Device for turbine disengagement in turbomachine overspeed

Abstract

The invention relates to an assembly for a turbomachine turbine (10) with longitudinal axis (A-A), comprising: - a turbine rotor disc (12) centred on the longitudinal axis, - a turbine shaft (14) centred on the longitudinal axis and rotated by the rotor disc, - first means for transmitting torque from the rotor disc to the shaft, the rotor disc being immobilised in translation relative to the shaft in the direction of the longitudinal axis by a member (22) screwed onto the shaft, and - second means for transmitting torque from the rotor disc to the screwed member, wherein the screwed member has an unscrewing direction identical to the direction of rotation of the rotor disc in operation, and the second torque transmission means are configured to transmit the rotational torque from the rotor disc to the screwed member when the first torque transmission means ceases to transmit the torque from the rotor disc to the shaft.

Description

Technical field of the invention

[0001] The invention relates to an assembly for a turbomachine turbine.

[0002] The invention relates more specifically to an assembly for a turbomachine turbine comprising a mechanism for disengaging the turbine in the event of overspeed. State of the prior art

[0003] In a turbomachine, a fan is driven in rotation by a turbine having a rotor disc equipped with moving blades and connected to a low-pressure compressor. In the event of a breakage of a shaft connecting the fan to the turbine, the resistive torque on the turbine is suddenly cancelled while the flow of engine gas continues to transmit energy to the rotor disc. This causes an uncontrolled increase in the rotation speed of the rotor disc(s) and therefore a risk of bursting causing the release of high-energy flows. In this case, the turbine is in "overspeed".

[0004] EP1640564 is known, which proposes a device using the downstream movement of the turbine to limit turbine overspeed. The device comprises means for destroying the moving blades arranged in downstream stator blades of the turbine. However, the downstream movement of the rotor disk can be prevented by means for fixing the turbine in translation relative to its axis of rotation. As a result, the moving blades are not damaged by the destruction means. Such devices therefore lack effectiveness and reliability in limiting overspeed.Furthermore, EP1505264 discloses an example of a turbomachine turbine assembly in which the low-pressure turbine comprises a system of splines for driving the low-pressure shaft by the low-pressure rotor and in which the rolling bearing is kept locked longitudinally on the low-pressure shaft by means of a nut tightened at the downstream end of the low-pressure shaft. Presentation of the invention

[0005] One of the aims of the invention is to ensure the downstream movement of the turbine in the event of shaft breakage so that an annular row of moving blades comes into contact with an annular row of stator blades, thus allowing destruction of the annular row of moving blades by the annular row of stator blades, braking the turbine.

[0006] Another aim of the invention is to limit the overspeed of the turbine in the event of shaft breakage in a reliable and efficient manner.

[0007] To this end, the invention proposes an assembly for a longitudinal axis turbomachine turbine comprising: a turbine rotor disc centered on the longitudinal axis, a turbine shaft centered on the longitudinal axis and driven in rotation by the rotor disc, first means for transmitting torque from the rotor disc to the shaft, the rotor disc being locked in translation relative to the shaft in the direction of the longitudinal axis by a member screwed onto said shaft, and second means for transmitting torque from the rotor disc to the screwed member, in which the screwed member has a direction of unscrewing identical to the direction of rotation of the rotor disc in operation and the second torque transmission means are configured to transmit the rotational torque of the rotor disc to the screwed member when the first torque transmission means cease to transmit the torque of the rotor disc to the shaft.

[0008] The invention is advantageous in that the screwed member has a direction of unscrewing identical to the direction of rotation so that the second transmission means cause the screwed member to unscrew when the first torque transmission means cease to transmit the torque from the rotor disc to the shaft. As a result, the turbine is no longer held in the axial direction and can move backward, thus causing the destruction of its moving blades against a stator of the turbomachine. This prevents the turbine from going into overspeed, the destroyed moving blades no longer supplying it with energy. The invention therefore ensures that the overspeed of the turbine is limited reliably and effectively in the event of loss of power transmission from the shaft to the rotor disc.

[0009] According to one embodiment, the first torque transmission means may comprise first longitudinal splines formed on the shaft and distributed circumferentially around the longitudinal axis and second longitudinal splines engaged with the first splines and formed in an internal annular face of the rotor disc.

[0010] The first torque transmission means may cease to transmit torque from the rotor disc to the shaft in the event of breakage or damage to the first and / or second splines.

[0011] The second torque transmission means may comprise a ring centered on the longitudinal axis and comprising first tenons cooperating with housings formed in the screwed member and second tenons cooperating with housings formed in the rotor disc.

