EP0174892B1 - Bypass valve for a compressor - Google Patents

Description

The invention relates to a turbomachine comprising a compressor fitted with a discharge device comprising a ring forming a valve movable axially under the action of one or more jacks the body of which is carried by a flange of the compressor casing between a first position where the ring closes an opening made in the wall of the compressor duct and a second position where it releases said opening allowing the deflection of part of the gas flow. Such devices are known from patent FR-A-2 349 740 opposite which was established the preamble of the main claim of the present application.

In a gas turbine engine, it is known to associate with the compressor valves, arranged in line with one or more stages, intended to divert towards the outside a part of the air flow when the compressor is brought to operate. outside the range for which it was designed, at partial load for example. This avoids the appearance of the so-called pumping phenomenon due to the separation of the fluid threads along the blades, causing instability of the flow.

The usual discharge means comprise several pivoting hatches distributed around the periphery of the casing and controlled synchronously. These hatches must offer a large passage section, be able to open and close quickly, and have a good seal in the closed position so as not to affect the performance of the engine. To fulfill these conditions, we are led to produce heavy, complicated devices and of considerable size. In addition, the opening of these hatches creates in the veins of the wakes, heterogeneities likely to disturb the operation of the downstream compressor. One solution has been to produce axial displacement devices comprising a ring-shaped valve mounted around the casing and whose axial sliding, possibly combined with a rotation, releases a slot formed around the periphery of the wall of the vein. It is thus possible to control a large air flow over a relatively short stroke of the ring whose size is reduced; we finally have a better distribution of efforts for a simpler implementation. Such a ring, being of large diameter, is actuated by a plurality of jacks distributed around its periphery, as indicated in the aforementioned patent FR-A-2,349,740. Similarly, patent FR-A-2 068 282 provides for the axial displacement of such a ring by jacks supported by a radial flange of the compressor housing. This teaching has been incorporated into the preamble to the main claim of the present application. Usually, the ring is supported and guides in its movement by means of pads, rollers cooperating with rolling sliding surfaces such as rails or slides. US-A-3,588,268, for example, shows a guiding device in which pads distributed regularly over the radially inner face of the ring are slidably mounted on longitudinal ribs attached to the outer wall of the casing. Patent DE-A-2 060 509 also shows guide means where rails integral with the ring cooperate with rollers mounted on the casing.

Such means are not satisfactory because they are subject to wear, seizure due to fouling by particles coming to be inserted between the surfaces in relative sliding. The inevitable deformations for diameters of this magnitude also lead to jamming which can block the mechanism; finally, the ring is not maintained sufficiently because of the clearances necessary for proper operation, which promotes the appearance of vibrations.

The invention aims to remedy these drawbacks and proposes to support the ring by means of one or more elastically deformable bodies made up of at least one plate made of elastomeric material or equivalent comprised between two rigid plates to which it is linked by bonding, vulcanization or any other means. These two plates are themselves integral one of the ring, the other of the casing and arranged parallel to the direction of movement. Preferably this body consists of an alternating stack of elastomeric plates and rigid plates adhering to each other and parallel to the first two. The centering of the ring can be obtained by the combination of at least three peripherally distributed bodies whose plates are arranged radially.

This type of laminated body or block is already known per se, its design results from the property of elastomers or the like to oppose a high resistance to compression loads and to offer a lower resistance in shear. Thus by correctly choosing the dimensions of the various elements and their number, blocks are produced which transmit the loads applied perpendicularly to the plates practically without deformation and which are liable to be deformed by sliding rigid plates parallel to each other by opposing an elastic restoring force.

Thanks to the use of this type of block, the risks of seizure are eliminated, which makes the operation of the device safer, and maintenance is thereby reduced. Furthermore, this material being less sensitive to wear, the service life of the device is extended. Finally, thanks to the incompressibility in the transverse direction, precise guiding of the ring is carried out and the latter remains isolated from the vibrations generated in the casing.

It is possible to choose the characteristics so that the restoring force exerted by the deformable body, when the ring is moved from its closed position to the open position is sufficient to allow the automatic return of the ring towards its closed position in the event of failure of the actuation mechanism. This is a safety factor in an aircraft and avoids possible loss of thrust during the critical phases of the flight.

Additionally, if the blocks are preloaded for assembly, they ensure that the ring is locked in the closed position even if the actuation mechanism is released.

