Device for axial retention of mobile vanes mounted on a rotor disc

A device for axial retention of mobile vanes mounted on a rotor disc includes two open rings, superimposed. At least one of the rings includes a rotating stop mechanism configured to cooperate with at least one hook of the disc. The two open rings are mounted in a discontinuous groove formed in the hooks, at the end of teeth situated on the periphery of the rotor disc, such that the rotating stop mechanism of the first ring is placed in the opening of the second ring. The significance of contact surfaces between the two rings allows a damping of vibrations during operation.

The present invention relates to the field of the axial retention of the mobile vanes mounted on a rotor of a turbomachine such as an airplane turbojet engine or turbo-prop.

As described in documents FR 2 729 709, FR 2 694 046 and FR 2 603 333, it is known for a turbomachine rotor to be equipped with a disc, mobile vanes supported by the disc and at least one retaining ring to prevent displacement of the mobile vanes in the axial direction, the axial direction being defined by the axis of rotation of the turbomachine.

Document FR 2 729 709 describes a device for retaining turbomachine rotor vanes including a slit lock ring and equipped with at least one anti-rotation stop. The lock ring is housed in a circular groove formed by hooks of the vanes and disc.

This device has the drawback of requiring precise machining of the anti-rotation stops and the hooks situated at the end of the teeth of the disc. Moreover, in certain operating configurations of the turbomachines, a disengagement of the lock ring may occur under the effect of significant vibrations and/or thermal and dynamic stresses and lead to the deterioration of the device.

Document FR 2 694 046 proposes using a device for retaining the foot of the turbomachine rotor blades made up of two rings, one of which is a slotted flange, elastic, equipped with a plurality of protuberances for stopping rotation, and the other of which is a lock ring for maintaining the flange in its mounted position.

This device has the drawback of requiring protuberances either on the rings or on the rotor disc, these protuberances being difficult and costly to produce.

Document FR 2 603 333 proposes using a first segment to ensure the sealing between the upstream and downstream of a rotor disc and a second segment ensuring the retention of the vanes on that rotor disc.

This device has the drawback that no anti-rotation means is provided for the second segment, a free end of which can disengage from the groove of the disc, causing the complete disengagement of the ring and the possible deterioration of the device and/or of the rotor disc.

It is also known to use a device for retaining vanes as illustrated inFIG. 2.

In this figure, a rotor disc1includes a disc body2, a plurality of teeth3and slots4, alternatingly distributed on its circumference and extending in the axial direction. Each tooth3is provided with at least one hook5, protruding in the axial direction of the disc, which defines, on said tooth, an elementary groove opening radially inward. The foot7of a vane8is inserted into a slot4and blocked axially by a ring9, housed in a discontinuous groove6, formed by the succession of elementary grooves. The retaining ring9is provided with a slit30, separating the two free ends31,32of the ring. The slit30allows the closing of the ring9and the decrease of its outer diameter necessary for the placement of the ring9in the groove6. The two free ends31,32are equipped with stops36and37that cooperate with a stop-hook35to stop the rotation of the ring and guarantee the presence of the slit30under the stop-hook35in order to ensure that the free ends of the ring9are kept under said stop-hook35.

This device has the drawbacks of needing a precise machining of the stop-hook35and, in certain operating configurations of the turbomachine, under significant dynamic and thermal stresses, of causing the jamming of the stop-hook35between the stops36and37, and causing disengagement of the lock ring9from the groove6and the deterioration of the retaining device. The vibrations due to the different set points of the turbomachine can also cause significant wear of the retaining device and/or promote the disengagement of a free end of the ring outside the groove. When the play between the lateral support faces of the stops36,37and the lateral faces of the stop-hook35is small, mounting the ring can also be difficult.

The aim of the invention is to realize a device for axial retention of mobile turbomachine vanes not having the drawbacks of the known devices and making it possible to resolve the problem of disengagement during operation of the retaining device.

