Device for centring and guiding the rotation of a turbine engine shaft, improving handling of an sfd lubricant supply failure

Abstract

The invention relates to a device (30) for centring and guiding the rotation of a turbine engine shaft comprising: – an annular damping cavity (52), formed between a bearing support (34) and an outer race (38) of a bearing; – a supply circuit (60) for the annular damping cavity (52), for supplying same with lubricant in order to form a damping film therein; – a lubricant discharge circuit (72) comprising an outlet pipe (74) defining a calibrated lubricant leakage port (76), the circuit (72) also comprising, on the outlet pipe (74), a lubricant check valve (78), wherein the check valve (78) comprises a closure member (92) for closing the outlet pipe, and an actuator (94) controlled according to a pressure of lubricant in the supply circuit (60).

Description

[0001] DEVICE FOR CENTERING AND ROTATING A TURBOMACHINE SHAFT, IMPROVING THE MANAGEMENT OF A LUBRICANT SUPPLY FAILURE CASE OF AN SFD

[0002] Technical field

[0003] The present invention relates to the field of turbomachines, in particular for aircraft, and it relates more particularly to a device for centering and guiding the rotation of a turbomachine rotor shaft, comprising a bearing with oil film compression damping, also called an "SFD" bearing (from the English "Squeeze Film Damper").

[0004] State of the prior art

[0005] A device for centering and guiding the rotation of a turbomachine rotor shaft of the SFD bearing type is a known means for damping vibrations of the shaft, as explained for example in document EP1650449B1.

[0006] With reference to the attached figure 1A, which shows such a device schematically, the reference 210 designates a rotor shaft of a turbomachine intended for the propulsion of an aircraft, such as an aircraft turbojet or turboprop. This rotor shaft 210 is centered and guided in rotation in a rolling bearing 212. The latter comprises an outer ring 214 carried by an elastically deformable perforated structure 216, commonly called a “squirrel cage” or “flexible cage”, itself carried by a stator structure of the turbomachine, so as to offer a certain degree of radial movement, or orbiting, to the outer ring of the bearing, under the effect of vibrations of the shaft, for example following an unbalance.

[0007] The outer ring 214 of the bearing is mounted in a cylindrical housing 218 defined by a bearing support 220 to form around the outer ring 214 an oil film compression damper (SFD). For this purpose, an annular damping cavity 222 is delimited around the outer ring 214 by the cylindrical surface 221 of the bearing support 220 defining the housing 218, and is axially closed by annular seals 224 mounted in annular grooves 226, formed in the external cylindrical surface of the ring 214. In the field of aircraft turbojets or turboprops, particularly in regions exposed to the highest temperatures, the annular seals 224 are generally elastically deformable split rings, made of a metal resistant to high temperatures.Seals of this type are sometimes called "metal segments", or "piston rings" in English terminology, due to the common use of seals of this type to ensure the sealing of pistons.

[0008] The annular cavity 222 is filled with a lubricant, typically oil, supplied by one or more inlet orifice(s) 228 formed by a radial bore in the casing 220 and opening opposite an annular groove 230 formed on the outer ring 214 and opening radially outwards, into the annular cavity 222.

[0009] Thus, any orbiting of the outer ring would lead to a crushing of the lubricant film defined by the aforementioned cavity, such crushing being the cause of damping.

[0010] Such damping capability makes it possible to reduce design loads, and therefore to lighten structures, resulting in an overall reduction in mass. This solution also makes it possible to increase the stability of a supercritical shaft (when the shaft has a bending mode in the operating range), to reduce vibrations, and also to reduce rotor / stator clearance consumption, thus improving the performance of the turbomachine.

[0011] To prevent excessive heating of the lubricant within such a cavity, the lubricant is continuously supplied to and removed from the cavity, so as to allow continuous circulation of the lubricant. The lubricant is generally removed via one or more leakage sections provided at the level of the annular sealing rings axially delimiting the cavity. These leakage sections are generally defined by the slots in the segments constituting the sealing rings and / or by notches formed in these segments.

[0012] Alternatively, a lubricant discharge circuit is provided outside the annular damping cavity, this circuit comprising an outlet pipe defining a calibrated lubricant leakage orifice. In this alternative, the segments are sealed or quasi-sealed, with leakage occurring via the calibrated orifice. In the sealed solution, corresponding to an ideal operating mode, the leakage rate is zero at the segments. In the quasi-sealed solution, which results from manufacturing tolerances and the tangential clearance of the overlap between the segments, the leakage can be from a few tenths of a L / h to a few L / h. This is to be compared to the leakage of the SFD, via the calibrated orifice, which is from a few tens of L / h to a few hundred L / h.

