Accessories drive system comprising a multi-disc clutch and a generator electric machine

Abstract

One aspect of the invention relates to an accessories drive system S comprising a generator electric machine (1) and a gearbox (2) comprising an input shaft (20), a first output shaft (21) coupled with a rotor (12) of the generator electric machine (1), and a multi-disc clutch (23) between the input shaft (20) and the first output shaft (21), characterized in that the multi-disc clutch (23) comprises a housing (231) constrained not to rotate independently of the first output shaft (21) and comprising internal teeth and notches, and driven discs (232) with external notches and teeth engaged with the internal teeth and notches of the housing (231) in order to constrain them not to rotate independently of the housing (231).

Description

DESCRIPTION TITLE: Accessory drive system comprising a disc clutch and an electric generating machine. TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of gas turbines for aeronautical engines, airplanes or helicopters, as well as for auxiliary power units (or APU, for "Auxiliary Power Unit").

[0002] The present invention relates to gas turbines and more particularly to an accessory drive system comprising an accessory gear box (AGB), the latter comprising a clutch for driving an electric generator machine. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] In a gas turbine, a number of equipment, or accessories, are driven by a mechanical transmission from mechanical power taken from a high-pressure or low-pressure shaft. This mechanical transmission, which comprises a set of gears housed in a casing, is called a transmission box, gearbox or accessory relay box. Accessories include, in particular, various pumps for hydraulic power generation, fuel supply, lubrication, as well as one or more starters and / or electrical generators. An electrical generator installed on an aircraft turbomachine is generally mounted on a transmission box comprising an input shaft mechanically coupled to a high-pressure shaft, or even a low-pressure shaft.In addition, the shaft line that drives the rotor of the electric generator machine is equipped with a passive protection device whose function is to physically separate the electric generator machine from the gearbox when an incident occurs. Conventionally, these protection devices are equipped with a breakable section (passive device) calibrated for a breaking torque corresponding, for example, to 5 to 10 times the nominal or maximum operational torque.

[0004] It is known in particular from document FR3120656A1, a main equipment, for example a generator permanently coupled with a shaft high pressure and an electric motor machine (which produces torque) coupled to the high pressure shaft by means of a clutch.

[0005] To limit the mass of the electric generator, it must not exceed a certain rotation speed. Thus, the electric generator must be deactivated when the turbomachine exceeds a certain rotation speed and can be reactivated as soon as the speed falls below a certain threshold.

[0006] In particular, in the case of an electric machine mounted on a gearbox coupled at the input to a low pressure shaft, called the LP shaft, the operating speed range of the electric generator machine is higher than the idling operating range of the LP shaft. Consequently, the kinematic chain between the LP shaft and the electric generator machine, particularly in the gearbox, must have a gear ratio well above 1, for example between 5 and 50 to prevent the electric generator machine from rotating below its operating range when the turbomachine is idling. On the other hand, when the speed of the LP shaft becomes higher, the speed of the driven electric generator machine may exceed its desired operating range. It is then necessary to decouple the electric generator machine without decoupling the other equipment driven by the gearbox.

[0007] This limitation of the operating range of the electric generator machine coupled to a gearbox is particularly interesting for its optimization and that of the electrical power system. However, the lightening of the electric generator machine is only accessible on condition of decoupling / re-engaging the equipment from a chosen threshold speed. There is therefore a need for a reversible clutch capable of supporting the drive torque of the electric generator machine as compact and light as possible. SUMMARY OF THE INVENTION

[0008] The invention provides a solution to the problems mentioned above, by allowing a disc clutch to be used in a compact manner.

[0009] One aspect of the invention relates to an accessory drive system comprising an electric generator machine and a gearbox comprising an input shaft adapted to be coupled to a power shaft of a turbomachine, a first output shaft coupled to a rotor of the electric generating machine, a disc clutch between the input shaft and the first output shaft, characterized in that the disc clutch comprises: driving discs with internal notches and teeth integral in rotation with the input shaft, a housing linked in rotation with the first output shaft, comprising internal teeth and notches, driven discs with external notches and teeth fitted with the internal teeth and notches of the housing coupling in rotation the housing to the driven discs.

