Abstract:
A turbine engine air blower including a rotor disk that includes, on an outer periphery thereof, longitudinal ribs, each including a radial lug for attaching the disk onto a downstream compressor rotor. The flanks of the lugs form abutments for holding vanes that are mounted onto the disk. A mechanism protecting flanks of the lugs is circumferentially inserted between the lugs and the vanes.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a fan of a turbine engine, such as an aircraft jet engine or turboprop engine. 
     2. Description of the Related Art 
     In a known fashion, a turbine engine fan comprises a rotor disc having at its external periphery a plurality of longitudinal ribs delimiting between them slots for the axial mounting and radial retention of blade roots. The downstream end of each rib comprises a radial lug comprising an orifice for a screw or bolt to pass for fixing the fan disc onto an upstream flange of a low-pressure compressor arranged downstream of the fan. The low-pressure compressor is thus driven in rotation with the rotor of the fan by a turbine shaft. 
     The flanks of each lug form stops for retaining the blades and thus limit their angular movement. In the event of loss of a blade, the blade disconnected from the disc impacts an adjacent blade, which tilts angularly and comes into abutment on the flank of a lug, which transfers the energy released by the impact of the disconnected blade on the adjacent blade to the whole of the disc and thus prevents losses of blades in a cascade. 
     When the aircraft is on the ground and the turbine engine is stopped, the rotating parts of the turbine engine may undergo autorotation (referred to as “windmilling”). This is because the air entering the turbine engine causes a rotation of the rotor of the fan at a speed of around 40 to 50 revolutions per minute. This low rotation speed does not allow sufficiently great centrifugation of the blades for locking thereof in position in the slots. As a result the blades of the fan may tilt on the flanks of the lugs of the disc ribs. These repeated contacts cause rubbing between the flanks of the lugs and the blades, leading to premature wear on the stops, which requires more frequent repairs to the stops. 
     At the present time, repair to the flanks of the lugs is carried out by plasma deposition of a metal layer. However, the lugs of the disc thus repaired have a lower fatigue strength than that of the lugs of a new disc. In addition, these depositions of material have limited impact resistance and may progressively disintegrate over time. 
     Finally, this operation cannot be performed under the wing and requires dismantling and repair in a maintenance workshop, which leads to lengthy and expensive immobilisation times and requires the use of expensive and complex tooling. 
     BRIEF SUMMARY OF THE INVENTION 
     The aim of the invention is in particular to afford a simple, economical and effective solution to these various problems. 
     To this end, it proposes a turbine engine fan comprising a rotor disc having on its external periphery slots for mounting blade roots delimited by longitudinal ribs each having a radial lug for fixing the disc on a downstream compressor rotor, the flanks of the lugs forming stops for retaining the blades mounted on the disc, characterised in that U-shaped clips are mounted on the lugs of the disc and each comprise two lateral tabs covering the flanks of a radial lug. 
     The invention thus proposes the integration of clips protecting the lugs of the disc, preventing wear on the flanks of the lugs by repeated contact of the blades when the fan is set in autorotation. 
     It is thus no longer necessary to dismantle the turbine engine to repair the lugs of the fan disc ribs. Integration of these clips is simple to achieve and can be effected on a turbine engine mounted under the wing of an aircraft, avoiding dismantling and transport to a maintenance workshop. 
     The clips may be engaged axially from the upstream side on the lugs. 
     In one embodiment of the invention, each clip comprises a transverse wall applied to a radial upstream face of a lug and comprising an orifice aligned with a corresponding orifice in the lug for a screw or bolt to pass for fixing on the downstream compressor rotor. 
     Thus each clip is clamped on a radial lug of a disc at the fixing with the downstream compressor rotor. The thickness of the transverse wall is sufficiently small not to require the replacement of the fixing screw or bolt with larger screws or bolts. 
     Advantageously, each lateral tab of a clip comprises a longitudinal U-shaped fold fitting on a stop of a flank of the radial lug, which ensures the axial mounting of the clip on a lug and the radial holding of this clip on this lug. 
     According to another feature of the invention, each transverse wall of the clip comprises at least one radial tab, the free end of which extends upstream along a rib of the disc. 
     Preferentially, each clip comprises two aforementioned radial tabs that are parallel and spaced apart circumferentially from each other, which prevents rotation of the clip when it is clamped on the lug. 
     The invention also concerns a clip for protecting the flanks of a radial lug of a peripheral rib of a fan disc as described previously, characterised in that it comprises two substantially parallel lateral tabs connected by a transverse wall comprising a central orifice, the transverse wall of each clip being extended by two angled tabs the free ends of which extend in a direction opposite to the lateral tabs of the clip. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention will be better understood and other details, advantages and features of the invention will emerge from a reading of the following description given by way of non-limitative example, with reference to the accompanying drawings, in which: 
         FIG. 1  is a partial schematic view in perspective of a fan disc according to the prior art; 
         FIG. 2  is a partial schematic view in transverse section of a blade mounted in a slot of a fan disc according to the prior art; 
         FIG. 3  is a schematic view from upstream of part of a disc comprising means of protecting the lugs of the disc according to the invention; 
         FIGS. 4A and 4B  are perspective views of clips for protecting the radial lugs of a disc of a fan according to the invention; 
         FIG. 5  is a schematic view in axial section of the fixing of the fan disc according to the invention to a low-pressure compressor rotor arranged downstream. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made first of all to  FIG. 1 , which shows schematically part of a turbine engine fan disc  10  comprising, at its external periphery, longitudinal ribs  12  delimiting between them slots  14  for the axial mounting and radial holding of blades  16 . Each blade  16  comprises a vane  18 , a platform  20  formed at the base of the vane and delimiting internally the annular stream for the air flow entering the turbine engine. A zone  22  known as the “prop” connects the platform  20  and the vane  18  to a blade root  24 . 