[0013] In the event of a lubricant supply failure, the latter empties from the annular damping cavity, via the calibrated orifice. This can lead to a rapid degradation of the damping power provided by the system, and thus reduce the stability of a supercritical shaft. Indeed, in the case of a turbomachine architecture with a supercritical shaft, having a bending mode in the operating range, in the event of a lubricant supply failure there is a risk of excessive vibrations appearing during shaft deceleration. These non-synchronous vibrations can lead to excessive / permanent deformations of the turbomachine rotor, as well as excessive clearance consumption resulting in contacts between the rotor and the stator, or between two rotors in the case of an inter-shaft bearing.

[0014] Therefore, the invention aims to optimize the design of this type of device for centering and guiding a turbomachine rotor shaft, so as to improve the management of cases of lubricant supply failure of an SFD.

[0015] Statement of the invention

[0016] To meet this aim, the invention firstly relates to a device for centering and guiding the rotation of a turbomachine rotor shaft, comprising the characteristics of claim 1.

[0017] By means of the invention, it is possible to retain lubricant in the annular damping cavity when a lubricant supply failure of an SFD is detected, via the pressure of this lubricant in the supply circuit. With such retention of lubricant in the discharge circuit and in the annular damping cavity located further upstream, it advantageously becomes possible to maintain minimal damping in the event of a lubricant supply cut-off / failure, or during so-called "zero g" maneuvers, also known as parabolic maneuvers. This allows the film to dampen the shaft for a little longer after the supply failure, typically the time for the viscosity of the lubricant to decrease due to the increase in temperature, namely for a period ranging for example from a few seconds to a few minutes, and preferably from about ten seconds to several tens of seconds.This feature gives the driver more time to shut down the engine before non-synchronous vibrations (NSV) occur.

[0018] Furthermore, the choice of lubricant pressure in the supply circuit, to detect a failure in the lubricant supply and control the lubricant check valve accordingly, allows for simple and reliable implementation.

[0019] Furthermore, the first reference pressure PI, also called the first cracking pressure, may be set at a value greater than or equal to the critical lubricant supply pressure, corresponding to the minimum pressure guaranteeing nominal operation of the damping film. Furthermore, the second reference pressure P2, also called the second cracking pressure, may for example be set at the nominal lubricant supply pressure value of the damping cavity.

[0020] Thus, closing the check valve at a pressure P2 higher than the pressure PI at which the lubricant flow control device closes through the inlet pipe ensures a good supply of lubricant. This also allows a high operating pressure to be maintained in the event that a flow restriction is present upstream in the lubricant circuit.

[0021] Thanks to this design, during normal operation, the damping cavity is correctly supplied with lubricant, which can then be evacuated through the calibrated leakage orifice. This is enabled by the opening of the check valve, as well as by the opening of the device controlling the passage of lubricant through the inlet pipe.

[0022] On the other hand, in the event of a failure in the supply of lubricant to the damping film, the inlet supply pressure drops, and this causes the non-return valve on the discharge circuit to close first, then the lubricant flow control device on the supply circuit to close. The lubricant is thus advantageously trapped in the annular damping cavity, allowing the film to dampen the shaft for a little longer after the supply failure. In other words, the invention makes it possible to keep lubricant in the annular damping cavity, when a case of failure in the supply of lubricant to an SFD is detected, via the pressure of this lubricant in the supply circuit.

[0023] Thus, in a preferred embodiment of the invention, the actuator of the check valve is a passive actuator, preferably controlled by the lubricant pressure in the supply circuit.

[0024] To do this, the check valve preferably comprises elastic return means exerting a first force on the actuator, and this actuator delimits a pressure chamber communicating with the supply circuit, so that the lubricant present in the chamber applies a second force to the actuator in the opposite direction to the first force.

[0025] Preferably, the device for controlling the passage of lubricant through this inlet pipe is a non-return valve, or a lubricant passage valve, the passage valve comprising a member for closing the inlet pipe, as well as an actuator controlled as a function of the lubricant pressure in the supply circuit.

