Assembly comprising a shaft and an electric machine for an aircraft turbine engine, and method for mounting the assembly

Abstract

The invention relates to an assembly comprising a shaft (10) and an electric machine (14) for an aircraft turbine engine, the shaft (10) being generally tubular and elongate in shape along an axis (X) and comprising, at a first longitudinal end (10a), first splines (12), wherein the electric machine (14) comprises a rotor (16), the axis of rotation of which is aligned with the axis (X) of the shaft (10) and which comprises, at a second end (16a), second splines (18) which fit into or onto the first splines (12) in order to rotationally couple the shaft (10) to the rotor (16), characterised in that it further comprises at least one torsionally elastically deformable member (20) that co-operates with the shaft (10) and the rotor (16) so as to impose a torsional preload between the first and second splines (12, 18) in the absence of transmission torque between the rotor (16) and the shaft (10).

Description

[0001] DESCRIPTION

[0002] TITLE: ASSEMBLY COMPRISING A SHAFT AND AN ELECTRIC MACHINE FOR AN AIRCRAFT TURBOMACHINE, AND METHOD FOR ASSEMBLING THIS ASSEMBLY

[0003] Technical field of the invention

[0004] The invention relates in particular to an assembly comprising a shaft and an electric machine for an aircraft turbomachine, as well as a method of mounting this assembly.

[0005] Technical background

[0006] The state of the art includes in particular documents FR-A1 -3 124 541, FRAI -3 123 375, JP-U-H03 72118, DE-A1-10 2017 117507, FR-A-1 311 970, W0-A1 -2016 / 091261, DE-A1 -10 2008 014445 and DE-A1 -10 2017 205657.

[0007] As is well known, an aircraft turbomachine extends along a longitudinal axis and comprises, from upstream to downstream in the direction of gas flow, a fan, at least one compressor, an annular combustion chamber, at least one turbine and finally a combustion gas exhaust nozzle. In the case of a twin-spool turbomachine, respectively low pressure and high pressure, the turbomachine comprises, between the fan and the nozzle, a low pressure compressor, a high pressure compressor, the combustion chamber, a high pressure turbine, and a low pressure turbine.

[0008] The high-pressure body comprises a high-pressure shaft that connects the rotor of the high-pressure compressor to the rotor of the high-pressure turbine. The high-pressure shaft is tubular and axially traversed by the low-pressure shaft of the low-pressure body. This low-pressure shaft connects the rotor of the low-pressure compressor to the rotor of the low-pressure turbine, and is further connected directly or via a mechanical reducer to the fan shaft. In order to seek hybridization solutions, it is known to equip a turbomachine with an electric machine. In the present application, the term "electric machine" means, for example, a motor, a generator or a motor / generator.

[0009] An electric machine can for example be mounted on an accessory or gear box, commonly called AGB (which is the acronym for Accessory Gear Box), and can take power from one of the turbomachine's shafts, or inject power into one of these shafts, via a radial shaft.

[0010] An electric machine can also be mounted at one end of a shaft and directly coupled to this shaft. The present application is concerned with this particular technology.

[0011] As can be seen in Figures 1 and 2, two configurations are possible. The shaft 10 has a generally tubular shape and is elongated along an axis X and has first grooves 12 at a first longitudinal end 10a.

[0012] The electrical machine 14 comprises a rotor 16 whose axis of rotation is aligned with the axis X and which comprises at a second end 16a second splines 18 which cooperate with the first splines 12 in order to ensure rotational coupling of the shaft 10 with the rotor 16.

[0013] The second splines 18 may be engaged in or on the first splines 12.

[0014] In Figure 1, the end 10a of the shaft 10 is a male end and its splines 12 are external splines. The end 16a of the rotor 16 is a female end and its splines 18 are internal splines. It is therefore understood that the end 10a is engaged in the end 16a and that the external splines 12 are engaged in the internal splines 18. In Figure 2, the end 10a of the shaft 10 is a female end and its splines 12 are internal splines. The end 16a of the rotor 16 is a male end and its splines 18 are external splines. It is therefore understood that the end 16a is engaged in the end 10a and that the external splines 18 are engaged in the internal splines 12.