     Each rib  12  of the fan disc  10  comprises a radial lug  26  formed at its downstream end. These lugs  26  each comprise an axial orifice  28  intended to be aligned with a corresponding orifice formed in an annular flange of a low-pressure compressor rotor arranged downstream (see  FIG. 5 ). Fixing screws are inserted in the orifices  28  in the lugs  26  of the disc  10  and in the orifices in the annular flange of the compressor rotor. 
     Each radial lug  26  comprises lateral flanks each having a projecting longitudinal stop  30 . Each stop  30  formed on the flank of a lug  26  is aligned circumferentially with a stop  30  of an adjacent lug ( FIG. 2 ). 
     When the blades  16  are mounted on the fan disc  10 , it is the props  22  that are situated opposite the longitudinal stops  30 . 
     In the event of the loss of a blade, the disconnected blade impacts an adjacent blade  16 , which tilts, and the prop  22  of which comes into contact with a stop  30  of a radial lug  26 . These stops  30  thus limit the angular movement of the blade  16  experiencing the pressure of the disconnected blade and allows a transfer of energy from the impact to the fan disc  10 . 
     It was found in the prior art that these stops  30  were subjected to relatively high wear due essentially to the impacts of the starting and stopping of the turbine engine and its occasional functioning in autorotation when at rest on the ground. This is because the air entering the turbine engine causes rotation of the fan that is not sufficiently high to achieve a centrifugation of the blade  16  and locking of the blade roots  24  in a stable position in the slots  14 . The result is successive tiltings of the blades  16  leading to rubbing between the props  22  and the stops  30 , resulting in wear on the stops  30  of the radial lugs  26 . 
     The solutions proposed in the prior art and disclosed previously are not lasting and require dismantling of the turbine engine in order to effect repair in a maintenance workshop and expensive equipment. 
     According to the invention, clips  32  are mounted on the radial lugs  26  of the fan disc  10  and cover the flanks of the lugs  26  for protection of the stops  30  ( FIG. 3 ). 
     Each clip has a U shape and comprises a transverse wall  34  of substantially rectangular shape connected to two parallel lateral tabs  36 ,  38 . The transverse wall  34  comprises a central orifice  40  and is extended by two radial flat tabs  42 ,  44  that are parallel and the ends of which are curved in a direction opposite to the lateral tabs  36 ,  38 , these two radial tabs  42 ,  44  being spaced apart from each other ( FIGS. 4A and 4B ). 
     The lateral tabs  36 ,  38  of a clip  32  each comprise a longitudinal fold  41  in a U, intended to fit on a longitudinal stop  30  of a lug  26  of the disc  10 . 
     For mounting a clip  32  on a lug  26  of the turbine engine disc  10 , the clip  32  is positioned on the disc  10  so that the radial lugs  42 ,  44  extend along a rib  12  and towards the upstream side of the disc  10 . The clip  32  is then translated downstream so that the U-shaped  41  folds of the lateral tabs  36 ,  38  fit on the longitudinal stops  30  of the radial lug  26  of the disc  10 , the transverse wall  34  of the clip  32  coming to be applied against the upstream radial face of the radial lug  26 . A fixing screw  46  is then inserted from the downstream side in the aligned orifices of the clip  32 , the lug  26  and the annular flange  48  of the low-pressure compressor rotor. A fixing nut  50  is tightened on the upstream face of the clip  32  ( FIG. 5 ). 
     Insertion of the clip  32  causes no change in the dimensions of the fixing screws  46  given the very small thickness of the transverse wall  34 , which is around a few tenths of a millimeter. 
     It is desirable to size a clip  32  so that the radial tabs  42 ,  44  are mounted with a radial clearance J with respect to a rib  12  on the disc  10  in order to compensate for the tolerances in the radial positioning of an orifice  28  on a radial lug  26  and thus guarantee in all circumstances an alignment of the orifice  40  in a clip  32  with an orifice  28  in a radial lug  26 . 
     This type of protective clip  32  for the flanks of the lugs can be used both on a new fan disc  10  and on a disc in the course of use. In the latter case, if the stop  30  exhibit any wear, it is necessary to carry out bleaching by grinding the surface of the stops  30  so as to have a smooth surface in contact with the clip  32 . This operation therefore consists of removing between 0.2 and 0.5 millimeters of material at the flanks of a worn lug. 
     The clips  32  can be integrated on the lugs  26  of a fan disc  10  when the turbine engine is in place under the wing of the aircraft, which reduces the immobilisation times and does not require complicated equipment since each clip  32  is secured by means of a pre-existing fixing element. 
     The clips  32  can be produced from a metal material such as INCONEL and the blades  16  can be made from titanium. In this way the clips  32  wear less quickly than the blades  16 . 
     The clips  32  can be produced by successive operations of folding and cropping a metal sheet or by machining a block of material.