Patent Publication Number: US-2023145886-A1

Title: Electric machine with helical cooling path

Description:
TECHNICAL FIELD 
     The present disclosure relates to electric machines, for use with electric and hybrid-electric vehicles, that are capable of acting either as a motor or as a generator. 
     BACKGROUND 
     Vehicles such as battery-electric vehicles and hybrid-electric vehicles contain a traction-battery assembly to act as an energy source. The traction-battery assembly, for example, is electrically connected to an electric machine that provides torque to driven wheels. The traction-battery assembly may include components and systems to assist in managing vehicle performance and operations. It may also include high-voltage components, and an air or liquid thermal-management system to control temperature. 
     Electric machines typically include a stator and a rotor that cooperate to convert electrical energy into mechanical motion or vice versa. Electric machines may include thermal-management systems to cool the stator, rotor, or both. 
     SUMMARY 
     According to one embodiment, an electric machine includes a stator core having a plurality of stacked laminations that are arranged in sets that each define a circumferentially extending slot through a thickness of the set. The sets are circumferentially rotated relative to each other in sequence such that each slot only partially overlaps with one or more adjacent slots to form a continuous helical cooling path around the stator core. Windings are supported on the stator core. 
     According to another embodiment, an electric machine includes a stator core having a plurality of lamination sets each with at least two circumferentially extending notches though a thickness of the lamination set. The lamination sets are circumferentially rotated relative to each other in sequence such that each notch partially overlaps with one or more adjacent ones of the notches to form two continuous helical cooling paths around the stator core. 
     According to yet another embodiment, a method of assembling a stator core includes forming laminations each having a circumferentially extending slot through a thickness of the lamination; stacking the laminations such that each lamination is circumferentially rotated relative to neighboring ones of the laminations so that the slots are circumferentially staggered by an angle that is less than an arc length of the slots and the slots partially overlap to define a helical cooling path; and joining the laminations to form the stator core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of an example hybrid vehicle. 
         FIG.  2    is side view, in cross section, of a portion of an example electric machine. 
         FIG.  3    is a top view of a stator lamination according to one or more embodiments of this disclosure. 
         FIG.  4    is a perspective view of a portion of the stator core illustrating a helical cooling path according to one or more embodiments of this disclosure. 
         FIG.  5    is a side view of a portion of the stator core illustrating a helical cooling path according to another embodiment of this disclosure. 
         FIG.  6    is a top view of the stator core according to an alternative embodiment. 
         FIG.  7    is a method of assembly for a stator core. 
     
    
    
     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. 
     Directional terms used herein are made with reference to the views and orientations shown in the exemplary figures. A central axis is shown in the figures and described below. Terms such as “outer” and “inner” are relative to the central axis. For example, an “outer” surface means that the surfaces faces away from the central axis, or is outboard of another “inner” surface. Terms such as “radial,” “diameter,” “circumference,” etc. also are relative to the central axis. The terms “front,” “rear,” “upper” and “lower” designate directions in the drawings to which reference is made. The terms, connected, attached, etc., refer to directly or indirectly connected, attached, etc., unless otherwise indicated explicitly or by context. 
     An example plugin-hybrid-electric vehicle (PHEV) is depicted in  FIG.  1    and referred to generally as a vehicle  16 . The vehicle  16  includes a transmission  12  and is propelled by at least one electric machine  18  with selective assistance from an internal combustion engine  20 . The electric machine  18  may be an alternating current (AC) electric motor depicted as “motor”  18  in  FIG.  1   . The electric machine  18  receives electrical power and provides torque for vehicle propulsion. The electric machine  18  also functions as a generator for converting mechanical power into electrical power through regenerative braking. 
