Electric motor rotor with circulating air cooling

Abstract

A rotor for an electric machine includes an air circulation cooling system. The rotor includes a rotor core having a cavity inside the rotor core. The rotor core extends longitudinally between the two ends. The cavity is defined by the rotor core. The cavity extends through the rotor core and through at least one of the end openings. The rotor core operates to circulate air through the cavity by rotation of the rotor core.

Description

Technical Field

[0001] The present invention relates to electric machines and rotors therefor, and more particularly to a rotor system having an internal cavity that can be used to remove heat from a rotor core and surrounding components. Background Art

[0002] A rotor such as an interior permanent magnet (IPM) motor or a synchronous reluctance (SR) motor comprises a rotor core assembled around a rotating shaft to rotate within a stator. These rotors may have a segmented structure comprising a plurality of stacked laminations forming a core. The core may include internal openings, at least some of which act as flux barriers to affect the operating characteristics of the motor. The laminations of the core are formed into a disc shape having a central opening for assembly on a rotating shaft. The flux barriers are distributed around the shaft opening. The laminations may be magnetic / magnetic. The flux barrier openings may or may not contain magnets or conductors / coils.

[0003] Cooling the motor may be desirable because increased temperatures may affect motor performance and component life. In addition, motor efficiency may decrease as temperature increases. Therefore, an optimized cooling system design for improved thermal management may increase the life, performance, and reliability of the motor. For example, rotor losses may cause heat to be generated inside the rotor. It is desirable to remove heat from the motor to avoid high operating temperatures.

[0004] A coolant such as oil can be used to remove the heat. Because the stator does not rotate, supplying coolant does not increase friction. If liquid is supplied around the rotor, friction is created as the rotor rotates through the oil, resulting in rotational losses. In applications such as electric vehicles, the reduced efficiency and friction / rotational losses associated with the added heat result in a lower vehicle range before the battery needs to be recharged.

[0005] It is desirable to provide efficient cooling for the rotor of an electric motor while minimizing the disadvantages of friction losses. It is also desirable to maximize the driving range of electric vehicles. Therefore, it is desirable to provide a system for an electric motor that achieves high performance through efficient cooling. In addition, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. Summary of the invention

[0006] In various embodiments, the rotor system has an air circulation cooling system for the motor. The rotor system includes a shaft that rotates about an axis. The rotor core has a cavity located inside the rotor core and is disposed on the shaft. The rotor core extends along the axis between two ends. The cavity extends through the rotor core and through at least one end opening. The rotor core operates to circulate airflow through the cavity by rotation of the rotor core.

[0007] In additional embodiments, the rotor core includes a lamination stack disposed between two end rings.At least one end ring includes an access opening in registration with the cavity.

[0008] In additional embodiments, the rotor core includes a lamination stack disposed between two end rings. At least one end ring includes an inlet opening registered with the cavity, and includes a ramp registered with the inlet opening to direct airflow into the cavity.

[0009] In an additional embodiment, the rotor core includes a lamination stack disposed between two end rings. The cavity extends completely through the lamination stack. One end ring includes an entry opening that is aligned with the cavity, and the other end ring includes an exit opening that is aligned with the cavity.

[0010] In an additional embodiment, the stator is disposed around the rotor core, defining an air gap between the rotor and the stator. The rotor core includes an outer periphery having at least one groove facing the air gap. The airflow circulates through the entry opening, the cavity, the exit opening, and the groove in the circuit.

[0011] In an additional embodiment, the rotor core includes a lamination stack with a baffle disposed in the lamination stack. End rings are disposed at the ends of the lamination stack. An inlet opening is defined by one end ring and another inlet opening is defined by another end ring. One air circuit is defined on one side of the baffle and a second air circuit is defined on the other side of the baffle.

[0012] In additional embodiments, the rotor core includes an outer periphery having grooves.One air circuit flows air through the grooves in one direction, and another air circuit flows air through the grooves in an opposite direction.

