Patent Description:
Typical aircraft propulsion systems include one or more gas turbine engines. For certain propulsion systems, the gas turbine engines generally include a fan and a core arranged in flow communication with one another. Additionally, the core of the gas turbine engine general includes, in serial flow order, a compressor section, a combustion section, a turbine section, and an exhaust section. In operation, air is provided from the fan to an inlet of the compressor section where one or more axial compressors progressively compress the air until it reaches the combustion section. Fuel is mixed with the compressed air and burned within the combustion section to provide combustion gases. The combustion gases are routed from the combustion section to the turbine section. The flow of combustion gasses through the turbine section drives the turbine section and is then routed through the exhaust section, e.g., to atmosphere.

For at least certain propulsion systems including the above gas turbine engines, it may be beneficial to include an electric fan to supplement propulsive power provided by the one or more gas turbine engines included with the propulsion system. However, inclusion of a sufficient amount of energy storage devices with the propulsion system to power the electric fan may be space and weight prohibitive. Accordingly, at least certain propulsion systems include one or more electric machines rotatable with one or more of the gas turbine engines to generate electrical power during operation to drive the electric fan.

Further, the inventors of the present disclosure have determined that utilizing permanent magnet electric machines like for example the one used in <CIT> may have certain benefits over other configurations of electric machines. Such benefits may include power density, efficiency and simplicity. One negative characteristic of permanent magnet electric machines, however, relates to their behavior after an internal coil fault has occurred. Specifically, after such an event, the permanent magnet electric machine may generate into the fault so long as the rotor is spinning, potentially causing significant drag on the driving engine and generating heat within the faulted coil. This unwanted generation may have negative consequences, and in the current art the only way to halt such unwanted generation is to stop rotation (i.e. turn the driving engine off). This action may cause further negative consequences, namely loss of thrust and power. Other types of electric machines do not have this same issue, as their rotor can be effectively deactivated.

Accordingly, a safety system for a permanent magnet electric machine that may be utilized with an engine, such as a gas turbine engine, to overcome the above obstacle would be useful.

<CIT> discloses an electrical machine system comprising a permanent magnet assembly having a magnetic field, a plurality of conductive coils, and a current injector electrically connected to said coils and arranged selectively to supply a current signal thereto. The current signal being asynchronous with the frequency of rotation between the permanent magnet assembly and coils so as to heat and thereby demagnetise one or more magnet within said permanent magnet assembly.

The invention is disclosed by the appended claims.

According to the invention, a method for operating a permanent magnet electric machine of an engine is provided. The method includes determining a fault condition of the permanent magnet electric machine; and reducing a magnetism of one or more permanent magnets of the permanent magnet electric machine by increasing a temperature of the one or more permanent magnets to irreversibly reduce or extinguish a magnetism of the one or more permanent magnets in response to determining the fault condition of the permanent magnet electric machine. The reducing of the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets comprises providing a heating fluid to the permanent magnet electric machine.

In certain exemplary embodiments the engine is a combustion engine.

In certain exemplary embodiments the engine is at least one of a turboshaft engine, a turboprop engine, or a turbofan engine.

In certain exemplary embodiments the engine is configured to generate a maximum amount of power during operation, wherein the permanent magnet electric machine is capable of extracting a maximum amount of power from the engine, and wherein the maximum amount of power the permanent magnet electric machine is capable of extracting from the engine is between about <NUM>% and about <NUM>% of the maximum amount of power the engine is configured to generate during operation.

For example, in certain exemplary aspects the maximum amount of power the permanent magnet electric machine is capable of extracting from the engine is greater than about <NUM>% of the maximum amount of power the engine is configured to generate during operation.

In certain exemplary embodiments determining the fault condition of the permanent magnet electric machine includes determining an internal coil fault of the permanent magnet electric machine.

In certain exemplary embodiments reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets includes driving current through a stator assembly of the permanent magnet electric machine to induce eddy current losses in a rotor assembly of the permanent magnet electric machine.

For example, in certain exemplary aspects the permanent magnet electric machine defines a designed current frequency operating range, and wherein driving current through the stator assembly of the permanent magnet electric machine to induce eddy current losses includes driving current through the stator assembly of the permanent magnet electric machine at a frequency other than the designed current frequency operating range.

For example, in certain exemplary aspects providing the heating fluid to the permanent magnet electric machine includes providing a bleed air to the permanent magnet electric machine.

In certain exemplary embodiments reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets includes reducing a cooling of the permanent magnet electric machine using a thermal management system.

For example, in certain exemplary aspects reducing the cooling of the permanent magnet electric machine using the thermal management system includes bypassing a heat sink heat exchanger of the thermal management system.

In certain exemplary embodiments reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets includes injecting a fluid into an air gap of the permanent magnet electric machine.

For example, in certain exemplary aspects the fluid defines a viscosity greater than a viscosity of air.

In certain exemplary embodiments reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets includes adding between about five kilowatts of heat energy and about five hundred kilowatts of heat energy.

In certain exemplary embodiments the permanent magnet electric machine includes a rotor assembly having a plurality of laminations and a shaft, wherein the plurality of laminations are fitted onto the shaft, and wherein reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets includes decreasing a contact pressure between the plurality of laminations and the shaft.

For example, in certain exemplary aspects the engine includes a thermal management system for providing a cooling fluid through one or more openings in the shaft.

According to the invention, an engine is provided defining an axis. The engine includes a stationary component; a rotary component rotatable about the axis of the engine relative to the stationary component; a permanent magnet electric machine including a stator assembly coupled to the stationary component and a rotor assembly coupled to the rotary component, the rotor assembly including one or more permanent magnets; and a controller operable with the permanent magnet electric machine, the controller configured to determine a fault condition of the permanent magnet electric machine and increase a temperature of the one or more permanent magnets of the permanent magnet electric machine to irreversibly reduce or extinguish a magnetism of the one or more permanent magnets in response to determining the fault condition. The reducing of the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets comprises providing a heating fluid to the permanent magnet electric machine.

In certain exemplary embodiments, the engine further includes an electric transfer bus in electrical communication with the permanent magnet electric machine, wherein the controller is further operably connected to the electric transfer bus.

For example, in certain exemplary embodiments the engine is configured to generate a maximum amount of power during operation, wherein the permanent magnet electric machine is capable of extracting a maximum amount of power from the engine, and wherein the maximum amount of power the permanent magnet electric machine is capable of extracting from the engine is between about <NUM>% and about <NUM>% of the maximum amount of power the engine is configured to generate during operation.

The terms "forward" and "aft" refer to relative positions within a component or system, and refer to the normal operational attitude of the component or system. For example, with regard to a robotic arm, forward refers to a position closer to a distal end of the robotic arm and aft refers to a position closer to a root end of the robotic arm.

