Patent Publication Number: US-2023134509-A1

Title: Electrified vehicle having electric machine stator with embedded wire support overmold

Description:
TECHNICAL FIELD 
     This disclosure relates to an electrified vehicle and electric machine having a stator with an embedded wire support overmold. 
     BACKGROUND 
     Electrified vehicles rely on a high voltage traction battery to provide power to an electric machine operable as a traction motor for propulsion. Electric machines include a stator that surrounds a rotor that rotates to generate electricity when operating as a generator or to produce torque when operating as a motor. The stator may be formed from stacked laminations having teeth that extend from a back iron or yoke to form an inner circumference with an air gap between the teeth and the rotor. The teeth define slots that may be lined with insulation paper prior to bending/twisting of the electrically conductive wires or windings to form multiple phases around sections of the circumference. During manufacturing, wires are inserted from the crown side of the stator and emerge on the weld-side (also referred to as the twist side) where they are bent into a hairpin using metal tools, commonly called “fingers”. These fingers provide protection for the delicate insulation paper in addition to imparting the curvature on the end windings. After the stator is wound, the windings are further insulated with a resin, epoxy, varnish, lacquer or similar material to protect the windings from contamination and electrical shorting, and also to make the windings more mechanically rigid. 
     SUMMARY 
     Embodiments of the disclosure include a vehicle comprising a traction battery and an electric machine powered by the traction battery and configured to provide propulsive power to the vehicle. The electric machine includes a rotor separated by an air gap from a stator surrounding the rotor. The stator includes teeth extending from a yoke portion toward the rotor and defining slots between adjacent teeth, the slots coated with an electrically insulating material having an arcuate surface exiting the slots and extending at least partially over the teeth on at least one end face of the stator. The stator further includes windings positioned within and extending from the slots in contact with the arcuate surface of the insulating material. Each slot may include a plurality of windings with the electrically insulating material comprising protuberances extending between the plurality of windings over the teeth on the end face of the stator. Each protuberance may extend from a first associated arcuate surface and ramp to a second associated arcuate surface exiting an adjacent slot. The electrically insulating material may comprise an epoxy, which is hardened or cured before the windings are positioned within the slots. The windings may comprise electrically conductive windings having a rectangular cross section. The slots may comprise closed slots. 
     In various embodiments, an electric machine includes a rotor and a stator surrounding the rotor and separated by an air gap. The stator comprises teeth extending from a yoke portion toward the rotor and defining slots between adjacent teeth. The stator includes a molded electrically insulating material coating the slots and having a curved surface extending from the slots and at least partially covering the teeth on at least one end face. The molded material is configured to guide associated windings extending from the slots. Each slot may have a plurality of associated windings. The electrically insulating material may extend between at least a portion of the windings for each slot. The electrically insulating material may form a ramped surface extending from a lower first curved surface associated with a first slot to a higher second curved surface associated with a second slot, the second slot being adjacent to the first slot. The electrically insulating material may form a second ramped surface extending from a higher third curved surface associated with the first slot to a lower fourth curved surface associated with the second slot. The molded electrically insulating material may comprise an epoxy that is cured or hardened before the windings are positioned within the slots. The windings may comprise electrical conductors each having a rectangular cross-sectional area. 
     Embodiments may also include a method of manufacturing an electric machine comprising forming a stator core from a plurality of laminations each having teeth extending from a yoke portion toward an inner circumference, adjacent teeth forming a slot therebetween, and molding a winding guide on the stator core using a fluid that hardens to form electrically insulating arcuate surfaces extending from the slots to the teeth of at least one end face of the stator core, and positioning windings within and extending from the slots, and bending the windings against the arcuate surfaces to form end windings. The method may include positioning a plurality of windings in each of the slots. The method may include molding a plurality of protuberances on the at least one end face, each of the protuberances having a ramped surface extending from an arcuate surface extending from a first one of the slots to an arcuate surface extending from a second one of the slots adjacent to the first one of the slots. The method may include molding a plurality of ramped protuberances for each of the slots, each slot having an associated first protuberance ramping from a lower arcuate surface associated with a first slot to a higher arcuate surface associated with a second slot adjacent to the first slot, and a second protuberance ramping from a higher arcuate surface associated with the first slot to a lower arcuate surface associated with the second slot. The method may include positioning a plurality of windings in each of the slots, wherein the plurality of windings corresponds in number to the plurality of ramped protuberances. The method may include molding the winding guide using an epoxy. 
     Various embodiments of the disclosure may provide one or more associated advantages. For example, an electric machine having a stator with an embedded wire support overmold eliminates the use of metal fingers or similar tools during manufacturing. The stator paper slot liners are replaced with a layer of epoxy with bending of conductor bars/wires directly against the epoxy. The bend radius is formed by the epoxy which provides the support and curvature needed for the bending operation. Replacing paper slot liners and metal finger tools, which require additional clearance to protect the slot liners, with epoxy reduces the winding profile resulting in a lower overall length of the end turns of the conductors. The embedded conductor support may be realized with stators having sealed or open slot designs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram illustrating an electrified vehicle having an electric machine with stator laminations having an overmold winding guide feature. 
