Abstract:
A device for locking a root of a rotor blade in a groove in a rotor disk of a turbomachine including: a circular ring sector configured to be mounted, transversely to the axis of the turbomachine, in a groove in the rotor disk; at least one locking wedge, which is rigidly secured and perpendicular to the ring sector, and extends parallel to the axis of the ring sector so as to hold the root of the blade radially in the groove; and at least one locking tooth extending from the ring sector radially with respect to the axis of the ring sector, so as to prevent the root of the blade from moving axially in the groove.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to the field of turboengine rotors and more specifically to the retention of rotor blades on a rotor disk. 
     2. Description of the Related Art 
     A turboreactor having a front fan and turn spool, for example, conventionally comprises, in sequence in a downstream direction, a fan, a low-pressure compressor stage, a high-pressure compressor stage, a combustion chamber, a high-pressure turbine stage and a low-pressure turbine stage. 
     In the present application, the terms “upstream” and “downstream” are, by convention, defined relative to the direction of circulation of air in the turboreactor. In the same manner, in the present application, the terms “inner” and “outer” are, by convention, defined radially relative to the axis of the engine. Thus, a cylinder which extends along the axis of the engine comprises an inner face which is directed toward the axis of the engine and an outer surface opposite the inner surface thereof. 
     In conventional manner, with reference to  FIG. 1 , a low-pressure turbine stage comprises, for example, successive rotor disks  1  which each comprise axial or oblique grooves  11  in which blades  2  are engaged by means of the roots  3  thereof, the blades  2  extending radially outward relative to the axis X of the engine. 
     The blades  2  are radially retained in the grooves by means of the fir-tree-like roots  3  thereof which further allows a space to be created between the root  3  and the base of the groove in order to allow a circulation of air which is guided in the body of the blades in order to ventilate them. The blades  2  are retained in an axially upstream direction by means of a sealing ring  4  which comprises sealing plates, the sealing ring  4  being known to the person skilled in the art as a “labyrinth ring”. 
     In order to retain the blades  2  in an axially downstream position, a circumferential ring sector  5  is mounted between a recess  6  of the rotor disk  1  and a downstream hook  7  of the root  3  of the blade  2 . In this manner, in the position for use, the ring sector  5  blocks the axial movement of the blade  2  in a downstream direction, the blade  2  remaining fixedly joined to the rotor disk  1 . 
     Currently, the roots  3  of the blades  2  are of metal material. In order to reduce the mass of the engine, it is proposed that the roots  3  be formed of composite material. The current method for fixing a metal root cannot be transferred to the fixing of a root made of composite material. This is because a conventional composite material does not allow concave zones to be formed simply in the blade root. Thus, it is difficult to form a downstream hook in the blade root in order to ensure the downstream axial retention of the blade by a ring sector. Furthermore, the production of a fir-tree-like blade root from composite material is not preferred. This is because during the operation of the engine, differential expansions appear and the teeth of the fir-tree-like root are no longer in abutment in the groove of the rotor disk. The radial retention of the blade is not satisfactory. 
     BRIEF SUMMARY OF THE INVENTION 
     In order to eliminate at least some of these disadvantages, the invention relates to a device for securing a root of a rotor blade in a groove of a rotor disk of a turboengine, comprising:
         a circular ring sector which is intended to be mounted, transversely relative to the axis of the turboengine, in a recess of the rotor disk;   at least one blocking wedge, which is fixedly joined and orthogonal relative to the ring sector and which extends parallel to the axis of the ring sector in order to radially support the root of the blade in the groove; and   at least one blocking tooth which extends from the ring sector radially relative to the axis of the ring sector in order to block the axial movement of the blade root in the groove.       

     Owing to the device, it is advantageously possible to secure the dovetail root of a rotor blade which does not comprise an axial blocking hook, in particular, a blade of composite material. Furthermore, this simple assembly device allows a blade to be secured radially and axially with a rotor disk according to the prior art. 
     Such a one-piece device ensures correct positioning of each tooth and each wedge which is intended to secure the blade root. Furthermore, the device can be rapidly fitted into the rotor since each device may comprise a plurality of teeth and a plurality of blocking wedges. 
     Preferably, the device comprises ventilation means which are formed in the ring sector and which are arranged to allow discharge of a flow of air which circulates between the base of the groove and the blocking wedge. The blocking wedge allows a ventilation space to be formed between the blade root and the base of the groove in which space a flow of air which is discharged by the ventilation means flows. 
