Multi-Rotor Hydraulic Drone

Abstract

Multi-rotor hydraulic drone (1) comprising: —a plurality of hydraulic motors (6) each receiving a pressurised fluid, —propellers (5) driven by the hydraulic motors (6), —at least one hydraulic pump (10) driven by at least one motor (11) for pressurising the fluid, —a system for supplying the hydraulic motors (6) with pressurised fluid, —a flight controller (14) for controlling the supply system according to the desired rotation speed for the hydraulic motors (6), the supply system comprising several channels (35; 36; 37; 38) for adjusting the power of at least one portion of the hydraulic motors (6).

Claims

1-15. (canceled)

16. A multi-rotor hydraulic drone comprising: hydraulic motors configured to receive a fluid; propellers configured to be driven by the hydraulic motors; a hydraulic pump configured to pressurize the fluid provided to the hydraulic motors; and a supply system comprising: paths configured to provide the pressurized fluid to respective hydraulic motors; and valves configured to control a flow rate of the pressurized fluid through the paths to the respective hydraulic motors, in order to control a speed of the respective hydraulic motors, wherein when the valves are in a first position, the pressurized fluid is provided to the respective hydraulic motors at a non-zero idle flow rate, and when the valves are in a second position, the pressurized fluid is provided to the respective hydraulic motors at a flow rate that is greater than the idle flow rate.

17. The drone of claim 16, the hydraulic motor that receives the fluid at the idle flow rate when the valve is in the first position is connected in series with this valve.

18. The drone of claim 16, further comprising a pressure limiter configured to limit the pressure of the pressurized fluid in the supply system to a predetermined limit value.

19. The drone of claim 16, wherein an amount of thrust generated by the hydraulic motors receiving the pressurized hydraulic fluid at the idle flow rate is sufficient to lift the drone into the air.

20. The drone of claim 16, further comprising bypasses connected in parallel with the valves, the bypasses configured to provide the pressurized hydraulic fluid to the hydraulic motors at the idle flow rate, when the valves are in the first position.

21. The drone of claim 20, wherein the valves are closed when in the first position, such that all of the pressurized hydraulic fluid is provided to the hydraulic motors through the bypasses.

22. The drone of claim 16, wherein the drone is configured to be supplied with electrical power from the ground by a cable.

23. The drone of claim 16, wherein the hydraulic motors comprise fast axial piston motors having a fixed displacement.

24. The drone of claim 18, further comprising supports, wherein the hydraulic motor, the valves, and the pressure limiter are attached to the supports.

25. The drone of claim 16, further comprising a heat exchanger configured to cool the fluid.

26. The drone of claim 25, wherein the heat exchanger receives the fluid from outlets of the hydraulic motors.

27. The drone of claim 16, further comprising a flight controller configured to control the valves, such that for the hydraulic motors are operated at a desired rotation speed.

28. The drone of claim 16, further comprising a tank configured to receive the fluid from the hydraulic motors and provide the fluid to the hydraulic pump.

29. The drone of claim 28, wherein the tank is arranged so that the hydraulic pump is provided with the fluid and operates under a load.

30. The drone of claim 20, wherein the bypasses each comprise a calibrated orifice.

31. The drone of claim 16, further comprising a flow divider configured to receive the pressurized fluid from the hydraulic pump and supply pressurized fluid to each of the paths.

32. A multi-rotor hydraulic drone comprising: propellers; hydraulic orientation motors and hydraulic lift motors configured to drive the propellers; a hydraulic pump configured to pressurize a fluid provided to the hydraulic orientation motors and the hydraulic lift motors; paths configured to provide the pressurized fluid to the hydraulic lift motors and the hydraulic orientation motors; valves configured to control a flow rate of the pressurized fluid through the paths to the hydraulic orientation motors, such that the pressurized fluid may be provided to the hydraulic orientation motors at at least two different flow rates; and calibrated orifices configured to control a flow rate of the pressurized fluid through the paths to the hydraulic lift motors, such that the pressurized fluid is provided to the lift motors at a constant flow rate.

33. A method for operating a multi-rotor hydraulic drone of claim 18, the method comprising: during takeoff, operating the hydraulic pump at a speed that pressurizes the fluid to a pressure that exceeds a threshold pressure, and reducing the pressure of the fluid, such that the pressure limiter operates to reduce the pressure of the pressurized fluid to at least the threshold pressure, before the pressurized fluid is provided to the valves; and during the flight, operating the valves, so as to vary a flow rate of the pressurized fluid to the hydraulic motors and modify the orientation of the drone, while the pressure limiter maintains the pressure of the pressurized fluid provided to the valves at the threshold pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0105] The invention will be better understood upon reading the following detailed description of non-limiting exemplary embodiments and upon examining the attached drawing, in which:

[0106] FIG. 1 schematically shows an example of a drone according to the invention.

