Patent Description:
Propulsion units that produce thrust for an aircraft via electrically driven fans or propellers are being explored as alternatives for conventional, pure-combustion driven engines. The incorporation of electrically-driven propulsion units in aircraft provide a number of opportunities for optimizing overall aircraft design and maneuverability. For example, entirely battery-powered propeller-driven aircraft and entirely turbo-electric aircraft have been considered.

Electric engines may include a propulsion system having a propeller driven by an electric motor that is governed by a motor converter. A pump system may also be provided to pump coolant through a cooling circuit through the motor converter to remove heat therefrom. In certain scenarios, air may become ingested and lodged in the circuit, causing the motor converter to overheat. If the motor converter overheats, the motor converter may cease to function, which would subsequently cause the motor to stop driving the propeller. <CIT> discloses a drive nacelle for an aircraft having a housing in which an electrical machine, an inverter unit and a control device are arranged. <CIT> describes an inverter control device including failure detection means, conduction control means and switching section cooling continuation means for continuing driving a cooling device in conjunction with the control by the conduction control means. <CIT> discloses a cooling system for first and second components including a first coolant path and a second coolant path. <CIT> describes an electric-power conversion apparatus with a heat sink in which one side portion is formed shorter than the other side portion thereof. <CIT> relates to a fault-tolerant power system architecture for aircraft electric propulsion in which systems continue to operate in the event of the failure of (or one or more faults within) some component.

The present disclosure may comprise one or more of the following features and combinations thereof, insofar as they fall within the scope of the claims.

According to the present disclosure, a propulsion system for an aircraft includes a propeller assembly, a controller, and a pump system. The propeller assembly includes a propeller configured to rotate around a central axis and a power system, the power system including an electric motor mechanically coupled to the propeller and configured to drive the propeller, and a motor converter electrically connected to the electric motor and configured to deliver electric power to the electric motor.

In some embodiments, the controller is connected to the power system and configured to switch the power system into a power-off arrangement in which the motor converter is powered off and blocked from delivering the electric power to the electric motor in response to a temperature of the motor converter being greater than a predetermined threshold temperature. The pump system includes a pump and a coolant circuit, the pump configured to pump coolant through the motor converter via the coolant circuit so as to cool the motor converter. According to the invention, the pump is mechanically coupled to the propeller and to the electric motor such that rotation of any one of the propeller and the electric motor drives the pump such that rotation of the propeller drives the pump to move the coolant through the coolant circuit and lower the temperature of the motor converter to less than the predetermined threshold temperature in response to the motor converter being in the power-off arrangement during operation of the propulsion system.

In some embodiments, the motor converter includes a plurality of converter switches configured to regulate incoming and outgoing current and a cooling plate thermally engaged with the plurality of converter switches and configured to remove heat from the plurality of converter switches. The coolant circuit is arranged so as to thermally engage with the cooling plate in order to remove heat from the cooling plate which subsequently removes heat from the plurality of converter switches. In response to the power system being in the power-off arrangement, the pump system is configured to pump the coolant through the coolant circuit so as to remove heat from the cooling plate which subsequently removes heat from the plurality of converter switches.

In some embodiments, the pump system further includes an expansion tank in fluidic communication with the coolant circuit. The pump system is configured to, in response to air bubbles accumulating within the coolant circuit and moving at a reduced speed past the cooling plate, move the air bubbles through the coolant circuit away from the cooling plate and into the expansion tank.

In some embodiments, the motor converter further includes at least one temperature sensor located proximate the plurality of converter switches so as to monitor a temperature of the plurality of converter switches.

In some embodiments, the temperature of the motor converter utilized by the controller is the temperature of the plurality of converter switches. The predetermined threshold temperature utilized by the controller is a predetermined threshold temperature of the plurality of converter switches.

In some embodiments, the predetermined threshold temperature of the plurality of converter switches is <NUM> degrees Celsius.

In some embodiments, the propeller includes a plurality of blades and the propeller assembly further includes a propeller governor configured to control a pitch angle of the plurality of blades. In response to the controller switching the power system into the power-off arrangement, the propeller governor is configured to change the pitch angle of the plurality of blades of the propeller from a first pitch angle to a second pitch angle different from the first pitch angle.

In some embodiments, the second pitch angle enables the propeller to continue to rotate at a maximum rotational speed in the power-off arrangement so as to continue to drive the pump for a maximum amount of time.