     More preferably, the ventilation means are aligned with the direction in which the blocking tooth extends. In this manner, the flow of ventilation air cools the blocking wedge, the blade root and the base of the groove which are aligned axially with the blocking tooth. 
     According to one embodiment of the invention, the ventilation means are in the form of at least one ventilation hole. A hole is simple to machine in the ring sector and allows the discharge of the flow of ventilation air. 
     According to another embodiment of the invention, the ventilation means are in the form of at least one ventilation notch which is formed in the portion of the ring sector which is intended to be inserted in the recess of the rotor disk. 
     A ventilation notch allows the mass of the device to be reduced, whilst allowing the flow of air to be discharged. Preferably, the ring sector comprises a notched inner edge. 
     According to one aspect of the invention, the ring sector comprises an inner radial portion which is intended to be mounted in the recess of the rotor disk, and an outer radial portion from which the blocking tooth extends, which portions are axially offset relative to each other along the axis of the ring. 
     Advantageously, this offset allows the securing device to be positioned in a precise manner without creating any significant overhang of the blocking wedge relative to its fixing in the recess. Tilting of the securing device is therefore limited. 
     The invention also relates to a rotor of a turboengine which comprises a rotor disk, at least one rotor blade and at least one securing device as set out above, the rotor disk comprising a groove in which a blade root is accommodated and a recess in which the securing device is mounted, the blocking wedge of the securing device extending between the root of the blade and the base of the groove. 
     Preferably, since the rotor disk extends axially in a downstream direction, the recess is formed at the downstream end of the rotor disk in order to block an axial downstream movement of the blade in the groove. 
     According to one aspect of the invention, the root of the rotor blade comprises a casing of composite material. 
     The blade root of composite material, preferably with a ceramic matrix, is simple to produce and allows a rotor to be formed which includes all the advantages of a rotor according to the prior art with metal blades. 
     According to another aspect of the invention, the root of the rotor blade is of dovetail form. Owing to the securing device according to the invention, the blade may be radially blocked which prevents any error in the positioning of the blade in its housing when the rotor is in the stopped state. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention will be better understood with reference to the appended drawings, in which: 
         FIG. 1  is a radial section of a rotor disk of a turboengine in which rotor disk a rotor blade according to the prior art is mounted; 
         FIG. 2  is a perspective view of a first embodiment of a securing device according to the invention; 
         FIG. 3  is a perspective view of a rotor according to the invention comprising a securing device in accordance with  FIG. 2 , the securing device axially securing a single rotor blade which is mounted in the rotor disk; 
         FIG. 4  is a radial section of the rotor of  FIG. 3  along the axis A-A; 
         FIG. 5  is a perspective view of a second embodiment of a securing device according to the invention; and 
         FIG. 6  is a perspective view of a third embodiment of a securing device according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will now be set out for a rotor of a turboengine which forms a low-pressure turbine stage. The rotor comprises a low-pressure turbine rotor disk  1  which extends axially along an axis X as illustrated in  FIG. 3 , in which there are formed axial or oblique grooves  11  in which blades  2  are engaged via the roots  3  thereof, the blades  2  extending radially outward relative to the axis X of the engine. The rotor disk  1  comprises an annular recess  6  which extends radially inward and which is formed downstream of the groove  11  of the rotor disk  1 . The invention is described in this instance for downstream blocking but it is self-evident that it can be used in a similar manner for axial upstream blocking. 
     The rotor further comprises a device  8  for securing a root  3  of a rotor blade  2  in a groove  11  of the rotor disk  1  which device will now be set out with reference to  FIGS. 2 to 6 . The securing device  8  preferably comprises the same number of blocking wedges  82  as teeth  83 . Preferably, each blade  2  of the rotor disk  1  is blocked by a wedge  82  and a blocking tooth  83 . 
     The number of wedges  82  is equal to the numbers of blades  2  to be blocked. In this example, the rotor disk  1  comprises  98  grooves  11  in order to receive the same number of blades  2 . In this example, in order to secure the blades  2  in the grooves  11 , there are  11  securing devices  8  provided, of which  10  comprise nine wedges  82  and of which one comprises eight wedges  82 , each device  8  comprising the same number of wedges  82  as blocking teeth  83 . 