[0013] In an additional embodiment, a rotor core includes a lamination stack with end rings at opposite ends of the lamination stack. An opening is defined by one end ring and another opening is defined by another end ring. The end rings are identical, one opening directs airflow into the rotor core, and the other opening directs airflow out of the rotor core.

[0014] In an additional embodiment, an end ring is disposed at a longitudinal end of the rotor core. The cavity extends radially outward within the rotor core to a radially outer end disposed substantially at an outer periphery of the rotor core. One end ring has an outer diameter defining a channel aligned with the radially outer end to allow air to flow along the rotor core near the radially outer end.

[0015] In an additional embodiment, the oil circuit provides cooling of the electric machine by liquid. An air gap is defined between the stator and the rotor core. The rotor core includes grooves to recirculate air flow in an air circuit around the rotor core, thereby inhibiting liquid from entering the air gap.

[0016] In a number of other embodiments, a rotor system for an electric machine has an air circulation cooling system. The rotor system includes a shaft that rotates about an axis. A cavity is formed inside a rotor core, which is disposed on the shaft and extends along the axis. The cavity extends through the rotor core and is open through at least one end of the rotor core. The rotor core circulates airflow through the cavity by the rotation of the rotor core.

[0017] In additional embodiments, the rotor core includes a lamination stack disposed between end rings. Each end ring includes an opening that is aligned with the cavity.

[0018] In additional embodiments, the rotor core includes a lamination stack disposed between end rings. At least one end ring includes an entry opening registered with the cavity and includes a ramp registered with the entry opening. The ramp directs airflow into the cavity.

[0019] In additional embodiments, the rotor core includes a lamination stack disposed between end rings. The cavity extends completely through the lamination stack. One end ring includes an entry opening that is aligned with the cavity, and the other end ring includes an exit opening that is aligned with the cavity.

[0020] In an additional embodiment, the stator is disposed around the rotor core, defining an air gap between the rotor and the stator. The rotor core includes an outer periphery having at least one groove facing the air gap. The airflow circulates through the entry opening, the cavity, the exit opening, and the groove in the circuit.

[0021] In an additional embodiment, the rotor core includes a lamination stack. A baffle is disposed in the lamination stack of the rotor core. An end ring is disposed at an end of the lamination stack. An inlet opening is defined by two end rings. One air circuit is defined on one side of the baffle, and another air circuit is defined on an opposite side of the baffle.

[0022] In additional embodiments, the rotor core includes an outer periphery having at least one groove.One air circuit flows air through the groove in one direction, and another air circuit flows air through the groove in an opposite direction.

[0023] In an additional embodiment, the rotor core includes a lamination stack, and end rings are disposed at the ends of the lamination stack. Openings are defined by the end rings. The end rings are identical, and the openings in one end ring direct the airflow into the rotor core, and the openings in the other end ring direct the airflow out of the rotor core.

[0024] In additional embodiments, end rings are disposed at longitudinal ends of the rotor core. The cavities may extend radially outward within the rotor core to a radially outer end disposed substantially at an outer periphery of the rotor core. One end ring has an outer diameter defining a channel that is aligned with at least some of the cavities at the radially outer end to allow air to flow along the rotor core near the radially outer end.

[0025] In a number of additional embodiments, a rotor system for an electric motor for a vehicle includes an air circulation cooling system. A shaft rotates about an axis. A rotor core has an internal cavity and is disposed on the shaft. A stator is disposed around the rotor core, and an air gap is defined between the stator and the rotor core. The cavity extends through the rotor core and is open through at least one end of the rotor core. The rotor core circulates airflow through the cavity and through the air gap by rotation of the rotor core. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Hereinafter, exemplary embodiments will be described in conjunction with the following drawings, wherein like numerals represent like elements, and wherein:

[0027] Figure 1 is a schematic diagram of a portion of an electric machine according to various embodiments;

[0028] Figure 2 According to various embodiments, Figure 1 A partial perspective cross-sectional view of the rotor of the motor taken along line 2-2;

[0029] Figure 3 According to various embodiments Figure 1 and Figure 2 A schematic cross-sectional view of a portion of an electric machine showing the rotor region;

