Abstract:
A turbomachine rotor blade comprising a root ( 14 ) mounted in a channel of the periphery of a disk and held by an annular flange ( 18 ) which presses on the root ( 14 ) of the blade ( 12 ), this root comprising a stop ( 44 ) engaging in a matching cavity of the flange in order to stop it rotating about the axis of the disk, the central portion of the stop having a thickness less than that of the ends of the stop.

Description:
The present invention relates to a rotor blade, in particular for a compressor of a turbomachine such as an aircraft turbojet or turboprop. 
     BACKGROUND OF THE INVENTION 
     The blades of a compressor stage comprise roots engaged in axial channels of the periphery of a rotor disk and held by an annular flange formed of several sectors that is mounted via an external annular rim in an internal annular groove of the downstream face of the disk. This flange presses axially at its radially external end on the downstream ends of the blade roots, and at its radially internal end on the downstream face of the disk by means of an annular sealing snap-ring. 
     The internal annular rim of the groove of the disk and the annular rim of the flange are scalloped or crenellated in a matching manner, which makes it possible to bring the flange inside the annular groove of the disk by axial translation when the solid portions of the scalloped rim of the flange are in line with the hollow portions of the scalloped rim of the annular groove. The flange is then axially locked by rotation in the annular groove of the disk until the solid portions of the scalloped rim of the flange are in line with the solid portions of the scalloped rim of the annular groove of the disk and are axially pressing on the latter. 
     The blades comprise stops that are formed on downstream faces of their roots and that are designed to be engaged with a slight circumferential clearance between adjacent solid portions of the annular rim of the flange in order to stop the flange rotating in the annular groove of the disk. Each stop has an elongated shape in the circumferential direction and extends from one lateral edge to the other of the downstream face of the blade root, the lateral ends of the stop interacting by abutment with the adjacent solid portions of the scalloped rim of the flange in order to stop it rotating. This stop is formed by a large volume of material which significantly adds weight to the blade and hence the rotor disk. 
     DESCRIPTION OF THE PRIOR ART 
     It has already been proposed to reduce the weight of the rotor blades by reducing the length of their stops in the circumferential direction. However, this solution is not satisfactory because it makes it necessary in consequence to modify the scalloped rim of the flange, by increasing the circumferential extent of the solid portions of its rim, in order to retain the aforementioned slight circumferential clearance between the stops and the solid portions of the rim of the flange, which also leads to an increase in the weight of the flange and hence of the rotor disk. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is in particular to provide a simple, effective and economic solution to these problems. 
     Accordingly it proposes a turbomachine rotor blade comprising a root having a stop formed in protrusion on one of its upstream and downstream end faces, wherein the central portion of this stop has a thickness in a direction substantially perpendicular to said end surface that is less than that of the ends of the stop. 
     The ends of the stop have a thickness determined by their function of abutment on solid portions of the rim of the flange, and the central portion of this stop may have a much lesser thickness, even zero, without adversely affecting the stopping of rotation of the flange. 
     The invention therefore makes it possible to reduce the weight of the rotor blades without, for all that, modifying the scalloped rim of the flange because the circumferential distance between the lateral ends of the stops remains unchanged. 
     The slight thickness of the central portion of the stop also has no effect on the seal of the assembly because this seal is provided by the radially external portion of the flange pressing on the blade roots and by an annular snap-ring mounted between the radially internal portion of the flange and the disk. 
     The central portion of each stop may be lightened by the removal of material. Preferably, it is removed by machining. This central portion has, for example, a length in a direction substantially perpendicular to the longitudinal axis of the blade and parallel to said end face that is at least equal to approximately ¾ or ⅘ of the length of the stop. 
     The root of the blade has, for example, a dovetail or dogtooth shape in cross section. The stop of the blade may be formed by machining or obtained by casting. As a variant, it may be fitted and attached by welding, riveting, screwing, bonding, etc., onto the blade root. 
