Motor for Aircraft

Abstract

A motor 100 for an aircraft, comprising a stator 110 comprising windings 111, a rotatable shaft 120, and an integrated planetary gearbox assembly 300 comprising a sun gear 310 fixed to the shaft to ro

Description

FIELD OF THE INVENTION The present invention relates to a motor for an aircraft, in particular to a motor for an electric vertical or short takeoff and landing aircraft. BACKGROUND OF THE INVENTION Various forms of vertical or short take-off and landing (VSTOL) aircraft are known. The most common VSTOL aircraft configuration is the helicopter. The lift arrangement of a helicopter comprises a series of elongate blade members, usually with an aerofoil section, which are driven in rotation about an axis which extends substantially vertically relative to the aircraft. A blade may be referred to as a wing, and one or more wings or blades rotatable about a common axis may be referred to as a propeller. Rotating the propeller about the common axis produces lift which allows vertical take-off and landing as well as hovering and forward flight. Electric vertical takeoff and landing aircraft (eVTOL) have also been developed, in which an electric power source is used to power one or more propellers. Compared to traditional VTOL aircraft, eVTOL have several advantages, such as being quieter in operation, and having reduced manufacturing costs and emissions. One known way of increasing efficiency with which a propeller generates lift is to increase the diameter and reduce the turning speed. This creates a demand for a high torque, low speed motor. Known high torque, low speed motors tend to be heavy and so may not be optimal for aircraft applications. There is a need for improved eVTOL motors. SUMMARY OF THE INVENTION The inventor has identified that in the design of eVTOL motors, the mass of the electric motor tends to increase as torque requirements increase, meaning that traditional motors tailored for eVTOL applications are relatively heavy. 10 02 25 Attempts to solve this problem include: • Increasing the number of motor poles, so that the iron required to carry the flux between poles can be thinner and lighter. However, there are practical limits to how small a pole magnet can be manufactured and assembled. 5 Combined with the switching frequency capability of current power electronics, this leads to a motor design optimised for operation at around several thousand RPM. When operating at much lower speeds, motor operation can be sub-optimal. • A reduction gearbox is on paper an attractive solution to this problem, and 10 is known to be used in a helicopter to drive the main rotor. However, typical gearbox designs are too heavy to be acceptable in eVTOL applications. • Typical gearbox designs in sequence with the motor are also considered. However, this would prevent the lift motor from being integrated into lifting surfaces or booms, as the overall assembly would be too long, in an axial 15 direction. These potential solutions all have significant disadvantages, including at least those noted above. The inventor has devised an improved eVTOL motor which has an integrated gearbox, which is weight-efficient and permits a reduction in speed of a 20 suitable factor. The inventor has achieved this by using an integrated planetary gearbox arrangement having a sun gear, at least one planet gear, and a ring gear, where stator windings are disposed radially about the ring gear to direct flux radially 25 between the rotor poles and the stator windings. By doing this, a weight efficient motor having a suitable speed reduction factor is provided. The integrated planetary gearbox arrangement has the further advantage of providing a substantially planar arrangement. 30 In view of the above, the invention provides an aircraft propulsion motor, comprising: a stator comprising a plurality of stator windings; a rotatable propulsion output shaft; and an integrated planetary reduction gearbox assembly, comprising: 10 02 25 a sun gear fixedly attached to the propulsion output shaft, so as to rotate with the propulsion output shaft; a ring gear surrounding the sun gear and configured so as to transmit drive to the sun gear, via at least one planet gear disposed relative to the sun gear 5 so as to transmit drive between the sun gear and the ring gear, the ring gear having a plurality of magnetic rotor poles; wherein the stator windings are disposed radially about the ring gear to direct flux radially between the rotor poles and the stator windings. 