Abstract:
The invention relates to a system for fastening the end of a gas turbine engine shaft ( 4 ) engaged inside a sleeve ( 15 ) supported by a bearing ( 3 ). Said system comprises a nut ( 16 ) and is characterized in that the nut ( 16 ) is screwed at one end inside said sleeve ( 16 ) and is connected by a segment-type connection ( 18 ) with the shaft at the other end.

Description:
BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART 
       [0001]    The present invention relates to a gas turbine engine, in particular in the aeronautical field, and is aimed at mounting a rotor shaft inside the engine. 
         [0002]    The operations of mounting and demounting a turbine engine are complicated owing to the number of parts which constitute it and of the small clearances between them even though their dimensions may be large. The cost of carrying out work on the engine which comprises such operations is consequently always high. It is therefore constantly sought to simplify them. In a twin-spool, front turbofan engine, such as the cfm56 engine, access to the support bearing of the high-pressure compressor shaft is particularly difficult since it is mounted, at the level of the intermediate casing, to the rear of the fan and of the two first bearings supporting the low-pressure compressor shaft and the fan shaft, respectively. The intermediate casing is that part of the machine casing which particularly supports the front bearings of the rotors. To avoid demounting the entire front part of the engine and of the fan in particular, the elements of this bearing are currently arranged is such a way as to allow mounting from the rear. Such a solution, although advantageous, still has a number of drawbacks which it would be desirable to eliminate. 
         [0003]    With reference to  FIGS. 1 and 2 , a solution corresponding to the teaching of the prior art is reviewed. The engine assembly is not represented, only the immediate surroundings of the bearing being visible. The front and rear are defined with respect to the forward travel direction of the engine. Part of the fixed structure of the intermediate casing  2  is shown, with the ball bearing  3  of the HP compressor shaft being supported by its outer race in this fixed structure. The bearing rotationally supports the front end of the HP compressor shaft  4 , of which the journal  4 ′ and a rotor disk  4 ″ can be seen. The bearing supports at its front a bevel gear  5  which drives the gear  5 ′ connected to a radial shaft, forming the inlet gearbox (IGB) used to drive the auxiliary equipment: pumps, electrical current generators or the like. The bevel gear meshes, for this purpose, with the gear of the radial transmission shaft which is housed in one of the radial arms of the intermediate casing so as to drive the gears of the accessory gearbox (AGB). The bevel gear is fixedly connected to the cylindrical sleeve supported by the bearing. 
         [0004]    To maintain the shaft  4  in the bearing  3 , a nut  6  is provided according to the prior art and is retained inside the gear  5 , at the upstream end, by a segment or snap ring  6 ′. The nut comprises a thread on its external surface by means of which it is screwed inside the upstream end of the shaft  4 , this end being provided with a suitable thread. A nut retainer  6 ″, which is secured against rotation by axial splines in the shaft  4  and has flexible tabs which lock into a circular groove in the shaft  4 , prevents the nut from accidentally loosening. Furthermore, axial splines on the internal wall of the sleeve of the gear  5  cooperate with splines on the external surface of the shaft  4  to prevent any rotation of one with respect to the other. This mounting incorporates the auto-extraction function of the HP compressor. The function is provided by the segment which axially secures the bearing nut to the bevel wheel. Thus, by screwing the nut into the thread of the HP compressor shaft, the compressor is mated with the bearing; conversely, by unscrewing the nut, the compressor is pushed away rearwardly since the nut is blocked axially by the segment. 
         [0005]      FIG. 2  shows the bearing before the shaft  4  is mounted. The nut, arranged in front of the bearing, is mounted beforehand on the gear before any mounting of the elements from the rear of the intermediate casing. To prepare for the mounting of the shaft  4 , the bearing  3  is heated at C in order to expand it and minimize the shrinkage forces. To avoid heating the nut  6  and minimize the friction in the thread when tightening it on the shaft  4 , a thermal protection P is placed around the nut. However, this protection is complicated to implement. It cannot be installed effectively. 
