ENGINE COOLING

Abstract

Aspects of the subject disclosure relate to an electric motor that provides cooling with a fluid flow through channels containing the rotor's magnets. The flow is initially directed from the shaft into an inner channel. From the inner channel, the flow travels to magnet channels in an axial center portion of the rotor and moves in opposite axial directions. This ensures flow symmetry.

Description

INTRODUCTION

[0001] The present disclosure generally relates to the automotive, manufacturing, and industrial equipment fields. More specifically, the present disclosure relates to systems and methods for achieving engine cooling using flow magnets. In the context of electric vehicles, providing cooling using flow magnets can help optimize engine efficiency and vehicle energy consumption, ultimately increasing vehicle battery range. SUMMARY

[0002] In some embodiments, the present disclosure is directed to a cooling device. A motor can provide cooling by flowing fluid through channels containing the rotor's magnets. This provides cooling where it is most beneficial to the magnets, which can then be selected without requiring maximum resistance to thermal conditions. The flux can be directed in different directions along the length of the rotor.

[0003] According to one or more aspects of the disclosure, a rotor assembly for a motor may include a rotor shaft comprising a shaft channel and a rotor core. The rotor core may be disposed around the rotor shaft and define internal channels extending between opposite axial ends of the rotor core and magnet channels extending between the opposite axial ends of the rotor core, each of the magnet channels containing a magnet. The shaft channel may be fluidly connected to the internal channels by inlet channels at opposite ends of the rotor shaft. The internal channels may be fluidly connected to the magnet channels by transition channels disposed axially between the inlet channels.

[0004] According to one or more aspects of the disclosure, a motor may include a stator and a rotor. The stator may include stator coils configured to generate a rotating magnetic field. The rotor may define a shaft channel extending along a rotor axis. The rotor may further define internal channels distributed around the shaft channel and configured to receive fluid from the shaft channel via inlet channels at opposite ends of the rotor shaft. The rotor may further define magnetic channels with magnets distributed around the internal channels and configured to receive fluid from the internal channels via transition channels disposed axially between the inlet channels.

[0005] According to one or more aspects of the disclosure, a method for cooling a rotor assembly of a motor may include: providing the rotor assembly comprising a rotor shaft and a rotor core; providing a fluid to a shaft channel of the rotor shaft; and directing the fluid to flow from the shaft channel through the magnet channels of the rotor core, wherein the fluid flow in each of the magnet channels is directed in opposite directions toward each of the opposite axial ends of the rotor assembly, and each of the magnet channels includes a magnet. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Certain features of the subject technology are set forth in the appended claims. However, for illustrative purposes, several embodiments of the subject technology are set forth in the following figures. Fig. 1 illustrates a perspective cut-away view of an electric motor according to one or more implementations of the subject technology. Fig. 2 illustrates a side cross-sectional view of a system for an electric motor according to one or more implementations of the subject technology. Fig. 3 illustrates a perspective cut-away view of a rotor assembly according to one or more implementations of the subject technology. Fig. 4 illustrates a side view of a rotor assembly according to one or more implementations of the subject technology. Fig. 5 illustrates a front cross-sectional view of a rotor core according to one or more implementations of the subject technology. Fig. Figure 6 illustrates another front sectional view of the rotor core of Fig. 5 according to one or more implementations of the subject technology. Fig. 7 illustrates a perspective view of a transition layer of a rotor core according to one or more implementations of the subject technology. Fig. 8 illustrates a perspective view of a transition layer of a rotor core according to one or more implementations of the subject technology. Fig. 9 illustrates a perspective view of a rotor assembly according to one or more implementations of the subject technology. Fig. 10 illustrates a perspective view of an end plate according to one or more implementations of the subject technology. Fig. 11 illustrates a perspective view of an end plate according to one or more implementations of the subject technology. Fig. 12 illustrates a flow diagram of an example process for directing fluid in symmetrical flow in a motor according to one or more implementations of the subject technology. Fig. 13 illustrates a flowchart of an example process for removing heat from components of an engine according to one or more implementations of the subject technology. DETAILED DESCRIPTION

[0007] The detailed description set forth below is intended as a description of various configurations of the subject technology and is not intended to represent the only configurations in which the subject technology may be practiced. The accompanying drawings are incorporated herein and form a part of the detailed description. The detailed description includes specific details for the purpose of providing a thorough understanding of the subject technology. However, the subject technology is not limited to the specific details set forth herein and may be practiced using one or more other implementations. In one or more implementations, structures and components are shown in block diagram form to avoid obscuring the concepts of the subject technology.

[0008] The present description generally relates to an electric motor including a rotor assembly with permanent magnets. One problem that can arise with motor cooling architectures is the concentration of motor losses near the outer surface of the rotor assembly. For example, motor losses result in heat generation that can be extracted by stator and rotor cooling. Excessive heating of the magnets of a motor (e.g., in the rotor assembly) can lead to damage to the magnets over time. In some embodiments, the present disclosure is directed to achieving cooling of the magnets of a rotor assembly, for example, by a fluid flow directed through end plates of the rotor assembly.Instead of cooling the magnets of a rotor assembly indirectly via the rotor core, the magnets may be provided in channels that receive a fluid flow to cool the magnets through direct contact with the cooling fluid flow. By managing the thermal conditions of the magnets, the magnets can be protected from demagnetization. In some embodiments, such management may enable the selection of magnets with lower thresholds for withstanding thermal conditions.

[0009] Accordingly, in some embodiments, the present disclosure is directed to a cooling device. A motor can provide cooling by fluid flow through channels containing the magnets of the rotor assembly. This provides cooling where it is most beneficial to the magnets, which can then be selected without requiring maximum resistance to thermal conditions. The flow can be directed in different directions along the length of the rotor.

[0010] Referring to Fig. 1, a motor may include a stator and a rotor to provide rotational power to a shaft. Fig. 1 is a partial perspective view of a motor 4 having a stator 6 and a rotor assembly 10.

[0011] In some embodiments, as in Fig. 1, a motor 4 may include a generally cylindrical rotor shaft 12 concentrically surrounded by a cylindrical rotor assembly 10. As used herein, "cylindrical" and "annular" refer to structures having a generally circular inner cross-sectional shape and a likely approximately circular outer cross-sectional shape, although this outer cross-sectional shape may vary somewhat, including flat or irregular portions. The rotor shaft 12 and the rotor assembly 10 are configured to rotate together, possibly at high speed (RPM), concentrically about a common central axis 20. The rotor assembly 10 may be made of electrical steel. The rotor shaft 12 may be made of steel and / or another possible metal or metal alloy.