In some embodiments, the propulsion system further includes a gearbox mechanically coupled to the propeller and to the pump system and the gearbox is configured to transfer mechanical energy from the propeller to the pump of the pump system so as to drive the pump.

In some embodiments, the coolant is one of a water and ethylene glycol mixture and a water and propylene mixture.

In some embodiments, the pump is a positive displacement pump configured to provide a constant flow of coolant in response to a constant rotational speed of the propeller.

According to another aspect of the present disclosure, a propulsion system for an aircraft includes a propeller assembly, a controller, and a pump system. The propeller assembly includes a propeller configured to rotate around a central axis and a power system, the power system including an electric first motor mechanically coupled to the propeller and configured to drive rotation of the propeller, and a motor converter electrically connected to the electric first motor and configured to deliver electric power to the electric first motor.

In some embodiments, a controller is connected to the power system and configured to switch the power system into a power-off arrangement in which the motor converter is powered off and blocked from delivering the electric power to the electric first motor in response to a temperature of the motor converter being greater than a predetermined threshold temperature. The pump system includes a pump and a coolant circuit, the coolant circuit configured to remove heat from the motor converter, the pump configured to pump coolant through the coolant circuit.

In some embodiments, the power system further includes a second motor operably connected to the pump and configured to drive the pump, and wherein the second motor is driven independent of the motor converter.

In some embodiments, the motor converter includes a plurality of converter switches configured to regulate incoming and outgoing current and a cooling plate thermally engaged with the plurality of converter switches and configured to remove heat from the plurality of converter switches. The coolant circuit is arranged so as to thermally engage with the cooling plate in order to remove heat from the cooling plate which subsequently removes heat from the plurality of converter switches. In response to the power system being in the power-off arrangement, the pump system is configured to pump the coolant through the coolant circuit so as to remove heat from the cooling plate which subsequently removes heat from the plurality of converter switches.

According to another aspect of the present disclosure, a method includes providing a propeller assembly including a propeller and a power system, the propeller configured to rotate around a central axis, the power system including an electric motor and a motor converter, mechanically coupling the electric motor to the propeller, the electric motor being configured to drive the propeller, electrically connecting the motor converter to the electric motor, providing a pump system including a pump and a coolant circuit, and mechanically coupling the pump to the propeller and to the electric motor such that at least one of the propeller and the electric motor drives the pump.

In some embodiments, the method further includes pumping, via the pump, coolant through the motor converter via the coolant circuit so as to cool the motor converter, determining that a temperature of the motor converter is greater than a predetermined threshold temperature, switching the power system into a power-off arrangement in which the electric motor and the motor converter are powered off, and driving the pump via only the propeller such that the coolant continues to pump through the coolant circuit in order to lower the temperature of the motor converter to less than the predetermined threshold temperature during operation of the propulsion system.

In some embodiments, the method further includes determining that the temperature of the motor converter is less than the predetermined threshold temperature, switching the power system into a power-on arrangement in which the motor converter is powered on, and driving the pump via at least the electric motor such that the coolant continues to pump through the coolant circuit.

These and other features of the present disclosure will become more apparent from the following description of the illustrative embodiments.

For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to a number of illustrative embodiments illustrated in the drawings and specific language will be used to describe the same.

An aircraft <NUM> including at least one propulsion system <NUM> according to the present disclosure is shown in <FIG>. In the illustrative embodiment, the aircraft <NUM> may include a fuselage <NUM> and a pair of wings <NUM> extending away from the fuselage <NUM> and configured to generate lift for the aircraft <NUM>. The aircraft <NUM> further includes a pair of propulsion systems <NUM>, each propulsion system <NUM> being coupled to an underside of a respective wing <NUM> via a pylon <NUM>. As suggested in <FIG>, each propulsion system <NUM> is configured to provide kinetic energy to a propeller assembly <NUM> of the propulsion system <NUM> such that a plurality of blades <NUM> of the propeller assembly <NUM> convert the kinetic energy to rotational energy so as to provide propulsive power to the aircraft <NUM>. In other embodiments, there may be greater than or fewer than two propulsion systems <NUM> coupled to the aircraft <NUM>, such as, for example, two propulsion systems <NUM> arranged on each wing <NUM> or a single propulsion system <NUM> arranged at the nose of the fuselage <NUM>.

