Turbine engine having an epicyclic reduction gear with rotation reversal and having a low-pressure turbine fitted with standby bearings

Abstract

The invention relates to a turbine engine comprising: - a fan and a low-pressure spool (16) which drives this fan via a reduction gear, the fan rotating in the opposite direction to the low-pressure spool (16); - an inter-turbine casing (11) and an exhaust casing (13); - the low-pressure spool (16) bearing a low-pressure turbine (12) rotor (38) extending longitudinally between the inter-turbine casing (11) and the exhaust casing (13); - an upstream standby bearing (36) comprising a stator face borne by the inter-turbine casing (11) and surrounding a rotor face borne by the low-pressure turbine (12) rotor (38); - a downstream standby bearing (37) comprising a stator face borne by the exhaust casing (13) surrounding a rotor face borne by the low-pressure turbine (12) rotor (38).

Description

[0001] DESCRIPTION

[0002] Title of the invention: Turbomachine with epicyclic gear reducer and reversing rotation, having a low-pressure turbine equipped with waiting bearings

[0003] TECHNICAL FIELD

[0004] The invention relates to the securing of a turbojet engine comprising a reduction gear with reversing direction of rotation, in the event of the loss of a blade at the level of its fan.

[0005] PREVIOUS STATE OF THE ART

[0006] Such a turbojet engine has an inlet sleeve through which air is admitted to pass through a fan before being split into a central primary flow and a secondary flow surrounding the primary flow.

[0007] The primary flow is then compressed in a low-pressure compressor and then in a high-pressure compressor before reaching a combustion chamber, after which it is expanded through a high-pressure turbine and a low-pressure turbine. The secondary flow, meanwhile, is propelled directly to the rear by the blower into a channel externally delimited by an outer casing.

[0008] The primary and secondary flows then pass through an exhaust casing located downstream of the low-pressure turbine.

[0009] In such an engine, a significant imbalance can occur in the fan, causing its rotating components to become unbalanced. This imbalance can result from ice buildup on a fan blade, or from the loss of a fan blade due to the ingestion of a foreign object or mechanical wear.

[0010] During such an event, the fan becomes eccentric, causing the free ends of its blades to contact and rub against the fan housing, slowing the engine to a standstill. During this deceleration, the engine passes through critical speeds, causing vibrational resonance of its rotating components. This generates very high radial rotational forces exerted by these rotating components on their bearings. These high radial forces cause deterioration of the engine's rotating components and structure, potentially leading to the loss of blades other than those of the fan, or even a loss of engine integrity. Such an event is considered dangerous as it jeopardizes passenger safety.

[0011] The aim of the invention is to provide a solution to further improve the performance of the motor in the event of the loss of a blade in the particular case of a motor whose rotating elements include a reducer reversing the direction of rotation.

[0012] DESCRIPTION OF THE INVENTION

[0013] To this end, the invention relates to a turbomachine arrangement through which a flow circulates from upstream to downstream, this turbomachine comprising:

[0014] - a blower and a low-pressure body which drives this blower via an epicyclic reducer, the blower rotating in the opposite direction to the low-pressure body;

[0015] - an interturbine housing and an exhaust housing;

[0016] - the low-pressure body carrying a low-pressure turbine rotor extending longitudinally between the interturbine casing and the exhaust casing;

[0017] - an upstream waiting bearing comprising a stator face of revolution carried by the interturbine casing and surrounding a rotor face of revolution carried by the low pressure turbine rotor, this upstream waiting bearing being located upstream of the low pressure turbine rotor;

[0018] - a downstream waiting bearing comprising a stator face of revolution carried by the exhaust casing surrounding a rotor face of revolution carried by the low pressure turbine rotor, this downstream waiting bearing being located downstream of the low pressure turbine rotor.

[0019] The two waiting bearings together constitute additional load paths that stiffen the rotor bearings, limiting the amplitude of resonance modes and thus preventing their occurrence. By limiting the rotor's displacements (eccentricity and / or tilt), the invention reduces the maximum value of the radial rotational forces exerted by the rotor 38 during engine deceleration.

[0020] The invention also relates to an arrangement defined as follows, in which the rotor face is part of a sleeve forming part of the low pressure turbine rotor, and / or in which the stator face is part of a sleeve forming part of the interturbine casing or the exhaust casing.

[0021] The invention also relates to an arrangement defined as follows, in which the rotor face is part of a sleeve terminating a flange which is fixed to the rotor of the low pressure turbine, and / or in which the stator face is part of a sleeve terminating a flange fixed to the interturbine casing or the exhaust casing.

[0022] The invention also relates to an arrangement defined thus, in which at least one flange is fixed to the rotor or stator by bolting.

