FR2961865A1 - Aircraft jet engine, has holding portion and complementary holding portion shaped such that relative movement of holding portion with respect to complementary portion drives holding portion to be recentered relative to complementary portion - Google Patents

Abstract

The engine has a connection unit (14b) for connecting an exterior ring of front rolling bearings and a rear bearing on a housing. The connection unit comprises a holding portion (20) located radially opposite a complementary holding portion (24) provided on the housing. The holding portion and the complementary holding portion are shaped such that relative movement of the holding portion with respect to the complementary holding portion drives the holding portion to be recentered with respect to the complementary holding portion by guiding ramps (30) and pins (32).

Description

BACKGROUND OF THE INVENTION The present invention relates to the field of aircraft turbojet engines, and more particularly, to the means for aeronautic turbojet engines. implemented within these turbojet engines to cope with the unbalance caused by a loss of fan blade. This problem is addressed in particular in documents EP 1 653 051, EP 1 916 431, FR 2 752 024 and FR 2 888 621. STATE OF THE PRIOR ART The loss of one or more fan blades usually generates a large unbalance on the fan rotor carrying the blades, this unbalance being likely to endanger the integrity of the structures of the turbojet engine. To cope with this problem and protect these structures, it is known to practice fuse zones on the path of recovery of radial forces. Indeed, it is for example provided to achieve fusible mechanical links between the outer ring of the two rolling bearings the most ready of the fan rotor, and the turbojet engine housing. These mechanical links are sized to withstand the radial forces in the normal flight configuration, and to break in the event of loss of at least one fan blade due to the imbalance caused by this loss. This system is also known as a mechanical decoupling system.

Following these two breaks, a single rolling bearing, of the three initially provided, continues to ensure the centering of the drive shaft. Since this single centering is insufficient to maintain the integrity of the turbojet engine, the coupling means of the intermediate bearing on the housing have a retaining portion located radially opposite a complementary retaining portion, provided on the housing and centered with the retaining portion. Before the rupture of the fusible mechanical links, these retaining portion and complementary retaining portion remain at a radial distance from one another, and are therefore not active. On the other hand, after the rupture of the fusible mechanical links following a loss of fan blade, the radially biased retaining portion is intended to come into contact with the complementary retaining portion, then to be moved relative to that -c, under the combined effect of a precession of the fan rotor and the contact with the complementary retaining portion. When the retaining portion and complementary retaining portion respectively take the form of two annular raceways, of different sizes, the relative movement of the retaining portion is a bearing thereof on the complementary retaining portion. During this rolling, the axis of rotation 3 of the retaining portion is in motion relative to the complementary retaining portion, which remains fixed to the housing. Although the active cooperation between the retaining portion and the complementary retaining portion makes it possible to limit the angle of the precession movement of the fan rotor and its drive shaft, caused by unbalance, this cooperation nevertheless has a disadvantage.

