1. Technical Field of the Invention

A mechanical fuse breakable by twisting. The invention also relates to a cooling unit of a turbine engine fitted with such a mechanical fuse.

2. BACKGROUND

In many technical fields, in particular for aeronautical applications, it is often necessary to have mechanical couplings of trees that can break when subjected to these couplings are pairs of opposite forces that exceed a predetermined value. This feature helps protect downstream parts of these couplings. To do this, it is known to spare frangible sections twist on tree lines. Such frangible section by twisting has the particularity of being able to break when subjected to the action of a pair of opposing forces greater than a predetermined value.

A known solution to form a frangible section by twisting a shaft line is to use a solid shaft that has a local reduction of its diameter so that the small diameter portion can be broken when the torque exceeds a predetermined value.

One disadvantage of this solution is that when the frangible section breaks, it is necessary to replace the whole tree, which requires, for certain applications, to dismantle all bodies connected to this tree. This is particularly the case for turbine cooling groups. A cooling unit comprises a pinion and a wheel mounted cantilever on the shaft carrying the pinion. If the frangible section formed on the shaft by locally reducing the diameter of breaks, it is necessary to disassemble the pulley and the gear module connected to the cooling unit to be able to replace the drive shaft. This makes the maintenance and replacement of such complicated frangible section and impractical to implement.

Also, if the maximum torque is relatively low, which is the case e.g. impellers cooling groups, the frangible section can be small, which may impose mounting constraints (not the request) and operating constraints (dynamics of the transmission line, displacement under load maneuvers) important.

Another solution for household section by a frangible twist on a shaft line is to use a hollow shaft with a local reduction of material on its inner or outer wall. The disadvantages of the previous solution are still present with this solution. In addition, breaking sizing couple of this solution gives too small thicknesses to be well controlled.

Alternatively Shrinkfit a mechanical member on the other and control the sliding effort. One disadvantage of this solution is the difficulty to master the shift in the temperature operating range of the bodies concerned. This drawback makes this solution particularly poorly adapted to turbine cooling groups.

There is therefore a need for an improved solution to spare a frangible section in torsion in a mechanical coupling of organs in a turbine engine. One particular such a need is expressed, but not only for uses within the turbine cooling groups.

In particular, there is a need for a solution that allows replacement of the frangible section without particular difficulties and especially without requiring complete disassembly of the mechanical parts involved in this coupling.

3. Objectives of the invention

The invention aims to alleviate at least some of the disadvantages of known solutions to spare breakable by twisting sections within mechanical coupling in a turbine engine.

The invention also provides, in at least one embodiment of

the invention to provide a frangible section inherently more robust mounting and efforts in flexion.

The invention also aims to provide, in at least one embodiment of the invention, a frangible section which can be replaced without particular difficulties, by an operator.

The invention also aims to provide a cooling unit equipped with a frangible section of the invention.

4. Summary of the Invention

To do this, the invention relates to a mechanical fuse designed to be mounted integrally in a gas turbine engine between a mechanical member driving said drive member and a driven mechanical member, said receiver member, each rotating about a same rotational axis.

The fuse according to the invention comprises a body extending along a longitudinal direction parallel to said axis of rotation, once the fuse connected between said motor and receptor bodies.

The fuse according to the invention is characterized in that said body comprises a plurality of longitudinal bars, each bar being adapted to be deformed by bending, under the action of a torque applied to all of the webs, so to form a mechanical fuse frangible.

The invention therefore provides a new way to arrange a frangible section by twisting in a mating mechanical components in a turbine engine. This solution is to use a mechanical fuse which is an insert that will connect the two mechanical members with each other. This insert can be replaced in case of breakage of the frangible section. This mechanical fuse has the particularity of comprise a plurality of bars each deformable in flexion under the action of a torque. This set of longitudinally arranged strips to the axis of rotation of the mechanical members connected by the fuse forms a frangible fuse by twisting. In other words, the torsional resistance of the fuse depends on the flexural strength of the webs. A fuse according to the invention allows to increase the bending stiffness, which reduces the sensitivity to unbalance. In

other words, a fuse according to the invention enables to form a frangible section twist that is less likely that the frangible sections of the prior art to break inappropriately.