Referring now to the drawings, wherein identical numerals indicate the same elements throughout the figures, <FIG> is a schematic cross-sectional view of an engine in accordance with an exemplary embodiment of the present disclosure. More particularly, for the embodiment of <FIG>, the engine is a gas turbine engine, and more specifically, the gas turbine engine is a high-bypass turbofan jet engine <NUM>, referred to herein as "turbofan engine <NUM>. " As shown in <FIG>, the turbofan engine <NUM> defines an axial direction A (extending parallel to a longitudinal centerline <NUM> provided for reference), a radial direction R, and a circumferential direction (i.e., a direction extending about the axial direction A; not depicted). In general, the turbofan <NUM> includes a fan section <NUM> and a turbomachine <NUM> disposed downstream from the fan section <NUM>.

The exemplary turbomachine <NUM> depicted generally includes a substantially tubular outer casing <NUM> that defines an annular inlet <NUM>. The outer casing <NUM> encases, in serial flow relationship, a compressor section including a booster or low pressure (LP) compressor <NUM> and a high pressure (HP) compressor <NUM>; a combustion section <NUM>; a turbine section including a high pressure (HP) turbine <NUM> and a low pressure (LP) turbine <NUM>; and a jet exhaust nozzle section <NUM>. The compressor section, combustion section <NUM>, and turbine section together define a core air flowpath <NUM> extending from the annular inlet <NUM> through the LP compressor <NUM>, HP compressor <NUM>, combustion section <NUM>, HP turbine section <NUM>, LP turbine section <NUM> and jet nozzle exhaust section <NUM>. A high pressure (HP) shaft or spool <NUM> drivingly connects the HP turbine <NUM> to the HP compressor <NUM>. A low pressure (LP) shaft or spool <NUM> drivingly connects the LP turbine <NUM> to the LP compressor <NUM>.

For the embodiment depicted, the fan section <NUM> includes a variable pitch fan <NUM> having a plurality of fan blades <NUM> coupled to a disk <NUM> in a spaced apart manner. As depicted, the fan blades <NUM> extend outwardly from disk <NUM> generally along the radial direction R. Each fan blade <NUM> is rotatable relative to the disk <NUM> about a pitch axis P by virtue of the fan blades <NUM> being operatively coupled to a suitable actuation member <NUM> configured to collectively vary the pitch of the fan blades <NUM> in unison. The fan blades <NUM>, disk <NUM>, and actuation member <NUM> are together rotatable about the longitudinal axis <NUM> by LP shaft <NUM> across a power gear box <NUM>. The power gear box <NUM> includes a plurality of gears for stepping down the rotational speed of the LP shaft <NUM> to a more efficient rotational fan speed.

Referring still to the exemplary embodiment of <FIG>, the disk <NUM> is covered by rotatable front nacelle <NUM> aerodynamically contoured to promote an airflow through the plurality of fan blades <NUM>. Additionally, the exemplary fan section <NUM> includes an annular fan casing or outer nacelle <NUM> that circumferentially surrounds the fan <NUM> and/or at least a portion of the turbomachine <NUM>. It should be appreciated that for the embodiment depicted, the nacelle <NUM> is supported relative to the turbomachine <NUM> by a plurality of circumferentially-spaced outlet guide vanes <NUM>. Moreover, a downstream section <NUM> of the nacelle <NUM> extends over an outer portion of the turbomachine <NUM> so as to define a bypass airflow passage <NUM> therebetween.

During operation of the turbofan engine <NUM>, a volume of air <NUM> enters the turbofan <NUM> through an associated inlet <NUM> of the nacelle <NUM> and/or fan section <NUM>. As the volume of air <NUM> passes across the fan blades <NUM>, a first portion of the air <NUM> as indicated by arrows <NUM> is directed or routed into the bypass airflow passage <NUM> and a second portion of the air <NUM> as indicated by arrow <NUM> is directed or routed into the LP compressor <NUM>. The ratio between the first portion of air <NUM> and the second portion of air <NUM> is commonly known as a bypass ratio. The pressure of the second portion of air <NUM> is then increased as it is routed through the high pressure (HP) compressor <NUM> and into the combustion section <NUM>, where it is mixed with fuel and burned to provide combustion gases <NUM>.

The combustion gases <NUM> are routed through the HP turbine <NUM> where a portion of thermal and/or kinetic energy from the combustion gases <NUM> is extracted via sequential stages of HP turbine stator vanes <NUM> that are coupled to the outer casing <NUM> and HP turbine rotor blades <NUM> that are coupled to the HP shaft or spool <NUM>, thus causing the HP shaft or spool <NUM> to rotate, thereby supporting operation of the HP compressor <NUM>. The combustion gases <NUM> are then routed through the LP turbine <NUM> where a second portion of thermal and kinetic energy is extracted from the combustion gases <NUM> via sequential stages of LP turbine rotor blades <NUM> that are coupled to the LP shaft or spool <NUM>, thus causing the LP shaft or spool <NUM> to rotate. Such thereby supports operation of the LP compressor <NUM> and/or rotation of the fan <NUM>.

The combustion gases <NUM> are subsequently routed through the jet exhaust nozzle section <NUM> of the turbomachine <NUM> to provide propulsive thrust. Simultaneously, the pressure of the first portion of air <NUM> is substantially increased as the first portion of air <NUM> is routed through the bypass airflow passage <NUM> before it is exhausted from a fan nozzle exhaust section <NUM> of the turbofan <NUM>, providing most of the propulsive thrust for the turbofan engine <NUM>. The HP turbine <NUM>, the LP turbine <NUM>, and the jet exhaust nozzle section <NUM> at least partially define a hot gas path <NUM> for routing the combustion gases <NUM> through the turbomachine <NUM>.

Additionally, the exemplary turbofan <NUM> depicted includes a permanent magnet electric machine <NUM> rotatable with the turbofan <NUM>. Specifically, for the embodiment depicted, the permanent magnet electric machine <NUM> is co-axially mounted to, and rotatable with, the LP shaft <NUM> (the LP shaft <NUM> also rotating the fan <NUM> through, for the embodiment depicted, the power gearbox <NUM>). As used herein, "co-axially" refers to the axes being aligned. It should be appreciated, however, that in other embodiments, an axis of the permanent magnet electric machine <NUM> may be offset radially from the axis of the LP shaft <NUM> and further may be oblique to the axis of the LP shaft <NUM>, such that the permanent magnet electric machine <NUM> may be positioned at any suitable location at least partially inward of the core air flowpath <NUM>.

