Patent Publication Number: US-2022216743-A1

Title: In slot cooling enhancement for coated stator

Description:
TECHNICAL FIELD 
     The present disclosure relates to a thermal management assembly for an electric machine of an electrified vehicle. 
     BACKGROUND 
     Extended drive range technology for electric vehicles, such as battery electric vehicles and plug in hybrid vehicles, continually increases demands on electric machines used for vehicle propulsion. Specifically, achieving increased driving ranges may require traction batteries and electric machines to have higher power outputs and associated thermal management systems. As the power output of electric machines increases to achieve extended driving ranges, demand for efficient heat removal technology may also increase. 
     SUMMARY 
     An electric machine has a stator including a core and an over-molded midsection arranged to define a plurality of slots, and a plurality of conductors wound within the slots. The portions of the midsection immediately adjacent to the slots define a plurality of protrusions disposed on opposite long faces of at least some of the slots. The protrusions extend into the at least some of the slots and between some of the conductors to establish a gap between the some of the conductors and to direct coolant between the some of the conductors. 
     A stator includes a core and an over-molded midsection. The core and the over-molded midsection are arranged to define a plurality of slots. The stator further includes a plurality of conductors wound within the slots. Portions of the midsection immediately adjacent to the slots define at least one groove, disposed on at least one long face of at least one of the slots, extending away from the conductors and toward the core to facilitate coolant flow. 
     A stator includes a core and an over-molded midsection. The core and the over-molded midsection are arranged to define a plurality of slots. The stator further includes a plurality of conductors wound within the slots. Portions of the midsection immediately adjacent to the slots define at least one groove, disposed on at least one short face of at least some of the slots, extending away from the conductors and toward the core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an example electric vehicle. 
         FIG. 2  is an exploded view of a disassembled stator. 
         FIG. 3  is an exploded view of a conventional stator slot. 
         FIG. 4  is an exploded view of a stator slot with transfer molded epoxy. 
         FIG. 5  is an exploded view of an exemplary stator slot with transfer molded epoxy having a groove feature. 
         FIG. 6  is an exploded view of an exemplary stator slot with transfer molded epoxy having both groove and protrusion features. 
         FIG. 7A  is an exploded view of an exemplary stator slot with transfer molded epoxy having a plurality of groove features. 
         FIG. 7B  is an exploded view of an exemplary stator slot with transfer molded epoxy having a plurality groove features. 
         FIG. 8  is an exploded view of an exemplary stator slot with transfer molded epoxy having both groove and protrusion features. 
     
    
    
     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 embodiments. 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. 
     As used in the specification and the appended claims, the singular form “a,” “an,” and “the” comprise plural referents unless the context clearly indicates otherwise. For example, reference to a component in the singular is intended to comprise a plurality of components. 
     Spatially relative terms, such as “top,” “bottom,” “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” “front,” “back,” and the like, may be used for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). The term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Vehicles that use a traction motor drive for propulsion are referred to as electric vehicles (EV). There are three main classes of electric vehicles. These three classes, which are defined by the extent of their electricity consumption, are namely: Battery Electric Vehicles (BEV), Hybrid Electric Vehicles (HEV), and Plug-in Hybrid Electric Vehicles (PHEV). Battery electric vehicles generally use an external electrical grid to recharge their internal battery and power their electric motors. Hybrid electric vehicles use a main internal combustion engine and a secondary supplemental battery to power their motors. Plug-in hybrid electric vehicles, in contrast to hybrid electric vehicles, use a main large capacity battery and a secondary internal combustion engine to power their motors. Some plug-in hybrid electric vehicles can also run solely on their internal combustion engine without engaging the motors. 
     Electric vehicles typically include one or more electric machines. The electric machine may be referred to as an electric motor, a traction motor, or a generator. The electric machine may be a permanent magnet machine or an induction machine. Depending on the operating conditions, the electric machine may be capable of working as a motor or a generator. For example, the electric machine may provide torque for vehicle propulsion or act as a generator for converting mechanical power into electrical power using regenerative breaking technology. The electric machine may also provide reduced pollutant emissions since electric vehicles may be operated in either electric mode or hybrid mode to reduce vehicle fuel consumption. While certain embodiments are described in the context of an electric vehicle, it is to be understood that nonautomotive applications are also contemplated, such as manufacturing equipment or power-generation machines. 
