Turbine for an aircraft turbine engine comprising an overspeed brake

Abstract

The invention relates to a turbine for an aircraft turbine engine, the turbine comprising a rotor (16) which is movable relative to a stator (17), the turbine comprising an overspeed brake (25) having a jaw (26) which is secured to the rotor (16) and which is surrounded by a drum (27) secured to the stator (17), the jaw (26) being urged radially towards the drum (27) by an elastically deformable member (28), the jaw (26) being radially immobilized by a triggering element (29) which is configured to deform by buckling from an unbuckled state to a buckled state under the action of the centrifugal forces exerted at a predetermined overspeed of the rotor (16), the brake (25) being configured to occupy a passive position in which the triggering element (29) is not buckled and the jaw (26) is at a distance from the drum (27), and an active position in which the triggering element (29) is buckled and the jaw (26) is in contact with the drum (27).

Description

[0001] DESCRIPTION

[0002] TITLE: TURBINE FOR AN AIRCRAFT TURBOMACHINE INCLUDING AN OVERSPEED BRAKE

[0003] Technical field of the invention

[0004] The present invention relates to a turbine for an aircraft turbomachine comprising an overspeed brake, and to an aircraft turbomachine comprising such a turbine.

[0005] Technical background

[0006] The prior art includes document FR-3.049.647-A.

[0007] A twin-body turbomachine classically comprises a high-pressure body and a low-pressure body.

[0008] The high-pressure unit includes, in particular, a high-pressure compressor, a combustion chamber, and a high-pressure turbine. The high-pressure compressor is mechanically driven by the high-pressure turbine via a high-pressure shaft.

[0009] The low-pressure unit comprises, among other things, a propulsion fan (shrouded or unshrouded), a low-pressure compressor, and a low-pressure turbine. The propulsion fan and the low-pressure compressor are mechanically driven by the low-pressure turbine via a low-pressure shaft. The propulsion fan can be driven by the low-pressure shaft via a speed reducer, in order to increase the efficiency of the turbomachine.

[0010] The low-pressure turbine (or high-pressure turbine) comprises one or more stages arranged axially one behind the other. Each stage includes a fixed bladed distributor that forms part of the turbine stator and a rotating bladed runner that forms part of the turbine rotor. Each bladed runner comprises a disc that carries an annular row of blades. The individual discs of the runners are flanged to one another and fixed to the low-pressure shaft.

[0011] The low-pressure turbine may be forced to operate at overspeed following, for example, a breakage (or failure) of the low-pressure shaft. Such an operating regime is undesirable as it can be destructive, especially if it persists over time.

[0012] To stop the overspeed, a commonly used solution is to detect the overspeed with a sensor and cut off the fuel injection into the combustion chamber, in order to slow down the turbine rotor.

[0013] Such a solution can be improved.

[0014] Indeed, safety requirements are becoming increasingly strict, and in other words, the required reaction times between the onset of overspeed and the cessation of overspeed are becoming increasingly shorter.

[0015] Engine manufacturers are therefore now looking for more responsive solutions.

[0016] The objective of the present invention is therefore to provide a simple and reliable solution to the aforementioned problem.

[0017] Summary of the invention

[0018] The invention thus proposes a turbine for an aircraft turbomachine, the turbine comprising a rotor which is free to rotate about an axis X relative to a turbine stator, characterized in that the turbine comprises an overspeed brake having a jaw fixed to the rotor which is surrounded by a drum fixed to the stator, the jaw being radially stressed in the direction of the drum by an elastically deformable member, the jaw being radially immobilized by a triggering element, the triggering element being configured to deform in buckling from a non-buckled state to a buckled state under the action of centrifugal forces which are exerted at a predetermined overspeed of the rotor, the brake being configured to occupy a passive position in which the triggering element is non-buckled and the jaw is at a distance from the drum,and an active position in which the triggering element is flexed and the jaw is in contact with the drum so as to brake the turbine rotor.