The permanent magnet electric machine <NUM> includes a rotor assembly <NUM> and a stator assembly <NUM>. As will be discussed below, the rotor assembly <NUM> may generally include a plurality of permanent magnets <NUM>, such that it may be referred to as a permanent magnet rotor assembly <NUM>. Additionally, the stator assembly <NUM> may generally include a plurality of coils <NUM> operable with the plurality of permanent magnets <NUM> of the rotor assembly <NUM>. When electrical power is provided to the plurality of coils <NUM> of the stator assembly <NUM>, the permanent magnet electric machine <NUM> may operate to add torque to the turbofan <NUM> through the LP shaft <NUM>. By contrast, in other exemplary aspects, the plurality of coils <NUM> of the stator assembly <NUM> may operate to extract electrical power, converting torque of the turbofan <NUM>, and more specifically, of the LP shaft <NUM>, into electrical power.

It will further be appreciated that, in certain exemplary embodiments, the turbofan engine <NUM> may be integrated into a propulsion system. With such an exemplary embodiment, the permanent magnet electric machine <NUM> may be electrically connected, or connectable, to one or more electric propulsion devices of the propulsion system (such as one or more electric fans), one or more power storage devices, etc..

It should be appreciated, however, that the exemplary turbofan engine <NUM> depicted in <FIG> is by way of example only, and that in other exemplary embodiments, the turbofan engine <NUM> may have any other suitable configuration. For example, in other exemplary embodiments, the turbine fan engine <NUM> may include any other suitable number or configuration of shafts or spools, compressors, turbines, etc., and/or may exclude, e.g., the power gearbox <NUM> and/or the pitch change mechanism <NUM>, etc. Accordingly, it will be appreciated that in other exemplary embodiments, the turbofan engine <NUM> may instead be configured as a direct drive turbofan engine, a fixed pitch turbofan engine, etc. Further, in still other exemplary embodiments, the turbofan engine <NUM> may be configured as any other suitable gas turbine engine, such as a turbojet engine, a turboshaft engine, a turboprop engine, etc. Further, still, in other embodiments, the turbofan engine may be configured as any other suitable engine, such as an electric propulsion fan for an aircraft propulsion system or any form of combustion engine (e.g., an internal combustion engine). With such a configuration, the engine may not include any of the turbomachinery, and instead may generally include the fan <NUM> and the permanent magnet electric machine <NUM>.

Referring now to <FIG>, a close-up, schematic view of the exemplary permanent magnet electric machine <NUM> of <FIG>, embedded within the engine of <FIG>, is provided. More particularly, for the embodiment depicted and as noted above, the permanent magnet electric machine <NUM> is embedded within the turbine section of the turbofan engine <NUM>, at a location inward of a core air flowpath <NUM> and positioned at least partially within or aft of the turbine section along an axial direction A. Of course, as discussed above, in other exemplary embodiments, the permanent magnet electric machine <NUM> may instead be positioned at any other suitable location within the turbofan engine <NUM>, such as within the compressor section, forward of the compressor section, radially outward of the core air flowpath <NUM> (e.g., under the cowling of the turbomachine <NUM>, such as part of an accessory gearbox), etc..

More specifically, for the exemplary embodiment depicted, the permanent magnet electric machine <NUM> is positioned inward of the core air flowpath <NUM>, and at least partially aft of the LP turbine <NUM> of the turbine section of the turbofan engine <NUM>. Briefly, as will be appreciated, the exemplary LP turbine <NUM> depicted generally includes a plurality of LP turbine rotor blades <NUM> and a plurality of LP turbine stator vanes <NUM> (although only one is shown). Further, it will be appreciated that the plurality of LP turbine rotor blades <NUM> are each generally coupled to a respective rotor <NUM>, with the plurality of respective rotors <NUM> coupled to, or otherwise rotatable with, the LP shaft <NUM>.

Moreover, for the embodiment of <FIG>, the turbofan engine <NUM> generally includes a rotary component and a stationary component. The rotary component is rotatable with a compressor within the compressor section (not shown) of the turbofan engine <NUM> and/or a turbine within the turbine section of the turbofan engine <NUM>. By contrast, the stationary component may be any suitable component which is configured to remain stationary relative to the various rotating components of the compressors and turbines.

For the exemplary embodiment depicted, the stationary component is part of a structural support member <NUM> of the turbofan engine <NUM>, the structural support member <NUM> being configured as part of an aft frame assembly and extending from an aft frame strut <NUM> of the aft frame assembly. The aft strut <NUM> extends through the core air flowpath <NUM> of the turbofan engine <NUM>, and is configured to provide structural support for the turbofan engine <NUM>. The structural support member <NUM> also extends forward to support an aft engine bearing <NUM>-the aft engine bearing <NUM> rotatably supporting an aft end of the LP shaft <NUM>.

Further, as also noted above, the permanent magnet electric machine <NUM> generally includes the rotor assembly <NUM> and the stator assembly <NUM>. The rotor assembly <NUM> is coupled to the rotary component of the gas turbine engine and the stator assembly <NUM> is coupled to the stationary component of the turbofan engine <NUM>. More particularly, for the embodiment depicted the rotary component to which the rotor assembly <NUM> is coupled is the LP shaft <NUM> of the turbofan engine <NUM>, such that the rotor assembly <NUM> is rotatable with the LP shaft <NUM>. By contrast, the stationary component to which the stator assembly <NUM> is coupled is the structural support member <NUM> of the turbine section.

More specifically, the rotor assembly <NUM> generally includes a rotor <NUM> and a shaft <NUM>. The rotor <NUM> may be formed of a plurality of sequentially arranged laminations <NUM> (see callout Circle A of <FIG>, below) arranged, e.g. axially, on the shaft <NUM>, with these plurality of sequentially arranged laminations <NUM> mounting a plurality of permanent magnets <NUM> of the rotor assembly <NUM>. The plurality of permanent magnets <NUM> may be arranged circumferentially about an axis of the permanent magnet electric machine <NUM> (which for the embodiment depicted is aligned with axis <NUM> of the turbofan engine <NUM>). Similarly, the stator assembly <NUM> generally includes a stator <NUM> and a shaft <NUM>. The stator <NUM> includes the plurality of coils <NUM>, which may also be arranged circumferentially about the axis of the permanent magnet electric machine <NUM>. The rotor assembly <NUM> is rotatable relative to the stator assembly <NUM> during operation, and is rotatably supported relative to the stator assembly <NUM> by, for the embodiment depicted, a forward roller bearing <NUM> and an aft ball bearing <NUM>. However, in other embodiments, any other suitable configuration may be provided for rotatably supporting the rotor assembly <NUM> relative to the stator assembly <NUM> (e.g., any other suitable configuration of mechanical bearings, use of suitable air bearings, etc.).