       SUMMARY OF THE INVENTION 
       [0006]    The objective set by the applicant is to prevent the problems associated with this mounting. 
         [0007]    More specifically, the problem to be solved concerns a type of connection between the HP compressor and the engine IGB that allows mounting and demounting of the HP compressor with sole access for the tools from the rear of the engine. 
         [0008]    According to the invention, the system for fastening the end of a gas turbine engine shaft engaged inside a sleeve supported by a bearing, by means of a nut, is characterized in that the nut is screwed at one end inside said sleeve, and is connected by a segment-type connection with the shaft at the other end. 
         [0009]    The solution of the invention is thus suitable for mounting the HP compressor shaft of a twin-spool engine whose power take-off for driving the gearbox of the auxiliary machines is provided by a bevel gear fixed thereto, the sleeve belonging to this driving bevel gear. 
         [0010]    The solution of the invention makes it possible, by virtue of the segment-type connection, to retract the nut inside the shaft while the shaft is being mated with the bearing and then, by simply displacing the nut axially with the aid of a tool situated remotely to the rear, to bring the nut into contact with the front thread of the sleeve and to screw the nut to ensure fastening. Demounting of the HP compressor is also carried out in a simple manner by acting solely from the rear of the engine, and is not compromised by the mounting means and tools currently used. 
         [0011]    Mounting/demounting from the rear of the engine is a major advantage for this type of engine and considerably reduces the cost of such an operation. 
         [0012]    Furthermore, the solution is compact, it can be incorporated within the available space and does not interfere with the flow of air between the IGB and the LP shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will now be described in more detail with reference to the appended drawings, in which: 
           [0014]      FIG. 1  represents in axial section a partial view of a mounting solution corresponding to the teaching of the prior art; 
           [0015]      FIG. 2  shows the elements of  FIG. 1  preassembled and prior to the mounting of the HP compressor shaft; 
           [0016]      FIG. 3  represents in axial half-section a partial view of a system for fastening the end of the HP compressor shaft according to the invention; 
           [0017]      FIG. 4  shows the first step of the mounting seen from the IGB side upstream of the HP compressor shaft; 
           [0018]      FIG. 5  shows the first step of the mounting seen from the HP compressor shaft side; 
           [0019]      FIG. 6  shows the second step with the mating of the compressor shaft; 
           [0020]      FIG. 7  shows the more advanced engagement of the compressor shaft; 
           [0021]      FIG. 8  shows that the screwing of the retractable nut onto the sleeve of the bearing is completed and that the nut retainer as described in  FIG. 3  can be fitted. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]      FIG. 3  and the figures which follow show an embodiment of the solution of the invention. The bearing  3  remains unchanged with respect to the prior art, as does the intermediate casing  2 . The upstream end of the shaft  14 , forming a journal and belonging to the HP compressor rotor of a twin-spool turbine engine, has an inner annular channel or groove  14   1  in which there is housed a split annular segment  18  having a rectangular cross section in this case. The segment  18  cooperates with an axial stop surface  16   1  formed on the external surface of a nut  16 . This nut  16  is of cylindrical shape and connects the shaft  14  to a bevel wheel  15 . The bevel wheel  15  comprises a bevel gear  15   1  for driving the IGB. It also comprises a cylindrical sleeve  15   4  shrink-fitted with the inner race  3   i  of the bearing  3 . At its front, the wheel  15  is fixedly connected here to a labyrinth seal  15   2 . Splines  15   3  are formed internally to cooperate with splines  14   3  on the journal  14  and keep them fixed against rotation. The wheel  15  also comprises an internal portion having a cylindrical surface with a thread  15   f  with which the cylindrical nut  16  cooperates by way of a thread  16   f.    
         [0023]      FIG. 4  shows the bearing  3  with the bevel wheel  15  mounted on the inner race  3   i  of the bearing  3 , and a heating means C′ depicted by wavy lines. 
         [0024]    The front mounting of the HP compressor shaft in the bearing  3  will now be described with reference to  FIG. 4  and the figures which follow. 