[0107] FIG. 2 is a view similar to FIG. 1 of a variant of the drone,

[0108] FIG. 3 shows schematically and partially, in perspective, a multi-rotor hydraulic drone according to an exemplary embodiment of the invention,

[0109] FIG. 4 shows the drone of FIG. 3 from a different viewing angle,

[0110] FIG. 5 shows the drone of FIG. 3 from below,

[0111] FIG. 6 shows the drone of FIG. 3 from above,

[0112] FIG. 7 shows an example of a hydraulic motor support,

[0113] FIG. 8 shows a view from below of the support of FIG. 7,

[0114] FIG. 9 shows a design detail of the support,

[0115] FIG. 10 shows another design detail of the support,

[0116] FIG. 11 shows a design detail of the drone,

[0117] FIG. 12 schematically shows another example of a drone according to another aspect of the invention,

[0118] FIG. 13 is a graph showing an example of the development of the hydraulic pressure at the inlet of the controllable valve and of the pressure at the outlet of the hydraulic pump as a function of time during the operation of the drone according to the invention, and

[0119] FIG. 14 is a graph showing the development of the speed of the pump drive motor as a function of time during the operation illustrated in FIG. 13.

DETAILED DESCRIPTION

[0120] FIG. 1 shows schematically various components forming a multi-rotor hydraulic drone 1 according to the invention. In this figure, the solid lines correspond to the high-pressure part of the hydraulic circuit, while the dashed lines correspond to the low-pressure part of the hydraulic circuit.

[0121] In this example, the drone 1 is a quadcopter and has four hydraulic motors 6 each driving a propeller 5 directly. In a variant, the drone can be hexacopter or octocopter, among other possibilities.

[0122] The drone 1 has a hydraulic pump 10 driven by an electric motor 11, which in this example is supplied with electrical power from the ground by a cable (not shown).

[0123] The pump 10 is supplied at the inlet with a hydraulic fluid contained in a storage tank 13 and pressurizes this fluid in order to supply the motors 6.

[0124] The pressurized fluid leaving the pump 10 is distributed by means of a flow divider 29 between a plurality of paths 35, 36, 37, 38 for adjusting the power of the hydraulic motors 6, each path supplying pressurized fluid to a corresponding motor 6. In the example shown in FIG. 1, the pressurized fluid leaving the pump 10 is thus distributed between four paths so as to supply the same number of hydraulic motors 6.

[0125] Each path comprises a proportionally controllable valve 17, which allows the flow rate of the pressurized fluid supply and thus the rotation speed of the associated propeller 5 to be varied at the inlet of the corresponding motor 6. Preferably, the controllable valve 17 is a direct electrically controlled servo valve.

[0126] The drone 1 comprises a flight controller 14 configured to control the speed of the drive motor 11 of the pump 10 and the opening of each valve 17 according to the flight speed and the orientation to be given to the drone in particular.

[0127] The valve 17 can be moved, in response to an electrical control signal from the flight controller 14, from a first position to a second position, so as to increase the flow rate of pressurized fluid through the valve 17.

[0128] Each path comprises a bypass in parallel with the valve 17, this bypass comprising a calibrated orifice 31 chosen to deliver a substantially constant flow rate of pressurized fluid to the inlet of the corresponding motor 6.

[0129] Each path has a pressure limiter 27 upstream of the valve 17 and the calibrated orifice 31, The pressure limiter 27 is used to limit the pressure of the fluid at the inlet of the valve 17 to a predefined and substantially constant value, regardless of the pressure upstream of the limiter, provided this value is large enough to make the limiter active. The operating speed of the pump 10 is sufficient to allow the pressure limiter to be active regardless of the position of the valve 17.

[0130] Each motor 6 is associated with a heat exchanger 8, which receives at its inlet the fluid leaving the motor 6 and the pressure limiter 27 and which delivers the cooled fluid to the storage tank.

[0131] When the drive motor 11 is electric, as in the example shown, the flight controller 14 controls a speed variator which is preferably switchable (not shown) and makes it possible to limit the current used and therefore the torque imposed by the pump 10.

[0132] The flight controller 14 advantageously comprises a microcontroller or other computer (not shown) making it possible to ensure a certain number of functions in an autonomous way, such as the maintenance of the drone 1 in a hovering or quasi-hovering position depending on measurement data coming from sensors installed on the drone 1, such as sensors of wind speed and also roll, pitch and yaw angles.

[0133] In the variant shown in FIG. 2, the drone 1 comprises a single pressure limiter 27 positioned between the outlet of the pump 10 and the inlet of the flow divider 29. Similarly, the drone 1 may comprise a single heat exchanger 8, positioned between the outlet of the hydraulic motors 6 and the inlet of the tank 13.