     The transmission  12  may be a power-split configuration. The transmission  12  includes the first electric machine  18  and a second electric machine  24 . The second electric machine  24  may be an AC electric motor depicted as “generator”  24  in  FIG.  1   . Like the first electric machine  18 , the second electric machine  24  receives electrical power and provides output torque. The second electric machine  24  also functions as a generator for converting mechanical power into electrical power and optimizing power flow through the transmission  12 . In other embodiments, the transmission does not have a power-split configuration. 
     The transmission  12  may include a planetary gear unit  26 , which includes a sun gear  28 , a planet carrier  30 , and a ring gear  32 . The sun gear  28  is connected to an output shaft of the second electric machine  24  for receiving generator torque. The planet carrier  30  is connected to an output shaft of the engine  20  for receiving engine torque. The planetary gear unit  26  combines the generator torque and the engine torque and provides a combined output torque about the ring gear  32 . The planetary gear unit  26  functions as a continuously variable transmission, without any fixed or “step” ratios. 
     The transmission  12  may also include a one-way clutch (O.W.C.) and a generator brake  33 . The O.W.C. is coupled to the output shaft of the engine  20  to only allow the output shaft to rotate in one direction. The O.W.C. prevents the transmission  12  from back-driving the engine  20 . The generator brake  33  is coupled to the output shaft of the second electric machine  24 . The generator brake  33  may be activated to “brake” or prevent rotation of the output shaft of the second electric machine  24  and of the sun gear  28 . Alternatively, the O.W.C. and the generator brake  33  may be eliminated and replaced by control strategies for the engine  20  and the second electric machine  24 . 
     The transmission  12  may further include a countershaft having intermediate gears including a first gear  34 , a second gear  36  and a third gear  38 . A planetary output gear  40  is connected to the ring gear  32 . The planetary output gear  40  meshes with the first gear  34  for transferring torque between the planetary gear unit  26  and the countershaft. An output gear  42  is connected to an output shaft of the first electric machine  18 . The output gear  42  meshes with the second gear  36  for transferring torque between the first electric machine  18  and the countershaft. A transmission output gear  44  is connected to a driveshaft  46 . The driveshaft  46  is coupled to a pair of driven wheels  48  through a differential  50 . The transmission output gear  44  meshes with the third gear  38  for transferring torque between the transmission  12  and the driven wheels  48 . 
     The vehicle  16  includes an energy storage device, such as a traction battery  52  for storing electrical energy. The battery  52  is a high-voltage battery that is capable of outputting electrical power to operate the first electric machine  18  and the second electric machine  24 . The battery  52  also receives electrical power from the first electric machine  18  and the second electric machine  24  when they are operating as generators. The battery  52  is a battery pack made up of several battery modules (not shown), where each battery module contains a plurality of battery cells (not shown). Other embodiments of the vehicle  16  contemplate different types of energy storage devices, such as capacitors and fuel cells (not shown) that supplement or replace the battery  52 . A high-voltage bus electrically connects the battery  52  to the first electric machine  18  and to the second electric machine  24 . 
     The vehicle includes a battery energy control module (BECM)  54  for controlling the battery  52 . The BECM  54  receives input that is indicative of vehicle conditions and battery conditions, such as battery temperature, voltage and current. The BECM  54  calculates and estimates battery parameters, such as battery state of charge and the battery power capability. The BECM  54  provides output (BSOC, P cap ) that is indicative of a battery state of charge (BSOC) and a battery power capability (P cap ) to other vehicle systems and controllers. 
     The vehicle  16  includes a DC-DC converter or variable voltage converter (VVC)  10  and an inverter  56 . The VVC  10  and the inverter  56  are electrically connected between the traction battery  52  and the first electric machine  18 , and between the battery  52  and the second electric machine  24 . The VVC  10  “boosts” or increases the voltage potential of the electrical power provided by the battery  52 . The VVC  10  also “bucks” or decreases the voltage potential of the electrical power provided to the battery  52 , according to one or more embodiments. The inverter  56  inverts the DC power supplied by the main battery  52  (through the VVC  10 ) to AC power for operating the electric machines  18 ,  24 . The inverter  56  also rectifies AC power provided by the electric machines  18 ,  24 , to DC for charging the traction battery  52 . Other embodiments of the transmission  12  include multiple inverters (not shown), such as one invertor associated with each electric machine  18 ,  24 . The VVC  10  includes an inductor assembly  14 . 