Indeed, during the rolling of the retaining portion, the movable point contact between the two portions generates considerable radial forces, highly likely to degrade these portions. These radial forces are high especially because of the eccentricity of the drive shaft of the fan rotor, observed during its precession movement. There is therefore a risk of destruction of these portions, and therefore a risk of endangering the integrity of the turbojet engine, particularly with regard to the axial retention of the rotor and its drive shaft. DISCLOSURE OF THE INVENTION The object of the invention is therefore to remedy at least partially the disadvantages mentioned above, relating to the embodiments of the prior art. For this purpose, the subject of the invention is an aircraft turbojet comprising a housing, a fan rotor carrying vanes, a rotor drive shaft, three rolling bearings cooperating with said drive shaft, and associated at each bearing, means for connecting an outer ring of the bearing to said housing, the connecting means associated with the two bearings located closest to the rotor being connected to the housing respectively by two mechanical fusible links provided to break in case of loss at least one fan blade due to the imbalance caused by this loss, and, for at least one of these two bearings, said associated connection means comprise a retaining portion located radially opposite a complementary retaining portion provided on said housing and centered with the retaining portion, said retaining portion being provided, after rupture of the fusible mechanical links following a loss of dawn of souf flante, to contact the complementary retaining portion and then be moved relative to it under the combined effect of precession of the rotor and contact with the complementary retaining portion. According to the invention, said retaining portion and complementary retaining portion are shaped such that said relative movement causes the retaining portion to refocus with respect to said complementary retaining portion. The invention is therefore remarkable in that it provides for using the retaining portion and complementary retaining portion not only to allow and then limit the radial deflection of the drive shaft immediately after the dawn loss, but Also, later, to recenter this shaft by recentering the retaining portion relative to the complementary retaining portion. After the shaft has been recentered, the radial contact forces between the retaining portion 5 and the complementary retaining portion are weakened, and the risks of degradation of these portions are reduced, as well as the risks of placing in danger of the integrity of the turbojet engine. The desired recentering may be obtained in any manner deemed appropriate by those skilled in the art, taking advantage of the drive of the retaining portion of the coupling means by the precession movement of the rotor drive shaft, caused in a natural way by the appearance of an imbalance following a loss of dawn. According to a preferred embodiment, the retaining portion comprises a raceway, the complementary retaining portion has a complementary raceway intended to cooperate with the raceway, and the retaining and retaining portions are furthermore equipped with recenter means for recentering the retaining portion relative to the complementary retaining portion. In such a case, the design preferably provides that the two tracks roll on one another, for a period that can be predetermined, before the refocusing means become active. Preferably, said raceway and complementary raceway are annular and centered on a longitudinal axis of the turbojet in normal configuration, that is to say before rupture of the two fusible mechanical links. In addition, it is expected that said race is located radially inward relative to said complementary raceway, or vice versa. Here, said recentering means then preferentially allow, during said relative movement of the retaining portion with respect to the complementary retaining portion, to replace the retaining portion centrally on said longitudinal axis of the turbojet, in order to recenter said shaft of the retaining portion. fan drive on the same axis. Nevertheless, the refocusing operated on the retaining portion could be different from the initial centering, without departing from the scope of the invention. Still preferentially, said recentering means comprise a plurality of guiding ramps secured to one of the two of said rolling track and said complementary rolling track, and, associated with each ramp, at least one lug integral with the other of these elements and able to cooperate with said ramp. In this regard, to mitigate shocks contacting between the ramps and lugs, they can be profiled, also shaped ramp. Preferably, said ramps and their lugs are designed so that after having caused the retaining portion to refocus, they also provide a rotational locking of this retaining portion with respect to the complementary retaining portion. Preferably, there is provided a number of ramps greater than or equal to three, the ramps being regularly spaced from each other. In general, the higher the number of ramps, the faster the re-centering of the drive shaft. Preferably, the ramps and the lugs are arranged so that during said relative movement of the retaining portion relative to the complementary retaining portion, the lugs are brought into contact with the ramps successively. This allows for a gradual refocusing. Preferably, each of the fusible mechanical links is made to Finally, the complementary retaining portions are using screws. retaining and preferably associated with the intermediate rolling bearing, allowing the axial retention of the drive shaft of the rotor. Alternatively or simultaneously, these portions could be associated with the rolling bearing closest to the rotor, usually the most forward bearing of the three that equip the drive shaft. Other advantages and features of the invention will become apparent in the detailed non-limiting description below. BRIEF DESCRIPTION OF THE DRAWINGS This description will be made with reference to the accompanying drawings, among which; Figure 1 shows a schematic longitudinal sectional view of a portion of a turbojet, according to a preferred embodiment of the present invention; FIG. 2 represents a sectional view taken along the line II - II of FIG. 1, showing means for retaining the fan rotor drive shaft, intended to be active after the loss of a fan blade; FIG. 3 represents a view similar to that of FIG. 1, with the turbojet engine in a configuration such as adopted immediately after the loss of a fan blade; FIG. 4 represents a view similar to that of FIG. 2, with the retaining means being in a configuration such as adopted immediately after the loss of a fan blade; - Figures 5 to 9 schematically different successive states of the retaining means, during their subsequent movement after the loss of a fan blade; and - Figure 10 shows a sectional view detailing the cooperation between a ramp and a pin belonging to the retaining means shown in the preceding figures. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference to FIG. 1, it is possible to see schematically a portion of an aircraft turbojet 1, according to a preferred embodiment of the present invention. In a conventional manner, this turbojet engine 1 has a longitudinal axis 2 on which are centered a fan rotor 4 carrying fan blades 6, and a drive shaft 8 integral in rotation with the rotor 4, also called fan disk. The turbojet engine 1 also comprises a casing 10 forming a fixed rigid casing, this casing being represented very schematically in FIG. 1. In order to maintain and guide the shaft 8, three rolling bearings are spaced apart one at a time. others in the direction of the axis 2, these bearings being respectively referenced, from front to rear, 12a, 12b and 12c.

The outer ring of each of these three rolling bearings is fixed to the casing 10 by connecting means referenced respectively 14a, 14b and 14c. As shown schematically in FIG. 1, these coupling means each take the form of an annular structure connecting the outer ring directly to the casing, or to an internal extension of the casing, as is the case for the two levels 12a, 12b, located the most ready rotor 4. The forward bearing 12a and the rearmost bearing 12c are each provided to take radial forces, while the intermediate bearing 12b is also provided to ensure the Axial retention of the shaft 8. With regard to the two front bearings 12a, 12b, their connecting means are each connected to the housing 10 by a mechanical fusible link 16a, 16b. These connections are for example made using screws, the number, dimensioning and position are retained so as to confer the desired fuse character, which will be explained below.