     The invention also relates to a turbomachine rotor disk comprising blades as described above whose roots are mounted in channels of the periphery of the disk and an annular flange that is mounted coaxially on the disk and that presses on the roots of the blades, the stop of each blade root being engaged in a matching cavity of the flange in order to stop it rotating about the axis of the disk. 
     The invention also relates to a turbomachine, such as an aircraft turbojet or turboprop, which comprises at least one rotor disk as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages and features of the invention will appear on reading the following description made as a nonlimiting example and with reference to the appended drawings in which: 
         FIG. 1  is a partial schematic view in axial section of a turbomachine rotor disk; 
         FIG. 2  is a schematic half-view in axial section of the annular flange of the rotor disk of  FIG. 1 , on a larger scale; 
         FIG. 3  is a partial schematic view in perspective of the rotor disk of  FIG. 1 , seen from downstream; 
         FIG. 4  is a partial schematic view in perspective of the root of a blade of the rotor disk of  FIG. 1 , seen from downstream; 
         FIG. 5  is a partial schematic view in perspective of the root of a blade of a rotor disk according to the invention, seen from downstream. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is made first to  FIGS. 1 to 4  which illustrate the technique involved in the present invention. 
     The rotor of a turbomachine compressor comprises a plurality of rotor disks, one of which is shown partially in  FIGS. 1 and 3 , each disk  10  supporting a plurality of substantially radial blades  12  whose roots  14  are engaged in axial channels  16  of the periphery of the disk  10 . 
     The roots  14  of the blades are retained radially in the channels  16  of the disk by interaction of shapes, these channels  16  being for example dovetailed as shown in  FIG. 3 . The blades  12  are immobilized axially in the channels  16  by an annular flange  18  mounted on the downstream face of the disk  10  and by a locking ring  20  mounted on the upstream face of the disk. 
     The locking ring  20  is split and is radially compressed in order to be inserted into an annular groove  22  opening radially toward the inside of the upstream face of the disk  10 . This ring  20  presses axially on the upstream ends of the roots  14  of the blades of the disk  10 , thereby ensuring that they are axially retained in the upstream direction. 
     The annular flange  18 , more visible in  FIG. 2 , is formed of angular sectors, for example five in number, and comprises upstream an annular rim  24  oriented radially toward the outside and housed in an annular groove  26  opening radially toward the inside of the downstream face of the disk  10 . The annular rim  24  of the flange is scalloped or crenellated, that is to say that it has solid portions  28  formed alternately with hollow portions  30  evenly distributed about the axis of the flange. 
     The radially external portion  32  of the flange  18  presses axially on the downstream ends of the roots  14  of the blades of the disk  10 , thereby ensuring that they are retained axially in the downstream direction. 
     The annular flange  18  comprises, in its radially internal portion  34 , an annular groove  36  opening axially upstream for the housing of an annular sealing snap-ring  38  designed to be clamped axially between the downstream face of the disk and the bottom of the groove  36  and to be deformed radially outward in operation under the effect of the centrifugal forces. 
     The internal annular rim  40  of the groove  26  of the disk is scalloped or crenellated like the annular rim  24  of the flange  18 , which makes it possible to engage the rim  24  of the flange  18  in the groove  26  of the disk by axial translation, when the solid portions  28  of the rim of the flange are in line with the hollow portions of the rim  40  of the groove  26 . The flange  18  is then immobilized axially by rotation in the groove  26  of the disk until the solid portions  28  of the rim  24  of the flange are in line with the solid portions  42  of the rim  40  of the groove and pressing axially on these solid portions. 
     The downstream flange  18  is prevented from rotating about the axis of the disk  10  by means of stops  44  formed on the downstream ends of the roots  14  of the blades and designed to nest with a slight circumferential clearance in the hollow portions  30  of the annular rim  24  of the flange  18  ( FIGS. 1 and 4 ). 
     In a known embodiment, the stop  44  of each blade  12  is formed in protrusion on a downstream radial face  46  of the blade root  14  and has a parallelepipedal shape that is elongated in the circumferential direction and extends from one lateral edge to the other of the downstream face  46  of the root. 
