HOLLOW TREE INCLUDING A FOAM RING

Abstract

HOLLOW SHAFT COMPRISING A FOAM RING One aspect of the invention relates to a hollow shaft (1) of a low-pressure turbine with an X-axis, consisting of two parts (10, 11) connected together in a zone comprising a cavity (12) with at least one drainage hole (120, 121) on its periphery. It is characterized in that a foam ring (3) is placed in the cavity (12). This foam ring preferentially condenses the oil within its structure, thus preventing it from depositing on the surface of the shaft parts. It also dissipates the heat radiated by the nearby bearings, thereby reducing the risk of coking. Figure to be published with the abbreviation: Figure 3

Description

Title of the invention: HOLLOW SHAFT COMPRISING A FOAM RING TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of aeronautical engines and more particularly the rotor and the hollow shaft equipping said engines. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Engine rotors include turbines, and in particular low-pressure turbines which are subjected to high temperatures. When the engines are stopped, the oil circulating in the engine stagnates, particularly in hot areas which may be poorly or not ventilated. The oil can then harden by cooking, i.e. coke and damage certain elements such as the shaft of the low-pressure turbine.

[0003] This coking occurs on the rotor parts and in particular inside the low pressure shaft. The oil leaking from the bearing enclosures can penetrate inside the shaft through holes, provided for ventilation, and in particular for the pressure balance between the different cavities, creating a deposit of coked oil on the entire inner face of the rotor shaft. This oil deposit cannot be cleaned easily without risking damage to the parts (risk of chemical attack): the parts are most of the time thrown away.

[0004] This problem is particularly critical in a connection area between two parts of a shaft because this area includes a cavity where oil can accumulate.

[0005] Patent FR 2 696 655 discloses a device for separating oil from air in a rotating annular chamber. It is composed of balls and uses centrifugal force to separate the oil from the air, but this device does not prevent the oil from depositing on the walls or coking.

[0006] Patent FR 3 083 570 describes a centrifugal degasser to prevent the evacuated air from being loaded with oil. This degasser comprises a metal foam placed in the air flow but does not prevent the deposition of oil on the walls or its coking.

[0007] Patent FR 3 096 402 concerns the structure of the metal foam of a degasser in order to prevent the foam from clogging and to allow air to pass through. This structure does not prevent the deposition of oil on the walls or its coking.

[0008] Patent FR 3 111 164 describes a system for removing internal deposits in an exhaust tube of a turbojet. This system consists of a fixed cutting device comprising a leading edge running along the internal surface of the tube and which cuts the coked oil present on this surface. This system allows the removal of coked oil but does not prevent its formation. Summary of the invention

[0009] The invention provides a solution to the problems mentioned above, by preventing oil from being deposited on the surface of the shafts and by allowing heat to be dissipated, thus reducing the risk of coking.

[0010] The hollow shaft of a low-pressure turbine of axis X according to a first aspect of the invention consists of two parts connected together in an area comprising a cavity with at least one drainage hole on its periphery, it is characterized in that a foam ring is placed in the cavity. This foam ring will allow the oil to be preferentially condensed in its structure and thus prevent it from being deposited on the surface of the parts of the shaft. It also allows the heat radiated by the nearby bearings to be dissipated, thus reducing the risk of coking.

[0011] This also has the advantage of not requiring modification of the existing geometries of the shaft.

[0012] In operation, the oil will begin to condense in the foam and the excess oil will be centrifuged out through the drainage hole(s) provided on the rotor parts.

[0013] According to a first embodiment, the foam ring is made of metal. This metal could be aluminum, which allows a weight saving.

[0014] According to a second embodiment, the foam ring is made of synthetic fibers. A fibrous material offers a larger specific surface area. Some synthetic materials (e.g. polyester resin) have a high affinity with vaporized oil.

[0015] Advantageously, the foam ring has a shape complementary to the shape of the cavity. This allows the cavity to be completely filled and more oil to be absorbed.

[0016] Advantageously, the foam ring has a permeability greater than 50%. This allows existing ventilation circuits not to be disturbed. The porosity corresponds to the pressure drop experienced by the oil-laden air through the material.

[0017] Advantageously, the foam ring is surrounded by a rigid envelope. This envelope facilitates the positioning of the foam ring. Preferably, this envelope resists centrifugal forces without bending or crushing the foam.

[0018] Advantageously, the rigid envelope has rounded edges. The overall shape of the foam and / or the envelope with rounded edges fits the cavity more easily and allows for more convenient assembly.

[0019] A second aspect of the invention also relates to a low pressure turbine comprising a hollow shaft with at least one of the preceding characteristics.

