Electromechanical actuator with stator teeth dimensioned to operate a saturation bend for electrical flight controls of an aircraft

Abstract

An electromechanical actuator for electrical flight controls of an aircraft, the actuator comprising a transmission shaft, four electromechanical conversion members, each having a respective stator and rotor secured to the transmission shaft, and four control systems, each dedicated to respective ones of the electromechanical conversion members. The stator has teeth and windings surrounding at least one tooth, whereas the rotor is provided with permanent magnets. Each electromechanical conversion member is a flux-concentrating member and each winding is concentric and has a single layer. The electromechanical actuator is intended in particularly for controlling a hydraulic actuator via a mechanical transmission within an electrical flight control device of an aircraft.

Claims

1. An electromechanical actuator for electrical flight controls of an aircraft, the electromechanical actuator comprising: a transmission shaft having an axis of rotation; at least three electromechanical conversion members, each respectively provided with a stator and a rotor secured to the transmission shaft and rotatable about the axis of rotation, the stator being provided with teeth and windings, each winding surrounding at least one tooth, the rotor being provided with permanent magnets each having a north magnetic pole and a south magnetic pole; and at least three control systems, each control system powering and controlling a respective electromechanical conversion member with one of the control systems being connected to a single electromechanical conversion member and powering the single electromechanical conversion member with AC; wherein the teeth are dimensioned so that each electromechanical conversion member operates at a saturation bend in a curve plotting variation of a magnetic induction of a ferromagnetic material constituting the teeth, thus enabling at least two of the electromechanical conversion members to mitigate a short-circuit type failure of another electromechanical conversion member, with one of the two electromechanical conversion members compensating a majority of the short-circuit torque coming from a failed electromechanical conversion member, while the other of the two electromechanical conversion members delivers the nominal torque needed to operate the electromechanical actuator.

2. The electromechanical actuator according to claim 1, wherein, when each stator is provided with a stator yoke and each stator yoke is made up of a stack of laminations, the width .sub.d of the teeth and the height h.sub.cs of the stator yoke are defined by the following formulas: $l_d=\frac{B_g.Math.T_d}{B_{\max }.Math.K_{\mathrm{fe}}}\mathrm{and}{h}_{cs}=\frac{{\Phi }_g}{B_{\max }.Math.L_{st}.Math.N_{st}}$ where T.sub.d is the axial length of a tooth, B.sub.g is the airgap induction in nominal operation, K.sub.fe is a swelling coefficient, B.sub.max is a maximum value of the induction, □.sub.g is an airgap flux at a pole in nominal operation, L.sub.st is an axial length of an electromechanical conversion member, and K.sub.st is a stacking factor.

3. The electromechanical actuator according to claim 1, wherein each winding is a single-layer winding, the teeth adjacent to a tooth surrounded by the winding not being surrounded by a respective winding.

4. The electromechanical actuator according to claim 1, wherein each electromechanical conversion member is a magnetic flux-concentrating member.

5. The electromechanical actuator according to claim 1, wherein each control system powers an electromechanical conversion member with polyphase AC, and each winding is concentric, each tooth being surrounded by the winding in which there flows a single phase of the polyphase AC.

6. The electromechanical actuator according to claim 1, wherein at least two electromechanical conversion members have a rotor in common, the common rotor co-operating with the stators of the at least two electromechanical conversion members.

7. The electromechanical actuator according to claim 1, wherein the magnetic poles are of sinusoidal shape so that a sinusoidal magnetic flux flows in each electromechanical conversion member.

8. The electromechanical actuator according to claim 1, wherein a first total number N.sub.p of pairs of magnetic poles and a second total number N.sub.d of the teeth are such that:
(4n−3).Math.N.sub.p<N.sub.d<(4n−1).Math.N.sub.p where n is a positive integer.

9. The electromechanical actuator according to claim 1, wherein each control system powers one of the electromechanical conversion members with three-phase AC, and two electromechanical conversion members have a rotor in common, the common rotor co-operating with stators of the electromechanical conversion members the stators of the two electromechanical conversion members being assembled so as to co-operate with the common rotor to constitute a six-phase architecture.

10. The electromechanical actuator according to claim 9, wherein the stators co-operating with the common rotor are magnetically isolated from each other by non-magnetic radial separation.

11. The electromechanical actuator according to claim 1, wherein each stator is separated from the rotor by an airgap greater than 1 mm.

12. The electromechanical actuator according to claim 11, wherein the airgap lies in a range from 1 mm to 2 mm.

13. An electrical flight control device comprising: at least one electromechanical actuator; at least one hydraulic actuator; and at least one mechanical transmission, each mechanical transmission enabling the electromechanical actuator to control a hydraulic actuator; wherein each electromechanical actuator is an actuator according to claim 1.