[0030] Figure 4 According to various embodiments Figure 1 and Figure 2 A schematic alternative cross-sectional view of a portion of an electric machine showing the rotor region;

[0031] Figure 5 According to various embodiments Figure 1 and Figure 2 A schematic end view of a portion of a rotor having airflow features;

[0032] Figure 6 According to various embodiments Figure 1 and Figure 2 a schematic partial end view of a portion of a rotor having alternative airflow features; and

[0033] Figure 7 According to various embodiments Figure 1 and Figure 2 Schematic partial end view of a portion of a rotor having airflow features in an end ring. DETAILED DESCRIPTION

[0034] The following detailed description is merely exemplary in nature and is not intended to limit the application and uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding introduction, brief summary or the following detailed description.

[0035] refer to Figure 1 , schematically illustrates selected components of an electric machine 20, including a stator assembly 22 and a rotor assembly 24, which is configured to rotate about an axis 25 by interacting with the stator assembly 22. In the illustration, for visibility, the rotor assembly 24 is shown as being moved to the outside of the stator assembly 22. In the present embodiment, the electric machine 20 is configured as an electric motor, wherein the current that produces torque in the rotor assembly 24 is induced by the magnetic field generated by energizing the stator assembly 22. In various embodiments, the electric machine 20 is an AC motor suitable for applications requiring adjustable speed control, such as AC motors for vehicle traction motors, although the present disclosure is not limited to these applications.

[0036] The stator assembly 22 is a generally annular component that can be constructed for single-phase power or multi-phase power such as three-phase. In the present embodiment, the stator assembly 22 includes a core 26 made of a lamination stack 28. The lamination stack 28 can be formed by a stamping that is slotted to receive a winding (not shown) and is made of a soft magnetic material such as silicon steel. The winding can be a winding extending through a slot of the core 26 of the stator assembly 22. The individual laminations in the lamination stack 28 can be insulated from each other by a thin non-conductive coating. In other embodiments, another ferromagnetic material can be used to construct the lamination stack 28. The stator assembly 22 may include the above-mentioned winding for energization. The energization of the winding can be controlled to generate a rotating magnetic field.

[0037] The rotor assembly 24 includes a core 30 that includes a lamination stack 32 and is configured to receive a shaft 34. The laminations in the lamination stack 32 may be stamped or otherwise formed and made of a ferromagnetic material and may be insulated from each other by a thin non-conductive coating, or may be made of another material. End rings 42, 44 are formed at the ends of the lamination stack 32 and may be part of the core 30. The end rings 42, 44 may help accommodate the lamination stack 32 on the shaft 34 and provide support for it. In the current embodiment, the end rings 42, 44 are made of an aluminum material to achieve lightness and provide structural integrity. One or both of the end rings 42, 44 may provide multiple functions, including operating as an airflow inducer / inductor / director in the cooling system 36, which will be described in more detail below.

[0038] The rotor assembly 24 may be made of permanent magnets, or may include a conductor that generates its own magnetic field. The rotor assembly 24 is configured with a plurality of poles to generate a magnetic circuit of the rotor assembly 24 that uses the angular position of the rotor assembly 24 for interacting with the field induced by the stator assembly 22 of the motor 20. These poles may be generated at least in part by flux barriers as described below. The magnetic field of the rotor may be generated by a source of magnetic elements such as permanent magnets or electrical conductors / coils.

[0039] exist Figure 2, a cross section of the rotor assembly 24 is shown with the side 48 of one lamination of the lamination stack 32 exposed and visible. Each lamination in the lamination stack 32 includes a plurality of slot-like openings, called cavities, which may be used for a variety of purposes. Eight cavity groups 51-58 are distributed around the rotor assembly 24 between the shaft 34 and the outer periphery 50 of the rotor assembly 24, each cavity group being formed as two angled layers spaced apart in a radial direction 60. The cavity groups 51-58 are formed as openings in the stacked laminations of the lamination stack 32. The cavities in the cavity groups 51-58 extend through the rotor lamination stack 32 of the core 30 in an axial direction 59 parallel to the axis 25. The cavity groups 51-58 act as magnetic flux barriers and help define the magnetic poles of the rotor assembly 24. Some or all of the cavities in the cavity groups 51-58 may contain a source of magnetic elements. In the current embodiment, the rotor assembly 24 has eight poles defined by the cavity groups 51-58. The rotor assembly 24 may also include additional open layers that may serve specific functions in the magnetic design or other aspects of the rotor assembly 24 .

