ASSEMBLY OF SHAFTS OF A TURBOMACHINE COMPRISING A SYSTEM FOR ACTIVELY CONTROLLING INTER-SHAFT AXIAL TRANSLATIONS OF A BODY AND METHOD FOR ACTIVELY CONTROLLING AXIAL CLEARANCES BETWEEN A ROTOR ELEMENT AND A STATOR ELEMENT OF A TURBINE

Abstract

ASSEMBLY OF SHAFTS OF A TURBOMACHINE COMPRISING A SYSTEM FOR ACTIVELY CONTROLLING INTER-SHAFT AXIAL TRANSLATIONS OF A BODY AND METHOD FOR ACTIVELY CONTROLLING AXIAL CLEARANCES BETWEEN A ROTOR ELEMENT AND A STATOR ELEMENT OF A TURBINE Assembly of shafts of an aircraft turbomachine comprising: a drive shaft (40) comprising a downstream and upstream axial stop; a compressor shaft (41) comprising a downstream and upstream axial stop axially aligned between those of the drive shaft; a system for controlling axial translations of the drive shaft relative to the compressor shaft, said control system comprising: a pair of upstream cams and a pair of downstream cams (46) housed respectively between the upstream axial stops (43a, 42) the downstream axial stops (43b, 46) each pair (46, 47) of cams comprising a fixed cam (46f, 47f) and a movable cam (46p, 47p) rotating about an axis Z to form an angle A with the movable cam of the pair of upstream cams.FIGURE 5.

Description

Title of the invention: ASSEMBLY OF SHAFTS OF A TURBOMACHINE COMPRISING AN ACTIVE CONTROL SYSTEM FOR INTER-SHAFT AXIAL TRANSLATIONS OF A BODY AND CONTROL METHOD ACTIVE AXIAL CLEARANCES BETWEEN AN ELEMENT OF ROTOR AND STATOR ELEMENT OF A TURBINE TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the field of aeronautics and particularly to the field of aircraft turbomachine shafts.

[0002] The invention relates to a shaft assembly with an active control system for axial translations between two shafts by means of a double pair of cams. Another object of the invention is a method for controlling axial clearances between two turbine rotor elements / turbine stator part by using the active control system for two shafts of a body. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] An aeronautical turbomachine conventionally comprises a combustion chamber and a body comprising a compressor and a turbine. The role of the turbine is to ensure the rotational drive of the compressor by rotational coupling by two shafts, by taking part of the pressure energy from the hot gases leaving the combustion chamber and transforming it into mechanical energy.

[0004] A turbomachine generally comprises a low pressure body and a high pressure body.

[0005] A compressor and a turbine of a high pressure or low pressure body, each comprise a rotor part rotating about an axis of rotation and a part of a stator of the turbomachine. The turbomachine comprises a stator comprising each stator part and a rotor per body each comprising the rotor part of the compressor and the rotor part of the turbine.2

[0006] The stator part is said to be fixed and comprises a casing and a plurality of fixed blades (because they do not rotate around the axis of rotation of the rotor part but can be mobile in rotation along their own axis) fixed circumferentially on the casing or on shells of the casing. The rotor part comprises a drum comprising an assembly of several discs on which are fixed circumferentially rotating blades. Each row of fixed blades of the stator part, called rectifiers, forms a rectifier or distributor. A row of moving blades and a row of fixed blades form a compressor stage.

[0007] In operation, the thermal inertia and the forces applied to the turbine, for example low pressure, imply a greater expansion on elements of the stator part of the turbine, than on elements of the rotor of the turbine. It is therefore necessary to dimension the clearances between the ends of the elements of the rotor of the turbine and the ends of the stator part of the turbine facing each other as close as possible to each other in order to maintain, at all times during a flight mission, positive clearances and to prevent the two ends from coming into contact.

[0008] On the other hand, these games involve leaks and therefore a loss of engine efficiency which can lead to a drop in performance and an increase in fuel requirements during a flight mission.

[0009] [Fig.l] illustrates the axial displacements y as a function of time t during a flight mission. Curve 10 shows the displacements of one end of an element of a stator part, curve 11 shows the displacements of one end of an element of a rotor part opposite the other end. Curve 12 illustrates the differential displacement (stator - rotor). A positive displacement means a shift of the assembly considered downstream of the axial flow. The positive values ​​of the differential displacement illustrate that the displacement of the stator part is greater than that of the rotor part, which implies a closing of the clearances where the stator and upstream of the rotor.

[0010] In order to avoid contact on this type of clearance, it is therefore necessary to provide a sufficient margin to absorb the relative displacement of the stator downstream of the flow. [Fig. 2] schematically represents a half-axial section of a gas turbine engine 1. The turbomachine 1 also called a gas turbine engine, comprises a fan 49 and 4 main zones: a low-pressure compressor 41, a high-pressure compressor 51, a high-pressure turbine 500 and a low-pressure turbine 400. The low-pressure compressor 41 and the low-pressure turbine 400 each comprise a rotor comprising rows of rotor blades 412, 402, each mounted on a specific shaft 414, 404 (called low-pressure compressor shaft 414 and low-pressure turbine shaft 404) rotationally fixed to each other by a low-pressure drive shaft 40.The low pressure compressor 41 and the low pressure turbine 400 each comprise rows of stator blades 416, 406 secured to a stator S.

