Device for centring and rotationally guiding a shaft line of a turbomachine, and turbomachine
Patent Information
- Application Number
- EP2024710145
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-02-07
- Filing Date
- 2024-02-02
- Publication Date
- 2025-12-17
AI Technical Summary
Existing turbomachine shaft line bearing systems have fixed radial rigidity, which does not adapt to changing engine parameters like axial thrust or rotation speed, leading to vibration modes that can be outside or too close to the operating range, causing inefficiencies and potential damage.
A device with a first ball bearing and a second roller bearing, supported by a flexible cage, where the stiffness evolves based on axial thrust and engine speed, allowing the radial stiffness to adjust and maintain isostatic conditions, minimizing vibration energies within the operating range.
The device effectively positions vibration modes away from the operating range, reducing energy consumption and ensuring stable operation by adapting stiffness according to engine speed, combining the benefits of flexible and stiff bearing systems.
Smart Images
Figure FR2024050139_15082024_PF_FP
Abstract
Description
[0001] DESCRIPTION
[0002] TITLE: Device for centering and guiding the rotation of a turbomachine shaft line and turbomachine
[0003] Technical field of the invention
[0004] The field of the present invention is that of aeronautical turbomachines and more particularly of devices for centering and guiding the rotation of a shaft line of a turbomachine.
[0005] State of the prior art
[0006] The bearings on the shafts of a gas turbine have a fixed or frozen radial stiffness. This stiffness does not change according to one or more parameters when the engine is operating.
[0007] It is known to arrange a single bearing per bearing. This bearing can be mounted in a "rigid" support or mounted in a flexible cage.
[0008] The stiffness of this flexible cage is calibrated to limit as much as possible the presence of vibration modes in the operating range of the motor. We therefore say that the dynamic situation of a shaft line is fixed because the positioning of the vibration modes does not change due to the stiffness of fixed bearings.
[0009] For example, in engine architectures containing a through shaft, a first shaft vibration mode is traversed when increasing the engine speed to reach the rated operating range of the engine. This first shaft vibration mode typically has a high percentage of elastic strain energy and is positioned outside, and away from, the rated operating range of the engine.
[0010] Then, a second vibration mode is often present within or beyond the engine's rated operating range. This second vibration mode is often too close to the engine speed when operating at the maximum permissible speeds.
[0011] It is also known to arrange two bearings in a bearing, as for example described in patent FR2951232. However, these two bearings do not have a stiffness which changes according to a motor parameter.
[0012] Presentation of the invention The aim of the present invention is to propose a device for centering and guiding the rotation of a shaft line having a stiffness which varies on one or more bearings as a function of at least one motor parameter such as, for example, the axial thrust of the motor or the rotation speed of the motor.
[0013] Summary of the invention
[0014] The present invention relates to a device for centering and guiding the rotation of a shaft line of a turbomachine, the shaft line being capable of being driven in rotation around an axis of rotation; said device comprising:
[0015] - a first inner ring fixed to a shaft line, a first outer ring, a first ball bearing arranged between the first inner ring and the first outer ring, a first support carrying the first outer ring, the first support having a defined stiffness,
[0016] - a second inner ring fixed to the shaft line, a second outer ring, a second bearing arranged between the second inner ring and the second outer ring, and a flexible cage supporting the second outer ring, characterized in that the flexible cage has a stiffness less than the stiffness of the first support and in that the second bearing is spaced from the first bearing by a predefined axial spacing.
[0017] The present invention makes it possible to improve the analyses of shaft line dynamics.
[0018] Advantageously, the present invention makes it possible, by means of the evolution of the axial thrust, to change the stiffness in the centering and guidance device, also called bearing, as a function of the engine speed.
[0019] The features set forth in the following paragraphs may, optionally, be implemented. They may be implemented independently of one another or in combination with one another: From a shaft deformation energy point of view, the present invention advantageously makes it possible to minimize the energies in the shaft line for the two vibration modes present around the operating range of the motor. The features set forth in the following paragraphs may, optionally, be implemented. They may be implemented independently of one another or in combination with one another:
[0020] - The first ball bearing, the first outer ring, and the first support are shaped so that a first clearance is provided between the first ball bearing and the first outer ring; the second ball bearing, the second outer ring, and the flexible cage are shaped so that a second clearance is provided between the second bearing and the second outer ring; the first clearance having a dimension greater than the second clearance in a radial direction.