[0026] In this context, the passage valve preferably comprises elastic return means exerting a first force on the actuator of this passage valve, and this actuator delimits a pressure chamber of the passage valve communicating with the supply circuit, so that the lubricant present in this pressure chamber of the passage valve applies a second force to the actuator, in the opposite direction to the first force.

[0027] For example, for a simple embodiment of the invention, the pressure chamber of the passage valve communicates with the pressure chamber of the check valve, via a fluid communication conduit.

[0028] Preferably, the two annular sealing joints are overlapping split rings, providing a seal or near-seal of the lubricant in the annular damping cavity. Finally, the invention also relates to a turbomachine, in particular for an aircraft, comprising a drive shaft, as well as at least one such device for centering and guiding the rotation of this shaft.

[0029] Other advantages and characteristics of the invention will appear in the detailed non-limiting description below.

[0030] Brief description of the drawings

[0031] The invention will be better understood, and other details, advantages and characteristics thereof will appear on reading the following description given by way of non-limiting example and with reference to the appended drawings in which:

[0032] [Fig IA], already described, is a schematic view in axial section and in perspective of a device for centering and guiding in rotation a shaft in a turbomachine, of known type;

[0033] [Fig IB] is a schematic axial sectional view of an aircraft turbomachine;

[0034] [Fig IC] is a schematic view in axial half-section, on a larger scale, of a rear part of a turbomachine;

[0035] [Fig 2A] is a schematic view in axial half-section of a device for centering and guiding the rotation of a shaft in a turbomachine such as that of FIG. 1B, according to a first preferred embodiment of the invention, and with the device shown in a normal operating configuration;

[0036] [Fig 2B] is a partial schematic perspective view of an annular sealing gasket belonging to the device of Figure 2A;

[0037] [Fig. 2C] is a view similar to that of Fig. 2A, with the device shown in a lubricant supply failure configuration;

[0038] [Fig. 3A] is a schematic view of a device for controlling the passage of lubricant through an inlet pipe, belonging to the device of FIG. 2A;

[0039] [Fig. 3B] is a view similar to that of Fig. 3A, illustrating an alternative;

[0040] [Fig. 3C] is a view similar to that of Fig. 3A, illustrating another alternative;

[0041] [Fig. 3D] is a schematic view of a lubricant check valve through an outlet pipe belonging to the device of Fig. 2A; [Fig. 4] is a diagram schematizing the operation of the device shown in the preceding figures;

[0042] [Fig. 5] is a view similar to that of Fig. 2A, illustrating another preferred embodiment of the invention; and

[0043] [Fig. 6] is a view similar to that of Fig. 2A, illustrating yet another preferred embodiment for the device for centering and guiding in rotation a shaft in a turbomachine.

[0044] Throughout the following description and accompanying drawings, like reference numerals designate similar or analogous elements.

[0045] Detailed disclosure of preferred embodiments

[0046] Figure 1B illustrates a turbomachine 10, for example a twin-spool, dual-flow turbojet engine for aircraft, generally comprising a fan 12 intended for the suction of an air flow F1 dividing downstream of the fan into a primary flow F2 circulating in a primary flow channel, hereinafter referred to as the primary flow path PV, and a secondary flow F3 circulating in a secondary flow channel, hereinafter referred to as the secondary flow path SV, and arranged around the primary flow path PV.

[0047] By way of illustration, the turbomachine generally comprises a low-pressure compressor 14, a high-pressure compressor 16, a combustion chamber 18, a high-pressure turbine 20 and a low-pressure turbine 22 which jointly define the primary flow path PV. The respective rotors of the high-pressure compressor and the high-pressure turbine are connected by a shaft 24 called the “high-pressure shaft”, while the respective rotors of the low-pressure compressor and the low-pressure turbine are connected by a shaft 26 called the “low-pressure shaft”, in a well-known manner. These rotors are rotatably mounted about a longitudinal central axis 28 of the turbomachine. For this purpose, devices 30A, 30B ensure the centering and rotational guidance of the high-pressure shaft 24, while devices 30C-30E ensure the centering and rotational guidance of the low-pressure shaft 26.These devices 30A-30E, which each comprise a rolling bearing, establish force paths between the shafts 24, 26, on the one hand, and casings of the turbomachine, on the other hand, in a well-known manner. Throughout this description, the axial direction X is the direction of the axis 28. A first cylindrical coordinate system centered on the axis 28 is also considered, in which a radial direction R is at all points orthogonal to the axis 28 and passes through the latter, while an ortho-radial or circumferential direction C is at all points orthogonal to the radial direction R and to the axis 28. A transverse plane is a plane orthogonal to the axis 28. The terms "internal" and "external" refer respectively to a relative proximity, and a relative distance, of an element relative to the axis 28.Finally, the "upstream" and "downstream" directions are defined by reference to the general direction FD of the gas flow in the primary PV and secondary SV veins of the turbomachine, in the axial direction X, in normal direct thrust configuration.

