FIELD OF THE INVENTION:

[001] This invention relates to electric propulsion and more particularly but not solely to an electrically powered device for providing propulsion for aircraft, and associated systems and methods.

BACKGROUND:

[002] The global aviation industry is one of the contributors to global warming and accounts for 2.5% of CO2 emissions and 3.5% of effective radiative forcing, which is a closer measure of its impact on global warming, as per studies. Most aircraft have propulsion systems powered by kerosene as fuel, which is converted to CO2 when burned. Such aircraft propulsion systems are inefficient and noisy i.e., the sound pressure level of a jet propulsion engine at 30m is 150dB.

[003] Several companies are working towards solutions to overcome the above-mentioned disadvantages including replacing aircraft having propulsion systems which are powered by fossil fuels with aircraft which have hybrid-electric or purely electric propulsion systems. Advantages of such hybrid-electric and electric propulsion systems is that they emit less greenhouse gases, are quieter, and more efficient.

[004] EP3647184 discloses an electric propulsion system for aircraft, the system comprising at least one propeller and at least one fan, wherein each propeller is mounted on a respective duct of the ducted fan outer perimeter and is adapted to be driven by a first respective electric motor, and at least one ducted fan is mounted within the duct and is adapted to be driven by a second respective electric motor. In use, the electric motors are controlled to vary the rotational speed of the ducted fan and propeller and the pitch of the blade angle. This offers optimized efficiency, reduction of noise and minimisation of combined torque of the system. A problem with the system of EP3647184 is scalability and it does not reap the full benefits of electric propulsion systems in terms of efficiency and specific power density to propel single aisle or larger commercial passenger aircraft. [005] US2021/0119499 discloses an electric propulsion system for aircraft, the system comprising one or more motors each having a stator assembly including a stator yoke having a hollow cylindrical shape with a length and a diameter, wherein the length is measured along a longitudinal thrust direction of the aircraft and is greater than the diameter, stator teeth integral with the stator yoke, wherein individual stator teeth extend from an inner surface of the stator yoke toward a centre line of the hollow cylindrical shape, stator windings attached to a set of the stator teeth, the stator windings configured to provide magnetic flux using electric power; and a rotor assembly inside the hollow cylindrical stator yoke, wherein the rotor assembly and the stator yoke are separated by an airgap, a shaft carrying the rotor assembly coaxially with the stator, wherein an end portion of the shaft extends along the longitudinal thrust direction past a peripheral edge of the stator assembly; and a support assembly contacting the end portion of the shaft, wherein the support assembly is configured to allow the shaft to rotate in place and provide support for the shaft along a direction perpendicular to the longitudinal thrust direction and against gravitational forces. In use, each shaft is coupled to a propeller and an electric battery is coupled to the or each electric motors to provide power. A disadvantage of systems that use electric propeller driven fans that rotate in an open space is that they become energy inefficient when the rotational speed of the tips of the propeller approaches the speed of sound. In addition, rotation of the propeller at speeds faster than the speed of sound must be avoided because it can cause shockwaves powerful enough to shatter them. Also, noise generated by propellers increases to levels which may exceed lOOdb, as they approach approximately 0.9 mach (1 mach = speed of sound).

[006] With the foregoing in mind, disclosed are improvements relating to the electric propulsion, including to electric propulsion in aircraft.

SUMMARY:

[007] In accordance with embodiments consistent with the present invention, as seen from first aspect, there is provided a propulsion device for aircraft, the device comprising a propulsion fan and a plurality of electrical machines connected to a driveshaft which is coupled to the fan, at least one of the machines being operable as an electric motor for propelling the aircraft and at least one of the machines being operable as an electric generator to convert kinetic energy and/or potential energy of the aircraft into electric energy. As the aircraft takes off, the energy is provided by the engines. As the speed of the aircraft increases, it gains kinetic energy. As it climbs from sea level to E.g.: 40,000 feet, it gains potential energy.

[008] In some embodiments, the propulsion device of the present invention may include a plurality of electrical machines which replace the central core of a conventional jet engine, in a manner which allows the system to be relatively easily retrofitted to conventional aircraft in place of jet engines or incorporated into new aircraft.