In addition, a fuse according to the invention allows an improved dimensioning of the frangible section by determining the number of strips, the length of the webs, the width of the webs, the thickness of the webs of the cross section of bars, and generally of all the dimensional and geometrical characteristics of the modules.

Advantageously, a mechanical fuse according to the invention comprises reversible coupling means of the fuse to said drive member arranged at a longitudinal end of said body, said distal end.

Advantageously and according to the invention said distal end of said body has a cylindrical portion or a tapered portion, formed to a cylindrical or conical portion of said drive member. These portions form the reversible coupling means.

A conical or cylindrical linkage between the mechanical fuse and the drive member ensures a minimum eccentricity, which allows to limit the unbalance of the receiver. In particular, in the case of using the mechanical fuse according to this embodiment as connecting piece between a pinion of a cooling group and an impeller mounted cantilevered on the pinion through the mechanical fuse, the conical connection forms an equilibration reference. This ensures that the connection between the gear and the wheel can be repeated identically in each assembly.

Advantageously, a fuse according to the invention comprises reversible coupling means of the fuse to said receiving member arranged at a longitudinal end of said body, said proximal end.

Advantageously and according to the invention, said proximal end of said body includes a mounting plate adapted to be fixed on said receiving member. This bracket forms the reversible coupling means.

The assembly and disassembly of a mechanical fuse according to this embodiment is particularly easy. In addition, through use of a cooling unit of a turbine engine, the fuse can be removed and replaced without requiring disassembly of the group including the gearbox.

Advantageously and according to the invention, the body is hollow.

A hollow body serves in particular to pass fasteners in the center of the body. Using strips keeps readily machinable material thicknesses and sized to control the torque out of range of the frangible section. These fasteners include, for example a nut or a screw which is received in the hollow body to the distal end of the fuse. These fasteners contribute to the assembly of the fuse on the driving member in connection with the conical portions.

Advantageously and according to this variant, the mechanical fuse comprises a spacer adapted to be housed in said hollow body by said proximal end and to be able to support said tapered portion of the distal end of said conical portion conjugated said drive member,

The use of a spacer allows to limit the internal diameter of the mechanical fuse for access to the fastening elements of the screw / nut type. In addition, this support of the tapered portion of the distal end on the conical portion of the drive member ensures the driving in rotation of the driven member by the drive member through the mechanical fuse.

Advantageously and according to this variant, said spacer has a shoulder to limit axial movement of said driven member in the event of mechanical failure of the fuse.

A shoulder formed on Γ spacer will block axial movement of the receiving member in the event of rupture of the breakable section formed by the mechanical fuse.

According to another variant, the mechanical fuse comprises a screw housed directly in said hollow body to support said tapered portion of the distal end on the conical portion conjugated said motor member.

Advantageously and according to the invention, the body is cylindrical and the fuse comprises three webs uniformly distributed around said body.

Of course, in other variants, the mechanical fuse can

comprise more than three modules.

The invention also relates to a cooling unit of a gas turbine engine comprising a drive shaft and an impeller mounted cantilevered on said shaft, characterized in that it comprises a mechanical fuse according to the invention.

The invention also relates to a mechanical fuse and a cooling unit for a gas turbine engine characterized in combination by all or some of the features mentioned above or below.

