Reversible hydraulic pump for adjusting propeller play angle and associated hydraulic system, turboprop and aircraft

Description

Technical field of the invention

[0001] The invention relates to hydraulic propeller pitch actuation systems fitted to turboprop engines, and more particularly to pumps delivering hydraulic pressure to activate such systems.

[0002] The invention further relates to a hydraulic system for propeller pitch setting equipped with such a pump, a turboprop equipped with such a hydraulic system and an aircraft comprising such a turboprop. State of the prior art

[0003] Typically, an aircraft equipped with turboprop engines, also known as turbofans, includes hydraulic propeller pitch actuation systems fitted to the turboprops. The propeller pitch is controlled by a propeller pitching device operated by a hydraulic cylinder.

[0004] The hydraulic cylinder and the rigging device rotate with the propeller.

[0005] Typically, a hydraulic pump is implemented in the fixed part of the turboprop and supplies the cylinder with pressurized oil via a rotating joint.

[0006] However, oil leaks from the rotating joint so it is necessary to collect the oil leaked from the rotating joint.

[0007] Oil recovery requires the addition of a recovery system in the turboprop engine, including oil recovery pumps and a reservoir.

[0008] Implementing such a system requires space in the turboprop and increases the turboprop's mass.

[0009] It is known to connect the hydraulic cylinder directly to the pump and to drive the hydraulic pump by an electric motor, the hydraulic pump and the electric motor being arranged in a rotating frame linked to the propeller.

[0010] Powering the electric motor requires the use of a rotating electrical transformer.

[0011] However, the rotor of the electric machine must be continuously driven at the propeller speed to prevent any variation in the pitch setting, leading to electrical power consumption and thermal oversizing of the electric machine.

[0012] In addition, the installation of the rotating electrical transformer increases the mass of the turboprop.

[0013] It is also known to arrange a non-reversible hydraulic pump in a rotating frame linked to the propeller and to arrange an electric motor in the fixed part of the turboprop to drive the hydraulic pump.

[0014] As the hydraulic pump is not reversible, it is necessary to add a piloted hydraulic valve between the pump and the cylinder to move the piston in and out of the cylinder.

[0015] However, adding a hydraulic valve requires providing space in the turbocharger positioned in the rotating reference and adding means of controlling the valve located in the fixed part.

[0016] Furthermore, a propeller pitch setting system is known comprising a hydraulic pump with axial pistons supplying a cylinder arranged in a rotating reference frame linked to the propeller of a turboprop.

[0017] The system has valves configured so that in the absence of rotation of a pump shaft, the pump does not deliver hydraulic fluid despite the pump body being driven at the speed of the propeller. The pump is driven by an electric motor.

[0018] However, the system does not allow for reversal of the pump flow when reversing the direction of rotation of the electric motor.

[0019] Document EP 2 674 622 discloses a reversible hydraulic pump providing flow in both directions of rotation of a pump shaft.

[0020] The pump has two axial piston pumps including out-of-phase inlet ports such that one axial piston pump delivers hydraulic fluid when the pump rotates in one direction, and the other axial piston pump delivers hydraulic fluid when the pump rotates in the other direction.

[0021] However, since both axial piston pumps are driven independently of the direction of rotation of the reversible hydraulic pump shaft, the axial piston pump that is not delivering hydraulic fluid cavitates, causing it to deteriorate.

[0022] Document DE102012218517 A1 discloses a reversible hydraulic pump for the hydraulic hybrid drive of a vehicle. Document FR2167697 A6 discloses a hydraulic force transmission device, comprising two axial piston machines with crowns connected to the barrels by clutches and meshed by a drive machine. Document FR2978953 A1 discloses a blade setting system with an axial pump and two separate cylinders to provide the hydraulic power for actuating the blades. The aim of the invention is to overcome all or part of these drawbacks. Statement of the invention

[0023] In view of the above, the subject of the invention is a reversible hydraulic pump for setting the propeller pitch of a turboprop comprising two barrels connected by a transmission shaft.

[0024] The first and second barrels are connected to the transmission shaft via first and second clutch means such that when the transmission shaft rotates in a first direction, only the first barrel is rotated by the transmission shaft, and such that when the transmission shaft rotates in a second direction opposite to the first direction, only the second barrel is rotated by the transmission shaft.