[0012] The motor 4 may include a stator 6 comprising stator coils 8 configured to generate a rotating magnetic field. The rotating magnetic field may be generated by passing multiphase currents through the stator coils 8. The stator coils 8 may form segments of their windings distributed around the rotor assembly 10. As shown, for example, in Fig. 1, the stator coils 8 may form segments, each extending in a direction generally parallel to the central axis 20 of the rotor assembly 10. The rotating magnetic field generated by the stator 6 may rotate about the central axis 20 of the rotor assembly 10. Neither the stator 6 nor the stator coils 8 need to move to generate the rotating magnetic field. The coils may, for example, be operated with an alternating current, with different segments thereof having a different current direction and / or current strength at a given time. Since the current direction and / or current strength for each segment of the stator coils 8 changes over time, the magnetic field generated near it may change accordingly. Accordingly, the resulting magnetic field may be referred to as a magnetic field (e.g.with alternating magnetic field directions extending circumferentially around the central axis 20) that rotates about the central axis 20. The rotating magnetic field may further extend through the rotor assembly 10, which may include permanent magnets 18. The rotating magnetic field generated by the stator 6 may magnetically interact with such components of the rotor assembly 10 to cause rotation of the rotor assembly 10 about the central axis 20.

[0013] End windings of the stator coils 8 (e.g., crown end windings and / or weld end windings) of the stator 6 may be made of a conductive material, such as copper or another suitable metal or material. The end windings of the stator coils 8 may extend axially beyond the rotor assembly 10 and / or concentrically surround the rotor assembly 10. The end windings of the stator coils 8 are connected in parallel and / or in series to form a set of windings with multi-phase terminals that are operatively connected to a driving force, such as an inverter consisting of electrical switches.

[0014] The rotor shaft 12 and / or the rotor assembly 10 can be rotated using a first bearing assembly 25 disposed at the first end of the rotor shaft 12 and a second bearing assembly 27 disposed at the second end of the rotor shaft 12. Thus, the rotor assembly 10 and / or the rotor shaft 12 can be rotated about the central axis 20 in response to the rotating magnetic field generated by the stator 6. The rotor shaft 12 can accordingly provide a torque output.

[0015] Fig. Figure 2 shows a block diagram of a system 2 including a fluid reservoir 100, a pump 110, and a rotor assembly 10 of an electric motor. In some embodiments, as shown in Fig. 2, the rotor assembly 10 may include a rotor core 14 and one or more end plates (e.g., a first end plate 32 and a second end plate 34) at each of the opposite axial ends of the rotor core 14. In some embodiments, the rotor assembly 10 is an inner permanent magnet (IPM) rotor, which can inherently produce a relatively higher torque density and power density due to the combined magnetic torque and reluctance torque, for example, relative to an induction motor. In some embodiments, although IPM rotor losses, core losses, and magnetic losses may be relatively lower than conventional induction motors, rotor loss still occurs with permanent magnet motors. For example, rotor losses can dissipate as heat, which can affect both the permanent magnet remanence (Br) and coercivity (Hcj), resulting in torque reduction and less demagnetization protection.Accordingly, rotor cooling can improve the operation of a motor (e.g., an IPM motor) to increase power and achieve improved demagnetization performance in the motor.

[0016] To achieve cooling of the rotor assembly 10, a fluid (e.g., a liquid lubricant such as oil) is provided through the rotor assembly 10 via first internal channels 46, second internal channels 48, first magnetic channels 56, and second magnetic channels 58. The fluid is provided from a fluid reservoir 100 and directed by a pump 110 to the rotor shaft 12, such as through a shaft channel 22. The fluid reservoir may include and / or be fluidly coupled to one or more other conditioning components, such as a heat exchanger and / or a cooler.

[0017] The rotor shaft 12 may define the shaft channel 22, for example, along a rotational axis of the rotor assembly 10. The rotor core 14 may be disposed around the rotor shaft 12. The rotor core 14 may include one or more layers and define one or more first magnetic channels 56 and one or more second magnetic channels 58, each extending between opposite axial ends of the rotor core 14. The rotor assembly 10 may further include one or more first end plates 32 and one or more second end plates 34 at each of the opposite axial ends of the rotor core 14.

[0018] The rotor shaft 12 may define one or more first inlet channels 42 that extend through a first portion of a wall at a first end of the rotor shaft 12. It should be understood that the first inlet channels 42 may be further defined by one or more channels of the first end plate 32, for example, facing the rotor core 14, as further described herein. In some embodiments, the first inlet channels 42 may be defined through and / or between the first end plate 32 and the rotor core 14. In some embodiments, the first inlet channels 42 may be defined entirely within the first end plate 32. The one or more first inlet channels 42 may provide fluid communication between the shaft channel 22 of the rotor shaft 12 and the first internal channels 46 of the rotor core 14.The one or more first transition channels 52 may provide fluid communication between the first inner channels 46 and the first magnetic channels 56 of the rotor core 14. First outlet channels 62 at opposite ends of the first magnetic channels 56 may be defined by one or more channels of the first end plate 32 and the second end plate 34, for example, facing the rotor core 14, as further described herein.

[0019] The rotor shaft 12 may further define one or more second inlet channels 44 that extend through a second portion of the wall at a second end of the rotor shaft 12. It should be understood that the second inlet channels 44 may be further defined by one or more channels of the second end plate 34, for example, facing the rotor core 14, as further described herein. In some embodiments, the first inlet channels 44 may be defined by and / or between the second end plate 34 and the rotor core 14. In some embodiments, the second inlet channels 44 may be defined entirely within the second end plate 34. The one or more second inlet channels 44 may provide fluid communication between the shaft channel 22 of the rotor shaft 12 and the second internal channels 48 of the rotor core 14.The one or more second inlet channels 54 may provide fluid communication between the second inner channels 48 and the second magnetic channels 58 of the rotor core 14. Second outlet channels 64 at opposite ends of the second magnetic channel 58 may be defined by one or more channels of the first end plate 32 and the second end plate 34, for example, facing the rotor core 14, as further described herein.