10 This motor is compact, lightweight and efficient, making it particularly suitable for use in an eVTOL aircraft. In particular, by using a sun, planet and ring gear arrangement in which the ring gear has a plurality of rotor poles, space which would otherwise be filled with a simple web in the motor is used to accommodate the gear arrangement. By providing stator windings which are disposed radially about the 15 ring gear to direct flux radially between the rotor poles and the stator windings, a compact arrangement which is particularly suitable for eVTOL flight is achieved. The rotor and stator poles are configured to conduct magnetic flux. The rotor poles and / or stator poles may be magnetic or magnetisable. The rotor poles may be fixed 20 magnets. The planet gears may each have a respective rotational axis. At least one rotational axis of one of the planet gears may be held in a fixed position relative to a casing of the gearbox. This has the advantage of providing a particularly efficient gear 25 arrangement. The planet gears may each have an outer edge or circumference, and may be configured such that the outer edge contacts the sun gear and the ring gear in use. This has the advantage of being a simple arrangement with reduced manufacturing 30 and assembly costs. Such an arrangement may provide a multiplier gearbox. The planet gears may have an outer edge or circumference, and an inner edge or circumference. The inner edge may have a smaller diameter than the outer edge. The inner edge may be configured to contact the sun gear in use, and the outer 35 edge may be configured to contact the ring gear in use. This has the advantage of providing an increased reduction ratio for a given volume. The at least one planet gear may comprise at least one main planet gear and at least one idler gear. The at least one planet gear may be a plurality of planet gears. This has the advantage of allowing loads in the motor to be balanced. The plurality of planet gears may comprise a plurality of main planet gears and a plurality of idler gears. The main planet gears may be configured to mesh with the ring gear. The idler gears may be configured to transmit drive between the main planet gears and the sun gear. This has the advantage of providing an increased reduction ratio, which may, for example, be 3:1. This also has the advantage of allowing for a rotatable shaft with an increased diameter, which is particularly advantageous where the rotatable shaft is subject to high bending loads in use. This arrangement is therefore particularly suitable in an eVTOL application. The main planet gears may have an outer edge or circumference, and an inner edge or circumference. The inner edge may have a smaller diameter than the outer edge. The inner edge may be configured to contact the sun gear in use, and the outer edge may be configured to contact an idler gear in use. The idler gears may have an outer edge or circumference, and an inner edge or circumference. The inner edge may have a smaller diameter than the outer edge. The inner edge may be configured to contact a planet gear in use, and the outer edge may be configured to contact the ring gear in use. These features have the advantage of providing an increased reduction ratio for a given volume. The gearbox assembly may provide a reduction ratio of at least 2 to 1, preferably at least 3 to 1. This has the advantage of providing a reduction ratio particularly suitable for an eVTOL aircraft. The ring gear may be spaced apart from the stator by an air gap of at most 1 mm. This has the advantage of providing a compact motor. The motor may comprise at least one power-electronic component, which may be disposed proximate the stator. The at least one power-electronic component may be radially outside the stator. This has the advantage of providing a planar configuration particularly suitable for eVTOL flight. The motor may have a casing configured to house other components of the motor. The stator may be fixedly mounted relative to the casing. The motor may further comprise at least one ancillary component. The or each ancillary component may be powered by one or more of the planet gears. Specifically, the or each ancillary component may be powered by one or more of the main planet or idler gears. The or each ancillary component may be powered via a shaft extending from a central axis of a planet gear. This has the advantage of using the high rotation speed of the planet gear, and providing weight saving, which is particularly advantageous in eVTOL flight. The ancillary component may be configured to provide cooling to the motor. The ancillary component may be or comprise a cooling fan. The cooling fan may be driven indirectly by a planet gear shaft, by means of at least one gear wheel. The cooling fan may be co-axial with the rotatable shaft. The cooling fan may be coaxial with a propeller of the aircraft. The cooling fan may be disposed outside of the casing. This has the advantage of providing a particularly efficient arrangement. The ancillary component may be or comprise a pump component. The pump component may be comprised in a fluid or liquid circuit for cooling and / or lubricating one or more components of the motor or gearbox. The oil pump component may be driven directly by a planet gear shaft. The oil pump component may be one or more of: a centrifugal pump; a regenerative oil pump; an oil flinger; a positive displacement pump. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a cross-section through an exemplary standard motor; Figure 2 is a cross-section through a motor with an integrated gear-box; Figure 3 is a schematic showing a first embodiment of an integrated gear-box; Figure 4 is a schematic showing a second embodiment of an integrated gear-box; Figure 5 is a rear view of the schematic of figure 4; Figure 6 is a schematic showing a third embodiment of an integrated gear-box; Figure 7 is a rear view of the schematic of figure 6; and Figure 8 is a schematic of motor with an integrated gear-box having ancillary components. DETAILED DESCRIPTION OF EMBODIMENT(S) Figure 1 shows an example of a standard motor 1 for a vertical takeoff and landing aircraft, having a stator 10 comprising a plurality of stator windings; a rotatable shaft 20; a rotor 30; a casing 40 to which the stator 10 is fixedly attached; and a power-electronic assembly 50. This exemplary motor 1 operates by supply of electrical power to the stator 10; which causes the rotor 30 to rotate. The rotor 30, which is fixed in rotation with the rotatable shaft 20, causes the shaft 20 to rotate. Electric power may be supplied by the power-electronic assembly 50. The exemplary motor 1 shown in figure 1 does not have a gear assembly, so the ratio of rotation of the rotor 30 to the rotatable shaft 20 is 1:1. Embodiments of the invention are shown in figures 2 to 8. In contrast to the exemplary motor 1 of figure 1, the motor 100 described in the following has an integrated gearbox assembly 300. With reference to figure 2, the motor 100 has a stator 110; a rotatable shaft 120; and an integrated planetary gearbox assembly 300. The integrated planetary gearbox assembly 300 is configured to transmit drive between a rotor, specifically the ring gear 330, and the rotatable shaft 120 at a suitable reduction ratio. The integrated planetary gearbox assembly 300 comprises a sun gear 310; at least one planet gear 320; and ring gear 330. The sun gear 310 is fixedly attached to the shaft 120, so as to rotate with the shaft 120. The at least one planet gear 320 is disposed relative to the sun gear 330 so as to transmit drive between the sun gear 310 and the ring gear 330. Where the at least one planet gear 320 is a plurality of planet gears 320, the plurality of planet gears 320 may surround the sun gear 310 so as to transmit drive between the sun gear 310 and the ring gear 330. The ring gear 330 surrounds the sun gear 310 and is configured so as to transmit drive to or from the sun gear 310 via the at least one planet gear 320. The ring gear 330 has a plurality of magnetic rotor poles 331 which are configured to conduct magnetic flux. The rotor poles 331 may be magnetic or magnetisable. The rotor poles 331 may be fixed magnets. The ring gear can be rotatably mounted to the casing via bearings 340 and 341. The stator 110 has a plurality of stator windings 111. The stator windings 111 are disposed radially about the ring gear 330 to direct flux radially between the rotor poles 331 and the stator windings 111. The stator windings 111 are configured to conduct an electric current. The stator windings 111 are configured to create a plurality of magnetic stator poles when a current runs through them. This motor 100 is configured to operate by supply of electrical power to the stator 110. The rotor poles 331 on the sun gear 310 may cause a magnetic field to pass through the stator 110. When a supply of electrical power is applied to the stator 110, an additional radially extending magnetic field between the stator 110 and the ring gear 330 is created, which interacts with the rotor poles 331 and induces a magnetic force which causes the ring gear 330 to rotate. This in turn causes the planet gears 320 to rotate, which causes the sun gear 310 and rotatable shaft 120 to rotate. The rotatable shaft 120 may be fixedly attached to one or more propellers. By using an integrated planetary gearbox assembly 300, comprising a sun 310, planet 320 and ring gear 330 in which the ring gear 330 has a plurality of rotor poles 331, space which would otherwise be filled with a web or simple rotor 30 in the motor 100 is used to accommodate the gear arrangement 300. By providing stator windings 111 which are disposed radially about the ring gear 330 to direct flux radially between the rotor poles 331 and the stator windings 111, a compact arrangement having a significant weight reduction, which is particularly suitable for eVTOL flight is achieved. The sun gear 310 may be fixedly attached to the rotatable shaft 120, or may be formed integrally as a single piece of material with the rotatable shaft 120. When fixedly attached to the shaft 120, any suitable fixing means or component may be used, including but not limited to a spline coupling, welding, or any other appropriate fixing mechanism. A spline coupling has the advantage of providing a particularly suitable connection, which is robust and can transmit high torque in a dynamic or vibrating environment. The rotatable shaft 120 may extend through the sun gear 310. Specifically, the rotatable shaft 120 may extend from a first side, and an opposite second side of the sun gear 310. The sun gear 310 may be co-axial with the rotatable shaft 120, such that the rotatable shaft 120 and