5. List of Figures

Other objects, features and advantages of the invention will appear on reading the following description given by way of non-limiting and which refers to the appended figures in which:

- Figure 1 is a schematic sectional view of a cooling unit of a turbine engine according to the prior art view including a motor shaft, an impeller mounted cantilevered on this shaft and a frangible section by torsion formed by a reduction diameter of the drive shaft,

- Figure 2 is a schematic sectional view of a cooling unit of a turbine engine according to an embodiment of the invention including a motor shaft, an impeller mounted overhung on the shaft, and a frangible section by torsion formed by a mechanical fuse according to one embodiment of the invention,

- Figure 3 is a perspective view of a mechanical fuse according to one embodiment of the invention,

- Figures 4a and 4b are schematic views respectively in section and from above of a bar with a mechanical fuse according to one embodiment of the invention.

6. Description of an embodiment of the invention In the figure, the scales and proportions are not strictly complied with, for purposes of illustration and clarity. Throughout the following detailed description with reference to the figures, unless otherwise indicated, each element of the mechanical fuse is described as it is arranged when the fuse is mounted in a cooling unit of a turbine engine, between the engine gear group and the impeller of the cooling unit mounted cantilevered on the pinion. This arrangement is shown in Figure 2.

A cooling unit of the prior art is shown partially in Figure 1. The cooling unit 8 comprises a sprocket mounted on a shaft 9 and a wheel 10 mounted cantilever on the shaft 9. The pinion 8 and shaft 9 are formed integrally so that means throughout the following description, interchangeably, the pinion 8 and the shaft 9, to designate the assembly formed by the pinion 8 and the shaft 9. this mechanical coupling between the impeller 9 and the shaft 10 includes a frangible section 11 by torsion, formed by reducing the diameter of the shaft 9. this frangible section is typically embodied by a local reduction of the diameter of the shaft 9 to about 5 mm.

It is clear from Figure 1 that when the frangible section 11 is broken, it is necessary to replace the shaft 9. In addition, to access the shaft 9, it is necessary to disassemble the mechanical members connected upstream of the gear, such as a gear, not shown in the figures for clarity, and the pulley 10.

Figure 2 is a schematic view of the same cooling unit 11 wherein the frangible section has been replaced with a mechanical fuse 12 according to one embodiment of the invention. The shape of the impeller 10 and the shape of the shaft 9 have been slightly modified for mounting of the mechanical fuse of the invention.

In particular, the mechanical fuse comprises a hollow body 13, a distal end 20 configured to be brought into abutment against one end of the shaft 9, and a proximal end 21 configured to be assembled to the wheel 10.

To do this, the distal end 20 includes an inner tapered portion (tapered portion that is visible in Figure 2) which is shaped to a conical portion 22 formed at the end of the shaft 9. In addition, a screw 23 can be accommodated in the hollow body 13 by the proximal end 21 in order to fixedly attach the mechanical fuse 12 and the shaft 9. for this purpose, the conical portion 22 of the shaft 9 has a threaded bore adapted to receive the screw 23.

The screw 23 and the tapered portions 20, 22 form the means for assembling the fuse 13 of the shaft 9.

The proximal end 21 of the fuse 25 includes a fastening plate. This plate comprises four bores 26, each bore being able to receive a hooped pin 27 for fixing the impeller 10 of the fixing plate. To do this, the impeller 10 also includes bores arranged opposite bores 26 of the bracket.

To facilitate the support of the tapered portions, the fuse further comprises a spacer 29 housed in the body 13. The housing of this spacer 29 is through the proximal end of the mechanical fuse. This spacer keeps bearing the conical portion 22 of the shaft 9 by the distal end 20 of conical shape of the fuse. A radial clearance is provided between Γ spacer 29 and the body 13 of the mechanical fuse 12 to avoid friction and ensure rupture at the desired torque of the fuse.

This spacer 29 also has a shoulder 30 to limit axial movement of the impeller 10 in the event of mechanical failure of the fuse. An axial clearance is provided between shoulder 30 of Γ Γ spacer 29 and the plate 25 of the mechanical fuse to avoid friction and ensure rupture at the desired torque of the fuse.

The mechanical fuse according to the embodiment of Figures further comprises, and as shown in more detail in Figure 3, three longitudinal strips 14 uniformly distributed around the hollow body 13, each bar 14 being adapted to be deformed in flexion. The bars 14 show the torque associated with the drive of the impeller 10 by the pinion 8 and working in bending.