[0012] The first tenons allow the screwed member to be driven in rotation when the ring is driven in rotation by the rotor disc through the second tenons, for example when the first torque transmission means cease to transmit the torque from the rotor disc to the shaft.

[0013] In one embodiment, the circumferential clearance between the first splines and the second splines may be less than the sum of the circumferential clearance between the second tenons and the rotor disc and the circumferential clearance between the first tenons and the screwed member. Thus, the transmission of the rotation of the rotor disc to the shaft is favored and the screwed member is not driven in rotation when the first transmission means are capable of transmitting the rotation of the rotor disc to the shaft.

[0014] According to one embodiment, the ring may comprise an annular portion, the first tenons extending upstream and the second tenons being arranged downstream of the first tenons.

[0015] In addition, at least one of the first tenons and the second tenons may comprise concave rounded portions for connection to the annular part. This allows for better mechanical strength of the ring.

[0016] The second tenons may extend primarily in the direction of the longitudinal axis. The second tenons may extend downstream in the direction of the longitudinal axis.

[0017] The second tenons may extend primarily in a radial direction perpendicular to the longitudinal axis.

[0018] The number of second pins may be greater than the number of rotor disc housings.

[0019] The number of first tenons may be greater than the number of housings of the screwed organ.

[0020] A greater number of pins than the number of housings makes it easier to tightly fit the ring on the one hand with the rotor disc and on the other hand with the screwed member.

[0021] The number of second tenons may be less than the number of first tenons.

[0022] The ring can be mounted in different ways. For example, the ring can be mounted around the screwed member. The ring can be locked in translation downstream by a retaining ring mounted in a groove in the screwed member.

[0023] According to one embodiment, an annular space may be provided immediately downstream of the screwed member. The annular space may have a longitudinal dimension greater than or equal to a longitudinal distance between moving blades connected to the rotor disk and stator blades immediately downstream of the turbine.

[0024] This allows the turbine to move back a sufficient distance for the stator blades to contact blades connected to the rotor disc.

[0025] The shaft can be connected to a low pressure compressor of the turbomachine.

[0026] According to another aspect, the invention provides a turbine, such as a low pressure turbine, comprising the aforementioned assembly.

[0027] According to one embodiment, the turbine may extend around a longitudinal axis, and comprise a stator and a rotor rotatably mounted in the stator. The rotor may comprise an assembly as mentioned above, the ring being able to be blocked in translation downstream by a stop ring mounted in a groove of the screwed member.

[0028] An annular space may be provided immediately downstream of the screwed member, said annular space having a longitudinal dimension greater than or equal to a longitudinal distance between moving blades connected to the rotor disk and stator blades located immediately downstream of the moving blades.

[0029] According to another aspect, the invention provides a turbomachine, such as an aircraft turbojet, equipped with the aforementioned assembly. Brief description of the figures

[0030] [ Fig. 1 ] there figure 1 represents a partial sectional view of a turbine of a turbomachine. Fig. 2 ] there figure 2 represents a partial couple view of a first example of the assembly according to the invention. Fig. 3 ] there figure 3 represents a perspective view of the first example of the assembly according to the invention. Fig. 4 ] there figure 4a and the figure 4b respectively represent a first example of a ring according to the invention and a second example of a ring according to the invention. Fig. 5 ] there figure 5 represents an example of an assembly according to the invention equipped with the ring of the figure 4a . [ Fig. 6 ] there figure 6 represents an example of an assembly according to the invention equipped with the ring of the figure 4b . Detailed description of the invention

[0031] In reference to the figures 1 à 3 , the turbine 10 comprises a plurality of stator blades 24 connected to a fixed casing 20 and a plurality of moving blades 26 connected to a rotor disc 12 rotating about a longitudinal axis of rotation AA. Each of the stator blades 24 is equipped with a domed protrusion 28 oriented upstream from an internal platform, this protrusion is shaped to shear the moving blades 26 when they come into contact with the protrusions. In particular, the protrusion 28 is domed by presenting a convex surface of the blade 24 oriented upstream.

[0032] The rotor disk 12 is arranged to rotate a shaft 14 of the turbine 10. For example, the shaft 14 can be connected to a low-pressure compressor of a turbomachine equipped with the turbine 10. The rotor disk 12 comprises an annular part arranged around the shaft 14 and comprises on an inner face, that is to say oriented radially inwards, grooves 16 distributed circumferentially around the axis of rotation AA. The splines 16 extend over a longitudinal portion of the inner face of the rotor disc 12. The shaft 14 comprises on its outer face splines 18, distributed circumferentially around the axis of rotation AA, and engaged with the splines 16 of the rotor disc 12 for the transmission of the torque from the latter to the shaft 14. The splines 18 extend over a longitudinal portion of the shaft 14.

