Liquid-cooled radial FLUX electric motors and electric vehicles comprising thereof

Abstract

Described herein are liquid-cooled radial flux electric motors and methods of operating thereof. A liquid-cooled radial flux electric motor comprises a rotor and a stator. The stator comprises a housing, a housing sleeve, and a plurality of stator windings. A first bearing and a second bearing are each mechanically coupled to both the rotor and the stator, enabling rotation of the rotor about a rotational axis relative to the stator. The housing and the housing sleeve together enclose a cooling fluid volume that is liquid-tight except for an inlet port and an outlet port. The plurality of stator windings is positioned within the cooling fluid volume. Cooling fluid may be circulated through the cooling fluid volume (in contact with the plurality of stator windings), thereby providing effective cooling of the plurality of stator windings. The cooling fluid volume separates the cooling fluid from the rotor.

Description

LIQUID-COOLED RADIAL FLUX ELECTRIC MOTORS AND ELECTRIC VEHICLES COMPRISING THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. § 119(e) of US Provisional Patent Application 63 / 676,580, filed on 2024-07-29, which is incorporated herein by reference in its entirety for all purposes.BACKGROUND

[0002] Both increased compactness and increased power density are desirable features for electric motors for many applications, including those in electric- powered transportation, for example, automobiles and aircraft. However, increasing power density applied to an electric motor can result in generation of significant heat. Removal of generated heat from an electric motor is important to preventing loss of performance or heat damage to components of the motor. This can be especially challenging in electric motors in electric-powered transportation applications, where space within the vehicle may be at a premium and motors may be positioned in tightly packed compartments with little air flow.

[0003] It should be noted that electric motors can be sensitive to their operating temperatures. For example, exposure of a motor to increased temperature may lead to damage to temperature-sensitive components (e.g., magnets) affecting the performance or even the successful operation of the motor. In addition, increased temperature of, for example, metal wire windings in a motor stator may cause an increase in electrical resistance and a resulting decrease in operating efficiency.

[0004] Air cooling is sometimes used to remove the heat generated during operation of an electric motor. However, due to the low heat capacity and metal-to-air heat transfer, air may provide insufficient cooling, especially forhigh-power applications such as automobiles and aircraft. Furthermore, motors can be often operated in enclosed spaces with limited airflow. Liquid cooling or, more generally, liquid-based thermal management of motors provides more efficient cooling in comparison to, e.g., air cooling because of the large heat capacities and heat transfer coefficient of many liquids in comparison to air. However, controlling the distribution of liquid within motors can be challenging. Furthermore, heat transfer from heat-generating components to cooling liquids may depend on various components positioned along this heat-transfer path.

[0005] What is needed are new liquid-cooled radial flux electric motors and methods for operating thereof.SUMMARY

[0006] Described herein are liquid-cooled radial flux electric motors and methods of operating thereof. A liquid-cooled radial flux electric motor comprises a rotor and a stator. The stator comprises a housing, a housing sleeve, and a plurality of stator windings. A first bearing and a second bearing are each mechanically coupled to both the rotor and the stator, enabling rotation of the rotor about a rotational axis relative to the stator. The housing and the housing sleeve together enclose a cooling fluid volume that is liquid-tight except for an inlet port and an outlet port. The plurality of stator windings is positioned within the cooling fluid volume. Cooling fluid may be circulated through the cooling fluid volume (in contact with the plurality of stator windings), thereby providing effective cooling of the plurality of stator windings. The cooling fluid volume separates the cooling fluid from the rotor.

[0007] Clause 1. A liquid-cooled radial flux electric motor comprising: a rotor having a rotational axis; a stator comprising a housing, a housing sleeve, and a plurality of stator windings; and a cooling fluid, wherein: the housing sleeve has a first cylindrical shape coaxial with the rotor and having a first end and a second end opposite of the first end, the housing and the housing sleeve together enclose a cooling fluid volume, the cooling fluid is positioned within the coolingfluid volume, and the plurality of stator windings is positioned within the cooling fluid volume.

[0008] Clause 2. The liquid-cooled radial flux electric motor of clause 1, further comprising a first bearing and a second bearing, each mechanically coupled to both the rotor and the stator, thereby enabling rotation of the rotor about the rotational axis relative to the stator.

[0009] Clause 3. The liquid-cooled radial flux electric motor of clause 2, wherein: the housing comprises a body housing section having an inner surface facing the rotor and having a second cylindrical shape coaxial with the rotor, the housing further comprises a drive end housing section mechanically coupled with the first bearing and fluidically sealed against the body housing section, the housing further comprises an inverter end housing section mechanically coupled with the second bearing and fluidically sealed against the body housing section, the first end of the housing sleeve is physically coupled with and fluidically sealed against the drive end housing section, and the second end of the housing sleeve is physically coupled with and fluidically sealed against the inverter end housing section.

[0010] Clause 4. The liquid-cooled radial flux electric motor of clause 3, wherein: the housing further comprises an outer surface facing away from the rotor, the body housing section comprises an inlet port and an outlet port, each protruding through the body housing section from the outer surface to the inner surface, and the cooling fluid volume is fluidically coupled to the inlet port and the outlet port.

[0011] Clause 5. The liquid-cooled radial flux electric motor of clause 4, further comprising a circular distribution ring having a third cylindrical shape coaxial with the rotor and comprising: an inner distribution ring surface facing the rotational axis and an outer distribution ring surface opposite the rotational axis; a first distribution ring edge along the outer distribution ring surface in physical contact with the inner surface; a channel fluidically coupled with the inlet port; a distribution surface different from the first distribution ring edge; and a pluralityof distribution orifices protruding through the distribution ring from the distribution surface to the channel.

[0012] Clause 6. The liquid-cooled radial flux electric motor of clause 5, wherein the channel has a depth measured perpendicular to the rotational axis of 2-10 millimeters.

[0013] Clause 7. The liquid-cooled radial flux electric motor of clause 5, wherein the channel is an opening in the distribution ring adjacent to the inner surface.

[0014] Clause 8. The liquid-cooled radial flux electric motor of clause 5, further comprising a plurality of distribution tubes positioned within the cooling fluid volume, wherein: each one of the plurality of distribution tubes has a first tube end and a second tube end opposite the first tube end, and each first tube end is fluidically coupled to one of the plurality of distribution orifices.