• La figure 1 représente en coupe longitudinale la partie du compresseur d'un turboréacteur à double flux au niveau du dispositif de décharge.
• La figure 2 est une vue partielle avec des parties arrachées suivant les flêches Il.11 de la figure 2; l'anneau est montré à moitié en position ouverte, à moitié en position fermée.

The explanations and figures given below by way of example will make it possible to understand how the invention can be implemented.

• FIG. 1 represents in longitudinal section the part of the compressor of a turbofan engine at the level of the discharge device.
• Figure 2 is a partial view with parts cut away according to arrows II.11 of Figure 2; the ring is shown half in the open position, half in the closed position.

Figure 1 is therefore an axial sectional view of part of the intermediate pressure compressor of a turbofan engine with high dilution ratio. The air from the low pressure compressor is divided into a primary flow and a secondary flow. The primary flow is compressed by the intermediate pressure compressor and the high pressure compressor arranged in series, then it passes through the combustion chamber and the successive stages of turbines before being ejected into the atmosphere. The secondary flow is ejected directly into the atmosphere and provides most of the thrust. In Figure 1 is shown in part, the vein 1 of the primary flow and the vein 2 of the secondary flow. The medium pressure compressor 3, the end of a movable fin 3 'of the top stage of which can be seen, and the end of a distributor fin 3 "is mechanically independent of the high pressure compressor (not shown) located downstream.

It may happen in certain engine operating phases, at start-up for example, that the compressor speeds are no longer adapted to each other and that the high pressure compressor cannot absorb the air supplied by the medium pressure compressor; to prevent the occurrence of the pumping phenomenon, part of the air is discharged downstream of the medium pressure rotor by opening a valve connecting the veins 1 and 2.

This valve is constituted by a ring 10 cooperating with an annular slot 4 formed in the external wall 5 of the vein 1. This slot has edges 41 and 42 parallel and perpendicular to the axis of the engine. In the embodiment shown it occupies a frusto-conical band between the fins 3 'and 3 ".

The ring 10 is axially movable in a space delimited on the one hand, by the wall 5 and the internal wall 7 of the vein 2, on the other hand, upstream, by a conical ferrule 53 connecting the wall 5, at the edge 41, to a radial flange 71 of the wall 7 and, downstream by a radial flange 72 connecting the walls 5 and 7. An internal ferrule 74 cylindrical connects the radial flanges 71 and 72; it includes cutouts, as sela appears in FIG. 1 for the passage of deflected air which crosses the wall 7 by exhaust grids 75 made up of sectors assembled peripherally in an annular cutout of the casing forming the wall 7. These sectors have vanes arranged in parallel rows and inclined so that the discharged air disturbs the flow in the secondary vein as little as possible.

The ring 10 is in the form of a gutter oriented along the axis of the engine. It consists of two skins 11 and 12 made of sheet metal or preferably of composite material, with a curved section, encased one inside the other so as to provide a cavity 13 between them. This cavity is filled with a filling material ensuring the stiffening of the ring, for example a resin loaded with hollow glass beads. The outer skin 11 has an inner wing 111 of cylindrical shape, the diameter of which corresponds to that of the outer surface formed on the wall 5 at the edge 42. This cylindrical wing 111 is extended by a frustoconical portion 112 whose geometry corresponds to the wall portion 5 missing by the slot 4 formed in this wall; to its largest diameter is connected a second frusto-conical portion 113 terminated by a second cylindrical wing 114 concentric with the first and of larger diameter. The second skin 12 also includes two wings 121 and 123 secured by any appropriate means, rivet, bonding, etc., etc. to the wings 111 and 114. The annular cavity 13 is thus delimited by the skin 11 and the part 122 of the skin 12 connecting the wings 121 and 123.

This ring 10 is movable in translation inside the ferrule 74 between a first position where the part 112 comes to close the slot 4 and a recessed position releasing the latter. In this first position, the sealing of the vein 1 is ensured by two beads. A bead 15 mounted on the inner face of the ring bears on a radial flange 51 of the wall 5. On the other hand, a bead 52 housed in the angle formed by the ferrule 53 and the wall 5 serves as a support at the front end of the ring. This is driven by several axial cylinders 6, with screws, synchronized, distributed regularly around the periphery. There are at least three cylinders, preferably six. The body 61 of each cylinder is subject to the radial flange 72, the latter has openings allowing the passage of two cylinder rods 62, one end of which is fixed to a guide 63 sliding in a lateral slide of the body 61 and the other end is connected to the ring 10.