The propulsion system <NUM> includes the propeller assembly <NUM> which includes a propeller <NUM> having the plurality of blades <NUM> and a power system <NUM>, and a pump system <NUM>, as shown in <FIG>. The power system <NUM> includes an electric motor <NUM> and a motor converter <NUM> that provides electrical power to the electric motor <NUM>. In the illustrative embodiment, the pump system <NUM> is mechanically coupled to the propeller <NUM> and to the electric motor <NUM> such that any one of the propeller assembly <NUM> and electric motor <NUM> can drive the pump system <NUM>.

In the event that the motor converter <NUM> exceeds a maximum tolerable temperature, the motor converter <NUM> will be shut down to prevent overheating. This excess temperature may be caused by a variety of factors, one of which is air bubbles in a coolant circuit <NUM> of the pump system <NUM> moving too slowly past a cooling plate <NUM> of the motor converter <NUM>. In normal operating conditions, the pump system <NUM> is driven by the electric motor <NUM>. As will be described in detail below, in the event the motor converter <NUM> overheats and shuts off, the propeller assembly <NUM> will drive the pump system <NUM> because of the mechanical connection between the propeller assembly <NUM> and the pump system <NUM>. As a result, the pump system <NUM> continues to pump coolant through the cooling circuit <NUM> so as to move the air bubbles away from the cooling plate <NUM>. Moving the air bubbles away from the cooling plate <NUM> allows the coolant fluid to continue removing heat from the cooling plate <NUM> efficiently to lower the temperature of the cooling plate <NUM>, which subsequently lowers the temperature of the motor converter <NUM> such that it may be switched back on. The motor converter <NUM> may then resume supplying power to the electric motor <NUM> which may then power to the propeller <NUM>.

The propeller <NUM> includes the plurality of blades <NUM> which are configured to rotate about a central axis <NUM> and provide propulsive power to the aircraft <NUM>. The plurality of blades <NUM> are arranged circumferentially around the axis central axis <NUM> and extend radially outward away from the central axis <NUM>.

In the illustrative embodiment, the power system <NUM> includes the electric motor <NUM> and the motor converter <NUM> electrically connected to the electric motor <NUM>, as shown in <FIG>. The electric motor <NUM> is mechanically coupled to the propeller assembly <NUM> so as to drive the blades <NUM> of the propeller <NUM>. The electric motor <NUM> may be an electric motor known in the art that is utilized to convert supplied electrical energy into kinetic energy which is transferred to the blades <NUM> which rotate and provide propulsive power to the aircraft <NUM>.

The motor converter <NUM> is electrically connected to the electric motor <NUM> and configured to deliver electric power to the electric motor <NUM>, as shown in <FIG>. In some embodiments, the motor converter <NUM> and the electric motor <NUM> may be integrated into a single unit. The motor converter <NUM> may be an converter known in the art that is utilized to regulate power supplied to the electric motor <NUM>. The motor converter <NUM> is arranged between a power supply and the electric motor <NUM>, and is configured to receive power from the power supply and convert DC current to AC current, AC current to DC current, and AC current to AC current that subsequently flows to the electric motor <NUM>. In some embodiments, the motor converter <NUM> may regulate current returning from the motor to the power supply and/or modify the properties of the incoming and exiting current. The motor converter <NUM> may also adjust frequency and voltage of the power supplied to the electric motor <NUM> based on the current operating condition of the propulsion system <NUM>.

In the illustrative embodiment, the motor converter <NUM> includes a plurality of converter switches <NUM> and a cooling plate <NUM>, as shown in <FIG>. The converter switches <NUM> are configured to convert an incoming power supply of electrical energy for example from AC power to DC power and from DC power to AC power. The cooling plate <NUM> is thermally engaged with the converter switches <NUM> and is configured to remove heat from the converter switches <NUM> so as to cool the switches <NUM>. The coolant circuit <NUM> is in thermal communication with the cooling plate <NUM> in order to remove heat from the cooling plate <NUM> which subsequently removes heat from the converter switches <NUM>. Thus, in response to the power system <NUM> being in a power-off arrangement in which the motor converter <NUM> has been shut off due to overheating, which will be described in detail below, the pump system <NUM> is configured to continue to pump coolant through the coolant circuit <NUM> so as to remove heat from the cooling plate <NUM> which subsequently removes heat from the converter switches <NUM> and allows the motor converter <NUM> to return to safe operating temperature.