         FIG.  2    is a perspective view of an electric machine stator illustrating stacked laminations with an epoxy overmold winding guide feature. 
         FIG.  3    illustrates an embodiment of a molded epoxy winding guide embedded with a stator core. 
         FIG.  4    illustrates another embodiment of a molded epoxy winding guide. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
     Electrified vehicles include one or more electric machines that may operate as a generator to power devices or store energy in a traction battery, or as a motor to provide torque to propel the vehicle. Electric machines include a rotor that rotates during operation within a stationary stator. The stator may be comprised of a plurality of stacked laminations. The laminations may be made of electric steel or other iron alloys. The laminations may have teeth extending from a back iron or yoke portion toward a center opening that accommodates the rotor. The teeth define or form slots between adjacent teeth. An insulating material, such as an epoxy or resin material, may be formed within the slots and extend to one or both faces of the laminations to form bending and/or positioning guides for conductive windings wound throughout the slots to carry electric current as described herein. 
     Windings may be used to conduct electric current through the slots in the stator iron core, which induces the magnetic field. The windings may be one solid conductor for a single-phase motor, or one solid conductor for each phase of a multiple phase motor. The individual conductors may have various cross-section geometries, such as round or rectangular (or square). Rectangular or square conductors may include rounded or filleted corners. The windings or individual conductors may have a coating (e.g., varnish, epoxy, resin, paint, enamel) to prevent cross-conduction between individual conductors. The windings may have the same cross-sectional areas to maintain uniform copper losses. 
     For multi-phase electric machines, the windings of different phases may be separated by an insulator to prevent short circuits between the windings because the electric potential between different phases may overcome insulation provided by ambient air and the varnish between the windings. Various embodiments according to the present disclosure replace insulation paper lining the slots with a molded epoxy or similar material, which also forms the conductor bending/positioning guides on the face of the stator. An additional electrically insulating coating such as a lacquer, resin, or epoxy (that may be thermally conductive) may be applied to the windings and epoxy overmold after the windings are installed in the stator slots to improve the heat transfer characteristics, prevent electrical short circuiting, and provide mechanical rigidity of the assembly. 
     Various techniques may be used to apply the electrically insulating coating compound or material, including a dip and cure/bake, a trickle application, vacuum pressure impregnation, and resin sealing. Dip and bake application includes immersing the motor windings into a tank of insulating liquid (often twice to ensure full coverage) followed by heating in an oven to cure/harden the compound. In a trickle application, the winding is connected to a rotating table and electrical resistance is used to generate heat while rotating and a trickle stream of material is introduced to the winding head. The compound follows the wire into the entirety of the slot to reduce or eliminate the possibility of partial discharge in random windings. Once fully saturated, the current is increased in the windings to cure the compound while rotating. Vacuum Pressure Impregnation (VPI) utilizes a vacuum pressure tank filled with insulating compound or material to fully impregnate motor windings and insulation with resin or varnish. The windings may be preheated to improve performance with capacitance measured over multiple cycles to determine acceptable fill. Another alternative involves resin sealing or potting to insulate the windings by completely impregnating the coils and insulation with a high molecular weight thermoset polymer resin. 
       FIG.  1    depicts a representative electrified vehicle, which is a plug-in hybrid electric vehicle (HEV) in this example. Vehicle  112  may comprise one or more electric machines  114  mechanically connected to a transmission  116  having a stator with a molded winding guide as described herein. The electric machines  114  may be capable of operating as a motor or a generator. In addition, the transmission  116  is mechanically connected to an internal combustion engine  118 . The transmission  116  is also mechanically connected to a drive shaft  20  that is mechanically connected to the wheels  122 . The electric machines  114  can provide propulsion and regenerative braking capability when the engine  118  is turned on or off. During regenerative braking, the electric machines  114  act as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in the friction braking system. The electric machines  114  may also reduce vehicle emissions by allowing the engine  118  to operate at more efficient speeds and allowing the hybrid-electric vehicle to be operated in electric mode with the engine  118  off under certain conditions. 