Further, the permanent magnet electric machine <NUM> is electrically connected to an electric transfer bus <NUM>. The electric transfer bus <NUM> includes an electric line <NUM> extending, for the embodiment depicted, through the core air flowpath <NUM>, and more specifically, through the aft strut <NUM>. The electric line <NUM> is electrically coupled to the stator assembly <NUM> of the permanent magnet electric machine <NUM>. The exemplary electric transfer bus <NUM> depicted generally includes power electronics <NUM> in communication with the electric line <NUM> that may be utilized to manipulate electrical power provided to the permanent magnet electric machine <NUM>, or to extract electrical power from the permanent magnet electric machine <NUM>, and more specifically, to or from the stator assembly <NUM> of the permanent magnet electric machine <NUM>.

Additionally, electric transfer bus <NUM> includes one or more sensors operable with the electric line <NUM>, the power electronics <NUM>, or both. More specifically, for the embodiment shown, the electric transfer bus <NUM> includes a first sensor <NUM> operable with the electric line <NUM> (i.e., to sense data from the electric line <NUM>) and a second sensor <NUM> operable with the power electronics <NUM> (i.e., to sense data from the power electronics <NUM>). The first sensor <NUM>, the second sensor <NUM>, or both may be configured to sense various parameters of the electric transfer bus <NUM> and/or the power electronics <NUM> to determine one or more operability parameters of the permanent magnet electric machine <NUM>. For example, the first sensor <NUM>, the second sensor <NUM>, or both may be utilized to determine an amount of electrical power being extracted from the permanent magnet electric machine <NUM>, an amount of electrical power being provided to the permanent magnet electric machine <NUM>, a voltage of such power, an amplitude of a current of such power, a frequency of such current, etc..

Briefly, a controller <NUM> is also provided in operable communication with the electric transfer bus <NUM>. Notably, although the controller <NUM> is depicted as being positioned physically separate from the turbofan engine <NUM> and permanent magnet electric machine <NUM>, in other embodiments, the controller <NUM> may be positioned, or otherwise integrated into, the turbofan engine <NUM>, an aircraft incorporating the turbofan engine <NUM>, the permanent magnet electric machine <NUM>, etc..

The exemplary controller <NUM> generally includes a network interface <NUM>. The network interface <NUM> may be operable with any suitable wired or wireless communications network for communicating data with other components of, e.g., the turbofan engine <NUM>, the permanent magnet electric machine <NUM>, the electric transfer bus <NUM>, and/or other components or systems not depicted. As depicted using phantom lines in <FIG>, for the embodiment depicted, the network interface <NUM> utilizes a wireless communication network to communicate data with other components, including the first sensor <NUM>, the second sensor <NUM>, and the power electronics <NUM>. In such a manner, the controller <NUM> may control operation of the power electronics <NUM>. It will be appreciated, of course, that although the network interface <NUM> utilizes the wireless communication network for the embodiment of <FIG>, in other embodiments, the network interface <NUM> may instead utilize a wired communication network, or a combination of wired and wireless communication networks.

Referring still to <FIG>, the exemplary controller <NUM> further includes one or more processors <NUM> and memory <NUM>. The memory <NUM> stores data <NUM> accessible by the one or more processors <NUM>. The one or more processor(s) <NUM> can include any suitable processing device, such as a microprocessor, microcontroller <NUM>, integrated circuit, logic device, and/or other suitable processing device. The one or more memory device(s) <NUM> can include one or more computer-readable media, including, but not limited to, non-transitory computer-readable media, RAM, ROM, hard drives, flash drives, and/or other memory devices. The data <NUM> may include instructions that when executed by the one or more processors <NUM> cause the system <NUM> to perform functions. One or more exemplary aspects of these functions may be described below with respect to the exemplary method <NUM> of <FIG>. The instructions within the data <NUM> can be any set of instructions that when executed by the one or more processor(s) <NUM>, cause the one or more processor(s) <NUM> to perform operations. In certain exemplary embodiments, the instructions within the data <NUM> can be software written in any suitable programming language or can be implemented in hardware. Additionally, and/or alternatively, the instructions can be executed in logically and/or virtually separate threads on processor(s) <NUM>. The memory device(s) <NUM> can further store other data <NUM> that can be accessed by the processor(s) <NUM>.

It will be appreciated, however, that the exemplary electric transfer bus <NUM> (including the power electronics <NUM> and electric line <NUM>), controller <NUM>, and sensors <NUM>, <NUM> are provided by way of example only. In other exemplary embodiments, one or more of these components may be configured in any other suitable manner, and/or any other suitable configuration may be provided for controlling operations related to the permanent magnetic electric machine <NUM>.

Referring still to <FIG>, it will be appreciated that the permanent magnet electric machine <NUM> may be configured to extract a relatively high amount of power from the turbofan engine <NUM>. For example, the turbofan engine <NUM>, or rather, the turbomachine <NUM> of the turbofan engine <NUM>, may be configured to generate a maximum amount of power during operation. This maximum amount of power may be a rated power level of the turbomachine <NUM>. Additionally, the permanent magnet electric machine <NUM> may be capable extracting a maximum amount of power from the turbofan engine <NUM>, or rather, the turbomachine <NUM> of the turbofan engine <NUM>, during operation. For example, the maximum amount of power the permanent magnet electric machine <NUM> is capable of extracting may be set based on design parameters of the permanent magnet electric machine <NUM> designed to allow the permanent magnet electric machine <NUM> to operate without significantly degrading. In at least certain exemplary embodiments, the maximum amount of power the permanent magnet electric machine <NUM> is capable extracting from the turbofan engine <NUM>, or rather, the turbomachine <NUM>, is between about <NUM> percent and about seventy-five percent (<NUM>%) of the maximum amount of power the turbofan engine <NUM>, or rather, the turbomachine <NUM> of the turbofan engine <NUM>, is configured to generate during operation. For example, in at least certain exemplary embodiments, the maximum amount of power the permanent magnet electric machine <NUM> is capable of extracting from the turbofan engine <NUM> is greater than about three percent (<NUM>%) of the maximum amount of power the turbofan engine <NUM> is configured to generate during operation, such as greater than about five percent (<NUM>%), such as greater than about ten percent (<NUM>%), such as greater than about twenty-five percent (<NUM>%).

By way of example only, the turbofan engine <NUM> may be rated to generate <NUM>,<NUM> horsepower, and the permanent magnet electric machine <NUM> may be capable of extracting approximately <NUM>,<NUM> kilowatts, or about <NUM>,<NUM> horsepower. Of course, in other embodiments, these numbers may vary greatly (e.g., the gas turbine engine may be significantly more or less powerful, and/or the permanent magnet electric machine <NUM> may be significantly more or less powerful). Regardless, such may allow for providing a desired amount of power to, e.g., an electric fan of a propulsion system including the turbofan engine <NUM> and permanent magnet electric machine <NUM>, and/or to any other suitable power sink of an aircraft.