[0011] Similarly, the high-pressure compressor 51 and the high-pressure turbine 500 each comprise a rotor comprising rotor blades 512, 502, each mounted on a specific shaft 514, 504 (called high-pressure compressor shaft 514 and high-pressure turbine shaft 504) rotationally secured to each other by a high-pressure drive shaft 50. The high-pressure compressor 51 and the high-pressure turbine pressure 500 each further comprises stator vanes 516, 506 secured to the stator.

[0012] It is further represented in pentagons, an example of a non-contact clearance zone 413, 513, 503, 403 for each of the four main zones 41, 51, 500, 400, between a rotor blade and a stator blade. [Fig. 3] schematically represents a stator blade 6 and a rotor blade 2 of one of the four main zones 41, 51, 500, 400 and in particular that of zone 403. Such a type of clearance, however, involves air losses from the main vein to the outside. To limit them, the designer ensures an axial overlap zone 3 between the rotor blades 2 and the stator blades 6 during operation. In order to achieve the axial overlap 3, each stator blade 6 comprises more or less long spoilers 36 covering or covered by a platform 32 of the rotor blade 2. The length of these spoilers 36 and platform 32 will be limited by the risk of contact between the rotor part and the stator part.

[0013] The axial wedging between the rotor blades is today ensured by a shim, also called shim D48. [Fig. 4] represents in the upper part a very simplified schematic diagram of an example of a turbomachine comprising the stator S, the low pressure compressor 41, the fan 49 which are mounted here on a low pressure compressor shaft 414 mounted on a front bearing Pla and a rear bearing Plr in the stator S. The turbomachine comprises the low pressure drive shaft 40 on which the low pressure turbine 400 is mounted and a rear bearing POr mounted in the stator S. The turbomachine further comprises the high pressure part 5 mounted between the low pressure turbine 400 and the low pressure compressor 410.The high pressure part 5 comprises the high pressure shaft 50 on which the high pressure compressor 51 and the high pressure turbine 500 are mounted, which are shown schematically without its bearings with the stator S, the high pressure shaft here surrounds a part of the drive shaft 40. The low pressure compressor shaft 414 is integral in rotation with the low pressure turbine shaft 40 in a zone D by grooves shown in [Fig.2] and in a dotted square illustrated in the lower part in [Fig.4]. The shim D48 is mounted in this area, and allows the same timing to be maintained between the low pressure drive shaft 40 and the low pressure compressor shaft 414. The inter-shaft timing is ensured by a tightening nut 420. The low pressure compressor shaft 414 mounted on the front bearing Pla and rear bearing Plr allows the junction of the upstream part of the low pressure drive shaft 40 with the stator S.Thus, the low pressure compressor 41 provides the axial shim connection between the stator and the low pressure drive shaft 40. The shim D48 has an axial thickness according to the specific axial measurements of the elements of the turbomachine in order to take into account the manufacturing tolerances of these elements.

[0014] This solution is however not satisfactory because it does not make it possible to compensate, during the different phases of a flight mission, for the differential displacement between the rotor part and the stator part, in particular in zones 503 and 406, due to the hot gases expelled after the combustion chamber. Summary of the invention

[0015] The invention offers a solution to the problems mentioned above by proposing a system for active control of axial clearances between a drive shaft and a compressor shaft making it possible to move the turbine rotor axially relative to the elements of the turbine stator part to compensate for its greater expansion than that of the turbine.

[0016] A first aspect of the invention relates to a set of shafts of an aircraft turbomachine comprising: • a drive shaft by a turbine having an axis of rotation X and comprising an upstream axial stop and a downstream axial stop; • a compressor shaft, said compressor shaft being coupled in rotation with the drive shaft and comprising an upstream axial stop and a downstream axial stop; • an axial translation control system between the drive shaft and the compressor shaft, said control system comprising: - a pair of upstream cams housed between the upstream axial stop of the compressor shaft and the upstream axial stop of the drive shaft; - a pair of downstream cams housed between the downstream axial stop of the compressor shaft and the downstream axial stop of the drive shaft;

[0017] Each pair of cams comprising a fixed cam rotating relative to a Z axis parallel to the X axis and a movable cam rotating around the Z axis, each cam having an external face and an internal face, each internal face having at least one ramp, the internal face of the fixed cam being in contact with the internal face of the movable cam, the movable cam of the downstream pair of cams being pivoted around the Z axis to form an angle A with the movable cam of the upstream pair of cams, so that when the distance between the external faces of the upstream pair is at its maximum, the distance between the external faces of the cams of the downstream pair is at its minimum.

[0018] In the description, the terms “upstream” and “downstream” are defined with respect to the direction of air flow from the air inlet into the turbomachine to the air outlet from the turbomachine, i.e. from the upstream end of the compressor shaft to the downstream end of the drive shaft located opposite the upstream end. in the shaft assembly according to the aspect of the invention, (downstream end of the compressor shaft being that closest to the drive shaft).

[0019] The internal face of a cam is understood to mean the face which is opposite and in contact with the other cam of the pair. In other words, the internal face of a cam is always opposite the internal face of another cam. The external face of a cam is understood to mean the face opposite the internal face. In other words, the external face of a cam is always opposite one of the two axial stops of the compressor shaft or the drive shaft.

