do not per se establish a serial or numerical limitation; unless expressly stated otherwise, these designations may be used to facilitate reference to similar features in the description and drawings and to distinguish between similar elements in the claims. For the purposes of this detailed description, unless expressly excluded: the singular includes the plural and vice versa; the words "and" and "or" are both subjunctive and disjunctive; the words "every" and "all" mean "every one and all"; and the words "including," "containing," "comprehensive," "with," and the like each mean "including without limitation." Furthermore, words of approximation, such as "approximately," "almost," "essentially," "generally," "about," and the like, may be used here to denote, for example, "at, close to, or almost at," 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", "starboard", "port", "vertical", "horizontal", "upwards", "downwards", "front", "backwards", "left", "right", etc. can be used.to refer to a motor vehicle, e.g. to the forward direction of travel of a motor vehicle when the vehicle is operated on a horizontal driving surface. With reference to the drawings, in which the same reference numerals refer to the same features in the different views, Fig. 1 shows a representative motor vehicle, generally designated 10, which is hereby represented for discussion purposes as an electric-powered sedan. The motor vehicle 10 shown—here also referred to simply as the “motor vehicle” or “vehicle”—is merely an exemplary application with which aspects of this disclosure can be put into practice. Likewise, the incorporation of the present concepts into an FEV powertrain driven by a single RESS package and a single drive motor should be understood as an unlimited implementation of the disclosed features.It goes without saying that aspects and features of this disclosure can be applied to other powertrain architectures, incorporated into any logically relevant type of motor vehicle, and used for both automotive and non-automotive applications. Furthermore, only selected components of the motor vehicles, SEM drives, and electrical HV systems are shown and described in detail here. Nevertheless, the vehicles, SEMs, and electrical systems discussed below may include numerous additional and alternative features and other available peripheral components to perform the various methods and functions of this disclosure. The representative vehicle 10 of Fig. 1 is originally equipped with a central telecommunications and information unit 14 (“telematics”) that communicates wirelessly, e.g., via cell towers, satellite services, etc., with a remote cloud computing host service 24 (e.g., OnStar®). Other hardware components 16 shown in Fig. 1 in the vehicle include, by way of non-limiting examples, an electronic video display unit 18, a microphone 28, audio speakers 30, and various user input controls 32 (e.g., buttons, knobs, switches, touchscreens, etc.). These hardware components 16 function as a human-machine interface (HMI), enabling the user to communicate with the telematics unit 14 and other components located both inside and outside the vehicle 10. The microphone 28, for example, allows the occupants to input verbal commands.Conversely, the loudspeakers 30 emit acoustic signals to the vehicle occupants and can be either a standalone loudspeaker for the telematics unit 14 or part of an audio system 22. The audio system 22 is operationally connected to a network interface 34 and an audio bus 20 to receive analog information and reproduce it as sound via one or more loudspeaker components. The network connection interface 34 is communicatively coupled to the telematics unit 14. Suitable examples for this are twisted-pair / fiber optic Ethernet switches, parallel / serial communication buses, LAN interfaces (local area network, LAN), CAN interfaces (controller area network, CAN), and the like. The network connection interface 34 enables the vehicle hardware 16 to send and receive signals among itself and with systems and subsystems both on board and outside the vehicle body 12. This allows the vehicle 10 to perform various vehicle functions, such as modulating the powertrain output, activating a vehicle braking system, controlling the vehicle steering, regulating the charging and discharging of the vehicle batteries, and other automated functions. For example, the telematics unit 14 can receive signals from / to a powertrain control module (PCM).: powertrain control module (PCM) 52, an onboard charging module (OBCM) 54, an electronic battery control module (EBCM) 56, a steering control module (SCM) 58, a brake system control module (BSCM) 60 and various other vehicle ECUs receive and transmit. With further reference to Fig. 1, the telematics unit 14 is an in-vehicle computing device that provides a mix of services both individually and through its communication with other networked devices. This telematics unit 14 generally consists of one or more processors 40, each of which can be implemented as a discrete microprocessor, an application-specific integrated circuit (ASIC), or a special control module. The vehicle 10 can