[0010] Thanks to the invention, the disc clutch allows decoupling in a compact and optimal manner to reduce weight. Indeed, by using the large diameter of the housing, this makes it possible to limit the mass and size while providing a high gear ratio (typically at least 10, and generally greater than 5) for driving the electric generator machine. In addition, the advantage of using a disc clutch as a decoupling means is to be able to operate in an enclosure of the gearbox which contains oil projections (oil bath clutch). This oil can even be used to cool the clutch discs and evacuate the particles emitted by the friction of the discs by adding an oil filtration system or using the one already present in the lubrication system of the electric generator machine or the gearbox.

[0011] By an element "coupled" to another element, it is meant that if one of the two elements is driven in rotation regardless of the direction of rotation, the other element is driven in rotation such that the rotation speed of one element is a function of the rotation speed of the other element. Thus, in this invention: the input shaft driven in rotation will therefore systematically drive the driving discs in rotation, the driven discs driven in rotation (for example by the driving discs in an engaged state) will systematically drive the housing in rotation, the rotating output shaft will therefore systematically rotate the rotor of the electric generating machine.

[0012] By housing "rotationally linked" with the output shaft, it is meant that the rotating output shaft drives the rotor of the electric generating machine in rotation even in the case of the clutch in a disengaged state, but can be decoupled for example, by a safety system comprising a part coupled to the housing and another part to the output shaft making it possible to protect the rotor of the electric generating machine.

[0013] In addition to the characteristics which have just been mentioned in the preceding paragraph, the accessory drive system according to one aspect of the invention may have one or more additional characteristics among the following, considered individually or according to all technically possible combinations:

[0014] According to one embodiment, the input shaft comprises a toothed wheel comprising notches and teeth coupled with the notches and teeth of the driving discs. This makes it possible to have an input shaft comprising a portion of the disc clutch and therefore to avoid driving an intermediate shaft between the input shaft and the rotor of the electric machine when the clutch is disengaged.

[0015] According to one embodiment, the gearbox further comprises a gear ratio between the first output shaft and the housing. This makes it possible to increase the ratio between the output shaft and the housing as simple as possible.

[0016] According to an example of this embodiment, the gearbox further comprises a first intermediate shaft comprising a first toothed wheel meshed with a toothed wheel of the housing and a second toothed wheel meshed with a toothed wheel rotationally integral with the output shaft.

[0017] According to one embodiment, the gearbox further comprises, between the output shaft and the housing, a decoupling safety device beyond a maximum predetermined speed greater than a maximum predetermined rotor engagement speed. This makes it possible to avoid damage to the electrical generator machine when the turbomachine exceeds a certain rotational speed, in the event of a defective clutch device remaining in an engaged state. According to one example, the decoupling safety device comprises a dog clutch and rotating weights that are moved by centrifugal force and are designed so that beyond the maximum predetermined speed this decouples the output shaft from the housing. For example, the safety system can also be equipped with a sensor to inform when the safety is activated. This allows an error on the clutch to be informed for inspection in the workshop. By "between the output shaft and the housing" we mean between the mechanical connection and not in space.

[0018] According to one embodiment, the disc clutch comprises: springs exerting a force to separate the driving discs from the adjacent driven discs in order to disengage the clutch, an axial compression activation system, such as a hydraulic cylinder or piston, controllable to engage the clutch by compressing the springs until the driving discs and the driven discs are compressed against each other axially to couple them.

[0019] According to one embodiment, the system comprises auxiliary equipment permanently coupled in rotation with the input shaft via several gears. This allows the auxiliary equipment to always be driven in order to maintain a load on the bearings of the power transmission shafts of the gearbox and thus preserve their service life.