14. The electrical flight control device according to claim 13, wherein each mechanical transmission does not have a speed reduction member.

15. The electrical flight control device according to claim 13, wherein each mechanical transmission system is a linkage comprising a connecting rod and a crank.

16. An electromechanical actuator for electrical flight controls of an aircraft, the electromechanical actuator comprising: a transmission shaft having an axis of rotation; at least three electromechanical conversion members, each respectively provided with a stator and a rotor secured to the transmission shaft and rotatable about the axis of rotation, the stator having teeth and windings, each winding surrounding at least one tooth, the rotor having permanent magnets each having a north magnetic pole and a south magnetic pole; pole; and at least three control systems, each of the control systems powering and controlling a respective electromechanical conversion member with one of the control systems being connected to a single electromechanical conversion member and powering the single electromechanical conversion member with AC; wherein the teeth are dimensioned so that each electromechanical conversion member operates at the saturation bend in a curve plotting variation of a magnetic induction of a ferromagnetic material constituting the teeth, thus enabling at least two of the electromechanical conversion members to mitigate a short-circuit type failure of another electromechanical conversion member, with one of the two electromechanical conversion members compensating the majority of the short-circuit torque coming from a failed electromechanical conversion member, while the other of the two electromechanical conversion members delivers the nominal torque needed to operate the electromechanical actuator; and wherein, each stator is provided with a stator yoke and each stator yoke is made up of a stack of laminations, wherein the permanent magnets are arranged in such a manner as to provide flux concentration in the airgap, thereby maximizing the torque of the electromechanical conversion member.

17. The electromechanical actuator according to claim 16, the width .sub.d of the teeth and the height h.sub.cs of the stator yoke are defined by the following formulas: $l_d=\frac{B_g.Math.T_d}{B_{\max }.Math.K_{\mathrm{fe}}}\mathrm{and}{h}_{cs}=\frac{{\Phi }_g}{B_{\max }.Math.L_{st}.Math.K_{st}}$ where T.sub.d is the axial length of a tooth, B.sub.g is the airgap induction in nominal operation, K.sub.fe is a swelling coefficient, B.sub.max is a maximum value of the induction, □.sub.g is an airgap flux at a pole in nominal operation, L.sub.st is an axial length of an electromechanical conversion member, and K.sub.st is a stacking factor.

18. The electromechanical actuator according to claim 16, wherein each electromechanical conversion member is a magnetic flux-concentrating member and wherein each control system powers an electromechanical conversion member with polyphase AC, and each winding is concentric, each tooth being surrounded by the winding in which there flows a single phase of the polyphase AC.

19. The electromechanical actuator according to claim 16, wherein each control system powers one of the electromechanical conversion members with three-phase AC, and two electromechanical conversion members have a rotor in common, the common rotor co-operating with stators of the electromechanical conversion members the stators of the two electromechanical conversion members being assembled so as to co-operate with the common rotor to constitute a six-phase architecture.

20. The electromechanical actuator according to claim 16, wherein a first total number N.sub.p of pairs of magnetic poles and a second total number N.sub.d of the teeth are such that:
(4n−3).Math.N.sub.p<N.sub.d<(4n−1).Math.N.sub.p where n is a positive integer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and its advantages appear in greater detail from the context of the following description of embodiments given by way of illustration and with Reference to the accompanying figures, in which:

(2) FIG. 1 shows an electrical flight control device for an aircraft;

(3) FIG. 2 shows a first embodiment of electromechanical conversion members of an electromechanical actuator of the invention;

(4) FIG. 3 is a fragmentary view of an electromechanical conversion member;

(5) FIGS. 4 and 5 show a second embodiment of an electromechanical conversion member; and

(6) FIG. 6 plots curves showing variation in the magnetic induction in a ferromagnetic material as a function of its coercive magnetic field.

(7) Elements present in more than one of the figures are given the same references in each of them.

DETAILED DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows an electrical flight control device 50 for aircraft enabling each control axis of the aircraft to be controlled. Such an electric flight control device 50 is intended in particular for controlling variations in the collective and cyclic pitches of the blades of a main rotor of a rotary wing aircraft, and also variations in particular in the collective pitch of the blades of its anti-torque rotor.

(9) The electrical flight control device 50 comprises an electromechanical actuator 1, a hydraulic actuator 4, and a mechanical transmission 30. The mechanical transmission 30 is a linkage comprising a connecting rod 31 and a crank 32 that serves to transmit movements of the electromechanical actuator 1 to an input lever of the hydraulic actuator 4, the input lever being secured to the crank 32.