[0134] In an exemplary operation the drone 1, the supply flow rate of pressurized fluid at the inlet of each motor 6 is such that:

Q=Q.sub.31+Q.sub.17 and Q.sub.31=r*Q with. 0.5≤r≤1 for example, where
Q: supply flow rate of pressurized fluid at the inlet of each motor 6,
Q.sub.31: flow rate of pressurized fluid at the outlet of element 31, and
Q.sub.17: flow rate of pressurized fluid at the outlet of the controllable valve 17.

[0135] The controllable valve 17 can be selected to be completely closed in the first position, so that the entire supply flow rate of pressurized fluid to the inlet of each motor 6 comes from the bypass with the calibrated orifice 31. When the controllable valve 17 is open in the second position, the supply flow rate of pressurized fluid to the inlet of each motor 6 comes partly from the valve and partly from the bypass. For example, half of the flow rate is provided by the valve 17 and the other half by the bypass

[0136] An example of the arrangement of the constituent components of a multi-rotor hydraulic drone 1 according to the invention is illustrated in FIGS. 3 to 6.

[0137] In this example, the drone 1 is a quadcopter and has four arms 3 each carrying a rotor. The drone 1 can rest on the ground by two feet 4 connected to the arms 3.

[0138] The hydraulic motors 6 each have a rotor 2 driving a propeller 5, and are each supported by a corresponding arm 3.

[0139] A cowling 9 houses the pump 10 and the electric (hive motor 11 of the pump 10, the coupling between the pump 10 and its electric motor 11 being protected by a housing 12, The pump 10 and its electric motor 11 are preferably, as illustrated, positioned vertically in the center of the drone 1.

[0140] The arms 3 and feet 4 of the drone 1 are formed by an assembly of tubes 7, for example made of carbon. These tubes can be used to conduct hydraulic fluid, when possible.

[0141] Each arm can comprise parallel tubes.

[0142] The heat exchangers 8 are each integrated within a corresponding arm 3, and stiffen the latter by connecting the tubes 8.

[0143] As shown in FIGS. 7 to 10, each arm 3 carries at its end a support 15 in which the corresponding hydraulic motor 6 is fixed. The support 15 can be mounted, as shown, at the end of the tubes and can connect them.

[0144] Each support 15 has a collar 16 on its outer side, in which the hydraulic motor 6 is engaged and can support the corresponding controllable valve 17 on its inner side.

[0145] As illustrated in FIG. 10, each support 15 may have on its inner side, on the one hand, holes 18 for fixing the corresponding valve 17, and, on the other hand, orifices 19, 20 and 21 respectively for leakage, outflow and inflow of fluid.

[0146] On its lower side, each support 15 has orifices 22, 23, 24 and 25 respectively for the admission of fluid from the pump 10, the sending of fluid to the corresponding heat exchanger 8, the outflow of fluid to the corresponding hydraulic motor 6, and the return of fluid from the corresponding hydraulic motor 6.

[0147] The orifices 22 and 24 are connected to hydraulic hoses (not shown), which are resistant to high pressure. The orifices 23 and 25 are connected to hydraulic hoses (not shown), which are not subject to high pressure and may be less resistant.

[0148] Each support 15 has a tube 26 receiving the corresponding pressure limiter 27.

[0149] As shown in FIG. 11, the cowling 9 is attached via a connecting element 28 to the flow divider 29, which can be formed as shown by a perforated block that accommodates the outlet of the pump 10. The connecting element 28 is for example cross-shaped.

[0150] Support plates 30 are fixed on the one hand to the perforated block 29 and on the other hand to the arms 3 and make it possible to hold the fluid tank 13 and the flight controller 14.

[0151] The drone 1 shown in FIG. 12 has a plurality of hydraulic lift motors 6a and a plurality of hydraulic orientation motors 6b. In FIG. 12, only two lift motors 6a and two orientation motors 6b have been shown, in order to simplify understanding of the figure.

[0152] Each of the hydraulic lift motors 6a comprises a supply path comprising a calibrated orifice 31 connected in series with the corresponding motor 6a in such a way that each of the motors 6a receives a predefined constant supply flow rate, this supply flow rate being able to correspond to a flow rate allowing each of the lift motors 6a to be driven in rotation at a speed sufficient to produce a thrust ensuring just the lift of the drone 1.

[0153] Each of the hydraulic orientation motors 6b comprises a supply path with a controllable valve 17 connected in series with the corresponding motor 6b, the valve 17 being controllable between a closed position and a maximum open position to control the supply flow rate to each of the orientation motors 6b.