[0020] According to one embodiment, the gearbox comprises an enclosure housing the rotating elements of the gearbox including a portion of the input shaft, the output shaft, and the clutch, and at least one nozzle for supplying lubricant into the enclosure to lubricate the various gears of the gearbox as well as the discs of the disc clutch. This allows the oil present in the gearbox to be used both as a lubricant for the meshing and to cool the discs of the clutch and to evacuate particles emitted by the friction of the discs. According to one example, the accessory drive system comprises an oil filtration system for filtering the oil.

[0021] According to one embodiment, the housing comprises on its external periphery teeth meshed with a toothed wheel of an intermediate shaft coupled to the output shaft.

[0022] Another aspect of the invention relates to an assembly comprising: an accessory drive system according to the first aspect (with or without the different characteristics of the embodiments and examples described above) a turbomachine, comprising: - a low pressure shaft coupled to the input shaft of the gearbox, -a high pressure shaft, a second gearbox comprising an input shaft coupled to the high pressure shaft and an output shaft coupled to an electric machine.

[0023] The installation of the gearbox driven by the LP shaft complements the gearbox, called AGB HP, coupled to the high-pressure shaft. This makes it possible to adapt the turbomachine to the electrical hybridization of the IPPS (i.e. the propulsion system including the turbomachine). This equipment complements an electric motor-generator installed on the AGB HP and allows the IPPS to transfer mechanical power from the LP shaft to the HP shaft via the LP electric generating machine operating as a generator and supplying the HP electric machine operating as a motor, better known by the English terms "power sharing" or reversible transfer of mechanical power from one shaft to the other LP, HP, better known by the English terms "power balance". These transfers are sought to optimize the operability of the engines according to the different flight phases.This optimization is one of the major challenges of reducing fuel consumption made accessible by the electric hybridization of future engines (turbomachine + electric machines etc.).

[0024] According to one embodiment, the second gearbox comprises a disc clutch mounted in a similar manner to that of the first gearbox.

[0025] Another aspect of the invention relates to an assembly comprising: an accessory drive system according to the first aspect (with or without the different characteristics of the embodiments and examples described above) a turbomachine, comprising: - a high pressure shaft coupled to the input shaft of the gearbox, - a low pressure shaft, a second gearbox comprising an input shaft coupled to the low pressure shaft and an output shaft coupled to an electric machine.

[0026] This allows when the HP shaft speed becomes high, to prevent the driven generator speed from exceeding its desired operating range by decoupling it.

[0027] Another aspect of the invention relates to a method for controlling the disc clutch of the accessory drive system according to the first aspect of the invention, with or without the different features of the different embodiments, of a turbomachine, for coupling and decoupling a torque transmission between the input shaft which is a power transmission shaft coupled to a low pressure shaft and the output shaft rotatably coupled with the electric generating machine, the method comprising: a step of controlling declutching when the rotational speed of the low pressure shaft is beyond a first predetermined rotational speed value of the low pressure shaft, the disc clutch device passing from an engaged state to a disengaged state in which driving discs are spaced from driven discs to decouple the electric generating machine from the power transmission shaft.

[0028] This makes it possible to decouple the electric generating machine from the power transmission shaft (also called the input shaft) and therefore from the low-pressure shaft of the turbomachine as soon as the electric generating machine is outside its maximum speed. In fact, the first predetermined rotational speed value of the low-pressure shaft is calculated according to the ratio between this low-pressure shaft and the rotor of the electric generating machine to correspond to a maximum rotor speed.

[0029] According to an example of this embodiment the disc clutch device comprises driving discs coupled to the coupled input shaft and driven discs coupled to the output shaft rotatably coupled with the generating electric machine.

[0030] According to one embodiment, the method further comprises a clutch step comprising a sub-step of clutch control when the rotational speed of the low pressure shaft is below a second predetermined speed value, of an axial compression activation system of the disc clutch device, then a sub-step of compression of the driving discs and the driven discs against each other by the activation system causing the disc clutch device to pass from the disengaged state to the engaged state.