The pump system <NUM> includes a pump <NUM> and the coolant circuit <NUM> that runs from the pump <NUM> to the motor converter <NUM> and back to the pump <NUM> in a fluid circuit among other possible locations. The pump <NUM> is configured to pump coolant through the motor converter <NUM> via the coolant circuit <NUM> so as to cool the motor converter <NUM>. The pump <NUM> is mechanically coupled to both the propeller assembly <NUM> and to the electric motor <NUM> such that rotation of any one of the propeller <NUM> and the electric motor <NUM> drives the pump <NUM>, as shown in <FIG> and <FIG>. Illustratively, the pump <NUM> is mechanically connected to the electric motor <NUM> and the propeller <NUM> via a gearbox <NUM>. The coolant circuit <NUM> includes a coolant that is configured to conduct heat away from the relevant components, including the cooling plate <NUM> of the motor converter <NUM>. The coolant may be, but is not limited to, a water/ethylene glycol mixture or a water and propylene mixture. In some embodiments, the pump <NUM> is configured to control the flow of coolant to be proportional to the rotational speed.

In the illustrative embodiment, the propulsion system <NUM> further includes the controller <NUM> connected to the power system <NUM>, as shown in <FIG>. In other embodiments, the power system <NUM>, the converter <NUM>, and the controller <NUM> may be integrated into a single unit. The controller <NUM> is configured to switch the power system <NUM> into the power-off arrangement in which the motor converter <NUM> is powered off and blocked from delivering the electric power to the electric motor <NUM> in response to a temperature of the motor converter <NUM> being greater than a predetermined threshold temperature. As discussed above, the temperature of the motor converter <NUM> may reach unsustainable levels in which the motor converter <NUM> must be shut down. This may be caused by a variety of factors, one of which is air bubbles that have accumulated throughout the coolant circuit <NUM> of the pump system <NUM> moving too slowly past the cooling plate <NUM> of the motor converter <NUM>. In some scenarios, the air bubbles flowing through the coolant circuit <NUM> may be caused by the aircraft <NUM> executing negative G maneuvers (negative gravity maneuvers).

In the event that the controller <NUM> determines that the temperature of the motor converter <NUM>, in particular the switches <NUM> of the motor converter <NUM>, is too high (i.e. above the predetermined threshold temperature), the controller <NUM> will turn off the motor converter <NUM>, in which the power system <NUM> is in the power-off arrangement. With the motor converter <NUM> being shut off, the electric motor <NUM> no longer receives power and does not power the propeller assembly <NUM>. However, as will be discussed in detail below, the blades <NUM> of the propeller <NUM> continue to rotate due to the ambient air continuing to flow over the blades <NUM>, sometimes called windmilling. This rotation of the propeller <NUM> continues to drive the pump <NUM> such that coolant continues to move through the coolant circuit <NUM>. This permits the coolant to continue to lower the temperature of the motor converter <NUM> to less than the threshold temperature, in which case the motor converter <NUM> may be turned back on and normal operation of the propulsion system <NUM> may resume.

In some embodiments, the controller <NUM> may be configured to determine that the temperature of the motor converter <NUM> has been lowered to below the threshold temperature. In response to determining that the temperature is below the threshold temperature, the controller <NUM> is configured to switch the power system <NUM> into a power-on arrangement in which the motor converter <NUM> is powered back on such that the pump <NUM> is driven by at least the electric motor <NUM> such that coolant continues to pump through the coolant circuit <NUM>. In other embodiments, the controller <NUM> of the propulsion system <NUM> may generate an alert for a pilot of the aircraft <NUM> via an alert system indicating that the temperature of motor converter <NUM> has returned back below the threshold temperature, and the pilot may then manually power the motor converter <NUM> back on.

The controller <NUM> may include at least one processor connected to a computer readable memory and/or other data storage. Computer executable instructions and data used by a processor may be stored in the computer readable memory included in an onboard computing device, a remote server, a combination of both, or implemented with any combination of read only memory modules or random access memory modules, optionally including both volatile and nonvolatile memory.

In the illustrative embodiment, the pump system <NUM> further includes an expansion tank <NUM> that is arranged in fluidic communication with the coolant circuit <NUM>, as shown in <FIG>. The pump system <NUM> is configured to, in response to the air bubbles accumulating within the coolant circuit <NUM> and moving at a reduced speed past the cooling plate <NUM>, move the air bubbles through the coolant circuit <NUM> away from the cooling plate <NUM> and into the expansion tank <NUM>.