[0015] Clause 9. The liquid-cooled radial flux electric motor of clause 8, wherein: the cooling fluid volume has a first cooling fluid volume end positioned adjacent to the drive end housing section and a second cooling fluid volume end positioned adjacent to the inverter end housing section, the outlet port is positioned adjacent to the second cooling fluid volume end, and each one of the plurality of distribution tubes extends from the distribution surface away from the second cooling fluid volume end.

[0016] Clause 10. The liquid-cooled radial flux electric motor of clause 9, wherein: the distribution ring further comprises a second distribution ring edge positioned along the outer distribution ring surface, the second distribution ring edge is separated from the first distribution ring edge along a direction parallel with the rotational axis by a width of the channel measured in a direction parallel with the rotational axis, and the second distribution ring edge interfaces the inner surface, such that cooling fluid entering the cooling fluid volume via the inlet port is directed to the plurality of distribution tubes.

[0017] Clause 11. The liquid-cooled radial flux electric motor of clause 1, wherein the housing sleeve is formed from a non-magnetic metal.

[0018] Clause 12. The liquid-cooled radial flux electric motor of clause 11, wherein the housing sleeve is formed from non-magnetic stainless steel.

[0019] Clause 13. The liquid-cooled radial flux electric motor of clause 3, further comprising a first housing sleeve seal forming a liquid-tight seal between the housing sleeve and the drive end housing section and a second housing sleeve seal forming a liquid-tight seal between the housing sleeve and the inverter end housing section.

[0020] Clause 14. The liquid-cooled radial flux electric motor of clause 3, further comprising a rotor-end housing seal forming a liquid-tight seal between the drive end housing section and the body housing section and an inverter-end housing seal forming a liquid-tight seal between the body housing section and the inverter end housing section.

[0021] Clause 15. The liquid-cooled radial flux electric motor of clause 5, further comprising a distribution-ring seal forming a liquid-tight seal between the distribution ring and the inner surface.

[0022] Clause 16. The liquid-cooled radial flux electric motor of clause 5, further comprising a stator spacer, wherein: the stator spacer has an inner spacer surface having a fourth cylindrical shape coaxial with the rotational axis and facing the rotational axis, the stator spacer has an outer spacer surface having a fifth cylindrical shape coaxial with the rotational axis facing away from the rotational axis, the stator spacer is positioned between the housing sleeve and the distribution ring and interfaces the inner distribution ring surface, and the stator spacer has a plurality of protrusions extending towards the rotational axis from the inner spacer surface and interfacing the housing sleeve.

[0023] Clause 17. A method for operating a liquid-cooled radial flux electric motor, the method comprising: (Block) receiving by the liquid-cooled radial flux electric motor comprising a stator comprising a plurality of stator windings and a cooling fluid positioned in a cooling fluid volume an alternating current from a power inverter; and (Block) circulating by a pump and heat exchanger the cooling fluid through the cooling fluid volume, thereby transferring heat from the plurality of stator windings.

[0024] Clause 18. The method of clause 17, wherein: the liquid-cooled radial flux electric motor further comprises a temperature sensor thermally coupled with the cooling fluid volume and a controller electronically coupled with the temperature sensor and the pump and heat exchanger, and the method further comprises measuring by the temperature sensor a temperature of the cooling fluid, recording at the controller the measured temperature, determining at the controller whether the measured temperature is greater than a predetermined set temperature, and increasing a flow rate of the cooling fluid by the pump and heat exchanger if the measured temperature is greater than the predetermined set temperature.

[0025] Clause 19. The method of clause 17, wherein: the liquid-cooled radial flux electric motor further comprises a current sensor electrically coupled with the plurality of stator windings and a controller electronically coupled with the current sensor and the pump and heat exchanger, and the method further comprises measuring by the current sensor a current supplied to the liquid- cooled radial flux electric motor, recording at the controller the measured current, determining at the controller a predetermined flow rate of cooling fluid for the measured current, and adjusting the flow rate of the cooling fluid by the pump and heat exchanger if the flow rate is different than the predetermined flow rate.

[0026] Clause 20. The method of clause 17, wherein the alternating current is a three-phase current.

[0027] Clause 21. An electric vehicle comprising: a pump and heat exchanger; a controller electronically coupled with the pump and heat exchanger; a temperature sensor; and a liquid-cooled radial flux electric motor comprising a rotor, a stator, and a cooling fluid, wherein: the rotor has a rotational axis, the stator comprises a housing, a housing sleeve, and a plurality of stator windings, the housing and the housing sleeve together enclose a cooling fluid volume, the cooling fluid is positioned within the cooling fluid volume, the plurality of stator windings is positioned within the cooling fluid volume, and the temperaturesensor is fluidically coupled with the cooling fluid volume and electronically coupled with the controller.

[0028] Clause 22. The electric vehicle of clause 21, wherein: the housing comprises a body housing section comprising an inner surface facing the rotor and having a second cylindrical shape coaxial with the rotor, the body housing section further comprises an outer surface facing away from the rotor, the body housing section further comprises an inlet port and an outlet port, each protruding through the body housing section from the outer surface to the inner surface, the electric vehicle further comprises an additional temperature sensor electronically coupled with the controller and fluidically coupled with the cooling fluid volume, the temperature sensor is positioned adjacent to the inlet port, the additional temperature sensor is positioned adjacent to the outlet port, and the controller is configured to receive an inlet temperature value from the temperature sensor and an outlet value from the additional temperature sensor, determine a difference between the inlet temperature value and outlet temperature value, determine whether the determined difference is greater than a preset difference limit, and increase a pumping rate of the pump and heat exchanger if the determined difference is greaterthan the preset difference limit.

[0029] These and other embodiments are described further below with reference to the figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The included drawings are for illustrative purposes and serve only to provide examples of possible structures and operations for the disclosed inventive systems, apparatus, and methods. These drawings in no way limit any changes in form and detail that may be made by one skilled in the art without departing from the spirit and scope of the disclosed implementations.

[0031] FIG. 1 is a schematic block diagram illustrating relationships between some components of a liquid-cooled radial flux electric motor, in accordance with some examples.

[0032] FIG. 2 is a perspective view of a liquid-cooled radial flux electric motor, in accordance with some examples.