[0025] The clutch means allow only one of the barrels to be driven in the direction of rotation of the transmission shaft so that the other barrel is not driven, preventing it from being subject to cavitation phenomena.

[0026] Preferably, the first clutch means comprise a first freewheel connecting the first barrel to the transmission shaft when the transmission shaft rotates in the first direction and decouples the first barrel from the transmission shaft when the transmission shaft rotates in the second direction, and the second clutch means comprise a second freewheel connecting the second barrel to the transmission shaft when the transmission shaft rotates in the second direction and decouples the second barrel from the transmission shaft when the transmission shaft rotates in the first direction.

[0027] Clutch means made from freewheels are simple to make.

[0028] Advantageously, the pump further comprises two symmetrical and opposite slanted plates and two casings, the first casing housing the first plate and the first barrel, and the second casing housing the second plate and the second barrel, the first and second plates and the first and second casings being fixed relative to the transmission shaft, central axes of the plates and barrels being coaxial.

[0029] Preferably, the second housing further comprises an electric motor for driving the transmission shaft, the motor comprising a rotor formed on the transmission shaft and a stator secured to the second housing.

[0030] Advantageously, each barrel comprises bores and hollow cylinders sliding in the bores when said barrel is rotated, each hollow cylinder comprising a radial bore and a suction valve so that a hydraulic fluid flows into at least one hollow cylinder via the bore and the suction valve during a phase of suction of the fluid into said barrel by the hollow cylinder.

[0031] Preferably, each barrel comprises bores and hollow cylinders sliding in the bores when said barrel is rotated, each hollow cylinder comprising a radial bore, the stroke of the hollow cylinder in the bore associated with the hollow cylinder and the position of the radial bore in the hollow cylinder being chosen so that a hydraulic fluid flows into at least one hollow cylinder via the bore during a phase of suction of the fluid into said barrel by the hollow cylinder, and so that the bore of said cylinder is covered by the bore associated with said hollow cylinder during a phase of compression of the fluid in said barrel and a phase of discharge of the fluid out of said barrel by the hollow cylinder.

[0032] Advantageously, the pump comprises sliding shoes, the hollow cylinders of the first barrel bearing on the first plate by means of sliding shoes, and the hollow cylinders of the second barrel bearing on the second plate by means of sliding shoes, the pump further comprising a third cylindrical casing housing the first and second casings, and intended to contain the hydraulic fluid sucked during the suction phase, a central axis of the third casing and a central axis of each plate being coaxial, the third casing rotating around the first and second casings and comprising two distribution plates each located at the end of a different barrel opposite the end of said barrel opposite a plate, each cylindrical distribution plate comprising a concentric groove connected to a different outlet of the casing,each end of the hollow cylinder opposite the end of said hollow cylinder in contact with a sliding pad comprising a discharge valve so that during the discharge phase, pressurized hydraulic fluid compressed by the hollow cylinders of one of the first and second barrels escapes from the casing through one of the outlets of the casing connected to said barrel, the third casing further comprising an inlet intended to supply the casing with hydraulic fluid.,

[0033] There is also provided a hydraulic system for setting the propeller pitch of a turboprop comprising a reversible hydraulic pump as defined above, a double-acting hydraulic cylinder comprising two inlets each connected to a different chamber of the cylinder and configured to drive a mechanical device for setting the propeller pitch, each inlet of the cylinder being connected to a different outlet of the third casing via hydraulic fluid regulation means, and the inlet of the third casing being connected to the inlets of the cylinder via the regulation means, the regulation means being configured to connect a first outlet of the third casing to a first inlet of the cylinder and to connect the second inlet of the cylinder to the inlet of the third casing when pressurized hydraulic fluid flows through the first outlet,and being configured to connect the second outlet of the third housing to the second inlet of the cylinder and to connect the first inlet of the cylinder to the inlet of the third housing when pressurized hydraulic fluid flows through the second outlet.,

[0034] The regulation means are controlled by the pressure of the hydraulic fluid delivered by the pump so that they operate autonomously without interaction with a turboprop control device.

[0035] Also provided is a turboprop comprising a propulsion propeller connected to a mechanical propeller pitch setting device and a hydraulic system as defined previously, the cylinder being connected to the mechanical propeller pitch setting device.

[0036] Advantageously, the turboprop further comprises control means configured to control the electric motor according to a set value and the pitch angle of the propeller.