However, by utilizing such a relatively powerful permanent magnet electric machine <NUM>, a failure of the permanent magnet electric machine <NUM> may create an undesirably high drag on the turbofan engine <NUM> and may generate undesirably high levels of heat. For example, the permanent magnet electric machine <NUM> may experience an internal coil fault (i.e., a stator winding short-circuit of the stator assembly <NUM>) if, e.g., an insulation of the coils <NUM> breaks down. In such a scenario the permanent magnet electric machine <NUM> may extract power from the turbofan engine <NUM> without generating a corresponding amount of electrical power for the propulsion system. For example, depending on the severity of the internal coil fault of the permanent magnet electric machine <NUM>, the permanent magnet electric machine <NUM> may not generate any electrical power, while still extracting a relatively high amount of power from the turbofan engine <NUM>, such as up to the maximum amount of power the permanent magnet electric machine <NUM> is capable of extracting, noted above (therefore acting as a significant drag on the engine). Notably, the internal coil fault may, in certain exemplary embodiments, be determined by the controller <NUM> based on data sensed by the one or more sensors, i.e., the first sensor <NUM> and the second sensor <NUM> for the embodiment depicted. Additionally, it will be appreciated that the internal coil fault may generate a relatively high amount of heat (potentially leading to further damage). Accordingly, in certain embodiments, the internal coil fault may be determined by the controller <NUM> based on sensed data indicative of a temperature of the permanent magnet electric machine <NUM> or a component or system indicative of a temperature of the permanent magnet electric machine <NUM>.

Further, given that the permanent magnets <NUM> are utilized with the rotor assembly <NUM>, the permanent magnets <NUM> may not be "switched off," as with other types of electric machines. Accordingly, the system of the present disclosure is configured to reduce a magnetism of one or more permanent magnets <NUM> of the permanent magnet electric machine <NUM>, or more specifically, to reduce a magnetism of the permanent magnets <NUM> of the rotor assembly <NUM> of the permanent magnet electric machine <NUM>, in response to determining the fault condition of the permanent magnet electric machine <NUM> (e.g., the internal coil fault - although it may also be appropriate in the event of other fault conditions of the permanent magnetic electric machine <NUM>). More specifically, for the embodiment shown, the system of the present disclosure is configured to reduce the magnetism of the permanent magnets <NUM> by increasing a temperature of the rotor assembly <NUM> of the permanent magnet electric machine <NUM>, and more specifically, of the permanent magnets <NUM> of the rotor assembly <NUM>.

Specifically, for the embodiment depicted, the system is configured to reduce the magnetism of the permanent magnets <NUM> utilizing electricity/induction. For example, for the embodiment depicted, the system is configured to increase the temperature the one or more permanent magnets <NUM> by driving current through the stator <NUM> of the stator assembly <NUM> of the permanent magnet electric machine <NUM> to induce eddy current losses. For example, the permanent magnet electric machine <NUM> may define a designed current frequency operating range. As used herein, the term "designed current frequency operating range" refers to a current frequency range for electric power that the permanent magnet electric machine <NUM> is configured to generate when extracting power from the turbofan engine <NUM>, and/or is configured to receive during normal operations when adding power to the turbofan engine <NUM>. With the present disclosure, the system may further be configured to increase the temperature of the one or permanent magnets <NUM> by driving current through stator <NUM> the stator assembly <NUM> at a frequency greater than the designed current frequency operating range. Such may further induce the eddy current losses, as noted above, which may in turn increase a temperature within the permanent magnet electric machine <NUM>, and more notably within the rotor assembly <NUM>.

Notably, it will be appreciated that the permanent magnets <NUM> of the rotor assembly <NUM> each generally define a Curie temperature. The Curie temperature refers to a temperature above which a magnetism of the permanent magnets <NUM> irreversibly is decreased or altogether lost. Accordingly, increasing the temperature of the permanent magnets <NUM> may include increasing the temperature of the permanent magnets above their respective Curie temperatures.

For example, in at least certain exemplary embodiments, in order to increase the temperature of the permanent magnets <NUM> of the permanent magnet electric machine <NUM>, the system may add between about five (<NUM>) kilowatts and about five hundred (<NUM>) kilowatts of heat energy to the permanent magnet electric machine <NUM>. More specifically, in at least some embodiments, the system may add at least about ten (<NUM>) kilowatts of heat energy, such as at least about twenty-five (<NUM>) kilowatts of heat energy.

It will be appreciated that by increasing the temperature in this manner, the system irreversibly reduces or extinguishes a magnetism of the permanent magnets <NUM> of the rotor assembly <NUM> of the permanent magnet electric machine <NUM>. However, it may be desirable to permanently damage the permanent magnet electric machine <NUM> in order to reduce or extinguish the drag the permanent magnet electric machine <NUM> may have on the turbofan engine <NUM> during, e.g., a flight of an aircraft incorporating the turbofan engine <NUM> having the permanent magnet electric machine <NUM> experiencing, e.g., an internal coil fault. For example, using the numbers provided in the non-limiting example above, it may be more desireable to permanently damage the electric machine <NUM> to avoid an approximately <NUM>,<NUM> horsepower drag on a <NUM>,<NUM> horsepower engine for an extended period of time.

Further, it will be appreciated that the exemplary turbofan engine <NUM> and permanent magnet electric machine <NUM> described above with reference to <FIG> and <FIG> is provided by way of example only. In other exemplary embodiments, the turbofan engine <NUM> and permanent magnet electric machine <NUM> may instead have any other suitable configuration. For example, in other embodiments, any other suitable means may be provided for increasing the temperature of the one or more permanent magnets <NUM> of the permanent magnet electric machine <NUM> to reduce the magnetism of such permanent magnets <NUM> in response to determining a fault condition of the permanent magnet electric machine <NUM>.

For example, <FIG> provide various alternative exemplary embodiments of the turbofan engine <NUM> and permanent magnet electric machine <NUM> described above with reference to <FIG> and <FIG>. Each of the embodiments of <FIG> may generally be configured in substantially the same manner as the embodiment described above with reference to <FIG> and <FIG>. For example, each of the exemplary turbofan engines <NUM> depicted in <FIG> generally include a permanent magnet electric machine <NUM> having a rotor assembly <NUM> coupled to a rotary component of the turbofan engine <NUM> (i.e., an LP shaft <NUM> for the embodiments shown) and a stator assembly <NUM> coupled to a stationary component of the turbofan engine <NUM> (i.e., a structural support member <NUM> for the embodiments shown). The stator assemblies <NUM> of the permanent magnet electric machines <NUM> each include a plurality of coils <NUM> and each is electrically coupled to a respective electric transfer bus <NUM> via an electric line <NUM>. Additionally, the rotor assemblies <NUM> of the permanent magnet electric machines <NUM> each generally include a rotor <NUM> having a plurality of permanent magnets <NUM> and a rotor shaft <NUM>.