the sun gear 310 are concentrically arranged. The rotatable shaft 120 may be substantially centrally arranged within a casing 140 of the motor 100. The motor 100 may have an upper side 101 and a lower side 102 in use, and the sun gear 310 may be disposed closer to the lower side 102 than the upper side 101. The sun gear 310 may be disposed closer to the upper side 101 than the lower side 102. The planet gears 320 may each have a respective rotational axis. The planet gears may each have a gear shaft 321, as depicted in figure 3, in which only one planet gear 320 is shown. There may be provided two planet gears 320, preferably three planet gears 320, more preferably four planet gears 320. The axes and / or gear shafts 321 of the planet gears 320 may be disposed an equal distance from one another, and / or an equal distance from the rotatable shaft 120, and / or an equal distance from a central axis of the ring gear 330. At least one rotational axis of one of the planet gears 320 may be held in a fixed position relative to a casing 140 of the motor. This may be achieved by fixing one or more gear shaft 321 of the planet gears 320 relative to the casing 140, such that it is rotatable but not displaceable. The planet gears 320 may be disposed around the sun gear 310, and may be configured to mesh with the sun gear 310. The planet gears 320 may be disposed within the ring gear 330. The planet gears 320 may be configured to mesh with the ring gear 330. The ring gear 330 may disposed radially outside of, so as to at least partly surround one or more of: the rotatable shaft 120, the sun gear 310, the at least one planet gear 320. The ring gear 330 may be circular, having a circular inner and / or outer surface. The ring gear may have a depth in the direction of the rotatable shaft 120, the depth being larger than a depth of one or more planet gears 320. The ring gear 330 may be co-axial with the rotatable shaft 120 and / or the sun gear 310, such that the rotatable shaft 120, sun gear 310 and ring gear 330 are concentrically arranged. The ring gear 330 may be spaced apart from the stator 110 by an air gap 112 of at most 2 mm, preferably at most 1.5 mm, more preferably at most 1 mm. The stator 110 may be disposed radially outside of the ring gear 330, so as to at least partly surround the ring gear 330. The stator 110 may wholly surround the ring gear 330. The stator 110 may be circular, having a circular inner and / or outer surface. The stator 110 may be substantially ring shaped. The stator 110 may have a width in a radial direction, which is substantially uniform around a circumferential direction of the stator 110. The stator 110 may have a depth in the direction of the rotatable shaft 120, which may be substantially uniform around a circumferential direction of the stator 110. The depth of the stator 110 may be larger than a depth of one or more planet gears 320. The depth of the stator 110 may be substantially equal to or greater than a depth of the ring gear 330. This has the advantage of capturing flux that could otherwise escape from one or each end of the ring gear 330. The stator width may be larger than a width in a radial direction of the rotor 330. The stator 110 may be dimensioned having an inner radius that is at most 2 mm greater than an outer radius of the ring gear 330, preferably at most 1.5 mm greater than an outer radius of the ring gear 330, more preferably at most 1 mm greater than an outer radius of the ring gear 330. The stator 110 may be dimensioned having an inner radius that is at least 0.5 mm greater than an outer radius of the ring gear 330. The motor 100 may have a casing 140, or chassis, configured to house other components of the motor 100. The casing 140 may comprise one or more of: a substantially cylindrical body, an upper plate disposed on its upper side 101, and a lower plate disposed on its lower side 102. The stator 110 may be fixedly mounted relative to the casing 140. At least one gear shaft 321 of one of the planet gears 320, the main planet gears 350 or the idler gears 360 may be rotatably held in a fixed position relative to the casing 140, specifically to an upper plate of the casing 140. The ring gear 330 may be rotatably attached to the casing 140, which may be by attachment to the upper plate, and / or to an intermediate plate within the casing 140. The upper plate of the casing 140 may be attached to an aircraft body, which may be at an outer edge of the upper plate of the casing 140. The sun gear 310 may have an outer edge 311. One or more planet gears 320 may have an outer edge 322. One or more of the planet gears 320 may be configured to contact the sun gear 310 and the ring gear 330. This contact may be such that the planet gear 320 meshes with both the sun gear 310 and the ring gear 330. One or more planet gears 320 may be configured having an outer edge 322, which may be a circumference, and the outer edge 322 may contact both the sun gear 310 and the ring gear 330, which may be such that the outer edge 322 meshes with both of the sun gear 310 and the ring gear 330. The