     The transmission  12  includes a transmission control module (TCM)  58  for controlling the electric machines  18 ,  24 , the VVC  10  and the inverter  56 . The TCM  58  is configured to monitor, among other things, the position, speed, and power consumption of the electric machines  18 ,  24 . The TCM  58  also monitors electrical parameters (e.g., voltage and current) at various locations within the VVC  10  and the inverter  56 . The TCM  58  provides output signals corresponding to this information to other vehicle systems. 
     The vehicle  16  includes a vehicle system controller (VSC)  60  that communicates with other vehicle systems and controllers for coordinating their function. Although it is shown as a single controller, the VSC  60  may include multiple controllers that may be used to control multiple vehicle systems according to an overall vehicle control logic, or software. 
     The vehicle controllers, including the VSC  60  and the TCM  58  generally includes any number of microprocessors, ASICs, ICs, memory (e.g., FLASH, ROM, RAM, EPROM and/or EEPROM) and software code to co-act with one another to perform a series of operations. The controllers also include predetermined data, or “look up tables” that are based on calculations and test data and stored within the memory. The VSC  60  communicates with other vehicle systems and controllers (e.g., the BECM  54  and the TCM  58 ) over one or more wired or wireless vehicle connections using common bus protocols (e.g., CAN and LIN). The VSC  60  receives input (PRND) that represents a current position of the transmission  12  (e.g., park, reverse, neutral or drive). The VSC  60  also receives input (APP) that represents an accelerator pedal position. The VSC  60  provides output that represents a desired wheel torque, desired engine speed, and generator brake command to the TCM  58 , and contactor control to the BECM  54 . 
     The vehicle  16  includes an engine control module (ECM)  64  for controlling the engine  20 . The VSC  60  provides output (desired engine torque) to the ECM  64  that is based on a number of input signals including APP, and corresponds to a driver&#39;s request for vehicle propulsion. 
     If the vehicle  16  is a PHEV, the battery  52  may periodically receive AC energy from an external power supply or grid, via a charge port  66 . The vehicle  16  also includes an on-board charger  68 , which receives the AC energy from the charge port  66 . The charger  68  is an AC/DC converter which converts the received AC energy into DC energy suitable for charging the battery  52 . In turn, the charger  68  supplies the DC energy to the battery  52  during recharging. Although illustrated and described in the context of a PHEV  16 , it is understood that the electric machines  18 ,  24  may be implemented on other types of electric vehicles, such as a hybrid-electric vehicle or a fully electric vehicle. 
     Referring to  FIG.  2   , an example electric machine  70  includes a stator  74  having a plurality of laminations  78 . The electric machine  70  has a central axis or centerline  75 . Each of the laminations  78  includes 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  80 . Each of the laminations  78  may define a hollow center. 
     Each lamination  78  includes an inner diameter defining a plurality of teeth extending radially inward toward the inner diameter. Adjacent teeth  90  cooperate to define slots. The teeth and the slots of each lamination  78  are aligned with adjacent laminations to define stator slots extending axially through the stator core  80  between the opposing end faces  112 . The end faces  112  define the opposing ends of the core  80  and are formed by the first and last laminations  79 ,  81  of the stator core  80 . A plurality of windings (also known as coils, wires, or conductors)  96  are wrapped around the stator core  80  and are disposed within the stator slots. The windings  96  may be disposed in an insulating material (not shown). Portions of the windings  96  generally extend in an axial direction along the stator slots. At the end faces  112  of the stator core, the windings bend to extend circumferentially around the end faces  112  of the stator core  80  forming the end windings  98 . While shown as having distributed windings, the windings could also be of the concentrated or hairpin type. 