[0037] An aircraft comprising a turboprop engine as defined above is also proposed. Brief description of the drawings

[0038] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which: [ Fig 1 ] schematically illustrates an aircraft according to the invention; [ Fig 2 ] schematically illustrates a partial section of a turboprop according to the invention; [ Fig 3 ] schematically illustrates an example of a freewheel according to the invention; [ Fig 4 ] schematically illustrates an example of a hollow cylinder according to the invention; [ Fig 5 ] schematically illustrates another example of a hollow cylinder according to the invention, and [ Fig 6 ] schematically illustrates an example of regulation means according to the invention. Detailed description of at least one embodiment

[0039] We refer to the figure 1 which schematically illustrates an example of an aircraft 1 comprising turboprop engines 2.

[0040] Each turboprop 2 comprises a propeller 3 rotating around an axis A of the turboprop 2 and a hydraulic system 4 for setting the pitch of the propeller 3.

[0041] There figure 2 schematically illustrates a partial section of the turboprop 2 comprising the hydraulic system 4.

[0042] The turboprop 2 comprises a mechanical setting device 5 connected to the propeller 3 varying the pitch of the propeller 3, a sensor 6 for the angle of the pitch of the propeller 3, a propulsion shaft 7 connected to the mechanical device 5 and driving the propeller, and propulsion means 8 driving the propulsion shaft 7.

[0043] The propulsion means 8 comprise, for example, first toothed wheels cooperating with second toothed wheels of the propulsion shaft 7 forming a gearbox, and a turbine, the first toothed wheels being driven by the turbine.

[0044] The turboprop further comprises a fixed part 9 relative to the propulsion shaft 7.

[0045] Bearings 10 connect the propulsion shaft 7 to the fixed part 9.

[0046] The hydraulic system 4 comprises a double-acting hydraulic cylinder 11 actuating the mechanical device 5 to vary the pitch of the propeller 3, a reversible hydraulic pump 12 and regulation means 13.

[0047] The jack 11 is supplied by the pump 12 via the regulating means 13.

[0048] The jack 11 comprises a piston 14 connected to the mechanical device 5 and a cylinder 15 housing the piston 14.

[0049] The piston 14 and the cylinder 15 define two chambers 16, 17, a first chamber 16 comprising a first inlet 160 (not shown) connected to the regulation means 13, and the second chamber 17 comprising a second inlet 170 (not shown) connected to the regulation means 13.

[0050] The piston 14 is for example annular and surrounds the pump 12 so that the hydraulic system 4 is more compact requiring less space for the installation of said system in the propulsion shaft 7.

[0051] The reversible hydraulic pump 12 comprises two plates 18, 19 at symmetrical and opposite angles, and two barrels 20, 21 comprising bores 22, 23.

[0052] The two plates 18, 19 are connected to each other by a rod 25.

[0053] The pump 12 further comprises hollow cylinders 26 sliding in the bores 22, 23 of the barrels 20, 21.

[0054] The hollow cylinders 26 of a first barrel 20 bear on a first plate 18 by means of sliding pads 27, and the hollow cylinders 26 of the second barrel 21 bear on the second plate 19 by means of sliding pads 27.

[0055] The barrels 20, 21 are connected by a transmission shaft 28.

[0056] The transmission shaft 28 comprises, for example, a central recess in which the rod 25 is inserted.

[0057] The transmission shaft 28, a central axis of the plates 18, 19, and the axis A are coaxial.

[0058] The first 20 and second 21 barrels are connected to the transmission shaft 28 via first 29 and second 30 clutch means.

[0059] When the transmission shaft 28 rotates in a first direction of rotation, the first clutch means 29 are engaged so that the transmission shaft 28 drives the first barrel 20, and the second clutch means 30 are disengaged so that the transmission shaft 28 does not drive the second barrel 21.

[0060] When the transmission shaft 28 rotates in the second direction of rotation opposite to the first direction of rotation, the first clutch means 29 are disengaged so that the transmission shaft 28 does not drive the first barrel 20, and the second clutch means 30 are engaged so that the transmission shaft 28 drives the second barrel 21.