[0023] The invention also relates to an arrangement thus defined, in which at least one rotor face and / or at least one stator face has a surface treatment.

[0024] The invention also relates to an arrangement defined as follows, in which the rotor face or the stator face is formed of an abradable material.

[0025] The invention also relates to an arrangement defined as follows, in which the upstream waiting bearing extends around a bearing of the low-pressure body, and / or in which the downstream waiting bearing extends around another bearing of the low-pressure body.

[0026] The invention also relates to a turbomachine comprising an arrangement as defined above.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The [Fig. 1] is a schematic longitudinal cross-sectional view of a turbojet engine according to the invention;

[0029] Figure 2 is a graph of the evolution of the bending moment at the low-pressure turbine rotor during engine deceleration following a significant imbalance at the fan, in the absence of the invention; Figure 3 is a schematic longitudinal cross-sectional view of a low-pressure turbine according to the invention;

[0030] Fig. 4 is a schematic longitudinal cross-sectional view of an upstream waiting platform according to the invention;

[0031] The [Fig. 5] is a schematic longitudinal cross-sectional view of a downstream waiting platform according to the invention;

[0032] The [Fig. 6] is a graph of the evolution of the bending moment at the level of the low pressure turbine rotor during the deceleration of the engine following a significant imbalance at the level of the blower, with the invention;

[0033] DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0034] In Figure 1, air is admitted into the turbojet 1 according to the invention to pass through a fan 2 before being split into a central primary flow Fl and a secondary flow F2 surrounding the primary flow. These two flows circulate in the turbojet parallel to its longitudinal axis AX, which corresponds to its axis of revolution, from its upstream AM to its downstream AV.

[0035] The primary flow passes through an inlet casing 3 before passing into a low-pressure compressor 4 and then through an inter-compressor casing 6 to be compressed in a high-pressure compressor 7. It then reaches a combustion chamber 8 to be burned, after which it is expanded in a high-pressure turbine 9 before passing through an inter-turbine casing 11 and then entering a low-pressure turbine 12. The primary flow Fl then passes through an exhaust casing 13 located downstream of the low-pressure turbine.

[0036] The secondary flow F2 is propelled directly backwards by the blower 2, after passing through straightening vanes 14, into a channel internally delimited by a line of casings 15. This line of casings 15 mainly comprises the inlet casing 3, the inter-compressor casing 6, the inter-turbine casing 11 and the exhaust casing 13.

[0037] As shown in Figure 1, the low-pressure compressor 4 and the low-pressure turbine 12 have bladed discs supported by the same rotating low-pressure housing 16. Similarly, the high-pressure compressor 7 and the high-pressure turbine 9 have bladed discs supported by the same rotating high-pressure housing 17, which rotates independently of the low-pressure housing.

[0038] The high-pressure body 17 surrounds the low-pressure body 16, extending longitudinally between the low-pressure compressor 4 and the low-pressure turbine 12.

[0039] The low-pressure body 16 is here supported by four bearings comprising a first and second bearing 18 and 19 located longitudinally between the inlet casing 3 and the inter-compressor casing 6, a third bearing 21 located between the high-pressure turbine 9 and the exhaust casing 13, and a fourth bearing 22 located at the level of the exhaust 13.

[0040] The first bearing 18 is carried by the inlet housing 3, the second bearing 19 is carried by the inter-compressor housing 6, the third bearing 21 is carried by the inter-turbine housing 11, and the fourth bearing 22 is carried by the exhaust housing 13.

[0041] The low-pressure housing 16 comprises a rotor formed of several elements joined along the axis AX and rigidly connected to one another. It is supported by an upstream bearing 24 located between the compressors, and by a downstream bearing 26 located between the high- and low-pressure turbines. The upstream bearing 24 is supported by the inter-compressor housing, while the downstream bearing 26 is supported by the inter-turbine housing.

[0042] As shown in Figure 1, this motor is equipped with an epicyclic reduction gear Tl interposed between the low-pressure housing 16 and an upstream shaft 28 carrying the fan 2, such that the low-pressure housing 16 drives the fan at a rotational speed lower than its own. As shown in Figure 1, the upstream shaft 28 is supported by a fan bearing 29 which is located upstream of the inlet housing 3.

[0043] This epicyclic reducer Tl comprises a planetary gear 31 corresponding to the upstream end of the low pressure body 16, surrounded by planetary gears 32 carried jointly by a planetary carrier, and an external ring 33 surrounding the planetary gears, this ring 33 being rigidly attached to the upstream shaft 28.