[0031] According to one embodiment, the electric generating machine comprises a motor mode, the clutch step comprising: a sub-step of pre-rotation of the discs carried out before the sub-step of compression of the discs, in which after the clutch control sub-step, the electric generating machine is controlled to be in motor mode in order to drive its rotor in rotation up to a predetermined speed of the rotor and A sub-step of interrupting the power supply in motor mode when the predetermined rotor speed is reached.

[0032] This reduces the speed differences between the driving and driven discs before the compression sub-stage, which considerably reduces clutch heating.

[0033] The invention and its various applications will be better understood by reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0034] The figures are presented for information purposes only and in no way limit the invention.

[0035] [Fig.1] shows a schematic representation of an accessory drive system according to a first embodiment of the invention.

[0036] [Fig.2] represents an enlargement of Figure 1.

[0037] [Fig.3] shows a schematic longitudinal section of an assembly comprising an aircraft turbomachine coupled to an accessory drive system according to the invention. DETAILED DESCRIPTION

[0038] The figures are presented for information purposes only and in no way limit the invention.

[0039] In the following, by "internal" tooth of an element, we mean that the teeth of the element face towards the axis of rotation of the element and conversely by external tooth of an element, we mean that the teeth extend radially opposite the axis of rotation of the element, that is to say that the tip of the tooth is the part of the tooth furthest from the axis of rotation.

[0040] [Fig. 1] shows a schematic representation of an accessory drive system S according to a first embodiment of the invention.

[0041] The accessory drive system S known by the acronym ADT for "Accessory Drive Train" comprises an electric generator 1 and a gearbox 2, better known by the acronym AGB for "Accessory GearBox". In this example, it further comprises auxiliary equipment 3, in this case an oil pump, but could include others such as a starter, a hydraulic circuit pump, a low-pressure or high-pressure fuel pump, etc.

[0042] The electric generator machine 1 comprises a rotor 12 and a stator 13. In this example, the electric generator machine 1 is an alternator or a dynamo and therefore only comprises an alternating or direct current generator mode.

[0043] According to a second example, the electric generating machine 1 is an electric machine comprising a motor mode. The electric generating machine 1 shown is of the radial air gap type but could be of the axial air gap type.

[0044] The gearbox 2 comprises an input shaft 20 capable of being coupled to a power shaft of a turbomachine T (shown in FIG. 3 explained below) or turboprop. The power shaft of the turbomachine may be a low-pressure shaft, for example of a fan or a low-pressure turbine, or may be coupled to a high-pressure shaft, for example the high-pressure shaft of the high-pressure compressor. The diameter of the fan may be between 20 inches and 140 inches. The turbomachine may have a compression ratio of 20 to 60, and may be single-flow, or double-flow, single-spool, double-spool and triple-spool, with single or double HP turbine, from 1 to 8 LP turbine stages. Gearbox 2 may be located in or against a blower compartment.

[0045] A radial shaft, known by the acronym RDS for "Radial Drive Shaft" can be meshed at one end with the power shaft of the turbomachine and at the other end with the input shaft 20, for example by an angle transfer gear, to couple them together.

[0046] The gearbox 2 comprises a first output shaft 21 coupled with the rotor 12 of the electric generating machine 1 and a disc clutch 23 for transmitting a torque between the input shaft 20 and the output shaft 21.

[0047] The disc clutch 23, shown in Figure 2 by an enlargement of Figure 1, comprises driving discs 230 comprising notches and internal teeth integral in rotation with the input shaft 20. In this case, the input shaft 20 comprises a toothed wheel 203 comprising notches and teeth coupled with the notches and teeth of the driving discs 230. In other words, the toothed wheel 203 is part of both the input shaft 2 and the disc clutch 23. The driving discs 230 can thus translate axially (for example over a few mm) on the toothed wheel 203. According to another example, an intermediate shaft coupled to the input shaft 20 comprises the toothed wheel on which the driving discs 230 translate.