[009] In some embodiments, during take-off and ascent of an aircraft, each electrical machine operable as an electric motor can be energised to provide thrust. When the aircraft starts to descend, each electrical machine operable as a generator can feed power back into any electrical machine being operated as an electric motor and/or into the on-board power source. This utilisation of power from the generator to the motor for propulsion system substantially reduces power requirements from external sources.

[010] In accordance with embodiments consistent with the present invention, generated propulsion can provide electric propulsion system for larger passenger aircraft with zero or reduced carbon emissions. The propulsion device is energy-efficient and can have a specific power density of at least 25 kW/kg with the efficiency of the electric propulsion device being up to 99%.

[OH] In some embodiments, the device may utilise electrical machines capable of rotating around or more than 20,000 rpm.

[012] In some embodiments, at least one of the electrical machines may be selectively operable as either a generator or as a motor. The electrical machines can be independently operated as propulsion motors and/or generators based on the operating conditions of the aircraft. During take-off and ascent of an aircraft, peak power will be required and therefore all the electrical machines may be used as a propulsion motor. When the aircraft reaches cruising altitude some of the propulsion motors may reduce their power as less overall power is required during cruise mode. Alternatively, some of the machines may operate as generators for onboard power generation. [013] In some embodiments, the electrical machines may be mounted at respective positions disposed along the axis of the driveshaft.

[014] In some embodiments, the electrical machines may be mounted in a tubular body which extends axially of the driveshaft, the propulsion fan being disposed at one end of the duct and adapted such, in use, that a proportion of the airflow through the fan is directed along the tubular body. The electrical machines are thus positioned such that a portion of the air from the propulsion fan is routed through the electrical machines to cool the machines and their drive control circuits and other electronics efficiently. The bulk of the volume of air passing the propulsion fan is used to generate thrust. The propulsion device and the electronics can also be liquid cooled.

[015] In some embodiments, a control circuit for each electrical machine may be mounted within the tubular body.

[016] In some embodiments, at least one fin may extend radially outwardly from the tubular body remote from said one end for supporting the electrical machines within the device.

[017] In some embodiments, one or more cables and/or liquid cooling pipes extend along a fin which extends between the electrical machines and a support structure. The fin may extend through an airflow passage of the device so that it acts as a heatsink for removing heat from the machines into an airflow generated by the propulsion fan.

[018] In some embodiments, said one end of the tubular body may comprise a plurality of radially outwardly extending support members which are connected at their outer ends to a tubular cowl which surrounds the propulsion fan.

[019] In some embodiments, said one end of the tubular body may be flared outwardly.

[020] Also in accordance with embodiments of the present invention, as seen from a second aspect, there is provided a propulsion system for aircraft, the system comprising at least one propulsion device as hereinbefore defined, a control unit configured to vary a speed of rotation of the plurality of electrical machines and configured to control the amount of electric and/or mechanical energy output by the electrical machines of the device.

[021] In some embodiments, a power supply may be provided for energising the at least one electric motor and for storing energy generated by the at least one electric generator.

[022] Also in accordance with embodiments consistent with the present invention, as seen from a third aspect, there is provided an aircraft comprising a propulsion system.

[023] In some embodiments, the method may comprise selectively controlling the at least one electric motor of the propulsion device to rotate the propulsion fan and propel the aircraft, selectively controlling the at least one generator of the propulsion device to convert kinetic energy and/or potential energy of the aircraft into electrical energy when the altitude of the aircraft is reduced and/or when the speed of the aircraft is reduced.

[024] In some embodiments, the electrical machines may be selectively controlled to operate as an electric generator or as an electric motor according to the selected operating conditions of the aircraft.

[025] In some embodiments, the electric energy generated by the at least one electric generator may be applied to the at least one electric motor and/or to said power supply.

