METHOD FOR STOPPING A PERMANENT MAGNET ELECTRIC GENERATOR BY DEMAGNETIZATION

Abstract

This method of implementing the stopping of an electric generator which has a rotor and permanent magnets adapted to be able to provide an electromotive force, this generator comprising superheating elements adapted to be able to raise the temperature of the permanent magnets to demagnetize them, said superheating elements comprising a heating mat in contact with the permanent magnets and a controller configured to be able to detect a short circuit of the electric generator and to be able to trigger the superheating means. Figure for the abstract: [Fig 3]

Description

Title of the invention: METHOD FOR STOPPING AN ELECTRIC GENERATOR WITH PERMANENT MAGNETS BY DEMAGNETIZATION Technical field

[0001] The present invention relates to methods for stopping permanent magnet electric generators in an aircraft.

[0002] The present invention aims to constitute a permanent magnet generator and a method implemented allowing a stop by demagnetization of the magnets. Prior techniques

[0003] In the context of hybrid aircraft engines, it is known to install electric generators on the high pressure and / or low pressure shafts.

[0004] If these generators have permanent magnets, these generate an electromotive force as long as the generator turns.

[0005] Thus, in the event of a short circuit, unlike electromagnet machines, it is not possible to simply cut the inductor current to stop the electric generator.

[0006] A problem which therefore arises is that in the event of a short circuit, the current generated by the electromotive force causes heating which can lead to ignition which could destroy the motor.

[0007] Currently, a solution of mechanically disconnecting the machine from the generator shaft is preferred, so that it stops rotating and therefore generating an electromotive force. Statement of the invention

[0008] The invention aims to propose an alternative to existing solutions, capable of combining advantages of speed, efficiency and reliability for its implementation.

[0009] In view of the above, the subject of the invention is an electric generator for an aircraft hybrid engine which has permanent magnets adapted to be able to provide an electromotive force, the machine comprising superheating elements adapted to be able to raise the temperature of the permanent magnets to demagnetize them, said superheating elements comprising a controller configured to be able to detect a short circuit of the electric generator and to be able to trigger the superheating means.

[0010] Preferably the superheating elements comprise a heating mat, which is for example of the resistive type or of the chemical type.

[0011] The invention also relates to a method for stopping a generator. permanent magnet electric motor of a machine as defined above, the method comprising the following steps:

[0012] - the detection of a short circuit in said electric magnet generator permanent,

[0013] - the detection of an increase in the temperature of the electric generator beyond of a predefined threshold,

[0014] - the triggering of an overheating, by which the controller triggers the means overheating.

[0015] In one embodiment, the electric generator is mounted along a longitudinal axis on a hoop in a housing, and when overheating occurs, the controller triggers the supply of electrical power to the overheating elements on the magnets until they are demagnetized and the hoop is damaged.

[0016] For example, friction heating is also carried out, whereby the permanent magnets are heated by dropping a mechanical part onto the rotor of the electric generator.

[0017] Advantageously, when overheating occurs, the permanent magnets are heated using the overheating means until said permanent magnets exceed their Curie temperature beyond which they irreversibly lose their ferromagnetic properties.

[0018] The method may further provide that the machine comprises means for cooling the electric generator, and that these cooling means are inhibited.

[0019] Preferably, when overheating occurs, a suitable additional electrical source is used to heat the generator.

[0020] The invention also relates to a method in which a generator is used having a first and a second stator which share a common rotor, and when a fault is detected in the electrical supply of the first rotor, the electrical supply of the second rotor is controlled at its maximum power beyond its normal operating conditions so as to generate overheating of the permanent magnets of the generator when overheating is triggered. Brief description of the drawings

[0021] The invention will be better understood from a detailed study of the embodiment taken as a non-limiting example and illustrated by the appended drawings, in which:

[0022] [Fig.l] represents a permanent magnet generator according to the invention, in side view.

[0023] [Fig.2] represents the generator of [Fig.l] in sectional view.

[0024] [Fig.3] represents the method of stopping the generator of Figures 1 and 2 according to a first mode.

[0025] [Fig.4] represents the method of stopping the generator of Figures 1 and 2 according to a second mode. Detailed description

[0026] Figures 1 and 2 illustrate the generator 1 of the invention.

[0027] The electric generator is for example included in a hybrid aircraft engine.

[0028] The electric generator 1 comprises a rotor 2 mounted along a longitudinal axis X on a holding hoop 3 in a casing 4 serving as a stator for said generator 1.

[0029] It has permanent magnets 5 adapted to provide an electromotive force depending on their rotational speed.

[0030] The generator 1 further comprises superheating elements adapted to raise the temperature of the permanent magnets 5.

[0031] Overheating allows the permanent magnets 5 to be demagnetized.

[0032] The superheating elements may comprise a heating mat 6 in contact with the permanent magnets 5.

[0033] The heating mat 6 is connected to a controller 8 which controls it.

