FR3093503A1 - Electric thruster for aircraft and method of using such a thruster - Google Patents

Abstract

An electric thruster (P) for an aircraft, the electric thruster (P) comprising at least a first propulsion member (1), a second propulsion member (2) and a single synchronous electric motor (6) configured to drive the control members. propulsion (1, 2) in rotation, the electric motor (6) comprising a peripheral stator element (4), a first rotor element (51), integral with the first propulsion member (1), comprising a first number N1 of pairs of poles and a second rotor element (52), integral with the second propulsion member (2), comprising a second number N2 of pairs of poles different from the first number N1 of pairs of poles so as to drive the propulsion members ( 1, 2) at different rotational speeds. Abstract figure: Figure 1

Description

Electric thruster for aircraft and method of using such a thruster

The present invention relates to the field of electric or hybrid-electric propulsion of an aircraft, in particular, allowing vertical take-off and landing.

In known manner, an aircraft has been proposed comprising a plurality of electric thrusters which are distributed in the aircraft. In known manner, an electric thruster comprises one or more propulsion members, propeller or fan. Each propulsion unit is connected to an electric drive motor. Each electric drive motor is connected to an electric inverter to control its operation. In general, the electrical inverter is connected to an electrical power source (for example an on-board battery or an electrical voltage generator associated with a rectifier) via a passive component, for example a capacitor of bus. The electrical inverter comprises a plurality of controllable switches which receive control commands from a control law implementation computer. In practice, this electric drive chain has a mass and a bulk that are high, which penalizes the performance of electric propulsion.

When you want to drive two propulsion units, from the same electric thruster, at different rotation speeds, in particular, to limit noise pollution. An immediate solution consists in using two different electric motors to drive the two propulsion devices. Such a solution has a mass and a bulk that are very high.

To eliminate these drawbacks, it is known to integrate a gear train driven by a single electric motor in order to adjust the speed ratio between the propulsion members. However, such a gear train also has the disadvantages of being heavy and bulky. In addition, it reduces the overall efficiency of the propulsion chain.

One of the objectives is thus to reduce the mass and size of an electric thruster comprising two propulsion units driven at different rotational speeds so as to improve propulsion efficiency and noise pollution.

The invention relates to an electric thruster for an aircraft, the electric thruster comprising at least a first rotary propulsion member about an X axis, a second rotary propulsion member about the X axis and a single synchronous electric motor configured to drive the first propulsion member and the second rotational propulsion member.

The invention is remarkable in that the electric motor comprises a peripheral stator element, a first rotor element, integral with the first propulsion member, comprising a first number N1 of pairs of poles configured to be driven magnetically by the rotating magnetic field generated by the peripheral stator element and a second rotor element, integral with the second propulsion member, comprising a second number N2 of pairs of poles configured to be driven magnetically by the rotating magnetic field generated by the peripheral stator element, the second number N2 being different from the first number N1 of pairs of poles P1, P2 so as to drive the propulsion members at different speeds of rotation.

Advantageously, a single stator element drives two rotor elements at different speeds due to their different numbers of poles. This advantageously makes it possible to reduce acoustic pollution while having a compact and light electric thruster, that is to say, with a high power density.

Preferably, the difference between the first number N1 and the second number N2 of pairs of poles P1, P2 is less than 10, preferably less than 4. More preferably, the difference between the first number N1 and the second number N2 of pairs of poles P1, P2 is equal to 2. A small difference advantageously makes it possible to obtain speeds of rotation which are different but close to each other so as to limit acoustic nuisance. Moreover, a small difference makes it possible to obtain rotor elements with dynamic and electromagnetic behaviors which are analogous, which makes it possible to optimize the thermal regulation and to improve the control.

According to one aspect of the invention, the first number N1 and the second number N2 of pairs of poles P1, P2 are each greater than or equal to 40, preferably to 48. Preferably, the first number N1 and the second number N2 of pairs of poles P1, P2 are each less than or equal to 50. Such a number of pairs of poles ensures a compromise between an optimum speed of rotation and an optimum density of power. In addition, this makes it possible to obtain an electrical frequency of the fundamental of the order of 2 kHz.