[026] According to some embodiments consistent with the present invention, disclosed is a method of operating a vehicle may comprise selectively controlling at least one electric motor to rotate a propulsion fan to provide thrust, wherein the at least one electric motor drives a shaft mechanically connected to the propulsion fan; and selectively controlling at least one generator to generate electrical energy from kinetic energy of the shaft when the thrust requirement of the aircraft is reduced and/or when the speed of the aircraft is reduced. In some embodiments, the at least one electric motor may be selectively controlled to operate as an electric generator according to an operating condition of the aircraft. [027] In some embodiments, the electrical energy generated by the at least one electric generator may be applied to the at least one electric motor and/or to said power supply. In some embodiments, the at least one electric motor and the at least one generator may each comprise an air channel that extends axially of the shaft. In some embodiments, the at least one electric motor and at least one generator may each be mounted within a duct which extends axially along the shaft. In some embodiments, a control circuit to perform the selective control steps may be mounted within the duct. In some embodiments, at least one fin may extend radially outwardly from the duct. In some embodiments, the at least one generator and at least one motor may be mounted at respective positions disposed along an axis of the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS:

[028] Embodiments of the present invention will now be described by way of example, is only with reference to the accompanying drawings, in which:

[029] Figure 1 is a perspective view of a passenger aircraft incorporating an electric propulsion system in accordance with embodiments consistent the present invention, with some parts being shown cut away;

[030] Figure 2 is a longitudinal sectional view of a propulsion unit of the system of Figure 1;

[031] Figure 3 is a perspective view of internal components of the propulsion unit of Figure 2, with some parts being shown cut away; and

[032] Figures 4a to 4c are perspective cut away views of various embodiments of drive motors of the propulsion unit of Figure 2.

DETAILED DESCRIPTION:

[033] Referring to Figure 1 of the drawings, an aircraft 10 comprises a fuselage 11, a pair of oppositely directed wings 12, each carrying at least one propulsion unit 13, although it will be appreciated that propulsion unit can be mounted anywhere on the aircraft, such as on its tail. In some embodiments, wing-mounted units are preferred as they require less cabling. [034] Each propulsion unit 13 can comprise a housing or so-called nacelle 14 that is configured to encircle and contain a propulsion device 15 which provides the propulsive force to move the aircraft 10 forward in a forward direction F, which may also be referred to as the fore direction. A supporting pylon 16 is configured to securely mount the nacelle 14. The nacelle 14 may contain propulsion device 15. The nacelle 14 may be mounted to structure of a vehicle, for example to the wing 12 of the aircraft 10. Pylon 16 or nacelle 14 may comprise supporting structures to handle stresses of propulsion device 15.

[035] Referring to Figures 2 and 3 of the drawings, the nacelle 14 can be generally tubular and can comprise a central through axis which extends substantially in the forward direction F of the aircraft 10. The propulsion device 15 can be mounted inside the nacelle 14, such that an elongate driveshaft 17 thereof extends along the central through-axis of the nacelle 14. The fore end of the propulsion device 15 can comprise a tubular cowl 18 which is releasably secured to the pylon 16. A plurality of fins 19 can extend radially inwardly from the cowl 18 to a centrally mounted neck 20 in the form of a truncated cone having fore and aft open ends. A plurality of fins 19 can be positioned aft of drive fan 26. A plurality of cooling fins 19 can structurally support the cowl 18 and be connected to pylon 16. In some embodiments, a plurality of fins 19 can be connected to an outer surface of neck 20.

[036] In some embodiments, the fore end of the neck 20 can have a diameter which is greater than the diameter of its aft end. A gearbox 21 can be supported inside the neck 20 by struts 27 which extend radially inwardly from the neck 20. The fore end of the elongate shaft 17 can extend rearwardly from the gearbox 21 towards the aft end of the propulsion device 15. A fan 26 can be rotatably mounted inside the nacelle 14 at the fore end thereof, the fan 26 having a central boss which is coupled to the gearbox 21. Gearbox 21 may be mechanically connected to shaft 17 to drive fan 26 at a ratio. In some embodiments, shaft 17 can be coupled directly to fan 26. In some embodiments, drive fan 26 or another fan can drive shaft 17 (e.g., incoming air can be harnessed by fan blades of a fan to drive shaft 17). Driving shaft 17 (via one or more fans, other electric motors, or other combustion or propulsion methods) can result in generating electricity as will be discussed herein. Shaft 17 can also be driven by one or more electric motors as will be discussed herein. [037] The propulsion device 15 can further comprise a plurality of electrical machines 22 which are arranged to convert electric energy into mechanical energy and vice versa. In the embodiment shown, there are 8 electrical machines 22 which may or may not be of identical construction. In some embodiments, the electrical machines 22 can be mounted side-by-side or with some gaps between them at respective positions along the axis of the elongate shaft 17. Each electrical machine 22 can comprise a rotor which is fixed to the shaft 17 and a stator which is fixed to an elongate tubular body 23. Elongate tubular body 23 may comprise a tube. The elongate tubular body 23 may cover and/or protect electrical machines 22. The elongate tubular body 23 may extend from neck 20 to an end and/or nozzle at an aft of the propulsion device. The elongate tubular body 23 may allow air to pass from a front of the propulsion device to the aft.