[0034] For example, the heating mat 6 is of the resistive type, that is to say that it heats by Joule effect depending on the electrical power which supplies it, in particular with the aid of resistors, for example in the form of a mesh of resistors.

[0035] Alternatively, the heating mat 6 is of the chemical type, that is to say that it comprises chemical components capable of forming an exothermic chemical reaction capable of heating the permanent magnets 5, and the triggering of the reaction of which is controlled by the controller 8.

[0036] The controller 8 is configured to be able to detect a short circuit of the generator 1 and to be able to trigger the overheating means according to a trigger request that it receives from an external system, for example by a control means 9.

[0037] The control means is for example chosen from: a “FADEC” type engine calculator (for the Anglicism “Full Authority Digital Engine Control”) for engine control, a calculator for management and distribution of electrical power, or even power electronics associated with the generator.

[0038] These computers can be connected to the generator either by an analog link 7 (a control current for example), or by a digital link (a communication bus for example).

[0039] [Fig. 3] describes a method according to a first mode for stopping an electric generator 1 with permanent magnets 5 as defined above.

[0040] The method comprises a step E1 of detecting a short circuit in said ge- neratrix 1.

[0041] Step E1 consists of detecting a short circuit via electrical measurements at the output of generator 1, making it possible, for example, to detect currents that deviate from the expected values ​​at a given operating point.

[0042] The method comprises a step E2 of detecting an increase in a temperature of the generator 1 beyond a predefined threshold.

[0043] Thus, step E2 consists of detecting the consequence on generator 1 of the short circuit detected during step EL

[0044] In the event of a temperature rise at the generator 1 beyond the predefined threshold, the risk of fire is high, and it must be demagnetized so that it ceases all supply of electromotive force and therefore any overheating effect induced by the fault.

[0045] Step E2 can be carried out using temperature sensors placed at the heart or near the windings of generator 1.

[0046] To be sure of detecting the fault, it is necessary to place a set of several temperature sensors positioned in such a way as to be able to detect any fault.

[0047] In the event of a failure detected in step E2, and / or a short circuit detected during step E1 followed by a rise in temperature beyond the predefined threshold detected during step E2, the method continues with the triggering of an overheating E3, by which the controller 8 triggers the overheating means.

[0048] When an overheating E3 is triggered, the controller 8 triggers the supply of electrical power to the overheating elements of the magnets 5 until the magnets are demagnetized and the hoop is damaged.

[0049] For example, the magnets 5 are heated using the superheating means until said magnets 5 exceed their Curie temperature beyond which they irreversibly lose their ferromagnetic properties.

[0050] The destruction of the ferromagnetic character of the magnets makes it possible to annihilate their capacity to generate an electromotive force on the shaft of the generator 1, thus contributing to the stopping of the generator 1.

[0051] The increase in temperature is also used other than to demagnetize the magnets 5 because it allows damage to the hoop 3, generally made of composite material.

[0052] Indeed, the Curie temperature of the magnets is quite high, whereas the mechanical strength of the hoop 3 holding the magnets 5 which is made of composite is much lower.

[0053] Thus the first effect of the increase in temperature will be to damage the hoop 3 which will then no longer perform its role of holding the magnets 5.

[0054] The damage to the fret 3a is such that it is no longer capable of hold the magnets 5 on the rotor, as a result of which the magnets 5 will no longer be held on the rotor and will no longer rotate.

[0055] The release of the magnets 5 in the casing 4 has the effect of making them move away from the shaft of the generator 1, because the latter will detach and become stuck to the casing 4, which prevents them from generating electromotive force on the shaft of the generator 1. Thus, the magnets are no longer mechanically linked to the shaft of the generator 1 and therefore no longer rotate.

[0056] This solution is mainly applicable in the case of generators with internal rotor so that the casing 4 retains the magnets released by the hoop 3.

[0057] The generator 1 may include means for cooling its rotor 1.

[0058] In this case, the method may comprise an additional step consisting of a E4 inhibition of these cooling means.

[0059] As illustrated by [Fig.4], in a first embodiment, steps E1 and E2 as well as steps E3 and E4 are alternative steps to each other or complementary, carried out for example simultaneously.

[0060] It is thus possible to only carry out step E4, for example in the particular case of a particularly hot environment.

[0061] Thus, in the method, the short-circuit detection can be done by step E1, or step E2, or a combination of the two steps; and the overheating can be done by step E3, step E4, step E5, or a combination of several of these steps.

[0062] These cooling means generally operate using oil circulating to a cold source coupled with an exchanger, for example of the air / oil type.

[0063] It is possible in certain generators to close the oil supply to eliminate cooling by this cold source.

[0064] It is also possible to keep the oil flow, but to bypass the exchanger so that the oil which will arrive at generator 1 will be hot.

[0065] It is possible in some generators to short-circuit the oil supply, if the machine 1 has a dedicated oil circuit with a dedicated pump for cooling the generator, which makes it possible to completely stop the oil flow.

