Patent Publication Number: US-7210909-B2

Title: Connection between bladed discs on the rotor line of a compressor

Description:
The invention relates to the field of high-pressure turbojet compressors, and more particularly to that of the connection between the bladed disc of the first stage of the compressor rotor and the bladed disc of the second stage of the compressor rotor. 
   In the case of aircraft turbojet engines, the compressor receives the intake air flow. The bladed disc at the intake of the compressor is liable to take in foreign bodies such as ice, birds or the like. Among the various bladed discs of the compressor, the first one is thus most exposed to damage by foreign bodies. For this reason, it is also the one that requires maintenance operations which may require removal of the bladed disc. Any dismantling of the rotor line of the compressor, which comprises various pieces, necessitates balancing and alignment operations that requires work in a properly qualified and well-equipped maintenance shop. During these dismantling operations, it is important for the rotor line not to be broken. 
   A solution has been proposed in EP 1 122 443, where a monobloc bladed disc (MBD) is used as a first bladed disc of the compressor. This bladed disc is fixed upstream by a flange to the intake of the compressor. This solution is not entirely satisfactory, however, since it does not make it possible to comply with certain criteria relating to the bladed disc, for example a vibration stability criterion, a service life criterion or a blade loss stability criterion. 
   It is an object of the present invention to improve the situation. 
   The invention relates to a part for attachment to the intake of a compressor rotor, this piece being suitable for forming a first piece of a compressor rotor. 
   According to an essential characteristic of the invention, the piece ends in a first ring provided with a succession of holes and notches. 
   According to another characteristic of the invention, the axis of the first ring is suitable for being centred on the axis of rotation of the compressor rotor in order to be attached to the intake of the compressor rotor, the first ring is suitable for being placed against an axisymmetric second piece of the rotor, which is fixed to an axisymmetric third piece of the rotor by fastening means and forms a second-piece/third-piece assembly of the rotor, the notches being suitable for fitting around the means of fastening the second-piece/third-piece assembly of the rotor, the holes of the first ring being suitable for being placed in alignment with the holes of the second-piece/third-piece assembly in order to fasten the first ring to the second-piece/third-piece assembly. 
   The first ring is preferably in a plane perpendicular to the axis of rotation of the rotor. 
   The piece advantageously comprises a disc and blades attached to its periphery. 
   The piece furthermore comprises a disc provided with a flange connected to the first ring, the flange and the ring being placed downstream of the disc so that the fastening of the disc to the second-piece/third-piece assembly can be carried out downstream of the disc with respect to the direction in which the flow travels through the compressor. 
   The invention likewise relates to a connection between a first piece as defined above, ending in a first ring provided with a succession of holes and notches, the axis of the first ring being centred on the axis of rotation of the compressor rotor in order to be attached to the intake of the compressor rotor, and an assembly formed by a second rotor piece fixed to a third rotor piece, the second piece forming the intake of the compressor rotor and ending downstream in a second ring comprising holes, the third piece ending upstream in a third ring comprising holes, the second and third rings being arranged against each other, so as to place their holes in alignment, and being fixed together by first fastening means, the first circular ring being arranged upstream of and against the second-piece/third-piece assembly so that the notches fit around the first means of fastening the second-piece/third-piece assembly of the rotor and so that at least some of the holes of the first ring are aligned with holes of the second-piece/third-piece assembly, with second fastening means fixing the first circular ring to the second-piece/third-piece assembly. 
   The second ring and the third ring are preferably in a plane perpendicular to the axis of rotation of the rotor. 
   The means of fastening the second-piece/third-pieceassembly of the rotor are advantageously shorter than the fastening means for fixing the first ring to the second-piece/third-piece assembly. 
   The fastening means furthermore comprise screw-nut systems. 
   The screw of the screw-nut system is preferably retained by a washer allowing the screw to hold when the nut is not there. 
   The invention relates in particular to a turbine engine comprising a high-pressure compressor provided with a connection as defined above. 