[0019] The incorporation of such an overspeed brake makes it possible to automatically brake the turbine rotor as soon as the predetermined overspeed appears (for example following the breakage of the rotor shaft), in order to prevent any damage that could be associated with overspeed operation.

[0020] The brake activation is automatic, as it is linked to the buckling of the triggering element, which is dimensioned accordingly. Indeed, the buckling of the triggering element releases the jaw, which then comes into contact with the drum under the action of the elastically deformable component, thus braking the turbine rotor.

[0021] Such a brake is simple and reliable since it is composed solely of mechanical elements (without using, for example, a sensor, software or an actuator whose reliability may be questionable).

[0022] Such a brake can also be easily integrated into the turbine.

[0023] The turbine according to the invention may comprise one or more of the following features, taken individually or in combination with each other:

[0024] - the jaw is supported by a rotor shaft, the elastically deformable element being arranged radially between an internal face of the jaw and the shaft, the triggering element being arranged radially between an external face of the jaw and a retaining element which is integral with the shaft;

[0025] - the jaw includes an external friction surface which is radially and directly opposite an internal friction surface of the drum, the elastically deformable member being radially aligned with the friction surfaces, the triggering element being axially offset with respect to the friction surfaces as well as the elastically deformable member; - the triggering element is axially downstream with respect to the friction surfaces as well as the elastically deformable member;

[0026] - the triggering element comprises a plurality of rectangular tabs arranged around the X axis, each rectangular tab having an external end housed in an external hook of the retaining element which is open radially inwards and an internal end housed in an internal hook of the jaw which is open radially outwards;

[0027] - the elastically deformable element is a coil spring, the coil spring having an external end bearing radially on the internal face of the jaw and an internal end bearing radially on the shaft;

[0028] - the outer end of the coil spring is housed in a blind hole in the jaw and the inner end of the coil spring is housed in a blind hole in the shaft;

[0029] - the turbine rotor is guided in rotation relative to an output casing via a roller bearing, the overspeed brake being located axially directly downstream of the roller bearing;

[0030] - the outlet housing delimits an internal enclosure in which the overspeed brake is located.

[0031] The present invention also relates to an aircraft turbomachine comprising a turbine as described above.

[0032] The turbomachine may include a propulsive blower which is driven into rotation by the turbine rotor via a speed reducer.

[0033] Brief description of the figures

[0034] The invention will be better understood and other details, features and advantages of the invention will become more apparent upon reading the following description, given by way of non-limiting example and with reference to the accompanying drawings in which:

[0035] [Fig.1] Figure 1 is a schematic axial half-section view of an aircraft turbomachine; [Fig.2] Figure 2 is a detailed view of the low-pressure turbine of the turbomachine illustrated in Figure 1;

[0036] [Fig.3] Figure 3 is a detailed view of the low-pressure turbine overspeed brake, with the overspeed brake in a passive position; [Fig.4] Figure 4 is a view similar to that of Figure 3 in which the overspeed brake is in an active position.

[0037] Detailed description of the invention

[0038] Figure 1 schematically represents a turbomachine 1 with longitudinal axis X for an aircraft 2, such as an airplane.

[0039] As illustrated in Figure 1, the turbomachine 1 is here a turbofan engine which classically includes a shrouded fan 3 and a gas generator 4.

[0040] More specifically, the fan 3 rotates about the X-axis. The fan 3 is driven in rotation by a low-pressure turbine 5 (hereinafter referred to as the "LP turbine") of the gas generator 4 via, in particular, a low-pressure shaft 6 (hereinafter referred to as the "LP shaft") and a speed reducer 7. The speed reducer 7 reduces the rotational speed of the fan 3 relative to that of the LP turbine 5, while simultaneously increasing its torque. The speed reducer 7 is, for example, an epicyclic gear reducer. The fan 3 has an annular row of blades 8 with fixed or variable pitch.