provide centralized vehicle control via a central processing unit (CPU) 36, which is operationally coupled with a real-time clock (RTC) 42 and one or more electronic storage devices 38, each of which can take the form of a CD-ROM, a solid-state drive (SSD), a hard disk drive (HDD), a semiconductor memory, etc. Long-range communication (LRC) with devices outside the vehicle can be provided via a cellular communication component, a navigation and positioning component (e.g., GPS transceiver), or a wireless modem, all of which are shown together in Figure 44. Short-range communication (SRC) can be provided via a wireless short-range communication device 46 (e.g., a Bluetooth® unit), a dedicated short-range communication component (DSRC) 48, and / or a dual antenna 50. It is understood that the vehicle 10 can be implemented without one or more of the components listed above, or may optionally include additional components and functions as required for a particular end application.The communication devices described above can provide data exchange as part of a periodic broadcast in a vehicle-to-vehicle (V2V) communication system or a vehicle-to-everything (V2X) communication system. The CPU 36 receives sensor data from one or more sensing devices that use, for example, photodetection, radar, laser, ultrasound, optics, infrared, or other suitable technologies, including short-range communication technologies (e.g., DSRC) or ultra-wideband (UWB) radio technologies, to perform, for example, automated vehicle operation or a vehicle navigation service. According to the example shown, the motor vehicle 10 can be equipped with one or more digital cameras 62, one or more distance sensors 64, one or more vehicle speed sensors 66, one or more vehicle dynamics sensors 68, and the necessary filtering, classification, fusion, and analysis hardware and software for processing raw sensor data.The type, placement, number and interoperability of the distributed assemblies of vehicle sensors can be individually or collectively adapted to a specific vehicle platform to achieve a desired level of autonomous vehicle operation. To propel the motor vehicle 10, an electrified powertrain is capable of generating tractive torque and transmitting it to one or more of the vehicle's drive wheels 26. The powertrain is represented in Fig. 1 by an electric traction motor 78 connected to a rechargeable energy storage system (RESS), which may be in the form of a chassis-mounted traction battery pack 70. The battery pack 70 may contain one or more battery modules 72, each accommodating a group of electrochemical battery cells 74, such as lithium-ion or lithium-polymer battery cells of the pouch, can, or prismatic type. One or more electric machines, such as a speed-controlled, multiphase SEM motor / generator (M) unit 78, draw electrical energy from one or more rechargeable battery units, such as...the traction battery pack 70 and optionally supply electrical energy to it. A high-voltage electrical system with an inverter 80 electrically connects the battery pack 70 to the motor / generator unit(s) 78 and modulates the transfer of electrical current between these units. The battery pack 70 can be configured so that the functions for module management, cell scanning, and communication between module and host are integrated directly into each module 72 and are performed wirelessly via a wireless cell monitoring unit (CMU) 76. Fig. 2 shows an unlimited example of a SEM drive system 200 suitable for electrically connecting and disconnecting a rechargeable battery assembly 202 from a high-voltage electrical source, such as an AC power supply network 201. Although they differ in appearance, it is intended that all features and options described herein relating to the electric traction motor 78 of Fig. 1 and the electric machine 310 of Fig. 3 can be incorporated individually or in any combination into the SEM drive system 200 of Fig. 2, and vice versa. While the SEM drive system 200 of Fig. 2 is not limited per se, it can be modified by a rechargeable battery unit / assembly 202, a power factor correction device (PFC) 204, a traction inverter module (TIM) 206, a power transmission circuit (TIM) 206, and a power transmission circuit (TIM) 206.: power transfer circuit, PTC) 208 and a separately excited motor unit (SEM) 210 are characterized. The rechargeable battery assembly 202 can adopt any of the battery options described herein, including one or more battery packs or one or more battery modules, each containing one or more rechargeable battery cells 212 (e.g., prismatic, pouch, or cylindrical lithium-ion cells). Furthermore, each battery assembly can include an array of solid-state relay contactors / switches (not shown) that respond independently to signals from a suitable control unit / module to control the electrical power of the battery system. While only one battery assembly 202 and one motor 210 are shown in Fig. 2 for simplicity, the SEM drive system 200 can include any number of battery units, motor units, and associated electrical hardware without departing from the intended scope of this disclosure. A DC-AC and AC-DC power inverter 