   The invention also relates to a method of fitting a connection as defined above, consisting in placing the second and third circular rings against each other, so as to place the holes in alignment, in fixing these second and third rings together with the first fastening means passing through some of the holes, in placing second fastening means, suitable for fixing the second-piece/third-piece assembly to the first piece, in the remaining holes, in placing the first circular ring upstream of and against the second-piece/third-piece assembly so that the notches fit around the means of fastening the second-piece/third-piece assembly of the rotor and so that the second fastening means pass through some of the holes of the first ring in order to fix the first circular ring to the second-piece/third-piece assembly. 
   The invention furthermore relates to a method of dismantling a connection as defined above, consisting in undoing the second fastening means in order to remove the first piece of the compressor rotor and retain the second-piece/third-piece assembly of the rotor. 

   
     The following figures illustrate embodiments of the invention without implying any limitation: 
       FIG. 1  represents in section a half-view along the axis of rotation of a turbojet compressor composed of various bladed discs, 
       FIG. 2  represents in detail the first and second bladed compressor discs of  FIG. 1 , which are joined together by a connection according to the invention, 
       FIG. 3  represents in relief a sector of the first disc according to the invention without blades, 
       FIG. 4  represents a sector of the journal according to the invention in relief, 
       FIG. 5  represents in relief a sector of the second disc according to the invention without blades, 
       FIG. 6  represents the first phase of fitting the connection according to the invention, which consists in assembling the journal and the second disc, 
       FIG. 7  represents the second phase of fitting the connection according to the invention, which consists in assembling the first disc with the assembly formed by the journal and the second disc, 
       FIG. 8  represents an alternative embodiment of the connection according to the invention. 
   

   The drawings essentially contain elements of a specific type. They can therefore serve not only to explain the description more clearly, but also contribute to defining the invention, as appropriate. 
     FIG. 1  represents a partial section of the rotor part of a high-pressure turbojet compressor composed of various compression stages E 1  to E 5 , each comprising a disc D 1  to D 5  provided with a ring of blades A 1  to A 5 . Downstream of each bladed disc, each compression stage is also composed of a flow rectifier (not shown) forming part of the stator part of the compressor. Each rectifier makes it possible to rectify the airflow before it enters the next compression stage. The rotor part and the stator part of the compression define a “stream” for the flow of air to be compressed. The term rotor line is used to describe the continuous outer surface of the rotor forming the lower boundary of this stream. The bladed discs D 2  to D 5  of the compressor are formed in a single piece, which is referred to as a disc assembly. The bladed disc D 1  is advantageously a monobloc bladed disc which is attached to the rotor upstream of the disc assembly, so that it can be removed easily for maintenance and servicing work. This monobloc first bladed disc, which forms the first stage of the high-pressure compressor, is liable to take in foreign bodies such as ice, birds and the like. The rotor part of the compressor is driven in rotation by a shaft S, which is itself driven in rotation by a turbine located downstream of the compressor. The axis of rotation is denoted as B. 
   The nomenclature “upstream” or “downstream” of the elements of the rotor is to be understood with reference to the direction SF of the airflow in the compressor. The nomenclature “internal” referring to the rings (or a ring part) ending a piece is to be understood as meaning rings which extend towards the inside the piece, namely rings which start from the piece and whose radius decreases, and “external” is to be understood as meaning rings which extend towards the outside of the piece, namely rings which start from the piece and whose radius increases. 
     FIG. 2  represents the connection between the bladed discs D 1  and D 2  according to the invention. The rotor line is advantageously continuous at the intake of the high-pressure compressor. At the intake of the compressor, the rotor comprises a journal  30  of flared shaped ending in a radial ring  32 . The disc D 2  comprises an upstream flange  20  which extends in the direction of the journal and ends in a radial ring  22 , the upstream surface of which comes in contact with the downstream surface of the radial ring  32  of the journal. The monobloc bladed disc D 1  comprises a downstream flange  10  which extends in the direction of the radial ring  32  of the journal and ends in a radial ring  12 , the downstream surface of which comes in contact with the upstream surface of the radial ring  32 . The monobloc bladed disc D 1 , the journal  30  and the disc D 2  are joined together by a fastening means, such as a screw-nut system  40  represented in  FIG. 2 , passing through mutually aligned holes of the rings  12 ,  32  and  22 . The axisymmetric downstream flange  10  of the monobloc bladed disc D 1  makes it possible to produce a downstream connection of this disc with the rotor in order to comply with the criteria of vibration endurance, service life and blade loss of this disc of the first compression stage. 