[0040] The use of air through the air circuit 35 in the cooling system 36 enables the use of the cavities of the cavity groups 51-58 of the core 30 as cooling conduits. In various embodiments, some or all of the cavities in both layers of the cavity groups 51-58 can be used as part of the air circuit. In various embodiments, the cooling system 36 can also include a liquid circuit 37, which can use pumped oil as the liquid, which can enter the rotor assembly 24 through the opening 38 in the shaft 34.

[0041] refer to Figure 3 , illustrates an area of ​​the electric machine 20 showing various aspects of the cooling system 36, including the air circuit 35 and the liquid circuit 37. A rotor assembly 24 having a shaft 34, a lamination stack 32, and end rings 42, 44 is shown. A stator assembly 22 is also shown. An air gap 68 exists between the outer periphery 50 of the rotor assembly 24 and the stator assembly 22 having a winding 69. The size of the air gap 68 is optimized to ensure free rotation of the rotor assembly 24 while minimizing magnetic losses. Typically, the cooling system 36 includes an air circuit 35 and, as shown, includes a liquid circuit 37. In some embodiments, the liquid circuit 37 may be omitted. The air circuit 35 extends through the rotor core 30 and the air gap 68. The liquid circuit 37 extends through the shaft 34, along the outside of one or both of the end rings 42, 44, and around an area of ​​the stator assembly 22.

[0042] Reference again Figure 2As shown, each cavity group 51-58 is similar, and the details of cavity group 51 will be described with the understanding that the other cavity groups 52-58 include the same elements. Cavity group 51 includes two layers of flux barriers, which in the current embodiment of the IPM motor are referred to as cavities. The radially outer layer includes cavities 73, 77, and the radially inner layer includes cavities 43, 47. Cavities 43, 47, 73, 77 define structural features of the remaining material / steel of the laminations of the lamination stack 32 in the form of struts and bridges, define the magnetic properties of the rotor core 30, and provide longitudinal openings through the lamination stack 32. As shown in FIG. Figure 3 As shown, cavity 43 corresponds to opening 74, and cavity 73 corresponds to opening 76. Openings 74, 76 each extend completely through lamination stack 32 to end rings 42, 44. It should be understood that each of the other cavities of cavity groups 51-58 also extend through lamination stack 32 in a longitudinal direction (parallel to axis 25).

[0043] The rotor assembly 24 also includes Figure 2 and Figure 3 Longitudinal features are shown in the form of grooves 78 in the outer periphery 50 of the rotor assembly 24 (specifically the lamination stack 32) and passages 80, 81, which may be scalloped, in the outer peripheries 82, 84 of the end rings 42, 44, respectively. Figure 5 Channel 80 is shown in FIG. 8 , and channel 81 is similar. Figure 3 As shown, the end ring 42 has inlets 61, 63 extending through the end ring 42 and registering / opening to openings 74, 76, respectively. The end ring 44 has outlets 65, 67 extending through the end ring 44 and registering / opening to openings 74, 76, respectively. The rotor assembly 24 and / or core 30 is configured such that during rotation, air circulates from the gap 86 outside the end ring 42 through the inlets 61, 63 in the end ring 42, through the openings 74, 76, through the outlets 65, 67 in the end ring 44, through the gap 88 outside the end ring 44, and recirculates to the gap 86 through the passage 81, the groove 78, and the passage 80. In this way, a complete air circuit 35 is provided through the rotor assembly 24. It should be understood that any or all of the cavities in the cavity groups 51-58 can be used for the air circuit 35.