[0020] As the relatively cool oil enters the shaft channel 22 (e.g., of the hollow rotor shaft 12, as illustrated), the fluid then flows to the first inlet channels 42 and the second inlet channels 44, which are open to the shaft channel 22, proximal to respective opposite axial ends of the rotor core 14. Each of the first inlet channels 42 and the second inlet channels 44 may include a respective set of channels arranged azimuthally about an axis of rotation (e.g., in a uniformly spaced pattern or other suitable arrangement). The fluid flows approximately axially in the first magnetic channels 46 in a first direction, and the fluid flows approximately axially in the second magnetic channels 48 in a second direction opposite the first direction, thereby forming an axial cross-flow arrangement.The fluid then flows through the first transition channels 52, which connect the first inner channels 46 to the first magnetic channels 56, and through the second transition channels 54, which connect the second inner channels 48 to the second magnetic channels 58. From the first transition channels 52 and the second inner channels 48, the fluid flows approximately axially in opposite directions into each of the first magnetic channels 56 and the second magnetic channels 58, forming a symmetrical flow arrangement. As the fluid flows through the first magnetic channels 56 and the second magnetic channels 58, the fluid absorbs heat generated by losses in the rotor assembly 10 through contact between the fluid, the magnets contained therein (not shown), and the walls of the rotor core 14 (which may include, for example, electrical steel).Where the first magnetic channels 56 and the second magnetic channels 58 form a symmetrical flow arrangement, the rotor assembly 10 may have a relatively more uniform temperature gradient (e.g., axial temperature gradients are reduced). After the fluid absorbs heat from losses in the rotor assembly 10, it flows out of the first outlet channels 62 and the second outlet channels 64, for example, along the first and second end plates 32 and 34 facing the respective sides of the rotor core 14. The fluid travels radially outward along the first outlet channels 62 and the second outlet channels 64 (e.g., due to centrifugal forces). The flow may optionally include cooling and / or other thermal management of the stator (e.g., at the end windings). The fluid may flow, drip, or otherwise return to the reservoir 100 to be recirculated in the fluid system (e.g.,by operating pump 110 to repeat the heat transfer in a continuous flow).

[0021] In one illustrative example, the electric motor 2 of the system may correspond to an electric motor with improved performance, at least in part due to effective heat extraction using fewer parts. To illustrate, a rotor, such as rotor assembly 10, may have a uniform thermal gradient as the fluid extracts heat from the core of the rotor assembly 10. In some embodiments, the rotor core 14 may include a plurality of laminations and the first and second end plates 32 and 34, which may have a common construction, resulting in relatively inexpensive parts and fewer parts or part types.

[0022] With reference now to Fig. 3, the magnetic channels can be arranged to allow current in one or more of a variety of directions. As shown in Fig. 3, the rotor core 14 may be arranged around the rotor shaft 12.

[0023] In some embodiments, the rotor assembly 10 may define one or more first inlet ports 42 extending through a first portion of a wall of the rotor shaft 12 and / or between the rotor core 14 and the first end plate 32. The first inlet ports 42 of the rotor core 14 are shown on radially opposite sides of the rotor shaft 12. It should be understood that one or more of the first inlet ports 42 may be positioned at any circumferential location on a first side of the rotor shaft 12. The second inlet ports (not shown) may be located at different circumferential positions along the rotor core 14.

[0024] In some embodiments, the rotor assembly 10 may define one or more first inlet channels 42 extending through a first portion of a wall of the rotor shaft 12 and / or between the rotor core 14 and the first end plate 32. The first inner channels 46, the first transition channels 52, and the first magnetic channels 56 of the rotor core 14 are shown on radially opposite sides of the rotor shaft 12. It should be understood that one or more of the first inner channels 46, the first transition channels 52, and / or the first magnetic channels 56 may be positioned at any circumferential positions within the rotor core 14. The second inner channels and / or second magnetic channels (not shown) may be located at different circumferential positions within the rotor core 14.

[0025] In some embodiments, the rotor assembly 10 may define one or more first exhaust ports 62, each extending between the rotor core 14 and the first end plate 32 or between the rotor core 14 and the second end plate 34. In some embodiments, the first exhaust ports 62 and / or the second exhaust ports 64 may be defined through and / or between the rotor core 14 and the first end plate 32 or between the rotor core 14 and the second end plate 34. The first inlet ports 62 are shown on radially opposite sides of the rotor shaft 12. It should be understood that one or more of the first exhaust ports 62 may be positioned at any circumferential locations with respect to the rotor shaft 12. The second exhaust ports (not shown) may be located at different circumferential positions along the rotor core 14 and / or on radially opposite sides of the rotor shaft 12.

[0026] With reference now to Fig. 4, the magnetic channels of a rotor can extend in one or more of different directions. For example, as in Fig. 4, the body of the rotor assembly 10 may include a plurality of laminations (e.g., steel) formed as layers 24 having first and second magnetic channels 56 and 58. Although five main layers 24 are illustrated, it should be understood that any number of main layers 24 may be provided. Each of the main layers 24 may be circumferentially offset with respect to an adjacent one of the other main layers 24. Such offset may provide flux in a non-axial path through each of the first and second magnetic channels 56 and 58. For example, the first and second magnetic channels 56 and 58 may extend on a linear or non-linear path that partially wraps around the central axis of the rotor assembly 10, rather than parallel to the central axis. The path may extend in a first direction (e.g.,around the central axis) on a first side of the rotor core 14 and / or through a first set of the main layers 24. The path may reach an apex at a location within the rotor core 14, such as at an axial midpoint and / or between a plurality of transition channels (not shown). On the other side of the apex, the path may wind in a second direction (e.g., around the central axis) opposite the first direction on a second side of the rotor core 14 and / or through a second set of the main layers 24. The shape of such a path may be generally spiral and / or zigzag. Thus, the path may be symmetrical along the length of the rotor core 14. If the windings have such symmetry, an inlet channel on one side (e.g., at the first end plate 32) of each of the first and second magnetic channels 56 and 58 may be parallel with respect to the outlet channel on the opposite side (e.g.,at the second end plate 34) of the corresponding one of the first and second magnetic channels 56 and 58. The winding directions of the path can be selected to promote fluid flow toward the ends of the rotor core 14. For example, the rotor core 14 can be rotated so that the apex of each path is in front of other portions of the paths. In such a configuration, rotation of the rotor core 14 can force the fluid toward the axial ends of the first and second magnetic channels 56 and 58.