[0015] The combination of a shaft and an electrical machine as illustrated in Figures 1 and 2 forms an assembly within the meaning of the present application.

[0016] In this technology, it is necessary to take into account the dynamics of the electric machine for the characterization of torsional oscillations.

[0017] In the case where the shaft of the assembly is a low pressure shaft for example, this shaft is generally free downstream so the torsion issues in this shaft depend only on the rotor of the low pressure turbine. The addition of an electric machine whose rotor is linked to the shaft in order to allow the transmission of torque adds a major contributor to the overall dynamics. The rotor line undergoes the variations in torque taken by the machine and generated by a regulation system controlled by the needs of the engines and the aircraft.

[0018] An identified risk is the loss of contact torque at the splines, which can lead to inversion of the support flanks of these splines. This inversion of torque in the splines modifies the dynamic properties of the connection (stiffness / damping), allowing other resonance modes to be excited by coupling and can generate premature wear of the various components.

[0019] Figure 3 is a graph showing the evolution of the torsional stiffness of splines as a function of the torque transmitted to these splines. It can be seen that at start-up, the stiffness does not evolve linearly and on the contrary varies greatly up to a certain torque level. Operating the splines in the torque range where its stiffness is highly variable can lead to the appearance of non-linear phenomena which can be a source of instability.

[0020] Furthermore, in the context of a supercritical rotor, the variation in the dynamic properties of the connection generates uncertainty regarding the rotating damping generated by the splines, a determining value for evaluating rotor stability. Traditionally, torque transmissions by splines between two rotors in a turbomachine are carried out by means of centered splines. The shrinking on either side of the splines makes it possible to overcome these dynamic disturbances. However, the positioning of the electric machine at the end of the shaft involves undergoing relative axial displacements which prevent the use of centered splines.

[0021] The invention provides a simple, effective and economical solution to at least some of these problems.

[0022] Summary of the invention

[0023] To this end, the invention proposes an assembly comprising a shaft and an electrical machine for an aircraft turbomachine, the shaft having a generally tubular shape and elongated along an axis and comprising at a first longitudinal end first splines, the electrical machine comprising a rotor whose axis of rotation is aligned with the axis of the shaft and which comprises at a second end second splines engaged in or on the first splines in order to ensure rotational coupling of the shaft with the rotor, characterized in that it further comprises at least one elastically deformable member in torsion which cooperates with the shaft and the rotor to impose a torsional preload between the first and second splines in the absence of transmission torque between the rotor and the shaft.

[0024] The invention thus proposes to use an elastic member to ensure a torsional prestress between the splines. This prestress makes it possible to overcome the non-linear operating range presented previously by guaranteeing a torque and therefore a minimum contact pressure in the connection in the nominal operating cases of the assembly. This is in order to guarantee a predictable and calculable behavior of the connection (stiffness, damping). The assembly according to the invention may comprise one or more of the following characteristics, taken in isolation from one another or in combination with one another:

[0025] - the organ is annular and is centered on the axis of the shaft;

[0026] - one of the first and second ends is a male end, and the other of the first and second ends is a female end, the splines of the male end being external splines and the splines of the female end being internal splines, the member being mounted in the female end;

[0027] - the member comprises a first axial end fixed to the male end and a second axial end which is opposite the first end and which is fixed to an externally toothed wheel, the external splines and the external teeth of this wheel being engaged in the internal splines;

[0028] - the member is axially interposed and axially compressed between the male end and a part of the female end.

[0029] - the member has its two axial ends which are axially supported respectively on the male end and the female end and which are integral in rotation respectively with the male end and the female end;

[0030] - the member also cooperates with the shaft and the rotor to impose an axial preload between the rotor and the shaft.

[0031] The present invention also relates to a turbomachine for an aircraft, this turbomachine comprising at least one assembly as described above.

[0032] Advantageously, the axis of the shaft coincides with the longitudinal axis of the turbomachine.

[0033] In a preferred embodiment, the shaft is a low pressure shaft which connects a rotor of a low pressure compressor to a rotor of a low pressure turbine. The present invention also relates to a method of mounting an assembly as described above, characterized in that it comprises the following steps: a) twisting the member, and b) engaging the second splines in or on the first splines.