Preferably, the second number N2 of pairs of poles P2 is defined with respect to the first number N1 of pairs of poles P1, according to the following formula:

• fmec1 est la fréquence mécanique du premier organe de propulsion
• fmec2 est la fréquence mécanique du deuxième organe de propulsion.

, in which

• fmec1 is the mechanical frequency of the first propulsion unit
• fmec2 is the mechanical frequency of the second propulsion unit.

Thus, by setting the numbers of pairs of poles, it is possible to precisely define the speed ratio between the rotor elements. In addition, by adjusting the electrical frequency of the phases of the peripheral stator element, it is possible to precisely define the rotational speed of each rotor element.

Preferably, the electric thruster comprises a peripheral hull extending along the X axis. The propulsion members are mounted in the peripheral hull. Advantageously, the use of a peripheral hull makes it possible to guide the flow of air during its acceleration by the propulsion components. In addition, the peripheral hull makes it possible to house the stator element. This dual function makes it possible to increase compactness and therefore power density.

Preferably, the rotor elements are guided in the peripheral hull. In other words, there is not a single guide via the central hub as in the prior art. Such a design makes it possible to increase the passage section of the air flow in the peripheral hull.

Preferably, the first rotor element and the second rotor element each have a peripheral shape. Thus, they can be conveniently guided around the entire circumference.

Preferably, the first rotor element and the second rotor element are respectively mounted outside the first propulsion member and the second propulsion member. This advantageously allows the rotor elements to cooperate directly with the peripheral hull. The propulsion components can thus freely accelerate the flow of air.

According to one aspect, the first rotor element is guided in rotation relative to the stator element, in particular, by at least one ball bearing or one magnetic bearing. Preferably, the second rotor element is guided in rotation relative to the stator element, in particular, by at least one ball bearing or a magnetic bearing.

The invention also relates to a method of using an electric thruster as presented previously, comprising a step of supplying current to the phases of the stator element, a step of magnetically driving in rotation the poles of the first element rotor by the rotating magnetic field generated by the stator element at a first speed and a step of magnetically driving the poles of the second rotor element in rotation by the rotating magnetic field generated by the stator element at a second speed .

The invention will be better understood on reading the following description, given solely by way of example, and referring to the accompanying drawings given by way of non-limiting examples, in which identical references are given to similar objects. and on which:
is a schematic representation of an embodiment of an electric thruster according to the invention comprising two propulsion members,
is a cross-sectional schematic representation of a first propulsion member comprising a first number of pairs of poles,
is a cross-sectional schematic representation of a second propulsion member comprising a second number of pairs of poles and
is a schematic representation of the implementation steps of the invention.

It should be noted that the figures expose the invention in detail to implement the invention, said figures can of course be used to better define the invention if necessary.

There will now be presented an electric thruster of new design which can be mounted on an aircraft. Preferably, several thrusters P are mounted in a distributed manner on an aircraft in order to allow its propulsion and, more particularly, its take-off and its vertical landing.

Referring to Figure 1, the electric thruster P comprises a first propulsion member 1 rotatable around an axis X and a second propulsion member 2 rotatable around the axis X. The electric thruster P comprises a single synchronous electric motor 6 configured to drive the first propulsion member 1 and the second propulsion member 2 in rotation around the axis X at different speeds so as to allow, in particular, to reduce noise pollution. The propulsion members 1, 2 are driven in the same direction.

Preferably, the electric thruster P comprises only two propulsion members 1, 2. Nevertheless, it goes without saying that the invention applies to more than 2 propulsion members 1, 2, in particular, an even number d propulsion units 1, 2.

In this example, the electric thruster P comprises a peripheral hull 3 extending along the axis X in which the propulsion members 1, 2 are mounted so as to accelerate the flow of air circulating in the interior cavity of the peripheral hull. 3, also called the "thruster vein".