[0027] It is understood that the first and second magnetic channels 56 and 58 may also extend in a manner other than Fig. 4. In some embodiments, the first and second magnetic channels 56 and 58 may form paths that wind in a single direction (e.g., helically) between opposite ends of the rotor core 14. This may result in an inlet channel on one side (e.g., at the first end plate 32) of each of the first and second magnetic channels 56 and 58 being circumferentially offset with respect to the outlet channel on the opposite side (e.g., at the second end plate 34) of the corresponding one of the first and second magnetic channels 56 and 58. Thus, the first and second magnetic channels 56 and 58 may form a generally helical path. Such a helical path may facilitate the travel of fluid therethrough as the rotor assembly 10 rotates.

[0028] In some embodiments, the first and second magnetic channels 56 and 58 may form paths that extend parallel to the central axis of the rotor assembly 10 and / or to each other. When the windings extend linearly and / or otherwise parallel in this manner, an exhaust channel on one side (e.g., at the first end plate 32) of each of the first and second magnetic channels 56 and 58 may be circumferentially aligned with the exhaust channel on the opposite side (e.g., at the second end plate 34) of the corresponding one of the first and second magnetic channels 56 and 58.

[0029] As in Fig. 4, one or more transition layers 26 may be disposed between and separating otherwise adjacent main layers 24 of the rotor core 14. The one or more transition layers 26 may each form transition channels that provide fluid communication from the inner channels (not shown) to the first and second magnetic channels 56 and 58. The main layers 24 provide structure to separate the inner channels (not shown) from the first and second magnetic channels 56 and 58. Although two transition layers 26 are illustrated, it is understood that any number of transition layers 26 may be provided.In general, the one or more transition layers 26 may be positioned on axial sides of one or more main layers 24 such that the transition channels formed by the transition layers 26 may provide fluid communication at axial locations that are more central than other portions of the channels to which they provide such fluid communication. This allows the current in the first and second magnetic channels 56 and 58 to be controlled from one or more substantially axially central locations and in substantially opposite directions.

[0030] With reference to the Fig. 5 and Fig. 6, the rotor core may provide different structures at different sections therein to form the desired channels and passages. Fig. Figure 5 shows a cross-sectional view of an illustrative rotor core 14 having first and second internal channels 46 and 48 and first and second magnetic channels 56 and 58, according to some embodiments of the present disclosure. Such a cross-sectional view may be taken along a main layer 24 of the rotor core 14.

[0031] The first and second magnetic channels 56 and 58 may be arranged azimuthally around a rotor shaft (not shown) fitted into the rotor core 14. For example, as in Fig. 5, the rotor core 14 includes 16 pairs of magnetic channels (e.g., eight pairs of first magnetic channels 56 and eight pairs of second magnetic channels 58), with each pair of first and second magnetic channels 56 and 58 forming a repeating pattern, with each corresponding pair being azimuthally spaced 45 degrees apart. Each of the first and second magnetic channels 56 and 58 may include one or more magnets 18 positioned therein. For example, the magnets 18 may occupy a portion of the corresponding one of the first and second magnetic channels 56 and 58. The magnets 18 may be fixed in position, for example, based on the geometry of the corresponding one of the first and second magnetic channels 56 and 58 and / or a magnetic coupling to a body 24 of the rotor core 14.The magnets 18 may occupy a space such that portions of the first and second magnet channels 56 and 58 remain open to allow fluid flow therethrough. Thus, the first and second magnet channels 56 and 58 may allow fluid to flow directly against the magnets 18 to cool them. The flow spaces may be provided on either side of any given magnet 18, including at its long ends.

[0032] The first and second inner channels 46 and 48 may be arranged azimuthally around a rotor shaft (not shown) fitted into the rotor core 14. For example, the rotor core 14 includes, as shown in Fig. 4, 16 inner channels (e.g., eight first inner channels 46 and eight second inner channels 48). As further shown in Fig. 5, each of the main layers 24 may provide a structure to separate the first and second inner channels 46 and 48 from the first and second magnetic channels 56 and 58.

[0033] Fig. 6 shows a cross-sectional view of an illustrative rotor core 14 having first and second internal channels 46 and 48, first and second transition channels 52 and 54, and first and second magnetic channels 56 and 58, according to some embodiments of the present disclosure. Such a cross-sectional view may be taken along a transition layer 26 of the rotor core 14. The one or more transition layers 26 may each form first and second transition channels 52 and 54 that provide fluid communication from the first and second internal channels 46 and 48 to the first and second magnetic channels 56 and 58. Therefore, the transition layers 26 may be provided where the formation of transition channels is desired.While the first and second inner channels 46 and 48 may be provided only where transition layers 26 are positioned, the first and second inner channels 46 and 48 and the first and second magnetic channels 56 and 58 may extend through both the main layers 24 and the transition layers 26. Accordingly, the first and second inner channels 46 and 48 and / or the first and second magnetic channels 56 and 58 may extend continuously across the rotor core 14.

[0034] In some embodiments, the first and second magnetic channels 56 and 58, such as those shown in the Fig. 5 and Fig. 6, and / or similar magnet channels, facilitate the passage of coolant (e.g., oil) to one or more sides of the magnets 18 positioned therein, thereby cooling the magnets 18 from such sides. While the portions of the first and second magnet channels 56 and 58 not occupied by magnets 18 may be located at opposite long ends of the magnets 18, it is understood that the gaps for fluid flow may be formed at any portion and / or side of the magnets 18. In some examples, most of the rotor losses and greatest heating occur at the outer periphery of the rotor. Accordingly, it may be advantageous to flow coolant on one or more sides (e.g., the top) of the magnets 18 where the losses are greatest.For example, a gap may be provided on one or more of a radially outermost side, a radially innermost side, and / or one or both opposite circumferential sides of a given magnet 18. To facilitate such flow, the first and second magnet channels 56 and 58 may be provided with sufficient width, height, and / or other dimensions to provide a gap between the magnets 18 and the corresponding adjacent portion of the main layer 24 and / or another layer forming the body of the rotor core 14.

[0035] With reference to Fig. 7 and Fig. 8, transition layers of a rotor core may provide one or more structures that facilitate fluid communication between radially adjacent channels of the rotor core. Fig. Figure 7 shows a perspective view of an illustrative transition layer of a rotor core having internal channels, transition channels, and magnetic channels according to some embodiments of the present disclosure. As shown in Fig. 7, each transition layer 26 may form the first and second transition channels 52 and 54 that provide fluid communication from the first and second interior channels 46 and 48 to the first and second magnetic channels 56 and 58. In some embodiments, the structure of the transition layer 26 may define the first and second interior channels 46 and 48, the first and second transition channels 52 and 54, and the first and second magnetic channels 56 and 58, respectively, in adjacent pairs separated by a wall or septum. Thus, each of the first and second interior channels 46 and 48 may be fluidly connected to a corresponding one of the first and second transition channels 52 and 54 to a corresponding one of the first and second magnetic channels 56 and 58.