To do this, according to the invention, the device for axial retention of mobile vanes, designed to be inserted in a discontinuous groove of a turbomachine rotor disc, includes two rings, superimposed, each having an opening separating free ends of the ring, at least the first ring being provided with a rotation stop means provided to engage in the opening of the second ring, such that the two rings form a double ring. The use of two rings, which cooperate with each other, makes it possible to ensure the axial retention of the mobile vanes on the entire double ring in particular, at the opening of one of the rings. The superposition of the two rings makes it possible, due to the significance of the surfaces in contact, to damp the operating vibrations and thereby decrease the risks of disengagement of one of the rings from the groove.

Preferably, the two rings have a same width, same thickness and identical outer diameter, which facilitates the provision of steel and the storage.

Preferably, the rotation stop means protrudes outwardly, in a radial direction of the first ring.

Preferably, the rotation stop means of the first ring is a brace, formed by a tab, bent, folded down and fixed on a face of the first ring.

According to a first variant of the rotation stop means, the brace is machined in an oversize of the first ring.

According to a second variant of the rotation stop means, the brace includes an inter-tooth lug for stopping rotation protruding radially toward the outside of the first ring.

Alternatively, according to a third variant of the rotation stop means, the inter-tooth lug has a thickness equal to twice that of the rest of the ring.

Preferably, the brace and the opening of the first ring are spaced angularly by an angle greater than 150°. The brace and the opening are then approximately diametrically opposite one another relative to the axis of rotation of the rotor.

Alternatively, the second retaining ring also includes a rotating brace stop.

The invention also concerns a turbomachine rotor including at least one rotor disc whereof the body is equipped with a plurality of slots and teeth provided with at least one hook, protruding in the axial direction of the disc, which defines, on that tooth, an elementary groove opening radially inwardly, the foot of a vane being inserted into the slot and stopped in translation in the slot by at least one axial retaining device as defined above for mobile vanes, placed in a discontinuous groove, formed by the succession of said elementary grooves.

The invention also concerns a turbomachine including a rotor as defined above.

The references ofFIG. 2, already commented on and used in the following figures, correspond to elements similar to those of the prior art and will only be described briefly.

FIG. 1shows a diagrammatic cross-sectional view of an example of turbomachine compressor with axis X including, from upstream to downstream, in a direction of airflow through the turbomachine, a fan100, a low-pressure compressor101and a high-pressure compressor102. The high- and low-pressure parts of the compressor include at least one disc1mobile in rotation around the axis X. A plurality of vanes are mounted on the circumference of the disc.

FIG. 3shows an example of a device for retaining vanes according to the invention. This figure shows a portion of rotor disc1including a plurality of teeth3, alternating with slots4, regularly distributed on its circumference. The teeth3extend in the axial direction and include, protruding in the axial direction of the disc, at their ends, hooks5. The foot7of the vane8is engaged in a slot4.

A double ring10, mounted in a discontinuous groove6, defined by the hooks5of the disc1, allows the axial retention of the vanes8toward the upstream and/or downstream of the turbomachine. The double ring10includes two open rings11,12, superimposed, the first ring being equipped with a rotating brace stop13, extending outwardly in the radial direction of the rotor disc1.

The first ring11includes a first face in contact with the disc1and a second face in contact with the second ring12. The brace13is positioned on the face of the first ring11in contact with the second ring12. The second open ring12is mounted such that its opening15frames the brace13of the first ring.

The brace13of the first ring11has a width significantly smaller than the space separating two successive hooks5.

FIG. 4shows a cross-sectional view along line A-A ofFIG. 3, of the assembled double ring10, made up of the rings11and12superimposed and mounted in the groove6.

According to a first embodiment of the invention, the double ring10, shown in perspective inFIG. 5, is made up of a first ring11equipped with a rotating brace stop13and a second simple ring, without brace. In this case, the second ring12has no favored mounting direction.

The first and second rings11,12are preferably obtained in a metal sheet. The brace13protrudes on one hand on the face18of the first ring and on the other hand, in the radial direction, toward the outside of the circumference of the first ring11.

The opening14,15of each ring11,12is large enough to allow the easy superposition of the rings11,12one on the other and to eliminate jamming problems during operation and the disengagement of one of the rings11,12from the groove6.

The width of the opening15of the second ring12is larger than the width of the brace13of the first ring11. One easily understands fromFIG. 5that the significance of the surfaces, in planar contact, of the rings11,12makes it possible to ensure, by the friction created, a function of damping vibrations during operation.