Referring particularly to <FIG>, the turbofan engine <NUM> further includes a thermal management system <NUM> for the permanent magnet electric machine <NUM>. For the embodiment of <FIG>, the thermal management system <NUM> utilizes a cooling airflow to maintain a temperature of the permanent magnet electric machine <NUM> within a desired operating temperature range during normal operations. For example, the thermal management system <NUM> generally includes an inlet conduit <NUM> which may receive a bleed airflow from, e.g., the compressor section of the turbofan engine <NUM>. The thermal management system <NUM> may further include a heat exchanger (not shown) for reducing a temperature of such bleed airflow. As is depicted schematically, the shaft <NUM> of the rotor assembly <NUM> is configured as a hollow shaft <NUM>, defining an opening <NUM> extending along a length thereof, i.e., along the axial direction A of the turbofan engine <NUM>. The inlet conduit <NUM> of the thermal management system <NUM> is positioned in airflow communication with the opening <NUM> in the rotor shaft <NUM>, such that the inlet conduit <NUM> may provide the cooling airflow to and through the opening <NUM> of the rotor shaft <NUM> to reduce a temperature of the rotor <NUM> and permanent magnets <NUM>.

The thermal management system <NUM> also includes an exhaust conduit <NUM> in airflow communication with the rotor shaft <NUM>. The exhaust conduit <NUM> extends to the core air flowpath <NUM> to exhaust the heated air to the core air flowpath <NUM>. For the embodiment depicted, the inlet conduit <NUM> is in airflow communication with the opening <NUM> through the rotor shaft <NUM> at a location forward of the rotor <NUM> of the rotor assembly <NUM> and the exhaust conduit <NUM> is in airflow communication with the opening <NUM> of the rotor shaft <NUM> at a location downstream of the rotor <NUM> of the rotor assembly <NUM>. However, in other embodiments, other configurations are contemplated.

Notably, for example, referring briefly to the callout Circle A in <FIG>, the rotor <NUM> is formed of a plurality of laminations <NUM> tightly fitted to the rotor shaft <NUM>. Torque of the permanent magnet electric machine <NUM> is transferred through this connection between the rotor shaft <NUM> and laminations <NUM> of the rotor <NUM>. Additionally, given this relatively tight fit, heat may be transferred through conduction between the laminations <NUM> of the rotor <NUM> and the rotor shaft <NUM>, and thus to the cooling fluid flowing through the opening <NUM> in the rotor shaft <NUM>.

In order to increase the temperature of the permanent magnets <NUM> of the rotor assembly <NUM> of the exemplary embodiment of <FIG> (i.e., in response to the determination of a fault condition of the permanent magnet electric machine <NUM>), the system may reduce a cooling of the permanent magnet electric machine <NUM> using the thermal management system <NUM> (i.e., reduce an operability of the thermal management system <NUM>). For example, the system may shut off or reduce a flow of cooling airflow through the inlet conduit <NUM> to the opening <NUM> of the rotor shaft <NUM>, allowing the permanent magnets <NUM> of the rotor assembly <NUM> to increase in temperature and lose magnetization. Additionally, or alternatively, the system may bypass a heat exchanger cooling the air provided through the inlet conduit <NUM>.

More specifically, for the embodiment depicted, a valve <NUM> is provided within, or otherwise operable with, the inlet conduit <NUM> of the thermal management system <NUM>. The valve <NUM> may also be operably connected to a controller <NUM> through a wireless communication network. The valve may shut off, or reduce the cooling airflow through the inlet conduit <NUM> to provide for such increase in temperature of the permanent magnets <NUM>.

Additionally, or alternatively, the thermal management system <NUM> is configured to provide a heating fluid to the permanent magnet electric machine <NUM> to increase the temperature of the permanent magnets <NUM>. More specifically, for the embodiment depicted, the thermal management system <NUM> is selectively in airflow communication with a high-temperature fluid source through a high temperature fluid conduit <NUM>, and more specifically, with a high temperature bleed airflow source through the high temperature fluid conduit <NUM>. For the embodiment shown, the high temperature bleed airflow source is the turbine section of the turbofan engine <NUM>. With such a configuration, the valve <NUM> of the thermal management system <NUM> may switch the airflow source from a relatively cool airflow source (providing the cooling airflow discussed above) to the high temperature bleed airflow source, such that the thermal management system <NUM> provides a heating fluid/heating airflow/high-temperature bleed airflow to the permanent magnet electric machine <NUM>, and more specifically, to the opening <NUM> through the rotor shaft <NUM> of the rotor assembly <NUM>. Such further, and more quickly, increase a temperature of the permanent magnets <NUM> to demagnetize such permanent magnets <NUM>. Notably, in other embodiments, the high temperature fluid source may be any other suitable high temperature fluid source (e.g., exhaust, compressor, etc.).

Referring now particularly to <FIG>, the exemplary turbofan engine <NUM> again includes a thermal management system <NUM> for the permanent magnet electric machine <NUM>. The thermal management system <NUM> is configured to provide a cooling fluid to an opening <NUM> through the rotor shaft <NUM> of the rotor assembly <NUM> of the permanent magnet electric machine <NUM>. The thermal management system <NUM> depicted is configured as a closed loop system, circulating and reusing the cooling fluid through a thermal bus <NUM>. For example, the cooling fluid may be a lubrication oil, such that the thermal management system <NUM> shares functionality with, e.g., a lubrication oil system for one or more sections of the turbofan engine <NUM>.

The thermal management system <NUM> additionally includes a heat sink heat exchanger <NUM> in thermal communication with the cooling fluid flowing through the thermal bus <NUM>. The heat sink heat exchanger <NUM> is additionally in thermal communication with a heat sink system <NUM>. The heat sink system <NUM> may include any suitable source of relatively cool fluid, such as bypass airflow, compressor bleed airflow, fuel, etc. The heat sink heat exchanger <NUM> is therefore configured to transfer heat from the cooling fluid in the thermal bus <NUM> of the thermal management system <NUM> to the relatively cool fluid of the heat sink system <NUM>. In such a manner, the thermal management system <NUM> may maintain a temperature of the permanent magnet electric machine <NUM> within a desired operating temperature range.

