Aircraft propulsion device

Abstract

An aero propulsion device includes an electric motor and at least one propeller provided with a plurality of blades and driven in rotation by the electric motor. The device is configured as a “rim drive” such that the electric motor comprises a first rotor of annular shape, with a plurality of the blades connected to the first rotor and arranged internally to form a first propeller.

Claims

1. An aero propulsion device comprising: an electric motor; and at least one propeller provided with a plurality of blades, the propeller being driven in rotation by the electric motor, wherein: the aero propulsion device is configured as a “rim drive” such that the electric motor comprises a first rotor of annular shape and a stator, the plurality of blades is connected to the first rotor and arranged internally to the first rotor to form a first propeller of the at least one propeller, and a core of the first rotor and/or a core of the stator are made from a non-ferromagnetic material, such that the motor is free of magnetic attraction between the first rotor and the stator.

2. The device according to claim 1, wherein the core of the first rotor and/or the core of the stator are made from a carbon fiber composite material.

3. The device according to claim 1, wherein the stator is movable and defines a second rotor of annular shape, and wherein an additional plurality of the blades is connected to the second rotor and arranged internally to the second rotor to form a second the propeller, the first and second propellers being counter-rotating.

4. The device according to claim 3, wherein the first rotor is provided with a plurality of permanent magnets and the second rotor is provided with a plurality of windings.

5. The device according to claim 4, wherein the windings are made of a transposed multipolar Litz wire conductor to minimize losses in high-frequency conductors.

6. The device according to claim 4, wherein the magnets are arranged in a Halbach configuration such that the magnets are divided into groups of three, each group having a first magnet oriented with a preferred magnetic field thereof toward the windings of the second rotor, a second magnet adjacent to the first magnet and oriented with a preferred magnetic field toward the first magnet, and a third magnet adjacent to the second magnet and oriented with a preferred magnetic field in a direction opposite to the windings of the second rotor.

7. The device according to claim 4, wherein at least the second propeller is provided with a central hub, further comprising a power supply circuit of the windings, the power supply circuit comprising electrical conductors provided in one or more blades of the second propeller and sliding connections in the central hub.

8. The device according to claim 4, wherein the first rotor surrounds the second rotor in an intermediate overlapping zone, respectively the permanent magnets and the windings being provided in the intermediate overlapping zone, the permanent magnets and the windings facing each other in a radial direction.

9. The device according to claim 1, wherein the device is configured as a fan of a turbofan.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] These and other features and advantages of the present invention will become clearer from the following description of some non-limiting exemplary embodiments illustrated in the attached drawings in which:

[0041] FIG. 1 illustrates an exploded view of an exemplary embodiment of the propulsion device;

[0042] FIG. 2 illustrates a detailed exploded view of the electric motor;

[0043] FIG. 3 illustrates a detailed view of the electric motor in assembled condition;

[0044] FIG. 4 illustrates the propulsion device inserted into a turbofan;

[0045] FIG. 5 illustrates the configuration of the magnets;

[0046] FIG. 6 illustrates the variation of field density in a B-H diagram in different configurations.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0047] FIG. 1 shows the aeronautical propulsion device in rim drive configuration. The propulsion device includes a permanent magnet electric motor. Said electric motor comprises a first annular-shaped rotor 11 connected to a plurality of blades arranged internally thereto to form a first propeller 10 and a second annular-shaped rotor 21 connected to a further plurality of blades arranged internally thereto to form a second propeller 20. The first and second rotors 11 and 21 therefore constitute circles arranged side by side and coaxial on a common axis of rotation, on which the blades of the first and second propellers 10 and 20 respectively are fixed, which blades extend in the direction of the axis of rotation to form a pair of intubated propellers.

[0048] Instead of being made up of a rotor and a stator, therefore, the motor comprises two rotors 11 and 21 bound to each other and counter-rotating, such that the first and second propellers 10 and 20 are counter-rotating.

[0049] However, it is possible to provide a configuration in which one of the two rotors is locked and only one propeller is driven. In this embodiment, the motor can be traced back to the classic rotor-stator configuration.

[0050] The pack consisting of the two rotors 11 and 21 and the respective propellers 10 and 20 is rotatably coupled with an external casing 4 by means of bearings 3.

[0051] The rotors 11 and 21 have a diameter of between 2 m and 3.5 m.

[0052] As can be seen in the detail view of the electric motor in FIG. 2, the first rotor 11 is provided with a plurality of permanent magnets 12 and the second rotor 21 is provided with a plurality of windings 22. The windings 22 are grouped into phase groups 23 arranged alternately in sequence along the entire second rotor 21 to create a polyphase motor.