(10) Each electromechanical actuator 1 receives an electrical control order coming from a flight control device 7 of the aircraft and transforms it into a mechanical control order of low power that is transmitted via the mechanical transmission 30 to the hydraulic actuator 4. The hydraulic actuator 4 can then act via the movements of its rod 9 to deliver a mechanical control order of high power to a control axis of the aircraft.

(11) Each electromechanical actuator 1 has four electromechanical conversion members 5 and four control systems 6, each control system 6 controlling the electrical power supply and the operation of a respective electromechanical conversion member 5. Thus, redundancy both in terms of the control system 6 and of the electromechanical conversion member 5 serves to mitigate any type of failure that might affect the electromechanical actuator 1, thereby guaranteeing reliable operation for the electromechanical actuator 1.

(12) Each control system 6 has a processor device 41 for processing electrical control orders from the flight control device 7, an electronic control and monitoring device 42 for controlling and monitoring the electromechanical conversion member 5, an electronic power device 44, sensors 45, 46, and 47, and an electrical power supply conditioning stage 43. Furthermore, the electromechanical actuator 1 is connected to an electrical power supply device 8 that delivers DC. The electronic power device 44 serves to transform the DC into a three-phase AC voltage. Nevertheless, the electronic power device 44 could equally well be a purely resistive lowpass circuit, e.g. filtering out high frequencies, with the electrical power supply device 8 delivering a three-phase AC voltage directly.

(13) FIG. 2 shows a first embodiment of the four electromechanical conversion members 5 of the electromechanical actuator 1. The electromechanical conversion members 5 share an axis of rotation 2 and a transmission shaft 3 in common. Furthermore, each electromechanical conversion member 5 has a stator 10 and a rotor 20, the rotor 20 rotating about the axis of rotation 2 inside the stator 10.

(14) FIG. 3 is a fragmentary view of an electromechanical conversion member 5.

(15) The rotor 20 secured to the transmission shaft 3 has permanent magnets 23 with north poles facing each other in pairs and south poles facing each other in pairs. This particular arrangement of the permanent magnets 23 characterizes a flux-concentrating rotor 20. A north magnetic pole 24 thus appears between two magnets 23 having their north poles facing each other. Likewise, a south magnetic pole 25 thus appears between two magnets 23 having their south poles facing each other.

(16) The stator 10 has teeth 14, a stator yoke 18, and windings 12. Every other tooth 14 is surrounded by a winding 12, characteristic of a single-layer winding. Thus, each wound tooth 14 lies between two teeth without windings.

(17) The teeth 14, the stator yoke 18, and the magnetic poles 24, 25 are made of ferromagnetic material, e.g. stacked laminations of iron-silicon alloy.

(18) Furthermore, the magnetic poles 24, 25 of the rotor 20 project and are of substantially sinusoidal shape where they face the teeth 14 of the stator 10. The electromechanical conversion members 5 are thus sinusoidal magnetic flux members. The airgap of each electromechanical conversion member 5 is thus variable between a tooth 14 of a stator 10 and a magnetic pole 24, 25 of a rotor 20. By way of example, this airgap varies between a minimum value e equal to 1 mm, and a maximum value e′, equal to 2 mm. This large airgap serves advantageously to guarantee reliable operation of the electromechanical actuator 1 by reducing, or even eliminating, any risk of any of the electromechanical conversion members 5 jamming as a result of a foreign body appearing in the airgap.

(19) Furthermore, depending on the magnetic characteristics of the ferromagnetic material constituting the teeth 14, the teeth 14 of the stator 10 are of dimensions such that each electromechanical conversion member 5 operates close to its saturation limit.

(20) A curve plotting variation of the magnetic induction of a ferromagnetic material as a function of its coercive magnetic field is shown in FIG. 6. The magnetic induction of the ferromagnetic material, generally referenced “B” and expressed in teslas (T) is plotted up the ordinate axis while the coercive magnetic field, generally referenced “H(B)” is expressed in amps per meter (A/m), and is plotted along the abscissa axis.

(21) This curve is specific for each material and has three distinct characteristics characterizing three different behaviors of the material.

(22) A linear first portion A corresponds to the usual utilization zone for a ferromagnetic material in an electromechanical conversion member 5. This linear first portion A is a straight line of gradient equal to the magnetic permeability of the ferromagnetic material.

(23) A bend second portion B corresponds to the beginning of the material saturating. This end second portion B constitutes a saturation bend of the ferromagnetic material.