As is depicted, the heat sink system <NUM> includes a main line <NUM>, a bypass line <NUM>, and a bypass valve <NUM> (or rather a pair of bypass valves <NUM>). In order to increase a temperature of the permanent magnets <NUM> of the rotor assembly <NUM> of the exemplary embodiment of <FIG> (i.e., in response to the determination of a fault condition of the permanent magnet electric machine <NUM>), the system may again reduce a cooling of the permanent magnets <NUM> of the permanent magnet electric machine <NUM> using the thermal management system <NUM> (i.e., reduce an operability of the thermal management system <NUM>). More specifically, the system may actuate the bypass valve <NUM> of the heat sink system <NUM> such that the relatively cool fluid through the main line <NUM> of the heat sink system <NUM> flows through the bypass line <NUM>, bypassing the heat sink heat exchanger <NUM> of the thermal management system <NUM>. In such a manner the cooling fluid flowing through the thermal bus <NUM> of the thermal management system <NUM> may be unable to reject heat from the permanent magnet electric machine <NUM>. The cooling fluid, and thus the permanent magnet electric machine <NUM>, may therefore continue to rise in temperature and a magnetism of the permanent magnets <NUM> may be reduced or eliminated.

Notably, although the bypass functionality is provided by the heat sink system <NUM> for the embodiment shown, in other embodiments, the bypass functionality may instead be built into the thermal bus <NUM> of the thermal management system <NUM>. Additionally, in certain exemplary embodiments, instead of bypassing the heat sink heat exchanger, the system may reduce a flow of cooling fluid through the heat sink system <NUM>, reduce a flow of cooling fluid through the thermal bus <NUM>, or both.

Referring now particularly to <FIG>, the exemplary permanent magnet electric machine <NUM>, as stated, includes a stator assembly <NUM> having a stator <NUM> and a rotor assembly <NUM> having a rotor <NUM>. Further, as will be appreciated from, e.g., <FIG>, the stator <NUM> of the stator assembly <NUM> and rotor <NUM> of the rotor assembly <NUM> together define an airgap <NUM> therebetween, generally along a radial direction R of the exemplary turbofan engine <NUM>. During operation of the permanent magnet electric machine <NUM>, the rotor assembly <NUM> will be rotating relatively quickly relative to the stator assembly <NUM>. Additionally, the airgap <NUM> defined between the stator <NUM> and the rotor <NUM> may be relatively small. Further, the system generally includes a fluid duct <NUM> in fluid communication with the airgap <NUM>.

In order to increase the temperature of the permanent magnets <NUM> of the rotor assembly <NUM> of the exemplary embodiment of <FIG> (i.e., in response to the determination of a fault condition of the permanent magnet electric machine <NUM>), the system may inject a fluid into the airgap <NUM> of the permanent magnet electric machine <NUM> using the fluid duct <NUM>. The fluid injected into the airgap <NUM> may create an increased amount of friction, therefore increasing a temperature of the permanent magnets <NUM> of the rotor assembly <NUM> of the permanent magnet electric machine <NUM> and reducing or eliminating the magnetism of such permanent magnets <NUM>.

Notably, in certain exemplary embodiments, the fluid injected may be air. However, in other embodiments, any other suitable fluid may be utilized. For example, in certain embodiments, the fluid may define a viscosity greater than a viscosity of air (such as at least <NUM>% greater, <NUM>% greater, <NUM>% greater, or <NUM>% greater, and up to, e.g., <NUM>,<NUM>% greater), further increasing the amount of friction created and heat added to the permanent magnet electric machine <NUM>.

It will be appreciated that in at least certain exemplary embodiments, features from the configurations depicted in <FIG> may be combined to create still further embodiments. Additionally, in still other embodiments, the system for heating the permanent magnets <NUM> discussed with reference to one figure may be combined with the means for heating the permanent magnets <NUM> discussed with reference to a different figure. For example, the induction system described above with reference to <FIG> may be used in conjunction with the thermal management system <NUM> described above with reference to <FIG>.

Further, it will be appreciated that the permanent magnetic electric machine <NUM> depicted is provided by way of example only. In other embodiments, the permanent magnetic electric machine <NUM> may be configured as an "outrunner" electric machine (with the rotor assembly arranged outward of the stator assembly), the permanent magnet electric machine <NUM> may be configured as an axial flow electric machine (with the rotor and stator being arranged along an axial direction and having an airgap with a substantially circular shape therebetween), etc..

Referring now to <FIG>, a flow diagram of a method <NUM> for operating a permanent magnet electric machine of an engine in accordance with an exemplary aspect of the present disclosure is provided. In at least certain exemplary aspects, the permanent magnet electric machine and engine operated using the method <NUM> may be configured in accordance with one or more of the exemplary permanent magnet electric machines and engines described above with reference to <FIG>. Accordingly, it will be appreciated that in at least certain exemplary aspects, the engine may be a gas turbine engine, such as one of a turboshaft engine, turboprop engine, turbojet engine, or a turbofan engine.

For the exemplary aspect depicted in <FIG>, the method <NUM> generally includes at (<NUM>) determining a fault condition of the permanent magnet electric machine. More specifically, for the exemplary aspect depicted, determining the fault condition of the permanent magnet electric machine at (<NUM>) includes at (<NUM>) determining an internal coil fault of the permanent magnet electric machine. The internal coil fault may refer to a stator winding short circuit fault, described in greater detail above. However, in other exemplary aspects, the fault condition may be any other suitable fault condition.

In at least certain exemplary aspects, determining the fault condition of the permanent magnet electric machine at (<NUM>) may include receiving data indicative of the fault condition through one or more sensors operably coupled to a stator assembly of the permanent magnet electric machine, to an electric line of an electric transfer bus (the electric line electrically coupled to the permanent magnet electric machine), to various power electronics of the electric transfer bus, etc. For example, in at least certain exemplary aspects, this data may be used in conjunction with various operating conditions of the engine to determine the fault condition, such as rotational speeds of the engine (e.g., of one or more shafts of the engine), temperatures within the engine (e.g., compressor inlet temperature, compressor exhaust temperature, turbine inlet temperature, turbine exhaust temperature, etc.), pressures within the engine, etc. For example, if the engine is operating in a manner consistent with a large drag on the engine, yet an amount of power being extracted by the permanent magnetic electric motor is less than an expected amount, the fault condition may be determined.

Referring still to <FIG>, the method <NUM> further includes at (<NUM>) reducing a magnetism of one or more permanent magnets of the permanent magnet electric machine by increasing a temperature of the one or more permanent magnets in response to determining the fault condition of the permanent magnet electric machine at (<NUM>). More specifically, for the exemplary aspect depicted, reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets at (<NUM>) includes at (<NUM>) increasing a temperature of a rotor assembly of the permanent magnet electric machine, the rotor assembly including the one or more permanent magnets. For example, the rotor assembly may include a rotor formed of a plurality of axially arranged laminations configured to mount a plurality of circumferentially arranged permanent magnets therein. The plurality of axially arranged laminations may be fitted to a rotor shaft, as discussed in greater detail above with reference to <FIG>.