[0044] In this embodiment, the motor 20 also includes a liquid circuit 37. The liquid circuit 37 includes a remote reservoir and a pump (neither shown), both of which supply liquid to the gap 86 through the opening 38 and the hole 90 in the shaft 34 to cool the stator assembly 22, especially at its end windings. Due to the rotation of the rotor assembly 24, the liquid is thrown radially outward. In order to prevent oil from flowing from the liquid circuit 37 into the air gap 68, the air circuit 35 returns air to the gap 86 through the groove 78, thereby inhibiting oil / liquid from entering the air gap 68.

[0045] refer to Figure 4 , illustrates an area of ​​the electric machine 20 that shows various aspects of an alternative version of the cooling system 36. The rotor assembly 24 is shown having a shaft 34, a lamination stack 32, and end rings 42, 44. The stator assembly 22 is also shown. An air gap 68 exists between the outer periphery 50 of the rotor assembly 24 and the stator assembly 22. Typically, the cooling system 36 includes an air circuit 35 and, as shown, a liquid circuit 37. The air circuit 35 extends through the rotor core 30 and the air gap 68. The liquid circuit 37 extends through the shaft 34, along the outside of the two end rings 42, 44, and around an area of ​​the stator assembly 22. In some embodiments, the liquid circuit 37 may not be included.

[0046] exist Figure 4 In an alternative version of the present invention, a baffle 92 is included in the lamination stack 32. The baffle 92 is configured to separate the air circuit 35 into two branches 91 and 93. The branch 91 draws air from the gap 86 into the rotor core 30 through channels 105, 106 formed by cavities (e.g., 43, 73) and returns the air to the gap 86. The branch 93 draws air from the gap 88 into the rotor core 30 through channels 107, 108 formed by cavities (e.g., 43, 73) and returns the air to the gap 88. The baffle 92 defines radial channels 94, 95 and separates the branches 91, 93. The baffle 92 includes an outer periphery 96 that does not include features corresponding to the grooves 78, thereby facilitating the movement of air on its outer periphery 96. In other words, the direction of the air flow is divided at the baffle 92 to be directed longitudinally outwardly at the outer periphery 50 in opposite directions from the radial channels 94, 95.

[0047] More specifically, in branch 91, air from gap 86 is drawn through inlets 61, 63 in end ring 42, through passages 105, 106, directed through baffle 92 through radial passages 94, and recirculated to gap 86 through air gap 68, grooves 78, and passages 80. In branch 93, air from gap 88 is drawn through outlets (inlets in this embodiment) 65, 67 in end ring 44, through passages 107, 108, directed through baffle 92 through radial passages 95, and recirculated to gap 88 through air gap 68, grooves 78, and passages 81. Thus, with two branches 91, 93, a complete air circuit 35 through rotor assembly 24 is provided. It should be understood that in this embodiment, any or all of the cavities of cavity groups 51-58 can be used for air circuit 35.

[0048] In addition, in the present embodiment, the motor 20 also includes a liquid circuit 37. The liquid circuit 37 includes a remote reservoir and a pump (neither shown), both of which supply liquid into the gap 86 through the opening 38 and the hole 90 in the shaft 34 and supply liquid into the gap 88 through the opening 38 and the hole 99 in the shaft 34 to cool the stator assembly 22. Due to the rotation of the rotor assembly 24, the liquid is thrown radially outward. In order to prevent the liquid from flowing into the air gap 68, the air circuit 35 returns air to the gap 86 and the gap 88, thereby inhibiting the liquid from entering the air gap 68.

[0049] refer to Figure 5 , inlets 61, 63 (and outlets 65, 67) are aligned with the cavities of cavity groups 51-58 to use the inner and outer cavity sets in cavity groups 51-58. In this embodiment, inlet 61 is aligned and registered with the radially inner ends of cavities 43, 47, and inlet 63 is aligned and registered with the radially inner ends of cavities 73, 77. Outlets 65, 67 can be in line with inlets 61, 63, or can be positioned further radially outward while still being aligned with the cavities.