[0061] When a barrel 20, 21 is driven by a rotational movement, the hollow cylinders 26 of said barrel translate in the bores of said barrel so as to suck a hydraulic fluid into said barrel during a suction phase, compress the fluid in the barrel during a compression phase and discharge the compressed fluid outside the barrel during a discharge phase.

[0062] The first 29 clutch means comprise for example a first freewheel connecting the first barrel 20 to the transmission shaft 28 when the transmission shaft rotates in the first direction and decoupling the first barrel 20 from the transmission shaft 28 when the transmission shaft rotates in the second direction.

[0063] The second clutch means 30 comprise for example a second freewheel connecting the second barrel 21 to the transmission shaft 28 when the transmission shaft rotates in the second direction and uncoupling the first barrel from the transmission shaft when the transmission shaft rotates in the first direction.

[0064] Since the first and second freewheels are structurally identical, only the first freewheel is detailed.

[0065] There figure 3 illustrates an example of the first freewheel 31.

[0066] The first freewheel 31 comprises notches 32 made on the transmission shaft 28, a ring 33 inserted in the center of the first barrel 20 and pawls 34 cooperating with the notches 32.

[0067] When the transmission shaft 28 rotates in the first direction, the pawls 34 are engaged in the notches 32 so that the transmission shaft 28 drives the ring 33, and so that when the transmission shaft 28 rotates in the second direction, the pawls 34 are no longer engaged in the notches 32.

[0068] Referring to the figure 2 , the pump 12 further comprises a first casing 35 housing the first plate 18, the first barrel 20, and the hollow cylinders 26 and the associated sliding shoes 27.

[0069] The pump 12 comprises a second casing 36 housing the second plate 19, the second barrel 21, and the associated hollow cylinders 26 and sliding shoes 27.

[0070] The rod 25 further connects the first and second casings 35, 36 to each other.

[0071] The second casing 36 is fixed to the fixed part 9 so that the first and second plates 19, 20, and the first and second casings 35, 36 are fixed relative to the transmission shaft 26.

[0072] The first and second housings 35, 36 comprise bearings 37 supporting the transmission shaft 28.

[0073] The second housing 36 further comprises an electric motor 38 driving the transmission shaft 28.

[0074] The motor 38 comprises a rotor 39 formed on the transmission shaft 28 and a stator 40 secured to the second casing 36.

[0075] The pump 12 further comprises a third casing 41 housing the first and second casings 35, 36 comprising the plates 18, 19, the first and second barrels 20, 21, and the hollow cylinders 26.

[0076] The propulsion shaft 7 (“fan rotor”) is formed by the third casing 41 of the pump 12.

[0077] The third sealed casing 41 contains the hydraulic fluid sucked in during the suction phase.

[0078] The first and second housings 35, 36 are sized so that the hydraulic fluid flows to the barrels 20, 21.

[0079] A central axis of the third casing 41 and a central axis of each plate 18, 19 are coaxial.

[0080] The third casing 41 is integral with the device 5 so that it rotates at the speed of the propeller 3, and is connected to the first and second casings 35, 36 by bearings 42 and seals 43 to prevent the hydraulic fluid from escaping from the pump 12.

[0081] The rotational speed of the third casing 41 is decorrelated from the rotational speed of the transmission shaft 28.

[0082] The third casing 41 comprises two cylindrical distribution glasses 44, 45 each located at the end of a different barrel 20, 21 and opposite the end of said barrel opposite a plate 18, 19.

[0083] Each distribution window 44, 45 comprises a concentric groove 46, 47 connected to a different outlet 48, 49 of the third casing 41.

[0084] The first barrel 20 is connected to the first output 48 of the third casing 41 and the second barrel is connected to the second output 49 of the third casing 41.

[0085] The outputs 48, 49 of the third casing 41 are connected to the regulation means 13.

[0086] The pump 12 delivers, for example, the hydraulic fluid at a pressure of up to 350 bars, making it possible to reduce the volume of the cylinder 11 for a force developed by the cylinder 11 that is predetermined compared to lower hydraulic fluid supply pressures, requiring a larger cylinder to develop said predetermined force.

[0087] Hydraulic fluid includes, for example, oil.

[0088] Each end of the hollow cylinder 26 of the two barrels 20, 21 opposite the end of said hollow cylinder in contact with a sliding pad 27 comprises a discharge valve 50 so that during the discharge phase, pressurized hydraulic fluid compressed by the hollow cylinders 26 of one of the first 20 and second 21 barrels escapes from the third casing 41 through one of the outlets 48, 49 of the third casing 41 connected to said barrel, and so that fluid does not flow into the grooves 46, 47 during the suction and compression phases.