It will be appreciated that for the exemplary aspect depicted, reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets at (<NUM>) includes at (<NUM>) adding between about <NUM> kilowatts of heat and about <NUM> kilowatts of heat. The amount of heat added to increase the temperature of the one or more permanent magnets and decrease the magnetism of the one or more permanent magnets may be sufficient to increase the temperature of the one or more permanent magnets to a temperature approaching or exceeding a Curie temperature for such permanent magnets. In such a manner, the permanent magnets may irreversibly demagnetize or reduce in magnetization.

Further, for the exemplary aspect of the method <NUM> depicted in <FIG>, a number of different ways are contemplated for reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets at (<NUM>). For example, in the exemplary aspect of the method <NUM> depicted, reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets at (<NUM>) may include at (<NUM>) driving current through a stator assembly of the permanent magnet electric machine to induce eddy current losses. More specifically, it will be appreciated that the permanent magnet electric machine defines a designed current frequency operating range and driving current through the stator assembly of the permanent magnet electric machine to induce eddy current losses at (<NUM>) may include driving current through the stator assembly of the permanent magnet electric machine at a frequency other than the designed current frequency operating range, and more specifically at (<NUM>) driving current through the stator assembly of the permanent magnet electric machine at a frequency greater than the designed current frequency operating range. The relatively high frequency electric current provided to the stator assembly will, as noted, induce eddy current losses within the permanent magnet electric machine, increasing a temperature of the permanent magnet electric machine.

Additionally, reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets at (<NUM>) includes at (<NUM>) providing a heating fluid to the permanent magnet electric machine. For example, in at least certain exemplary aspects, providing the heating fluid to the permanent magnet electric machine at (<NUM>) may include at (<NUM>) providing a bleed airflow to the permanent magnet electric machine. The bleed airflow may be relatively high temperature airflow bled off of, e.g., a compressor within a compressor section of the engine, a turbine within a turbine section of the engine, or an exhaust of the engine. The heating fluid provided to the permanent magnet electric machine at (<NUM>) may be provided using a thermal management system, and may be provided to an area surrounding the rotor assembly of the permanent magnet electric machine, an opening through a rotor shaft of the rotor assembly of the permanent magnet electric machine, or any other suitable location capable of increasing a temperature of the one or more permanent magnets.

Additionally, or alternatively still, reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets at (<NUM>) may include at (<NUM>) reducing a cooling of the permanent magnet electric machine using a thermal management system of the permanent magnet electric machine (i.e., reducing an operability of the thermal management system). For example, in certain exemplary aspects, reducing the cooling of the permanent magnet electric machine at (<NUM>) may include at (<NUM>) bypassing a heat sink heat exchanger of the thermal management system of the permanent magnet electric machine. Additionally, or alternatively, however, reducing the cooling of the permanent magnet electric machine using the thermal management system at (<NUM>) may include, e.g., slowing down or stopping a cooling flow through the thermal management system (e.g., for an open-loop, or closed loop thermal management system), slowing down or stopping a cooling flow to the permanent magnet electric machine from thermal management system (e.g., for an open-loop thermal management system), etc..

By reducing the cooling of the permanent magnet electric machine using the thermal management system at (<NUM>), heat generated through the operation of the permanent magnet electric machine may stay with the permanent magnet electric machine, thereby increasing a temperature of the one or more permanent magnets and reducing a magnetism of such one or more permanent magnets.

Additionally, or alternatively still, reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets at (<NUM>) may include at (<NUM>) injecting a fluid into an air gap of the permanent magnet electric machine. In certain exempt aspects, the fluid may be air. However, in other exemplary aspects, the fluid may define a viscosity greater than a viscosity of air. Regardless, it will be appreciated that the airgap of the permanent magnet electric machine, defined between a rotor of the rotor assembly and a stator the stator assembly, may be relatively small, such that introducing a fluid therein at (<NUM>) may increase an amount of friction created during operation of the permanent magnet electric machine, thereby increasing an amount of heat generated and a temperature of the one or more permanent magnets, and therefore decreasing a magnetism of the one or more permanent magnets. Notably, although not depicted, the method <NUM> may further include evacuating all, substantially all, or at least a portion of the fluid from the airgap once the permanent magnets have been demagnetized to a desired degree (which may be determined in any suitable manner, such as by sensing a drag on the engine, a temperature of the permanent magnets and/or duration of increased temperature of the permanent magnets, etc.). Such may reduce an amount of viscous drag generated by the electric machine on the engine.

As is discussed above with reference to certain of the above embodiments, the rotor assembly of the permanent magnet electric machine may include a rotor formed of a plurality of laminations and a shaft. The plurality of laminations may be fitted onto the shaft, such that the heat may be exchanged between the plurality of laminations and the shaft through conduction. Therefore, a cooling flow (e.g., airflow, coolant flow, etc.) through an opening of the shaft of the rotor assembly may accept heat transferred from the laminations to the shaft. For the exemplary aspect of the method <NUM> depicted in <FIG>, reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets at (<NUM>) may include at (<NUM>) decreasing a contact pressure between the plurality of laminations and the shaft. By decreasing the contact pressure between the plurality of laminations and the shaft at (<NUM>), a heat rejection path from the permanent magnets / rotor assembly to a coolant flow may be disrupted. More specifically, by decreasing the contact pressure between the plurality of laminations and the shaft at (<NUM>), a conductive heat transfer between the laminations and the shaft may be frustrated, such that a temperature of the laminations and the one or more permanent magnets mounted thereto increases as desired. In at least certain exemplary aspects, decreasing the contact pressure between the plurality of laminations and the shaft at (<NUM>) may be accomplished by forming the laminations and the shaft of specific materials having desired coefficients of thermal expansion. For example, the laminations may be designed to expand more than the shaft at certain temperatures, such that once the shaft and laminations reach such temperatures, which may be indicative of a fault condition of the permanent magnet electric machine, the contact pressure between the plurality of laminations in the shaft decreases (potentially even forming a gap therebetween), thereby further increasing a temperature of the laminations and the plurality of permanent magnets as desired.

Claim 1:
A method (<NUM>) for operating a permanent magnet electric machine of an engine, the method comprising:
(<NUM>) determining a fault condition of the permanent magnet electric machine; and
(<NUM>) reducing a magnetism of one or more permanent magnets of the permanent magnet electric machine by increasing a temperature of the one or more permanent magnets to irreversibly reduce or extinguish a magnetism of the one or more permanent magnets in response to determining the fault condition of the permanent magnet electric machine;
characterized by reducing the magnetism of the one or more permanent magnets by increasing the temperature of the one or more permanent magnets comprises (<NUM>) providing a heating fluid to the permanent magnet electric machine.