   The term radial ring is intended to mean a ring which lies in a radial plane, that is to say a plane perpendicular to the axis of rotation of the rotor. The rings could, however, be inclined with respect to the radial plane, so long as their inclination allows the relative placement of the surfaces of the rings against one another as described above. 
   Details of each element or piece of the connection will be described more particularly with reference to  FIGS. 3 ,  4  and  5 . 
     FIG. 3  represents the monobloc disc D 1  without blades, this disc being suitable for accommodating blades. This first piece of the rotor comprises a circular base  11 , on top of which there is a circular plate  18  suitable for accommodating blades. The circular base  11  comprises a downstream circular flange  10  which, by way of example, extends in the direction of the axis of rotation B and ends in the radial ring  12 , which is provided with a succession of holes  14  and notches  16 . In one exemplary embodiment, the radial ring  12  comprises thirty-two holes and eight notches, distributed symmetrically among the thirty-two holes. In the embodiment of the figure, the radial ring  12  is an external ring. 
     FIG. 4  represents a second piece of the rotor, namely the journal  30  comprising an upstream cylindrical first part  31  flaring into a frustoconical part  33 , the latter ending downstream in a radial ring  32 . This radial ring is composed of an internal radial part  35 , referred to as a base, and an external radial part which ends in a rim  38  extending axially in an upstream direction and in a downstream direction. The external radial part comprises holes  34  intended to be placed in alignment with the holes and the notches of the external radial ring  12  of the upstream disc D 1  on the upstream surface side of the radial ring  32 , and with the holes of the radial ring  22  of the downstream disc D 2  on the downstream surface side of the radial ring  32 . 
     FIG. 5  represents the disc D 2  without blades, this disc being suitable for accommodating blades. This second piece of the rotor comprises a circular base  21 , on top of which there is a circular plate  28  suitable for accommodating blades. The circular base  21  comprises the upstream circular flange  20  which narrows in the upstream direction with a frustoconical shape and ends in the radial ring  22 , which is provided with a succession of holes  24 . In one exemplary embodiment, the radial ring  22  is internal and comprises forty holes. Notches  26  are distributed among the holes  24  so as to reduce the amount of material of the radial ring  22 . These notches are also used as a means of indicating the position of the holes  24 . 
     FIGS. 6 and 7  represent the steps involved in fitting a connection according to the invention. 
   According to  FIG. 6 , in a first step, the journal is connected to the disc D 2  by positioning the downstream surface of the external radial ring  32  against the upstream surface of the internal radial ring  22  of the downstream disc D 2 , while aligning the holes of the external radial ring  32  and the holes of the internal radial ring  22 . First fastening means  42  such as screw-nut systems, are placed in some of the aligned holes, these holes being identifiable on the basis of the notches  26  of the internal radial ring  22 , for example. The identified holes should correspond to the distribution of the notches  16  of the disc D 1 , for reasons which will be explained below. Owing to the presence of the connection between the journal and the disc D 2 , the rotor line is continuous even when the upstream disc D 1  is not there, in other words the stream of the airflow is sustained. The journal  30  and the disc D 2  form an assembly which is fixed by the first fastening means, this assembly being referred to as the second-piece/third-piece assembly of the rotor. The remaining holes are provided with a part of second fastening means, for example screws without nuts, with the head of the screw being pressed against the downstream surface of the internal radial ring  22  of the disc D 2  and the end of the stem of the screw protruding significantly on the upstream surface side of the external radial ring  32  of the journal  30 , so that it can accommodate the thickness of the external radial ring  12  of the disc D 1 , followed by the fastening nut. The screws of the second fastening means are advantageously retained by a washer, thus preventing the screws from coming out of the holes when the nuts have not yet been engaged on the screw stems. 