(24) A linear third portion C corresponds to a zone in which the ferromagnetic material is totally saturated. This linear third portion C is a straight line of gradient equal to the magnetic permeability of air. The slope of this linear third portion C is thus identical regardless of the ferromagnetic material. This linear third portion C does not constitute a nominal operating zone for an electromechanical conversion member. Nevertheless, after a failure of short-circuit type in an electromechanical conversion member, the material becomes magnetically saturated and the flux flowing through the material is determined by this linear third portion C.

(25) Advantageously, each electromechanical conversion member 5 operates close to or at the saturation bend B of this curve plotting variation in magnetic induction, and there is only a small increase in the magnetic flux consequently in the torque of the electromechanical conversion member 5 in the event of a short-circuit type failure. As a result, from among the four electromechanical conversion members 5 of the electromechanical actuator 1, one electromechanical conversion member 5 is capable of compensating for the short-circuit torque that appears from an electromechanical conversion member 5 that has suffered a short-circuit type failure. Consequently, two other electromechanical conversion members 5 remain available for delivering the torque needed to operate the electromechanical actuator 1.

(26) Furthermore, the short-circuit torque disappears as soon as the power supply to the electromechanical conversion member 5 that has suffered this failure is interrupted by the corresponding control system 6, once the failure has been detected.

(27) The dimensions of the teeth 14 are thus defined so that depending the magnetic characteristics of the ferromagnetic material constituting the teeth 14, each electromechanical conversion member 5 operates close to the saturation bend B, or indeed in the saturation bend B. When the teeth 14 and the stator yoke 18 are made as a stack of laminations, the width .sub.d of the teeth 14 and the height h.sub.cs of the stator yoke 18 are defined respectively by the following formulas:

(28) $l_d=\frac{B_g.Math.T_d}{B_{\max }.Math.K_{\mathrm{fe}}}\mathrm{and}{h}_{cs}=\frac{{\Phi }_g}{B_{\max }.Math.L_{st}.Math.K_{st}};$
where T.sub.d is the axial length of a tooth expressed in meters (m), B.sub.g is the airgap induction in nominal operation expressed in teslas (T), K.sub.fe is the swelling coefficient, B.sub.max is the maximum value of this induction expressed in teslas, Φ.sub.g is the airgap flux at a rotor pole in nominal operation expressed in webers (Wb), L.sub.st is the axial length of the electromechanical conversion member expressed in meters, and K.sub.st is a staking factor.

(29) Finally, the first total number N.sub.p of pairs of magnetic poles 24, 25 of the rotor 20 and the second total number N.sub.d of the teeth 14 of the stator 10 of an electromechanical conversion member 5 satisfy the following formula:
(4n−3).Math.N.sub.p<N.sub.d<(4n−1).Math.N.sub.p
where n is a positive integer. This formula corresponds in particular to an electromechanical conversion member of the brushless motor type having permanent magnets with flux concentration and a single-layer winding with three-phase AC.

(30) A second embodiment of four electromechanical conversion members 5 of the electromechanical actuator 1 is shown in FIGS. 4 and 5. The four electromechanical conversion members 5 are assembled in pairs and each pair of electromechanical conversion members 5a, 5b has a rotor 20 in common. Furthermore, in order to obtain balanced operation, each electromechanical conversion member 5a, 5b has a stator 10a, 10b in two portions, these two portions being diametrically opposite, as shown in FIG. 5.

(31) The common rotor 20 thus co-operates simultaneously with both stators 10a, 10b included respectively in the two electromechanical conversion members 5a, 5b.

(32) Furthermore, with each control system 6 powering an electromechanical conversion member 5 with three-phase AC, each pair of electromechanical conversion members 5a, 5b co-operates with the common rotor 20 to constitute a six-phase architecture made up by assembling two three-phase electromechanical conversion members 5a and 5b.

(33) This six-phase architecture is designed for the purpose of maintaining magnetic equilibrium. It can then be controlled by a conventional three-phase system, such as for example by using pulse width modulation (PWM), which control may be operated by automatic control of stator currents in the Park plane.

(34) In addition, non-magnetic radial separators 11 serve to provide magnetic isolation between the two stators 10a and 10b of this six-phase architecture. These non-magnetic radial separators 11 thus serve to avoid magnetic leaks appearing between the stators 10a and 10b, and also to avoid any other mutual magnetic disturbance.

(35) Naturally, the present invention may be subjected to numerous variants as to its implementation. Although several embodiments are described, it will readily be understood that it is not conceivable to identify exhaustively all possible embodiments. It is naturally possible to envisage replacing any of the means described by equivalent means without going beyond the ambit of the present invention.