The connection means 14b of the outer ring 18 of the intermediate bearing 12b, on the casing 10, have the further feature of comprising a retaining portion 20 forming an annular raceway 22 centered on the axis 2. As can be seen in FIGS. 1 and 2, this annular track 22 is oriented radially outwards, and situated radially facing a complementary retaining portion 24 provided on the casing 10. More specifically, this portion 24 comprises a complementary rolling track 26, also annular and centered on the axis 2. In normal flight configuration as shown schematically in these Figures 1 and 2, the track 26 is located around and away from the track 22, so they do not cooperate not one with the other. In addition, according to a feature of the present invention, the portions 20, 24 are equipped with recentering means comprising a plurality of guide ramps 30 and lugs 32. The ramps 30 are integral with the complementary raceway 26, and therefore belong to the portion 24 fixed to the housing 11 10. They are spaced regularly from each other in the circumferential / tangential direction, and are axially offset from the complementary raceway 26 with which they can be made in one piece . Here at the number of three and distributed at 120 °, these ramps each have an active surface oriented generally radially inwardly. In addition, these ramps 30 project radially inwards relative to the track 26. The lugs 32 are secured to the raceway 22, and therefore belong to the portion 20 of the connecting means 14b. They are also spaced regularly from each other in the circumferential / tangential direction, and are axially offset from the raceway 22 with which they can be made in one piece. Here also three in number and distributed at 120 °, these lugs 32 remain located radially inward with respect to the track 22, and are arranged in a transverse plane also passing through the ramps 30. As will be described later, each lug 32 is intended to come into contact with one of the ramps 30 in the event of the loss of a fan blade. To mitigate shocks contact between the ramps and lugs, they are preferably profiled, also shaped ramp. In the normal flight configuration, the retaining means constituted by the two portions 20, 24 remain inactive, on the one hand because the rolling tracks 22, 26 are at a radial distance from one another forming an annular clearance. 34 substantially constant all around them, and secondly because the lugs 32 are located at a distance from the guide ramps 30. In this normal configuration, the mechanical fusible links 16a, 16b are sufficiently resistant to withstand the forces radial transmitted by the front bearings 12a, 12b, for maintaining the rotation of the shaft 8 along the longitudinal axis 2 of the turbojet engine. A case of exceptional problem leading to the loss of one or more fan blades 6, the rotor 4 undergoes an unbalance which causes extremely high radial forces in the structures of the turbojet, and in particular in the connecting means 14a, 14b and 14c. As mentioned above, the two fusible mechanical links 16a, 16b are provided to break when the connecting means 14a, 14b are subjected to these extremely high radial forces, of predetermined size. With reference to FIG. 3, the immediate consequence of these breaks lies in the radial displacement of the shaft 8 bearing the rotor 4 undergoing unbalance, this displacement causing the raceway 22 to move also radially with all the means fitting 14b, until it comes into contact with the complementary rolling track 26 after consumption of the radial clearance 34.

A point contact 36 is then established between the two 13 races 22, 26 initially spaced apart from each other, as shown schematically in FIG. 4. Once the contact is established, the radial clearance of the shaft 8 is stopped. This tree is then, in a manner known to those skilled in the art, a precession movement during which it continues to rotate on itself, and also rotates about the longitudinal axis 2 of which it remains angularly offset. In this respect, it is specified that the rear bearing 12c continues to guide and center punctually this shaft 8 on the axis 2. The precession of the shaft 8 and its rotor 4, combined with the contact 36 of the retaining portions 20, 24, causes the retaining portion 20 to be moved relative to the complementary retaining portion 24. This relative movement begins with a rolling, usually without sliding due to the very high contact forces, the track 22 on the fixed track 26 of greater diameter. During this initial phase of rotation, the ramps and lugs all remain inactive. The observed bearing, corresponding to the initial phase of said relative movement of the retaining portion 20, is substantially identical to the movement encountered in the embodiments of the prior art. One of the peculiarities of the present invention lies in the fact that this rolling is not continued until the shutdown of the turbojet engine. Indeed, the bearing of the retaining portion 20 causes the lugs 32 to move relative to the ramps 30 along the track 26, until they enter into cooperation with them. Thus, said relative movement, initially taking the form of a simple bearing, is deliberately disturbed by the recentering means 30, 32 which, cooperating by contact, cause the retaining portion 20 to refocus relative to the retaining portion. complementary, 24, along the axis 2. Preferably, the refocusing is operated gradually, providing that the three contacts of the lugs 32 with their associated ramp 30 operate successively, as shown schematically in FIGS. to 9. During this progressive refocusing, obtained by dimensioning and judiciously placing the recentering means 30, 32, the precessional movement of the shaft 8 and its rotor 4 also gradually attenuates, until this shaft 8 is again centered on the axis 2 once the refocusing of the portion 20 completed. Once the three contacts obtained between the lugs 32 and the associated ramps 30, the raceway 22 is no longer in contact with the raceway 26, but the portion 20 is still driven by its relative movement relative to the portion 24, still under the combined effect of the precession movement of the rotor 4 and the contact between the portions 20, 24 at the level of the recentering means. During this terminal phase of said relative movement, which completes the recentering of the portion 20 and the shaft 8, the lugs 32 slide on their associated ramp 30, until jamming of the recentering means. This wedging, shown diagrammatically in FIG. 9, then ensures a rotational locking of the retaining portion 20 with respect to the complementary retaining portion 24, and makes it possible to maintain the centering of the shaft 8 and of the fan rotor 4 on the axis 2 via the intermediate bearing 14b recentered, until the shutdown of the turbojet whose fan usually reaches its autorotation speed quickly after the blade loss. As mentioned above, to mitigate shocks contact between the ramps and lugs, they are profiled, also shaped ramp. FIG. 10 schematizes the fact that whatever the place of contact between each lug 32 and its associated ramp 30 during said relative movement of the retaining portion 20, the angle 40 between the contact slope 42 and the normal 44 to the radial line 46 passing through the contact is between 3 and 8 °. Of course, various modifications may be made by those skilled in the art to the invention which has just been described, solely as non-limiting examples.

