Device for damping vibration of a ring for axially retaining turbomachine fan blades

A device for damping vibration of a retention ring for axially retaining turbomachine fan blades, the blades being designed to be mounted via their roots on a rotary disk having an annular flange extending axially and provided with a plurality of radial crenellations for coming into contact with a plurality of complementary radial crenellations of a retention ring designed to be mounted around the disk flange, the device comprising an abutment element of elastomer material designed to be received axially between two adjacent crenellations of the flange and two adjacent complementary crenellations of the retention ring, and radially between the flange of the rotary disk and the retention ring, said abutment element presenting contact surfaces for coming into contact with the adjacent crenellations, with the retention ring, and with the flange of the rotary disk.

BACKGROUND OF THE INVENTION

The present invention relates to the general field of mounting fan blades on a rotary disk of a turbomachine. The invention relates more particularly to a device serving to damp the vibration to which the ring for axially retaining the fan blades is subjected.

The fan of a turbomachine typically comprises a plurality of blades mounted on a rotary disk via blade roots which are received in slots in the disk. In certain technologies for mounting fan blades, a ring is also placed around an annular flange extending axially from the upstream side of the rotary disk. Such a ring is held axially against the flange via crenellations formed around the entire circumference thereof. The ring is also mounted in axial abutment against the roots of the blades so as to retain said roots axially.

In practice, that type of fan blade mounting raises numerous problems. In particular, wear is observed on the axial retention ring and on the rotary disk. The wear is mainly caused by the vibration to which the axial retention ring is subject during rotation of the disk. In particular, rotation of the disk leads to small movements of the axial retention ring, causing wear on the tops of the crenellations of the annular flange for holding the ring on the disk. In addition, during rotation of the disk, the axial retention ring tends to move tangentially around the disk flange.

OBJECT AND SUMMARY OF THE INVENTION

A main object of the present invention is thus to mitigate such drawbacks by proposing a device for damping the vibration to which the ring for axially retaining fan blades is subject.

To this end, the invention provides a device for damping vibration of an axial retention ring for retaining fan blades of a turbomachine, said fan blades being designed to be mounted via their roots on a rotary disk including an annular flange extending axially and provided with a plurality of radial crenellations for coming into contact with a plurality of complementary radial crenellations of the retention ring that is to be mounted around said flange of the disk, said device being made up of an abutment element of elastomer material that is to be received axially between two adjacent crenellations of the flange and two adjacent complementary crenellations of the retention ring, and radially between the flange of the rotary disk and the retention ring, said abutment element presenting contact surfaces for coming into contact with said adjacent crenellations, with the retention ring, and with the flange of the rotary disk.

By adding contact surfaces with the axial retention ring and the disk flange, the device of the invention serves to modify the natural modes of vibration of the retention ring. In addition, since the device is constituted by an element made of elastomer material, its surfaces that come into contact with the retention ring and the disk flange tend, under the centrifugal effect, to become pressed against the retention ring and the flange. Thus, the vibration to which the retention ring is subject is damped and any risk of wear is avoided. The use of such a damper device can also serve to block the retention ring tangentially around the disk flange.

The abutment element of the damper device may be substantially in the form of a flat rectangular block. It may also have a geometrical shape for error-avoidance purposes while it is being mounted on the disk.

Preferably, the elastomer material of the abutment element presents hardness lying in the range 50 to 90 on the Shore scale. This elastomer material is preferably a silicone, a fluorosilicone, or a fluorocarbon.

The invention also provides a ring for axially retaining the fan blades of a turbomachine, the ring including at least one of the above-specified vibration damper devices.

The invention also provides a rotary disk for a turbomachine for mounting blades of a fan, the disk including an annular flange extending axially and provided with a plurality of radial crenellations for coming into contact with a plurality of complementary radial crenellations of a retention ring for axially retaining fan blades and designed to be mounted around the flange of the disk, the disk further comprising at least two damper devices as defined above. Finally, the invention provides a turbomachine including at least one rotary disk as defined above.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIGS. 1 and 2show a portion of a turbomachine fan disk10. The disk10is suitable for rotating about a longitudinal axis X-X of the turbomachine.

The rotary disk10includes a plurality of slots12that are regularly distributed around its outer circumference, each slot being designed to receive the root14of a fan blade16(only one blade is shown in part inFIG. 1). More precisely, the root14of each blade16is dovetail-shaped and is engaged axially in a corresponding one of the slots12that are provided for this purpose.

The rotary disk10also has an annular flange18extending axially upstream. At its end remote from the disk, the flange18is provided with a plurality of outer crenellations (or teeth)20which extend radially outwards relative to the disk and which are regularly distributed around the entire circumference of the disk.

It should be observed that the number of outer crenellations20on the flange18is identical to the number of slots12in the disk for receiving the fan blades16. Furthermore, the outer crenellations20are substantially in alignment (in the axial direction) with respective ones of the slots12.