[0089] The third casing 41 further comprises an inlet 51 connected to the regulation means 13.

[0090] Each plate 18, 19 comprises a supply lunule so that the hydraulic fluid flows into the hollow cylinders 26 during the suction phase of the hydraulic fluid by the hollow cylinders and the bores associated with said hollow cylinders.

[0091] There figure 4 illustrates a second embodiment of the hollow cylinder 26.

[0092] The hollow cylinder 26 comprises a radial bore 52 and a suction valve 53 so that the hydraulic fluid flows into the hollow cylinder via the bore 52 and the suction valve 53 during the suction phase.

[0093] During the compression and discharge phases, the suction valve prevents hydraulic fluid from escaping into the third casing 41 through the bore 52.

[0094] According to a third embodiment ( Figure 5 ), the cylinder 26 comprises a radial bore 54.

[0095] In this embodiment, the stroke of the hollow cylinder 26 in the bore associated with said hollow cylinder and the position of the radial bore 54 in the hollow cylinder 26 are chosen so that the hydraulic fluid flows into the hollow cylinder 26 via the bore 54 during the suction phase, and so that the bore 46 is covered by the bore associated with said cylinder during the compression and discharge phases.

[0096] When implementing the second and third embodiments of the cylinder 26, the trays 18, 19 do not include feed lunules facilitating the production of the trays 18, 19.

[0097] Furthermore, the third embodiment of the cylinder 26 makes it possible to simplify the production of said hollow cylinder 26 compared to the second embodiment of the hollow cylinder 26 by eliminating the suction valve 53.

[0098] Referring again to the figure 2, the turboprop 2 comprises on the fixed part 9 control means 55 connected to the engine 38.

[0099] The control means 55 control the motor 38 from the angle measurement recorded by the sensor 6 and from a CONS instruction received for example from a controller of the aircraft 1, and are produced for example from a processing unit configured to control the motor 38 according to the angle value recorded by the sensor 6 and the CONS instruction.

[0100] The sensor 6 communicates with the control means 55, for example via a wireless link.

[0101] The control means 55 control the direction of rotation and the speed of rotation of the motor 38 so that the propeller pitch angle measured by the sensor 6 is equal to the angle setpoint CONS.

[0102] Depending on the direction of rotation of the motor 38, the transmission shaft 28 drives the first 20 or the second 21 barrel generating a pressurized fluid supplying the first 16 or the second 17 chamber of the cylinder 11.

[0103] The cylinder 11 actuates the device 5.

[0104] If the motor 38 does not drive the transmission shaft 28 in rotation, neither of the first nor second barrels compresses hydraulic fluid so that the cylinder 11 is not supplied with fluid.

[0105] There figure 6 illustrates an example of embodiment of the regulation means 13.

[0106] The regulating means 13 comprise a first inlet 56 connected to the first inlet 48 of the third casing 41, a second inlet 57 connected to the second inlet 49 of the third casing 41, and a third inlet 58 connected to the outlet 51 of the third casing 41.

[0107] The regulating means 13 further comprise a first output 59 connected to the first input 160 of the jack 11 and a second output 60 connected to the second input 170 of the jack 11.

[0108] The regulating means comprise two hydraulic distributors 61, 62 of the two-position, three-port “3 / 2” type, a non-return valve 63 and a hydraulic accumulator 64.

[0109] The first distributor 61 comprises an inlet 65 connected to the first inlet 56 of the regulating means 13, a first outlet 66 connected to the third inlet 58 of the regulating means 13, a second outlet 67 connected to the first outlet 59 of the regulating means 13, a control inlet 68 connected to the first inlet 65 of said distributor 61 and cooperating with a return spring 69 of said distributor 61 to control the position of the distributor.

[0110] In a first position of the first distributor 61, when the first barrel 20 is rotated and supplies fluid to the inlet 65 of said distributor 61, the control inlet 68 supplied with fluid cooperates with the return spring 69 so that the inlet 65 supplies the second outlet 67 of the distributor 61 to supply the first chamber 16 of the jack 11, the first outlet 66 being blocked.