[0020] The distance between the outer faces of two cams belonging to the same pair of cams is also called the length of the pair of cams. The maximum distance between the outer faces of a pair of cams is understood to be the maximum distance between the two outer faces, the inner faces being in contact at at least one point. The minimum distance between the outer faces of a pair of cams is understood to be the minimum distance between the two outer faces, the inner faces being in contact at at least one point.

[0021] A ramp is understood to mean a portion of the internal face of a cam projecting along the Z axis. In other words, each cam has a thickness along the Z axis which varies along its periphery. For example, each cam may be a drum cam type cam.

[0022] The external faces of each pair of cams are in contact respectively with an axial stop of the drive shaft and the compressor shaft, so as to ensure the displacement of the compressor shaft relative to the drive shaft and therefore the displacement of the turbine rotor.

[0023] Thanks to the presence of the offset angle A between the movable cam of the upstream pair and the movable cam of the downstream pair, it is possible to simultaneously control the two movable cams so as to axially move the turbine shaft relative to the compressor shaft while keeping the sum of the lengths of the two pairs of cams constant. This makes it possible to maintain the axial inter-shaft clamping. The compressor shaft being in axial abutment against the stator, when the drive shaft is moved relative to the compressor shaft in axial abutment, the blades of the turbine move axially relative to the stator. The parts of the turbine are thus moved axially to compensate for the movement of the parts of the stator linked to the expansion.

[0024] In other words, the axial translation control system of the shaft assembly according to one aspect of the invention makes it possible to modify the clearance between the first ends of the elements of the turbine rotor relative to the ends (facing the first ends) of the “hot” turbine stator part, namely during operation of the low pressure or high pressure turbine, for example during a flight mission. This is achieved by implementing two variable-length shims instead of a single constant-length shim in the prior art. These two shims are here respectively the upstream pair of cams and the downstream pair of cams. Each pair of cams includes a cam that can be driven in rotation about the Z axis. In other words, the two cams of a pair of cams can rotate relative to each other (one is stationary in rotation relative to the Z axis and the other is movable in rotation relative to the Z axis) to lengthen or reduce the overall thickness of a pair of cams measured between the outer surface of the movable cam and the outer surface of the fixed cam of each pair. The two cams of an upstream or downstream pair of cams rotate relative to each other by driving the rotation of the movable cam about the Z axis.The two moving cams can be controlled by a device for controlling the two moving cams by an individual or simultaneous rotation drive system. When the moving cam of each pair of cams rotates around the X axis, the sum of the distance separating the external faces of the cams of the upstream pair of cams and the distance separating the external faces of the cams of the downstream pair of cams is constant. This thus makes it possible to maintain a timing of the drive shaft and therefore of the turbine shaft relative to the compressor shaft, while moving them axially relative to the upstream axial stop to avoid contact between stator blades and rotor blades, particularly at the level of the spoilers and platforms of the turbine.Thus the solution makes it possible to maintain the function of the prior art shim while being able to control the axial displacement of the turbine shaft to avoid contact between one end of an element of the rotor and one end of an element of the stator part of the turbine.

[0025] Thanks to the positioning on either side of the upstream / downstream axial stops of the compressor shaft or the drive shaft, the pair of upstream cams and the pair of downstream cams cooperate to shift the compressor shaft upstream or downstream relative to the drive shaft. Since the compressor shaft, when mounted in a bearing of a turbomachine, is axially abutted in an immobile axial translational manner relative to the stator bearing, the compressor shaft does not translate axially relative to the stator. Thus, the offset of the drive shaft relative to the compressor shaft makes it possible to offset the elements of the turbine rotor part axially relative to the stator in the upstream or downstream direction. This thus makes it possible to maintain a constant distance between the elements of the rotor part and the stator part.

[0026] It is important to note that, thanks to the angular offset of the movable cam of the downstream wedge (pair of cams) relative to the movable cam of the upstream wedge (pair of cams) and thanks to the simultaneous control of these two movable cams, an axial lengthening or reduction of the downstream wedge by a length l corresponds to respectively an axial reduction or lengthening of the upstream wedge by the same length l. By axial elongation of a shim, we mean that the two external surfaces of the cams of a pair of cams move away and conversely by an axial reduction of a shim we mean the bringing together of the two external surfaces of the cams of a pair of cams. For example, the elongation of the downstream shim by a rotation of its movable cam is compensated by a reduction of the upstream shim obtained by an opportune rotation of its movable cam. This makes it possible to keep the sum of the axial lengths of the two shims constant and therefore to keep the axial inter-shaft tightening (compressor / drive shaft) for any offset of the rotor part relative to the stator part.

[0027] Finally, the invention is suitable for a low-pressure body or a high-pressure body. The drive shaft may be mounted axially and rotatably connected to a turbine shaft (low pressure or high pressure) or may be integral with the turbine shaft or may be the turbine shaft. Thus, the compressor shaft may be that of a low-pressure or high-pressure compressor and the drive shaft may be that driven by a low-pressure or high-pressure turbine or may be the low-pressure or high-pressure turbine shaft, respectively.

[0028] According to one example, the fixed cam of the upstream pair is identical to the fixed cam of the downstream pair. According to one example, the movable cam of the upstream pair is identical to the movable cam of the downstream pair. According to one embodiment, all the cams have an identical internal face, namely an internal face having the same ramp or the same set of ramps.