At its end remote from the disk10, the flange18is also provided with an annular collar22extending radially inwards relative to the disk (i.e. towards its axis of rotation X-X). The collar22has orifices24distributed around its entire circumference. It is desired to receive an annulus26that is held thereagainst by means of screws28that are received in the orifices24. The function of such an annulus is to prevent the ring from moving tangentially and to perform other functions within the fan of the turbomachine (in particular to hold the inter-blade platforms).

A retention ring30for axially retaining the blades16is designed to be mounted around the flange18of the disk10. This retention ring30has a plurality of inner crenellations (or teeth)32extending radially inwards relative to the disk that are designed to come into contact axially with the outer crenellations20of the flange18when the ring is mounted around the flange. The number of flange crenellations is thus identical to the number of retention ring crenellations.

Furthermore, the retention ring30is provided with outer crenellations (or teeth)34that extend radially outwards relative to the disk and that are in radial alignment with the inner crenellations32of the ring. When the retention ring30is mounted on the flange, these outer crenellations34are designed to come into axial abutment against abutment elements36mounted to bear against each of the blade roots14.

As shown inFIGS. 3 and 4, the retention ring30is held axially against on the flange18of the disk by contact between its inner crenellations32and the outer crenellations20of the flange. By means of these outer crenellations34which are in axial abutment against the abutment elements36, the retention ring can thus hold the blade roots14axially in their respective slots12.

The retention ring30is mounted on the disk flange18as follows: the ring is centered on the longitudinal axis X-X of the turbomachine with its inner crenellations32offset axially from the outer crenellations20of the disk flange18. By being moved in axial translation, the ring is brought to surround the flange with each of its inner crenellations32being inserted between two adjacent outer crenellations20of the flange. Once mounted, the ring is then turned about the longitudinal axis X-X of the turbomachine so that its inner crenellations32come into axial contact with the outer crenellations20of the flange.

This type of assembly of the fan disk10presents certain drawbacks. Firstly, rotation of the disk10leads to small movements of the retention ring30that cause wear on the tops of the outer crenellations20of the disk flange18. In addition, during rotation of the disk, the retention ring30tends to pivot about the disk flange with a risk of the ring becoming disengaged.

In the invention, a device is provided for damping the vibration to which the retention ring30is subjected, thereby enabling those drawbacks to be eliminated.

Such a device comprises an abutment element38of elastomer material designed to be received firstly axially between two adjacent outer crenellations20of the flange18on the disk10and to complementary adjacent inner crenellations32of the retention ring30, and secondly radially between the flange18and the retention ring30.

Such an abutment element38, as shown inFIG. 5, is substantially in the form of a flat rectangular block and presents contact surface40that are designed to come into contact firstly with the adjacent crenellations20and32between which it is mounted, and secondly with an inside surface of the retention ring30and with the flange18of the rotary disk10.

By the effect of centrifugal force due to the disk10rotating, the contact surfaces40of the abutment element38made of elastomer material deform and press against the retention ring30and the disk flange18, closely matching the outlines thereof. This deformation of the contact surfaces40is represented inFIG. 6by arrows F1.

Adding contact surfaces between the abutment element38and the retention ring30and the flange18of the disk10serves to modify the natural modes of vibration of the retention ring. In addition, the contact surfaces40of the abutment element38deform and therefore damp the vibration to which the retention ring is subject. As a result, any risk of wear is avoided.

By deformation of its contact surfaces40, the abutment element38also serves to provide tangential blocking of the retention ring30about the flange18of the disk10, as represented by arrows F2inFIG. 6.

FIGS. 7A and 7Bshow various embodiments of the abutment element forming the vibration damper device.

In the example ofFIG. 7A, the abutment element38′ of elastomer material is substantially identical to that ofFIG. 5, but also has two grooves42extending longitudinally in its material. These grooves42serve to make it easier to extract the abutment element.

Compared with the embodiment ofFIG. 7A, the abutment element38″ ofFIG. 7Badditionally presents two flats44for coming into contact with the inside surface of the retention ring. The particular geometrical shape of this embodiment serves to provide an error-avoidance function to prevent the abutment element being wrongly mounted on the disk; i.e. with this shape the abutment element can be mounted on the disk one way around only.

The elastomer material of the abutment elements38,38′, and38″ may be a silicone (50D6/50D7, 50D8), a fluorosilicone, or a fluorocarbon, or any other material having equivalent properties.

The elastomer material of the abutment element38,38′, or38″ preferably presents hardness lying in the range 50 to 90 on the Shore scale.

The number and the angular disposition of the vibration damper devices mounted on the disk may vary. In the example ofFIGS. 1 and 2that show a 90° angular sector of the disk, there are provided three damper devices for seven blades, giving 12 devices for the entire disk which supports a total of 28 blades.

It is nevertheless possible to mount a larger or smaller number of damper devices on the disk. The minimum number is two and the maximum number corresponds to the number of available locations on the disk (i.e. the number of blades supported by the disk). When the number of damper devices is less than the number of blades, these devices need not necessarily be distributed in equidistant manner.