[0021] Advantageously, at low speeds and under low axial load, the second clearance is absorbed. The stiffness of the centering and guiding device corresponds to the stiffness of the flexible cage. Under high axial load, the radial stiffness of the centering and guiding device gradually approaches the radial stiffness of the first bearing.
[0022] - The predefined axial spacing is less than four times the diameter of the balls of the ball bearing so that the difference between the mass temperature of the first inner ring and the mass temperature of the second inner ring is less than 20°.
[0023] - The predefined axial spacing is chosen to guarantee the isostatism of the shaft line.
[0024] - The second bearing is a roller bearing
[0025] - An oil ring (called a Squeeze Film in English) surrounds the second bearing.
[0026] - The first ball bearing has curvatures between 0.51 and 0.52 so as to guarantee low radial stiffness of the centering and rotational guidance device under low axial load.
[0027] The invention also relates to a turbomachine comprising a frame, a shaft line arranged in the frame, said shaft line being capable of driving a turbine in rotation and a device for centering and guiding the rotation of said shaft line according to the characteristics mentioned above, said centering and guiding device being mounted on at least one shaft line among the shaft line of the speed reducer, the shaft line of the drive chain of the accessories, a front part of the shaft line of the gas generator, and the shaft line of the free turbine.
[0028] Brief description of the figures
[0029] [Fig. 1] is a schematic view of a turbo machine; [Fig. 2] is a schematic view of a device for centering and guiding a shaft line according to the present invention, the centering and guiding device being shown when the turbo machine is stopped;
[0030] [Fig. 3] is a schematic view similar to the view of Figure 2, the centering and guiding device being shown when the turbomachine is operating at low speed and under low load;
[0031] [Fig. 4] is a schematic view similar to the view of Figure 2, the centering and guiding device being shown when the turbomachine is operating under high axial load;
[0032] [Fig. 5] is a graph showing the evolution of the thrust or axial force as a function of the engine speed;
[0033] [Fig. 6] is a graph showing the evolution of the stiffness in the centering and guidance device as a function of the engine speed;
[0034] [Fig. 7] is a graph showing the unbalance response of the shaft line as a function of engine speed when the shaft line is mounted on a flexible cage, when it is mounted on a rigid supporting structure and when it is mounted on a centering and guiding device according to the invention.
[0035] Detailed description of the invention
[0036] The present invention relates to a device 12 for centering and guiding in rotation a shaft line of a turbomachine 1.
[0037] With reference to Figure 1, the device 12 according to the invention can advantageously be placed on the bearings and pinions of the speed reducer 2, on the bearings and pinions of the drive chain of the accessories 4, on the front bearing of the gas generator 6 and on the bearing of the free turbine 10.
[0038] With reference to figures 1 and 2, the centering and rotational guiding device 12 according to the invention, also called bearing, is arranged between a frame 13 and a shaft line 14 or a drive shaft mounted to rotate around an axis of rotation AA.
[0039] The centering and rotational guidance device 12 comprises a first internal ring 16 fixed to the shaft line 14, a first external ring 18, a first bearing 20 arranged between the first internal ring and the first external ring, a first support 22 carrying the first external ring.
[0040] The first bearing 20 is a ball bearing. The radii of curvature of the ball bearing are defined to ensure low radial stiffness under low axial load.
[0041] The first ball bearing, the first outer ring and the first support are shaped so that a first clearance J1 is provided between the first bearing 20 and the first outer ring 18.
[0042] The centering and rotational guidance device 12 comprises a second inner ring 24 fixed to the shaft line 14, a second outer ring 26, a second bearing 28 arranged between the second inner ring 24 and the second outer ring 26, and a flexible cage 30 supporting the second outer ring. The second bearing 28 is for example a roller bearing.