In some embodiments, the propulsion system <NUM> further includes the gearbox <NUM> mechanically coupled to the propeller <NUM> and to the pump system <NUM>, as shown in <FIG>. The gearbox <NUM> is configured to transfer mechanical energy from the propeller <NUM> to the pump <NUM> of the pump system <NUM> so as to drive the pump in the event that the motor converter <NUM> is powered off. In other embodiments, as shown in <FIG>, an accessory gearbox <NUM> is operably connected with the pump <NUM>, the governor <NUM>, and the motor <NUM>. The motor <NUM> is directly connected to the propeller <NUM>. In other embodiments, as shown in <FIG> and <FIG>, a gearbox may be omitted, and the governor <NUM> is operably connected to the motor <NUM> which is directly connected to the propeller <NUM>.

In the illustrative embodiment, the propeller assembly <NUM> further includes a propeller governor <NUM> configured to control a pitch angle of the plurality of blades <NUM> as shown in <FIG> and <FIG>. The propeller governor <NUM> may be any propeller governor known in the art that is utilized to regulate the rotational speed of the propeller <NUM> by moving fluid to and from the propeller which alters the pitch of the blades <NUM>.

In some embodiments, the propeller governor <NUM> is configured to rotate the plurality of blades <NUM> of the propeller <NUM> from a first pitch angle to a second pitch angle different from the first pitch angle in response to the motor converter <NUM> being shut off. As shown in <FIG>, the propeller governor <NUM> may be configured to rotate the plurality of blades <NUM> to any pitch angle of <NUM> degrees to <NUM> degrees relative to the plane of rotation about the central axis <NUM>. For example, as shown in <FIG>, the propeller governor <NUM> may rotate the blades <NUM> to a positions <NUM>, <NUM>, <NUM>, <NUM> which may be useful for various operating conditions of the aircraft. In the illustrative embodiment, in response to the motor converter <NUM> overheating, the governor <NUM> adjusts the blade angle to allow for the propeller <NUM> to continue to rotate for a maximum amount of time, thus allowing for a maximum amount of time for the air bubbles to clear the cooling plate <NUM> and for the temperature of the motor converter <NUM>, in particular the temperature of the converter switches <NUM>, to return to below the threshold temperature.

It should be understood that in other embodiments, the propeller assembly <NUM> may include fixed pitch propeller blades <NUM> and thus would not utilize a propeller governor <NUM>. In such an embodiment, the fixed propeller blades <NUM> could be utilized so long as the blades <NUM> allow the propeller <NUM> to continue to rotate after motor <NUM> shutdown for a long enough period of time to allow for the air bubbles to clear the coolant circuit <NUM>.

In some embodiments, the motor converter <NUM> further includes at least one temperature sensor <NUM> located proximate to the plurality of converter switches <NUM> as shown in <FIG>. The temperature sensor <NUM> is configured to monitor a switch temperature of the plurality of converter switches <NUM> and relay the temperature to the controller <NUM> for execution of the above-described processes. It is noted that, in the illustrative embodiment, the temperature of the motor converter <NUM> utilized by the controller <NUM> for determination of whether the motor converter <NUM> should be shut off is the switch temperature of the plurality of converter switches <NUM>. Moreover, the predetermined threshold temperature utilized by the controller <NUM> for determination of whether the motor converter <NUM> should be shut off is a predetermined threshold switch temperature of the plurality of converter switches <NUM>. In the illustrative embodiment, the predetermined threshold temperature of the plurality of converter switches <NUM> is <NUM> degrees Celsius.

Another embodiment of a propulsion system <NUM> which may be utilized in the aircraft <NUM> in accordance with the present disclosure is shown in <FIG>. The propulsion system <NUM> is substantially similar to the propulsion system <NUM> shown in <FIG> and described herein. Accordingly, similar reference numbers in the <NUM> series indicate features that are common between the propulsion system <NUM> and the propulsion system <NUM>. The description of the propulsion system <NUM> also applies to the propulsion system <NUM>, except in instances when it conflicts with the specific description and the drawings of the propulsion system <NUM>.

Similar to the propulsion system <NUM>, the propulsion system <NUM> includes a propeller assembly <NUM> that includes a propeller <NUM> having a plurality of blades <NUM> and configured to rotate around a central axis <NUM>, and a power system <NUM>, as shown in <FIG>. The power system <NUM> includes an electric first motor <NUM> mechanically coupled to the propeller <NUM> and configured to drive rotation of the propeller <NUM>, and a motor converter <NUM> electrically connected to the electric first motor <NUM> and configured to deliver electric power to the electric first motor <NUM>.