[0020] A third aspect of the invention relates to a method of maintaining a low pressure turbine comprising a shaft having at least one of the pre-defined characteristics preceding, characterized in that it comprises a step of removing the foam ring and replacing it with a degreased or new ring. BRIEF DESCRIPTION OF THE FIGURES

[0021] The figures are presented as examples and in no way limit the invention.

[0022] [Fig. 1] is a section of a state-of-the-art hollow shaft with a deposit of coked oil;

[0023] [Fig.2] is a photograph of a portion of the state-of-the-art hollow shaft with coked oil;

[0024] [Fig.3] is a sectional view of a hollow shaft according to an example of the invention. DETAILED DESCRIPTION

[0025] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0026] The shaft 1 of the state of the art illustrated [Fig. 1] has an axis X, is hollow and is in two parts 10 and 11. A cavity 12 is located between the two parts 10 and 11. This cavity 12 comprises holes 120 and 121 arranged opposite each other and allowing the circulation of the oil.

[0027] This cavity 12 being located in a hot zone, coked oil 2 is deposited on its walls 122 as can be seen [Fig.2] in particular when the engine is stopped because the ventilation no longer works and can no longer sufficiently cool the shaft 1. The coked oil 2 hinders the lubrication of the parts which accelerates their wear. This is particularly critical on moving parts such as those of the rotor.

[0028] As visible [Fig.3], a foam ring 3 has been placed in the cavity 12. Here, this foam ring 3 has a shape complementary to the cavity 12, and it is in contact with the walls 122 and close to the bottom of said walls 122 in order to be able to absorb the oil which arrives through the holes 120 and 121 and from the inside of the hollow shaft 1. Thanks to its large specific surface area, this foam 30 will preferentially condense the oil in its structure and thus prevent it from being deposited on the surfaces 122 of the parts of the shaft 1. It also makes it possible to dissipate the heat radiated by the nearby bearings, and thus reduces the local risk of coking.

[0029] The foam 30 constituting the foam ring 3 has sufficient permeability so as not to disturb the existing ventilation circuits and to facilitate the cooling of the oil present in the foam 30.

[0030] The foam 30 of the ring 3 is contained in a rigid casing 31 to facilitate its positioning. The casing 31 is adapted to resist centrifugal forces without bending or crushing the foam 30 and allowing oil to enter.

[0031] The foam 30 of the ring and, possibly, the rigid envelope 31 have rounded edges so that they fit more easily into the cavity 12, under centrifugal force.

[0032] We will now describe the use of this foam ring 3 and how it allows easier and more economical maintenance of the hollow shaft 1 and the low pressure turbine which it equips.

[0033] The foam ring 3 will condense the oil arriving from inside the hollow shaft 1 and the holes 120 and 121, thus preventing it from accumulating on the walls 122 of the cavity 12 and from coking there when the heat is too high.

[0034] Thanks to its porosity, the foam 30 allows ventilation to be maintained in the area of ​​the cavity 12 and in the foam itself containing the oil, thus limiting the temperature in this area.

[0035] The excess oil in the foam ring 3 will be evacuated by centrifugation through the drainage holes 120 and 121 provided on the parts 10 and 11 of the hollow shaft 1.

[0036] At each maintenance stage, the oil-filled foam ring 3 can be replaced with a new one or degreased and replaced. It is understood that in this way it is no longer necessary to replace the rotor parts, which is more economical and faster.

Claims

Claims

1. Hollow shaft (1) of a low pressure turbine of axis X consisting of two parts (10, 11) connected together in an area comprising a cavity (12) with at least one drainage hole (120, 121) on its periphery characterized in that a foam ring (3) is placed in the cavity (12).

2. Hollow shaft (1) according to claim 1, characterized in that the foam ring (3) is made of metal.

3. Hollow shaft (1) according to claim 1, characterized in that the foam ring (3) is made of synthetic fibers.

4. Hollow shaft (1) according to one of the preceding claims, characterized in that the foam ring (3) has a shape complementary to the shape of the cavity (12).

5. Hollow shaft (1) according to one of the preceding claims, characterized in that the foam ring (3) has a permeability greater than 50%.

6. Hollow shaft (1) according to one of the preceding claims, characterized in that the foam ring (3) is surrounded by a rigid casing (31).

7. Hollow shaft (1) according to the preceding claim, characterized in that the rigid casing (31) has rounded edges.

8. Low pressure turbine comprising a hollow shaft (1) according to one of the preceding claims.

9. Method for maintaining a low pressure turbine according to the preceding claim, characterized in that it comprises a step of removing the foam ring (3) and replacing it with a degreased or new ring.

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