[0033] FIG. 3A is a cross-sectional view illustrating the relationships of some components of a liquid-cooled radial flux electric motor 100, in accordance with some examples.

[0034] FIG. 3B is a perspective view of a liquid-cooled radial flux electric motor with the body housing section, the inverter end housing section, and the drive end housing section removed, in accordance with some examples.

[0035] FIG. 4B is a cross-sectional view of a distribution ring of a liquid-cooled radial flux electric motor at the line A-A in FIG. 4A, in accordance with some examples.

[0036] FIG. 4C is a cross-sectional view of a distribution ring of a liquid-cooled radial flux electric motor at the line A-A in FIG. 4A, in accordance with some examples.

[0037] FIG. 4D is a cross-sectional view of a distribution ring of a liquid-cooled radial flux electric motor at the line A-A in FIG. 4A, in accordance with some examples.

[0038] FIG. 5 is a perspective view of the stator spacer of a liquid-cooled radial flux electric motor, in accordance with some examples.

[0039] FIG. 6 is a process flowchart of a method for operating liquid-cooled radial flux electric motors, in accordance with some examples.

[0040] FIG. 7 is a block diagram illustrating relationships of some components of an electric vehicle comprising a liquid-cooled radial flux electric motors, in accordance with some examples.DETAILED DESCRIPTIONIntroduction

[0041] In radial flux electric motors, magnets are distributed about a rotor's axis of rotation such that the direction of their magnetic fields are orientedperpendicular to the rotor e.g., by offsetting the motor windings and magnets radially. A stator surrounds but does not contact the rotor assembly and comprises electrical wire-wound cores arranged in such a way that the application of electrical current to the wire-wrapped cores causes the magnets to apply torque to cause the rotor to rotate.

[0042] Most (e.g., 95%+) of the electrical energy applied to operate an electric motor is converted to mechanical energy in the form of rotor rotation.However, a small percentage of the energy applied to the motor is converted to heat through a number of undesirable effects including resistance to current flow through the windings in the stator.

[0043] Electric motors can be sensitive to operating temperatures. These temperatures can be influenced by the environment and by the motor's operation (e.g., self-heating). For example, the temperature coefficient of copper is about 0.00404 C1. Therefore, increasing the temperature of copper windings by 50°C will cause the resistivity to increase by about 20%. This will cause an undesirable decrease in the efficiency of the motor and an increase in heat generated by electric current passing through the windings without temperature control of the windings. Liquid-based thermal management provides efficient ways of controlling the temperature of components of electric motors. However, the thermal coupling of electric motors and cooling fluid can be challenging. The immersion cooling of the plurality of stator windings 130 brings windings in direct contact with cooling fluids, which is beneficial for thermal transfer. The key challenges include controlling the distribution and flow of cooling fluids around components of the electric motor.

[0044] In order to increase the power provided by an electric motor, the motor may be increased in size. However, in space-constrained applications, for example in electric vehicles, it is desirable instead to increase the power from a smaller motor by increasing the supplied current. Because increasing the supplied current results in more heat generated in the stator windings, a cooling method with a high capacity for heat removal is highly desirable.

[0045] As noted above, sufficiently cooling electric motors may be difficult, especially during high-power output operation. In particular, the windings haveends that are particularly challenging to effectively cool for two reasons. First, the stator windings are enclosed within a stator enclosure in most radial-flux electric motors. Overheating of the stator winding ends is especially easy because they are not thermally coupled to components that can transfer sufficient heat away from them. Also, each wire in the stator winding is individually electrically insulated from the others and from the stator. The electrical insulation provides insulation against transfer of heat away from the wires.

[0046] Air cooling is sometimes used to remove the heat generated during electric motor operation. However, due to the low heat capacity of air and metal-to-air heat transfer, air may provide insufficient cooling, especially for high-power applications such as automobiles and aircraft. Furthermore, motors may be located in enclosed spaces with limited airflow.

[0047] One solution in electric motors is to encapsulate, or pot, the stator winding ends in a thermally conductive epoxy. The thermally conductive epoxy may transfer heat from the windings to other, thermally conductive components of the motor. However, there are limits to the amount of heat that can be removed by a thermally conductive epoxy potting. The amount of heat that can be removed by the thermally conductive epoxy potting may not be sufficient to support successful operation of a motor at higher current.

[0048] Liquid cooling or, more generally, liquid-based thermal management of motors provides more efficient cooling in comparison to, e.g., air cooling because of the large heat capacities and heat transfer coefficient of many liquids in comparison to air. Immersion of heat-generating components in circulating cooling fluid may provide significant advantages over air-cooled thermal management and other forms of liquid-cooled thermal management. Some forms of liquid-cooled thermal management may also present challenges. For example, contacting surfaces of components of the stator with a heat- conductive channel conducting cooling fluid removes heat but may not remove heat effectively from all parts of the stator. For example, the cooling fluid does not remove heat as effectively from the last component it contacts as it does the first because the heat transfer varies with the temperature differencebetween the component and the temperature of the fluid at the time of contact. The temperature of the cooling fluid will be much closer to the temperature of the last component it contacts than the first because of the heat it has accepted from previously contacted components.

[0049] A significant challenge to liquid-cooled thermal management of the stator windings is contacting the stator windings with the cooling fluid while not immersing the rotor in the cooling fluid. If the enclosure for the cooling fluid exposes the rotor to the cooling fluid, the drag of the liquid on the spinning rotor will greatly decrease the efficiency of the motor.

[0050] Described herein are liquid-cooled radial flux electric motors and methods of operating thereof. Specifically, heat-generating components of the motor are positioned within a cooling fluid volume formed from stator components and, within the volume, thermally coupled with flowing cooling fluid. In the described motors, flowing cooling fluid enters the volume and contacts the stator windings. The cooling fluid volume prevents contact of cooling fluid with the rotor. The temperature of the flowing cooling fluid is increased as it contacts the stator windings and then exits the motor. In some examples, the fluid may then pass to a heat exchanger and be cooled before reentering the cooling fluid volume. In this way, the cooling fluid provides effective cooling of the stator windings, thereby enabling operating of the motor at higher currents.FIGS. 1, 2, 3A-3B, and 4A-4C: Examples of liquid-cooled radial flux electric motors

[0051] FIG. 1 is a schematic block diagram illustrating relationships between some components of a liquid-cooled radial flux electric motor 100, in accordance with some examples. The liquid-cooled radial flux electric motor 100 comprises a rotor 110, a stator 120, and a cooling fluid 205. FIG. 3A is a cross-sectional schematic diagram illustrating the relationships of some components of the liquid-cooled radial flux electric motor 100, in accordance with some examples. As shown in FIG. 3A, the rotor 110 has a rotational axis115. As shown in FIG. 3A the stator 120 comprises a housing 140, a housing sleeve 180, and a plurality of stator windings 130.