[0048] Figure IC illustrates on a larger scale a rear part of a turbomachine such as the turbomachine of Figure IB, and in particular allows a view to be seen of a rotor of the low-pressure turbine 22, formed of bladed discs 22A arranged alternately with distributors 22B and connected to the low-pressure shaft 26, as well as an exhaust casing 29 arranged downstream of the turbine 22.

[0049] Figure 1C further shows a device 30 for centering and guiding the rotation of the low pressure shaft 26, corresponding for example to the device 30E of Figure 1B, or to any other centering and guiding device described with reference to this figure.

[0050] The device 30 generally comprises a rolling bearing 32, and a bearing support 34 rigidly connected to the exhaust casing 29.

[0051] The rolling bearing 32 comprises an inner ring 36, an outer ring 38, and an annular row of rolling elements 40, for example rollers or balls, interposed between the inner ring 36 and the outer ring 38.

[0052] The outer ring 38 is for example carried by an elastically deformable openwork structure 31 or “squirrel cage” similar to the structure 216 of FIG. 1A, itself fixed to a flange 33 secured to the bearing support 34 and, more generally, secured to the exhaust casing 29.

[0053] An annular cavity called a damping cavity 52, intended to receive lubricating liquid to form a fluid film compression damper (SFD), is formed between an inner annular surface of the bearing support 34, and an outer annular surface of the outer ring 38.

[0054] Furthermore, the lubrication of the bearing 32 is ensured by a lubrication cannula 39 designed to bring lubricant from a radially external, and downstream, region relative to the bearing 32, and to project this lubricant upstream towards a downstream face of the bearing 32. This cannula extends for example through one of the openings defined by the squirrel cage 31.

[0055] The invention is generally applicable to any type of turbomachine, whether single-flow or multi-flow, single-body or multi-body. One of its particular features will now be described with reference to Figures 2A to 4.

[0056] The invention relates more specifically to a device for centering and guiding the rotation of a shaft within such a turbomachine, of the SFD bearing type.

[0057] Figure 2A illustrates such a device 30. The latter comprises in particular the rolling bearing 32, and the bearing support 34.

[0058] The rolling bearing 32 comprises an inner ring (not shown) of the type of that of FIG. 1C, an outer ring 38, and an annular row of rolling elements 40 interposed between an outer annular surface of the inner ring, and an inner annular surface 44 of the outer ring 38. The rolling elements 40 are typically associated with an annular cage, in a well-known manner.

[0059] The outer ring 38 is typically intended to be carried by an elastically deformable openwork structure such as the structure 31 of FIG. 1C, in a “squirrel cage”. In cases where the rolling elements 40 are rollers, the internal annular surface 44 of the outer ring 38 has a cylindrical shape of revolution along an axis defined as axis 46 of the bearing 32, and which preferably coincides with the axis 28 of the turbomachine.

[0060] Furthermore, the outer ring 38 has an external annular surface 48. The latter is, in this case, defined by the annular hoop 34B.

[0061] In addition, the bearing support 34 has an internal annular surface 50 surrounding the external annular surface 48 of the outer ring 38. An annular cavity called a damping cavity 52, intended to receive lubricant to form a damping film or “squeeze film”, is formed between the internal annular surface 50 of the bearing support 34, and the external annular surface 48 of the outer ring of the bearing.

[0062] This cavity 52 is defined axially between two annular sealing gaskets 54A, 54B mounted in corresponding annular grooves, formed on the surface 48 so as to each be in contact over 360 degrees with the surface 50.

[0063] These seals 54A, 54B are configured to axially close the annular damping cavity 52 in a sealed or substantially sealed manner, unlike seals commonly used in known squeeze film bearings, configured to provide at least one leakage section.