Claims (10)

REVENDICATIONS1. Turbeactor (1) for an aircraft comprising a housing (10), a fan rotor (4) carrying vanes (6), a rotor drive shaft (8), three rolling bearings (12a, 12b, 12c) cooperating with said drive shaft, and, associated with each bearing, connection means (14a, 14b, 14c) of an outer ring of the bearing on said housing, the connecting means associated with the two bearings (12a, 12b) located the most ready of the rotor (4) being connected to the housing respectively by two mechanical fusible links (16a, 16b) provided to break in case of loss of at least one fan blade due to the imbalance caused by this loss, and, for at less one of these two bearings (12b), said associated connecting means (14b) comprise a retaining portion (20) located radially facing a complementary retaining portion (24) provided on said housing and centered with the retaining portion, said retaining portion being provided, after rupture of the liaiso fusible mechanicals (16a, 16b) following a loss of fan blade, to come into contact with the complementary retaining portion and then be moved relative to it with the combined effect of a movement of precession of the rotor and contact with the complementary retaining portion, characterized in that said retaining portions (20) and complementary retaining portions (24) are shaped such that said relative movement causes the retaining portion (20) to become recentering with respect to said complementary retaining portion (24). 2. Turbojet engine according to claim 1, characterized in that said retaining portion (20) comprises a raceway (22), in that the complementary retaining portion (24) comprises a complementary raceway (26) for cooperate with the raceway, and in that the retaining portions (20) and complementary retaining portions (24) are furthermore equipped with recentering means (30, 32) for recentering the retaining portion relative to the portion additional restraint. 3. Turbojet engine according to claim 2, characterized in that said raceway (22) and complementary raceway (26) are annular and centered on a longitudinal axis (2) of the turbojet engine in normal configuration before breaking the two mechanical fusible links. (16a, 16b). 4. Turbojet engine according to claim 3, characterized in that said raceway (22) is located radially inwardly relative to said complementary raceway (26). 5. Turbojet engine according to claim 3 or claim 4, characterized in that said recentering means (30, 32) allow, during said relative movement of the retaining portion relative to the complementary retaining portion, to replace the 18 portion. retaining (20) centrally on said longitudinal axis (2) of the turbojet, to recenter said drive shaft (8) on the same axis. 6. Turbojet engine according to any one of claims 2 to 5, characterized in that said recentering means comprise a plurality of guide rails (30) integral with one of the two of said track (22) and said complementary bearing track (26), and, associated with each ramp (30), at least one lug (32) integral with the other of these elements and capable of cooperating with said ramp. 7. Turbojet engine according to claim 6, characterized in that there is provided a number of ramps (30) greater than or equal to three, the ramps being regularly spaced from each other. 8. Turbojet engine according to any one of claims 6 and 7, characterized in that the ramps (30) and the lugs (32) are arranged such that during said relative movement of the retaining portion relative to the retaining portion. complementary, contacting the lugs with the ramps occur successively. 9. Turbojet engine according to any one of the preceding claims, characterized in that each of the mechanical fusible links (16a, 16b) is made using screws. 19 10. Turbojet engine according to any one of the preceding claims, characterized in that the retaining portions (20) and complementary retaining portion (24) are associated with the intermediate rolling bearing (12b), allowing the axial retention of the shaft d drive (8) of the rotor (4).