[0111] In a second position of the first distributor 61, when the first barrel 20 is not rotated, no fluid flows through the inlet 50 so that the control inlet 68 is not supplied with fluid. In this position, the inlet 65 is blocked and the first and second outlets 66, 67 are connected to each other.

[0112] The second distributor 70 comprises an inlet 71 connected to the second inlet 57 of the regulating means 13, a first outlet 72 connected to the third inlet 58 of the regulating means 13, a second outlet 73 connected to the second outlet 60 of the regulating means 13, a control inlet 74 connected to the first inlet 71 of said distributor 70 and cooperating with a return spring 75 of said distributor 70 to control the position of the distributor.

[0113] In a first position of the second distributor 70, when the second barrel 21 is not rotated, no fluid flows through the inlet 71 so that the control inlet 74 is not supplied with fluid. In this position, the inlet 71 is blocked and the first and second outlets 72, 73 are connected to each other.

[0114] In a second position, when the second barrel 21 is rotated and supplies fluid to the inlet 71 of said distributor 70, the control inlet 74 supplied with fluid cooperates with the return spring 75 so that the inlet 71 supplies the second outlet 73 of the distributor 70 to supply the second chamber 17 of the jack 11, the first outlet 72 being blocked.

[0115] The regulating means 13 make it possible to supply one or other of the chambers 16, 17 of the jack 11 according to the barrel 20, 21 driven in rotation.

[0116] The hydraulic fluid contained in the chamber of the cylinder 11 which is not supplied is discharged through the inlet 51 into the third casing 41.

[0117] The regulating means 13 are controlled by the pressure of the hydraulic fluid delivered by the pump 12 so that it is not necessary to implement in the rotating part (propulsion shaft 7) control members requiring to be connected to pilot members arranged in the fixed part of the turboprop such as a computer.

[0118] Since the cylinder 11, the third casing 41 of the pump 12 and the regulating means 13 of the hydraulic system 4 forming a closed circuit rotate at the rotation speed of the propeller 3, the system does not require the implementation of a hydraulic rotating joint.

[0119] In addition, the closed circuit is independent of a turboprop lubrication circuit so that it operates independently of the other hydraulic components of the aircraft, minimizing the risks of failure of said systems when the other hydraulic components of the aircraft fail.

[0120] Furthermore, since the pump 12 is driven in rotation by the electric motor 38 located on the fixed part of the turboprop, the system does not require an electric rotating joint.

[0121] Furthermore, since the rotational speed of the third casing is decorrelated from the rotational speed of the transmission shaft 28, the electric motor 38 rotates at a lower rotational speed than that of the propeller 3 so that it consumes less electrical energy, improving the energy efficiency of the system 4.

[0122] The clutch means 29, 30 drive only one of the barrels in the direction of rotation of the transmission shaft 28 so that the other barrel is not driven, preventing it from being subjected to cavitation phenomena.

[0123] In addition, the clutch means 29, 30 made from freewheels are simple to produce.

[0124] The accumulator 64 is connected to one end of the valve 63, the other end of the valve being connected to the third inlet 58 of the regulating means 13.

[0125] Accumulator 64 is sized to form a low pressure reference for the closed hydraulic circuit.

[0126] The accumulator 64 cooperates with the valve 63 so as to compensate for leaks in the closed circuit and absorb temperature variations in the closed circuit.

Claims

1. A reversible hydraulic pump (12) for setting the pitch of a propeller (3) of a turboprop (2) comprising two barrels (20, 21) connected by a transmission shaft (28), characterised in that the first and second barrels (20, 21) are connected to the transmission shaft (28) via first and second clutch means (29, 30) so that, when the transmission shaft rotates in a first direction, only the first barrel is rotatably driven by the transmission shaft, and so that, when the transmission shaft rotates in a second direction opposite to the first direction, only the second barrel is rotatably driven by the transmission shaft.

2. The pump according to claim 1, wherein the first clutch means (29) comprise a first flywheel (31) connecting the first barrel (20) to the transmission shaft (28) when the transmission shaft rotates in the first direction and uncouples the first barrel from the transmission shaft when the transmission shaft rotates in the second direction, and the second clutch means (30) comprise a second flywheel connecting the second barrel (21) to the transmission shaft when the transmission shaft rotates in the second direction and uncouples the second barrel from the transmission shaft when the transmission shaft rotates in the first direction.