According to the invention, the electric thruster P comprises a peripheral stator element 4 which is, in this example, mounted in the peripheral hull 3. The electric thruster P further comprises a first rotor element 51, secured to the first propulsion member 1, comprising a first number N1 of pairs of poles P1, configured to be driven magnetically by the peripheral stator element 4.

The electric thruster P further comprises a second rotor element 52, integral with the second propulsion member 2, comprising a second number N2 of pairs of poles P2 configured to be driven magnetically by the peripheral stator element 4. According to the invention , the second number N2 is different from the first number N1 of pairs of poles P1 so as to drive the propulsion members 1, 2 at different speeds of rotation V1, V2.

In this embodiment, as illustrated in Figures 2A, 2B, each propulsion member 1, 2 is in the form of a propeller comprising a central hub 10, 20 and a plurality of radial vanes 11, 21 whose ends radially inner are connected to the central hub 10, 20 and whose radially outer ends are connected to a rotor element 51, 52.

In this example, the stator element 4 comprises three phases which are supplied so as to simultaneously allow rotation of the first rotor element 1 and rotation of the second rotor element 2. With reference to FIG. 1, the electric thruster P comprises a propulsion inverter 7 in order to control the stator element 4, in particular, the current flowing in its phases as will be presented subsequently. Preferably, the electric thruster P includes a computer 8 for implementing the control laws. The propulsion inverter 7 is connected to an electric power source SE (for example an on-board battery or an electric voltage generator associated with a rectifier) via a passive component, for example a bus capacitor . The propulsion inverter 7 comprises a plurality of controllable switches which receive control commands from the computer 8 for implementing the control laws. Preferably, the bus capacitor is circular in order to make it possible to limit the size constraints when it is mounted in the electric thruster P. The use of a polyphase electric motor 6 makes it possible to increase fault tolerance, this which increases the availability of the electric thruster P. The stator 4 makes it possible to generate a rotating magnetic field to drive the rotor elements 51, 52.

With reference to FIG. 2A, the first rotor element 51 is in the form of a peripheral crown of axis X defining an interior cavity in which the first propulsion member 1 is mounted, the radially outer ends of the blades 11 being connected to the first rotor element 51, in particular to the radially inner surface of the peripheral ring of which the first rotor element 51 has the shape. The first rotor element 51 is rotatably mounted in the peripheral hull 3 facing the stator element 4. The interior cavity of the first rotor element 51 is also called the “thruster section”.

Similarly, with reference to FIG. 2B, the second rotor element 52 is in the form of a peripheral ring with axis X defining an internal cavity in which the second propulsion member 2 is mounted. The radially external ends blades 21 are connected to the second rotor element 52, in particular to the radially inner surface of the peripheral ring whose shape the second rotor element 52 has. The second rotor element 52 is rotatably mounted in the peripheral hull 3 facing the stator element 4. The internal cavity of the second rotor element 52 is also called “thruster vein”. Thus, the first rotor element 51 and the second rotor element 52 are respectively integrated into the first propulsion member 1 and the second propulsion member 2.

In this example, as illustrated in FIGS. 2A and 2B, each rotor element 51, 52 comprises a plurality of magnetic poles P1, P2 so as to have a barycenter situated on the axis X. In known manner, the pairs of poles P1 and P2 interact with the rotating magnetic field generated by the electric currents flowing in the phases of the stator element 4 so as to rotate each rotor element 51, 52 and the propulsion member 1, 2 with which it is associated .

In this example, the first rotor element 51 comprises a first number N1 of pairs of poles P1, which are distributed peripherally. In other words, two adjacent poles are separated by the same angle. Preferably, the first number N1 of pairs of poles P1 is greater than or equal to 40, preferably 48, so as not to exceed a maximum electrical frequency of 2 kHz at the maximum speed of rotation. Preferably, the first number N1 of pairs of poles P1 is less than 50. For the sake of clarity and conciseness, only 12 pairs of poles P1 are represented in FIG. 2A.