     A rotor  72  is disposed within the cavity  88  of the stator  74 . The rotor  72  is fixed to a shaft  76  that is operably connected to the gearbox. When current is supplied to the stator  74 , a magnetic field is created causing the rotor  72  to spin within the stator  74  generating a torque that is supplied to the gear box via one or more shafts or gears, or the like. The electric machine may also act as generator by mechanically rotating the rotor  72  to generate electricity. 
     The stator core  80  includes an inner diameter  104  and an outer diameter  106  that are each concentric with the centerline  75  of the stator core  80 . The stator  74  is received within a housing  114 . The housing  114  may be cylindrical to match the shape of the stator. The housing  114  includes an inner circumferential surface  116  that is disposed tightly against the outer diameter  106  of the stator core  80  and an outer circumferential surface  118 . 
     The electric motor  70  may be cooled by circulating a fluid through the stator core. This may be in addition to any spray cooling (optional). The fluid may be any dielectric fluid such as oil, e.g., automatic transmission fluid. The following figures and text describe one or more example thermal management systems for the electric machine  70 . 
     Referring to  FIG.  3   , an example lamination  120  includes opposing faces  122  and an outer circumferential edge or surface (outer diameter)  124 . An inner diameter  126  of the lamination defines teeth  128 , that when stacked with other laminations, defines the stator slots  130  for receiving the windings. The lamination defines one or more openings or slots  132  located near or at outer diameter  124 . The slots  132  extend through a thickness of the lamination  120 , which is defined between the opposing faces  122 . In the illustrated embodiment, slots  132  are an open slots cut out of the outer diameter  124  to be recessed inwardly from the outer diameter. Each slot  132  has a circumferential width  134  extending between the opposing ends and a radial depth  136  that is measured from the outer diameter  124  to the inner circumferential surface  138  of the slot  132 . 
     The number of slots  132  may vary by embodiment depending upon the cooling requirements of the electric machine. As will be explained in detail below, the number of slots increases the amount of cooling channels through the stator core and also increases the number of laminations in direct contact with cooling fluid. In the illustrated embodiment, the lamination  120  includes four slots  132  that are spaced equidistant every 90 degrees. This places the slots  132  diametrically opposite from another of openings. The circumferential width  134  of the slots  132  may be measured by arc length  140 , which is an angle about the center  142 , which lies on the centerline  75 . The arc length  140  may be increased or decreased based on the cooling needs of the electric machine. The arc length of each of the slots  132  may be the same or may be different. In the illustrated embodiment, each of the slots  132  has a same arc length  140  and also a same width  134  and depth  136 , i.e., the openings  138  are all designed to be the same size. 
     The laminations may be formed of metal or metal alloy and maybe fabricated by stamping. The stamping process may start with a donut-shaped blank that is stamped in a single process to have all of the various openings, teeth, etc. The plurality of same laminations may then be stacked and permanently joined together the form a stator core. 
     Referring to  FIG.  4   , a stator core  150  is formed of a plurality of the laminations  120  that have been arranged in a linear stack  151 . The stator core  150  includes a plurality of helical cooling paths  152  that wrap around stator core  150 . Each of the cooling paths  152  begin at the first lamination  154  and terminate at a last lamination (not visible in  FIG.  4   ) to traverse the axial length of the stator core albeit in a spiral manner. The number of helical cooling paths  152  corresponds to the number of slots or openings  132  in each lamination such that the paths are equal to the number of slots in each lamination. Thus, the illustrated embodiment of  FIG.  4    has four cooling paths that commence and end 90 degrees apart around the stator core  150 . The cooling paths  152  are continuous from the first lamination  154  to the last lamination and do not intermix with the other the cooling paths. The cooling paths  154  are directly formed by the laminations  120  placing the cooling fluid is in direct contact with stator core  150  and resulting in efficient transfer of thermal energy. 