       FIG. 1  depicts a hybrid electric vehicle (“HEV”)  112 . The HEV  112  includes an electrified propulsion system having one or more electric machines  114  mechanically coupled to a hybrid transmission (not shown). In addition, the hybrid transmission is mechanically coupled to an internal combustion engine  118  (i.e., ICE). The electric machines  114  are arranged to provide propulsion torque as well as slowing torque capability either while the engine  118  is operated or turned off. When the engine  118  is off, the HEV  112  may be operated in an electric-only drive mode using the electric machines  114  as the sole source of propulsion. The hybrid transmission is also mechanically coupled to road wheels to output torque from the electric machines  114  and/or combustion engine  118 . 
     A traction battery or battery pack  124  stores energy that can be used to power the electric machines  114 . The battery pack  124  provides a high-voltage direct current (DC) output. One or more contactors  142  may isolate the traction battery  124  from a DC high-voltage bus  154 A when opened and couple the traction battery  124  to the DC high-voltage bus  154 A when closed. The traction battery  124  is electrically coupled to one or more power electronics modules  126  via the DC high-voltage bus  154 A. The power electronics module  126  is also electrically coupled to the electric machines  114  and provides the ability to bi-directionally transfer energy between AC high voltage bus  154 B and the electric machines  114 . According to some examples, the traction battery  124  may provide a DC current while the electric machines  114  operate using a three-phase alternating current (AC). The power electronics module  126  may convert the DC current to a three phase AC current to operate the electric machines  114 . In a regenerative mode, the power electronics module  126  may convert the three-phase AC current output from the electric machines  114  acting as generators to DC current compatible with the traction battery  124 . The description herein is equally applicable to an all-electric vehicle without a combustion engine. 
     In addition to providing energy for propulsion, the traction battery  124  may provide energy for other vehicle electrical systems. The vehicle  112  may include a DC/DC converter module  128  that is electrically coupled to the high-voltage bus  154 . The DC/DC converter module  128  may be electrically coupled to a low-voltage bus  156 . The DC/DC converter module  128  may convert the high-voltage DC output of the traction battery  124  to a low-voltage DC supply that is compatible with low-voltage vehicle loads  152 . The low-voltage bus  156  may be electrically coupled to an auxiliary battery (e.g., 12V battery). The low-voltage loads  152  may be electrically coupled to the low-voltage bus  156 . The low-voltage loads  152  may include various controllers within the vehicle  112 . One or more high-voltage electrical loads  158  may be coupled to the high-voltage bus  154 . The high-voltage electrical loads  158  may further include compressor and electric heaters. 
     The traction battery  124  of vehicle  112  may be recharged by an off-board power source  136 . The off-board power source  136  may be a connection to an electrical outlet. The external power source  136  may be electrically coupled to a charger or another type of electric vehicle supply equipment (EVSE)  138 . The off-board power source  136  may be an electrical power distribution network or grid as provided by an electric utility company. The EVSE  138  provides circuitry and controls to regulate and manage the transfer of energy between the power source  136  and the vehicle  112 . The off-board power source  136  may provide DC or AC electric power to the EVSE  138 . The EVSE  138  may have a charge connector  160  for plugging into a charge port  162  of the vehicle  112 . The charge port  162  may be electrically coupled to an on-board power conversion module or a charge module  164 . The charge module  164  may condition the power supplied from the EVSE  138  to provide proper voltage and current levels to the traction battery  124 . 
     The various components discussed may have one or more associated controllers to control, monitor, and coordinate 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 vehicle system controller  148  may be provided to coordinate the operation of the various components such as governing electrical flow to and from the one or more electric machines. 
     An electric machine may comprise a stator and a rotor.  FIG. 2  depicts an exploded view of a disassembled stator  200 . The stator  200  may comprise a plurality of laminations (not shown) having a front side and a back side. When stacked, the front and back sides are disposed against adjacent front and back sides to form a stator core  202 . Each lamination also includes an outer diameter (or outer wall) and an inner diameter (or inner wall). The outer diameters cooperate to define an outer surface of the stator  200 , and the inner diameters cooperate to define a cavity  204 . 