[0029] According to one embodiment: - the drive shaft comprises a recess forming on either side the upstream axial stop and the downstream axial stop of the drive shaft and - the compressor shaft comprises a tooth housed in the recess forming on either side the upstream axial stop and the downstream axial stop of the compressor shaft.

[0030] According to another embodiment: - the drive shaft comprises a tooth forming on either side the upstream axial stop and the downstream axial stop of the drive shaft and - the compressor shaft comprises a recess housing the tooth, forming on either side the upstream axial stop and the downstream axial stop of the compressor shaft.

[0031] According to an example of one of the two preceding embodiments: - The external face of the fixed cam of the upstream pair of cams is in contact with the upstream axial stop delimiting the recess; - The external face of the movable cam of the upstream pair of cams is in contact with an upstream face of the tooth forming the upstream axial stop; - The external face of the fixed cam of the downstream pair of cams is in contact with a downstream face of the tooth forming the downstream axial stop; - The external face of the movable cam of the downstream pair of cams is in contact with the downstream axial stop delimiting the recess.

[0032] This arrangement makes it possible to obtain good contact between the external faces of the cams and respectively the axial stops delimiting the recess for example of the turbine shaft and the tooth for example of the compressor shaft. This makes it possible to offset, thanks to the variation of the lengths of the shims, the compressor shaft relative to the turbine shaft.

[0033] It is important to note that this arrangement of the fixed and movable cams in each pair of cams can be reversed. For example, the outer face of the upstream fixed cam can be in contact with an upstream wall of the tooth and the outer face of the upstream movable cam can be in contact with the upstream axial stop of the recess. Similarly, the arrangement of the downstream fixed cam and the downstream movable cam can be reversed.

[0034] According to one example, the drive shaft comprises a clamping nut screwed onto a thread portion of the drive shaft and spaced from a rim of the drive shaft forming the recess between them, the clamping nut comprising a downstream face forming the upstream axial stop delimiting the recess and the rim forms the downstream axial stop delimiting the recess; this makes it possible to use an element already in place in the junction of the two shafts using a shim of constant thickness (axial length) while having a clamping means making it possible to avoid significant play between the drive shaft and the compressor shaft causing vibrations and friction.

[0035] In one or more embodiments, each cam has a circular section along a cutting plane normal to the Z axis, the outer face of each cam being flat and normal to the Z axis; the use of flat outer faces makes it possible to improve the contact between the cams and respectively the axial stops.

[0036] In one or more embodiments, the fixed cam of the upstream pair of cams and the fixed cam of the downstream pair of cams are shrunk to the turbine shaft; this makes it possible to improve the guarantee of rotational tightening along the Z axis in operation between the fixed cam and the rotor shaft in order to improve control of the axial translation along the Z axis of the two movable cams relative to the turbine shaft and therefore of the turbine shaft during their rotation. This solution also makes it possible to improve the tightening axially along the Z axis and thus to avoid movement at the level of the nut that is not provided for or wear.

[0037] In one or more embodiments, each internal face comprises a single ramp and the pivot angle A of the downstream movable cam is equal to 180 degrees. This arrangement makes it possible to adjust the position of the movable cams so as to keep the sum of the lengths of the two shims constant while offsetting the low-pressure compressor shaft relative to the turbine shaft. Furthermore, using this pivoting of 180° avoids friction between the moving cams and the axial stops in order to reduce or even avoid wear. In addition, in the case of the example, of a nut with one face forming an upstream axial stop, this avoids the risk of the nut loosening and also wear of this face.

[0038] According to one example in one or more embodiments, the movable cams comprise a material allowing sliding between the movable cams and the low pressure drive shaft.

[0039] According to one embodiment, the compressor shaft and the low pressure drive shaft are secured in rotation to each other by splines allowing only axial translation relative to each other.

[0040] According to one embodiment, the set of shafts is a set of low pressure shafts.

[0041] According to one embodiment, the set of shafts is a set of high pressure shafts.

[0042] According to one embodiment, comprising a turbine shaft integral in rotation and axially with the drive shaft. According to one example, the turbine shaft is mounted on the drive shaft in a manner integral in rotation and axially. According to another example, the drive shaft and the turbine shaft are in one piece.

[0043] According to another embodiment, the drive shaft is a turbine shaft.

[0044] According to one example, the drive shaft is a high pressure turbine shaft.

[0045] According to one embodiment, the drive shaft is adapted to axially pass through an orifice surrounded by a combustion chamber of the turbomachine to couple the turbine in rotation to a compressor of the same body of the turbomachine. In other words, the combustion chamber surrounds a portion of the drive shaft.

[0046] According to another embodiment, the compressor shaft axially passes through a combustion chamber and in that the drive shaft is a turbine shaft adapted to drive the blades of a turbine in rotation.

[0047] Another aspect of the invention relates to a turbomachine comprising: - a stator comprising a turbine stator part and a compressor stator part, - a rotating part comprising the set of shafts according to the first aspect of the invention, in which • the drive shaft is movable in translation relative to the stator by the axial translation control system, • rotating turbine blades integral in rotation and axially with the drive shaft, • fixed blades of the turbine stator part opposite the moving turbine blades, - a front bearing mounted in the compressor stator part, in which the compressor shaft is mounted for rotation and is in axial abutment, - in which the control system axially moves the moving blades relative to the fixed blades of the turbine during rotation of the moving cams.