sun gear 310 and / or the planet gears 320 may be sized or dimensioned so that the outer edge 311 of the sun gear 310 may contact the outer edge 322 of one or more planet gears 320, for example as shown in figure 3. The sun gear 310 and / or one or more planet gears 320 may be configured such that the outer edge 311 of the sun gear 310 meshes with the outer edge 322 of one or more planet gears 320 in use. One or more planet gears 320 may be configured such that the outer 322 edge of the planet gear or gears 320 meshes with the ring gear 330 in use. Alternatively, the integrated planetary gearbox assembly 300 may be configured such that different parts of the or each planet gear 320 contact and / or mesh with the sun gear 310 and the ring gear 330. The planet gear or gears 320 may be configured such that an outer edge 322 of the, or each, planet gear 320 does not mesh with an outer edge of the sun gear 310. This may be as shown in figures 4 and 5. The planet gears may have an outer edge or circumference 322, and an inner edge or circumference 324. The inner edge 324 may have a smaller diameter than the outer edge 322. The inner edge 324 may be configured to contact the sun gear 310 in use, and the outer edge 322 may be configured to contact the ring gear 330 in use. One or more planet gears may comprise a meshing surface 323, which may be provided on one or both sides of the or each planet gear 320. The meshing surface 323 may have a diameter between a diameter of the planet gear 320 and the planet gear shaft 321. The meshing surface 323 may form a step between the planet gear 320 and the planet gear shaft 321. The meshing surface 323 may be configured such that an inner edge 324 is provided on the meshing surface 323, and such that an outer edge 311 of the sun gear 310 meshes with the inner edge 324 on the meshing surface 323. As an alternative to a meshing surface 323, the sun gear 310 may be configured such that an outer edge 311 of the sun gear 310 meshes with an inner edge 325 on the planet gear shaft 321. In these arrangements, the or each planet gear 320 may be configured such that the outer edge 322 of the planet gear or gears 320 contacts or meshes with the ring gear 330 in use. The sun gear 310 and one or more planet gears 320 may be configured so as to overlap in at least a radial direction of the motor 100. The planet gears 320 may all be disposed on the same side of the sun gear 310. Alternatively, the plurality of planet gears 320 may comprise a plurality of idler gears 350 and a plurality of main planet gears 360, for example as shown in figures 6 and 7. The main planet gears 360 may be configured to mesh with the ring gear 330. The idler gears 350 may be configured to transmit drive between the main planet gears 360 and the sun gear 310. The idler gears 350 may be configured to mesh with the main planet gears 360 and the sun gear 310. There may be provided two main planet gears 360, preferably three main planet gears 360, more preferably four planet gears 360. At least two main planet gears has the advantage of providing a balanced configuration. There may be provided a first set of main planet gears and a second set of main planet gears, each arranged with the sun gear axially therebetween. This has the advantage of providing a balanced arrangement. The main planet gears 360 may have an outer edge or circumference 362, and an inner edge or circumference 364. The inner edge 362 may have a smaller diameter than the outer edge 364. The inner edge 362 may be configured to contact the sun gear 310 in use, and the outer edge 364 may be configured to contact an idler gear 350 in use. The idler gears 350 may have an outer edge or circumference 352, and an inner edge or circumference 354. The inner edge 354 may have a smaller diameter than the outer edge 352. The inner edge 354 may be configured to contact a main planet gear 360 in use, and the outer edge 352 may be configured to contact the ring gear 330 in use. There may be provided an equal number of idler gears 350 as main planet gears 360. One or more of the plurality of idler gears 350 may comprise a meshing surface 353, which may be provided on one or both sides of the or each idler gear 350. The meshing surface 353 may have a diameter between a diameter of idler gear 350 and the idler gear shaft 351. The meshing surface 353 may form a step between the idler gear 350 and idler gear shaft 351. The meshing surface 353 may be configured such that an outer edge 311 of the sun gear 310 meshes with an edge 354 provided on the meshing surface 353. As an alternative to a meshing surface 354, the sun gear 310 may be configured such that an outer edge 311 of the sun gear 310 meshes with an inner edge 355 provided on the planet gear shaft 351. In these arrangements, the or each idler gear 350 may be configured such that the outer edge 352 of the idler gear or gears 350 contacts or meshes with a corresponding main planet gear 260 in use. The sun gear 310 and one or more idler gears 350 may be configured so as to overlap in at least a radial direction of the motor 100. The