[0048] The disc clutch 23 further comprises a housing 231 integral in rotation with the output shaft 21. In this example, the housing 231 comprises a toothed wheel 2314 meshed with a toothed wheel 243 integral in rotation with the output shaft 21. In this embodiment, the gearbox 2 comprises an intermediate shaft 24 comprising a first intermediate toothed wheel 243 meshed with the toothed wheel of the housing 321 and a second intermediate toothed wheel 241 meshed with a toothed wheel 214, in this case a second intermediate shaft integral in rotation with the output shaft 21. The different toothed wheels (2314, 243, 241, 214) form a gear ratio, for example multiplied by 15, between the housing 231 and the first output shaft 21 to adapt a low speed of the low pressure power shaft of the turbomachine to the speed of the electric generator machine 1.Preferably the final multiplication ratio between the rotational speed of the rotor 12 and that of the input shaft 20 is greater than 10, for example. around 30. In the case of a lower final multiplication ratio between the rotational speed of the rotor 12 and that of the input shaft 20, for example between 10 and 20, the toothed wheel 214 can be directly meshed with the toothed wheel 2314 of the housing 231 (that is to say that the gearbox 2 would be devoid of the first intermediate shaft 24).

[0049] The disc clutch 23 further comprises driven discs 232 with notches and external teeth integral in rotation with the housing 231. More precisely, the housing 231 comprises splines forming teeth housed in the external notches of the driven discs 232 and notches housing the external teeth of the driven discs 232. The driven discs 232 can thus move axially, for example by a few millimeters, relative to the housing 231.

[0050] The driven discs 232 and the driving discs 230 are arranged alternately axially along the axis of rotation of the input shaft 20, delimited between the axial ends of the housing 231 and the axial ends of the toothed wheel 203 of the input shaft 20.

[0051] The housing 231 can be open radially between two teeth or can also cover the driven discs 232 and the driving discs 230. The toothed wheel 203 is therefore surrounded by the driven discs 232 and the driving discs 230.

[0052] The disc clutch 23 comprises springs (not shown) exerting a force to separate the discs from each other in order to disengage the clutch, and an axial compression activation system 237, for example one or more hydraulic cylinders, in this case a plurality of hydraulic cylinders arranged in a crown shape coaxially with the input shaft 20, controllable to compress the springs until the driving discs and the driven discs are compressed against each other axially to couple them in rotation. The power transmitted by the clutch in the engaged state is between 0.2 kW and 1000 kW.

[0053] The disc clutch 23 thus comprises a disengaged state in which the driven discs 232 are spaced apart or at least are not compressed against the driving discs 230 and an engaged state in which the driven discs 232 are compressed against the driving discs 230 and are thus rotationally integral.

[0054] The axial compression activation system 237 can thus be controlled by a control unit not shown, to activate the clutch (switch to the engaged state) at the start of the phase, that is to say at the start of the turbomachine, for example up to a maximum predetermined speed value received from a speed sensor measuring a rotational speed of a shaft between the power shaft of the machine and the input shaft 20. The maximum predetermined rotational speed corresponds (according to the ratio) to a predetermined safety rotational speed of the engaged rotor. The control can thus come as a function of a speed sensor already used, for example measuring the rotational speed of the low pressure shaft coupled to the power shaft of the turbomachine. For example, the maximum predetermined rotational speed is determined by the ratio between the rotor and the low pressure shaft, multiplied by the predetermined safety rotational speed of the engaged rotor.

[0055] The control unit can of course control the axial compression activation system 237 to switch from the deactivated (disengaged) state to the clutch-activated state when the measured speed is below a second predetermined rotational speed value lower than the maximum predetermined speed value.