[0052] The housing sleeve 180 has a first cylindrical shape coaxial with the rotor 110. The housing sleeve 180 has a first end and a second end opposite the first end. As will be described in more detail below, the housing sleeve 180 and the housing 140 together enclose a cooling fluid volume 250. The plurality of stator windings 130 is positioned within the cooling fluid volume 250.

[0053] The cooling fluid 205 is also positioned within the cooling fluid volume 250. In some examples, the cooling fluid 205 may be selected from liquids with low electrical conductivity. The cooling fluid 205 may be an oil or any other liquid with low electrical resistance. Specifically, the cooling fluid 205 may have an electrical conductivity of less than 10 microsiemens / meter, less than 1 microsiemens / meter, less than 100 microsiemens / meter, less than 10 microsiemens / meter, or even less than 1 microsiemens / meter. A low electrical conductivity of the cooling fluid 205 may enable effective cooling of motor components without forming undesirable electrical pathways between motor components. In some examples, the cooling fluid 205 may be a dielectric fluid. In some examples, the cooling fluid 205 may comprise hydrocarbons.

[0054] In some examples, the liquid-cooled radial flux electric motor 100 further comprises a first bearing 230 and a second bearing 232. The first bearing 230 and the second bearing 232 are each mechanically coupled to both the rotor 110 and the stator 120, thereby enabling rotation of the rotor 110 about the rotational axis 115 relative to the stator 120.

[0055] In some examples, the housing 140 comprises a body housing section 170. The body housing section 170 has an inner surface 172 and an outer surface 174. The inner surface 172 faces the rotor 110 and has a second cylindrical shape coaxial with the rotor 110. The outer surface 174 faces away from the rotor 110. Also shown in FIG. 3A is a drive end housing section 150 and an inverter end housing section 160. The drive end housing section 150 is mechanically coupled with the first bearing 230 and fluidically sealed against the body housing section 170. The inverter end housing section 160 is mechanically coupled with the second bearing 232 and fluidically sealed againstthe body housing section 170. The first end of the housing sleeve 180 is physically coupled with and fluidically sealed against the drive end housing section 150. The second end of the housing sleeve 180 is physically coupled with and fluidically sealed against the inverter end housing section 160.

[0056] In some examples, the body housing section 170 also comprises an inlet port 210 and an outlet port 220. The inlet port 210 and the outlet port 220 each protrude through the body housing section 170 from the outer surface 174 to the inner surface 172. In these examples, the cooling fluid volume 250 is fluidically coupled to both the inlet port 210 and the outlet port 220. In some further examples, the inlet port 210 and the outlet port 220 are fluidically connected to a pump and heat exchanger 650.

[0057] FIG. 2 is a perspective view of a liquid-cooled radial flux electric motor 100, in accordance with some examples. Shown in FIG. 2 are the drive end housing section 150, the inverter end housing section 160, and the body housing section 170. Also shown in FIG. 2 is a portion of the rotor 110, protruding through an opening in the drive end housing section 150.

[0058] As shown in FIG. 3A, the plurality of stator windings 130 is positioned within the cooling fluid volume 250. In some examples, the housing sleeve 180 is formed from a non-magnetic material. For example, the housing sleeve 180 may be formed from a non-magnetic metal or a polymer resin. In some examples, the housing sleeve 180 is formed from non-magnetic stainless steel. The material of the housing sleeve 180 may be chosen to have suitable chemical resistance to the cooling fluid 205.

[0059] In some examples, the liquid-cooled radial flux electric motor 100 further comprises a circular distribution ring 190. The relationship of the components of the distribution ring 190 and the relationship of the distribution ring 190 with some other components of the liquid-cooled radial flux electric motor 100 are illustrated in FIGS. 3A and 3B. A front view of the distribution ring 190 illustrating some components is shown in FIG. 4A, in accordance with some examples. The distribution ring 190 has a third cylindrical shape coaxial with the rotor 110. The distribution ring 190 comprises an inner distribution ring surface 195, an outer distribution ring surface 197, a first distribution ringedge 192, a channel 198, a distribution surface 196, and a plurality of distribution orifices 199. The inner distribution ring surface 195 faces the rotational axis 115. The outer distribution ring surface 197 is opposite the rotational axis 115. The first distribution ring edge 192 is positioned along the outer distribution ring surface 197 in physical contact with the inner surface 172. The channel 198 is fluidica lly coupled with the inlet port 210. The distribution surface 196 is different from the first distribution ring edge 192. The plurality of distribution orifices 199 protrudes through the distribution ring 190 from the distribution surface 196 to the channel 198.

[0060] In some examples, the distribution ring 190 comprises a second distribution ring edge 194 along the outer distribution ring surface 197. The second distribution ring edge 194 is in physical contact with the inner surface 172 and separated from the first distribution ring edge 192 along the direction of the rotational axis 115 by a width of the channel 198 measured in a direction parallel with the rotational axis 115. Placement of the second distribution ring edge 194 is such that fluid entering the cooling fluid volume 250 via the inlet port 210 is directed to the plurality of distribution tubes 200.

[0061] FIGS. 4B, 4C, and 4D are all cross-sectional views of the distribution ring 190 at the line A-A in FIG. 4A, in accordance with some examples. As shown in FIGS. 4B, 4C, and 4D, the plurality of distribution orifices 199 is fluidically coupled with the channel 198. As shown in FIGS. 4B and 4C, in some examples, the channel 198 is an opening in the distribution ring 190 adjacent to the inner surface 172. In other words, in these examples, the inner surface 172 forms an internal wall of the channel, as shown in FIG. 3A. In some examples, the channel 198 has a depth, measured perpendicular to the rotational axis 115, of 2-10 millimeters. In some examples, the channel 198 has a depth of greater than 0.5 millimeters, greater than 1.5 millimeters, greater than 2.5 millimeters, or even greater than 5 millimeters. In some examples, the channel 198 has a depth less than 10 millimeters, less than 4.5 millimeters, less than 3 millimeters, or even less than 2.5 millimeters. In some other examples, as shown in FIG. 4D, the channel is an opening through the distribution ring 190,forming a ring that is fluidically coupled with the plurality of distribution orifices 199 and the inlet port 210.