206, which can be part of a traction inverter module (TIM), is connected to the SEM unit 210 via multiphase windings 214A, 214B, and 214C to transfer electrical energy between the SEM 210 and the battery assembly 202. In Fig. 2, the TIM device 206 (also referred to as an "inverter stage" or "inverter sub-circuit") is directly electrically connected to and positioned between the PFC device 204 and the SEM unit 210. In the example shown, the TIM device 206 has no direct electrical connection to the rotor unit 218 of the SEM unit 210. A DC battery output voltage is supplied from the battery 202 to the TIM 206 and the PTC 208 via the positive and negative voltage bus rails 220A and 220B respectively, with an optional DC bus capacitor 222 (Fig. 2) being connected across the rails 220A, 220B. Representative inverter topologies can include multiple inverters and corresponding motor control modules that can receive motor control commands and control inverter states to provide motor drive or regenerative functions. The TIM device 206 of Fig. 2 can include one or more pairs of electromechanical or semiconductor switches connected in series, which together convert direct current from one or more energy storage devices (e.g., the battery assembly 202) into alternating current to power one or more electrical machines (e.g., the SEM unit 210) via high-frequency circuits. According to the example shown, the TIM device 206 includes six semiconductor switches SI1, SI2, SI3, SI4, SI5, and SI6, arranged in three pairs 224A, 224B, and 224C of series-connected semiconductor TIM switches. These three pairs of switches 224A, 224B and 224C can be electrically connected in parallel to each other.Each switch SI1-SI6 can be implemented as a voltage-controlled bipolar switching device in the form of an insulated gate bipolar transistor (IGBT), a metal-oxide semiconductor field-effect transistor (MOSFET), a wideband GaN device (WBG), or another suitable switch with a corresponding gate to which a gate signal is applied to change the on / off state of a particular switch. Each pair of semiconductor TIM switches 224A, 224B, and 224C can be electrically connected in series with one of the stator-supported field windings 214A, 214B, 214C of a SEM stator assembly 216. Power inverters, such as the TIM device 206 of Fig. 2, can use fast, control-unit-automated switching control techniques, e.g., pulse-width modulation (PWM) signals, to convert direct current supplied during the discharge of the battery unit 202 into alternating current suitable for driving the SEM unit 210. A pre-charging circuit (not shown) can be used to charge a DC intermediate circuit capacitor 226 within the TIM device 206 at a controlled rate to equalize a voltage across the various switch pairs 224A-224C before contactors / switches within the battery unit 202 are closed. A multi-stage PFC device 204 is selectively electrically connected to the power source 201 and, once connected, is positioned between the power source 201 and the rest of the SEM drive system 200 (i.e., the battery unit 202, the TIM 206, the PTC 208, and the SEM 210). This PFC device 204 (also referred to as a "PFC stage" or "PFC converter") corrects the power factor by shaping the input current, for example, to comply with the harmonic oscillation limits of the system 200. In Fig. 2, the PFC device 204 is directly electrically connected to and positioned between the power source 201 and the TIM device 204. In the example shown, the PFC device 204 is located either in the stator-side circuit or in the rotor-side circuit of the SEM drive system 200, depending on which side is opposite that of the battery unit 202.A PFC partial circuit can adopt a variety of different topologies, including single- and multi-phase PFC designs, multi-level (2-level, 3-level ... N-level) PFC designs, active and hybrid switching PFC designs, etc. A multi-phase PFC may be suitable for applications such as the one shown in Fig. 2, where the PFC is arranged on the stator side of the SEM in series with the multi-phase windings of the motor. A multi-stage PTC device 208 (also referred to as a "PTC stage" or "rotor excitation circuit") is electrically connected on the output side to the rotor side of the SEM unit 210 and on the input side to both the battery unit 202 and the PFC device 204. The PTC device 208 of Fig. 2 can provide a single-phase rotor excitation function for the rotor assembly 218 of the SEM, e.g., for optimized motor control and system charging. In Fig. 2, the PTC device 208 is directly electrically connected to and positioned between the battery unit 202 and the SEM rotor assembly 218. In the illustrated example, the PTC device 208 lacks a direct electrical connection to the stator assembly 216 of the SEM unit 210. A separately excited motor unit 210 (SEM unit 210) is arranged between the TIM 206 and the PTC 208 and is powered by the rechargeable battery assembly 202 to generate the motor's output torque, for example, to rotate the drive wheels 12 of Fig. 1 and thereby propel the vehicle 10, or to perform work in a non-automotive SEM drive application. In contrast to multiphase PM electric motors