[0056] In the example where the electric generator machine 1 comprises a motor mode, the control unit can control the electric generator machine 1 in motor mode when the clutch is in the deactivated state and the rotational speed measured by the sensor falls below a predetermined value and then control the electric generator machine 1 in alternator mode when a predetermined rotor speed is reached.

[0057] For example, when the clutch is in the deactivated state and the measured speed is above the second predetermined rotational speed value, and as soon as the measured speed falls below the second predetermined rotational speed value, the control unit first controls the electric generator machine 1 in motor mode, then before controlling the axial compression activation system 237 to switch from the deactivated (disengaged) state to the clutch-activated state, controls the electric generator machine 1 in low-torque alternator mode when a predetermined rotor speed is reached.

[0058] Using the motor mode reduces the speed differences between the driving and driven discs before the compression sub-stage, which considerably reduces clutch heating. Using the low-torque motor mode before the engaged state prevents jolts or jerks between the rotor 12 of the electric generator machine 1 and the input shaft 20 when switching to alternator mode.

[0059] The toothed wheel 2314 of the housing 231 is shown schematically as axially offset relative to the tooth and notch integral in rotation with the driven discs 232 but could be formed on the external periphery of the housing 231 by surrounding the driven discs 232 and the driving discs 230.

[0060] The gearbox 2 optionally comprises, here shown in dotted lines, a decoupling safety device 22 coupled between the second intermediate shaft comprising the toothed wheel 214 and the output shaft 21.

[0061] The decoupling safety device 22 is provided so that beyond a predetermined safety rotational speed greater than the predetermined safety rotational speed of the engaged rotor. The decoupling safety device 22 comprises for example a dog clutch and rotating weights which are movable by centrifugal force and are provided so that beyond the predetermined safety rotational speed this decouples the output shaft 21 from the second intermediate shaft and therefore from the housing 231.

[0062] The gearbox 2 comprises, in this example, a fourth intermediate shaft 26 comprising an intermediate toothed wheel 260 meshed between a transmission toothed wheel 206 of the input shaft 20 and an output wheel 207 of a second output shaft 27 coupled to the auxiliary equipment 3. The auxiliary equipment 3 is therefore always coupled in rotation with the input shaft 20. Of course, the gearbox 2 can comprise a plurality of output shafts and intermediate shafts, for example around twenty shafts and gears.

[0063] In particular, Figure 3 represents another aspect of the invention which also relates to an assembly comprising an accessory drive system S according to the invention, for example that described previously, the turbomachine T, comprising the low pressure shaft 510 coupled to the input shaft 20 of the gearbox 2 by means in this case of a radial transmission shaft R1. turbomachine T further comprises a high pressure shaft 410 coupled to a transmission shaft R2 of a second accessory drive system S2 comprising an electric motor machine (which produces torque) and a second gearbox comprising an output shaft coupled to the electric motor machine.

[0064] The turbomachine T shown is of the double-body, double-flow type and comprises, upstream, a fan 520 mounted in a fan casing 300 in which the two accessory drive systems S, S2 are mounted. The turbomachine T comprises, from upstream to downstream, the fan 520, a low-pressure compressor 530, a high-pressure compressor 420, a combustion chamber 600, a high-pressure turbine 430 and a low-pressure turbine 540. The low-pressure turbine 540 is coupled to the low-pressure shaft 510 to rotate the low-pressure compressor 530 and the fan 520, together forming a low-pressure body 500. The high-pressure turbine 430 is coupled to the high-pressure shaft 410 to rotate the high-pressure compressor 420, together forming a high-pressure body 400. The high-pressure shaft 410 extends externally around the low-pressure shaft 510 along the longitudinal axis X.