[0048] According to one embodiment, the turbomachine comprises - a low-pressure turbine comprising the moving rotor blades and the stator blades, a low-pressure turbine shaft integral in rotation and axially with the drive shaft and the rotor blades to couple them, - a rear bearing mounted between the drive shaft and the stator to support the drive shaft, in which the drive shaft is movable in axial translation relative to the bearing.

[0049] Another aspect of the invention relates to a method of controlling axial clearances between an end of a turbine rotor element and an end of an element of a turbine stator part by using the shaft assembly according to the first aspect of the invention by controlling the translation control system, said control method comprising the following steps: • Determination of a target distance between a stator element and a rotor element; • Measurement of the distance between the stator element and the rotor element; • Determination of the difference between the target distance and the measured distance; • Pivoting, on the basis of the determined gap, the movable cams so as to reduce the gap determined during the determination step, the sum of the distance separating the external faces of the cams of the upstream pair of cams and the distance separating the external faces of the cams of the downstream pair of cams being constant.

[0050] The term "target distance" between a stator element and a rotor element is understood to mean a previously determined distance which makes it possible both to reduce losses in the main air stream and to avoid contact between the rotor part and the stator part. The target distance may vary during a flight mission and depend, for example, on the phase of the flight mission.

[0051] By means of the method according to the second aspect of the invention, it is possible to actively control the distance between the rotor elements and the stator elements, so as to compensate for the differential displacement between these two series of elements. The method according to the second aspect of the invention makes it possible to adapt the axial translation of the transmission shaft relative to the stator so as to axially move the turbine rotor elements relative to those of the stator part of the turbine in order to avoid contact between them, while avoiding degradation of engine performance.

[0052] Thanks to the arrangement of the two pairs of cams, an axial elongation of one of the two pairs corresponds to a simultaneous reduction in axial length of the other pair, so as to maintain the sum of the lengths of the two shims. This also makes it possible to ensure inter-shaft clamping for any offset of the rotor part relative to the stator part.

[0053] In one or more embodiments, the distance between the rotor element and the stator element is measured using a distance sensor or a contact sensor.

[0054] In one or more embodiments, the pivoting step comprises simultaneously pivoting the movable cam of the upstream cam pair and the movable cam of the downstream cam pair.

[0055] In one or more embodiments, the pivoting step is performed using an automatic flight parameter control system.

[0056] The invention and its various applications will be better understood upon reading the following description and examining the accompanying figures. BRIEF DESCRIPTION OF THE FIGURES

[0057] Other advantages and characteristics of the invention will appear on reading the following description, illustrated by the figures among which:

[0058] [Fig. 1] illustrates a graph representing the axial displacements of the rotor part and the stator part of a low pressure turbine according to the state of the art;

[0059] [Fig.2] schematically illustrates an axial half-section of a turbomachine to illustrate axial clearances between elements of the rotor part and the stator part;

[0060] [Fig.3] illustrates a schematic diagram of a stator blade and a rotor blade to illustrate an axial overlap zone in a low pressure turbine;

[0061] [Fig.4] illustrates a schematic diagram of a turbomachine and an enlargement of an area comprising an example of inter-shaft timing between a low-pressure drive shaft and a low-pressure compressor shaft according to the state of the art;

[0062] [Fig.5] illustrates an embodiment of a part of a low pressure shaft assembly with an active axial translation control system according to the first aspect of the invention;

[0063] [Fig.6a] schematically illustrates a side view of one embodiment of a cam;

[0064] [Fig.6b] illustrates a sectional view of the cam illustrated in [Fig.6a];

[0065] [Fig.6c] illustrates a sectional view of an embodiment of a pair of upstream cams and a pair of downstream cams;

[0066] [Fig.7] schematically illustrates a flowchart of an embodiment of a method according to the second aspect of the invention;

[0067] [Fig.8] illustrates a graph representing the axial displacements of the rotor part and the stator part of a low pressure turbomachine according to the first aspect of the invention. DETAILED DESCRIPTION

[0068] Figures 1 and 4 have been described in relation to the state of the art and figures 2, 3 already described also apply to an aspect of the invention described below.

[0069] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0070] For the understanding of the invention, the radial R, tangential T and axial A orientations will be adopted according to the reference RTA indicated in the figures, the tangent T and axial A axes of which extend in a horizontal plane according to the orientation in the figures. The axial axis A is parallel to an axis of rotation X of an aircraft turbomachine comprising the axial translation control system according to one aspect of the invention.

[0071] The shaft assembly of the invention may be that of a low pressure body or that of a high pressure body. The description is described for a low pressure body but may be applied to a high pressure body. The same applies to a method for controlling axial clearances between one end of a turbine rotor element and one end of an element of a turbine stator part by using the shaft assembly.

[0072] [Fig.5] illustrates an embodiment of a set of shafts, in this case low pressure, according to one aspect of the invention.

[0073] According to the example illustrated in [Fig.5], the assembly comprises a drive shaft 40 secured to the rotor of the low-pressure turbine (not shown) and a compressor shaft 414 of the low-pressure compressor. The compressor shaft 414 is radially external to the low-pressure drive shaft 40. The two shafts are coaxial. The low-pressure drive shaft 40 and the compressor shaft 414 are secured in rotation by splines 40.1.

[0074] The low pressure drive shaft 40 comprises an upstream axial stop 42 and a downstream axial stop 45 delimiting between them in this example a recess 44.