[0034] In one embodiment, the method comprises:

[0035] - before step a), a step i) of engaging the external teeth of the wheel in the internal splines,

[0036] - in step a), twisting the member by rotating the male end relative to the female end, or vice versa, up to a predetermined load and until the external grooves are in a position such that they can be axially engaged in the internal grooves, and

[0037] - in step b), the engagement of the external grooves in the internal grooves.

[0038] Alternatively, the method comprises:

[0039] - before step a), a step i) of mounting the member in the female end, the member comprising a first axial end which is axially supported on the female end and which is integral in rotation with the female end, then a step ii) of engaging the male end in the female end from a first position in which the male end is axially aligned with the female end and is not yet engaged in it, to a second position in which the male end is engaged in the female end and the male splines are axially spaced from the female splines, passing through an intermediate position in which the male end is engaged in the female end and the male splines are engaged in the female splines, step ii) causing the male end to be axially supported on a second axial end of the member opposite the first end,and the axial compression of the member as well as the rotational connection of the member with the male end,

[0040] - in step a), twisting the member by rotating the male end relative to the female end, or vice versa, up to a predetermined load and until the external grooves are in a position such that they can be axially engaged in the internal grooves, and

[0041] - in step b), engaging the external splines in the internal splines by moving the male end in the female end from the second position to the intermediate position.

[0042] Brief description of the figures

[0043] Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which:

[0044] [Fig.1] Figure 1 is a partial schematic view in axial section of an assembly comprising a shaft and an electric machine;

[0045] [Fig.2] Figure 2 is a partial schematic view in axial section of another assembly comprising a shaft and an electric machine;

[0046] [Fig.3] Figure 3 is a graph showing the evolution of the torsional stiffness of splines as a function of the torque transmitted to these splines;

[0047] [Fig.4a-4c] Figures 4a-4c are very schematic partial views in axial section of an assembly according to a first embodiment of the invention;

[0048] [Fig.5a-5c] Figures 5a-5c are very schematic partial views in axial section of an assembly according to a second embodiment of the invention;

[0049] [Fig.6a-6c] Figures 6a-6c are very schematic partial views in axial section of an assembly according to a third embodiment of the invention. Detailed description of the invention

[0050] Figures 1 to 3 have been described in the above.

[0051] The present invention relates to an assembly comprising a shaft 10 and an electric machine 14 for an aircraft turbomachine.

[0052] Conventionally, the turbomachine has a longitudinal axis denoted X. The turbomachine can be of the double-body type and include a low-pressure body and a high-pressure body.

[0053] The turbomachine conventionally comprises a gas generator which comprises from upstream to downstream, in the direction of flow of the combustion gases, a low pressure compressor, a high pressure compressor, an annular combustion chamber, a high pressure turbine, and a low pressure turbine.

[0054] The rotor of the high-pressure compressor is connected by a high-pressure shaft to the rotor of the high-pressure turbine, to form the high-pressure body. The rotor of the low-pressure compressor is connected by a low-pressure shaft to the rotor of the low-pressure turbine, to form the low-pressure body.

[0055] The shaft 10 of the assembly is preferably a low pressure shaft although this aspect is not limiting.

[0056] The shaft 10 has a generally tubular and elongated shape along the axis X and comprises at a first longitudinal end 10a first splines 12.

[0057] The electrical machine 14 is for example a motor, a generator or a motor / generator.

[0058] The electric machine 14 is mounted at one end of the shaft 10 in the axial extension thereof.

[0059] The electrical machine 14 comprises a rotor 16 whose axis of rotation is aligned with the axis X and which comprises at a second end 16a second splines 18 engaged in or on the first splines 12 in order to ensure rotational coupling of the shaft with the rotor. As explained in the foregoing and illustrated in Figures 1 and 2, one of the ends 10a, 16a among the first and second ends is a male end, and the other of the ends 16a, 10a among the first and second ends is a female end, the splines of the male end being external splines and the splines of the female end being internal splines.