[0043] Alternatively, the second bearing 28 is a tapered roller bearing or the like.
[0044] An example of a flexible cage is described in patent application FR 3098 239 filed in the name of the applicant.
[0045] Preferably, a lubricant ring 32 surrounds the second bearing.
[0046] This lubricant ring constitutes a damping device. An example of such a damping device is also described in patent application FR 3098 239. Advantageously, this lubricant ring 32 greatly limits the expansion of the outer ring of the second bearing due to an oil temperature lower than the temperature of the outer ring of the bearing.
[0047] The first ball bearing 20 is characterized by a dissipated power greater than that of the second bearing 28, thus allowing for greater expansion of the constituent elements of the bearing.
[0048] The second bearing 28, the second outer ring 24 and the flexible cage 30 are shaped so that a second clearance J2 is provided between the second bearing 28 and the second outer ring 26.
[0049] Advantageously, the first clearance J1 has a dimension greater than the second clearance J2 in a radial direction R, as visible in FIG. 2. Advantageously also, the second bearing 28 is spaced from the first bearing 20 by a predefined axial spacing E so as to guarantee a temperature of the shaft line that is almost identical for the two bearings. This predefined axial spacing E is sufficiently small to guarantee similar average temperatures for the first inner ring 16 and for the second inner ring 24, which helps to control the hierarchy of the clearances. Advantageously, this predefined axial spacing E guarantees the isostatism of the shaft line.
[0050] The predefined axial spacing E is less than four times the diameter of the balls of the ball bearing so that the difference between the mass temperature of the first inner ring 16 and the mass temperature of the second inner ring 24 is less than 20°.
[0051] The first support 22 is a rigid support. It has a defined stiffness K1.
[0052] The flexible cage 30 has a determined stiffness K2 lower than the stiffness K1 of the first support.
[0053] Advantageously, the centering and guiding device 12 has an overall radial stiffness K(R) which varies as a function of the engine speed R, as visible in FIG. 6 and as explained below.
[0054] Figure 3 shows the centering and guiding device 12 when the turbomachine is operating at low speed and under low load.
[0055] With reference to Figure 3, during operating phases at low speed and under low axial load, the radial displacement of the shaft line 14 directly stresses the second bearing 28 mounted in the flexible cage 30. At this moment, the stiffness K(R) of the centering and guiding device 12 is that of the flexible cage 30. The first ball bearing 20 is not stressed or is only weakly stressed due to the fact that the first clearance J1 is greater than the second clearance J2.
[0056] At low speed and under low axial load, the second clearance J2 is absorbed. The rigidity of the centering and guiding device corresponds to the rigidity of the flexible cage 30. This makes it possible to position, with sufficient margin, the first vibration mode to be crossed below the desired stabilized operating range of the shaft line.
[0057] Figure 4 shows the centering and guiding device 12 when the turbomachine is in operation.
[0058] As the speed increases, the axial thrust (Fax) increases, the clearance J1 in the first bearing 20 is reduced so as to gradually take up the radial loading of the centering and guiding device 12. Thus, the second bearing 28 is less and less stressed and the radial stiffness K(R) of the centering and guiding device 12 gradually switches to the radial stiffness of the first ball bearing 20 until this axial loading is so significant compared to the radial loading that the second bearing 28 unloads in favor of the first ball bearing 20 as illustrated in Figure 4.
[0059] The second shaft line mode is then pushed beyond and away from the operating speeds due to this increase in rigidity of the centering and guidance device. This thus ensures a satisfactory critical speed positioning situation for the highest operating speeds.
[0060] Furthermore, by judiciously choosing the spacing E between the two bearings, the loading angle a makes it possible to guarantee the isostatic character of the assembly as illustrated by the dotted lines in Figure 4. Thus, the spacing E between the first bearing 20 and the second bearing 28 must be controlled during the design phase in order to guarantee this condition. The predefined axial spacing E thus serves to guarantee the hierarchy of the clearance between the two bearings but also the isostatic character of the assembly.