Figures 4a and 4b are schematic views of a bar 14 and its bending deformation. As shown, if a torque C is applied to the fuse, then each bar is subjected to a tangential force F in the hollow body 13. This force F is such that C = NRf, where r is the radius of the neutral axis with respect to the axis 7 of rotation and n is the number of strips (in the present case, n = 3). According to the theory of dual-flush beams, bending the moment M

maximum is defined by the relation M = FL / 2, where L is the length of a strip. Figure 4b is a top view of the bar 14 subjected to the force F. The strip deforms in bending. One can then determine a failure criterion of the webs when the stress value in the section of the beam is equal to the maximum stress regardless of the beam area. This value depends on the plasticization of the web and dispersion of the materials.

According to the embodiment of the figures, each bar 14 has a rectangular transverse cross-section whose length is 2.95 mm and width of 2.9 mm. The neutral axis is located on a radius of 6.475 mm relative to the axis 7 of the shaft. In addition, each strip has a length of 11.85 mm. Of course, these dimensions are only exemplary and the invention is not limited to this single embodiment. Calculations show with stainless steel strips, a range of torque Out of 18.3 Nm 40.5 Nm. Furthermore, the experiments show that under a radial load of 100 N, a 15453 bending stiffness N / mm is obtained, much better than the stiffness of 7545 N / mm in the prior art.

The invention is not limited to the embodiments described. In particular, a mechanical fuse may comprise more than three lugs and equip other couplings as the couplings of turbine cooling group.

CLAIMS

1. mechanical fuse designed to be mounted integrally in a gas turbine engine between a mechanical member driving said driving member (8, 9) and a driven mechanical member, said receiver member (10), each rotating about a same axis (7 ) of rotation, said fuse comprising a body (13) extending in a longitudinal direction parallel to said axis (7) of rotation once the fuse connected between said motor means (8, 9) and receiver (10),

characterized in that said body (13) comprises a plurality of webs (14) longitudinal, each lug (14) being adapted to be deformed by bending, under the action of a torque applied to all of the webs, so as to form a mechanical fuse frangible.

2. A fuse according to Claim 1, characterized in that it comprises reversible means for coupling the fuse to said motor member (8, 9) arranged at a longitudinal end of said body (13), said distal end (20).

3. mechanical fuse according to claim 2, characterized in that said distal end of said body (13) has a tapered portion or a cylindrical portion, formed in a tapered portion (22) or a cylindrical portion of said drive member.

4. Fuse according to one of claims 1 to 3, characterized in that it comprises reversible means for coupling the fuse to said receiver member (10) arranged at a longitudinal end of said body (13), said proximal end ( 21).

5. mechanical fuse according to claim 4, characterized in that said proximal end of said body (13) comprises a plate (25) for fixing adapted to be secured on said receiver member (10).

6. mechanical fuse according to one of claims 1 to 5, characterized in that said body (13) is hollow.

7. mechanical fuse according to Claims 3, 4 and 6 taken together, characterized in that it comprises a spacer (29) adapted to be housed in said hollow body (13) by said proximal end (21) and to put in supporting said conical portion of the distal end (20) on said conical portion (22) coupled said drive member (8, 9).

8. A fuse according to Claim 7, characterized in that said spacer (29) has a shoulder (30) for limiting axial movement of said receiver member (10) in case of mechanical failure of the fuse.

9. A fuse according to one of claims 1 to 8, characterized in that said body (13) is cylindrical and in that it comprises three webs (14) uniformly distributed around said body (13).

10. A cooling system for a turbine engine comprising a drive shaft (9) and an impeller (10) mounted in cantilever fashion on said shaft (9), characterized in that it comprises a fuse (12) mechanically according to the one of claims 1 to 9 arranged between said motor shaft (9) and said impeller (10).