[0041] As illustrated in Figure 1, the gas generator 4 comprises, from upstream to downstream along the direction of gas flow, a low-pressure compressor 10, a high-pressure compressor 11, a combustion chamber 12, a high-pressure turbine 13 and the BP turbine 5. The low-pressure compressor 10 is driven in rotation by the BP turbine 5 via the BP shaft 6. The high-pressure compressor 11 is driven in rotation by the high-pressure turbine 13 via a high-pressure shaft 52.

[0042] As illustrated in Figure 1, the airflow F generated by the blower is divided, by the fixed structure 9 of the turbomachine 1, into a primary flow f1 which enters a primary channel 14 to supply the gas generator 4, and into a secondary flow f2 which flows into a secondary channel 15 around the gas generator 4, to provide most of the thrust.

[0043] By convention in this application, the terms "upstream" and "downstream" are defined with respect to the direction of flow of the F1, f1, f2 flows, when the turbomachine 1 is in "propeller" mode.

[0044] The example illustrated in Figure 1 is by no means limiting; turbomachine 1 could, for example, be a differently configured turbojet, a turboprop, a turbomotor, or even a turbomachine generally comprising one or more shrouded or unshrouded fans.

[0045] As illustrated in Figure 2, the BP 5 turbine comprises a rotor 16 which is mobile in rotation about the X axis relative to a stator 17 of the BP 5 turbine.

[0046] More specifically, the BP 5 turbine comprises several stages 18 arranged axially one behind the other (only two stages 18 are shown in Figure 2). Each stage 18 includes a fixed bladed distributor 19, which is part of the stator 17 of the BP 5 turbine, and a movable bladed runner 20, which is part of the rotor 16 of the BP 5 turbine. Each distributor 19 comprises two rings 21 between which is an annular row of blades 22. Each distributor 19 may or may not be sectored around the X-axis. Each bladed runner 20 comprises a disc 23 carrying an annular row of blades 24. The various discs 23 of the runners 20 are clamped to one another and fixed to the BP 6 shaft.

[0047] According to the invention, the BP 5 turbine includes an overspeed brake 25 comprising a jaw 26 integral with the rotor 16 which is surrounded by a drum 27 integral with the stator 17. The jaw 26 is radially stressed in the direction of the drum 27 by an elastically deformable member 28. The jaw 26 is radially immobilized by a release element 29 (or an actuation element). The triggering element 29 is configured to deform in buckling from an unbuckled state to a buckled state under the action of centrifugal forces exerted at a predetermined overspeed of the rotor 16. The brake 25 is configured to occupy a passive position (Figures 2 and 3) in which the triggering element 29 is unbuckled and the jaw 26 is away from the drum 27, and an active position (Figure 4) in which the triggering element 29 is buckled and the jaw 26 is in contact with the drum 27 so as to brake the rotor 16 of the BP 5 turbine.

[0048] The incorporation of such an overspeed brake 25 allows the rotor 16 of the turbine 5 to be automatically braked as soon as the predetermined overspeed appears (for example following the breakage of the shaft 6 of the rotor 16), so as to prevent any damage which could be associated with overspeed operation.

[0049] The brake 25 is automatically activated, as it is linked to the buckling of the release element 29, which is dimensioned accordingly. Indeed, the buckling of the release element 29 frees the jaw 26, which then comes into contact with the drum 27 under the action of the elastically deformable member 28, thereby braking the rotor 16 of the turbine 5.

[0050] Such a brake 25 is simple and reliable since it is composed solely of mechanical elements (without using, for example, a sensor, software or an actuator whose reliability may be questionable).

[0051] Such a brake 25 is also easily integrated into the turbine 5.

[0052] Advantageously, the turbine 5 can include several overspeed brakes 25 distributed around the X-axis. Each overspeed brake 25 includes in particular a jaw 26, an elastically deformable member 28 and a release element 29. The overspeed brakes are preferably distributed regularly around the X-axis.