     The stop  44  comprises a substantially radial downstream face  48  that is connected to the lateral faces  50  of the blade root  14  by faces  52 ,  53  designed to come into abutment in the circumferential direction on adjacent solid portions of the annular rim  24  of the flange in order to stop it rotating in the groove  26  of the disk. The faces  52 ,  53  may be in line with the lateral faces  50  of the blade root. The face  52  of the stop, situated on the right in the drawing, is designed to come into abutment on a solid portion  28  of the scalloped rim of the flange in order to stop the flange  18  rotating in one direction of rotation (arrow  54 —to the left in the drawing) about the axis of the disk, and its face  53 , situated on the left in the drawing, is designed to come into abutment on an adjacent solid portion  28  of the rim of the flange in order to stop it rotating in the opposite direction of rotation (arrow  56 —to the right in the drawing) about the axis of the disk. 
     The invention makes it possible to lighten this type of blade thanks to a lesser thickness of the central portion of the stop. The “thickness” of the stop means the dimension of the stop in a direction parallel to the axis of the disk. The central portion of the stop has a slight or even zero thickness and the lateral ends of the stop that comprise the aforementioned abutment faces have a thickness that is substantially identical to that of the stop of the prior art. 
     In the exemplary embodiment of the invention shown in  FIG. 5 , the central portion of the stop  144  has been removed by machining, the lateral ends of the stop  144  being substantially identical and independent and at a circumferential distance from one another. 
     Each end of the stop  144  comprises a substantially radial downstream face  148  connected to the lateral face  150  of the nearest blade root via an abutment face  152 ,  153 . The abutment face  152  of the stop  144 , situated on the right in the drawing, makes it possible to lock the flange in the direction of rotation  154  about the axis of the disk, and the abutment face  153  of the stop  144 , situated on the left in the drawing, makes it possible to lock the flange in the direction of rotation  156  about the axis of the disk. 
     The length and width of the stop according to the invention are substantially identical to those of the stop of the prior art. The “length” of the stop means the dimension of the stop in a circumferential direction relative to the axis of the disk, and the “width” of the stop means the dimension of the stop in a radial direction relative to this axis. The length of the central portion of the stop  144  is determined partly in order to significantly reduce the weight of the blade  12  and partly so that the ends of the stop retain a sufficient mechanical strength so as not to be damaged by butting against solid portions of the scalloped rim of the flange. Typically, the lightened or removed central portion of each stop has a length at least equal to approximately ¾ or ⅘ of the length of the stop. 
     The rotor disk according to the invention is assembled in the following manner: 
     The sectors of the flange  18  are mounted one after the other onto the downstream face of the disk  10  by axially aligning the solid portions  28  of the scalloped rim of the flange with the hollow portions of the scalloped rim  40  of the disk and by moving the sectors toward the disk, in a direction parallel to the axis of rotation of the disk, until the annular rim  24  of the flange is engaged in the groove  26  of the disk. 
     The sectors of the flange are then moved in rotation in the groove of the disk until the solid portions  28  of the annular rim of the flange are axially in line with the solid portions  42  of the rim of the groove  26  of the disk in order to axially immobilize the flange on the disk. 
     The blades  12  are mounted one after the other onto the disk by axially engaging their roots  14  from upstream in the channels  16  of the periphery of the disk, until the stops  144  of the blades are engaged in the hollow portions  30  of the scalloped rim of the flange and these stops are in line transversely with the solid portions  28  of the scalloped rim of the flange. The ring  20  is then compressed radially and engaged in the annular groove  22  of the upstream face of the disk in order to axially lock the blades  12  onto the disk. 
     The stop  144  according to the invention may be obtained by machining the root of a blade according to the prior art. For this, an appropriate tool is moved one or more times in a direction  160  substantially parallel to the longitudinal axis A of the blade on the central portion of the stop  144  in order to remove material by machining. The central portion of the stop may also be removed by ECM (Electrochemical Machining) or EDM (Electrical Discharge Machining). 
     As a variant, the stop  144  may be cast with the blade  12  or be fitted and attached to the blade root.