   According to  FIG. 7 , in a second step, the axis of the disc D 1  is centred on the axis of rotation of the compressor rotor in order to be attached to the intake of the compressor rotor. The external radial ring  12  is thus placed against the upstream surface of the external radial ring  32  of the journal. In order to do this:
     the notches  16  are initially placed in alignment with the first fastening means, and are then fitted around the latter once the external radial ring  12  has been placed against the upstream surface of the external radial ring  32 ,   the holes  14  of the first ring  12  are placed in alignment with the remaining holes of the second-piece/third-piece assembly of the rotor, or in other words the ends of the screw stems of the second fastening means, which protrude from the upstream surface of the external radial ring  12  of the disc D 1 , penetrate the holes  14 .   

   Nuts are screwed onto the ends of the screws and are tightened against the upstream surface of the external radial ring  12  of the disc D 1 . The rim  38  of the external radial ring  32  of the journal advantageously covers the radial external edge of the external radial ring  12  of the disc D 1  in the upstream direction, and the radial external edge of the internal radial ring  22  of the disc D 2  in the downstream direction. The axial rim  38  thus makes it possible to exert a centripetal radial force on the external radial ring  12  of the disc D 1  and on the internal radial ring  22  of the disc D 2 , in particular during operation. 
   The connection between the disc D 1  and the journal/disc D 2  assembly is dismantled in the following way. In the embodiment of  FIG. 2 , the stator is partly removed in order to gain access to the fastening means located behind the disc D 1 . 
   The nuts of the second fastening means are unscrewed and removed. The disc D 1  can then be withdrawn by pulling axially in the upstream direction. The journal and the disc D 2  remain, fixed together by the first fastening means, for example by eight screw-nut systems, and the ends of the screw stems of the second fastening means also remain, retained by the washers. The monobloc disc D 1  can thus be removed from the rotor with great ease and without having to break the rotor line. The monobloc disc D 1  can be repaired or replaced by another monobloc disc D 1  in good condition. This disc D 1  is fitted as explained above, by making the notches  16  coincide with the first fastening means and making the holes  14  coincide with part of the second fastening means, that is to say the screw stems. 
   The connection according to the embodiment of  FIGS. 6 and 7  is fitted in the absence of the stator, which is installed after the connection has been set up. A variant of this embodiment could allow the connection to be fitted with the stator present: the screw-nut systems then need to be reversed (the nut being put in place of the head of the screw, and vice versa). 
     FIG. 8  represents an alternative embodiment of the connection according to the invention. 
   The disc DD 1  accordingly consists of a flange  110  extending axially in a slightly inclined fashion and ending in an internal radial ring  112 , which is suitable for being placed against the upstream surface of the external radial ring  132  of the journal  130 . The ring  112  comprises a succession of holes and notches like the ring  12 . The disc DD 2  is the same as the disc D 2 , and its internal radial ring  122  is suitable for being placed against the downstream surface of the external radial ring  132  of the journal  130 . The rings  132  and  122  are formed like the rings  32  and  22 . The disc DD 1  comprises a base which is shortened in comparison with the previous embodiment of the disc D 1 , so that it is possible to access the fastening means  140 , which are similar to the fastening means  40  of the previous embodiment, via a passage between the base of the disc DD 1  and the journal  130 . 
   In particular, this embodiment makes it possible to avoid having to remove the stator when fitting or removing the disc DD 1 . In other regards, the fitting method and the dismantling method correspond to those described above. 
   In general, the first fastening means of the journal/disc D 2  assembly are shorter than the second fastening means enabling the first circular ring to be fixed to the journal/disc D 2  assembly. 
   The invention thus makes it possible to replace the monobloc bladed disc without special maintenance or time loss, this piece being the one most exposed to problems in service and having the greatest impact on the performance of the compressor. 
   The invention is not limited to a bolted connection between a disc, as a first rotor piece, and a fixed assembly of second and third rotor pieces, but extends to any piece requiring separate removal from connection with an assembly of pieces that are fixed together. 
   The invention is also not limited to the fastening device embodiments described above merely by way of example, but covers all variants which a person skilled in the art could envisage within the scope of the claims which follow.