Compact structure for accessory gearbox of an aircraft turbine engine

An aircraft drive chain including a plurality of main gears engaging with each other, a first main gear including a wall defining an inner space, an outer set of gear teeth being placed on an outer surface of the wall, the outer set of gear teeth engaging with at least one second main gear, a gear system being built into the inner space, the first main gear and the gear system being jointly configured so as to form a gearbox or reducer and ensure mechanical power transfer between a drive member and a slave member, the gear system being mounted onto the wall with a decoupling member.

TECHNICAL FIELD AND PRIOR ART

This invention relates to gear chains (or drive chains) present in aircraft.

These gear chains are used to transfer mechanical power between drive members, for example a starter or a compressor of a turbine engine and slave members, for example accessories such as an electrical generator or hydraulic pump, or even the turbine engine compressor itself during its start-up phase, when it is driven in rotation by the starter. The accessory gearbox or AGB is one specific example of a gear chain for driving accessories. An accessory gearbox structure of this type is described in the American patent application US 2012/0006137.

A speed-increasing or reducer function is generally used to adapt the rotational speed of the input movement to the specific parameters of each drive member or slave member.

For example, a starter comprises two portions: a mobile member referred to as an impeller and a reducer.

However, in some specific cases, the drive member and the slave member must be decoupled. For example, the function itself of a starter is to assist in the start-up of the turbine engine. When the turbine engine reaches the desired rotational speed, the starter must be disconnected.

The invention aims at proposing a compact structure integrating a speed-increasing or reducer function and which can be disconnected in order to reduce the dimensions of the drive chain and/or accessories.

DESCRIPTION OF THE INVENTION

The invention therefore relates to an aircraft drive chain, for example an accessory drive chain of a turbine engine, including a plurality of main gears engaging with each other, a first main gear comprising a wall defining an inner space, an outer set of gear teeth being placed on an outer surface of the wall, the outer set of gear teeth engaging with at least one second main gear, a gear system separate from the plurality of main gears being built into the inner space, the first main gear and the gear system being jointly configured so as to form a speed-increaser or reducer and ensure mechanical power transfer between a drive member and a slave member, said gear system being mounted onto the wall by means of a decoupling member.

The invention further relates, for example, to an aircraft drive chain, for example an accessory drive chain of a turbine engine, the drive chain including a plurality of gears engaging with each other, the drive chain further including a second plurality of gears forming a gear system, as well as a decoupling member, the first plurality of gears and the second plurality of gears being connected by means of the decoupling member, a first gear of the first plurality of gears comprising a wall defining an inner space, an outer set of gear teeth being placed on an outer surface of the wall, the outer set of gear teeth engaging with at least one second gear of the first plurality of gears, the gear system being built into the inner space, the first gear and the gear system being jointly configured so as to form a speed-increaser or reducer and ensure mechanical power transfer between a drive member and a slave member, said gear system being mounted onto the wall by means of a decoupling member.

The invention thus allows for the integration and association of a speed-increasing (and/or reducer) structure and a decoupling member for a drive member or slave member of an aircraft in the inner space of a gear of an aircraft gear chain rather than in the inner space of the drive member or slave member itself. This reduces the volume occupied by this accessory and the weight located in the cantilever position. This advantageously results on the one hand in reduced stresses on the couplings supporting this member and on the other hand in an optimised inner volume of the module in which the gear chain is assembled. Furthermore, this integration takes place in the space defined by the gear without increasing the volume of the drive chain.

In the specific case of an AGB, the reduced accessories volume eases the integration of the latter in the turbine engine.

Moreover, the decoupling member enables a drive member or a slave member to only operate under certain rotation conditions at the movement input and movement output. For example, the starter of the aircraft turbine engine whose speed-increaser is integrated into a gear as described hereinabove, could advantageously only operate on turbine engine start-up.

According to one advantageous characteristic, said gear system comprises a member forming a crown, at least two planet gears, a member forming a planet carrier and a sun gear teeth set, the sun gear teeth set being placed on a first shaft connected to the drive member or the slave member, an inner set of gear teeth being placed on an inner surface of the member forming a crown, the planet gears engaging with the inner set of gear teeth and with the sun gear teeth set.

Advantageously, the member forming a crown comprises a rim on which an inner track of the decoupling member is made, the member forming the planet carrier being fixed with regard to an aircraft frame.

Alternatively, the member forming a crown comprises a ring-shaped wall that is fixed in relation to an aircraft frame, the member forming the planet carrier comprising a rim on which an inner track of the decoupling member is made.

According to one advantageous characteristic, a movement towards the first main gear is initiated by the outer set of gear teeth.

Alternatively, a movement towards the first main gear is initiated by the first shaft.

According to one advantageous characteristic, the decoupling member is configured to allow for a rotational decoupling of the gear system and the first main gear when the rotational speed of the first main gear is greater than the rotational speed of the member forming a crown or by disengagement caused by centrifugal force when the rotational speed of the gear reaches a set value.