[0036] Fig. Figure 8 shows a perspective view of another illustrative transition layer of a rotor core having internal channels, transition channels, and magnetic channels according to some embodiments of the present disclosure. As shown in Fig. 8, each transition layer 26 may form the first and second transition channels 52 and 54 that provide fluid communication from the first and second interior channels 46 and 48 to the first and second magnetic channels 56 and 58. In some embodiments, the structure of the transition layer 26 may define the first and second interior channels 46 and 48, the first and second transition channels 52 and 54, and the first and second magnetic channels 56 and 58 with open spaces that allow fluid communication. Thus, each of the first and second interior channels 46 and 48 may be fluidly connected to a plurality of the first and second magnetic channels 56 and 58 through a corresponding one of the first and second transition channels 52 and 54.

[0037] With reference to Fig. 9 to 11, a rotor assembly may include end plates to facilitate fluid flow. As shown in Fig. 9, the rotor assembly 10 may include the rotor shaft 12, the first and second end plates 32 and 34, and the rotor core 14. The rotor shaft 12 includes the shaft channel 22, which opens to first inlet channels 42 formed at least partially by the first end plate 32. The second end plate 34 may at least partially form second inlet channels (not shown). The first and second end plates 32 and 34 may be identical but azimuthally spaced (e.g., by approximately 45 degrees) from each other such that the first inlet channels 42 are azimuthally aligned with corresponding first exhaust channels 62 and second exhaust channels 64 are azimuthally aligned with corresponding second inlet channels (not shown). It will be understood that the circumferential arrangement of the first and second end plates 32 and 34 can accommodate any spiral or zigzag winding of the first and second magnetic channels 56 and 58, such as that shown in Fig. 4 is illustrated.

[0038] A fluid, such as oil, enters the first inlet ports 42 and fills the first end plate 32 (e.g., the cavities defined by the first inlet ports 42 of the first end plate 32). Similarly, the fluid enters second inlet ports (not shown) and fills the second end plate 34. After entering the first inlet ports 42 and the second inlet ports, the fluid travels axially through the rotor core 14 (e.g., the rotor core 14 may be formed of electrical steel). For example, the rotor core 14 includes the first and second internal channels, which correspond to first and second outlet channels 62 and 64. As the fluid flows through the first and second internal channels, the first and second transition channels, and the first and second magnet channels, heat (e.g., caused by rotor loss) is absorbed by the fluid due to contact between the fluid and the rotor core 14 and / or the magnets therein.

[0039] In some embodiments, the first inlet channels 42 (e.g., cavities) of the first end plate 32 are aligned with the first internal channels 46 in the rotor core 14 (e.g., the rotor lamination stack), and similarly, the second inlet channels 44 (not shown) of the second end plate 34 are aligned with the second magnetic channels 48 in the rotor core 14 (e.g., the rotor lamination stack). The first and second internal channels 46 and 48 direct flow to the first and second magnetic channels to enable symmetrical outward fluid flow for rotor heat dissipation with a uniform temperature gradient in the rotor assembly 10. After absorbing heat from the rotor loss, the fluid exits the first and second end plates 32 and 34 via the first and second outlet channels 62 and 64 and then travels radially outward, thereby heating the stator end windings on each axial end (e.g.,The fluid extracts heat symmetrically from the end windings, resulting in equalization of end windings at both axial ends of the stator. In another illustrative example, the use of common first and second end plates 32 and 34 enables lower cost and fewer parts. Furthermore, symmetrical oil flows to both end windings result in equalized cooling at the ends of the stator.

[0040] In some embodiments, each of the first and second inlet channels 42 and 44 may extend to and be fluidly connected to one or more of the first and / or second internal channels 46 and 48. Thus, fluid may be directed from any one or more of the first and second inlet channels 42 and 44 to a plurality of the first and second internal channels 46 and 48.

[0041] In some embodiments, each of the first outlet channels 62 may be fluidly connected to one or more of the first magnetic channels 56, and each of the second outlet channels 64 may be fluidly connected to one or more of the second magnetic channels 58. Thus, fluid may be routed from a plurality of the first and second magnetic channels 56 and 58 to any one or more of the first and second outlet channels 62 and 64.

[0042] Fig. Figure 10 shows a perspective view of an illustrative first end plate 32 having first inlet channels 42, first outlet channels 62, and second outlet channels 64 according to some embodiments of the present disclosure. For illustration, the first end plate 32 may, but need not, be the same as or similar to the first and second end plates 32 and 34 of the Fig. 2 to 4 and 9. As in Fig. 10, the first end plate 32 may include four first inlet channels 42, indicated as cavities or recesses. For example, a fluid, such as oil, is directed from a shaft channel of a rotor shaft into the first inlet channels 42 and then flows from the first inlet channels 42 into longitudinally (e.g., axially or helically) directed inner channels and out of outlet channels of another end plate (e.g., identical to the first end plate 32, but azimuthally spaced at 45 degrees). In some embodiments, the first inlet channels 42 may extend or branch into one or more paths that may extend to each of the plurality of inner channels and / or across multiple portions of such inner channels. The first and second end plates 32 may also include first and second outlet channels 62 and 64 through which the fluid may exit after flowing from a recess of the other (e.g.,opposite) end plate through magnetic channels of the rotor (e.g. as in . Fig. 2 through 4 and 9). The first and second outlet ports 62 and 64 may include closed channels and / or recesses to expose a corresponding magnetic channel. In one illustrative example, a rotor may include two endplates (e.g., a front plate and a back plate), each identical to the first endplate 32 and timed relative to each other to form one or more of the flow patterns described herein.