The propulsion system <NUM> further includes a controller <NUM> connected to the power system <NUM> and configured to switch the power system into a power-off arrangement in which the motor converter <NUM> is powered off and blocked from delivering the electric power to the electric first motor <NUM>, as shown in <FIG>. The controller <NUM> is configured to make the switch to the power-off arrangement in response to a temperature of the motor converter <NUM> being greater than a predetermined threshold temperature. In some embodiments, the motor converter <NUM> includes a plurality of converter switches <NUM> and a cooling plate <NUM> engaged with the converter switches <NUM> so as to cool the switches <NUM>. A temperature sensor <NUM> may be operably engaged with the converter switches <NUM> to monitor a temperature of the switches <NUM> and relay the temperature to the controller <NUM>. In some embodiments, the propulsion system <NUM> further includes a propeller governor <NUM>.

The propulsion system <NUM> further includes a pump system <NUM> including a pump <NUM> and a coolant circuit <NUM>, as shown in <FIG>. The coolant circuit <NUM> is configured to remove heat from the motor converter <NUM>. The pump <NUM> is configured to pump coolant through the coolant circuit <NUM>, and is mechanically coupled to the propeller <NUM> and to the electric first motor <NUM> such that rotation of any one of the propeller <NUM> and the electric first motor <NUM> drives the pump <NUM>. In some embodiments, the pump system <NUM> may further include an expansion tank <NUM> in fluidic communication with the coolant circuit <NUM>.

As opposed to the propulsion system <NUM>, the propulsion system <NUM> further includes a second motor <NUM> operably connected to the pump <NUM> and configured to drive the pump <NUM>, as shown in <FIG>. The second motor <NUM> is powered independent of the motor converter <NUM> such that, in the event of a shutdown of the motor converter <NUM>, the second motor <NUM> may be utilized to power the pump <NUM> along with the propeller <NUM> or by itself and without assistance from the propeller <NUM>. In the illustrative embodiment, in response to the motor converter <NUM> being shut down, the controller <NUM> is configured to instruct the second motor <NUM>, which may already be operating, to continue to provide power to the pump <NUM> such that the pump <NUM> continues to function. In some embodiments, the second motor <NUM> is an electric motor. In other embodiments, the second motor <NUM> may be mechanically driven, for example, via a shaft and gearbox assembly.

Another embodiment of a propulsion system <NUM> which may be utilized in the aircraft <NUM> in accordance with the present disclosure is shown in <FIG>. The propulsion system <NUM> is substantially similar to the propulsion systems <NUM>, <NUM> shown in <FIG> and described herein. Accordingly, similar reference numbers in the <NUM> series indicate features that are common between the propulsion system <NUM> and the propulsion systems <NUM>, <NUM>. The description of the propulsion systems <NUM>, <NUM> also apply to the propulsion system <NUM>, except in instances when it conflicts with the specific description and the drawings of the propulsion system <NUM>.

Similar to the propulsion systems <NUM>, <NUM>, the propulsion system <NUM> includes a propeller assembly <NUM> that includes a propeller <NUM> having a plurality of blades <NUM> and configured to rotate around a central axis <NUM>, and a power system <NUM>, as shown in <FIG>. The power system <NUM> includes an electric first motor <NUM> mechanically coupled to the propeller <NUM> and configured to drive rotation of the propeller <NUM>, and a motor converter <NUM> electrically connected to the electric first motor <NUM> and configured to deliver electric power to the electric first motor <NUM>.

The propulsion system <NUM> further includes a pump system <NUM> including a pump <NUM> and a coolant circuit <NUM>, as shown in <FIG>. The coolant circuit <NUM> is configured to remove heat from the motor converter <NUM>. The pump <NUM> is configured to pump coolant through the coolant circuit <NUM>. The propulsion system <NUM> further includes a second motor <NUM> operably connected to the pump <NUM> and configured to drive the pump <NUM>. The second motor <NUM> is powered independent of the motor converter <NUM> such that, in the event of a shutdown of the motor converter <NUM>, the second motor <NUM> may be utilized to power the pump <NUM>. As opposed to the propulsion system <NUM>, the pump <NUM> is not connected to the motor <NUM> or the propeller <NUM> such that the second motor <NUM> is the only source of power for the pump <NUM>. In this way, in response to the motor converter <NUM> being shut down, the controller <NUM> is configured to instruct the second motor <NUM>, which may already be operating, to continue to provide power to the pump <NUM> such that the pump <NUM> continues to function. In some embodiments, the second motor <NUM> is an electric motor. In other embodiments, the second motor <NUM> may be mechanically driven, for example, via a shaft and gearbox assembly.