     It is self-evident that the number of wedges  82  per device  8  may vary in accordance with the number of blades of the rotor disk  1  or the number of devices  8  used to block the blades  2  of a rotor disk  1 . 
     With reference to  FIG. 2 , the securing device  8  generally comprises a circular ring sector  81 , at least one blocking wedge  82  and at least one blocking tooth  83  in order to axially secure the root  3  of a rotor blade  3  which is arranged in a groove  11  of the rotor disk  1  whilst allowing the ventilation of the groove  11 . 
     More precisely, the circular ring sector  81  is intended to be mounted transversely relative to the axis of the turboengine, in a recess  6  of the rotor disk  1 . By definition, a circular ring sector is defined relative to an axis which is referred to below as the ring axis S which is orientated in a forward direction in  FIG. 2  and which defines the axial direction. Below, the terms “front” and “rear” are defined relative to the ring axis S. 
     The ring sector  81  extends radially relative to the ring axis S in the radial direction of axis R, illustrated in  FIG. 2 , which is directed from the inner side to the outer side. The circular ring sector  81  has a constant radius of curvature and is flattened in the axial direction S, the radial dimension thereof being longer than the axial dimension thereof. 
     The ring sector  81  has an open angle in the order of 30 □ , but this angle may of course be different. 
     The inner radial portion  84  of the ring sector  81  is axially offset relative to the outer radial portion  85  thereof, as illustrated in  FIG. 2 . In other words, the inner radial portion  84  is ahead of the outer radial portion  85  in order to allow the inner radial end  84  to be accommodated in the recess  6  of the rotor disk  1  whilst allowing the outer radial portion  85  to move radially into abutment in the groove  11  of the rotor disk  1  as illustrated in  FIG. 3 . This feature will be set out below with reference to the embodiment of the invention. 
     The rectangular blocking wedge  82  of the securing device  8  is fixedly joined and orthogonal relative to the ring sector  81 , the wedge  82  extending from the rear face of the ring sector  81 , parallel to the ring axis S. The blocking wedge  82  is arranged so as to radially support the root  3  of the blade  2  in the groove  11  of the rotor disk  1 . With reference to  FIG. 2 , the blocking wedge  82  is fixedly joined to the upper portion  85  of the ring sector  81  in order to raise the root  3  of the blade  2  relative to the base of the groove  11  in order to allow a circulation of air in the groove  11  of the rotor disk  1 . 
     The blocking wedge  82  of the securing device  8  is flattened in the radial direction R, the axial dimension thereof being longer than the radial dimension thereof. The length of the blocking wedge  82  defined along the ring axis S is configured in order to support the root  3  of the blade  2 . By way of example, the length of the blocking wedge  82  corresponds to approximately 80% of the length of the root  3  of the blade  2  as illustrated in  FIG. 4 . It is self-evident that the length of the blocking wedge  82  may vary. Preferably, the length of the blocking wedge  82  is at least equal to half of the length of the blade root  3  in order to distribute the forces over the blocking wedge  82 . 
     The blocking tooth  83  of the securing device  8  is fixedly joined and orthogonal relative to the blocking wedge  82 . The blocking tooth  83 , which is rectangular, extends from the upper portion  85  of the ring sector  81  in the radial direction R toward the outer side, that is to say, radially relative to the axis of the ring sector S, in order to block the axial movement of the blade root  3  in the groove  11  of the rotor disk  1 . The length of the tooth  83 , defined along the radial axis R, is configured in this example so as to extend as far as the outer diameter of the rotor disk  1  when the securing device  8  is in the fitted position as illustrated in  FIG. 3 . 
     The dimensions of the blocking tooth  83 , in particular the length and the width thereof, are defined in order to resist the axial movements of the root  3  of the blade  2  during a rotation of the rotor. The blocking tooth  83  is arranged so as to be axially aligned with the groove  11  of the rotor disk  1 . Preferably, the rear face of the blocking tooth  83 , also called the stop face, has a surface of which size is less than the cross section of the groove  11  of the rotor disk  1 , as illustrated in  FIG. 3 . Such a blocking tooth  83  is able to carry out the blocking function, but at the same time is of reduced mass owing to the reduced dimensions thereof. According to a specific embodiment which is not illustrated, the blocking tooth  83  can be folded/retracted in order to allow simple fitting of the securing device  8  in the recess  6 , the tooth  83  being unfolded/deployed only after assembly. 