[0050] like Figure 5 As shown, the end rings 42, 44, such as the end ring 42, may have a channel 80 (which is aligned with the groove 78) that is positioned so that the groove 78 is positioned directly outside the radially outer ends of the cavities 43, 47, 73, 77 of the cavity groups 51-58. This location is adjacent to the ends of the cavities 43, 47, 73, 77 at the outer periphery 50 of the core 30. In addition to allowing flow from the groove 78 through the channel 80, this alignment and positioning configuration directs airflow near the radially outer ends of the cavities 73, 77, where heat may be concentrated.

[0051] refer to Figure 6 , illustrates the inlet / outlet features of the end rings 42, 44. The inlet / outlet 61, 65 includes a scoop-shaped feature in the form of a ramp 100. The ramp 100 is an elongated portion of the inlet / outlet 61, 65 that extends in a circumferential direction about the axis of rotation to capture / exhaust air. The ramp 100 is formed as a recess in the corresponding end ring 42, 44, which forms a portion of the inlet / outlet 61, 65 and provides an inclined transition that slopes inward from the outer surface of the end ring 42, 44 to the main opening of the inlet / outlet 61, 65, and the inlet / outlet 61, 65 becomes deeper as it slopes. Similarly, the inlet / outlet 63, 67 includes a scoop-shaped feature in the form of an elongated and inclined ramp 102. The ramps 100, 102 can be operated to direct flow into the rotor core 30 and / or direct / draw flow out of the rotor core 30 depending on their orientation and the direction of rotation of the rotor assembly 24. For example, when as Figure 6As shown, as the rotor assembly 24 rotates in direction 104, the ramps 100, 102 operate to scoop / introduce airflow into the respective end rings 42, 44. In an embodiment, the end rings 42, 44 are identical / interchangeable, and the openings of the inlets / outlets 63, 67 are configured to direct airflow into the rotor core 30 at one end and to direct / draw airflow out of the rotor core 30 at the other end due to the direction of rotation and their orientation.

[0052] exist Figure 6 In the embodiment of FIG. 1 , the ramps 100, 102 have radial dimensions 110, 112 that are similar in size to the radial dimensions of the inlet / outlet 61, 65. This provides a selected amount of airflow consistent with the desired level of cooling. Figure 7 As shown, ramps 114, 116 taper and have radial dimensions 118, 120 that are narrower than the radial dimensions of inlet / outlet 61, 65. Otherwise, the operation of ramps 114, 116 is similar to ramps 100, 102. The selected characteristics provide for adjustment of the airflow for the desired amount of cooling. In other embodiments, ramps 100, 102 may have radial dimensions that are larger than the radial dimensions of inlet / outlet 61, 65, such as expanding outward to induce / drain greater airflow rates. When ramps 100, 102, 114, 116 are oriented at the front end of inlet 61 in the direction of rotation, they operate to draw in air. When ramps 100, 102, 114, 116 are oriented at the rear end of outlet 65 in the direction of rotation, they operate to exhaust air. It should be understood that if the direction of rotation of rotor assembly 24 is different from that of inlet / outlet 61, 65, the rotor assembly 24 may be configured to have a plurality of radial dimensions that are smaller than those of inlet / outlet 61, 65. Figure 6 If the direction of rotation of the rotor core 30 is opposite to the direction of rotation of the rotor core 30 , the ramps 100 , 102 will have the effect of directing flow away from the rotor core 30 .

[0053] Thus, the rotor of the electric machine includes a core, which may be formed from a stack of sheets, with an internal cavity forming a housing for an electromagnetic field source (such as a permanent magnet or an electrical conductor). A portion of the cavity near the electromagnetic field source may be occupied by a cavity extending through the length of the rotor and through the end rings of the rotor. The air circuit of the electric machine includes an airflow through the cavity, the end rings, and through the air gap between the rotor and the stator. The oil flow in the electric machine may also be used for cooling. The air circuit may be designed to inhibit oil from penetrating into the air gap. In addition, the end rings may include features for achieving desired airflow characteristics. The inlet / outlet features are designed to be easily cast in the end rings. The speed / rotation of the rotor and its end rings promotes air flow through the rotor core, and the inlet / outlet features are optimized to maximize airflow. Air cooling may be used in conjunction with an oil cooling feature on the end rings that directs oil from the center of the shaft to the end rings and then to the stator end windings, where the oil is not directed through the rotor core.