[0062] In some examples, the first distribution ring edge 192 and second distribution ring edge 194 are parallel with the inner surface 172, as shown in FIGS. 4B and 4D. In some examples, as in FIG. 4B, the first distribution ring edge 192 and the second distribution ring edge 194 are portions of the outer distribution ring surface 197. In some other examples, as in FIG. 4D, the first distribution ring edge 192 and the second distribution ring edge 194 are the outer distribution ring surface 197. In some examples, as shown in FIG. 4B, the distribution surface 196 is in a plane perpendicular to the rotational axis 115. In other examples, as shown in FIG. 4C, the distribution surface 196 is not in a plane perpendicular to the rotational axis 115. The shape of components of the distribution ring 190 may vary, as well, as illustrated by the differences between the distribution ring 190 shown in FIG. 4B and the distribution ring 190 shown in FIG. 4C. In some examples, the first distribution ring edge 192 and the second distribution ring edge 194 may have a cross-sectional shape that is rectangular where interfacing the inner surface 172. In other examples, one or both of the first distribution ring edge 192 and the second distribution ring edge 194 may have a cross-sectional shape that is another shape, rounded, for example, as the second distribution ring edge 194 is shown in FIG. 4C. Other cross-sectional shapes of the first distribution ring edge 192 or second distribution ring edge 194 that interface the inner surface 172 are within the scope.

[0063] In some examples, the liquid-cooled radial flux electric motor 100 further comprises a plurality of distribution tubes 200. The plurality of distribution tubes 200 is positioned within the cooling fluid volume 250. FIG. 3B is a perspective view of the liquid-cooled radial flux electric motor 100 with the body housing section 170, the inverter end housing section 160, and the drive end housing section 150 removed, in accordance with some examples. As shown in FIG. 3B, each one of the plurality of distribution tubes 200 has a first tube end 201 and a second tube end 202 opposite the first tube end 201. Each first tube end 201 is fluidically coupled to one of the plurality of distribution orifices 199 in the distribution surface 196. The plurality of distribution tubes200 may comprise one or more tubes, two or more tubes, four or more tubes, eight or more tubes, or even 15 or more tubes. Each of the tubes in the plurality of distribution tubes 200 as shown in FIG. 3B have the same length between the first tube end 201 and the second tube end 202, but tubes with different lengths within the plurality of distribution tubes 200 are within the scope. Varying the lengths of the ones of the plurality of distribution tubes 200 may enable control of the flow path of cooling fluid 205 within the cooling fluid 205. Each one of the plurality of distribution tubes 200 is formed from a material chemically compatible with the cooling fluid 205. For example, each one of the plurality of distribution tubes 200 may be formed from stainless steel or an aluminum alloy. Each one of the plurality of distribution tubes 200 has a diameter measured in a direction different from the direction between the first tube end 201 and the second tube end 202. In some examples, the diameter of each one of the plurality of distribution tubes 200 is equal to the diameters of each of the other ones of the plurality of distribution tubes 200. In other examples, the diameter of each one of the plurality of distribution tubes 200 differs from the diameter of one or more of the other ones of the plurality of distribution tubes 200. Varying the diameters of the ones of the plurality of distribution tubes 200 may enable different flow rates of cooling fluid 205 to be distributed to different ones of the plurality of stator windings 130.

[0064] In some examples, the liquid-cooled radial flux electric motor 100 comprises a stator spacer 240. FIG. 5 is a perspective view of the stator spacer 240, in accordance with some examples. The stator spacer 240 has an inner spacer surface 242 having a fourth cylindrical shape coaxial with the rotational axis 115. The inner spacer surface 242 faces the rotational axis 115. The stator spacer 240 also has an outer spacer surface 244 opposite the rotational axis 115. In some further examples, the outer spacer surface 244 has a fifth cylindrical shape coaxial with and facing away from the rotational axis 115. The stator spacer 240 is positioned between the housing sleeve 180 and the distribution ring 190. The stator spacer 240 physically contacts the inner distribution ring surface 195. In some examples, the stator spacer 240 forms a liquid-tight seal against the inner distribution ring surface 195. The statorspacer 240 has a plurality of protrusions 246 extending towards the rotational axis 115 from the inner spacer surface 242. The plurality of protrusions 246 interfaces the housing sleeve 180. The space between each pair of adjacent ones of the plurality of protrusions 246 and between the inner spacer surface 242 and the housing sleeve 180 forms a lumen. One of the plurality of stator windings 130 may be positioned within each lumen. Each lumen may further provide a path for the cooling fluid 205 to flow around the plurality of stator windings 130. In some examples, the plurality of stator windings 130 is immersion liquid-cooled by the cooling fluid 205.

[0065] In some examples, the cooling fluid 205 may enter the liquid-cooled radial flux electric motor 100 through the inlet port 210 and may pass into the channel 198. From the channel 198, fluid may pass through the plurality of distribution orifices 199 and into the plurality of distribution tubes 200. The fluid may then pass out of the second tube end 202 of each one of the plurality of distribution tubes 200. The fluid may then pass between the inner spacer surface 242 and the housing sleeve 180 and outside one of the plurality of stator windings 130. The fluid may then flow out of the outlet port 220. In this way, the plurality of stator windings 130 may be cooled by contact with the cooling fluid 205 while the rotor 110 is isolated from the cooling fluid 205. In some examples, the plurality of stator windings 130 may be entirely immersed in the cooling fluid 205 within the cooling fluid 205 and be cooled by liquid immersion cooling. Heat may be transferred from the plurality of stator windings 130 as the cooling fluid 205 flows from each second tube end 202 to the outlet port 220, thereby providing cooling of the plurality of stator windings 130.