     The securing device  8  further comprises ventilation means which are formed in the ring sector  81 , preferably in the outer portion  85  thereof, between the zone of connection of the securing wedge  82  and the inner portion  84  of the annular sector  81  as illustrated in  FIG. 4 . These ventilation means are in the form of openings which extend through the ring sector  81  in the axial direction in order to allow a flow of air F which circulates between the base of the groove  11  and the blocking wedge  82  to be discharged, as illustrated in  FIG. 4 . 
     Preferably, the ventilation means are radially aligned with the blocking tooth  83  which allows the root  3  of the blade  2  to be axially secured whilst allowing the groove  11  to be ventilated. 
     According to a first embodiment, the ventilation means are in the form of circular through-holes  91 , whose diameter is calibrated for the ventilation, as illustrated in  FIGS. 2 to 4 . Circular holes  91  have the advantage of being simple to machine. 
     According to a second embodiment, with reference to  FIG. 5 , the ventilation means are in the form of through-holes  92  having an elliptical cross section whose minor diameter preferably extends in the radial direction. Holes  92  which have an elliptical cross section and which are produced, for example, by means of angled drilling, have the advantage of providing a great flow of air without affecting the mechanical strength in the radial direction of the ring sector  81 . This is because the distance between the inner edge of the ring sector  81  and an elliptical hole is greater than the distance between the inner edge of the ring sector  81  and a circular hole, thus offering greater mechanical strength. 
     According to a third embodiment, with reference to  FIG. 6 , the ventilation means are in the form of notches  93  which are formed from the inner portion  84  of the ring sector  81  as far as the outer portion  85  thereof. In other words, the inner end of the ring sector  81  is notched in order to allow the ventilation of the grooves  11 . Notches  93  have the advantage of reducing the mass of the ring sector  81  whilst being simple to machine by means of drilling. Furthermore, the notches  93  provide a great flow of ventilation air. 
     The fitting of a securing device  8  in the rotor will be described in greater detail. This fitting is described with reference to a device which comprises ventilation means in accordance with the first embodiment (circular holes). The description of the fitting method applies similarly to the other embodiments of the ventilation means. 
     With reference to  FIG. 3  illustrating the rotor disk  1  of axis X, the securing device  8  of  FIG. 2  is fitted in the rotor disk  1  by placing the blocking wedges  82  axially in the grooves  11  of the rotor disk  1  and inserting the inner portion  84  of the securing device  8  in the downstream recess  6  of the rotor disk  1  so that the upper portion  85  of the ring sector  81  is in radial abutment in the base of the groove  11  in order to form a space for circulation of a flow of air F between the blocking wedge  82  and the base of the groove  11 . The axial offset further allows tilting of the securing device  8  to be prevented by limiting the overhang of the securing device  8 . Indeed, if the blade  2  is in abutment with the wedge  82 , the inner portion  84  of the securing device  8  moves into contact with the downstream portion of the recess  6  and this blocks the upstream tilting of the wedge  82 . The blocking wedge  82  is parallel to the base of the groove  11  once fitted. The blocking tooth  83  extends radially relative to the axis of the engine and is axially aligned with the groove  11 . 
     With reference to  FIG. 4 , the ventilation means, in this instance circular holes  91 , extend at mid-height in respect of the space for circulation of the flow of air F between the blocking wedge  82  and the base of the groove  11 , which ensures good circulation of air. 
     The root  3  of the blade  2  is then inserted into the groove  11  by means of axial movement in a downstream direction so that the root  2  is in abutment with the outer surface of the blocking wedge  82  in order to be retained radially and thus to prevent an error in the positioning of the blade  2  in the disk  1  and, in particular, when the engine is in the stopped state. Furthermore, the root  3  of the blade  2  is in abutment with the upstream surface (stop surface) of the blocking tooth  83  in order to be axially secured. 
     Owing to the securing device  8  according to the invention, it is not necessary to use a blade in the form of a fir-tree-like root or to form a hook in the blade root in order to axially secure the blade  2 . 
     Preferably, the root  3  of the rotor blade  2  has a simple dovetail form whose casing is of composite material. It is the securing device  8  and not the root  3  of the blade  2  that carries out the functions of axial blocking, radial blocking and ventilation of the groove  11  of the rotor disk  1 . Such a root  3  is simple to produce and has a reduced mass. 
     Preferably, the casing of the root  3  of the blade  2  is of a ceramic matrix composite (CMC) material.