3. The pump according to one of claims 1 and 2, further comprising two symmetrical and opposite angled plates (18, 19), and two casings (35, 36), the first casing accommodating the first plate and the first barrel, and the second casing accommodating the second plate and the second barrel, the first and second plates and the first and second casings being fixed with respect to the transmission shaft, central axes of the plates and of the barrels being coaxial with each other.

4. The hydraulic pump according to claim 3, wherein the second casing further comprises an electric motor (38) to drive the transmission shaft (28), the motor including a rotor (39) formed on the transmission shaft and a stator (40) integral with the second casing.

5. The pump according to any one of claims 1 to 4, wherein each barrel comprises bores (22, 23) and hollow cylinders (26) sliding in the bores when said barrel is rotationally moving, each hollow cylinder (26) including a radial aperture (52) and a suction valve (53) so that a hydraulic fluid flows into at least one hollow cylinder via the aperture and the suction valve during a phase of sucking the fluid into said barrel by the hollow cylinder.

6. The pump according to any one of claims 1 to 4, wherein each barrel comprises bores (22, 23) and hollow cylinders (26) sliding in the bores when said barrel is rotationally moving, each hollow cylinder (26) comprising a radial aperture (54), the stroke of the hollow cylinder in the bore (22) associated with the hollow cylinder and the position of the radial aperture in the hollow cylinder being selected so that a hydraulic fluid flows into at least one hollow cylinder via the aperture during a phase of sucking the fluid into said barrel by the hollow cylinder, and so that the aperture of said cylinder is covered by the bore associated with said hollow cylinder during a phase of compressing the fluid into said barrel and a phase of discharging the fluid out of said barrel by the hollow cylinder.

7. The pump according to one of claims 5 and 6, comprising sliding pads (27), the hollow cylinders of the first barrel (20) bearing on the first plate (18) via sliding pads (27), and the hollow cylinders of the second barrel (21) bearing on the second plate (19) via the sliding pads (27), the pump further comprising a third cylindrical casing (41) accommodating the first and second casings (35, 36), and intended to contain the hydraulic fluid sucked in during the suction phase, a central axis of the third casing and a central axis of each plate being coaxial with each other, the third casing rotating about the first and second casings and comprising two port plates (44, 45) each located at the end of a different barrel opposite to the end of said barrel facing a plate (18, 19), each cylindrical port plate comprising a concentric groove (46, 47) connected to a different outlet (48, 49) of the casing, each end of the hollow cylinder opposite to the end of said hollow cylinder in contact with a sliding pad (27) comprising a discharge valve (50) so that, during the discharge phase, pressurised hydraulic fluid compressed by the hollow cylinders of one among the first and second barrels escapes from the casing via one of the outlets of the casing connected to said barrel, the third casing further comprising an inlet (51) intended to supply the casing with hydraulic fluid.

8. A hydraulic system (4) for setting the pitch of a propeller (3) of a turboprop (2) comprising a reversible hydraulic pump (12) according to claim 7, a double-acting hydraulic ram (11) including two inlets (160, 170) each connected to a different chamber (16, 17) of the ram and configured to drive a mechanical propeller pitch setting device (5), each inlet of the ram being connected to a different outlet (48, 49) of the third casing (41) via hydraulic fluid regulation means (13), and the inlet (51) of the third casing (41) being connected to the inlets of the ram via the regulation means, the regulation means being configured to connect a first outlet (48) of the third casing (41) to a first inlet (160) of the ram and to connect the second inlet (170) of the ram to the inlet (51) of the third casing (41) when pressurised hydraulic fluid flows through the first outlet (48), and being configured to connect the second outlet (49) of the third casing (41) to the second inlet (170) of the ram and to connect the first inlet (160) of the ram to the inlet (51) of the third casing (41) when pressurised hydraulic fluid flows through the second outlet.

9. A turboprop (2) comprising a propulsion propeller (3) connected to a mechanical propeller pitch setting device (5) and a hydraulic system (4) according to claim 8, the ram being connected to the mechanical propeller pitch setting device.

10. The turboprop according to claim 9, further comprising control means (55) configured to control the electric motor according to a setpoint value (CONS) and the pitch angle of the propeller.

11. An aircraft (1) including a turboprop (2) according to claim 9 or 10.