Similarly, the second rotor element 52 comprises a second number N2 of pairs of poles P2 which are distributed in a peripheral manner. In other words, two adjacent poles are separated by the same angle. Preferably, the second number N2 of pairs of poles P2 is greater than or equal to 40, preferably 48, so as not to exceed a maximum electrical frequency of 2 kHz at the maximum speed of rotation. Preferably, the second number N2 of pairs of poles P2 is less than 50. For the sake of clarity and conciseness, only 8 pairs of poles P2 are represented in FIG. 2B.

Preferably, the difference between the first number N1 and the second number N2 of pairs of poles P1, P2 is less than 10, preferably less than 4. More preferably, the difference between the first number N1 and the second number N2 of pairs of poles P1, P2 is equal to 2. A small difference is advantageous in the present application in order to maintain close electromagnetic behavior for the two propulsion members 1, 2.

Preferably, the second number N2 of pairs of poles P2 is defined with respect to the first number N1 of pairs of poles P1, according to the following formula:

, in which

-fmec1 is the mechanical frequency of the first propulsion member 1;

-fmec2 is the mechanical frequency of the second propulsion member 2.

In a known way, the mechanical frequency is defined as the ratio of the electrical frequency to the number of pairs of poles. The following formulas are thus obtained for the various rotor elements 51, 52:

• [Math. 5]

Preferably, the electrical frequency is the same for the two rotor elements 51, 52 given that it is dictated by the stator element 4, itself controlled by the propulsion inverter 7. The formula stated above

• [Math. 5]

.
As the numbers of pairs of poles N1 and N2 are integers, the mechanical frequencies of rotation of the rotor elements 51, 52 must be selected so as to respect the formula.

By way of example, the electrical frequency of the stator element 4 is 2kHz. The first rotor element 51 comprises 48 pairs of poles N1 so as to be driven at a speed of rotation of 2500 revolutions/minute. The second rotor element 52 comprises 50 pairs of poles N2 so as to be driven at a speed of rotation of 2400 revolutions/minute.

In this example, the second rotor element 52 is arranged so that the efficiency and the transmitted electromagnetic power are identical to the first rotor element 51 so as to improve control and optimize thermal management. Preferably, the size of the pairs of poles N1 and the size of the pairs of poles N2 are different in order to reduce the overall rotor flux of the second rotor element 52. The torque constant Kt of the second propulsion member 2 is thus advantageously adapted . The losses/heating are advantageously similar on the two rotor elements 51, 52.

Advantageously, the two faces of the rotor element 51, 52 and the two faces of the stator element 4 are in contact with an air flow, which makes it possible to improve their cooling. Preferably, the peripheral hull 3 comprises a ventilation opening, in particular a slot, in order to facilitate the cooling of the stator element 4.

Preferably, the rotor elements 51, 52 are guided in rotation in the peripheral hull 3 via guide bearings, in particular ball bearings or magnetic bearings. In other words, the rotor elements 51, 52 are driven peripherally and not centrally as in a conventional thruster. The central hub has a lighter structure that does not impact the circulation of the airflow.

Preferably, the electric motor 6 is a synchronous motor, in particular, radial flux. Preferably, in this application example, an electric motor 6 of the Halbach type is preferred because it makes it possible to increase the power density of the system (increased power for constant size/mass).

An example of implementation of a method of using an electric thruster P according to the invention will now be presented.

With reference to FIG. 3, the method includes a step of supplying current E1 to the phases of the stator element 4 via the propulsion inverter 7 following a command from the control law calculator 8.

Following the power supply step E1, the method comprises a magnetic drive step E2 in rotation of the poles of the first rotor element 1 by the rotating magnetic field generated by the electrical supply of the phases of the stator element 4 at a first speed V1. Indeed, the N1 pairs of poles P1 of the first rotor element 1 interact magnetically with the rotating magnetic field generated by the electrical supply of the phases of the stator element 4. This then results in a rotation of the first propulsion member 1 .