According to the invention, the ring 10 is supported in the casing by means of elastically deformable bodies 8, also providing guidance during its movement from the open position to the closed position. Each body consists of two blocks 81, 82 formed of alternating layers parallel to the axis of the ring of plates of elastomeric material 83 and rigid plates 84, metallic for example, vulcanized together or linked by any other means. These laminated blocks are of rectangular shape and are assembled by their metal end plate 85 so as to constitute a V-shaped body whose opening is directed upstream. The plates 85 of the top of the body are fixed by a pin 86 to a yoke 66 integral with the body of the jack 61. Each end of the branches of the V comprises two metal plates 87, welded together, the downstream end of which flares out to form a yoke 88 which agrees with that of the end of the arms 62, of the jack 6. These plates 87 also include lugs by which they are fixed by gluing or riveting or any other means to the wings of the ring. During assembly, the blocks are prestressed so that, already in the closed position, shown on the upper rise in FIG. 2, a restoring force on the ring is exerted.

The operation of the device is as follows.

In the closed position, the rods of the cylinders are pushed back feels the ring upstream in abutment on the annular seals 15 5 and 52.

When the opening of the discharge device is ordered, the six jacks are actuated simultaneously. The rods of the cylinders move downstream, causing the ring to slide and the opening of the annular slot through which the compressor discharges. The ring is guided by laminated blocks which gradually deform; referring to the lower half of Figure 2 we see the two forms taken by these blocks.

The elasticity of these blocks is maximum in a direction parallel to the plane of the plates constituting it, but it is minimal in a direction perpendicular to these planes. The centering of the ring is ensured by the combination of the six bodies 8, the plates of which are arranged radially.

To guarantee the integrity of the laminated blocks and reduce the risks of detachment of the plates between them, it is necessary to avoid making them undergo efforts in extension transversely to the plates; the V-shaped arrangement allows them to work essentially in compression while allowing a significant stroke of the ring. This stroke corresponds to the symmetrical reversal of the branches of the V as shown in Figure 2.

Furthermore, during assembly, these blocks are prestressed so that already in closing function, the ring is subjected to a pressing force against the seals. This avoids vibrations and any untimely opening in the event of the cylinders being released. In the event of failure of the control while the ring is in the open position, the restoring force is sufficient to cause the ring to close on its own.

Claims (8)

1. Turbo-machine having a compressor provided with a blow-off arrangement comprising a ring (10) forming a valve movable axially, under the action of one or more actuators (6) of which the body is supported by a flange (72) of the compressor casing, between a first position where the ring seals an opening (4) provided in the wall of the compressor flow path and a second position where it uncovers the opening to permit the deflection of a part of the gas flow, characterised in that the ring (10) is supported by the casing with the aid of one or more resiliently deformable bodies (8) associated with said actuator(s) (6) and constituted by at least one plate (83) of an elastomeric material included between two rigid plates (85, 87) to which it is adhered by glueing, vulcanisation or any other means, one of said rigid plates being rigidly secured to the ring (10) and the other to the compressor casing, said plates being arranged parallel to the axial direction of movement of the ring.

2. Turbo-machine according to claim 1, characterised in that the resiliently deformable body (8) comprises a stack of elastomeric plates (83) alternating with rigid plates (84), adjacent plates adhering to each other.

3. Turbo-machine according to one of the preceding claims, characterised in that the resiliently deformable body (8) is V-shaped and arranged so as to exert a return force sufficient to restore the ring (10) to the first position from the second position.

4. Turbo-machine according to the preceding claim, characterised in that the body is prestressed on assembly so as to exert a locking force when the ring is in the first position.

5. Turbo-machine according to any one of the preceding claims, characterised in that the ring (10) is supported by at least three resiliently deformable bodies (8) of which the plates (83, 84, 85, 87) are radially oriented.

6. Turbo-machine according to any one of the preceding claims, characterised in that the actuator (6) comprises two slidable operating rods (62), the body (8) being mounted between the said rods (62) on both sides of fixing means (66) to the body of the actuator (6) which is rigid with the casing.

7. Turbo-machine according to the preceding claim, characterised in thatthe body (8) is of V-shape and is fixed to the actuator by a median plate (85) and to the ring by the ends (87) of the branches of the V.

8. Turbo-machine according to any one of the preceding claims, characterised in that the ring (10) is of channel shape and the body (8) is housed between the limbs of the channel.

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