A method according to another aspect of the present disclosure includes a first operation of providing a propeller configured to rotate around a central axis and a power system, the power system including an electric motor and a motor converter. The method includes a second operation of mechanically coupling the electric motor to the propeller, the electric motor being configured to drive the propeller. The method includes a third operation of electrically connecting the motor converter to the electric motor. The method includes a fourth operation of providing a pump system including a pump and a coolant circuit. The method includes a fifth operation of mechanically coupling the pump to the propeller and to the electric motor such that at least one of the propeller and the electric motor drives the pump.

The method includes a sixth operation of pumping, via the pump, coolant through the motor converter via the coolant circuit so as to cool the motor converter. The method includes a seventh operation of determining that a temperature of the motor converter is greater than a predetermined threshold temperature. The method includes an eighth operation of switching the power system into a power-off arrangement in which the electric motor and the motor converter are powered off. The method includes a ninth operation of driving the pump via only the propeller such that coolant continues to pump through the coolant circuit in order to lower the temperature of the motor converter to less than the predetermined threshold temperature during operation of the propulsion system.

In some embodiments, the method further includes an additional operation of determining that the temperature of the motor converter is less than the predetermined threshold temperature. The method may further include an additional operation of switching the power system into a power-on arrangement in which the motor converter is powered on. The method may further include an additional operation of driving the pump via at least the electric motor such that coolant continues to pump through the coolant circuit.

Claim 1:
A propulsion system (<NUM>, <NUM>, <NUM>) for an aircraft, the propulsion system (<NUM>, <NUM>, <NUM>) comprising
a propeller assembly (<NUM>, <NUM>, <NUM>) that includes a propeller (<NUM>, <NUM>, <NUM>) configured to rotate around a central axis (<NUM>) and a power system (<NUM>, <NUM>, <NUM>), the power system (<NUM>, <NUM>, <NUM>) including an electric motor (<NUM>) mechanically coupled to the propeller (<NUM>, <NUM>, <NUM>) and configured to drive the propeller (<NUM>, <NUM>, <NUM>), and a motor converter (<NUM>, <NUM>, <NUM>) electrically connected to the electric motor (<NUM>) and configured to deliver electric power to the electric motor (<NUM>),
a controller (<NUM>, <NUM>, <NUM>) connected to the power system (<NUM>, <NUM>, <NUM>) and configured to switch the power system (<NUM>, <NUM>, <NUM>) into a power-off arrangement in which the motor converter (<NUM>, <NUM>, <NUM>) is powered off and blocked from delivering the electric power to the electric motor (<NUM>) in response to a temperature of the motor converter (<NUM>, <NUM>, <NUM>) being greater than a predetermined threshold temperature, and
a pump system (<NUM>, <NUM>, <NUM>) including a pump (<NUM>, <NUM>, <NUM>) and a coolant circuit (<NUM>, <NUM>, <NUM>), the pump (<NUM>, <NUM>, <NUM>) configured to pump coolant through the motor converter (<NUM>, <NUM>, <NUM>) via the coolant circuit (<NUM>, <NUM>, <NUM>) so as to cool the motor converter (<NUM>, <NUM>, <NUM>),
characterised in that the pump (<NUM>, <NUM>, <NUM>) is mechanically coupled to the propeller (<NUM>, <NUM>, <NUM>) and to the electric motor (<NUM>) such that rotation of any one of the propeller (<NUM>, <NUM>, <NUM>) and the electric motor (<NUM>) drives the pump (<NUM>, <NUM>, <NUM>) such that rotation of the propeller (<NUM>, <NUM>, <NUM>) drives the pump (<NUM>, <NUM>, <NUM>) to move the coolant through the coolant circuit (<NUM>, <NUM>, <NUM>) and lower the temperature of the motor converter (<NUM>, <NUM>, <NUM>) to less than the predetermined threshold temperature in response to the motor converter (<NUM>, <NUM>, <NUM>) being in the power-off arrangement during operation of the propulsion system (<NUM>, <NUM>, <NUM>).