[0043] Fig. Figure 11 shows a perspective view of another illustrative first end plate 32 having a common annular chamber 36 forming the first inlet channels, according to some embodiments of the present disclosure. For illustration, the first end plate 32 may, but need not, be the same as or similar to the first and second end plates 32 and 34 of the Fig. 2 to 4 and 9. As in Fig. 11, the first end plate 32 may include an annular chamber 36 for collecting fluid. The annular chamber 36 may be continuous around a central region (e.g., to receive the rotor shaft) and may be fluidly connected to each of the internal channels, which may be at least partially defined by the rotor core. The collection of fluid in the annular chamber 36 may help direct fluid into the first and second internal channels, particularly as the rotor assembly rotates about an axis and centrifugal forces push the fluid radially outward. For example, a fluid, such as oil, is directed from a shaft channel of a rotor shaft into the annular chamber 36 and then flows out of the annular chamber 36 into longitudinal (e.g., axial or spiral) internal channels. In one illustrative example, a rotor may have two end plates (e.g.,a front plate and a rear plate), each identical to the first end plate 32 and clocked relative to each other to form the flow pattern described herein.

[0044] Fig. 12 illustrates a flowchart of an exemplary process 1200 for directing fluid flow in a motor according to one or more implementations of the subject technology. For purposes of explanation, the process 1200 is primarily described herein with reference to components of the system, motor, rotors, and / or assemblies of Fig. 1 to 11. However, the process 1200 is not limited to the systems, motor, rotors and / or assemblies of the Fig. 1 through 10, and one or more blocks (or acts) of process 1200 may be performed by one or more other components of other suitable devices, apparatus, or systems. Further, for purposes of explanation, some of the blocks of process 1200 are described herein as occurring serially or linearly. However, multiple blocks of process 1200 may occur in parallel. In addition, the blocks of process 1200 need not be performed in the order shown, and / or one or more blocks of process 1200 need not be performed and / or may be replaced by other acts.

[0045] Block 1202 includes providing fluid to an interior of a rotor shaft. Block 1202 may include pumping the fluid to an increased pressure to cause the fluid to flow into the interior of the rotor shaft (e.g., a hollow interior region, such as the shaft channel 22 of Fig. 1 and Fig. 2). In some embodiments, block 1202 may include filtering the fluid, regulating a pressure of the fluid, controlling one or more flow paths of the fluid, controlling a flow rate of the fluid, controlling a temperature of the fluid (e.g., using a radiator or other heat exchanger), or a combination thereof. In one illustrative example, block 1202 may include providing an interior of the rotor shaft with pressurized oil based on the oil flow.

[0046] Block 1204 includes directing fluid in a first path from a first inlet channel to first magnet channels in a first direction. In some embodiments, the fluid inside the rotor shaft provided in block 1202 is caused to flow in the first path based on a pressure field in the first path (e.g., the fluid flows in a path of decreasing pressure). For example, the first path may be open to the interior of the rotor shaft, allowing fluid to flow from the interior of the rotor shaft through the first path. The first path may include, for example, a first inlet channel connected to the interior of the rotor shaft (e.g., in fluid communication with or otherwise open to it), one or more first channels, and a first outlet channel through which the fluid exits.

[0047] Block 1206 includes directing fluid from the first magnetic channels to first end windings. In some embodiments, after the fluid flows through the first magnetic channels, the fluid flows radially outward to spray or otherwise impinge on first end windings (e.g., of a stator corresponding to the rotor). The fluid may flow to the first end windings under the effects of centrifugal acceleration, pressure forces, gravity, or a combination thereof. It should be understood that block 1206 may optionally be omitted, so that flow need not be directed to first end windings.

[0048] Block 1208 includes directing fluid in a second path from a second inlet channel to second magnet channels in a second direction. In some embodiments, the fluid inside the rotor shaft provided in block 1202 is caused to flow in the second path based on a pressure field in the second path (e.g., the fluid flows in a path of decreasing pressure). For example, the second path may be open to the interior of the rotor shaft, allowing fluid to flow from the interior of the rotor shaft through the second path. The second path may include, for example, a second inlet channel connected to the interior of the rotor shaft (e.g., in fluid communication with or otherwise open to it), one or more second magnet channels, and a second outlet channel through which the fluid exits.

[0049] Block 1210 includes directing fluid from the second magnetic channels to second end windings. In some embodiments, after the fluid flows through the second magnetic channels, the fluid flows radially outward to spray or otherwise impinge upon second end windings (e.g., of a stator corresponding to the rotor). The fluid may flow to the second end windings under the effects of centrifugal acceleration, pressure forces, gravity, or a combination thereof. It should be understood that block 1210 may optionally be omitted, so that the flow need not be directed to second end windings.

[0050] It is understood that blocks 1208 and / or 1210 may be omitted or modified, for example, when the current within the magnetic channels is in a single direction (e.g., axial direction). It is further understood that in addition to one or more of the embodiments described herein with respect to Fig. 12 described paths, other paths with corresponding directions can also be provided.

[0051] Block 1212 includes collecting and recirculating the fluid. For example, after the fluid flows through or otherwise past the first and second end windings, the fluid is collected and recirculated. Block 1212 may include collecting the fluid in a basin or a region of an oil pan or sump, drawing (e.g., via fluid pressure) or gravity draining the fluid to a filter, pump, radiator, storage space, any other suitable components, or any combination thereof. In some embodiments, for example, fluid (e.g., oil) is directed past the first and second end windings and then collected in a basin for recirculation into the interior of the rotor shaft (e.g., after removing heat via a radiator or heat exchanger).

[0052] Fig. 13 illustrates a flowchart of an exemplary process 1300 for removing heat from components of an engine according to one or more implementations of the subject technology. For purposes of explanation, the process 1300 is primarily described herein with reference to components of the system, engine, rotors, and / or assemblies of Fig. 1 to 11. However, the process 1300 is not limited to the systems, motor, rotors and / or assemblies of the Fig. 1 to 10, and one or more blocks (or acts) of process 1300 may be performed by one or more other components of other suitable devices, apparatus, or systems. In another example, process 1300 or any blocks thereof may be combined with any or all of the blocks of process 1200 of Fig.12. Further, for purposes of explanation, some of the blocks of process 1300 are described herein as occurring serially or linearly. However, multiple blocks of process 1300 may occur in parallel. In addition, the blocks of process 1300 need not be performed in the order shown, and / or one or more blocks of process 1300 need not be performed and / or may be replaced by other operations.

[0053] Block 1302 includes providing current to windings of an electric motor to transfer torque to a rotor shaft relative to a stator. In some embodiments, block 1302 includes generating control signals for power electronics to apply current to phases of the electric motor to generate torque on a rotor and cause rotational movement of the rotor relative to a stator. For example, in some embodiments, the rotor may include permanent magnets, and the stator may include phase windings, including end windings and stator teeth.

