System for connecting an engine shaft with a retractable nut

A system for fastening the end of a gas turbine engine shaft engaged inside a sleeve supported by a bearing is disclosed. The system includes a nut that is screwed at one end inside the sleeve, and is connected by a split annular ring with the shaft at the other end.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART

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.

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.

With reference toFIGS. 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 casing2is shown, with the ball bearing3of 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 shaft4, of which the journal4′ and a rotor disk4″ can be seen. The bearing supports at its front a bevel gear5which drives the gear5′ 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.

To maintain the shaft4in the bearing3, a nut6is provided according to the prior art and is retained inside the gear5, at the upstream end, by a segment or snap ring6′. The nut comprises a thread on its external surface by means of which it is screwed inside the upstream end of the shaft4, this end being provided with a suitable thread. A nut retainer6″, which is secured against rotation by axial splines in the shaft4and has flexible tabs which lock into a circular groove in the shaft4, prevents the nut from accidentally loosening. Furthermore, axial splines on the internal wall of the sleeve of the gear5cooperate with splines on the external surface of the shaft4to 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.

FIG. 2shows the bearing before the shaft4is 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 shaft4, the bearing3is heated at C in order to expand it and minimize the shrinkage forces. To avoid heating the nut6and minimize the friction in the thread when tightening it on the shaft4, 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

The objective set by the applicant is to prevent the problems associated with this mounting.

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.

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.

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.

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.

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.

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.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3and the figures which follow show an embodiment of the solution of the invention. The bearing3remains unchanged with respect to the prior art, as does the intermediate casing2. The upstream end of the shaft14, forming a journal and belonging to the HP compressor rotor of a twin-spool turbine engine, has an inner annular channel or groove141in which there is housed a split annular segment18having a rectangular cross section in this case. The segment18cooperates with an axial stop surface161formed on the external surface of a nut16. This nut16is of cylindrical shape and connects the shaft14to a bevel wheel15. The bevel wheel15comprises a bevel gear151for driving the IGB. It also comprises a cylindrical sleeve154shrink-fitted with the inner race3iof the bearing3. At its front, the wheel15is fixedly connected here to a labyrinth seal152. Splines153are formed internally to cooperate with splines143on the journal14and keep them fixed against rotation. The wheel15also comprises an internal portion having a cylindrical surface with a thread15fwith which the cylindrical nut16cooperates by way of a thread16f.

FIG. 4shows the bearing3with the bevel wheel15mounted on the inner race3iof the bearing3, and a heating means C′ depicted by wavy lines.

The front mounting of the HP compressor shaft in the bearing3will now be described with reference toFIG. 4and the figures which follow.

The bearing is already assembled with the bevel wheel15shrink-fitted inside the race3iof the bearing. The first step consists in heating the bearing3by placing a heater below the race3i. 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.

At the same time, the nut16is fitted on the shaft as shown inFIG. 5. The nut16, of cylindrical general shape, has an external diameter equal to the internal diameter of the shaft14. It additionally comprises a transverse groove162of sufficient depth to ensure that the segment18will be housed entirely therein when it is deformed by radial compression and its diameter reduced. For this purpose, a sleeve19which keeps the segment18retracted has been engaged. The internal diameter of the sleeve19is the same as the internal diameter of the shaft. In this way, as can be seen fromFIG. 5, in the retracted position the outside diameter of the segment allows it to slide inside and along the shaft14. The nut is slid until the segment18meets the groove141. By virtue of its elasticity the segment now adopts its natural shape and is pressed into the groove141. The groove162in the nut forms an axial stop which allows the segment to be brought up to the groove141in the shaft14and which prevents the nut from being inserted further forward into the shaft14. It can be observed that the shaft comprises a number of radial orifices142level 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 segment18can be retracted into the groove162in the nut.

FIG. 6shows that the shaft will be engaged in the bearing from which the heater has been removed and which is in the expanded state. The nut16is retracted and secured axially in the shaft14by the segment18which bears both in the channel141and against the stop formed by the groove162.

FIG. 7shows that the shaft has been completely engaged in the bearing3. The splines143cooperate with the splines153of the sleeve of the bevel wheel15so as to secure them against rotation. The front end145of the shaft butts against the rear labyrinth-forming part that bears on the inner race of the rolling bearing3. It can also be observed that the outer cylindrical surface of the end portion on the shaft14is engaged in an internal shrink-fitting surface of the wheel15. This arrangement provides effective support for the gear151to ensure that it will not deform and will turn round truly during operation.

As can be seen fromFIG. 8, the nut has been screwed by engaging the respective threads15fof the bevel wheel15and16fof the nut16. The screwing has been carried out by means of a suitable tool from the rear of the shaft14. This screwing has been carried out until the stop surface16, of the nut comes to bear against the segment18housed in the groove141.

Returning toFIG. 3, it can be seen that the shaft now butts against the various internal shoulders of the bevel wheel. A nut retainer17has been fitted. It cooperates with the nut16by way of notches to prevent it from rotating with respect to the shaft. It comprises elastically deformable branches171which are housed in a groove146made in the shaft14. It is possible to observe the presence of the front part152of the bevel wheel which, together with a scoop155, forms a surface for receiving lubricating oil for the gear151and for the bearing3. The oil distribution nozzle is not represented. This oil collected by the scoop155is guided through longitudinal ducts156, between the splines153and some specially leveled splines143, toward the bearing3which is provided with known orifices suitable for lubricating the balls.

The nut16may be termed retractable in so far as it is retracted into the shaft14. 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 tenons157, produced at the front of the wheel to prevent any rotation during the mounting, and a shoulder158.