[0066] The cooling fluid volume 250 has two ends extending away from one another along the direction of the rotational axis 115, a first cooling fluid volume end and a second cooling fluid volume end. The first cooling fluid volume end is positioned closer to the drive end housing section 150 than the second cooling fluid volume end. The second cooling fluid volume end is positioned closer to the inverter end housing section 160 than the first cooling fluid volume end. In some examples, the outlet port 220 is positioned adjacentone end of the cooling fluid volume 250 and each second tube end 202 is positioned at the end of the cooling fluid volume 250 opposite from the outlet port 220. In this way, the cooling fluid exiting each second tube end 202 travels past the plurality of stator windings 130 to the outlet port 220.

[0067] In some examples, the liquid-cooled radial flux electric motor 100 comprises one or more seals forming liquid-tight seals between components enclosing the cooling fluid volume 250. In some examples, the liquid-cooled radial flux electric motor 100 comprises a first housing sleeve seal 260 and a second housing sleeve seal 262. The first housing sleeve seal 260 forms a liquid- tight seal between the housing sleeve 180 and the drive end housing section 150. The second housing sleeve seal 262 forms a liquid-tight seal between the housing sleeve 180 and the inverter end housing section 160. In some examples, the liquid-cooled radial flux electric motor 100 comprises a rotor-end housing seal 265 and an inverter-end housing seal 267. The rotor-end housing seal 265 forms a liquid-tight seal between the drive end housing section 150 and the body housing section 170. The inverter-end housing seal 267 forms a liquid-tight seal between the body housing section 170 and the inverter end housing section 160. In some examples, the liquid-cooled radial flux electric motor 100 comprises a distribution-ring seal 270. The distribution-ring seal 270 forms a liquid-tight seal between the distribution ring 190 and the inner surface 172. In some examples, the liquid-cooled radial flux electric motor 100 further comprises an additional distribution-ring seal 272. In examples where the liquid-cooled radial flux electric motor 100 comprises both a distribution-ring seal 270 and an additional distribution-ring seal 272, the distribution-ring seal 270 and the additional distribution-ring seal 272 are positioned on opposite sides of the channel 198. The materials of first housing sleeve seal 260, the second housing sleeve seal 262, the rotor-end housing seal 265, the inverterend housing seal 267, and the distribution-ring seal 270, when present, may be chosen from materials with suitable chemical resistance to the cooling fluid 205.

[0068] In some examples, the distribution of the plurality of distribution orifices 199 around the outer distribution ring surface 197 and length of each one ofthe plurality of distribution tubes 200 is configured to distribute the inflowing cooling fluid at an approximately even flow rate past the surface of each one of the plurality of stator windings 130. The end windings of the plurality of stator windings 130 are expected to dissipate heat from all sides roughly evenly due to the consistent electrical resistance of the wire comprising the plurality of stator windings 130. In some examples, the distribution of the plurality of distribution orifices 199 around the outer distribution ring surface 197 and length of each one of the plurality of distribution tubes 200 may be configured to distribute the inflowing cooling fluid equally on a rotor-facing surface of each one of the plurality of stator windings 130 and an opposite surface of each one of the plurality of stator windings 130. Other configurations are within the scope. For example, a flow rate of cooling fluid past one surface of each one of the plurality of stator windings 130 may be greater than a flow rate past another surface.FIG. 6: Examples of methods for operating liquid-cooled radial flux electric motors

[0069] FIG. 6 is a flowchart corresponding with a method 600 for operating a liquid-cooled radial flux electric motor 100. The method 600 may commence with (Block 601) receiving by the liquid-cooled radial flux electric motor 100 alternating current from a power inverter 620. The liquid-cooled radial flux electric motor 100 comprises a stator 120. The stator 120 comprises a plurality of stator windings 130 and a cooling fluid 205. The plurality of stator windings 130 and the cooling fluid 205 are both positioned in a cooling fluid volume 250. In some examples, the stator 120 further comprises a housing 140 and a housing sleeve 180. In these examples, the housing 140 and the housing sleeve 180 together form the cooling fluid volume 250. In some examples, the alternating current is a two-phase current. In other examples, the alternating current is a three-phase current.

[0070] The method 600 may proceed with (Block 602) circulating by a pump and heat exchanger 650 the cooling fluid 205 through the cooling fluid volume 250, thereby transferring heat from the plurality of stator windings 130.

[0071] In some examples, the liquid-cooled radial flux electric motor 100 further comprises a temperature sensor 710 and a controller 720. The temperature sensor 710 is thermally coupled with the cooling fluid volume 250. The controller 720 is electronically coupled with the temperature sensor 710 and the pump and heat exchanger 650. In these examples, the method 600 further comprises measuring by the temperature sensor 710 a temperature of the cooling fluid 205, recording at the controller 720 the measured temperature, and determining at the controller 720 whether the measured temperature is greater than a predetermined set temperature. If the measured temperature is greater than the predetermined set temperature, the method may comprise increasing a flow rate of the cooling fluid 205 by the pump and heat exchanger 650. In this way, the amount of heat removed from the plurality of stator windings 130 by the cooling fluid 205 may be varied with the temperature of the cooling fluid. For example, if the amount of electrical current supplied to the liquid-cooled radial flux electric motor 100 is increased, the amount of heat generated by the plurality of stator windings 130 may increase. An increase in generated heat transferred to the cooling fluid 205 passing through the cooling fluid volume 250 at a given rate will increase the temperature of the cooling fluid 205. If the temperature increases above a predetermined set temperature, the flow rate of the cooling fluid 205 may be increased, thereby enabling removal of more heat from the plurality of stator windings 130.

[0072] In some examples, the liquid-cooled radial flux electric motor 100 further comprises a current sensor 715 and a controller 720. The current sensor 715 is electrically coupled with the plurality of stator windings 130. The controller 720 is electronically coupled with the current sensor 715 and the pump and heat exchanger 650. In these examples, the method further comprises measuring by the current sensor 715 a current supplied to the liquid- cooled radial flux electric motor 100, recording at the controller 720 the measured current, determining at the controller 720 a predetermined flow rate of the cooling fluid 205 for the measured current, and adjusting the flow rate of the cooling fluid 205 by the pump and heat exchanger 650 if the flow rate isdifferent than the predetermined flow rate. In this way, the amount of heat removed from the plurality of stator windings 130 by the cooling fluid 205 may be varied with the current supplied to the liquid-cooled radial flux electric motor 100. For example, when the current supplied to the liquid-cooled radial flux electric motor 100 is greater, the amount of heat generated by the plurality of stator windings 130 will be greater. Increasing the flow rate of the cooling fluid 205 to the cooling fluid volume 250 enables removal of an increased amount of generated heat.FIG. 7: Examples of electric vehicles comprising liquid-cooled radial flux electric motors