[0044] The satellite carrier is supported by the inlet housing 3 to which it is rigidly attached, so that the upstream shaft 28 is driven, thanks to the reducer Tl, by the low pressure body 16 to rotate at a lower speed than that of this low pressure body, while rotating in the opposite direction to this low pressure body 16.

[0045] The invention is based on the analysis that, due to the reversal of the direction of rotation of the reducer, a significant imbalance at the level of the blower located upstream of the motor generates so-called retrograde resonance modes, which cause a very significant bending of the low pressure body at the level of the rotor of the low pressure turbine which is located downstream of the motor.

[0046] This bending of the low-pressure turbine body results in an eccentricity and tilt of the rotor relative to the AX axis, which generates very high rotating radial loads on the low-pressure turbine bearings. These rotating radial loads can cause the turbine blade tips to come into contact with their casing, leading to engine integrity loss through degradation of its supporting structure.

[0047] The curve Cl in Figure 2 shows the evolution of the bending moment of the low-pressure turbine rotor, between the onset of significant imbalance at the fan and the engine shutdown, during a given time interval. This bending moment corresponds to the moment about an axis AY normal to Figure 2 that is exerted by this rotor 38 on the two bearings 21 and 22 considered as a single unit.

[0048] The retrograde resonance modes cause a bending moment at the low pressure turbine rotor that can reach a maximum value corresponding to the peak of the Cl curve in Figure 2.

[0049] According to the invention, the engine is equipped with two waiting bearings 36 and 37 which are located longitudinally upstream and downstream of the rotor 38 of the low-pressure turbine 12, as shown in Figure 3. These two waiting bearings limit the inclination and eccentricity of the rotor 38 with respect to the axis AX. The rotor inclination corresponds to the angle formed by its central axis with the axis AX; it is schematically represented by the arrow labeled F in Figure 3. In the example shown in the figures, the upstream waiting bearing 36 extends around the third bearing 21, and the downstream waiting bearing 37 extends around the fourth bearing 22, so as to constitute a compact arrangement.

[0050] The rotor 38 essentially consists of discs joined longitudinally to each other, each disc carrying turbine blades on its periphery to constitute a stage of the turbine 12, this turbine being able to have one or more stages.

[0051] As can be seen more clearly in Figure 4, the upstream waiting bearing 36 essentially comprises a sleeve 39 carried by the rotor 38 and having a rotor face of revolution 41 which is surrounded by a sleeve 42 carried by the interturbine housing 11 and having a stator face of revolution 43. These two faces are radially spaced from each other by a radial functional clearance noted JR.

[0052] This radial clearance JR is chosen to prevent any contact between these two faces during normal operation, and to ensure they only come into contact when the rotor becomes eccentric or tilted excessively relative to the AX axis. During normal operation, the rotor 38 is neither eccentric nor tilted, so the rotor face 41 and the stator face 43 remain separated by the radial clearance JR, which corresponds to the difference in radius between these two cylindrical faces. As an order of magnitude, the JR clearances typically range from half a millimeter to ten millimeters.

[0053] In the event of excessive eccentricity or inclination of the rotor 38, the radial loads exerted by this rotor 38 on the bearings 21 and 22 become much higher than normal. In such a situation, the rotor 38 becomes eccentric and / or tilts, particularly when it passes through the critical speed during deceleration, and when this eccentricity exceeds the value of the radial clearance JR, the rotor face 41 comes into contact with the stator face 43.

[0054] Under these conditions, faces 41 and 43, bearing against each other, ensure the transmission of radial forces from the rotor 38 to the stator, i.e., to the inter-turbine casing 11 and the exhaust casing 13. This has the effect of limiting the eccentricity of the rotor 38 to reduce the value of the maximum forces experienced by the rotor, thus creating an intermediate force path. Furthermore, faces 41 and / or 43 advantageously have a surface treatment to adjust their mutual friction coefficient to a predetermined value, in order to generate a controlled, i.e., predictable, deceleration of the rotor. The fact that the contact occurs between the two cylindrical faces also makes the contact more rigid and more predictable than the contact between the blades of the low-pressure turbine and their casing.This surface treatment is advantageously chosen to limit heating in order to prevent the contact surfaces from welding together under the effect of the heat resulting from their friction, in order to avoid a blockage of the rotor.

[0055] Under these conditions, the forces and friction of the rotor face 41 on the stator face 43 are known, that is to say their intensity is predictable, so that the slowing down of the rotor takes place according to a predetermined profile of evolution of its regime.

[0056] Similarly, the downstream waiting bearing 37 also includes a sleeve 44 carried by the rotor 38 and having a rotor face 46 surrounded by a sleeve 47 carried by the exhaust housing 13 and having a stator face 48, visible in Figure 5, so that it reacts in the same way as the upstream waiting bearing in the event of excessive eccentricity or inclination of the rotor 38 with respect to the axis AX.