[0054] Block 1304 includes the generation of heat in bearings, windings, and rotor components. For example, when the rotor rotates about an axis, heat may be generated in the rotor (e.g., due to losses), in bearings (e.g., due to friction), and in end windings (e.g., due to losses such as resistive losses). In some embodiments, the amount of heat generated in the electric motor depends on the current profile applied in block 1302. For example, when larger currents, a greater duration of currents, or both are applied, more heat may be generated in the electric motor and its components.

[0055] Block 1306 includes directing a fluid in one or more flow paths over the magnets in the rotor to absorb the heat. In some embodiments, block 1306 includes directing the fluid in a first flow path and a second flow path that may directly contact one or more magnets. In some embodiments, block 1306 includes providing a pressurized fluid to inlet channels of the rotor, causing the fluid to flow under pressure forces through the flow paths to respective outlet channels.

[0056] Block 1308 includes directing the fluid radially outward toward end windings. In some embodiments, the fluid flows through the flow paths of block 1306 and then flows out of respective outlet ports at each axial end of the rotor. The fluid then flows radially outward along the rotor end plates in block 1308 to impinge upon or otherwise flow over the end windings located radially outward of the rotor. In block 1308, the fluid may flow under centrifugal forces, gravity, pressure forces, or a combination thereof. For example, in some embodiments, the fluid flows radially outward as the rotor rotates and sprays onto the end windings, cooling the windings via convective heat transfer through a boundary layer.

[0057] Block 1310 involves transferring the heat to the circulating fluid. The fluid absorbs heat via convection from the rotor (e.g., magnets) and the end windings and transports the heat (e.g., thermal energy stored in the fluid) away from the rotor. For example, the fluid may be directed to a radiator or other heat exchanger to reject the heat transferred in block 1310 and then returned to the rotor for further cooling.

[0058] In one illustrative example, an illustrative process (e.g., process 1200, process 1300, or a combination thereof) may include providing coolant to a plurality of magnetic channels extending axially through a rotor assembly and configured to provide coolant flow (e.g., in block 1202 and / or block 1306). The process may also include generating heat in the rotor assembly (e.g., in block 1304) and transferring the heat from the plurality of magnetic channels to the coolant (e.g., in blocks 1306 and 1310, or during blocks 1204 and 1208, or a combination thereof).

[0059] In another illustrative example, a plurality of magnetic channels may include a first magnetic channel and a second magnetic channel. The first magnetic channel may extend axially in a first direction toward a first outlet channel, and the second magnetic channel may extend axially in a second direction opposite the first direction toward a second outlet channel. Providing the coolant to the plurality of magnetic channels may include, for example, providing the coolant to a first magnetic channel coupled to a first inlet channel and providing the coolant to a second magnetic channel coupled to a second inlet channel (e.g., in blocks 1204 and 1208, block 1306, or a combination thereof).

[0060] In another illustrative example, the rotor assembly may include a first end plate disposed at a first axial position that includes a first outlet port, and a second end plate disposed at a second axial position that includes a second outlet port. An illustrative process (e.g., process 1200, process 1300, or a combination thereof) may include causing coolant to flow radially outward along the first end plate to first end windings (e.g., in block 1206 or block 1308), causing the coolant to flow radially outward along the second end plate to second end windings (e.g., in block 1210 or block 1308), and transferring the heat from the first end windings and from the second end windings to the coolant.

[0061] A reference to an element in the singular shall not mean one and only one, unless expressly stated so, but rather one or more. For example, "a" module may refer to one or more modules. An element preceded by "a," "an," or "the" does not exclude the presence of additional, identical elements, without further limitation.

[0062] Headings and subheadings, if any, are used for convenience only and do not limit the invention. The word "exemplary" is used herein to mean serving as an example or illustration. To the extent the term "including," "comprising," or the like is used, such term is intended to be inclusive in a similar manner to the term "comprising" when used as a transitional word in a claim. Relational terms such as first and second and the like may be used to distinguish one entity or act from another without necessarily requiring or implying any actual such relationship or order between such entities or acts.

[0063] Phrases such as an aspect, the aspect, another aspect, some aspects, one or more aspects, an implementation, the implementation, another implementation, some implementations, one or more implementations, an embodiment, the embodiment, another embodiment, some embodiments, one or more embodiments, a configuration, the configuration, another configuration, some configurations, one or more configurations, the subject technology, the disclosure, the present disclosure, other variations thereof, and the like are for convenience and do not imply that a disclosure related to such phrases is essential to the subject technology or that this disclosure applies to all configurations of the subject technology.A disclosure referring to such formulations may apply to all configurations or to one or more configurations. A disclosure referring to such formulations may provide one or more examples. A formulation such as one aspect or some aspects may refer to one or more aspects, and vice versa, and this applies similarly to other formulations above.

[0064] A phrase "at least one of" preceding a list of items, with the term "and" or "or" separating one of the items, modifies the list as a whole, rather than each item of the list. The phrase "at least one of" does not require selection of at least one item; rather, the phrase allows for a meaning that includes at least one of any of the items, and / or at least one of any combination of the items, and / or at least one of each of the items. For example, each of the phrases "at least one of A, B, and C" or "at least one of A, B, or C" means only A, only B, or only C; any combination of A, B, and C; and / or at least one each of A, B, and C.

[0065] It is understood that the specific order or hierarchy of disclosed steps, acts, or processes is illustrative of exemplary approaches. Unless expressly stated otherwise, it is understood that the specific order or hierarchy of steps, acts, or processes may be performed in various orders. Some of the steps, acts, or processes may be performed concurrently. The appended method claims, if any, present elements of the various steps, acts, or processes in a sample order and are not limited to the specific order or hierarchy in which they are presented. These may be performed serially, linearly, in parallel, or in different orders.It is understood that the instructions, operations, and systems described may generally be integrated together in a single software / hardware product or may be packaged into multiple software / hardware products.

[0066] Terms such as top, bottom, front, back, side, horizontal, vertical, and the like refer to any reference frame other than the usual gravitational frame. Thus, such a term can extend upward, downward, diagonally, or horizontally in a gravitational frame.

[0067] The disclosure is provided to enable any person skilled in the art to practice the various aspects described herein. In some cases, well-known structures and components are shown in block diagram form to avoid obscuring the concepts of the subject technology. The disclosure provides various examples of the subject technology, and the subject technology is not limited to these examples. Various modifications to these aspects will be readily apparent to those skilled in the art, and the principles described herein may be applied to other aspects.