based on permanent magnets in the rotor, a synchronous wound-field SEM is generally characterized by armature windings in the rotor that interact electromagnetically with field windings in the stator to convert electrical energy into mechanical energy. As shown, the SEM unit 210 includes a rotor assembly 218, which is arranged coaxially with and rotatable relative to a stator assembly 216.In radial flow designs with an internal rotor, the stator assembly 216 comprises an annular stator core 246, which carries several electromagnetic stator "field" windings 214A-214C. In contrast, the rotor assembly 218 comprises a cylindrical rotor core 248, which carries one or more electromagnetic rotor "armature" windings 234. In this example, the rotor core 248 is rotatably mounted within a hollow center of the stator core 246, so that the stator assembly 216 circumscribes the rotor assembly 218. The field and armature windings 214A-214C and 234 are supplied with electrical energy provided by the battery assembly 202; once energized, the stator-supported field windings 214A-214C couple electromagnetically with and drive the rotor-supported armature winding 234 (the electromagnetic coupling is represented in Fig. 2 by the S-shaped parallel lines connecting the stator assembly 216 and the rotor assembly 218). A motor output element, which may be in the form of a rotor shaft (not shown), may be toothed, keyed, bolted, or otherwise firmly connected to the rotor core 248 to rotate in unison with it and deliver motor torque. Although not limited per se, the stator and rotor cores 246, 248 may be manufactured as laminated core constructions, each consisting of a stack of iron or other iron sheets.Although the SEM unit 210 is represented and described as an electric radial flux machine, it can also assume axial flux and transverse flux architectures within the scope of this disclosure. Figure 3 shows another example of an electric machine 310, depicted as a separately excited radial-flow internal rotor motor unit cooled by heat pipes or vapor chambers embedded in the winding slots, heat sinks integrated into the end cap, and spray or splash cooling of the ATM. As mentioned above, it is provided that all features and options described in relation to the traction motor 78 of Figure 1 and the SEM unit 210 of Figure 2 can be incorporated individually or in any combination into the electric machine 310 of Figure 3, and vice versa. The electric machine 310 of Figure 3 is equipped with a protective and insulated outer housing 302 (e.g., an integrated cast metal EDU (electric drive unit) housing) which provides the mechanical interface for mounting on a system support structure (e.g., a chassis, frame, or chassis).a unibody or body-on-frame chassis) to illustrate some non-limiting similarities. A multiphase, field-wound, AC-fed stator assembly 316 is rigidly mounted inside the housing 302, e.g., via an axial clamping ring 308. Spaced apart from the stator assembly 316 by an air gap is a single-phase, armature-wound, DC-fed rotor assembly 318, which is rotatably mounted in the housing 302, e.g., via high-speed precision roller bearings 304. The rotor assembly 318 is fixedly mounted, e.g., via a key, a toothed connection, a collar, a hub, etc., on a power-transmitting (motor or output) shaft 306 to rotate together with it. This shaft 306 serves to transmit the torque generated by the electric machine 310 and / or to receive the input torque generated by an external source. Similar to the stator assembly 216 of Fig. 2, the stator assembly 316 of Fig. 3 is constructed with a flux-permeable, layered, annular stator core 320, which has several circumferentially spaced stator slots 321 that are radially aligned with the stator core 320 and extend axially through it. A corresponding set of electromagnetic "field" conductors 326, which can be of the type of hairpin, I-pin, D-pin, or flat-bar copper conductors, is wound through each axially elongated slot 321 of the stator core 320. The radially innermost ends of the stator slots 321 are separated by stator teeth that point toward the outer diameter (OD) periphery of the rotor assembly 318.The stator teeth conduct the magnetic flux generated by the stator windings 326 across the air gap to electromagnetically connect with the electromagnets supported by the rotor assembly 318, before completing the flux path back to the stator assembly 316. Similar to the rotor assembly 218 of Fig. 2, the rotor assembly 318 of Fig. 3 is constructed with a magnetically permeable, stacked-laminated cylindrical rotor core 322, which has several circumferentially spaced rotor slots 323 that are radially recessed into the rotor core 322 and extend axially through it. The rotor core 322 is located within and is circumscribed by the stator core 320, so that both cores 320, 322 are coaxial with the shaft 306. An electromagnetic “armature” conductor 328 is wound through the axially elongated rotor slots 323, which can be designed in the form of a single- or multi-wire winding composition of solid wire or stranded copper coils.To passively cool the rotor assembly 318 during operation of the electric machine 310, at