EP0470907B1 - Cam damper for the fan blades of a jet engine - Google Patents

Description

One of the problems to be solved in the design of turbomachines, such as turboblowers, is that of seeking to reduce or eliminate the vibrations to which the blades are subjected.

Various arrangements have already been proposed such as, for example, by FR-A-1 263 677, relating to the assembly of a rotary disc of a turbomachine and blades fixed to the periphery of the disc, in which, on the one hand, said periphery of the disc is shaped into a plurality of teeth, of which any two successive of them delimit between them a first space having a cross section shaped like at least one dovetail, on the other hand, each blade has a root having a shape also in a dovetail complementary to that of the cross section of said first space, as well as a rod, which connects said root to the blade proper, and two platforms which s 'extend transversely to said rod, one on one side, the other on the other side of the rod, and which separate the rod from the blade proper, however that a second space is delimited between the stem and the platform of a first blade e, the stem and the platform of a second blade adjacent to the first blade, and the top of the tooth separating the roots of said first and second blades, and that a flyweight is contained in said second space and is susceptible, under the effect of the centrifugal force generated during the rotation of the disc, to be supported on the platforms and / or on the rods of said first and second blades.

However, it is observed that the known solutions have, for the most part, generally an insufficient efficiency, in relation to a direct, undemultiplied effect of the flyweight (s).

The invention, taking up the general known arrangement, proposes to increase the efficiency thereof by multiplying the reaction forces both in magnitude, as regards their areas of application.

To this end, according to the invention, two rigid rockers are arranged in said second space, being interposed between the counterweight and the rods and platforms of the first and second blades, and are likely, under the effect of the centrifugal force to which the counterweight is subjected, to be in support, on the one hand, mutual one on the other, on the other hand, each on a platform of one of the blades, on a rod of one of the blades and on the counterweight, the bearing zones of a rocker on the platform and on the stem of a blade being distinct.

• la surface d'un basculeur, qui est en contact avec la masselotte, est profilée en une came, de manière que la distance entre la zone du contact mutuel entre les deux basculeurs et la masselotte soit variable avec le basculement des basculeurs ;
• un ressort est attelé à la masselotte et à chacun des basculeurs, de manière à réaliser le maintien de l'assemblage de ces éléments, tout en en permettant de légers déplacements relatifs ;
• le ressort est constitué par un anneau ouvert ayant deux extrémités qui sont en appui élastique sur des faces des deux basculeurs opposées à celles de l'appui mutuel desdits basculeurs ;
• la masselotte comporte une partie oblongue entourée par le ressort ;
• ladite partie oblongue est munie d'une gorge, qui reçoit partiellement le ressort ;
• chaque masselotte possède une face transversale d'extrémité qui est en appui sur une butée axiale solidaire du disque ;
• ladite butée axiale est constituée par la tête d'un boulon fixé sur le disque ;
• chaque masselotte et les deux basculeurs, qui y sont associés, sont contenus dans ledit deuxième espace sans être fixés ni au disque, ni aux aubes.

The following advantageous arrangements are also preferably adopted:

• the surface of a rocker, which is in contact with the counterweight, is profiled in a cam, so that the distance between the zone of mutual contact between the two rockers and the counterweight is variable with the rocking of the rockers;
• a spring is coupled to the counterweight and to each of the rockers, so as to maintain the assembly of these elements, while allowing slight relative displacements;
• the spring consists of an open ring having two ends which are in elastic support on the faces of the two rockers opposite to those of the mutual support of said rockers;
• the counterweight has an oblong part surrounded by the spring;
• said oblong part is provided with a groove, which partially receives the spring;
• each counterweight has a transverse end face which is supported on an axial stop integral with the disc;
• said axial stop consists of the head of a bolt fixed on the disc;
• each flyweight and the two rockers, which are associated therewith, are contained in said second space without being fixed either to the disc or to the blades.

The main advantage of the arrangements according to the invention resides in the reduction separately of the vibrations to which the rods and the platforms of the blades are subjected. In addition, the realization of the rockers in the form of cams reinforces the effort of dissipation of vibrational energy and thus also increases the overall effectiveness of the fight against vibrations.

The invention will be better understood, and secondary characteristics and their advantages will appear during the description of an embodiment given below by way of example.

It is understood that the description and the drawings are given for information only and are not limiting.

• la figure 1 est une coupe, sensiblement radiale, suivant I-I de la figure 3, d'une turbo-soufflante conforme à l'invention ;
• les figures 2 et 3 sont des sections, respectivement suivant II-II et III-III de la figure 1 ; et,
• la figure 4 est un grossissement d'une partie de la figure 3, montrant une particularité de la disposition représentée.