[0068] All structural and functional equivalents to the elements of the various aspects described in the disclosure that are known or later become known to those skilled in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Furthermore, nothing disclosed herein is intended to be made available to the public regardless of whether such disclosure is expressly recited in the claims. No claim element is to be construed within the provisions of 35 USC § 112(f) unless the element is expressly recited using the phrase "means for" or, in the case of a method claim, the element is recited using the phrase "step for."

[0069] Those skilled in the art would recognize that the various illustrative blocks, modules, elements, components, methods, and algorithms described herein may be implemented in hardware, electronic hardware, computer software, or combinations thereof. To illustrate this interchangeability of hardware and software, various illustrative blocks, modules, elements, components, methods, and algorithms have been described above generally in terms of their functionality. Whether such functionality is implemented in hardware or software depends on the particular application and design constraints to which the overall system is subject. Those skilled in the art may implement the described functionality in different ways for each particular application. Various components and blocks may be arranged differently (e.g.,arranged in a different order or partitioned in a different way) without departing from the scope of the present technology.

[0070] The title, brief description of the drawings, abstract, and drawings are hereby incorporated into the disclosure and are provided as illustrative examples of the disclosure, not as limiting descriptions. They are submitted with the understanding that they will not be used to limit the scope or meaning of the claims. Additionally, it will be apparent in the detailed description that the description provides illustrative examples and the various features are grouped into various implementations to streamline the disclosure. The method of the disclosure should not be interpreted to reflect an intent that the claimed subject matter requires more features than are expressly recited in each claim.Rather, as the claims reflect, the inventive subject matter lies in less than all features of a single disclosed configuration or process. The claims are incorporated into the detailed description, with each claim standing alone as separately claimed subject matter.

[0071] The claims are not intended to be limited to the aspects described herein, but are intended to give the full scope of protection consistent with the language of the claims and including all legal equivalents. Notwithstanding the foregoing, none of the claims are intended, nor should they be interpreted, to encompass subject matter that does not meet the requirements of applicable patent law.

Claims

[1] Rotor assembly for a motor, the rotor assembly comprising: a rotor shaft comprising a shaft channel; and a rotor core arranged around the rotor shaft and defining: internal channels extending between opposite axial ends of the rotor core; and Magnetic channels extending between the opposite axial ends of the rotor core, each of the magnetic channels containing a magnet, where: the shaft channel is fluidly connected to the inner channels by inlet channels at opposite ends of the rotor shaft; and the inner channels are fluidly connected to the magnetic channels by transition channels arranged axially between the inlet channels. [2] The rotor assembly of claim 1, further comprising: a first end plate coupled to a first end of the rotor core, the first end plate at least partially defining the first inlet ports; and a second end plate coupled to a second end of the rotor core, the second end plate at least partially defining the second inlet ports. [3] The engine of claim 2, wherein the first end plate and the second end plate at least partially define an exhaust port at each of the axially opposite ends of each of the magnet channels. [4] The rotor assembly of claim 1, wherein each of the magnetic channels radially overlaps a corresponding one of the inner channels. [5] The rotor assembly of claim 1, wherein each of the first inlet channels and the transition channels extends transversely to a rotor axis extending through the shaft channel, and wherein the rotor assembly is configured to rotate thereabout. [6] The rotor assembly of claim 1, wherein each of the inner channels is fluidly connected to a corresponding magnetic channel by at least two transition channels. [7] The rotor assembly of claim 1, wherein the rotor core is formed from a plurality of layers arranged along a rotor axis, each of the plurality of layers being circumferentially offset with respect to an adjacent one of the plurality of layers such that the magnetic channels wrap around the rotor axis between the opposite axial ends of the rotor core. [8] Engine, comprising: a stator having stator coils configured to generate a rotating magnetic field; and a rotor that defines: a shaft channel extending along a rotor axis; internal channels distributed around the shaft channel and configured to receive a fluid from the shaft channel via inlet channels at opposite ends of the shaft channel; and Magnetic channels containing magnets distributed around the inner channels and configured to receive fluid from the inner channels via transition channels arranged axially between the inlet channels. [9] The motor of claim 8, wherein the magnet channels provide space for fluid flow on each of the opposite sides of each of the magnets. [10] The motor of claim 8, wherein a rotor core of the rotor is formed from a plurality of layers arranged along the rotor axis, each of the plurality of layers being circumferentially offset with respect to an adjacent one of the plurality of layers such that the magnetic channels wrap around the rotor axis between the opposite axial ends of the rotor core. [11] The engine of claim 8, wherein the rotor further comprises end plates coupled to opposite ends of a rotor core, the end plates at least partially defining the intake ports. [12] The engine of claim 11, wherein the end plates at least partially define an exhaust port at each of the axially opposite ends of each magnet channel. [13] The engine of claim 8, wherein the internal channels comprise: first inner channels connected to the shaft channel at a first end of the rotor; and second inner channels connected to the shaft channel at a second end of the rotor. [14] The motor of claim 8, further comprising a pump configured to receive the fluid from the magnetic channels and to direct the fluid to the shaft channel. [15] A method of cooling a rotor assembly of an engine, the method comprising: Providing the rotor assembly comprising a rotor shaft and a rotor core; Providing a fluid for a shaft channel of the rotor shaft; and Directing the fluid to flow from the shaft channel and through the magnetic channels of the rotor core, wherein the fluid flow in each of the magnetic channels is directed in opposite directions to each of the opposite axial ends of the rotor assembly, and each of the magnetic channels contains a magnet. [16] The method of claim 15, wherein the fluid within the magnetic channels flows over each magnet. [17] The method of claim 15, wherein providing the fluid to the shaft channel comprises operating a pump to receive the fluid from the rotor core and to direct the fluid to the shaft channel. [18] The method of claim 15, wherein passing the fluid comprises: Directing the fluid from the shaft channel through a wall of the rotor shaft; Directing the fluid from the wave channel through inlet channels; Directing the fluid from the inlet channels through internal channels of the rotor core; Directing the fluid from the inner channels through transition channels of the rotor core; Directing the fluid from the transition channels through the magnetic channels and over any magnet; and Directing the fluid from the magnetic channels via outlet channels. [19] The method of claim 18, wherein the fluid flows in opposite directions through two of the inner channels. [20] The method of claim 15, wherein directing the fluid flow comprises rotating the rotor assembly.

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