[0053] Advantageously, the jaw 26 is supported by a shaft 6 of the rotor 16, the elastically deformable member 28 being arranged radially between an internal face 30 of the jaw 26 and the shaft 6, the triggering element 29 being arranged radially between an external face 31 of the jaw 26 and a retaining element 32 (or support element) which is integral with the shaft 6.

[0054] The retaining element 32 can be one piece (or monobloc) with the shaft 6. Alternatively, the retaining element 32 could be attached to the shaft 6 and rotationally connected to the shaft 6 via, for example, a pin.

[0055] Advantageously, the jaw 26 includes an external friction surface 33 which is radially and directly opposite an internal friction surface 34 of the drum 27, the elastically deformable member 28 being radially aligned with the friction surfaces 33, 34, the triggering element 29 being axially offset with respect to the friction surfaces 33, 34 as well as the elastically deformable member 28.

[0056] Advantageously, the friction surface 33 of the jaw 26 is formed in a lining 35 which is attached to a body 36 of the jaw 26. Advantageously, the friction surface 34 of the drum 27 is formed in a lining 37 which is attached to a base 38 (or a sole) of the drum 27.

[0057] The triggering element 29 can be located axially upstream or downstream with respect to the friction surfaces 33, 34 and the elastically deformable member 28.

[0058] Advantageously, the triggering element 29 comprises a plurality of rectangular tabs 29a arranged around the axis X, each rectangular tab 29a having an external end housed in an external hook 39 of the retaining element 32 which is open radially inwards and an internal end housed in an internal hook 40 of the jaw 26 which is open radially outwards.

[0059] Alternatively, the triggering element 29 could include a single tab 29a.

[0060] The elastically deformable member 28 can be any form of spring working in a radial direction. Advantageously, the elastically deformable member 28 is a coil spring 28, the coil spring 28 having an external end bearing radially on the internal face 30 of the jaw 26 and an internal end bearing radially on the shaft 6.

[0061] The outer end of the coil spring 28 can be housed in a blind hole 41 in the jaw 26, and the inner end of the coil spring 28 can be housed in a blind hole 42 in the shaft 6. The blind holes 41 and 42 allow for the stable positioning of the ends of the spring 28. Advantageously, the rotor 16 of the turbine 5 is guided in rotation relative to an outlet housing 43 of the turbine 5 via a roller bearing 44, the overspeed brake 25 being located axially directly downstream of the roller bearing 44. This arrangement of the overspeed brake 25 notably protects it from the thermal stresses of the turbine 5. The outlet housing 43 is also called the exhaust housing and is known by the English acronym TRF for "Turbine Rear Frame".

[0062] Advantageously, the outlet housing 43 delimits an internal enclosure 45 in which the overspeed brake 25 is located. Such an arrangement of the overspeed brake 25 makes it possible in particular to protect it against the thermal stresses of the turbine 5.

[0063] Each jaw 26 can be associated with one or more elastically deformable elements 28 (for example one or more coil springs 28).

[0064] The brake shoes 26 of the overspeed brakes 25 can each be associated with a separate release element 29. Alternatively, the brake shoes 26 can be associated with a common release element 29.

[0065] Each of the triggering elements 29 can be dimensioned according to Euler's buckling formula, which defines the limit load Ffiambage causing buckling, namely Ffiambage = TT 2 X El / L 2, WHERE E is the Young's modulus of the triggering element 29, I is the geometric inertia of the section of the triggering element 29 and L is the length of the triggering element 29.

[0066] The limit load Ftiambage causing buckling is equal to the sum of the preload force of the elastically deformable member 28 Feiast and the centrifugal force of the jaw 26 at a limit regime Fcentrituge limit from which the brake is designed to release.

[0067] The preload force of the elastically deformable organ 28, Feiast, is determined from the following formula: Feiast = kê, where k is the stiffness of the elastically deformable organ 28 and 5 is the distance by which the elastically deformable organ 28 has been compressed. The centrifugal force of the jaw 26 at a limiting regime, Fcentrituge limit, is determined from the following formula: Fcentrituge limit = rneQ 2iim, where m is the mass of the jaw 26, e is the eccentricity of the jaw 26 with respect to the axis of symmetry of the rotor and Qüm is the limiting regime from which the brake is designed to trigger.