idler gears 350 may all be disposed on the same side of the sun gear 310. These arrangements have the advantage of an improved reduction ratio. One or more of the plurality of main planet gears 360 may comprise a meshing surface 363, which may be provided on one or both sides of the or each main planet gear 360. The meshing surface 363 may have a diameter between a diameter of main planet gear 360 and the main planet gear shaft 361. The meshing surface 363 may form a step between the main planet gear 360 and the main planet gear shaft 361. The meshing surface 363 may be configured such that an outer edge 352 of a neighbouring idler gear 350 meshes with an inner edge 364 of the meshing surface 363. As an alternative to a meshing surface 363, the neighbouring idler gear 350 may be configured such that an outer edge 352 of the neighbouring idler gear 350 meshes with an edge 365 provided on the main planet gear shaft 361. In these arrangements, the or each main planet gear 360 may be configured such that the outer edge 362 of the main planet gear or gears 360 contacts or meshes with the ring gear 330 in use. The idler gears 350 and main planet gears 360 may be configured so as to overlap in at least a radial direction of the motor 100. The main planet gears 360 may all be disposed on the same side of the idler gears 350. The idler gears 350 may be disposed between the sun gear 310 and the main planet gears 360 in a longitudinal direction of the rotatable shaft 120. This arrangement, incorporating idler gears 350, has the advantage of providing an increased reduction ratio, which may, for example, be 3 to 1. This also has the advantage of allowing for a rotatable shaft 120 with an increased diameter, which is particularly advantageous as the rotatable shaft 120 may be subject to high bending loads in use. The gearbox assembly may provide a reduction ratio of at least 2 to 1, preferably at least 3 to 1. The motor 100 may comprise at least one power-electronic component 150. The at least one power-electronic component 150 may be disposed radially outside the stator 110. The at least one power-electronic component 150 may be disposed axially above or below the stator 110. The motor 100 may further comprise at least one ancillary component 400. The or each ancillary component 400 may be powered by one or more planet gears 320, idler gears 350 or main planet gears 360. The or each ancillary component 400 may be powered via a shaft 321, 351, 361 extending from a central axis of a planet gear 320, idler gear 350 or main planet gear 360. The ancillary component 400 may be configured to provide cooling to the motor 100. The ancillary component 400 may be a cooling fan 410 or a gear 410 to drive a cooling fan. The cooling fan 410 may be driven indirectly by a shaft 321 of a planet gear 320, by means of at least one gear wheel 320. The cooling fan 410 may be co-axial with the rotatable shaft 120. The cooling fan 410 may be co-axial with a propeller of the aircraft. The cooling fan 410 may be disposed outside of the casing 140. The cooling fan 410 may be configured to rotate at a faster speed than a propeller of the aircraft. There may additionally be provided a diffuser and / or an additional a cooling fan, which may be fixedly attached to the casing 140. The ancillary component 400 may be an oil pump component 420. The oil pump component 420 may be driven directly by a shaft 321, 351, 361 extending from a central axis of a planet gear 320, idler gear 350 or main planet gear 360. The oil pump component 420 may be one or more of: a centrifugal pump; a regenerative oil pump; an oil flinger; a positive displacement pump. The motor 100 may comprise one or a plurality of ancillary components 400, which may be the same as one another or different to one another. As demonstrated in figure 8, there may be provided a cooling fan 410 and an oil pump component 420 in the same motor 100. Both of these ancillary components 410, 420 may be driven by different planetary gears 320, idler gears 350 or main planet gears 360. One or more, or all, of: the sun gear 310, the or each planet gear 320, the or each main planet gear 360, the or each idler gear 350, may be substantially circular, and / or substantially planar, and / or substantially disc-shaped. One or more, or all, of: the sun gear 310, the or each planet gear 320, the or each main planet gear 360, the or each idler gear 350, and the ring gear 330, may be provided partly or substantially wholly within the stator 110. One or more, or all, of: the sun gear 310, the or each planet gear 320, the or each main planet gear 360, the or each idler gear 350, the ring gear 330, may comprise a metal and / or alloy, and / or may comprise a magnetisable material such as steel. Although the invention has been described above with reference to one or more 5 preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims. Any reference numerals used in the claims should be construed as a guide to a 10 possible embodiment or embodiments only, and not be construed as limiting on the scope of the claims. 10 02 25

