LOW-VIBRATION DRONE

Abstract

A drone includes a fuselage and a plurality of housing structures for a plurality of engine units. The mechanical connection between each engine unit and each housing structure for the engine unit has: a ball joint arranged in the axis of rotation of the engine unit, opposite the rotor; and a flexible connecting member connecting the engine unit to the housing structure for the engine unit.

Claims

1. A drone, comprising a fuselage and a plurality of housing structures in which are arranged a plurality of powertrains, a mechanical connection between each powertrain and each housing structure of a powertrain, wherein said mechanical connection between each powertrain and each housing structure of a powertrain comprises a flexible connecting member connecting the powertrain to the housing structure of the powertrain, wherein said mechanical connection between each powertrain and each housing structure of a powertrain further comprises a universal joint arranged in the axis of rotation of the powertrain, opposite the rotor.

2. The drone according to claim 1, wherein the flexible connecting member is at a distance (I) from the universal joint.

3. The drone according to claim 1, wherein the universal joint is anti-torque.

4. The drone according to claim 1, wherein the flexible connecting member is an elastomeric membrane attached to the upper portion of the powertrain and to the housing structure.

5. The drone according to claim 1, wherein the universal joint comprises a spiral membrane cooperating with the housing structure and with the powertrain and a flexible multiaxial connection in which a prominent portion of the powertrain is inserted.

6. The drone according to claim 1, comprising a damping ratio R=I/L between 0.01 and 1, where L corresponds to the distance between the universal joint and the plane of the rotor, and I corresponds to the distance between said joint and the point of attachment of the flexible connection with the powertrain.

7. The drone according to claim 6, wherein the damping ratio is between 0.4 and 1.

8. The drone according to claim 7, wherein the damping ratio is between 0.6 and 0.9.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] All the embodiment details are given in the description which follows, supplemented by FIGS. 1 to 5B, presented solely for purposes of non-limiting examples, and in which:

[0022] FIG. 1A is a schematic view illustrating the main efforts to be taken into account in a multirotor drone architecture;

[0023] FIG. 1B is a sectional view in the vertical plane of the powertrain housing and of the powertrain, with a symbolic representation of the damping system according to the invention;

[0024] FIG. 1C is a perspective view of an example of a drone provided with a plurality of powertrain housing structures arranged at the end of arms carried by the fuselage of the drone;

[0025] FIG. 2 is a sectional view in the vertical plane of an example of housing structure of the powertrain and an example of implementation of a damping system;

[0026] FIG. 3 is a top view of the housing structure of the powertrain enabling the extreme positrons allowed by the damping system according to the invention to be seen;

[0027] FIGS. 4A and 4B illustrate an example of a joint or ball joint according to the invention; and

[0028] FIGS. 5A and 5B illustrate two examples of flexible fastening according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Drone 1 means a remotely piloted aircraft as defined in the decree of 11 Apr. 2012 on the design of civil aircraft that operate without any person on board, the conditions of their use and the capabilities required of the persons who use them. In short, it refers to any aircraft capable of unmanned flight, which is controlled either by a computer (on board or on the ground) or by an operator on the ground, used for recreational, competition, or professional purposes.

[0030] Rotary wing means any drone whose lift in the air is obtained by means of at least one rotor 6, allowing the drone to hover. The invention relates preferentially to multirotor drones equipped with three to eight rotors.

[0031] Powertrain 4 means a powertrain comprising a motor, a rotor with fixed pitch or variable pitch, and all the transmission elements between the motor and the rotor 6 (gearbox, rotor head, axis of rotation 5, blade holders, etc.).

[0032] MTOW means maximum take off weight, which is the maximum take-off weight of an aircraft, i.e. the mass beyond which an aircraft cannot take off without potentially harming the safety of the aircraft. flight.

[0033] Rolling Shutter means the image acquisition technique on a digital sensor, which consists of recording line by line the image received by the sensor. This technique causes geometric aberrations, or image distortions, during the acquisition of moving objects or when the sensor is subjected to vibrations.

[0034] FIG. 1A illustrates the key efforts involved in a rotor arrangement. The latter must be able to transmit the traction force. The torque transmitted by the motor must be supported by the fastening means. The fastening assembly, in addition to being adapted to the latter constraints, must be able to dampen the vibrations as well as possible. As these various technical requirements are often contradictory, it is relatively complex to reach a right balance between these various constraints, which explains why drones known to date still do not comprise an optimal solution.

[0035] FIG. 1C illustrates an example of a multirotor drone 1 comprising a plurality of housing structures 3 such as that illustrated in the example of FIG. 1B.

[0036] The objective sought by vibratory isolation is to modify the stiffness of the connection between the exciting element and its support in the direction of excitation, so that the cutoff frequency of this connection is much lower than the frequency of excitation.

[0037] The exciting element is the powertrain 4, and more precisely the rotor 6 where most of the vibrations originate (imbalance, geometric defect, etc.). The direction of the excitation is the plane materialized by the rotor disk 6. The support of the exciting element is the structure of the drone. The connection between the exciting element and its support is the attachment of the powertrain 4 in the housing structure 3 of the powertrain.