     The stator core  202  may include a number of slots  206  spaced about a circumference of the stator core  202 . A plurality of windings (also known as coils, wires, or conductors)  208  may be wrapped around the stator  200  and are disposed within the stator slots  206 . The windings  208  may be routed throughout the slots  206  in a serpentine fashion to create one or more winding paths to transmit current through the stator  200 . Based on the arrangement of the windings  208 , portions of the windings may protrude from an end face  210  of the stator core  202 . In some specific examples, the windings  208  comprise copper hairpin windings that are routed throughout an iron alloy stator core. A plurality of individual hairpins may be inserted axially through slots  206  and have end portions that protrude beyond end face  210  to adjoin hairpins in adjacent slots. 
     The stator  200  may also include an overmolded midsection  212  formed about the stator core  202 . The midsection  212  may be in-situ injection molded from a polymeric material in order to match the shape and features of the stator core  202 . The midsection  212  may also include slots  216  arranged to correspond to slots  206  of the stator core  202  defining a substantially rectangular slot to house windings  208 . This substantially rectangular slot defined by the arrangement of slots  216  and slots  206  may be defined by the cooperation of the opposite long faces (long side walls) and opposite short faces (short side walls). The opposite long faces, here, may refer to the length of the slot (commonly known as length of the teeth) extending toward the center of the stator core  200  and the opposite short faces may refer to the width of the slot perpendicular to the opposite long faces. 
     While the electric machine operates as a motor, current supplied to the windings  208  generates an electromechanical field urging rotation of the rotor. While the electric machine operates as a generator, current is generated in the windings  208  from inertial rotation of the rotor, and energy may be stored in the battery and/or utilized to power other vehicle components. During operation of the electric machine both as a motor and as a generator, heat may be generated throughout the stator core  202  and windings  208 . This heat may be removed from the electric machine using a cooling medium (e.g., by circulating transmission oil or other suitable cooling mediums). The cooling medium reduces the temperature of the windings  208  and the stator core  202  thereby increasing the amount of current capable of being provided to the electric machine without causing an undesirable degree of heat generation. 
     A thermal management assembly may be used to facilitate the cooling medium. Accordingly, an electric machine may include a thermal management assembly that introduces an oil or other dielectric fluid to portions of the electric machine for cooling purposes. In some examples, the oil may be dripped or sprayed onto wires or windings of the electric machine. However, non-uniformity of coolant flow as applied to the windings may reduce cooling efficacy. An air-cooled thermal management assembly may alternatively be provided to assist in managing thermal conditions of an electric machine. Airflow cooling may require a fan or blower to be in fluid flow connection to the end windings to push air thereto for cooling purposes. Such a configuration may also require additional components such as ducting that consume package space. 
     To address these drawbacks, a closed coolant channel assembly may be provided to assist in managing thermal conditions of the windings of the electric machine. In some specific examples, the closed coolant channel assembly is formed from one or more injection molded polymeric components and mounted to the stator. In some embodiments, the closed coolant channel assembly is formed from injection molded epoxy. The closed coolant channel assembly may define an internal cavity arranged to direct coolant flow to be in thermal communication with windings  208 . In some embodiments, for example, a pair of end caps  214  may be provided near the end face  210  of the stator  200 . The end caps  214  and the stator core  202  may be arranged with respect to one another to create a fluid seal therebetween and such that coolant routed through a channel is contained therein. In some embodiments, end caps  214  may include one or more inlet ports  218  to receive a coolant flow from a reservoir or other source, and one or more outlet ports  220  to exhaust coolant from the electric machine thermal management system. Coolant flow into stator  200  allows heat removal from the end portions of the windings  208  that protrude beyond the end face  210  of the stator core  202 . 