[0064] For this purpose, the seals 54A, 54B are for example overlapping split metal rings. As illustrated in FIG. 2B, such a seal, without notches, has two ends defined on either side of the slot, one of which 56A forms a tenon and the other of which 56B has a cutout of a shape substantially complementary to the tenon and formed on one side of the seal opposite the annular damping cavity 52, to receive the tenon with a small clearance in the circumferential direction. Typically this clearance is of the order of a few tenths of a millimeter to a few millimeters, so that such a seal does not have any fluid passage section opening directly into the annular damping cavity 52, which makes it possible to maximize the sealing with respect to the lubricant present in the annular damping cavity 52.These seals 54A, 54B are then considered as forming a seal, or quasi-seal with respect to the lubricant present in the annular damping cavity 52.

[0065] In the examples described below, the support 34 is formed of an outer annular body 34A, inside which is mounted a hoop 34B, which defines an inner annular surface 50 of the support 34. This feature makes it easier to manufacture the support 34, even if the latter can be produced in one piece, for example by means of an additive manufacturing technique. It is noted that such an assembly with a hoop can simultaneously and / or alternatively be provided by the outer ring 38 of the bearing, without departing from the scope of the invention. Furthermore, the device 30 comprises a circuit 60 for supplying the annular damping cavity 52. ​​This supply circuit 60 is intended to supply the damping cavity 52 with lubricant, in order to form a damping film therein. At least a portion of this supply circuit 60 passes through the bearing support 34.It comprises in particular an inlet pipe 62, equipped with a device 64 for controlling the passage of the lubricant through this inlet pipe 62. By "pipe", it is generally understood, in the present description, any channel or network of channels adapted to the circulation of a liquid. Downstream of the lubricant passage control device 64, the supply circuit comprises an annular plenum 66, into which one or more radial distribution passages 68 open, made through the hoop 34B. These passages open radially inwards into the damping cavity 52, opposite an annular distribution groove 70, which promotes the homogenization of the lubricant upon its arrival in the annular damping cavity 52. ​​The inlet pipe 62 of the circuit 60 can be supplied from any source available for this purpose in the turbomachine.Also, the device 30 comprises a circuit 72 for discharging lubricant outside the annular damping cavity 52. ​​Here too, at least a portion of this discharge circuit 72 passes through the bearing support 34. It comprises in particular an outlet pipe 74 defining a calibrated orifice 76 for lubricant leakage, this orifice 76 being arranged at the downstream end of the circuit 72, preferably opening onto a radially external surface of the bearing support 34. The discharge circuit 72 comprises, on the outlet pipe 74 and preferably upstream near the calibrated orifice 76, a lubricant retention valve 78 specific to the invention, and which will be described later. Upstream of the outlet pipe 74, the evacuation circuit 72 comprises an annular plenum 80, into which one or more radial collection passages 82 open, made through the hoop 34B.These passages open radially inwards into the damping cavity 52.

[0066] The lubricant escaping through the calibrated orifice 76 reaches the lubricated bearing enclosure 86 in which the rolling bearing 32 is located.

[0067] The calibrated orifice 76 therefore comprises, in a known manner, a fluid passage section determined as a function of the desired flow rate and pressure for the lubricant ejected through this orifice 76, and to ensure an appropriate liquid pressure within the annular damping cavity 52, as a function of the desired damping level. The calibrated orifice 76 preferably constitutes the only lubricant outlet of the discharge circuit 72, while the inlet pipe 62 preferably constitutes the only lubricant inlet of the supply circuit 60. In other words, the damping film 52 is supplied with lubricant by a single inlet pipe 62 equipped with the lubricant passage control device 64, while the lubricant of this film is extracted from the device 30 by a single outlet pipe 74 equipped with the lubricant retention valve 78.

[0068] The lubricant passage control device 64, as exemplified in FIGS. 3A to 3C, comprises a controlled member 88 for closing the inlet pipe 62, preferably at its downstream end, just before the plenum 66. In this first preferred embodiment of the invention, the control device 64 is a non-return valve. Its movable element thus forms the controlled member 88 for closing the inlet pipe 62. The member 88 is controlled by the pressure of the lubricant which is applied to it, when this lubricant circulates through the supply pipe 62. In this regard, it is noted that elastic return means, such as a spring 90 of the non-return valve 64, exert a first force F1 on the controlled movable member 88, just as the lubricant circulating through the inlet pipe 62 applies to this member 88 a second force F2, in the opposite direction to the first force F1.In a known manner, it is the difference in intensity between these two forces F1, F2 which allows the valve 64 to occupy an open position allowing the lubricant to circulate towards the damping cavity 52, or a closed position preventing such circulation of the lubricant towards the cavity 52, and therefore also preventing the lubricant from escaping outside the cavity 52, through this valve.