[0073] FIG. 7 is a schematic block diagram illustrating relationships between some components of an electric vehicle 700, in accordance with some examples. The electric vehicle 700 comprises a liquid-cooled radial flux electric motor 100, a pump and heat exchanger 650, a controller 720, and a temperature sensor 710. The liquid-cooled radial flux electric motor 100 comprises a rotor 110, a stator 120, and a cooling fluid 205. The rotor 110 has a rotational axis 115. The stator 120 comprises a housing 140, a housing sleeve 180, and a plurality of stator windings 130. The housing 140 and the housing sleeve 180 together enclose a cooling fluid volume 250. The temperature sensor 710 is fluidically coupled with the cooling fluid volume 250 and electronically coupled with the controller 720. The plurality of stator windings 130 and the cooling fluid 205 are positioned within the cooling fluid volume 250.

[0074] In some examples, the housing 140 comprises a body housing section 170. The body housing section 170 has an inner surface 172 and an outer surface 174. The inner surface 172 faces the rotor 110 and has a cylindrical shape coaxial with the rotor 110. The outer surface 174 faces away from the rotor 110. The body housing section 170 comprises an inlet port 210 and an outlet port 220, each protruding through the body housing section 170 from the outer surface 174 to the inner surface 172. The cooling fluid volume 250 is fluidically coupled with the inlet port 210 and the outlet port 220.

[0075] In some examples, the housing 140 further comprises a drive end housing section 150 and an inverter end housing section 160. The drive end housing section 150 is fluidically sealed against the body housing section 170. The inverter end housing section 160 is fluidically sealed against the body housing section 170.

[0076] The housing sleeve 180 has a first cylindrical shape coaxial with the rotor 110 and has a first end and a second end opposite the first end. One of the ends is physically coupled with and fluidically sealed against the drive end housing section 150. An opposite end is physically coupled with and fluidically sealed against the inverter end housing section 160.

[0077] In some examples, the electric vehicle 700 further comprises a plurality of terminals 730. Each one of the plurality of terminals 730 is electrically coupled with the power inverter 620 and with a portion of the plurality of stator windings 130. In two-phase liquid-cooled radial flux electric motor 100, the plurality of terminals 730 may comprise two terminals. In three-phase liquid-cooled radial flux electric motor 100, the plurality of terminals 730 may comprise three terminals. In some examples, portions of one or more of the plurality of terminals 730 protrude into the cooling fluid volume 250 and interface the cooling fluid 205.

[0078] In some examples the electric vehicle 700 further comprises an additional temperature sensor 712. The additional temperature sensor 712 is electronically coupled with the controller 720 and fluidically coupled with the cooling fluid volume 250. The temperature sensor 710 is adjacent to the inlet port 210 and the controller 720 is adjacent to the outlet port 220. In these examples, the controller 720 is configured to receive an inlet temperature value from the temperature sensor 710 and an outlet value from the additional temperature sensor 712. The controller 720 is further configured to determine a difference between the inlet temperature value and outlet temperature value and determine whether the determined difference is greater than a preset difference limit. The controller 720 is configured to increase a pumping rate of the pump and heat exchanger 650 if the determined difference is greater than a preset difference limit. In some examples, the preset difference limit isgreater than 35 °C, greater than 50 °C, greater than 50 °C, or even greater than 75°C.

[0079] In some examples, the electric vehicle 700 further comprises a current sensor 715. The current sensor 715 is electrically coupled with the plurality of stator windings 130 and electronically coupled with the controller 720. In these examples, the controller 720 is configured to receive a current measurement from the current sensor 715. The controller 720 is further configured to determine a flow rate for the cooling fluid 205 corresponding to the measured current. The controller 720 is further configured to provide a signal to the pump and heat exchanger 650 to increase or decrease the flow rate of the cooling fluid 205 such that the flow rate matches the determined flow rate for the measured current. In this way, as current supplied to the liquid-cooled radial flux electric motor 100 in the electric vehicle 700 is increased, and heat generated by the plurality of stator windings 130 is increased, the flow rate of the cooling fluid 205 through the cooling fluid volume 250 may be increased to effectively transfer heat away from the plurality of stator windings 130.Conclusion

[0080] Although the foregoing concepts have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing processes, systems, and apparatuses. Accordingly, the present embodiments are to be considered illustrative and not restrictive.

Claims

CLAIMS1. A liquid-cooled radial flux electric motor comprising: a rotor having a rotational axis; a stator comprising a housing, a housing sleeve, and a plurality of stator windings; and a cooling fluid, wherein: the housing sleeve has a first cylindrical shape coaxial with the rotor and having a first end and a second end opposite of the first end, the housing and the housing sleeve together enclose a cooling fluid volume, the cooling fluid is positioned within the cooling fluid volume, and the plurality of stator windings is positioned within the cooling fluid volume.

2. The liquid-cooled radial flux electric motor of claim 1, further comprising a first bearing and a second bearing, each mechanically coupled to both the rotor and the stator, thereby enabling rotation of the rotor about the rotational axis relative to the stator.

3. The liquid-cooled radial flux electric motor of claim 2, wherein: the housing comprises a body housing section having an inner surface facing the rotor and having a second cylindrical shape coaxial with the rotor, the housing further comprises a drive end housing section mechanically coupled with the first bearing and fluidically sealed against the body housing section, the housing further comprises an inverter end housing section mechanically coupled with the second bearing and fluidically sealed against the body housing section, the first end of the housing sleeve is physically coupled with and fluidically sealed against the drive end housing section, andthe second end of the housing sleeve is physically coupled with and fluidica lly sealed against the inverter end housing section.

4. The liquid-cooled radial flux electric motor of claim 3, wherein: the housing further comprises an outer surface facing away from the rotor, the body housing section comprises an inlet port and an outlet port, each protruding through the body housing section from the outer surface to the inner surface, and the cooling fluid volume is fluidically coupled to the inlet port and the outlet port.