     While this is an effective system for heat removal from end windings (i.e., the windings  208  that protrude beyond the end face  210 ), they may be inefficient at removing heat from the windings as bundled in the grooves and/or stator slots. To remedy that problem direct winding cooling may be used. While direct winding cooling is an effective way to control the temperature of an electric machine, creating room in the grooves and/or stator slots reduces the space available for the material such as steel and copper that contribute directly to torque production. This in turn results in an undesirable increase in the machine size.  FIG. 3 , for example, shows a conventional stator core  300  comprising at least one winding  302 , at least one stator slot  304 , and at least one slot liner  306  to provide insulation between the windings  302  and the stator core  300 . The slot liner  306  may be made of multiple layers of specialized paper, plastic, or the like for optimal dielectric and mechanical strength. To maximize efficiency, typically, only a minimum clearance necessary to insert the conductors is left as free space. 
     To further maximize efficiency, encased cooling of an electric machine, explained above, may be adopted. A cavity may be defined via transfer molding to enable encased cooling of an electric machine. This application also discloses creation of a cooling channel inside the stator slot. In some embodiments, for example, an epoxy coated transfer molded mid-section may be used to replace the slot liners. 
       FIG. 4  shows a detailed view of a stator  350  having a core  352  with a transfer molded epoxy midsection  354 . The stator core  352  together with the transfer molded epoxy midsection  354  define a plurality of slots  356 . More specifically,  FIG. 4  shows a slot  356  detail with rectangular copper conductors  358  occupying the interior of the slot  356 . Slot clearance, in embodiments that use epoxy coated transfer molded mid-section  354 , may be equal to or better than the cases where paper slot liners are used. In embodiments where the stator is varnished (vacuum impregnated) the clearance space is likely to be occupied by the varnish and the only viable cooling passage left would be the semicircular area at the top of the slot. In other embodiments where the stator is not varnished, there is potential for increased NVH. Embodiments herein are intended for both the varnished and non-varnished stator, to improve coolant flow and direct it where it can be most beneficial. 
     Cooling effects may be further optimized by defining additional cooling paths and by optimal directing of the coolant how to minimize the machine size. More specifically, features inside the stator slot may define additional cooling paths and optimally direct the coolant flow. While these features may be made from/in any appropriate material, such as a variety of impregnated and non-impregnated thermoset polymers, the explanation herein uses an exemplary epoxy coating. 
       FIG. 5  shows an exemplary embodiment where the feature created—a groove—increases clearance to promote in slot coolant flow. In particular,  FIG. 5  shows a stator core  400  with a transfer molded epoxy midsection defining a stator slot  402  having groove  404  to enhance in slot coolant flow. The groove  404  increases the space available for coolant flow thereby aiding heat removal from the stator core  400  and winding  406  without flooding the airgap. The groove  404  may be defined by increasing the size of the stator slot  402 , reducing the size of the winding  406 , by utilizing an epoxy layer that is thinner than the original slot liner, or any combination thereof. In some embodiments, the groove  404  may extend away from the conductors  406  and toward the stator core  400 . While in exemplary embodiment shown in  FIG. 5 , the groove  404  is defined by/on one short face of the stator slot  402 , it is to be understood, that it may be disposed on both opposing short faces, both opposing long faces, one of the opposing long faces, or any combination thereof. 
       FIG. 6  shows another exemplary embodiment where the features created—grooves and protrusions—increase in slot clearance to promote coolant flow and increase the surface area available for heat removal. In particular,  FIG. 6  shows a stator core  410  with a transfer molded epoxy midsection defining a stator slot  412  having at least one groove  414  to enhance in slot coolant flow wherein at least one protrusion  416  is used to further separate one or more windings  418  from each other. The at least one groove  414  may increase the space available for coolant flow thereby aiding heat removal from the stator core  410  and winding  418  without flooding the airgap, while the at least one protrusion  416  helps create spacing or increase the space (path) between the windings  418  to optimize distribution of in slot coolant flow. In some embodiments, the windings  418  are spaced apart to define slits  420  therebetween. The at least one protrusion  416  may be used to increase the space already defined by the slits  420 . 