Claims

1. An aircraft propulsion motor, comprising:a stator comprising a plurality of stator windings;5 a rotatable propulsion output shaft; andan integrated planetary reduction gearbox assembly, comprising:a sun gear fixedly attached to the propulsion output shaft, so as to rotate with the propulsion output shaft;a ring gear surrounding the sun gear and configured so as to transmit10 drive to the sun gear, via at least one planet gear disposed relative to the sun gear so as to transmit drive between the sun gear and the ring gear, the ring gear having a plurality of magnetic rotor poles;wherein the stator windings are disposed radially about the ring gear to direct flux radially between the rotor poles and the stator windings.

152. The motor of claim 1, wherein the planet gears each have a respective rotational axis and wherein at least one rotational axis of one of the at least one planet gear is held in a fixed position relative to a casing of the gearbox.20 3. The motor of claim 1 or claim 2, wherein the at least one planet gear is aplurality of planet gears, preferably comprising a plurality of main planet gears and a plurality of idler gears.

4. The motor of claim 3, wherein the main planet gears are configured to mesh 25 with the ring gear; and wherein the idler gears are configured to transmit drive between the main planet gears and the sun gear.

5. The motor of any of the preceding claims, wherein the gearbox assembly provides a reduction ratio of at least 2 to 1, preferably at least 3 to 1.

306. The motor of any of the preceding claims, comprising at least one power-electronic component, disposed proximate the stator.

7. The motor of claim 6, wherein the at least one power-electronic component 35 is disposed radially outside the stator.10 02 258. The motor of any of the preceding claims, wherein the motor has a casing configured to house other components of the motor, and the stator is fixedly mounted relative to the casing.5 9. The motor of any of claims 2 to 8, further comprising at least one ancillarycomponent, the ancillary component being powered by one or more of the planet gears.

10. The motor of any of the preceding claims, wherein the or each ancillary10 component is powered via a shaft extending from a central axis of a planet gear.

11. The motor of claim 9 or claim 10, wherein the ancillary component isconfigured to provide cooling to the motor.15 12. The motor of any of claims 9 to 11, wherein the ancillary component is acooling fan.

13. The motor of claim 12, wherein the cooling fan is driven indirectly by a planet gear shaft, by means of at least one gear wheel.2014. The motor of claim 13, wherein the cooling fan is co-axial with the rotatable propulsion output shaft.

15. The motor of any of claims 12 to 14, wherein the cooling fan is co-axial with 25 a propeller of the aircraft.

16. The motor of any of claims 12 to 15, wherein the cooling fan is disposed outside of the casing.30 17. The motor of any of claims 9 to 11, wherein the ancillary component is apump component.

18. The motor of claim 17, wherein the pump component is driven directly by a planet gear shaft.3519. The motor of claim 17 or claim 18, wherein the pump component is one or more of: a centrifugal pump; a regenerative oil pump; an oil flinger; a positive displacement pump.5LDCM

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