least one heat tube 340 is mounted in one or more of the rotor slots 323 to extract heat energy from a winding 328 located in the rotor. According to the example shown, each rotor slot 323 is an open, axially elongated channel that extends radially inward into the outer surface of the rotor core 322 and securely houses a corresponding bundle of rotor windings 328 (e.g., a bundle of winding segments of a single-wire winding or of multi-wire windings). A single heat tube 340 or a set of heat tubes 340' can be embedded in each rotor slot 323, anchored in the bundle of rotor windings 328 in that slot 232. For high-speed, high-torque applications, several heat tubes 340 (e.g.,The five heat tubes 340' (shown in the drawings) can be stacked one above the other in a straight line extending radially with respect to the rotor core 322, as best seen in Fig. 4. The overall height of the tube stack 340' can be substantially equal to the radial depth of the groove 323. When stacked in this way, the individual heat tubes 340 can be parallel to each other and radially spaced apart, as best seen in Fig. 3. These straight heat tube stacks 340' can be spaced circumferentially around the rotor core 322 at equal intervals, with each stack 340' oriented at an oblique angle (e.g., about 45 degrees) with respect to its immediately adjacent stacks 340'. Although the use of slot-embedded heat tubes is shown and described herein, the electric machine 300 of Fig. 3 can replace some or all of the heat tubes 340 with heat-dissipating steam chambers. For example, a single planar steam chamber can replace each stack 340' of heat tubes 340 within a given rotor slot 323. As another option, the slot-embedded heat tubes and steam chambers described herein can be integrated into one or more of the stator slots 321 to passively cool the stator assembly 316. It is also conceivable that the rotor assembly 318 includes more or fewer heat tubes 340, which can assume different shapes, sizes, and installation locations than the configurations shown.The presented rotor-mounted heat tubes and vapor chambers are closed, passive heat management devices that do not interact with or interfere with the stator, thus reducing system complexity while ensuring that operating speeds, inertial mass and structural integrity of the rotor are maintained for high-speed operation. For operation at higher speeds, the heat tubes 340 can be encased in optional slotted wedge sleeves 334, which help to hold the rotor windings 328 in position during excitation of the rotor assembly 318. It may be desirable for each slotted wedge sleeve 334 to be manufactured as a single, uniform structure of a thermally conductive polymer (e.g., high-density polyethylene (HDPE) or aromatic polyimide) that is wound or overmolded around a corresponding stack 340 of the heat tubes 340. The slotted wedge sleeve 334 not only aids in the placement of the windings but can also prevent direct physical contact between the electromagnetic windings 328 and the heat tubes 340 (e.g., to avoid damage to the winding insulation). Each heat tube 340 projects axially from one or both opposite axial ends of the rotor core 322 in order to extract the thermal energy generated by the adjacent rotor windings 328 and to carry the extracted thermal energy away from the rotor core 328. The heat tubes 340 effectively act as thermodynamic conduits, connecting the windings 328 embedded in the slots to the convectively cooling rotor end caps 350, 352 and to the conductively cooling dielectric fluid 332, which circulates through an internal coolant chamber of the housing 302. As can best be seen in the inspection view of Fig. 4, each heat tube 340 can be constructed with a hermetically sealed and thermally conductive container 342, which can be made as a rigid, hollow tube of copper or aluminum. The sealed container 342 of the heat pipe 340 contains a working medium / fluid (shown in Fig. 4 by arrows 344), such asWater, acetone, methanol, ammonia or a mixture of water and refrigerant that converts thermal energy (heat) into mechanical energy (and vice versa) by changing phases between a liquid phase 344' and a gas phase 344". The working fluid can flow freely through five different sections along the length of the vessel 342: a central “evaporator” section S1E, a pair (first and second) “adiabatic” sections S2A and S3A flanking the left and right ends of the evaporator section S1E, and a pair (first and second) “condensation” sections S4C and S5C located outside the adiabatic sections S2A and S3A. Inside the vessel 342 is a wick structure 346 that draws the working fluid 344’ in liquid phase, e.g., by capillary action, from the condensation sections S4C and S5C at the axial ends of the vessel 342 to the evaporator section S1E in the center of the vessel 342. The wick structure 346 can assume countless shapes, e.g., B. a strand of fine fibers, a wound textile, interwoven metal wires, a mesh sieve, a sintered powder wick, etc.As shown, the wick structure 346 presses against an inner surface of the container 342 and, if desired, substantially covers it. An elongated vapor channel 347 extends through the center