     A traction battery or battery pack  124  stores energy that can be used by the electric machines  114 . A vehicle battery pack  124  typically provides a high voltage DC output. The traction battery  124  is electrically connected to one or more power electronics modules. One or more contactors may isolate the traction battery  124  from other components when opened and connect the traction battery  124  to other components when closed. A power electronics module  126  is also electrically connected to the electric machines  114  and provides the ability to bi-directionally transfer energy between the traction battery  124  and the electric machines  114 . For example, a typical traction battery may provide a DC voltage while the electric machines  114  may require a three-phase AC current to function. The power electronics module  126  may convert the DC voltage to a three-phase AC current as required by the electric machines  114 . In a regenerative mode, the power electronics module may convert the three-phase AC current from the electric machines  114  acting as generators to the DC voltage required by the traction battery  124 . The description herein is equally applicable to an electrified vehicle implemented as a pure electric vehicle, often referred to as a battery electric vehicle (BEV). For a BEV, the hybrid transmission  116  may be a gear box connected to an electric machine and the engine  118  may be omitted. 
     In addition to providing energy for propulsion, the traction battery  124  may provide energy for other vehicle electrical systems. A typical system may include a DC/DC converter module that converts the high voltage DC output of the traction battery  124  to a low voltage DC supply that is compatible with other vehicle loads. Other high-voltage loads, such as compressors and electric heaters, may be connected directly to the high-voltage without the use of a DC/DC converter module  128 . The low-voltage systems may be electrically connected to an auxiliary battery  130  (e.g., 12V, 24V, or 48V battery). 
     The electrified vehicle  112  may be a BEV or a plug-in hybrid vehicle in which the traction battery  124  may be recharged by an external power source  136 , or a standard hybrid that charges traction battery from operating electric machines as a generator but does not receive power from an external power source. The external power source  136  may be a connection to an electrical outlet. The external power source  136  may be electrically connected to electric vehicle supply equipment (EVSE)  138 . The EVSE  138  may provide circuitry and controls to manage the transfer of energy between the power source  136  and the vehicle  112 . In other embodiments, the vehicle  112  may employ wireless charging, which may be referred to as hands-free or contactless charging that uses inductive or similar wireless power transfer. 
     The external power source  136  may provide DC or AC electric power to the EVSE  138 . The EVSE  138  may have a charge connector  140  for plugging into a charge port  134  of the vehicle  112 . The charge port  134  may be any type of port configured to transfer power from the EVSE to the vehicle  112 . The charge port  134  may be electrically connected to a charger or on-board power conversion module  132 . The power conversion module  132  may condition the power supplied from the EVSE  138  to provide the proper voltage and current levels to the traction battery  124 . The power conversion module  132  may interface with the EVSE  138  to coordinate the delivery of power to the vehicle  112 . The EVSE connector  140  may have pins that mate with corresponding recesses of the charge port  134 . Alternatively, various components described as being electrically connected may transfer power using a wireless inductive coupling as previously described. 
     One or more wheel brakes  144  may be provided for friction braking of the vehicle  112  and preventing motion of the vehicle  112 . The wheel brakes  144  may be hydraulically actuated, electrically actuated, or some combination thereof. The wheel brakes  144  may be a part of a brake system  150 . The brake system  150  may include other components that are required to operate the wheel brakes  144 . For simplicity, the figure depicts a single connection between the brake system  150  and one of the wheel brakes  144 . A connection between the brake system  150  and the other wheel brakes  144  is implied. The brake system  150  may include a controller to monitor and coordinate the brake system  150 . The brake system  150  may monitor the brake components and control the wheel brakes  144  to achieve desired operation. The brake system  150  may respond to driver commands and may also operate autonomously to implement features such as stability control. The controller of the brake system  150  may implement a method of applying a requested brake force when requested by another controller or sub-function. 
     One or more electrical loads  146  may be connected to the high-voltage bus. The electrical loads  146  may have an associated controller that operates the electrical load  146  when appropriate. Examples of electrical loads  146  may be a heating module or an air-conditioning module. 
     The various components described may have one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a serial bus (e.g., Controller Area Network (CAN)) or via discrete conductors. In addition, a system controller may be present to coordinate the operation of the various components. 
       FIG.  2    is a perspective view of a representative stator formed by stacked laminations each having stator slots with molded epoxy winding guide features according to various embodiments of the present disclosure (best shown in  FIGS.  3 - 4   ). Electric machine  114  ( FIG.  1   ) includes a stator  210  having a plurality of laminations  212 . When stacked, the laminations  212  form a stator core  214 . Each of the laminations  212  may have an annular or donut shape to accommodate a rotor (not shown) separated by an air gap and surrounded by the stator core  214 . The rotor may be mechanically connected to a shaft using a complementary key and slot configuration. 
     Each lamination  212  includes a plurality of teeth  220  integrally formed of unitary construction and extending radially inward from a back iron or yoke portion  222  toward the inner diameter. Adjacent teeth  220  cooperate to define slots  224 . The teeth  220  of each lamination  212  are aligned such that stator slots  224  extend through the stator core  214  between the opposing end faces  226 . The end faces  226  define the opposing ends of the core  214  and are formed by the first and last laminations  212 . A molded epoxy electrically insulating slot liner ( FIGS.  3 - 4   ) is formed in the slots  224 . A plurality of windings  230  are wrapped around various groups of teeth  220  and are disposed within the stator slots  224 . Each slot  224  includes several passes or turns of the conductors or wires that form the windings  230 . The number of conductor passes or turns within each slot may vary depending on the particular application and implementation. In one embodiment, each slot  230  includes eight conductor turns or passes. 