Reference will be made to the accompanying drawings, in which:

• Figure 1 is a section, substantially radial, along II of Figure 3, of a turbofan according to the invention;
• Figures 2 and 3 are sections, respectively along II-II and III-III of Figure 1; and,
• Figure 4 is a magnification of part of Figure 3 showing a feature of the arrangement shown.

The arrangement shown is that of a disc 1 of a turbo-fan, which is rotatably mounted around an axis 2 and whose periphery is formed by teeth 3, angularly regularly spaced and sparing, between any two successive between them a housing 4 shaped like a dovetail.

Blades 5 are each formed by a root 6, of complementary shape, in dovetail shape, that of a housing 4, by a rod 7 which surmounts the root 6, by the active profile 8 of the blade , placed in the extension of the rod 7, and by two platforms 9, which extend on either side of the rod 7, substantially perpendicular to the general axis 10 of the blade, and which constitute the separation limit of the active profile 8 from the rod 7.

Each blade 5 is mounted on the disk 1 by introducing its root 6 into a housing 4, the general axis 10 of this blade extending substantially radially relative to the axis of rotation 2 of the disk 1, and the platforms 9 extending substantially parallel to the vertices 3A of the teeth 3 of the disc 1, the ends of the platforms 9 of two successive teeth being adjacent. The faces 9A of the platforms 9 oriented towards the axis of rotation 2, the lateral faces 7A of the rods 7 and the apex 3A of a tooth together define a space 11.

This space 11 contains, on the one hand, a counterweight 12, which either rests by its lower face 12A on the apex 3A delimiting said space 11, or, under the effect of centrifugal force, is slightly detached from said apex 3A, on the other hand, two rockers 13, each having a generally triangular shape.

The two upper corners of each rocker 13 constitute two contact zones 14 and 15 with the face 9A of the platform 9 and with the lateral face 7A of a rod 7 of a blade, respectively.

The counterweight 12 comprises an oblong part 16, here prismatic with a trapezoidal section, which constitutes its upper part, which has an upper face 16A and in which a groove 17 is formed.

The face of the third angle of a rocker 13 is shaped as a cam 18 in contact, in the zone 18A with the upper face 16A of the oblong part 16 of the counterweight, and, in a zone 18B with the cam 18 of the second rocker 13. As can be seen from FIG. 4, the distance D18B of the area 18B relative to the upper face 16A of the oblong part 16 of the counterweight has a variable value, a function of the relative positions of the two rockers 13 mutually and relative to the rods 7 and to the platforms 9 of the blades, this being in relation to the shape of the cam 18. Thus, the more the area 18B has been moved away from the axis of rotation 2, the greater the distance D 18B, the greater is the multiplication of contact reactions in zones 18B and more important and more effective are the contact reactions in zones 14 and 15.

The counterweight 12 further comprises an end face 12B, transverse, perpendicular to the axis of rotation 2, which is in axial abutment on the face 19A of the head 19 of a fixing bolt 20, on the disc 1, of a flange 21. The periphery of the flange 21 has a cross section shaped like a U, one of which, 23, of the branches is supported on one, 22, of the axial ends of each dawn 5.

Finally, note that a spring 24, of open annular shape, having two ends 25, surrounds the oblong part 16 of the counterweight, being held in position relative to it by being introduced, partially in the groove 17. The ends 25 constitute hooks and are supported, each on a flange 26 which comprises the third angle of each rocker 13. The flanges 26 are arranged substantially on the faces of the triangular ends of the rockers 13, which are opposite to the faces 18B of their mutual contact. The spring 24 thus constitutes a means of maintaining the assembly of the two rockers 13 and the counterweight 12, which however allows very small relative displacements of these various elements. On this subject, it should be observed that the positions in solid lines and in broken lines of the rockers 13 shown in FIG. 4 have been deliberately exaggerated and are in reality much weaker than in this FIG. 4.

The embodiment shown allows the dissipation of vibrational energy by means of small frictions which occur between the faces in contact: 16A-18A; 9A-14; 7A-15; and, 18B-18B, and, between the ends 22 of the blades and the branch 23 of the flange 21.

• les zones d'appui de chaque basculeur 13, et, finalement, par l'intermédiaire des basculeurs, de la masselotte 12 sur les aubes 5 sont des zones distinctes : la zone 14 d'appui sur la face 9A de la plate-forme 9 est entièrement distincte de la zone 15 d'appui sur la face 7A de la tige 7, ce qui donne l'assurance d'une répartition satisfaisante des réactions sur les aubes, notamment sur les plates-formes et sur les tiges ;
• comme déjà noté précédemment, les valeurs de ces réactions sont en outre accrues par la démultiplication obtenue par la came 18 ;
• la multiplication des zones de frottement et l'augmentation des valeurs des réactions conduit en outre à l'obtention d'une bonne dissipation de l'énergie vibratoire ;
• l'ensemble de la masselotte 12-16 et des basculeurs 13 n'est fixé, ni au disque 1, ni aux aubes 5, mais est uniquement contenu dans l'espace 11, dans lequel il est maintenu par appui des faces 12A et 12B de la masselotte sur les faces supérieures 3A des dents 3 et axiales 19A des têtes des boulons 20, et par appui des basculeurs 13 sur les aubes 5 dans les zones 14 et 15.