[0066] Step E4 thus leads to an increased or more rapid rise in the temperature of the generator 1.

[0067] The method may further provide that friction heating E5 is also carried out, by which the magnets 5 are heated by dropping a mechanical part onto the rotor of the generator 1.

[0068] This will not only have the effect of stopping the generation of electromotive force because the magnets 5 dissociate and no longer rotate, but also of generating sufficient torque to break a fusible section provided for this purpose on the generator shaft. 1.

[0069] Indeed, a fusible section is systematically provided on the shaft of the generator 1 so that it breaks in the event of overtorque which could be caused for example by a rotor breakage or a failure of the bearing 3. This part must in particular rub on the shaft of the generator 1, which will have the effect of heating the magnets 5 by friction and increasing the torque on the shaft of the generator 1, which can lead to a desired rupture of the fusible section for the mechanical disconnection of the generator and then its stopping.

[0070] When overheating occurs in step E3 and / or in step E4 and / or in step E5, it is also possible to use a suitable additional electrical source to heat the generator 1.

[0071] This additional heating can be done by placing heating mats around the generator 1, the heat released contributing to warming the magnets of the generator 1 and therefore stopping the latter.

[0072] The method can also be implemented with several generators, since it is common to use a duplex generator for safety or availability reasons.

[0073] In this case, the generator having two independent stators and a common rotor is used, these two independent stators sharing the same rotor and each having a separate electrical power supply.

[0074] Thus, when a fault is detected in the electrical power supply of the first stator, the electrical power supply of the second stator is controlled at its maximum power, beyond its normal operating power, so as to generate overheating of the permanent magnets of the second generator when overheating E3 is triggered.

[0075] During this step E3, high level currents beyond the nominal operating currents are then injected into the windings of the generator.

[0076] An electronic converter designed to supply these currents must be associated with each stator of the generator to supply the two separate electrical supplies to the two stators.

[0077] The electrical power source of this step E3 for the duplex generator can also be the motor electrical power network.

[0078] Thus the method of the invention allows the temperature increase of the overheating elements, the damage to the hoop 3 and the destruction of the latter so as to release the magnets 5, the temperature increase being used to demagnetize the magnets 5 and therefore detach them.

[0079] Among the heating means, friction heating of step E5 by releasing a mechanical part on the rotor of the generator 1 allows, in addition to heating, to increase the torque on the shaft of the generator 1 which can lead to a desired rupture of the fusible section.

Claims

Claims

1. Electric generator for an aircraft hybrid engine (1) comprising a rotor (2) and permanent magnets (5) adapted to be able to provide an electromotive force, characterized in that it comprises superheating elements adapted to raise the temperature of the permanent magnets (5) to demagnetize them, said superheating elements comprising a controller (8) configured to be able to detect a short circuit in said permanent magnet electric generator (1) and an increase in a temperature of the electric generator (1) beyond a predefined threshold and to be able to trigger the superheating means, and in that the rotor (2) is mounted along a longitudinal axis (X) on a hoop (3) in a casing (4),and the controller (8) is configured to be able to trigger the supply of electrical power to the overheating means on the permanent magnets (5) until they are demagnetized and until the hoop (3) is damaged when overheating is triggered.,

2. Generator (1) according to claim 1, wherein the superheating elements comprise a heating mat (6) in contact with the permanent magnets (5).

3. Generator (1) according to claim 2, wherein the heating mat (6) is of the resistive type or of the chemical type.

4. Method for stopping a permanent magnet electric generator (1) according to any one of claims 1 to 3, comprising the following steps: - the detection (El) of a short circuit in said permanent magnet electric generator (1), - and / or the detection (E2) of a rise in a temperature of the electric generator (1) beyond a predefined threshold, - the triggering of an overheating (E3), by which the controller (8) triggers the overheating means.

5. Method according to the preceding claim 4, in which when overheating (E3) is triggered, the permanent magnets (5) are raised in temperature using the overheating means, until said permanent magnets (5) exceed their Curie temperature beyond which they irreversibly lose their ferromagnetic properties.

6. A method according to any one of claims 4 and 5, wherein the generator (1) comprises means for cooling the rotor (2) of the electric generator (1), and an inhibition (E4) of these cooling means is carried out.

7. Method according to any one of claims 4 to 6, in which friction heating (E5) is also carried out, by which the permanent magnets (5) are heated by dropping a mechanical part onto the rotor (2) of the electric generator (1).

8. Method according to any one of claims 4 to 7, in which when overheating (E3) is triggered, a suitable additional electrical source is used to heat the machine (1).

9. A method according to any one of claims 4 to 8, wherein a generator according to any one of preceding claims 1 to 3 is used, said generator having a first and a second stator which share a common rotor, and when a fault is detected in the power supply of the first stator, the power supply of the second stator is controlled at its maximum power beyond its normal operating conditions so as to generate overheating of the permanent magnets of the generator when an overheating condition (E3) is triggered.

10. Aircraft comprising a generator according to any one of claims 1 to 3.

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