[0061] During the engine shutdown phase, the trend reverses. As the engine speed decreases, the axial thrust decreases and, in this example, the centering and guiding device behaves again like a flexible bearing. This allows the first vibration mode to be overcome again under satisfactory conditions.
[0062] With reference to Figure 5, the axial force (Fax) applied to the shaft line 14 increases when the engine speed R increases.
[0063] Figure 7 represents the unbalance response of the shaft line as a function of the engine speed when the shaft line is mounted on a flexible cage (curve 34), when it is mounted on a rigid supporting structure (curve 36) and when it is mounted in a centering and guiding device 12 according to the invention (curve 38). With reference to Figure 7, as shown by curve 34, when the shaft line is mounted in a flexible bearing, the forces generated on the bearing are reduced but a second vibration mode is positioned in the vicinity of the operating speed. The second vibration mode is positioned too close to the nominal operating speed of the engine.
[0064] As shown in curve 36, when the shaft line is mounted in a stiff bearing, the forces generated on the bearing are significant and the first vibration mode is close to the operating range of the engine. As shown in curve 38, when the shaft line is mounted in a centering and guiding device 12 according to the invention, the first vibration mode is sufficiently low in speed and is damped. The second vibration mode is pushed out of the nominal operating range of the engine speed.
[0065] Ultimately, the vibration mode present at the top of the operating range is pushed back by the change in stiffness. On the other hand, the level of force at the bearing on the first vibration mode as well as the position of the first vibration mode remain identical to a solution using a flexible bearing. At the stabilized nominal operating speed, the forces in the bearings are also significantly reduced compared to the configuration with a flexible bearing. Advantageously, the centering and guiding device 12 thus makes it possible to benefit from the advantages of a flexible bearing and the advantages of a stiff bearing.
[0066] From a shaft deformation energy point of view, the present invention advantageously makes it possible to minimize the energies in the shaft line for the two vibration modes present around the operating range of the engine.
Claims
CLAIMS 1. Device (12) for centering and guiding in rotation a shaft line (14) of a turbomachine; the shaft line (14) being capable of being driven in rotation around an axis of rotation (AA); said device (12) comprising: - a first inner ring (16) fixed to a shaft line (14), a first outer ring (18), a first ball bearing (20) arranged between the first inner ring (16) and the first outer ring (18), a first support (22) supporting the first outer ring (18), - a second inner ring (24) fixed to the shaft line (14), a second outer ring (26), a second bearing (28) arranged between the second inner ring (24) and the second outer ring (26), and a flexible cage (30) supporting the second outer ring, and in that the second bearing (28) is spaced from the first ball bearing (20) by a predefined axial spacing (E), characterized in that the first support (22) has a stiffness greater than the stiffness of the flexible cage (30) and in that the first ball bearing (20), the first outer ring (18), and the first support (22) are shaped so that a first clearance (J1) is provided between the first ball bearing (20) and the first outer ring (18); the second bearing (28), the second outer ring (26), and the flexible cage (30) are shaped so that a second clearance (J2) is provided between the second bearing (28) and the second outer ring (26);the first set (J1) having a dimension greater than the second set (J2) in a radial direction.; 2. Device (12) according to claim 1, characterized in that the predefined axial spacing (E) is less than four times the diameter of the balls of the ball bearing.
3. Device (12) according to any one of claims 1 and 2, in which the second bearing (28) is a roller bearing.
4. Device (12) according to any one of claims 1 to 3, in which a lubricant ring (32) surrounds the second bearing.
5. Device (12) according to any one of claims 1 to 3, in which the first ball bearing (20) has curvatures of between 0.51 and 0.52 so as to guarantee low radial stiffness of the centering and rotational guidance device under low axial load.
6. Turbomachine (1) comprising a frame (13), a shaft line arranged in the frame (13), said shaft line (14) being suitable for driving a turbine in rotation and a device (12) for centering and guiding in rotation said shaft line according to any one of claims 1 to 5, said centering and guiding device (12) being mounted on at least one shaft line among the shaft line of a speed reducer (2), the shaft line of a drive chain (4) of the accessories, a front part (6) of the shaft line of a gas generator and the shaft line of a free turbine (10).