According to one specific embodiment, the decoupling member comprises an overrunning clutch device.

In one specific embodiment, the planet gears of the gear system each have a first and a second set of gear teeth of different diameters.

Such a dual set of gear teeth advantageously offers a high transmission shift range in a minimum amount of space.

In one specific embodiment, said first main gear comprises a second shaft that is coaxial to the first shaft.

The invention therefore advantageously enables two accessories to be positioned opposite each other, rotating at very different speeds as a function of the dimensioning of the gear on the one hand and of the gearbox on the other hand.

In one specific configuration, the first main gear forms part of a ring and pinion.

It is, for example, possible that the first main gear of an AGB is the gear the closest to the compressor shaft.

The invention can also relate to an accessory gearbox comprising a drive chain as described hereinabove.

The invention can further relate to a propeller gearbox comprising a drive chain as described hereinabove.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1Aillustrates a gear10having a general funnel shape oriented in a longitudinal direction X.

The gear10comprises a ring-shaped rim21a, a wheel disc22, a strut23and an outer set of gear teeth24.

The rim21aand the strut23are cylindrical, coaxial and have a circular cross-section, the diameter of the strut23being less than the diameter of the rim21a. The strut23is in this example a hollow shaft. Alternatively, the strut23is a solid shaft.

The wheel disc22in this example has a frustoconical shape. The wheel disc22is connected by a first circular edge22ato an end edge of the rim21a, and by a second circular edge22b, having a diameter less than the first edge22a, to an end edge of the strut23. Alternatively and not shown in the figures, the wheel disc22is flat. The wheel disc22can also comprise openings onto a portion of its surface.

The rim21aand the wheel disc22jointly define an inner housing12.

The strut23extends from the wheel disc22opposite the inner housing12.

The outer set of gear teeth24extends radially outwards from the rim21a. The set of gear teeth24in this example comprises straight teeth. Alternatively and not shown in the figures, this set of gear teeth is helical or another type of gear teeth.

FIG. 1Billustrates a mechanical device9wherein a speed-increaser11aand a decoupling member11bare mounted in the inner housing12of the gear10described hereinabove. InFIG. 1B, the speed-increaser11aand the decoupling member lib are shown in a simplified form by a half-cylinder.

In the device9shown inFIGS. 3 and 4, the speed-increaser11acomprises a crown30, planet gears40for planets), a planet carrier41and a shaft42.

The crown30comprises a ring-shaped rim21band an inner set of gear teeth25. The rim21bhas a circular cross-section. The set of gear teeth25extends radially on the inner surface of the rim21b. The set of gear teeth25in this example comprises straight teeth. Alternatively and not shown in the figures, this set of gear teeth is helical or another type of gear teeth.

The planets40are in this example gears with a double set of straight teeth49aand49b. More precisely, the planets40comprise two different outer sets of gear teeth, one set49ahaving in this example a diameter greater than the other set49b. In this example, there are four planets40. Alternatively and not shown in the figures, the sets of gear teeth49aand49bare helical or another type of gear teeth, and/or the number of planet gears40is different to four, for example two or three.

In this example, the set of gear teeth49bis engaged with the set of gear teeth25of the crown30.

In the embodiment shown, the planet carrier41comprises two shells41aand41band four shafts44.

The first shell41a, located the furthest from the wheel disc22, comprises a wall43a, a cylindrical portion45a, a frustoconical portion47and a coupling48. The wall43ais a flat flange. The cylindrical portion45aextends longitudinally from the wall43a, opposite the strut23. The frustoconical portion47extends by shrinking into the protrusion of the cylindrical portion45a. Finally, the strut48of the planet carrier41is positioned at the distal end of the frustoconical portion47, transversally to the longitudinal orientation X. The coupling48holds the planet carrier41in position in relation to a fixed frame, for example one of the gearboxes4aor4b.

The second shell41b, located the closest to the wheel disc22, comprises a wall43band a cylindrical portion45b. The wall43bis a flat flange. Alternatively, the walls43aand/or43bhave shapes that differ from those shown. For example, either of these walls can include openings or be different from a flat element. The cylindrical portion45bextends longitudinally from the wall43b, towards the strut23.

Two bearings46b, in this example roller bearings, provide a mechanical, rotational link between the rim21bof the crown30and the cylindrical portions45aand45b.

The walls43aand43bare parallel to each other. These walls43aand43bjointly support the shafts44on which the planet gears40are mounted and able to move in rotation.

The shaft42has a straight set of gear teeth50in an end housed in the planet carrier41. In a version not shown in the figures, this set of gear teeth is helical or another type of gear teeth. This set of gear teeth50is engaged with the set of gear teeth49aof each of the four planets40. The shaft42in this example is coaxial with the strut23and the rim21a.

The decoupling member11bin this example comprises an overrunning clutch device51and two bearings46a, in this example ball bearings.

The overrunning clutch device51and the two bearings46aare inserted between the rim21aof the gear10and the rim21bof the crown30, the overrunning clutch device51being positioned between the two bearings46a.