[0075] According to the embodiment illustrated in [Fig. 5], the low pressure drive shaft 40 comprises an inter-shaft tightening nut 420 mounted on a threaded portion of an axis of the drive shaft 40, the downstream face of the nut 420 forms the upstream axial stop 42. The downstream axial stop 45 is a rim of the low pressure drive shaft 40.

[0076] The compressor shaft 414 comprises an upstream axial stop 43a and a downstream axial stop 43b aligned with the upstream and downstream axial stops 42, 45. In this case, the compressor shaft comprises a tooth 43 comprising on each of its axial end faces, the upstream axial stop 43a and the downstream axial stop 43b.

[0077] The recess 44 is sized to accommodate: • the tooth 43 at least partially housed in the recess 44; • a pair of upstream cams 46 positioned upstream of tooth 43 and at less partially housed in the recess 44; • a pair of downstream cams 47 positioned downstream of the tooth 43 and at least partially housed in the recess 44.

[0078] The two pairs of cams 46 and 47 form an active control system for axial translations in both directions between the compressor shaft 414 and the drive shaft 40 to control the axial clearances between the elements of the rotor part and the stator part of the turbine, in this case low pressure.

[0079] [Fig.6a] illustrates a three-dimensional side view of an embodiment of a cam C. According to the example illustrated in [Fig.6a], the cam C comprises an inner face Ci and an outer face Ce opposite the inner face Ci. The inner face Ci is intended to be in contact with another cam, for example in contact with an inner face of another cam. The outer face Ce is intended to be in contact with an axial stop element or in contact with the tooth 43. The cam C further comprises a ramp R, namely a region of the inner face Ci extending axially along the Z axis and projecting.

[0080] [Fig.6b] illustrates a sectional view of the cam C along a sectional plane passing through Fasse Z. In the example illustrated in [Fig.6b], the external face Ce of the cam C is flat and normal to the Z axis. The internal face Ci comprises a flat part and a part comprising the ramp R. The ramp R projects along the Z axis relative to the flat part of the internal face Ci.

[0081] In other embodiments, each cam may comprise a plurality of ramps R extending axially along the Z axis.

[0082] [Fig.6c] illustrates an example of an embodiment of the two pairs of upstream 46 and downstream 47 cams.

[0083] In the example illustrated in [Fig.6c], the pair of upstream cams 46 comprises an upstream fixed cam 46f and an upstream movable cam 46p. The upstream fixed cam 46f comprises an outer face 46f.e and an inner face 46f.i. The upstream movable cam 46p also comprises an inner face 46p.i and an outer face 46p.e. The inner face of the upstream fixed cam 46f.i is opposite and in contact with the inner face of the upstream movable cam 46p.i. Each internal face includes a ramp R extending axially from the cam along the Z axis.

[0084] According to the example illustrated in [Fig.6c], the pair of downstream cams 47 comprises a downstream fixed cam 47f and a downstream movable cam 47p. The downstream fixed cam 47f comprises an external face 47f.e and an internal face 47f.i. The downstream movable cam 47p also comprises an internal face 47p.i and an external face 47p.e. The internal face of the downstream fixed cam 47f.i is opposite and in contact with the internal face of the downstream movable cam 47p.i. Each internal face comprises a ramp R extending axially from the cam along the Z axis.

[0085] In the example illustrated in [Fig.6c], the downstream movable cam 47p is mounted pivoted around the Z axis relative to the upstream movable cam 46p. Thanks to this assembly, when the length of the upstream pair of cams 46 is at its maximum Lmax, the length of the downstream pair of cams 47 is at its minimum Lmin. In the case illustrated in [Fig.6c], the angular offset A between the upstream movable cam 46p and the downstream movable cam 47p is 180 degrees.

[0086] It is important to note that thanks to the assembly illustrated in [Fig.6a] and [Fig.6c], simultaneous control of the movable cams 46p and 47p makes it possible to keep the sum of the lengths of the two pairs of cams 46 and 47 constant. Here, the length of a pair of cams is understood to mean the distance separating the two external faces of the pair of cams, measured along the Z axis.

[0087] This mechanism makes it possible to control the axial offset between the compressor shaft 414 and the drive shaft 40, thus making it possible to control the axial clearances between elements of the rotor part of the turbine and elements of the stator part while maintaining the inter-shaft clamping.

[0088] It is important to note that the order of mounting of the fixed and movable cams of the pairs of cams illustrated in [Fig.6c] is not important for the implementation of the invention, provided that the angular offset and the simultaneous pivoting of the two movable cams are carried out as explained above. In other words, it is not necessary to position the fixed cams upstream of the movable cams. Indeed, it would also be possible to position the movable cams upstream of the fixed cams.

[0089] Each movable cam is driven in rotation by any known rotational drive means, whether by a motor directly or by means of gears, or by one or more connecting rods. The drive means may be a system driving the two movable cams simultaneously or two systems driving the movable cam individually but are controlled to rotate simultaneously. For example, a connecting rod system to actuate the two movable cams simultaneously in a phase-shifted manner to modify the clearances but maintain the clamping between the two shafts (compressor and drive) or a system controlling each movable cam in rotation independently. According to a example each cam includes on its periphery teeth meshed in a corresponding wheel, the two wheels being driven in rotation by the same motor or a hydraulic system.