[0033] The rotor disc 12 is held in translation in the direction of the axis of rotation AA by a nut 22 screwed onto the shaft 14 and coming into abutment against a collar 30 of the rotor disc 12. The nut 22 is mounted on the shaft 14 so that its direction of unscrewing is identical to the direction of rotation of the turbine 10. For this purpose, a thread is provided in the shaft 14 to ensure such a direction of unscrewing.

[0034] In the event of breakage of the shaft 14 or of the connection between the shaft 14 and the rotor disk 14, the turbine 10 risks going into uncontrolled overspeed due to the rotating drive of the moving blades by the hot gases coming from an upstream combustion chamber. In order to limit the overspeed, the domed protrusions 28 of the stator blades 24 are arranged to shear and feather the moving blades 26 to reduce or even cancel the energy received by the turbine 10. These protrusions are formed at the leading edge of the blades. More particularly, the leading edge of each blade thus comprises a convex surface. To ensure that the protrusions 28 come into contact with the moving blades 24, the turbine comprises a ring 32 configured to unscrew the nut 22 in the event of damage to the shaft 14, thereby releasing the rotor disc 12 in translation in the direction of the axis of rotation AA.

[0035] The ring 32 is annular and arranged between the nut 22 and the rotor disc 12. The ring 32 comprises first tenons 34, distributed circumferentially around the axis of rotation AA, engaged with housings provided in the shaft 14. The ring 32 also comprises second tenons 36, distributed circumferentially around the axis of rotation AA, engaged with housings provided in the rotor disc 12.

[0036] When the shaft 14 breaks or the splines 16 and the splines 18 are disengaged from each other, the ring 32 transmits the rotation of the rotor disc 12 to the nut 22. Thus, the nut 22 is unscrewed by the rotation of the turbine 10 which releases the turbine 10 in translation. The turbine 10 moves downstream along the axis of rotation AA, which causes the shearing of the moving blades 26 by the protrusions 28 of the stator blades 24 downstream of said moving blades 26.

[0037] The turbine 10 comprises a space downstream of the nut 22 having a length greater than the distance between the protrusions 28 of the stator vanes 24 and the moving vanes 26. For example, the length of said space may be greater than or equal to twice said distance. The circumferential clearance between the splines 16 of the rotor disc 12 and the splines 18 of the shaft 14 may be less than the sum of the circumferential clearance between the second tenons 36 and the rotor disc 12 and the circumferential clearance between the first tenons 34 and the nut 22.

[0038] Furthermore, an annular retaining ring 38 is arranged downstream of the ring 32 in a location provided in the nut 22 and projecting in the radial direction away from the nut 22. The retaining ring 38 makes it possible to keep the ring 32 fixed in translation in the direction of the axis of rotation AA.

[0039] There figure 4a and the figure 5 represent a first example of embodiment of a ring 100 which can be installed in the turbine 10 of the figures 1-3 The ring 100 comprises an annular portion 102, for example having a radius greater than the external radius of the nut 22.

[0040] The ring 100 comprises on the one hand first tenons 104 and on the other hand second tenons 106. The first tenons 104 extend upstream in the direction of the axis of rotation AA from the annular part 102 and are engaged with housings provided in the nut 22. In the same way, the second tenons 106 extend downstream from the annular part 102 in the direction of the axis of rotation AA and are engaged with housings provided in the rotor disc 12.

[0041] The number of first tenons 104 is less than the number of housings of the nut 22 and the number of second tenons 106 is less than the number of housings of the rotor disk 12. Thus, the mounting of the ring 100 on the one hand in the rotor disk 12 and on the other hand in the nut 22 is facilitated. For example, the number of housings of the nut 22 may be equal to or greater than twice the number of the first tenons 104. The number of housings of the rotor disk 12 may be equal to twice the number of second tenons 106. Furthermore, the number of first tenons 104 may be less than the number of second tenons 106. Each of the first tenons 104 has a rounded connection with the annular portion 102. Similarly, each of the second tenons 106 has a rounded connection with the annular portion 102. Thus, the mechanical strength of the ring 32 is improved.

[0042] The ring 100 further has an annular shoulder 108 carried by the annular part 102 and delimited by the first tenons 10, this shoulder 108 winding in abutment upstream on an annular shoulder of the nut 22.

[0043] The ring 100 may be made of a material identical to the material of the nut 22 and / or the rotor disc 12.