[0065] The installation of the gearbox 2 of the first system S driven by the LP shaft complements the gearbox, called AGB HP of the second system S2, coupled to the high pressure shaft. This makes it possible to adapt the turbomachine to the electrical hybridization of the IPPS (i.e. the propulsion assembly comprising the turbomachine). The electric motor installed on the AGB HP and allows the IPPS to carry out the transfer of mechanical power from the low pressure shaft 510 to the high pressure shaft 410 via the electric generator machine 1 operating as a generator and supplying the electric motor of the second system S2 operating as a motor, better known by the English terms "power sharing" or reversible mechanical power transfer, better known by the English terms "power balance". These transfers are sought for the optimization of the operability of the engines according to the different phases of flight.This optimization is one of the major challenges of reducing fuel consumption made accessible by the electric hybridization of future engines (turbomachine + electric machines etc.).

[0066] Unless otherwise specified, the same element appearing in different figures has a single reference.

Claims

CLAIMS

1. Accessory drive system (S) comprising an electric generator machine (1) and a gearbox (2) comprising an input shaft (20) capable of being coupled to a power shaft of a turbomachine, a first output shaft (21) coupled to a rotor (12) of the electric generator machine (1), a disc clutch (23) between the input shaft (20) and the first output shaft (21), characterized in that the disc clutch (23) comprises: - driving discs (230) with notches and internal teeth integral in rotation with the input shaft (20), - a housing (231) rotatably connected to the first output shaft (21), comprising internal teeth and notches, - driven discs (232) with external notches and teeth fitted with the internal teeth and notches of the housing (231) coupling the housing (231) in rotation to the driven discs (232).

2. An accessory drive system according to claim 1, wherein the input shaft (20) comprises a gear wheel (203) comprising notches and teeth coupled with the notches and teeth of the drive discs (230).

3. An accessory drive system according to claim 1 or 2, wherein the gearbox (2) further comprises a gear ratio between the first output shaft (21) and the housing (231).

4. An accessory drive system according to claim 3, wherein the gearbox (2) further comprises a first intermediate shaft (24) comprising a first gear wheel (243) meshed with a gear wheel (2314) of the housing (321) and a second gear wheel (241) meshed with a gear wheel (214) rotatably fixed to the output shaft (21).

5. Accessory drive system according to any one of the claims, in which the gearbox (2) further comprises between the output shaft (21) and the housing (321), a decoupling safety device (22) beyond a maximum predetermined speed greater than a maximum predetermined clutch speed of the rotor (12).

6. An accessory drive system according to one of claims 1 to 5, wherein the disc clutch (23) comprises: - springs exerting a force to separate the driving discs from the adjacent driven discs in order to disengage the clutch, - an axial compression activation system (237), such as a hydraulic cylinder or piston, controllable to engage by compressing the springs until the driving discs and the driven discs are compressed against each other axially to couple them.

7. Accessory drive system according to one of claims 1 to 6, comprising auxiliary equipment (3) permanently coupled in rotation with the input shaft (20) by means of several gears.

8. An accessory drive system according to one of claims 1 to 6, wherein the gearbox (2) comprises an enclosure housing the rotating elements of the gearbox (2) including a portion of the input shaft (20), the output shaft, as well as the clutch, and at least one nozzle for supplying lubricant into the enclosure to lubricate the various gears of the gearbox (2) as well as the discs of the disc clutch (23).

9. Method for controlling the disc clutch (23) of the accessory drive system (S) according to one of the preceding claims in a turbomachine, for coupling and decoupling a torque transmission between the input shaft coupled to a low pressure shaft and the output shaft rotatably coupled to the generating electric machine, the method comprising: - a disengagement control step when the rotational speed of the low pressure shaft is beyond a first predetermined rotational speed value of the low pressure shaft, the disc clutch device passing from an engaged state to a disengaged state in which driving discs are moved away from the driven discs to decouple the electric generating machine from the input shaft.

10. A method of controlling the disc clutch of the accessory drive system (S), according to claim 9, further comprising a step of controlling the clutch when the rotational speed of the low pressure shaft is below a second predetermined speed value, wherein an axial compression activation system of the disc clutch device is activated to compress the driving discs and the driven discs against each other.

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