         [0025]    The bearing is already assembled with the bevel wheel  15  shrink-fitted inside the race  3   i  of the bearing. The first step consists in heating the bearing  3  by placing a heater below the race  3   i . The advantage of the solution of the invention will already be appreciated since, in the absence of a nut, no unwanted heating will adversely affect the surrounding parts. 
         [0026]    At the same time, the nut  16  is fitted on the shaft as shown in  FIG. 5 . The nut  16 , of cylindrical general shape, has an external diameter equal to the internal diameter of the shaft  14 . It additionally comprises a transverse groove  16   2  of sufficient depth to ensure that the segment  18  will be housed entirely therein when it is deformed by radial compression and its diameter reduced. For this purpose, a sleeve  19  which keeps the segment  18  retracted has been engaged. The internal diameter of the sleeve  19  is the same as the internal diameter of the shaft. In this way, as can be seen from  FIG. 5 , in the retracted position the outside diameter of the segment allows it to slide inside and along the shaft  14 . The nut is slid until the segment  18  meets the groove  14   1 . By virtue of its elasticity the segment now adopts its natural shape and is pressed into the groove  14   1 . The groove  16   2  in the nut forms an axial stop which allows the segment to be brought up to the groove  14   1  in the shaft  14  and which prevents the nut from being inserted further forward into the shaft  14 . It can be observed that the shaft comprises a number of radial orifices  14   2  level with the groove in order, when it is desired to extract the nut from the shaft, to apply a tool by means of which the segment  18  can be retracted into the groove  16   2  in the nut. 
         [0027]      FIG. 6  shows that the shaft will be engaged in the bearing from which the heater has been removed and which is in the expanded state. The nut  16  is retracted and secured axially in the shaft  14  by the segment  18  which bears both in the channel  14   1  and against the stop formed by the groove  16   2 . 
         [0028]      FIG. 7  shows that the shaft has been completely engaged in the bearing  3 . The splines  14   3  cooperate with the splines  15   3  of the sleeve of the bevel wheel  15  so as to secure them against rotation. The front end  14   5  of the shaft butts against the rear labyrinth-forming part that bears on the inner race of the rolling bearing  3 . It can also be observed that the outer cylindrical surface of the end portion on the shaft  14  is engaged in an internal shrink-fitting surface of the wheel  15 . This arrangement provides effective support for the gear  15   1  to ensure that it will not deform and will turn round truly during operation. 
         [0029]    As can be seen from  FIG. 8 , the nut has been screwed by engaging the respective threads  15   f  of the bevel wheel  15  and  16   f  of the nut  16 . The screwing has been carried out by means of a suitable tool from the rear of the shaft  14 . This screwing has been carried out until the stop surface  16 , of the nut comes to bear against the segment  18  housed in the groove  14   1 . 
         [0030]    Returning to  FIG. 3 , it can be seen that the shaft now butts against the various internal shoulders of the bevel wheel. A nut retainer  17  has been fitted. It cooperates with the nut  16  by way of notches to prevent it from rotating with respect to the shaft. It comprises elastically deformable branches  17   1  which are housed in a groove  14   6  made in the shaft  14 . It is possible to observe the presence of the front part  15   2  of the bevel wheel which, together with a scoop  15   5 , forms a surface for receiving lubricating oil for the gear  15   1  and for the bearing  3 . The oil distribution nozzle is not represented. This oil collected by the scoop  15   5  is guided through longitudinal ducts  15   6 , between the splines  15   3  and some specially leveled splines  14   3 , toward the bearing  3  which is provided with known orifices suitable for lubricating the balls. 
         [0031]    The nut  16  may be termed retractable in so far as it is retracted into the shaft  14 . The nut is turned by known tools through the shaft particularly from the rear. To prevent forces from passing through the bearing, the bevel wheel can be clamped axially by means of a suitable tool which is placed, for example, in an axial clamping region formed between tenons  15   7 , produced at the front of the wheel to prevent any rotation during the mounting, and a shoulder  15   8 .