[0069] The forces F1 and F2 have been represented schematically by arrows in Figure 3C, in which the valve 64 is of the ball valve type. In the other similar examples, Figure 3A represents a swing valve, while Figure 3B represents a valve 64 of the guided valve type.

[0070] The non-return valve 64 is configured to occupy an open position, and to allow circulation of the lubricant through the inlet pipe, when the pressure of the lubricant which is exerted on the controlled closure member 88 is greater than or equal to a first reference pressure PI. The spring 90 of the valve is then dimensioned accordingly, to allow such opening of the closure member 88 at the first reference pressure PI, corresponding to the cracking pressure. The value of the reference pressure PI can be set at a value greater than or equal to the critical lubricant supply pressure, corresponding to the minimum pressure guaranteeing nominal operation of the damping film in the cavity 52.

[0071] Furthermore, the valve 64 is also configured to occupy a closed position, and prohibit the circulation of the lubricant through the inlet pipe 62, when the pressure of the lubricant in the supply circuit is lower than the first reference pressure PI. In other words, if the pressure of the lubricant in the inlet pipe 62 remains lower than the first reference pressure PI, the lubricant no longer circulates downstream through the closed valve 64, and the lubricant located in the damping cavity 52 cannot flow back upstream.

[0072] The check valve 78, which equips the outlet pipe 74, can for example take the form of that shown in FIG. 3D. It comprises a member 92 for closing the outlet pipe 74, close to the calibrated leak orifice 76, as well as an actuator 94 of the closing member 92. The actuator 94 is preferably of passive design, preferably being controlled by the pressure of lubricant circulating in the lubricant supply circuit 60. On the contrary, active design means a control requiring regulation by external elements, such as an electronic sensor, electrical control and regulation, etc.

[0073] To do this, the check valve 78 comprises elastic return means, such as a spring 96, which exerts a first force F'1 on the actuator 94. Furthermore, the piston-shaped actuator 94 delimits a pressure chamber 98 filled with lubricant, and communicating with the inlet pipe 62. For example, the end of the pressure chamber 98, located opposite the actuator 94 in the sliding direction of the piston, is directly connected to the inlet pipe 62. Thus, the lubricant present in the chamber 98 applies to the actuator 94 a second force F'2 in the opposite direction to the first force F'1.In a known manner, it is the difference in intensity between these two forces F'1, F'2 which allows the check valve 78 to occupy an open position allowing the lubricant to escape from the circuit through the orifice 76, or a closed position preventing such escape, thus maintaining the lubricant in the evacuation circuit 72 and in the damping cavity 52.

[0074] The forces F'1 and F'2 have been represented schematically by arrows in Figure 3D. It is noted that the check valve 78 can be of any design type. For example, the sliding movement of the actuator 94, applied by the resultant of the two forces F'1, F'2, can lead to a pivoting of the closure member 92 in the outlet pipe 74, thanks to an appropriate kinematic system. This member 92 therefore corresponds to a leaf of the check valve 78.

[0075] The lubricant retaining valve 78 is configured to occupy an open position, and to allow circulation of the lubricant through the outlet pipe 74 and its orifice 76, when the pressure of the lubricant in the supply circuit 60 is greater than or equal to a second reference pressure P2. The spring 96 of the valve 78 is then dimensioned accordingly, to allow such opening of the closure member 92 at the second reference pressure P2, corresponding to the cracking pressure. The value of the reference pressure P2 can for example be set to the nominal pressure value for supplying lubricant to the damping cavity 52. ​​In any event, the second reference pressure P2 is strictly greater than the first reference pressure P1.

[0076] Furthermore, the check valve 78 is also configured to occupy a closed position, and prohibit the circulation of the lubricant through the outlet pipe 74, when the pressure of the lubricant in the supply circuit is lower than the second reference pressure P2. In other words, if the pressure of the lubricant in the inlet pipe 62, and therefore also in the pressure chamber 98 with which it communicates, remains or becomes lower than the second reference pressure P2, the lubricant no longer circulates downstream through the closed valve 78. The lubricant thus remains maintained in the outlet pipe 74, and in the damping cavity 52.The operation of the device 30 will be described below, in particular with reference to the graph in FIG. 4, the lower curve of which shows the opening / closing position of the valve 64 as a function of the lubricant pressure in the supply circuit 60, and the upper curve of which shows the opening / closing position of the check valve 78, still as a function of this same pressure.