[0154] Each of the lift motors 6a can receive a predefined constant supply flow rate making it possible to ensure the lift of the drone 1 while the orientation motors 6b are stopped, the valves 17 being in the closed position. By playing on the degree of opening of the valves 17, it is possible to vary the rotation speed of the orientation motors 6b and thus to control the orientation of the drone and/or to stabilize it, i.e. to maintain it in stationary or quasi-stationary position.

[0155] Reference will now be made to FIGS. 13 and 14 to describe the operation of a drone according to the first aspect of the invention, all of the motors of which are connected in series with a controllable valve and receive a non-zero flow rate of fluid when the valve is in the first position, as is the case with drones of which the hydraulic circuits are illustrated in FIGS. 1 and 2.

[0156] FIG. 13 shows the development 100 of the pressure p at the outlet of the hydraulic pump 10 as a function of time t and the development 200 of the pressure p at the inlet of the controllable valve 17 and of the calibrated orifice 31 as a function of time t.

[0157] FIG. 14 shows the development 300 of the speed v of the drive motor 11 of the hydraulic pump 10 as a function of time t.

[0158] In a first step A, the hydraulic motors 6 are started. To do this, the speed of the drive motor 11 of the hydraulic pump 10 is increased according to its torque capabilities so as to increase the pressure of the fluid at the outlet of the hydraulic pump 10 and at the inlet of the controllable valve 17 and of the calibrated orifice 31.

[0159] Then, in step B, the drone 1 is waiting to take off. In this step B, the speed of the drive motor 11 of the hydraulic pump 10 remains constant. The rotation speed of the hydraulic motors 6 is then close to that necessary to ensure the takeoff of the drone 1.

[0160] In order to make the drone take off, which corresponds to step C, the speed of the drive motor 11 of the hydraulic pump 10 is further increased according to its torque capacities so as to increase the pressure of the fluid at the outlet of the hydraulic pump 10 until this pressure reaches a predefined limit value allowed by the pressure limiters 27, called a limited pressure p.sub.L.

[0161] Then, in step D, the speed of the drive motor 11 of the hydraulic pump 10 is further increased according to its torque capabilities so as to increase the pressure of the fluid at the outlet of the hydraulic pump 10 to a value higher than the limited pressure p.sub.L allowed by the pressure limiters 27. The pressure limiter 27 makes it possible to have the limited pressure p.sub.L at the inlet of the controllable valve 17 and of the bypass comprising the calibrated orifice 31. This limited pressure p.sub.L is transformed, through the calibrated orifice 31, into a constant idle flow rate which ensures a rotation speed of the hydraulic motors 6 sufficient to produce a thrust necessary for the lift of the drone 1.

[0162] During the next step E, the speed of the drive motor 11 of the hydraulic pump 10 is constant so that the fluid pressure at the outlet of the hydraulic pump 10 and at the inlet of the controllable valve 17 and the calibrated orifice 31 are constant. In this step F, the hydraulic pump 10 generates a pressure higher than the limited pressure p.sub.L allowed by the pressure limiter 27. Thus, the pressure of the fluid at the outlet of the hydraulic pump 10 is higher than the pressure at the inlet of the controllable valve 17 and of the calibrated orifice 31.

[0163] In this step E, the speed of the drive motor 11 of the hydraulic pump 10 associated with the necessary torque defines the nominal power needed for the drive motor 11. This nominal power is in a range typically defined around 1.6 times the power necessary to ensure the lift of the drone 1. Setting the nominal power of the drive motor 11 of the hydraulic pump 10 to this value ensures that the drive motor 11 meets the durability requirements without excessive fatigue, because the drive motor 11 will not exceed this nominal power, regardless of the operating mode of the drone. Moreover, this range makes it possible to ensure all the power variation needs of the hydraulic motors 6, whatever the flight conditions defined as acceptable for the drone 1, such as the speed of the wind gusts against which the drone 1 must be able to respond and remain stable.

[0164] In this step E, the control of the valves 17 via the flight controller 14 makes it possible to ensure the stability of the drone 1. The valves 17 make it possible to modulate the supply flow rate of the hydraulic motors 6, thus ensuring a modification of the rotation speed according to the need defined by the flight controller 14, in particular through control algorithms.

[0165] To descend, which corresponds to step F, the rotation speed of the hydraulic motors 6 is modulated by acting on the valves 17 and by decreasing the speed of the drive motor 11 of the hydraulic pump 10 to ensure the landing of the drone 1.

[0166] Lastly, in a step G, while the drone 1 is on the ground, the speed of the drive motor 11 of the hydraulic pump 10 is further reduced in order to ensure a gradual shutdown of the motors, and the valves 17 are deactivated.

[0167] Of course, the invention is not limited to the examples described above. For example, the pump may be driven by a heat engine.