The brace13and the opening14of the first ring11are angularly spaced by an angle α. The angle α is not a whole multiple of the angle β formed between two successive notches5of the disc1.

FIG. 6shows a double ring10, according to a second embodiment of the invention. According to this embodiment, each of the two rings11,12is equipped with a rotating brace stop13,16, respectively. The brace13of the first ring11is placed in the opening of the second ring12. The brace16of the second ring is placed in the opening14of the first ring11.

In the continuation of the description, each embodiment of the rotating stop means13of the first ring11may be applied to the rotating stop means16of the second ring12.

The presence of the brace16on the second ring12advantageously participates in the dynamic balancing of the double ring10through better distribution of the masses and participates in reducing stresses on the rotating stop braces13,16.

FIGS. 7 and 8show a first embodiment of a brace according to the invention. The brace13,16is obtained for example by punching in a metal sheet, so as to cause a tab17to appear. The tab17extends in the radial direction toward the outside of the ring11,12over a sufficient length to be bent, folded down and fixed, for example by brazing, on a face18of the ring and to thereby form a brace13,16.

FIGS. 9 and 10illustrate first and second variants of the brace13,16according to the invention. The brace13,16includes a tab17and an inter-tooth lug21,22that can advantageously be obtained during a cutting operation of the sheet, for example by punching. The tab17and the inter-tooth lug21,22extend in the radial direction protruding toward the outside of the ring11,12. The width of the inter-tooth rotating stop lug21,22is smaller than the space separating two lateral faces25facing two successive teeth5of the rotor disc1receiving the mobile vanes8. The inter-tooth lug ensures the rotational stop of the double ring while allowing a rotation of small amplitude of the first ring11, for example less than 3°.

The thickness of the inter-tooth lug22being equal to twice that of the rest of the ring11,12, the rotational stop stresses of the double ring and the risks of flaws in the braze24are decreased.

FIG. 11illustrates a third variant of a brace20. The brace20is machined in one piece (not shown) including an oversize and fixed on the ring11before the opening14is formed. This piece is fixed, preferably by welding. Such an operating method makes it possible to obtain the majority of the ring thus defined from sheet metal having a small thickness.

These embodiments of the double ring10and the variant embodiments of the brace make it possible to obtain ring openings14,15with dimensions larger than those of the prior art, and to ensure axial retention of the mobile vanes8, continuous over the entire periphery of the disc.

The slot30, known from the prior art (seeFIG. 2), with a width in the vicinity of 1 mm, necessary to mount the ring9in the groove6of the disc1, to allow closing of the ring9, is replaced in the present invention by an opening14,15with a larger width, for example 5 mm, allowing closing and a more significant decrease in the outer diameter of the ring11,12, thereby facilitating the successive placement of each ring11,12in the groove6. This easier assembly is a first advantage in relation to the known solutions of the prior art.

Another advantage of the invention is obtained by the fact that it is no longer necessary to master generally small assembly and operating play, between the support faces of the brace13,16and the lateral faces of the hooks5cooperating in the rotating stop of the axial retaining device, unlike the solutions known from the prior art. The production tolerances of the brace13,16and the width tolerances of the opening of each ring11,12, for example in the vicinity of +/−0.5 mm, are greater than the production tolerances of the solutions of the prior art.

The angular sector of the double ring10, corresponding to the opening of one of the rings11,12, also ensures the function of axial maintenance of a vane8, the openings never being facing each other on the two rings11,12. The axial retention efforts of the vanes8cannot, regardless of the phases or operating temperature variations of the turbomachine, cause the free ends of one of the rings11,12to disengage outside the slot6.

Moreover, the brace13of the first ring11cooperates with the lateral faces of the non-machined hooks5of the disc1, to ensure the rotating stop of the double ring10while allowing a rotation of small amplitude, for example less than 3°, so as to maintain a position of the opening of the first11and second ring12between two feet of successive mobile vanes8.

Another advantage of the invention is obtained with the possibility of dividing the closing efforts of the rings11,12in half during their placement in the slot relative to a single ring with the same axial retention capacity as the double ring10presented above. Each ring11,12is successively inserted in the groove formed by the hooks5at the end of the teeth3.