     In the exemplary embodiment shown in  FIG. 6  the at least one protrusion  416  is added midway through the long face of the slot  412  to separate (or further separate) the windings  418  and create a/larger path for coolant flow. It is to be understood, however, that the at least one protrusion  416  need not necessarily be added midway through the long face of the slot  412 . Rather, depending on the application at hand, said protrusions  416  may be used anywhere in the slot  412  to separate the windings  418  and create a larger coolant flow path and minimize the temperatures at the hottest locations. In other words, like the grooves  414 , the protrusions  416  may be defined by any portion of the midsection immediately adjacent to the slot  412  such that said protrusions  416  are disposed anywhere along the length of the opposite long faces of at least some of the slots  412 . In some embodiments, these protrusions extend into at least some of the slots  412  and between the conductors  418  to further establish a gap between the conductors  418  or increase the space already defined by the slits  420 . In some embodiments, the windings  418  are in direct contact with the protrusions  416 . Similarly, in some embodiments, the protrusions  416 , which may be disposed along the opposing long faces of the slot  412  may extend toward each other. Similarly, in the exemplary embodiment shown in  FIG. 6 , two symmetrical protrusions  416  are shown. It is to be understood, however, that depending on the application at hand, one or more protrusions may be added. Additionally, the protrusions  416  need not be symmetrical. 
     In the exemplary embodiment shown in  FIG. 6 , the at least one groove  414  is added to the opposing short faces of the slot  412  to increase the space available for coolant flow and aid the heat removal from the stator core  410  and winding  418 . It is to be understood, however, that depending on the application at hand, one or more of the grooves  414  may be used to increase the space available for coolant flow and enhance the heat removal efficiency. Similarly, the grooves  414  need not be symmetrical or of the same size and shape. While the exemplary embodiment shown in  FIG. 6  demonstrates two grooves  414  and two protrusions  416 , these features are independent and need not be implemented together. Like the protrusions  416  which may be placed anywhere along the length of the long face of the slot  412 , the grooves  414  may also be added anywhere along the length of the long face of the slot  412 . In other words, this disclosure teaches placement of as many features—grooves and/or protrusions—as needed anywhere across the length of one or both of the short and/or long faces of the slot  412  to adequately remove the heat generated via the passage of electrical current through the windings  418  or the heat generated in the core  410 . 
       FIG. 7A  shows another exemplary embodiment. This embodiment shows a stator core  450  with transfer molded epoxy midsection defining a stator slot  452  encasing windings  456  and having at least one groove  454  to enhance in slot coolant flow. In some embodiments, the at least one groove  454  may have the same or different size or shape. In the exemplary embodiment shown in  FIG. 7A , for example, small grooves  454  may be added to the epoxy corresponding to the corners of the windings  456  which facilitate the passage of electrical current. Addition of the grooves  454  to the epoxy corresponding to the corners of the windings  456  may promote coolant flow along the slot  452  walls even in the presence of varnish. In other words, in some embodiments the at least one groove  454  may be radially aligned with the slits  458  defined by separation of the conductors  456  such that the aligned grooves  454  and the slits  458  are concentric with respect to the stator  450 .  FIG. 7B , shows another exemplary embodiment of the present disclosure with an alternative distribution of the grooves  454 . This exemplary embodiment demonstrates at least two larger grooves  454  at the opposing short faces of the stator slot  452  with smaller grooves  454  corresponding to both the corners of the windings  456  (i.e., radially aligned with the slits  458  defined by spacing of the conductors  456 ) and midway between them disposed along the opposing long faces of the stator slot  452 . 
       FIG. 8  shows yet another exemplary embodiment. In particular,  FIG. 8  shows a stator core  500  with transfer molded epoxy midsection defining a stator slot  502  having at least one groove  504  to enhance in slot coolant flow and at least one protrusion  506  to direct the flow of the coolant, wherein the at least one protrusion  506  may be used to separate (or further increase the existing space between windings  508  referred to as slits  510 ) one or more windings  508 . The at least one groove  504  may increase the space available for coolant flow thereby aiding heat removal from the stator core  500  and winding  508 , while the at least one protrusion  506  may help create/increase spacing (path) between the windings  508  to optimize distribution of in slot coolant flow. While the present disclosure may depict the shape of the at least one protrusion  506  as rectangular, it is to be understood, that said protrusions  506  may assume any shape including, but not limited to, triangular or semicircle. Similarly, while the present disclosure may depict the shape of the at least one groove  504  as semicircle, it is to be understood, that said grooves  504  may assume any shape including, but not limited to, triangular, rectangular, or elliptical. 
     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 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, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, case 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.