[0044] There figure 4b and the figure 6 represent a second example of embodiment of a ring 200 which can be installed in the turbine 10 of the figures 1-3The ring 200 comprises an annular portion 202, for example having a radius greater than the external radius of the nut 22. The ring 200 comprises on the one hand first tenons 204 and on the other hand second tenons 206. The first tenons 204 extend in the direction of the axis of rotation AA and are engaged with housings provided in the nut 22. In the same way, the second tenons 206 extend in the direction of the axis of rotation AA and are engaged with housings provided in the rotor disk 12.

[0045] The number of first tenons 204 is less than the number of housings of the nut 22 and the number of second tenons 206 is less than the number of housings of the rotor disk 12. Thus, the mounting of the ring 200 on the one hand in the rotor disk 12 and on the other hand in the nut 22 is facilitated. For example, the number of housings of the nut 22 may be equal to or greater than twice the number of the first tenons 204. The number of housings of the rotor disk 12 may be equal to twice the number of second tenons 206. Furthermore, the number of first tenons 204 may be less than the number of second tenons 206. Each of the first tenons 204 has a rounded connection with the annular portion 102. Similarly, each of the second tenons 106 has a rounded connection with the annular portion 202. Thus, the mechanical strength of the ring 32 is improved.

Claims

1. An assembly for a turbine engine turbine (10) having a longitudinal axis (A-A) comprising: a turbine rotor disc (12) centered on the longitudinal axis, a turbine shaft (14) centered on the longitudinal axis and driven in rotation by the rotor disc, first means for transmitting torque from the rotor disc (12) to the shaft (14), wherein the rotor disc (12) is locked in translation with respect to the shaft (14) in a direction of the longitudinal axis by a screwed member (22) screwed onto said shaft (14), and characterized in that it comprises second means of transmitting torque from the rotor disc (12) to the screwed member (22), wherein the screwed member (22) has an unscrewing direction identical to a direction of rotation of the rotor disc (12) in operation and the second means of transmitting torque are configured to transmit torque from the rotor disc (12) to the screwed member when the first means of transmitting torque cease to transmit torque from the rotor disc (12) to the shaft (14).

2. The assembly according to claim 1, wherein the first means of transmitting torque comprise first longitudinal splines (18) formed on the shaft (14) and distributed circumferentially around the longitudinal axis (A-A) and second longitudinal splines (16) engaging with the first splines and formed in an inner annular side of the rotor disc (12).

3. The assembly according to claim 1 or 2, wherein the second means of transmitting torque comprise a ring (32, 100, 200) centered on the longitudinal axis (A-A) and comprising first pins (34, 104, 204) cooperating with recesses formed in the screwed member (22) and second pins (36, 106, 206) cooperating with recesses formed in the rotor disc (12).

4. The assembly according to claim 2 or 3, wherein a circumferential clearance between the first splines (18) and the second splines (16) is less than the sum of a circumferential clearance between the second pins (36) and the rotor disc (12) and a circumferential clearance between the first pins (34) and the screwed member (22).

5. The assembly according to claim 3 or 4, wherein the ring (100, 200) comprises an annular section (102, 202), the first pins (104, 204) extending upstream and the second pins (106, 206) being arranged downstream from the first pins, at least one of the first pins and the second pins comprises concave rounded portions for connection to the annular section.

6. The assembly according to one of the claims 3 to 5, wherein the second pins (106) extend in the direction of the longitudinal axis (A-A), or extend in a radial direction perpendicular to the longitudinal axis (A-A).

7. The assembly according to one of the claims 3 to 6, wherein the number of second pins (36, 106, 206) is less than the number of first pins (34, 104, 204).

8. The assembly according to one of the claims 3 to 7, wherein the ring (32, 102, 202) is mounted around the screwed member (22).

9. A turbine extending around the longitudinal axis (A-A), comprising a stator and a rotor rotatably mounted in the stator, wherein the rotor comprises the assembly according to any of the claims 3 to 8, wherein the ring (32) is locked in downstream translation by a circlip (38) installed in a groove in the screwed member (22).

10. The turbine according to claim 9, wherein an annular space is arranged immediately downstream from the screwed member (22), wherein said annular space has a longitudinal dimension greater than or equal to a longitudinal distance between moving vanes (26) connected to the rotor disc (12) and stator vanes (24) located immediately downstream from the moving vanes (26).

11. A turbine engine, such as an aircraft turbojet engine, characterized in that it is equipped with the assembly according to one of claims 1 to 8 or is equipped with a turbine according to claim 9 or 10.

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