[0057] The two waiting bearings 36 and 37 are located upstream and downstream of the rotor 38, so that together they create additional force paths which make it possible to stiffen the rotor bearings 21 and 22, to limit the amplitude of the resonance modes in order to limit the eccentricity and / or inclination of the rotor 38.

[0058] Thus, as represented by curve C2 in Figure 6, by limiting the displacements (eccentricity and / or inclination) of the rotor 38, the invention makes it possible to reduce the maximum value of the radial rotational forces exerted by the rotor 38 during engine deceleration. In other words, thanks to the invention, the maximum forces are one-third of what they are in the case of Figure 2, Figures 2 and 6 being to the same scale with respect to time and bending moment. More specifically, the peak of curve C2 is at a moment value corresponding to one-third of the peak of curve C1. In the example shown in the figures, the rotor face 41 and stator face 43 are integrated into the rotor 38 and the inter-turbine housing 11, which includes the sleeves with these faces.

[0059] Advantageously, the rotor face and the stator face are part of elements added to the motor, which allows the invention to be integrated into an existing motor without having to modify its existing components such as its rotor and stator elements.

[0060] Thus, in the case of the upstream waiting bearing 36, the sleeve 39 can be part of a cylindrical shell ending in a flange fixed to a downstream face of the rotor 38, for example by bolting this flange. Similarly, the sleeve 42 can be part of another cylindrical shell ending in a flange fixed to the inter-turbine housing 11, for example by bolting.

[0061] Furthermore, the stator face 43, which is metallic in the example described, can be made of an abradable material bonded to the face of the corresponding sleeve, so as to promote faster rotor deceleration. This abradable material can, alternatively or in addition, constitute the rotor face 41.

[0062] The variants described above are given by way of illustration, but the invention covers any combination based on these examples. These combinations include, in particular, an upstream waiting bearing having rotor and / or stator faces supported by attached elements. They also include a downstream waiting bearing whose stator and / or rotor faces are part of the rotor and / or stator. They further include a downstream waiting bearing having a stator and / or rotor face formed from an abradable material.

Claims

DEMANDS 1. Turbomachine arrangement through which a flow circulates from upstream (AM) to downstream (AV), this turbomachine comprising: - a blower (2) and a low pressure body (16) which drives this blower (2) by means of an epicycloidal reducer (27), the blower (2) rotating in the opposite direction to the low pressure body (16); - an interturbine housing (11) and an exhaust housing (13); - the low pressure body (16) carrying a low pressure turbine rotor (38) (12) extending longitudinally between the interturbine casing (11) and the exhaust casing (13); - an upstream waiting bearing (36) comprising a stator face of revolution (43) carried by the interturbine casing (11) and surrounding a rotor face (41) of revolution carried by the rotor (38) of low pressure turbine (12), this upstream waiting bearing (36) being located upstream of the rotor (38) of the low pressure turbine (12); - a downstream waiting bearing (37) comprising a stator face of revolution (48) carried by the exhaust casing (13) surrounding a rotor face (46) of revolution carried by the rotor (38) of low pressure turbine (12), this downstream waiting bearing (37) being located downstream of the rotor (38) of low pressure turbine (12).

2. Arrangement according to claim 1, wherein the rotor face (41, 46) is part of a sleeve (39, 44) forming part of the rotor (38) of low pressure turbine (12), and / or wherein the stator face (43, 48) is part of a sleeve (42, 47) forming part of the interturbine housing (11) or the exhaust housing (13).

3. Arrangement according to claim 1, wherein the rotor face (41, 46) is part of a sleeve (39, 44) terminating a flange which is fixed to the rotor (38) of the low pressure turbine (12), and / or wherein the stator face (43, 48) is part of a sleeve (42, 47) terminating a flange fixed to the interturbine housing (11) or to the exhaust housing (13).

4. Arrangement according to claim 3, wherein at least one flange is fixed to the rotor or stator by bolting.

5. Arrangement according to claim 1, wherein at least one rotor face (41, 46) and / or at least one stator face (43, 48) has a surface treatment.

6. Arrangement according to claim 1, wherein the rotor face (41, 46) or the stator face (43, 48) is formed of an abradable material.

7. Arrangement according to claim 1, wherein the upstream waiting bearing (36) extends around a bearing (21) of the low pressure body (16), and / or wherein the downstream waiting bearing (37) extends around another bearing (22) of the low pressure body (16).

8. Turbomachine comprising an arrangement according to one of the preceding claims.

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