[0038] The objective is therefore to modify the stiffness with which the powertrain 4 is held in the plane of the rotor 6, while transmitting the torque and the traction provided by the powertrain as shown in the diagram of FIG. 1A. For this, the invention proposes a mounting, as shown diagrammatically in FIG. 2, composed of a connection of the universal joint 10 or finger ball joint type, arranged at a reasonable distance from the rotor 6, and connecting the powertrain 4 to the structure of the drone 1, as well as flexible connecting members 20, arranged between the universal joint 10 and the rotor 6, also connecting the powertrain 4 to the housing structure 3 and whose mechanical characteristics (stiffness and damping) are adapted to the frequencies to be isolated.

[0039] As shown in FIG. 1 B and FIG. 2, this architecture makes it possible to transmit the traction and torque forces of the powertrain to the structure via the universal joint, while isolating the motions of the powertrain 4 in the plane of the rotor 6 thanks to the flexible connecting members 20.

[0040] FIG. 3 illustrates the beneficial effect of this configuration, with a view from above of a powertrain 4 arranged in a housing structure 3. The solid lines represent the initial position of the ball bearing 7 of the rotor axis. The dashed lines represent the powertrain 4 in maximum deflection position.

Characteristic Length L

[0041] As shown in FIG. 1B, the characteristic length is defined as the distance L between the universal joint 10 and the plane of the rotor. To maximize the efficiency of the invention, this characteristic length must be related to the diameter D of the rotor 6, and a characteristic length is preferably chosen in the following ranges: an extended characteristic length range for which the distance L is greater than or equal to 0.5.D and less than or equal to 2.D. A first preferred characteristic length range for which the distance L is greater than or equal to 0.2.D and less than or equal to 1.5.D. Finally, a second preferred characteristic length range for which the distance L is greater than or equal to 0.5.D and less than or equal to 1.D.

Damping Ratio

[0042] The damping ratio is defined by R=I/L where L is the distance between the universal joint 10 and the plane of the rotor 6 and I is the distance between the joint 10 and the point of attachment of the flexible connecting members 20 to the powertrain 4. For maximum efficiency of the invention, R is selected in the following ranges: an extended damping ratio range in which the ratio R is greater than or equal to 0.01 and less than or equal to 1. A first range of preferential damping ratio in which the ratio R is greater than or equal to 0.4 and less than or equal to 1. Finally, a second range of preferential damping ratio in which the ratio R is greater than or equal to 0.6 and less than or equal to 0.9.

Universal Joint

[0043] In the context of the present invention, the concrete embodiment of a universal joint connection 10 is made more complicated by the restricted space and the mass constraints imposed by a multirotor drone. Added to this is the need to transmit the traction force provided by the powertrain 4 to the structure. However, conventional solutions such as blade coupling, Cardan joints or Rzeppa joint do not take up, or take up only inadequately, the traction.

[0044] The preferential solution, illustrated in FIGS. 4A and 4B, the powertrain comprises a protruding portion 11 which fits into a homothetic hole of the joint, and is of larger dimensions, by means of a flexible multiaxial connection 13 implemented for example by an elastomeric part that cooperates with the structure of the drone around the hole. Furthermore, a spiral membrane 12 is fastened at its center on the powertrain 4, for example with the aid of the fastening elements 14, and at its ends on the structure of the drone 1. It transmits rigidly the torque of the powertrain 4 to the structure of the drone while the multiaxial flexible connection 13 transmits almost rigidly the traction of the powertrain 4, while leaving it swivel around the joint, thanks to local deformations of the elastomer part.

Soft Link Elements

[0045] FIGS. 5A and 5B show two examples of embodiments of a flexible connecting member 20. FIG. 5A shows an exemplary interface between the upper zone of a hollow-axis powertrain with a brushless motor with a rotating cage with the housing structure 3. The figure illustrates the rotor 5 and the stator 8, the latter serving as an attachment point for an inner attachment 21 of a flexible membrane 20, cooperating on the other hand with the housing structure 3 by means of an external fastener 22. FIG. 5B shows an example similar to that of FIG. 5A, for a full-axis powertrain. The figure illustrates the rotor 5 and the stator 8, the latter serving as an attachment point for an inner attachment 21 of a flexible membrane 20, cooperating on the other hand with the housing structure 3 by means of an external fastener 22.

[0046] The main difficulty in choosing the flexible connecting members 20 is that a rotor 6 must accelerate to reach a nominal speed. During this acceleration phase, the natural frequency of the device will be reached and exceeded. While passing this natural frequency, it is necessary to have a damping coefficient sufficient to avoid a phenomenon of divergent and potentially destructive resonance. However, this damping must not be too high to avoid canceling the insulating effect of the connection beyond this natural frequency.

[0047] In the examples presented here, the flexible connecting members 20 are preferably made using elastomeric materials (rubbers, silicones, latex, etc.).

[0048] The figures and their descriptions made above illustrate the invention rather than limiting it. In particular, the invention and its various variants have just been described in connection with a particular example comprising a drone provided with four arms 2 and four rotors 6.

[0049] Nevertheless, it is obvious to one skilled in the art that the invention can be extended to other embodiments in which, in variants, a different number of arms and rotors is provided, preferably between four and eight.