[0090] Intentional shift of the turbine rotor downstream

[0091] The downstream movable cam 47p is controlled so as to lengthen the downstream pair of cams 47. At the same time, the upstream movable cam 46p is controlled so as to reduce the length of the pair of cams 46 by an amount equal to the increase in the length of the downstream pair of cams 47. This double pivoting makes it possible to shift the rotor part downstream. The tightening of the nut 420 is ensured by the fact that the sum of the lengths of the two pairs of cams is constant.

[0092] Intentional shift of the turbine rotor towards the upstream

[0093] The movable cam 46p of the upstream pair of cams 46 is controlled in order to increase its length. At the same time, the downstream movable cam 47p is controlled in order to reduce its length by an amount identical to the increase in length of the upstream pair of cams. This makes it possible to shift the rotor part downstream, while maintaining the inter-shaft clamping, namely while maintaining the sum of the lengths of the two pairs of cams.

[0094] Thus the turbomachine 1 according to one aspect of the invention is similar to that shown in [Fig. 2] and 3 of the prior art except in that it comprises a set of shafts according to the first aspect of the invention. The turbomachine therefore comprises a stator S comprising a turbine stator part and a compressor stator part, a rotary part comprising the set of shafts according to the first aspect of the invention, for example that described in the description of a low-pressure body. The drive shaft 40 is movable in translation relative to the stator by the axial translation control system. The turbine comprises rotor blades 2 such as, for example, that described with reference to [Fig. 3], movable in rotation relative to the stator and integral in rotation and axially with the drive shaft 40. The turbine 400, 500 comprises fixed stator blades 6, 406, such as, for example, that described with reference to [Fig.3], of the turbine stator part opposite the rotor blades 2, 402 of the turbine. The turbomachine comprises a front bearing Pla mounted in the compressor stator part, in which the compressor shaft 414 is mounted in rotation and in axial abutment while being integral in axial translation with the front bearing Pla and therefore with the stator S.

[0095] The control system axially moves the moving rotor blades relative to the fixed blades during rotation of the moving cams.

[0096] The turbomachine 1, in the case of the example described previously, comprises a low-pressure turbine 400 comprising the moving blades 2, 402 and the turbine blades fixed 6, 406, a low pressure turbine shaft 404 integral in rotation and axially with the drive shaft 40 and the turbine blades to couple them.

[0097] The turbomachine 1 comprises a rear bearing POr mounted between the drive shaft 40 and the stator S to support the drive shaft 40, in which the drive shaft is movable in axial translation relative to the bearing POr.

[0098] According to one embodiment, the rotation control of the movable cams to lengthen and reduce the distance between two external surfaces of the cams of the two pairs of cams are managed by an automatic flight parameter control system such as the FADEC system. The rotation is carried out by an individual or simultaneous system.

[0099] [Fig.7] illustrates an example of an embodiment of a method 90 for controlling axial clearances between one end of a turbine rotor element and one end of an element of a turbine stator part by using the shaft assembly by controlling the system for controlling axial translations between a turbine drive shaft and a compressor shaft, here in this case low pressure, according to another aspect of the invention.

[0100] As illustrated in [Fig.7], the method 90 according to one aspect of the invention comprises a step 91 of determining a target distance between an element of the stator and an element of the rotor.

[0101] The target distance can be determined for example as a function of the phase of the flight mission or as a function of other parameters of the turbomachine.

[0102] The method 90 further comprises a step 92 of measuring the distance between the stator element and a rotor element. The distance is for example measured using a sensor, such as an optical sensor or a contact sensor.

[0103] The difference between the target distance and the measured distance is determined during a determination step 93. The comparison of these two distances makes it possible to determine whether it is necessary to offset the rotor part relative to the stator part in order to maintain the target distance.

[0104] In the example illustrated in [Fig.7], the method 90 further comprises a step of pivoting the movable cams. During the pivoting step 94 the angular positions of the two movable cams are modified simultaneously so as to move the rotor part relative to the stator part while maintaining the sum of the axial lengths of the pairs of cams.

[0105] The pivoting step 94 may for example comprise the simultaneous pivoting of the two movable cams.

[0106] [Fig.8] shows a graph representing the difference between the axial displacements y of the stator part and the rotor part as a function of time t during a flight mission, namely the gap between an element of the stator part and an element of the rotor in with respect to each other, as a function of time. Curve 80 shows the difference in axial displacements in the absence of an active control system according to one aspect of the invention. The offset between the stator part and the rotor part varies over time and is always positive. Curve 81 shows the difference in axial displacements in the presence of the active control system for axial translations of the shaft assembly according to one aspect of the invention. It is obvious that in a low-pressure turbine according to one aspect of the invention the distance between the rotor part and the stator part is constant thanks to the dynamic compensation of the axial offset.