[0068] According to the embodiment illustrated in the figures and in particular figure 2, the overspeed brake 25 is located axially directly downstream of the bearing 44 which is used to guide the rotor 16 of the turbine 5 relative to the outlet casing 43 of the BP 5 turbine.

[0069] More specifically, the bearing housing 44 comprises an inner ring 46 mounted on the shaft BP 6, an outer ring 47 housed in the output housing 43, and rolling elements 48 (here rollers) arranged radially between the rings 46, 47. The inner ring 46 is axially held upstream by a nut 49 screwed onto the shaft BP 6, and downstream by a shoulder 50 formed in the shaft BP 6. The outer ring 47 is axially held downstream by a shoulder 51 formed in the output housing 43.

[0070] As illustrated in particular in Figure 2, the overspeed brake 25 is located in an internal enclosure 45 defined by the outlet housing 43.

[0071] This positioning of the overspeed brake 25 helps to protect it from the thermal stresses of the turbine 5. As illustrated in the figures, particularly Figures 3 and 4, the brake shoe 26 is supported by the BP shaft 6. The brake shoe 26 comprises an external friction surface 33 which is radially and directly aligned with an internal friction surface 34 of the drum 27. More precisely, the friction surface 33 of the brake shoe 26 is formed in a lining 35 which is attached to a body 36 of the brake shoe 26. The friction surface 34 of the drum 27 is formed in a lining 37 which is attached to a base 38 (or a sole) of the drum 27. The base 38 of the drum 27 is here a single piece (or monobloc) with the output housing 43.As illustrated in the figures, and in particular figures 3 and 4, the elastically deformable member 28 is here a coil spring 28 which is arranged radially between an inner face 30 of the jaw 26 and the shaft BP 6. More precisely, the coil spring 28 is radially aligned with the friction surfaces 33, 34, so as to effectively brake the rotor 16 when the brake 25 is in the active position.

[0072] The coil spring 28 has an external end which is radially supported on the internal face 30 of the jaw 26 and an internal end which is radially supported on the shaft BP 6. In order to be positioned stably, the external end of the spring 28 is housed in a blind hole 41 of the jaw 26 and the internal end of the spring 28 is housed in a blind hole 42 of the shaft BP 6.

[0073] As illustrated in the figures, and in particular figures 3 and 4, the triggering element 29 here comprises a plurality of rectangular tabs 29a arranged around the axis X. The tabs 29a are arranged radially between an external face 31 of the jaw 26 and a retaining element 32 which is integral (or monobloc) with the shaft BP 6. The tabs 29a are axially offset downstream with respect to the friction surfaces 33, 34 and the spring 28.

[0074] Each rectangular tab 29a has an external end which is housed in an external hook 39 of the retaining element 32 which is open radially inwards and an internal end which is housed in an internal hook 40 of the body 36 of the jaw 26 which is open radially outwards.

[0075] In figures 2 and 3, the overspeed brake 25 is in a passive position, and in other words the overspeed brake 25 does not brake the rotor 16 of the turbine BP 5.

[0076] In the passive position, each tab 29a is not buckled. Indeed, the speed of the rotor 16 of the BP 5 turbine is less than the predetermined overspeed, the centrifugal forces exerted on each tab 29a are thus insufficient to cause it to buckle.

[0077] In passive position, the jaw 26 is at a distance from the drum 27. Indeed, as indicated above, each tab 29a is not bent and thus opposes the spring 28 which radially stresses the jaw 26 in the direction of the drum 27.

[0078] In Figures 2 and 3, the overspeed brake 25 is in the active position, meaning that the overspeed brake 25 is braking the rotor 16 of the BP 5 turbine. In the active position, each tab 29a is buckled. This is because the speed of the rotor 16 of the BP 5 turbine is greater than or equal to the predetermined overspeed, and the centrifugal forces acting on each tab 29a are sufficient to cause it to buckle.