     In this example, the laminations  120  are circumferentially rotated relative to each other in sequence such that each slot  132  only partially overlaps with one or more adjacent slots to form the continuous helical cooling path(s)  152  around the stator core  150 . The amount of circumferential rotation (R) or twist between adjacent laminations is less than the arc length  140  so that the slots partially overlap to form a hole  153  for cooling fluid to drop to the next level. The partial overlap places the adjacent slots in fluid communication to form the path  152 . The rotation (R) is in a forward direction of the helical cooling path and may be the same for all laminations of the stack, i.e., all laminations are rotated by same amount relative to their neighbors. By modifying the amount of rotation (R) relative to arc length, the hydraulic properties (such as flow rate, pressure, and velocity) of the coolant paths can be adjusted based on design needs. Modifying the rotation also adjusts the number of spirals a cooling path has around the stator core, however, the rotation (R) cannot exceed the arc length otherwise the fluid path would be cutoff. The rotation R may be measured between the midpoints of the slots  132  of two adjacent laminations. Generally, increasing the rotation (R) beyond the arc length divided by 2 increases the pressure and number of spirals, whereas decreasing the rotation (R) to be less than the arc length divided by 2 decreases the pressure and the number of spirals. 
     The laminations  120  may be arranged in sets in which each lamination of the set has a same circumferential position, i.e., the slots  132  are aligned. Used herein, “a set of laminations” refers to one or more laminations. In  FIG.  4   , each set includes a single lamination resulting in all of the laminations being rotated relative to each other, but this need not be the case. 
     In the open slot embodiment, the outer diameter of the stator core is disposed tightly against the inner diameter of the housing to enclose the cooling paths. That is, the stator core and the housing cooperate to define the cooling paths. 
     Referring to  FIG.  5   , another stator core  200  has laminations  202  arranged in sets  204 . In the illustrated embodiment, each set has three laminations. Within each set, the laminations  202  are aligned so that their individual slot(s)  206  form one or more collective slots  208  of the set  204 . Like  FIG.  4   , the sets  204  are circumferentially rotated relative to each other to form the helical cooling path  210 . Like above, the slots  208  have arc lengths and the amount of the circumferential rotation of the sets is less than the arc lengths so that the slots partially overlap. While  FIG.  5    illustrates each set  204   a ,  204   b , and  204   c  as having three laminations each, this is just one example. The sets  204  they include significantly more laminations, such as 10 laminations, depending upon the number of laminations in the stack, the arc length of the slots, the thickness of the laminations, and the rotation (R). 
       FIG.  6    illustrates an alternative embodiment in which the slots are closed slots  220 . That is, rather than forming the slots into the outer diameter of the stator core, the slots  220  are disposed completely within the stator core  222  and inboard of the outer diameter  224 . In this embodiment, the stator core  222  completely defines the fluid path rather than relying on cooperation of the housing to partially bound cooling path. The details of the embodiment of  FIG.  6    are the same as  FIGS.  4  and  5    as described above and will not be repeated for brevity. 
       FIG.  7    illustrates a method  250  of assembling an electric machine having helical cooling paths as described above. At step  252 , laminations are formed with the cooling slots as described above. The slots may be open slots or closed slots. At step  254 , the laminations are arranged in sets that include one or more lamination. The laminations are stacked at step  256 . During the stacking step, the sets laminations are rotated or twisted relative to each other by an amount of rotation (R) as described above. The twisting combined with the overlap of the slots forms the helical cooling path through the stator core. At step  258 , the laminations are joined to each other to form a solid stator core. The windings are installed at operation  260 . At operation  262 , the stator is installed in the housing. In the open slot embodiment, the stator is received in the housing with the outer diameter tightly against the inner diameter of the housing to fully enclose the helical cooling paths. The rotor is installed within the stator at operation  264 . 
     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 can include, but are not limited to, strength, durability, 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.