[0054] Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that there are a large number of variations. It should also be understood that the exemplary embodiment or multiple exemplary embodiments are only examples and are not intended to limit the scope, applicability or configuration of the present disclosure in any way. On the contrary, the foregoing detailed description will provide a convenient roadmap for implementing the exemplary embodiment or multiple exemplary embodiments for those skilled in the art. It should be understood that various changes can be made in the function and arrangement of the elements without departing from the scope of the present disclosure as set forth in the attached claims and their legal equivalents.

Claims

1. A rotor system with an air circulation cooling system for an electric machine, the rotor system comprising: a shaft configured to rotate about an axis; and a rotor core having at least one cavity inside the rotor core, the rotor core being disposed on the shaft and extending along the axis from a first end to a second end, The at least one cavity extends through the rotor core and through at least one opening in the first end and the second end, and the rotor core is configured to circulate airflow through the at least one cavity through rotation of the rotor core. 2 . The rotor system of claim 1 , wherein the rotor core comprises a lamination stack disposed between a first end ring and a second end ring, wherein the first end ring comprises an access opening in registration with the at least one cavity.

3. The rotor system of claim 1 , wherein the rotor core comprises a lamination stack disposed between a first end ring and a second end ring, wherein at least one of the first end ring and the second end ring comprises an entry opening aligned with the at least one cavity, wherein at least one of the first end ring and the second end ring comprises a ramp aligned with the entry opening, the ramp being configured to direct the airflow into the at least one cavity.

4. The rotor system of claim 1, wherein: The rotor core includes a lamination stack disposed between a first end ring and a second end ring, The at least one cavity extends completely through the lamination stack, The first end ring includes an access opening in registration with the at least one cavity, and The second end ring includes an exit opening in registration with the at least one cavity.

5. The rotor system of claim 4, comprising a stator disposed about the rotor core, an air gap defined between the rotor core and the stator, wherein the rotor core comprises an outer periphery having at least one groove facing the air gap, wherein the airflow is configured to circulate through the entry opening, the at least one cavity, the exit opening, and the at least one groove in a loop.

6. The rotor system of claim 1 , wherein the rotor core comprises a lamination stack, and comprises: a baffle disposed in the lamination stack of the rotor core; a first end ring on one end of the lamination stack; and a second end ring at the other end of the lamination stack, a first access opening defined by the first end ring and a second access opening defined by the second end ring, Wherein a first air circuit is defined on a first side of the baffle, and a second air circuit is defined on a second side of the baffle.

7. The rotor system of claim 6, wherein the rotor core comprises an outer periphery having at least one groove, wherein the first air circuit is configured to move the airflow through the at least one groove in a first direction, and the second air circuit is configured to move the airflow through the at least one groove in a second direction, wherein the second direction is opposite to the first direction.

8. The rotor system of claim 1 , comprising a lamination stack in the rotor core, one end of the lamination stack having a first end ring and the other end of the lamination stack having a second end ring, a first opening defined by the first end ring and a second opening defined by the second end ring, wherein the first end ring is identical to the second end ring, and the first opening is configured to direct the airflow into the rotor core and the second opening is configured to direct the airflow out of the rotor core.

9. The rotor system of claim 1, comprising at least one end ring disposed at a longitudinal end of the rotor core, wherein: The at least one cavity extends radially outward within the rotor core to a radially outer end disposed substantially at an outer periphery of the rotor core, The at least one end ring has an outer diameter defining a passage adjacent the radially outer end and configured to allow the airflow to pass through the rotor core at the radially outer end.

10. The rotor system of claim 1 , comprising an oil circuit configured to provide cooling of the electric machine by liquid and comprising a stator, an air gap being defined between the stator and the rotor core, wherein the rotor core comprises grooves configured to recirculate the air flow in an air circuit surrounding the rotor core, the air circuit being configured to inhibit the liquid from entering the air gap.

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