[0079] In the passive position, the jaw 26 is in contact with the drum 27 so as to brake the rotor 16 of the turbine BP 5. Indeed, as indicated above, each tab 29a is bent and thus releases the spring 28 which radially forces (or presses) the jaw 26 against the drum 27.

[0080] The embodiment illustrated in the figures is in no way limiting. The overspeed brake(s) 25 according to the invention could, for example, be integrated into the high-pressure turbine 13 of the turbomachine 1, or into another turbine.

Claims

DEMANDS 1. Turbine (5) for an aircraft turbomachine (1) (2), the turbine (5) comprising a rotor (16) which is free to rotate about an axis (X) relative to a stator (17) of the turbine (5), characterized in that the turbine (5) comprises an overspeed brake (25) having a jaw (26) integral with the rotor (16) which is surrounded by a drum (27) integral with the stator (17), the jaw (26) being radially loaded in the direction of the drum (27) by an elastically deformable member (28), the jaw (26) being radially immobilized by a release element (29), the release element (29) being configured to deform by buckling from a non-buckled state to a buckled state under the action of centrifugal forces exerted at a predetermined overspeed of the rotor (16), the brake (25) being configured to occupy a passive position in which the triggering element (29) is not flanged and the jaw (26) is at a distance from the drum (27),and an active position in which the triggering element (29) is flexed and the jaw (26) is in contact with the drum (27) so as to brake the rotor (16) of the turbine (5).

2. Turbine (5) according to claim 1, characterized in that the jaw (26) is supported by a shaft (6) of the rotor (16), the elastically deformable member (28) being arranged radially between an inner face (30) of the jaw (26) and the shaft (6), the triggering element (29) being arranged radially between an outer face (31) of the jaw (26) and a retaining element (32) which is integral with the shaft (6).

3. Turbine (5) according to the preceding claim, characterized in that the jaw (26) comprises an external friction surface (33) which is radially and directly opposite an internal friction surface (34) of the drum (27), the elastically deformable member (28) being radially aligned with the friction surfaces (33, 34), the release element (29) being axially offset with respect to the friction surfaces (33, 34) as well as to the elastically deformable member (28).

4. Turbine (5) according to the preceding claim, characterized in that the triggering element (29) is located axially downstream with respect to the friction surfaces (33, 34) as well as to the elastically deformable member (28).

5. Turbine (5) according to any one of claims 2 to 4, characterized in that the triggering element (29) comprises a plurality of rectangular tabs (29a) arranged around the axis (X), each rectangular tab (29a) having an external end housed in an external hook (39) of the retaining element (32) which is open radially inwards and an internal end housed in an internal hook (40) of the jaw (26) which is open radially outwards.

6. Turbine (5) according to any one of claims 2 to 5, characterized in that the elastically deformable member (28) is a coil spring (28), the coil spring (28) having an external end bearing radially on the internal face (30) of the jaw (26) and an internal end bearing radially on the shaft (6).

7. Turbine (5) according to the preceding claim, characterized in that the outer end of the coil spring (28) is housed in a blind hole (41) of the jaw (26) and the inner end of the coil spring (28) is housed in a blind hole (42) of the shaft (6).

8. Turbine (5) according to any one of the preceding claims, characterized in that the rotor (16) of the turbine (5) is guided in rotation relative to an outlet housing (43) via a roller bearing (44), the overspeed brake (25) being located axially directly downstream of the roller bearing (44).

9. Turbine (5) according to the preceding claim, characterized in that the outlet housing (43) delimits an internal enclosure (45) in which the overspeed brake (25) is located.

10. Aircraft turbomachine (1) (2) comprising a turbine (5) according to any one of the preceding claims.

11. Turbomachine (1) according to the preceding claim, characterized in that the turbomachine (1) comprises a propulsive blower (3) which is driven in rotation by the rotor (16) of the turbine (5) via a speed reducer (7).

Images