The following points should be noted:

• the bearing zones of each rocker 13, and, finally, by means of the rockers, of the counterweight 12 on the blades 5 are separate zones: the zone 14 of bearing on the face 9A of the platform 9 is entirely separate from the support zone 15 on the face 7A of the rod 7, which gives the assurance of a satisfactory distribution of the reactions on the blades, in particular on the platforms and on the rods;
• as already noted previously, the values of these reactions are further increased by the reduction obtained by the cam 18;
• the multiplication of the friction zones and the increase in the values of the reactions also leads to obtaining good dissipation of the vibratory energy;
• the assembly of the counterweight 12-16 and of the rockers 13 is neither fixed to the disc 1 nor to the blades 5, but is only contained in the space 11, in which it is held by pressing the faces 12A and 12B the counterweight on the upper faces 3A of the teeth 3 and axial 19A of the heads of the bolts 20, and by pressing rockers 13 on the blades 5 in the zones 14 and 15.

The invention is not limited to the embodiment shown, but on the contrary covers all the variants which could be made to it without departing from its scope.

Claims (9)

1. Fan of a turboshaft engine comprising an assembly of a rotating disc (1) and of blades (5) fixed around the periphery of the disc, in which, on the one hand, the said periphery of the disc is formed with a plurality of teeth (3) of which any two successive ones define between themselves a first space having a transverse section shaped like at least one dovetail (4), on the other hand, each blade has a root (6) also having the shape of a dovetail complementing that of the transverse section of the said first space, as well as a stem (7) which connects the said root (6) to the blade proper (8), and two platforms (9) which extend transversally in relation to the said stem (7), one on one side, the other on the other side of the stem, and which separate the stem (7) from the blade proper (8), whilst a second space (11) is defined between the stem (7) and the platform (9) of a first blade, the stem (7) and the platform (9) of a second, blade, adjacent to the first blade, and the top 3A of the tooth (3) separating the roots (6) of the said first and second blades, and a bobweight (12) is contained in the said second space and is capable, under the effect of the centrifugal force generated by the rotation of the disc, of pressing against the platforms (9) and/or the stems (7) of the said first and second blades,
   characterised in that two rigid rockers (13) are placed in the said second space, being interposed between the bobweight (12-16) and the stems (7) and platforms (9) of the first and second blades and are capable, under the effect of the centrifugal force to which the bobweight is subjected, of pressing, on the one hand, mutually against each other (18B), on the other hand, each one against (14) a platform (9) of one of the blades, against (15) a stem of one of the blades and against (16A) the bobweight (16), the areas of pressure (14,15) of a rocker against the platform (9) and against the stem (7) being separate.
2. Fan of a turboshaft engine in accordance with Claim 1, characterised in that the surface of a rocker which is in contact with the bobweight (16-12), is profiled in the shape of a cam (18) so that the distance (D 18B) between the area (18B) of the said mutual contact between the two rockers (13) and the bobweight (16-12) may vary with the rocking of the rockers.
3. Fan of a turboshaft engine in accordance with either of Claims 1 and 2, characterised in that a spring (24) is coupled to the bobweight (16-12) and to each of the rockers (13), so as to maintain these elements as an assembly, whilst allowing them small relative movements.
4. Fan of a turboshaft engine in accordance with Claim 3, characterised in that the spring (24) is constituted by an open ring having two ends (25) which press elastically against the faces (26) of the two rockers (13) opposite those (18B) of mutual contact between the said rockers.
5. Fan of a turboshaft engine in accordance with Claim 4, characterised in that the bobweight comprises an oblong part (16) encircled by the spring (24).
6. Fan of a turboshaft engine in accordance with Claim 5, characterised in that the said oblong part (16) is fitted with a groove (17) which partially receives the spring (24).
7. Fan of a turboshaft engine in accordance with any one of Claims 1 to 6, characterised in that each bobweight (12) has a transverse end (12B) which presses against an axial stop (19A) fixed to the disc (1).
8. Fan of a turboshaft engine in accordance with Claim 7, characterised in that the said axial stop (19A) is constituted by the head (19) of a bolt (20) fixed to the disc (1).
9. Fan of a turboshaft engine in accordance with any one of Claims 1 to 8, characterised in that each bobweight (12-16) and the two rockers which are associated with it, are contained in the said second space (11) without being fixed either to the disc (1) or to the blades (5).

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