[0060] In Figure 1, the end 10a of the shaft 10 is a male end and its splines 12 are external splines. The end 16a of the rotor 16 is a female end and its splines 18 are internal splines. It is therefore understood that the end 10a is engaged in the end 16a and that the external splines 12 are engaged in the internal splines 18. In Figure 2, the end 10a of the shaft 10 is a female end and its splines 12 are internal splines. The end 16a of the rotor 16 is a male end and its splines 18 are external splines. It is therefore understood that the end 16a is engaged in the end 10a and that the external splines 18 are engaged in the internal splines 12.

[0061] The present invention proposes adding to the assembly at least one elastically deformable member 20 in torsion which is configured to cooperate with the shaft 10 and the rotor 16 to impose a torsional preload between the first and second splines 12, 18 in the absence of transmission torque between the rotor 16 and the shaft 10.

[0062] Preferably, the member 20 is annular and is centered on the X axis.

[0063] The member 20 may be selected from a compression spring, a torsion spring, a helical spring, a ring, a sleeve, etc.

[0064] We now refer to Figures 4a to 4c which illustrate a first embodiment of the invention.

[0065] In these figures, the end 10a of the shaft 10 is a male end and includes external splines 12. The shaft 10 is on the left in the drawing. The end 16a of the rotor 16 is a female end and includes internal splines 18. The rotor 16 is on the right in the drawing. In the drawings, it can be seen that the splines 18 have a length L2 greater than the length L1 of the splines 12 as an example.

[0066] The member 20 is for example a torsion spring.

[0067] The member 20 comprises a first axial end 20a fixed to the end 10a of the shaft 10, and a second axial end 20b which is opposite the first end 20a and which is fixed to a wheel 22 with external teeth 24. It can be seen that the cumulative lengths L1 + L3 + L4 of the splines 12, of the member 20 and of the wheel 22, are substantially equal to the length L2 of the splines 18. In practice, it would be advantageous for the cumulative lengths L1 + L3 + L4 to be less than the length L2. This would ensure the engagement of all the splines in operation while maintaining a certain margin to take into account the relative displacements of the parts in the axial direction in operation.

[0068] The toothing 24 of the wheel 22 is capable of being engaged in the splines 18 of the end 16a of the rotor 16 (figure 4b). Furthermore, the splines 12 and the toothing 24 are capable of being engaged at the same time in the splines 18 (figure 4c).

[0069] Figures 5a to 5c illustrate a second embodiment of the invention. In these figures, the end 10a of the shaft 10 is a female end and includes internal splines 12. The shaft 10 is on the left in the drawing. The end 16a of the rotor 16 is a male end and includes external splines 18. The rotor 16 is on the right in the drawing.

[0070] In the drawings, it can be seen that the grooves 18 have a length L2 less than the length L1 of the grooves 12 for example.

[0071] The member 20 is for example a torsion spring.

[0072] The member 20 comprises a first axial end 20a fixed to the end 16a of the rotor 16, and a second axial end 20b which is opposite the first end 20a and which is fixed to a wheel 22 with external teeth 24. It can be seen that the cumulative lengths L2+L3+L4 of the splines 18, of the member 20 and of the wheel 22, are substantially equal to the length L1 of the splines 12. In practice, it would be advantageous for the cumulative lengths L2+L3+L4 to be less than the length L1, as mentioned above.

[0073] The teeth 24 of the wheel 22 are capable of being engaged in the splines 12 of the end 10a of the shaft (figure 5b). Furthermore, the splines 18 and the teeth 24 are capable of being engaged at the same time in the splines 12 (figure 5c).

[0074] Figures 6a to 6c illustrate a third embodiment of the invention. In these figures, the end 10a of the shaft 10 is a female end and includes internal splines 12. The shaft 10 is on the left in the drawing. The end 16a of the rotor 16 is a male end and includes external splines 18. The rotor 16 is on the right in the drawing.

[0075] It can be seen that the grooves 12, 18 have similar lengths L1, L2. In practice, it would be advantageous if the lengths L1 and L2 were optimized to take into account possible relative displacements of the parts in the axial direction during operation.

[0076] The member 20 is for example a compression spring.

[0077] The member 20 is axially interposed and axially compressed between the end 16a and a portion of the end 10a.