of the vessel 342 and the wick structure 346, conveying the gaseous working medium 344" from the evaporator section S1E through the adiabatic sections S2A and S3A to the condensation sections S4C and S5C. As the working medium 344 condenses, the vapor channel 347 directs the working medium 344', once it has condensed into a liquid, into the wick structure 346. To facilitate manufacturing and simplify the design, it may be desirable for all heat tubes 340 embedded in the grooves to be essentially identical. Furthermore, each heat tube 340 can be a liquid-tight, discrete unit without liquid connections, for example, for liquid exchange with the inner coolant chamber of the housing 302. During operation of the electric machine 310, the rotor windings 328 generate a considerable amount of heat, especially at high speeds (e.g., 10,000+ RPM). Some of this heat generated by the windings is transferred through the sealed containers 342 and into the wick structures 346 of the heat tubes 340. The thermal energy of this heat tends to concentrate in the axial centers of the wire bundles; the thermal energy is conducted through the central area of ​​the sealed container 342 of the heat tube 340—the central “evaporator” section S1E—causing some of the working fluid 344 sealed in the container 342 to evaporate. When the working fluid 344 has evaporated through the absorption of the heat generated by the device, the wick structure 346 directs the working fluid 344 in the gas phase 344" into the vapor channel 347. The working fluid 344 in the gas phase 344" migrates axially outwards, e.g.to the left and right in Fig. 4, through the vapor channel 347, and condenses at the opposite longitudinal ends of the heat pipe 340 in the condensation sections S4C and S5C. Once condensed, the wick structure 346 draws the working fluid 344 out of the vapor channel 347. The working fluid 344, in the liquid phase 344', is drawn inwards by capillary action through the wick structure 346 to the evaporator section S1E to begin the cycle anew. To facilitate the dissipation of the thermal energy emitted from the rotor core 322 via the heat tubes 340, a pair (first and second) rotor end caps 350 and 352 are fixedly mounted on the opposite (first and second) axial surfaces of the rotor core 322 in abutment to the opposite (first and second) longitudinal ends of the heat tubes 340. It may be desirable for each rotor end cap 350, 352 to be manufactured with circumferentially spaced sets of heat tube cavities 351 and 353 (e.g., one cavity per heat tube) that are connected to the rotor-supported stacks 340' of heat tubes 340. Each heat tube cavity 351, 353 can be recessed into an axially inwardly facing surface of the rotor end cap 350, 352 and accommodates a longitudinal tip of a corresponding heat tube 340 therein.These heat pipe cavities 351, 353 increase the contact area between the end caps 350, 352 and the heat pipes 340, thereby increasing the heat transfer rate between the adjacent structures. The end caps 350, 352 not only serve as heat sinks but also help to minimize winding losses and ensure that the winding 328 is supported for the high-speed operation of the machine. Each rotor end cap 350, 352 can be manufactured with a corresponding set of end cap ribs 354 and 356 to facilitate the dissipation of accumulated heat from the end caps 350, 352, and thus from the rotor assembly 318, into the inner coolant chamber of the housing 302. These end cap ribs 354, 356 are located on the outwardly facing surfaces of the rotor end caps 350, 352 and project axially away from the rotor core 322 and into the inner coolant chamber of the housing. The pin ribs (i.e., the end cap ribs) 354, 356 increase the total surface area of ​​the rotor assembly 318 exposed within the housing 302 to enhance the dissipation of the extracted heat energy absorbed by the rotor end caps 350, 352, for example, by convective and, if desired, conductive heat transfer. To dissipate the heat energy generated by the windings from the machine housing 302, an active thermal management system (ATM) (represented in Fig. 3 by the oil pump 360) circulates dielectric coolant 332 into and out of the housing 302 to cool the rotor end caps 350, 352 and the end cap fins 354, 356 by spraying or spraying. The coolant 332 can be an electrically non-conductive, magnetically inert oil, which is sprayed, for example, via spray nozzles in the stator end caps 360 and 362 onto the stator windings 326 and the rotor end caps 350, 352 to accelerate the dissipation of the rotor field winding heat. In addition to the enhanced convective cooling through the rotor end caps 350, 352 and the end caps 354, 356, the spray / jet of the coolant 332 provides conductive heat transfer of the immersion type.The spray cooling for the rotor assembly 318 can also be directed towards the stator assembly 316 to further improve the peak power of the electric machine 310. For spray cooling, it may be desirable for a set of rotor pin fins to be arranged in a helical, turbine-like pattern to excite the cooling fluid 332 and thereby generate a desired spraying effect during the excitation of the rotor assembly 318.