Similarly, due to the generation of a rotating magnetic field induced by the flow of current in the phases of the stator element 4, the method includes a magnetic drive step E3 in rotation of the N2 pairs of poles P2 , of the second rotor element 2 by the stator element 4 at a second speed V2. This then results in a rotation of the second propulsion member 2.

As presented previously, the speed V1, V2 of rotation of a rotor element 51, 52 is a function of the number N1, N2 of pairs of poles P1, P2. Thus, in the example of implementation present, the speeds of rotation V1, V2 are different and there is a speed differential between the propulsion members 1, 2, which reduces the acoustic nuisances.

In this example, each propulsion member 1, 2 is guided in rotation about the axis X in the peripheral hull 3 via guide bearings positioned at the interface between the peripheral hull 3 and the rotor elements 51 , 52 respectively connected to the propulsion members 1, 2. Preferably, the stator element 4 comprises heat dissipation means to prevent any overheating during operation of the electric thruster P.

Claims (10)

Electric thruster (P) for aircraft, the electric thruster (P) comprising at least a first propulsion member (1) rotatable around an axis X, a second propulsion member (2) rotatable around the axis X and a single synchronous electric motor (6) configured to drive the first propulsion member (1) and the second propulsion member (2) in rotation,electric thruster characterized by the fact that theelectric motor (6) comprises:

• a peripheral stator element (4),
• a first rotor element (51), integral with the first propulsion member (1), comprising a first number N1 of pairs of poles (P1) configured to be driven magnetically by the rotating magnetic field generated by the peripheral stator element ( 4)
• a second rotor element (52), integral with the second propulsion member (2), comprising a second number N2 of pairs of poles (P2) configured to be driven magnetically by the rotating magnetic field generated by the peripheral stator element ( 4), the second number N2 being different from the first number N1 of pairs of poles (P1) so as to drive the propulsion members (1, 2) at different speeds of rotation (V1, V2).

Electric thruster (P) for aircraft according to claim 1, in which the difference between the first number N1 and the second number N2 of pairs of poles (P1, P2) is less than 10, preferably less than 4. Electric thruster (P) for aircraft according to claim 2, in which the difference between the first number N1 and the second number N2 of pairs of poles (P1, P2) is equal to 2. Electric thruster (P) for aircraft according to one of Claims 1 to 3, in which the first number N1 and the second number N2 of pairs of poles (P1, P2) are each greater than or equal to 40, preferably 48. Electric thruster (P) for aircraft according to one of Claims 1 to 4, in which the second number N2 of pairs of poles (P1, P2) is defined with respect to the first number N1 of pairs of poles (P1, P2) according to the following formula:

in which
-fmec1 is the mechanical frequency of the first propulsion unit (1)
-fmec2 is the mechanical frequency of the second propulsion member (2). Electric thruster (P) for aircraft according to one of Claims 1 to 5, in which the electric thruster (P) comprising a peripheral hull (3) extending along the axis X, the propulsion members (1, 2) are mounted in the peripheral hull (3). Electric thruster (P) for aircraft according to claim 6, in which the rotor elements (51, 52) are guided in the peripheral hull (3). Electric thruster (P) for aircraft according to one of Claims 1 to 7, in which the first rotor element (51) and the second rotor element (52) each have a peripheral shape. Electric thruster (P) for aircraft according to one of Claims 1 to 8, in which the first rotor element (51) is guided in rotation with respect to the stator element (4). Method of using an electric thruster (P) according to one of Claims 1 to 9, comprising a step of supplying current to the phases of the stator element (4), a step of magnetically driving of the poles (P1) of the first rotor element (1) by the rotating magnetic field generated by the stator element (4) at a first speed (V1) and a step of magnetically driving the poles (P2) of the second rotor element (2) by the rotating magnetic field generated by the stator element (4) at a second speed (V2).