[0078] The member 20 has its two axial ends 20a, 20b which are axially supported respectively on the ends 16a, 10a and which are integral in rotation respectively with these ends 16a, 10a. For this, the end 20b of the member 20 can be fixed to the end 10a or to the part on which it is supported. The end 20a of the member 20 can be made integral in rotation with the end 16a by complementarity of shapes. For example, the end 16a can comprise one or more teeth 26 axially engaged in a housing complementary to the end 20a and capable of cooperating by support in the circumferential direction with the sides of this housing.

[0079] In Figure 6a, the member 20 is in the free state without constraint.

[0080] In Figure 6b, the member 20 is axially compressed between the ends 10a, 16a. In Figure 6c, the member 20 is axially constrained between the ends 10a, 16a and axially biases the ends 10a, 16a to axially separate them from each other. The member 20 thus imposes an axial preload between the rotor 16 and the shaft 10.

[0081] In a variant not shown, the configuration of figures 6a to 6c could be applied to the case where the shaft 10 is on the right and the rotor 16 is on the left in the drawing.

[0082] Other variants not shown are also conceivable. This is particularly the case where the element used for applying torsional stress comprises female rather than male splines in the context of the first embodiments. This is also the case where the member 20 used for applying torsion is located outside the male rotor 16 and rests on the shaft 10 in the context of the last embodiment.

[0083] We will now describe a method according to the invention for mounting an assembly according to the invention.

[0084] This method essentially comprises two steps a) and b), namely a step a) of twisting the member 20, and a step b) of engaging the grooves 12, 18 in each other.

[0085] In the embodiments of Figures 4a-4c and 5a-5c, the method may comprise the following steps:

[0086] - before step a), a step i) of engagement of the external teeth 24 of the wheel 22 in the internal splines 18 (see figures 4a and 4b, or 5a and 5b),

[0087] - in step a), twisting the member 20 by rotating the male end 10a or 16a with respect to the female end 16a or 10a, or vice versa (see arrow F1 in figure 4b or arrow F2 in figure 5b), up to a predetermined load and until the external splines 12 or 18 are in a position such that they can be axially engaged in the internal splines 18 or 12, and

[0088] - in step b), the engagement of the external splines 12 or 18 in the internal splines 18 or 12 (see figure 4c or 5c). It is therefore understood that the member 20 is kept under torsional stress between the end 10a or 16a and the wheel 22, and imposes a torsional preload on the splines 12, 18 which are kept in circumferential support on each other.

[0089] In the embodiments of Figures 6a-6c, the method may comprise the following steps:

[0090] - before step a), a step i) of mounting the member 20 in the female end 10a, the member 20 comprising a first axial end 20b which is axially supported on the female end 10a and which is rotationally integral with the female end 10a, then a step ii) of engaging the male end 16a in the female end 10a from a first position in which the male end 16a is axially aligned with the female end 10a and is not yet engaged therein (see figure 6a), to a second position in which the male end 16a is engaged in the female end 10a and the male splines 18 are axially spaced from the female splines 12 (see figure 6b), passing through an intermediate position in which the male end is engaged in the female end 10a and the splines 18 males are engaged in the 12 female grooves (cf.figure 6c), step ii) causing the male end 16a to bear axially on a second axial end 20a of the member 20 opposite the first end 20b, and the axial compression of the member 20 as well as the rotational securing of the member 20 with the male end 16a.

[0091] - in step a), twisting the member 20 by rotating the male end 16a with respect to the female end 10a, or vice versa, up to a predetermined load and until the external grooves 18 are in a position such that they can be axially engaged in the internal grooves 12 (see arrow F3 in figure 6b), and

[0092] - in step b), the engagement of the external grooves 18 in the internal grooves 12 by moving the male end 16a in the female end 10a from the second position to the intermediate position (see figure 6c). It is therefore understood that the member 20 is kept stressed in compression and in torsion between the ends 10a, 16a, and imposes a torsional preload on the grooves 12, 18 which are kept in circumferential support on each other.

[0093] For example:

[0094] - the nominal torque at the splines can vary between 100 Nm and 1000 Nm depending on the operating points, and / or

[0095] - the torque preload would compensate for an oscillating torque whose amplitude could reach 30% of the nominal torque, and / or

[0096] - the number of teeth on the splines is between 10 and 100, and / or

[0097] - the torsional stiffness of the prestressed member is between 10 Nm / rad and 2500 Nm / rad depending on the number of teeth and the nominal torque.