Claims

Electric machine (78, 210, 310) comprising: a housing (302); a stator assembly (216, 316) with a stator core (246, 320) attached to the housing (302) and an electromagnetic stator winding (214A, 214B, 214C, 326) mounted in a stator slot (321) of the stator core (246, 320); a rotor assembly (218, 318) with a rotor core (248, 322) rotatably attached to the housing (302) adjacent to the stator assembly (216, 316), and an electromagnetic rotor winding (234, 328) mounted in a rotor slot (323) of the rotor core (248, 322) and configured to be magnetically connected to the stator winding (214A, 214C ... 214B, 214C, 326) fits together;a heat pipe (340) mounted in the rotor slot (323) next to the rotor winding (234, 328) and projecting axially from an axial end of the rotor core (248, 322), wherein the heat pipe (340) is configured to passively draw thermal energy from the rotor winding (234, 328) and carry the thermal energy out of the rotor core (248, 322); further comprising a rotor end cap (350, 352) attached to the axial end of the rotor core (248, 322) and bearing against a longitudinal end of the heat pipe (340) to absorb the thermal energy transferred from the rotor core (248, 322); wherein the rotor end cap (350, 352) has a heat pipe cavity (351, 353) extending into an axial surface of the rotor end cap (350, 352) is embedded and in which the longitudinal end of the heat pipe (340) is embedded;wherein the rotor end cap (350, 352) has a plurality of end cap ribs (354, 356) projecting away from the rotor core (248, 322) and configured to dissipate the extracted heat energy transferred from the rotor core (248, 322) and absorbed by the rotor end cap (350, 352). Electric machine (78, 210, 310) according to claim 1, wherein the rotor winding (234, 328) comprises a bundle of rotor windings (234, 328) mounted in the rotor slot (323), and the heat tube (340) comprises a plurality (340') of heat tubes (340) mounted in the rotor slot (323) and embedded in the bundle of rotor windings (234, 328). Electric machine (78, 210, 310) according to claim 2, wherein the heat tubes (340) are stacked in a straight line extending radially with respect to the rotor core (248, 322). Electric machine (78, 210, 310) according to claim 3, wherein the heat tubes (340) are parallel to each other and radially spaced apart from each other. Electric machine (78, 210, 310) according to claim 1, wherein the heat pipe (340) contains a sealed container (342) containing a working fluid (344) configured to change phases between a liquid phase (344') and a gas phase (344'') in order to extract thermal energy from the rotor winding (234, 328) and transfer the extracted thermal energy to the outside through the axial end of the rotor core (248, 322). Electric machine (78, 210, 310) according to claim 5, wherein the heat pipe (340) further comprises a wick structure (346) located inside the sealed container (342) and configured to direct the working fluid (344), when it is in the liquid phase (344'), from the axial ends of the sealed container (342) to a central section (S1E) of the sealed container (342). Electric machine (78, 210, 310) according to claim 6, wherein the wick structure (346) abuts an inner surface of the sealed container (342) and defines an elongated central vapor channel (347) configured to direct the working fluid (344) through the vapor channel (347) to the axial ends of the sealed container (342) when it has evaporated to the gas phase (344'') and to direct the working fluid (344) into the wick structure (346) when it has condensed to the liquid phase (344').

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