[0053] The first rotor 11 surrounds the second rotor 21 in an intermediate zone of overlap that extends for a predetermined length in the axial direction, in which intermediate zone the said permanent magnets 12 and the said windings 22, facing each other in the radial direction, are respectively provided.

[0054] The propellers 10 and 20 are provided with a central hub and there is a power supply circuit for the windings 22 present on the second rotor. Said circuit comprises electrical conductors provided in one or more blades of said second propeller 20 and sliding connections in said hub. The electrical circuit is connected to an electrical power source, preferably a battery system and a DC-AC converter suitable for driving the motor.

[0055] The first rotor 11 and the second rotor 22 consist of annular elements of carbon fiber composite material, on which the magnets 12 and the windings 23 are respectively fixed.

[0056] It is possible to use other composite materials, known in the art, of sufficient lightness and mechanical strength.

[0057] FIG. 3 illustrates the propulsion device inserted in a turbofan, wherein it acts as a fan and works in combination with a combustion jet engine 5. The jet engine 5 is provided with an air inlet 50, a compressor 51, a combustion chamber 52, a compressor drive turbine 53, and an exhaust nozzle 54 that provides thrust. The amount of gas exiting the exhaust nozzle 54 is much higher than that of the inlet air because a thermal expansion takes place in the combustion chamber 52. In the turbofans currently used, the turbine 53 is connected to both the compressor and the fan, and the fan is intubated with a larger diameter than the air inlet 50, so as to create a double outflow. The larger the diameter of the fan compared to the air inlet 50, the higher the bypass ratio. This is a design parameter of the turbofans that indicates the ratio between the secondary or cold mass flow, i.e. the mass flow of air passing through the bypass, and the primary or hot mass flow, i.e. processed by compressor 51, combustion chamber 52 and turbine 53. In transport aircraft turbofans, a high bypass ratio is preferred, so that most of the thrust is generated by the fan rather than by the expansion of the combustion gases in the exhaust nozzle so as to ensure low specific consumption and low noise.

[0058] As shown in FIG. 4, 1 magnets 12 are arranged on the rotor 10 in a Halbach configuration. According to this arrangement, the magnets 12 are divided into groups of three. Each group comprises a first magnet 12′ oriented with its own preferential magnetic field in the direction of the windings 22 of the second rotor 21, a second magnet 12″ adjacent to the first magnet 12′ and oriented with its own preferential magnetic field in the direction of the first magnet 12′ and a third magnet adjacent to the second magnet 12″ and oriented with its own preferential magnetic field in the opposite direction to the windings 22 of the second rotor 21.

[0059] FIG. 5 shows the diagram B-H corresponding to the magnetic circuit consisting of the magnets 12 and the windings 22, in which B is the magnetic field density and H is the reluctance of the magnetic path, that is, the resistance that opposes the magnetic path.

[0060] A magnet perfectly short-circuited, i.e. with zero reluctance, has a magnetic field density B.sub.r, which is the maximum possible value. Due to the presence of air, the reluctance necessarily increases and the magnetic field descends along line 6. Since the rotors 11 and 21 are made of carbon fiber, due to the absence of iron the reluctance increases again, resulting in a lower magnetic field B.sub.1. Since the delivered torque is proportional to the magnetic field strength, it is evident that in this condition the motor suffers significant losses. The replacement of iron with composite material, however, makes it possible to reduce the weight of the engine by about 75%, and in the aeronautical field this can represent a positive balance in the calculation of costs/benefits related to weight/performance of the engine.

[0061] However, the Halbach configuration illustrated in FIG. 3 allows the magnetic field to be better conveyed in the magnets 12, i.e. at least in the part relating to the first rotor 11. This significantly improves the overall magnetic field density, allowing it to rise along line 6 and to a value of B.sub.2.

[0062] In addition, the Halbach configuration makes it possible to minimize the magnetic flux dispersed on the opposite side with respect to the windings; this flux, which constitutes a rotating field, could generate losses due to eddy currents in any metal parts in the vicinity, such as the nacelle fairing.

[0063] Thanks to the combination of these measures, it is possible to realize an aeronautical electric motor with a very high specific power. Calculations indicate that it is possible to build an electric motor with a power density between 20 and 30 KW/Kg, compared to 7-7.5 KW/Kg of the currently known motors, and at the same time to create a motor that can be supported by the fan's own blades, as they are not subject to magnetic forces other than torque, and can therefore be mounted on the blades with a certain amount of mechanical clearance, which is essential to compensate for the variation in length of the same for temperature and centrifugal force.