[038] The stator may extend rearwardly from the aft end of the neck 20. The stator may extend radially outwardly from shaft 17. A plurality of fins 24 may extend radially outwardly from the aft end of the body 23. The plurality of fins 24 may extend radially outwardly from shaft 17. The outer end of the fins 24 may be secured to pylon 16 via a metal brace (not shown) or other means known to one of ordinary skill in the art for attaching fins or the fins 24 may be secured to a main outer duct of the engine which extends rearwardly from the front cowl 18, the duct then being bolted to the pylon 16 or as would be known to one of ordinary skill in the art for attaching the duct to the pylon 16, for example in a conventional jet engine.

[039] In some embodiments, each or one of electrical machine 22 may be mounted separately from shaft 17 and be connected to shaft 17 through a mechanical drive (e.g., belts, chains, gears, etc.).

[040] Each electrical machine 22 can comprise its own electronic solid-state drive circuit 25 at its radially outer portion, although a shared solid-state drive circuit used by several electrical machines 22 may alternatively be used. Solid-state drives are contemplated but other memory devices may be used in addition or alternatively. A control circuit (not shown) can be arranged to selectively operate the electrical machines 22 as a propulsion motor, a generator or combination of according to the operating conditions of the aircraft 10. The control circuit may be operatively connected to the solid-state drive circuit 25. The control circuit may comprise one or more processors configured to execute instructions stored on solid-state drive circuit 25, wherein the instructions are consistent with operating the control circuit. The control circuit may be configured to control a speed of the rotors of the electrical machines 22, an amount of liquid cooling, an input rate of fuel and/or air, starting, and/or any other functions of the electrical machines 22 or other components of propulsion device 15. One or more relays may be associated with control circuit 25 to accomplish commands instructed by the processor to affect mechanical changes of components of propulsion device 15 (e.g., controlling a pump to increase/decrease liquid cooling; controlling one or more control surfaces of an inlet to control air and/or fuel inputs into propulsion device 15; turning on or off one or more electrical machines 22; changing a speed of electrical machines 22; using stored electric energy to input mechanical energy through electrical machines 22 to shaft 17; generating electricity from electrical machines 22; and/or one or more battery management systems).

[041] The neck 20 at the fore end of the body 23 may act as an air collector behind the fan 26, so that in use a high airflow is channelled along the elongate tubular body 23 in which the electrical machines 22 are mounted act, so as to cool the electrical machines 22 and/or their drive circuits 25. It will be appreciated that each electrical machine 22 may have its own control circuit.

[042] The fins 24 may be positioned in the main airflow behind the fan 26 and act to dissipate heat from the electrical machines 22 into the airflow generated by the propulsion device 15. The fins 24 may comprise means such as heat pipes in order to improve heat extraction from the electrical machines 22. Further, the fins 19 and/or 24 can comprise a profiled configured to offer efficient airflow from the main fan to the exit openings at the aft of the propulsion unit 13. It is envisaged that most propulsion units will only require air-cooling for the propulsion system. However, larger propulsion units may require forced liquid cooling. Cabling may include power cables and control signal cables and any liquid cooling channels may pass through the rear cooling fins 24. In some embodiments, power cables, cooling, and/or control signal cables may be contained within the rear cooling fins.

[043] In use, the tubular nacelle 14 and the cowl 28 defined by the internal wall of the tubular nacelle 14 can streamline air flowing through the fan 26. The internal wall of the tubular nacelle 14 can allow the tips of the blades of the fan 26 to reach supersonic speeds without structural damage. The airflow between the cowl 28 and the elongate tubular body 23 is called ultra-high bypass air B, which produces thrust for a vehicle, for example the aircraft 10. For example, where the requirement of the propulsion system is to produce around 10 MW of power for a thrust equivalent to approximately 120 kN, two of these electric propulsion devices, as shown in FIG.1 would be able to power an aircraft. The aircraft could be for example, a short to medium haul commercial aircraft of the kind having seating for approximately 130 to 140 passengers. Other sizes of aircraft with more or less propulsion devices are contemplated as well.