The overrunning clutch device51is shown inFIGS. 3 and 4in a simplified form by one ring-shaped unit. In a general manner, the overrunning clutch device51comprises two ring-shaped tracks. The outer track is formed in the rim21aor in a separate ring mounted in the rim21a. The inner track is formed in the rim21bor in a separate ring mounted around the rim21b.

In the specific and non-limitative example of an aircraft turbine engine starter, on start-up of the aircraft, the power firstly travels from a turbine of the starter to the motor of the aircraft via an AGB. The overrunning clutch device51is engaged as the torque is transmitted from the crown30to the main gear10. Once the motor is started, the overrunning clutch device51enables the crown30and the gear10to be decoupled in rotation:when the torque transmission direction is reversed until the torque is transmitted from the motor of the aircraft to the starter, orby disengagement caused by centrifugal force when the rotation speed of the gear10reaches a set value.

As can be seen inFIGS. 2A and 2B, the gear10can be integrated in different manners in a gear chain (or kinematic linkage).

InFIG. 2A, the gear10is mounted in a first kinematic linkage5of a gearbox4a. More precisely, the gear10is engaged upstream in24awith a cogwheel13and downstream24bwith a cogwheel14. The term upstream is understood as meaning that the cogwheel13is, within the kinematic linkage5, the closest to a compressor shaft from which a mechanical movement is taken. The start of rotation of the cogwheel13thus drives the gear10and the cogwheel14mounted downstream.

InFIG. 2B, the gear10is mounted in a second kinematic linkage6of a gearbox4b. In this example, the gear10is engaged in24cwith a cogwheel15and is mounted at the end of the kinematic linkage6.

Alternatively, the movement in the gearbox4afrom the compressor shaft is initiated by the gear10, i.e. the gear10provides the power to the gear chains5or6, respectively comprising the gears13and14(FIG. 2A) or15(FIG. 2B).

The examples inFIGS. 2A and 2Bare not limitative and the gear10can be mounted in different locations in a kinematic linkage or even in a different kinematic linkage to that shown inFIGS. 2A and 2B.

Alternatively and not shown in the diagrams, the gear is part of a ring and pinion and the outer set of gear teeth is, for example, formed on a conical or frustoconical rim.

The gear10can be held in position in relation to a fixed frame of the aircraft by a coupling mounted on the strut23via a bearing, for example a roller bearing or a plain bearing (the fixed frame, the coupling and the bearing are not shown herein).

The device9shown inFIGS. 3 and 4can be used as a gearbox or as a reducer, depending on whether the upstream part of the drive system is located on the side nearest the strut23, the set of gear teeth24or the shaft42.

The speed-increaser11ais present in this example in the form of a compound planetary-gear system (i.e. comprising planets40with two sets of gear teeth49aand49b) wherein the crown30is the outer planet gear via the inner set of gear teeth25and wherein the set of gear teeth50positioned on the shaft42play the role of an inner mobile planet gear (or sun gear), the planet carrier41being secured to a fixed frame. The use of planets with two sets of gear teeth produces a greater transmission shift range than single gears. Nonetheless, the invention also covers the implementation of planet gears in the form of single gears, i.e. having the same set of gear teeth engaged both with the crown and the set of gear teeth50of the shaft42.

Advantageously, the invention further enables two members to be positioned opposite each other, rotating at very different speeds, one being rotatably connected with the shaft42, the other with the strut23or with a shaft connected to the strut23.

The device209illustrated inFIG. 5is an alternative to the device9described with reference toFIGS. 3 and 4. The parts that are common to the devices9and209carry the same references and are not described again.

The device209comprises a gear210, a crown241and a wall243.

The wall243forms a planet carrier on which the shafts44and therefore the planet gears40are mounted. The wall243has a rim421bon which is made an inner track of the overrunning clutch device51.

The crown241has a ring-shaped portion221bcoaxial with the rim21aof the gear210. This ring-shaped portion221bhas an inner set of gear teeth225that engages with the set of gear teeth49. The crown241is in this example secured to a frame of the gearbox that is fixed via a coupling48.

The device209shown inFIG. 5is present in the form of a single planetary gearset wherein the gear210plays the role of the mobile planet carrier by means of the overrunning clutch system51.

With reference toFIGS. 2A and 2B, the gear chains5and6have been described as being mounted in an accessory gearbox4aor4b(or AGB). Alternatively, a propeller gearbox (PGB) comprises a gear chain such as5or6. In this case, for example, the torque is initiated by the strut23, the propeller is mounted on the shaft42and the accessories are powered via the set of gear teeth24. Alternatively, an auxiliary power unit (APU) or a ram air turbine (RAT) comprise a gear chain5or6and provide a torque to the latter.

It should be noted that the invention is not limited to aircraft starters, and can apply to any mechanical device implementing a gear and a speed-increasing or reducer device, requiring decoupling between these two elements under certain rotation conditions.