Claims

CLAIMS 1. Assembly comprising a shaft (10) and an electrical machine (14) for an aircraft turbomachine, the shaft (10) having a generally tubular shape and elongated along an axis (X) and comprising at a first longitudinal end (10a) first splines (12), the electrical machine (14) comprising a rotor (16) whose axis of rotation is aligned with the axis (X) of the shaft (10) and which comprises at a second end (16a) second splines (18) engaged in or on the first splines (12) in order to ensure rotational coupling of the shaft (10) with the rotor (16), characterized in that it further comprises at least one member (20) elastically deformable in torsion which cooperates with the shaft (10) and the rotor (16) to impose a torsional preload between the first and second splines (12, 18) in the absence of transmission torque between the rotor (16) and the shaft (10).

2. Assembly according to claim 1, in which the member (20) is annular and is centered on the axis (X) of the shaft (10).

3. An assembly according to claim 2, wherein one of the first and second ends (10a, 16a) is a male end, and the other of the first and second ends (16a, 10a) is a female end, the splines (12, 18) of the male end being external splines and the splines (18, 12) of the female end being internal splines, the member (20) being mounted in the female end.

4. Assembly according to claim 3, in which the member (20) comprises a first axial end (20a) fixed to the male end and a second axial end (20b) which is opposite the first end and which is fixed to a wheel (22) with external teeth (24), the external splines and the external teeth (24) of this wheel (22) being engaged in the internal splines.

5. An assembly according to claim 3, wherein the member (20) is axially interposed and axially compressed between the male end and a portion of the female end.

6. Assembly according to claim 3 or 5, in which the member (20) has its two axial ends (20a, 20b) which bear axially respectively on the male end and the female end and which are integral in rotation respectively with the male end and the female end.

7. Assembly according to one of the preceding claims, in which the member (20) further cooperates with the shaft (10) and the rotor (16) to impose an axial preload between the rotor (16) and the shaft (10).

8. Turbomachine for an aircraft, this turbomachine comprising at least one assembly according to one of the preceding claims.

9. Turbomachine according to claim 8, in which the axis (X) of the shaft (10) coincides with the longitudinal axis of the turbomachine.

10. Turbomachine according to claim 8 or 9, in which the shaft (10) is a low pressure shaft which connects a rotor of a low pressure compressor to a rotor of a low pressure turbine.

11. Method for mounting an assembly according to one of claims 1 to 7, characterized in that it comprises the following steps: a) twisting the member (20), and b) engaging the second grooves (18) in or on the first grooves (12).

12. Mounting method according to claim 11, the assembly being as defined in claim 4, in which it comprises: - before step a), a step i) of engaging the external teeth (24) of the wheel (22) in the internal splines, - in step a), twisting the member (20) by rotating the male end with respect to the female end, or vice versa, up to a predetermined load and until the external grooves are in a position such that they can be axially engaged in the internal grooves, and - in step b), the engagement of the external grooves in the internal grooves.

13. Mounting method according to claim 11, the assembly being as defined in claim 6, in which it comprises: - before step a), a step i) of mounting the member (20) in the female end, the member (20) comprising a first axial end (20a) which is axially supported on the female end and which is rotationally integral with the female end, then a step ii) of engaging the male end in the female end from a first position in which the male end is axially aligned with the female end and is not yet engaged therein, to a second position in which the male end is engaged in the female end and the male splines are axially spaced from the female splines, passing through an intermediate position in which the male end is engaged in the female end and the male splines are engaged in the female splines, step ii) causing the male end to be axially supported on a second axial end (20b) of the member (20) opposite the first end,and the axial compression of the member as well as the rotational connection of the member with the male end, - in step a), twisting the member (20) by rotating the male end with respect to the female end, or vice versa, up to a predetermined load and until the external grooves are in a position such that they can be axially engaged in the internal grooves, and - in step b), engaging the external splines in the internal splines by moving the male end in the female end from the second position to the intermediate position.

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