[0077] Under normal operating conditions, the lubricant pressure in the supply circuit 60, and therefore in its inlet pipe 62, is greater than the first reference pressure PI, and more preferably greater than or equal to the second reference pressure P2. If this pressure is between the values ​​PI and P2, the lubricant circulates through the valve 64 towards the damping cavity 52 and the discharge circuit 72, without being able to escape through the leakage orifice 76 due to the closed position of the check valve 78. This makes it possible to bring the damping film to a suitable operating pressure, despite the low lubricant pressure in the supply circuit 60.This also allows, in the case where the drop in supply pressure is due to a restriction in upstream flow and not a malfunction of the lubrication unit, to ensure quasi-nominal operation, by reducing the effective temporal flow of the calibrated orifice, by a succession of open / closed states. The closed position allows the pressure in the supply line to increase, while the open position allows the calories to be evacuated when the pressure becomes sufficient.

[0078] If the lubricant pressure in the supply circuit 60 reaches or exceeds the value of the second reference pressure P2, the damping film then adopts an optimum operating pressure. The lubricant circulating in the damping cavity 52 can then escape through the leakage orifice 76, passing through the valve 78 which has opened. One of the particularities of the invention lies in the fact that when the lubricant pressure in the supply circuit 60 falls below the second reference pressure P2, indicating for example a failure of the lubricant supply, the check valve 78 which is located opposite the circuit, closes automatically. This has the effect of trapping the lubricant in the discharge circuit 72, and especially in the damping cavity 52 within which the damping film can continue to operate for a few moments, despite the failure of the lubricant supply.For example, it can last from several seconds to several tens of seconds, giving the driver enough time to turn off the engine.

[0079] If, during this failure period, the lubricant pressure in the inlet pipe 62 falls below the first reference pressure PI, the valve 64 closes, and it therefore advantageously contributes to maintaining the lubricant in the damping cavity 52. ​​This situation has been shown diagrammatically in FIG. 2C, showing the lubricant retained between the valve 78 and the valve 64, in order to temporarily maintain a functional damping film in the cavity 52.

[0080] Figure 5 shows another preferred embodiment of the invention, having many similarities with the previous one. In this embodiment, the pressure chamber 98 of the check valve 78 communicates with the inlet pipe 62, via a fluid communication conduit 100, preferably made partly through the support 34. As shown in Figure 5, an upstream end of this conduit 100 communicates with the pressure chamber 98 of the check valve 78, while a downstream end of this conduit 100 communicates with the inlet pipe 62, preferably close to and upstream of the valve 64.

[0081] Figure 6 shows yet another preferred embodiment of the invention, having many similarities with the previous ones. The modification here lies in the nature of the device for controlling the passage of lubricant through the inlet pipe 62, since instead of a valve, a lubricant passage valve 164 is implemented. This valve 164 is preferably of identical or similar design to that of the check valve 78, in particular with the presence of a shutter member 192 of the swing type in the downstream end of the inlet pipe 62.

[0082] The closure member 192 is controlled by an actuator 194, of the piston type, preferably of passive design, being preferably controlled by the pressure of lubricant circulating in the lubricant supply circuit 60.

[0083] To do this, the passage valve 164 comprises elastic return means, such as a spring 196, which exerts a first force F1 on the actuator 194. In addition, the piston-shaped actuator 194 delimits a pressure chamber 198 filled with lubricant, and communicating with the inlet pipe 62, via the conduit 100 to which this chamber 198 is connected. This connection is preferably made between the two opposite ends of the conduit 100, one of which is connected to the chamber 98 of the check valve 78, and the other of which is connected to the inlet pipe 62. The two pressure chambers 98, 198 are thus in communication with each other, via the fluid circulation pipe 100.

[0084] Thus, the lubricant present in the chamber 198, under a pressure corresponding to that of the lubricant in the supply circuit 60, applies to the actuator 194 a second force F2 in the opposite direction to the first force F1.

[0085] In a known manner, it is the difference in intensity between these two forces F1, F2 which allows the passage valve 164 to occupy an open position allowing the lubricant to circulate towards the damping cavity 52, or a closed position preventing such circulation of the lubricant towards the cavity 52.

[0086] The forces Fl and F2 have been represented schematically by arrows in Figure 6.