Claims

1. Claims Set of shafts of an aircraft turbomachine comprising: - a drive shaft (40, 50) adapted to be driven by a turbine (400, 500), having an axis of rotation X and comprising an upstream axial stop (42) and a downstream axial stop (45); - a compressor shaft (414, 514), said compressor shaft (414) being rotatably coupled with the drive shaft (40) and comprising an upstream axial stop (43a) and a downstream axial stop (43b); - a system for controlling axial translations between the drive shaft (40) and the compressor shaft (414), said control system comprising: • a pair of upstream cams (46) housed at least between the upstream axial stop (43a) of the compressor shaft (414) and the upstream axial stop (42) of the drive shaft (40); • a pair of downstream cams (47) housed between the downstream axial stop (43b) of the compressor shaft (414) and the downstream axial stop (46) of the drive shaft (40); - each pair (46, 47) of cams comprising a fixed cam (46f, 47f) rotatable relative to a Z axis parallel to the X axis and a movable cam (46p, 47p) rotatable around the Z axis, each cam (46f, 47f, 46p, 47p) having an external face (46f.e, 46p.e, 47f.e, 47p.e) and an internal face (46f.i, 46p.i, 47f.i, 47p.i), each internal face (46f.i, 46p.i, 47f.i, 47p.i) having at least one ramp (R), the internal face of the fixed cam (46f.i, 47f.i) being in contact with the internal face of the movable cam (46p.i, 47p.i), the movable cam of the downstream pair of cams (47p) being pivoted about the Z axis to form an angle A with the movable cam of the upstream pair of cams (46p), so that when the distance between the external faces (46f.e,46p.e) of the cams of the upstream pair (46) is at its maximum, the distance between the external faces (47f.e,47p.e) of the cams of the downstream pair (47) is at its minimum.

2. Shaft assembly according to the preceding claim in which: - the drive shaft (40, 50) or the compressor shaft (414, 514) comprises a recess (44) forming on either side the upstream axial stop (42) and the downstream axial stop (45) respectively of the drive shaft (40, 50) or of the compressor shaft (414, 514) and - respectively the compressor shaft (414, 514) or the drive shaft (40, 50) comprises a tooth (43) housed in the recess (44), the tooth (43) forming on either side the upstream axial stop (43a) and the downstream axial stop (43b) respectively of the compressor shaft (414, 514) or the drive shaft (40, 50).

3. Shaft assembly according to the preceding claim in which: - The external face (46f.e) of the fixed cam of the upstream pair of cams is in contact with the upstream axial stop (42) delimiting the recess (44); - The external face (46p.e) of the movable cam (46p) of the upstream pair of cams (46) is in contact with an upstream face of the tooth (43) forming the upstream axial stop (43a); - The external face (47f.e) of the fixed cam (47f) of the downstream pair of cams (47) is in contact with a downstream face of the tooth (43) forming the downstream axial stop (43b); - The external face (47pe) of the movable cam (47p) of the pair of downstream cams (47) is in contact with the downstream axial stop (45) delimiting the recess (44).

4. Shaft assembly according to the preceding claim in which the drive shaft (40, 50) comprises a clamping nut (420) screwed onto a thread portion of the drive shaft (40, 50) and distant from a rim of the drive shaft (40, 50) forming between them the recess (44), the clamping nut (420) comprising a downstream face forming the upstream axial stop (42) delimiting the recess (44) and the rim forms the downstream axial stop (45) delimiting the recess (44).

5. A shaft assembly according to any preceding claim wherein the fixed cam of the upstream pair of cams (46) and the fixed cam of the downstream pair of cams (47) are shrunk to the drive shaft (40, 50).

6. A set of shafts according to one of the preceding claims in which each internal face comprises a single ramp and the pivot angle A of the downstream movable cam is equal to 180 degrees.

7. Turbomachine comprising: - a stator (S) comprising a turbine stator part and a compressor stator part, - a rotary part comprising the set of shafts according to one of the preceding claims, in which • the drive shaft (40, 50) is movable in translation relative to the stator by the axial translation control system, • rotor blades (2, 402) of the turbine (400, 500), movable in rotation relative to the stator (S) and integral in rotation and axially with the drive shaft (40, 50), • fixed stator blades (6, 406) of the turbine stator part opposite the rotor blades (2, 402), - a front bearing (Pla) mounted in the compressor stator part, in which the compressor shaft (414) is mounted in rotation and in axial abutment, - in which the control system moves axially the rotor blades (2,402) movable relative to the fixed stator vanes (6, 406) during rotation of the movable cams.,

8. Turbomachine according to the preceding claim, comprising: - a low pressure turbine (400) comprising the movable rotor blades (2, 402) and the fixed stator blades (6, 406), a low pressure turbine shaft (404) integral in rotation and axially with the drive shaft (40) and with the rotor blades (2, 402) to couple them, - a rear bearing (POr) mounted between the drive shaft and the stator (S) to support the drive shaft (40), in which the drive shaft (40) is axially movable in translation relative to the bearing (POr).

9. Method (90) for controlling axial clearances between one end of a turbine rotor element and one end of an element of a

10. turbine stator part by using the shaft assembly according to one of the preceding claims 1 to 6 in controlling the translation control system, the method comprising the following steps: - Determination (91) of a target distance between an element of the stator and an element of a rotor turbine; - Measurement (92) of the distance between the stator element and the rotor element; - Determination (93) of the difference between the target distance and the measured distance; - Pivoting (94), on the basis of the determined gap, the movable cams so as to reduce the gap determined during the determination step (93), the sum of the distance separating the external faces of the cams of the upstream pair of cams and the distance separating the external faces of the cams of the downstream pair of cams being constant. Method (90) according to the preceding claim wherein the pivoting step (94) comprises simultaneously pivoting the movable cam of the upstream pair of cams and the movable cam of the downstream pair of cams.

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