[044] A central control circuit 33 may control the solid-state drive circuits 25 and/or their associated control circuits of the electrical machines 22 to cause the electrical machines 22 to start rotating in synchronisation with each other. The machines 22 may be powered up with varying speed and torque profiles to achieve a desired efficiency. Speed and torque profiles may be selected to choose maximum efficiency for altitudes, air density, vehicle configuration (e.g., an aircraft taking off, an aircraft in cruise). For example, the machines 22 may be controlled to operate anywhere in the range of 1 rpm to 100,000 rpm or more.

[045] The electrical machines 22 are coupled to the gearbox 21, which for example may have a ratio of around 20: 1. For example, the fan 26 coupled to the gearbox 21 can rotate at a speed which is for example 20 times less than that of the electrical machines 22. The high gear ratio allows the size of the electrical machine 22 to be small and the specific power density to be high (e.g., 25 kW/Kg). The solid-state drive circuits 25 are operated with as high voltage as possible (e.g., 3,000 volts). The high voltage may allow manageable currents in the machine windings of the electrical machines 22. A problem with using high voltage is that the level of the dielectric breakdown voltage in the windings decreases dramatically at high altitudes such as 40,000 feet, which means that distances between all supply conductors, must be increased or the conductors wrapped in a material to increase the dielectric strength to avoid electric short-circuits. This applies to all electric conductors, such as those of the electrical machines 22, the solid-state drive circuits 25 and of all other electronics onboard the vehicle, for example aircraft 10.

[046] During incidents such as bird strikes or hailstorms, any debris or other material may pass through the fan 26 and into the elongate tubular body 23 will not have a detrimental impact on the electrical machines 22 due to the fact that the air gap between the rotor and stator of each machine 22 is large (typically around 3mm but other air gaps are contemplated) and the windings of the electrical machines 22 are protected. For example, electrical machines 22 may be constructed using a special potting compound, which does not fracture/break on debris impact. The potting may be used around the windings. Any debris or other material may also pass straight through the electrical machines 22 because the electrical machines 22 can have an open structure that do not comprise endcaps. This arrangement also allows air to flow freely through the electrical machines 22 in a direction which extends axially of the driveshaft 17.

[047] The present system is more reliable than a traditional jet propulsion system. Hence the life of the disclosed propulsion system is comparatively high. The windings of the electrical machines 22 can be concentric, distributed or any other type to reduce the active material usage. The high voltage windings of the electrical machines are insulated to withstand 10 of 1000s of voltage to prevent a short-circuit.

[048] The weight of the windings of the electrical machines 22 can be reduced by having an aluminium inner lining through a copper tube. A cooling fluid may be passed through the centre of the tube to assist with cooling the electrical machines 22. Additionally, the heat generated by the electrical machines 22 can be transferred via the tubes into the aircraft for heating purposes. The heated fluid from the electrical machines 22 can also be fed to the fuselage 11 and wings 12 of the aircraft to prevent ice formation.

[049] The preferred kind of electrical machines 22 can be permanent magnet machines including but not limited to an inner rotor, outer rotor, embedded, IPM machines, axial flux machines, hybrid switch reluctance machines with or without hard magnetic materials. The solid-state drive circuits 25 can be provided in independent chambers for redundancy purposes. In some embodiments, the solid-state drive circuits 25 can be provided in two independent chambers

[050] Referring to Figure 4a of the drawings, in one embodiment each electrical machine 22 can be a permanent magnet inner rotor machine with a wound annular stator 29a surrounding a rotor 30a embedded with magnets. The solid-state drive circuits 25 are positioned radially outwardly of the stator 29a. The driveshaft 17 extends through the centre of the rotor 30a and a plurality of circumferentially-spaced air channels 31a extend axially through the rotor 30a so as to allow cooling air from the neck 20 to flow through the rotor. Also, as mentioned previously, cooling air from the neck 20 can flow through the large air gap between the rotor 30a and stator 29a of each electrical machine 22.