[0087] This embodiment allows the same operation of the device 30 as that described previously, in particular with regard to the case of a lubricant supply failure.

[0088] Of course, various modifications may be made by those skilled in the art to the invention which has just been described, solely by way of non-limiting examples and within the scope defined by the appended claims. In particular, the different embodiments and their alternatives may be combined.

Claims

CLAIMS 1. Device (30) for centering and guiding in rotation a shaft (24, 26) of a turbomachine, comprising: - a rolling bearing (32) comprising an outer ring (38) having an outer annular surface (48); - a bearing support (34) having an internal annular surface (50) surrounding the outer ring (38); - an annular damping cavity (52), formed between the inner annular surface (50) of the bearing support (34) and the outer annular surface (48) of the outer ring (38), and defined axially between two annular sealing joints (54A, 54B); - a circuit (60) for supplying the annular damping cavity (52), for supplying the latter with lubricant in order to form a damping film therein, at least part of the supply circuit (60) passing through the bearing support (34); - a circuit (72) for discharging lubricant outside the annular damping cavity (52), at least part of the discharge circuit (72) passing through the bearing support (34), and this discharge circuit (72) comprising an outlet pipe (74) defining a calibrated orifice (76) for lubricant leakage; characterized in that the device further comprises, on the outlet pipe (74), a valve (78) for retaining the lubricant, the retaining valve (78) comprising a member (92) for closing the outlet pipe, as well as an actuator (94) controlled as a function of a lubricant pressure in the supply circuit (60), in that the supply circuit (60) comprises an inlet pipe (62) equipped with a device (64, 164) for controlling the passage of the lubricant through this inlet pipe, the control device (64, 164) comprising a controlled member (88, 192) for closing the inlet pipe (62),in that the lubricant passage control device (64, 164) is configured to occupy an open position, and to allow circulation of the lubricant through the inlet pipe (62), when the pressure of the lubricant in the supply circuit is greater than or equal to a first reference pressure (PI), and also configured, to occupy a closed position, and prohibit the circulation of the lubricant through the inlet pipe (62), when the pressure of the lubricant in the supply circuit is lower than the first reference pressure (P1), and in that the lubricant retaining valve (78) is configured to occupy an open position, and allow circulation of the lubricant through the outlet pipe (74), when the pressure of the lubricant in the supply circuit (60) is greater than or equal to a second reference pressure (P2), and also configured to occupy a closed position, and prohibit the circulation of the lubricant through the outlet pipe (74), when the pressure of the lubricant in the supply circuit (60) is lower than the second reference pressure (P2), the latter being strictly higher than the first reference pressure (P1).

2. Device according to claim 1, characterized in that the actuator (94) of the check valve (78) is a passive actuator, preferably controlled by the lubricant pressure in the supply circuit (60).

3. Device according to claim 2, characterized in that the check valve (78) comprises elastic return means (96) exerting a first force (F'1) on the actuator (94), and in that this actuator delimits a pressure chamber (98) communicating with the supply circuit (60), so that the lubricant present in the chamber (98) applies to the actuator (94) a second force (F'2) in the opposite direction to the first force (F'1).

4. Device according to any one of the preceding claims, characterized in that the device for controlling the passage of the lubricant through this inlet pipe is a non-return valve (64), or a valve (164) for the passage of the lubricant, the passage valve (164) comprising a member (192) for closing the inlet pipe, as well as an actuator (194) controlled as a function of the lubricant pressure in the supply circuit (60).

5. Device according to claim 4, characterized in that the passage valve (164) comprises elastic return means (196) exerting a first force (F1) on the actuator (194) of this passage valve, and in that this actuator delimits a pressure chamber (198) of the passage valve communicating with the circuit supply (60), so that the lubricant present in this pressure chamber (198) of the passage valve (164) applies to the actuator (194) a second force (F2), in the opposite direction to the first force (F1).

6. Device according to claim 5 combined with claim 3, characterized in that the pressure chamber (198) of the passage valve (164) communicates with the pressure chamber (98) of the check valve (78), via a fluid communication conduit (100).

7. Device according to any one of the preceding claims, characterized in that the two annular sealing joints (54A, 54B) are overlapping split rings.

8. Turbomachine (10), in particular for aircraft, comprising a drive shaft (24, 26), as well as at least one device (30) for centering and guiding in rotation this shaft, according to any one of the preceding claims.

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