5. The liquid-cooled radial flux electric motor of claim 4, further comprising a circular distribution ring having a third cylindrical shape coaxial with the rotor and comprising: an inner distribution ring surface facing the rotational axis and an outer distribution ring surface opposite the rotational axis; a first distribution ring edge along the outer distribution ring surface in physical contact with the inner surface; a channel fluidically coupled with the inlet port; a distribution surface different from the first distribution ring edge; and a plurality of distribution orifices protruding through the distribution ring from the distribution surface to the channel.

6. The liquid-cooled radial flux electric motor of claim 5, wherein the channel has a depth measured perpendicular to the rotational axis of 2-10 millimeters.

7. The liquid-cooled radial flux electric motor of claim 5, wherein the channel is an opening in the distribution ring adjacent to the inner surface.

8. The liquid-cooled radial flux electric motor of claim 5, further comprising a plurality of distribution tubes positioned within the cooling fluid volume, wherein: each one of the plurality of distribution tubes has a first tube end and a second tube end opposite the first tube end, and each first tube end is fluidically coupled to one of the plurality of distribution orifices.

9. The liquid-cooled radial flux electric motor of claim 8, wherein: the cooling fluid volume has a first cooling fluid volume end positioned adjacent to the drive end housing section and a second cooling fluid volume end positioned adjacent to the inverter end housing section, the outlet port is positioned adjacent to the second cooling fluid volume end, and each one of the plurality of distribution tubes extends from the distribution surface away from the second cooling fluid volume end.

10. The liquid-cooled radial flux electric motor of claim 9, wherein: the distribution ring further comprises a second distribution ring edge positioned along the outer distribution ring surface, the second distribution ring edge is separated from the first distribution ring edge along a direction parallel with the rotational axis by a width of the channel measured in a direction parallel with the rotational axis, and the second distribution ring edge interfaces the inner surface, such that cooling fluid entering the cooling fluid volume via the inlet port is directed to the plurality of distribution tubes.

11. The liquid-cooled radial flux electric motor of claim 1, wherein the housing sleeve is formed from a non-magnetic metal.

12. The liquid-cooled radial flux electric motor of claim 11, wherein the housing sleeve is formed from non-magnetic stainless steel.

13. The liquid-cooled radial flux electric motor of claim 3, further comprising a first housing sleeve seal forming a liquid-tight seal between the housing sleeve and the drive end housing section and a second housing sleeve seal forming a liquid-tight seal between the housing sleeve and the inverter end housing section.

14. The liquid-cooled radial flux electric motor of claim 3, further comprising a rotor-end housing seal forming a liquid-tight seal between the drive end housing section and the body housing section and an inverter-end housing seal forming a liquid-tight seal between the body housing section and the inverter end housing section.

15. The liquid-cooled radial flux electric motor of claim 5, further comprising a distribution-ring seal forming a liquid-tight seal between the distribution ring and the inner surface.

16. The liquid-cooled radial flux electric motor of claim 5, further comprising a stator spacer, wherein: the stator spacer has an inner spacer surface having a fourth cylindrical shape coaxial with the rotational axis and facing the rotational axis, the stator spacer has an outer spacer surface having a fifth cylindrical shape coaxial with the rotational axis facing away from the rotational axis, the stator spacer is positioned between the housing sleeve and the distribution ring and interfaces the inner distribution ring surface, and the stator spacer has a plurality of protrusions extending towards the rotational axis from the inner spacer surface and interfacing the housing sleeve.

17. A method for operating a liquid-cooled radial flux electric motor, the method comprising:(Block) receiving by the liquid-cooled radial flux electric motor comprising a stator comprising a plurality of stator windings and a cooling fluidpositioned in a cooling fluid volume an alternating current from a power inverter; and(Block) circulating by a pump and heat exchanger the cooling fluid through the cooling fluid volume, thereby transferring heat from the plurality of stator windings.

18. The method of claim 17, wherein: the liquid-cooled radial flux electric motor further comprises a temperature sensor thermally coupled with the cooling fluid volume and a controller electronically coupled with the temperature sensor and the pump and heat exchanger, and the method further comprises measuring by the temperature sensor a temperature of the cooling fluid, recording at the controller the measured temperature, determining at the controller whether the measured temperature is greater than a predetermined set temperature, and increasing a flow rate of the cooling fluid by the pump and heat exchanger if the measured temperature is greater than the predetermined set temperature.

19. The method of claim 17, wherein: the liquid-cooled radial flux electric motor further comprises a current sensor electrically coupled with the plurality of stator windings and a controller electronically coupled with the current sensor and the pump and heat exchanger, and the method further comprises measuring by the current sensor a current supplied to the liquid-cooled radial flux electric motor, recording at the controller the measured current, determining at the controller a predetermined flow rate of cooling fluid for the measured current, and adjusting the flow rate of the cooling fluid by the pump and heat exchanger if the flow rate is different than the predetermined flow rate.

20. The method of claim 17, wherein the alternating current is a three-phase current.

21. An electric vehicle comprising: a pump and heat exchanger; a controller electronically coupled with the pump and heat exchanger; a temperature sensor; and a liquid-cooled radial flux electric motor comprising a rotor, a stator, and a cooling fluid, wherein: the rotor has a rotational axis, the stator comprises a housing, a housing sleeve, and a plurality of stator windings, the housing and the housing sleeve together enclose a cooling fluid volume, the cooling fluid is positioned within the cooling fluid volume, the plurality of stator windings is positioned within the cooling fluid volume, and the temperature sensor is f luidica lly coupled with the cooling fluid volume and electronically coupled with the controller.

22. The electric vehicle of claim 21, wherein: the housing comprises a body housing section comprising an inner surface facing the rotor and having a second cylindrical shape coaxial with the rotor, the body housing section further comprises an outer surface facing away from the rotor, the body housing section further comprises an inlet port and an outlet port, each protruding through the body housing section from the outer surface to the inner surface, the electric vehicle further comprises an additional temperature sensor electronically coupled with the controller and f luidica lly coupled with the cooling fluid volume, the temperature sensor is positioned adjacent to the inlet port,the additional temperature sensor is positioned adjacent to the outlet port, and the controller is configured to receive an inlet temperature value from the temperature sensor and an outlet value from the additional temperature sensor, determine a difference between the inlet temperature value and outlet temperature value, determine whether the determined difference is greater than a preset difference limit, and increase a pumping rate of the pump and heat exchanger if the determined difference is greater than the preset difference limit.

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