[051] Referring to Figure 4b of the drawings, there is shown an alternative embodiment of electrical machine 22 and like parts to those of Figure 4a are given like reference numerals with the suffix b. In this embodiment, the electrical machine 22 is a permanent magnet outer rotor machine, in which the rotor 30b is annular and surrounds only on one side of the inner wound stator 29b. The inner wound stator 29b is connected to the inner surface of the elongated tubular body 23. The solid-state drive circuits 25b are attached to the inner surface of the elongated tubular body 23 so as to clear the rotating rotor 30b with a substantial airgap of around 10mm or more.

[052] Referring to Figure 4c of the drawings, there is shown another embodiment of electrical machine 22 and like parts to those of Figure 4a are given like reference numerals with the suffix c. In this embodiment, the electrical machine 22 is an axial flux machine, in which the stator 29c and rotor 30c are disposed axially of each other on the shaft 17.

[053] The start-up sequence of a propulsion system in accordance with the present invention is very simple compared with that of a traditional jet propulsion system. In the present invention, all of the electrical machines 22 are instructed to power up via the central control circuit 33 to provide torque to rotate the fan 26 of the or each electric propulsion unit (e.g., propulsion unit 13 of Figure 1). The central control circuit 33 may be operated from a command center of a vehicle such as a cockpit of an aircraft or a central computing system of a vehicle. The rotational speed of the fan 26 is controlled via an engine throttle lever (not shown) disposed in the vehicle (e.g., aircraft 10 of Figure 1). The engine throttle lever may be configured to or connected to a controller to send a signal to the central control circuit 33, to control the thrust applied by one or more electric propulsion unit 13 to the vehicle (e.g., aircraft 10 of Figure 1).

[054] For an aircraft, such as aircraft 10 of Figure 1, during take-off, all of the electrical machines 22 can act as propulsion motors. For the aircraft, during cruising, the power of the propulsion motors 22 can be reduced to match the required cruising thrust, whereupon some may also act as generators. For the aircraft, during descent, some of the propulsion motors 22 act as generators and feed the generated power into the remaining propulsion motors 22 which act to maintain a suitable airspeed to keep the aircraft in the air. In this manner, the amount of power drawn from the on-board power supply can be substantially reduced. The onboard power supply may be battery in the form of fuel cells. During steeper descent, conventional aircraft use airbrakes to control the speed and slow the aircraft down. In order to harness this lost energy, more of the propulsion motors 22 can be configured to act as generators during descents and landings, saving additional kinetic and/or potential energy. In this manner, the kinetic and/or potential energy of the vehicle (e.g., an aircraft such as aircraft 10) can be converted into electrical energy, reducing or eliminating lost energy. The generated energy can be fed back to the power supply for storage and subsequent use. Excessive power can also be fed into supercapacitors, which can then later be used as a power source. Similar techniques as discussed herein can be used with the propulsion device to store power in other vehicles during deceleration.

[055] In view of the foregoing mode of operation, it will be appreciated that a propulsion system in accordance with embodiments of the present invention can enable a substantial amount of kinetic and/or potential energy to be harnessed, thereby substantially reducing or eliminating the carbon emissions of vehicles, including aircraft.

[056] Each electrical machine (e.g., electrical machine 22) may be selectively operable as either an electric motor for propelling the vehicle (e.g., an aircraft such as aircraft 10) or as a generator for converting kinetic and/or potential energy of the aircraft into electric energy. All of the electrical machines can operate as a propulsion motor during take-off and ascent to meet the power demands of a vehicle, for example a commercial aircraft. During descent of the aircraft, some of the electrical machines operate as a generator to generate electrical energy which is either used to assist with propulsion or fed to a storage device. In this manner, the electric propulsion device has an extremely high efficiency. Furthermore, the device is simpler in construction than a conventional jet engine and is thus far more reliable with substantially increased duty cycles, meaning less maintenance and downtime of the device. The device is also substantially lighter than conventional jet engines thereby further enhancing the efficiency of aircraft fitted with such devices. [057] Those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above-described embodiments, methods, and examples, but by all embodiments and methods within the scope of the invention as claimed.