     The conductors or wires forming windings  230  may have various cross-sectional geometries, such as circular or rectangular (including square) depending on the particular application and implementation. The windings  230  may be disposed or potted in an insulating material or compound (not shown) such as a varnish, lacquer, epoxy, or resin, for example, that is applied as a liquid or fluid during assembly and at least partially fills gaps between windings in the slots prior to curing or hardening to form a rigid structure. Portions of the windings  230  generally extend in an axial direction along the stator slots  224 . At the end faces  226  of the stator core  214 , the windings  230  bend as guided by the end face of the embedded epoxy winding guide to extend in a circumferential direction around the end faces  226  forming the hairpins or end windings  240 . 
       FIG.  3    illustrates an embodiment of a molded epoxy winding guide  300  embedded with a stator core  310 . The molded epoxy winding guide  300  is formed using an overmold positioned within the stator core and filled with liquid epoxy that cures and hardens as a thermoset polymer to form the winding guide features illustrated. The cured epoxy provides electrical insulation and thermal conductivity for the windings positioned within, and extending from the slots formed between adjacent teeth of the stator. The slots may include a small opening toward the inner circumference  312 , or may be closed or sealed slots depending on the particular design of the stator. In the embodiment of  FIG.  3   , the winding guide feature  316  of winding guide  300  includes a first arcuate surface  320  extending from a first slot  322  over at least a portion of an end face of an associated tooth  324  and joining to a second arcuate surface  326  extending from a second slot  328 . In one embodiment, the epoxy extends within each slot  322 ,  328  to replace/eliminate electrically insulating slot liner paper. The arcuate surfaces  320 ,  326  are configured to provide a bending radius to associated windings exiting the slots to form hairpin end windings. After forming of the molded epoxy winding guide, the windings are positioned within the slots with at least one end of the windings bent or formed against a corresponding arcuate surface of the associated slot. Each slot  322 ,  328  may include a single winding, or a plurality of windings as generally illustrated in the embodiment of  FIG.  4   , depending on the number of phases and particular design of the electrical machine. 
       FIG.  4    illustrates another embodiment of a molded epoxy winding guide  400  formed on a stator  410  with representative rectangular windings  420 . Winding guide  400  includes a plurality of protuberances  430  molded over at least a portion of a corresponding tooth of stator  410 . Each protuberance  430  includes a ramped portion  440  extending from a lower first arcuate or curved surface portion  442  associated with a first slot  444  to a higher second curved surface portion  446  associated with a second slot  448 . In the embodiment of  FIG.  4   , each tooth includes a second protuberance  450  having a second ramped surface extending from a higher third curved surface associated with the first slot  444  to a lower fourth curved surface associated with the second slot  448 . The number of protuberances  430  associated with each tooth corresponds to the number of windings  420  of each slot. Protuberances  430  provide a bending guide (arcuate surface portion  442 ) in addition to radially spacing of windings  420  exiting a common slot  444 . 
     As illustrated in  FIGS.  2 - 4   , a method of manufacturing an electric machine includes forming a stator core from a plurality of laminations each having teeth extending from a yoke portion toward an inner circumference, adjacent teeth forming a slot therebetween. The method includes molding a winding guide on the stator core using a fluid that hardens to form electrically insulating arcuate surfaces extending from the slots over the teeth of at least one end face of the stator core. The method further includes positioning windings within and extending from the slots and bending the windings against the arcuate surfaces to form end windings. Positioning the windings may include positioning a plurality of windings in each of the slots. Molding the winding guide may include molding a plurality of protuberances on the at least one end face, each of the protuberances having a ramped surface extending from an arcuate surface extending from a first one of the slots to an arcuate surface extending from a second one of the slots adjacent to the first one of the slots. The method may include molding a plurality of ramped protuberances for each of the slots, each slot having an associated first protuberance ramping from a lower arcuate surface associated with a first slot to a higher arcuate surface associated with a second slot adjacent to the first slot, and a second protuberance ramping from a higher arcuate surface associated with the first slot to a lower arcuate surface associated with the second slot. The number of ramped protuberances may correspond to the number of windings for each slot, with at least a portion of the protuberances extending between windings extending from the same slot. The molded winding guide may be formed by a fluid epoxy after curing or hardening. The method may also include coating the stator, windings, and winding guide with an electrically insulating fluid that is cured or hardened to increase mechanical rigidity of the assembly. 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to strength, durability, life cycle, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.