Propulsion unit for an aircraft

Abstract

Aircraft turbomachine (10) comprising: - an engine (12), - an annular panel (16) which extends around the engine (12), - a structure (14) for supporting the engine (12), - an annular duct (18) for the flow of a gas flow (F12) between the panel (16) and the structure (14), - a mast (20) for connecting the panel (16) to the structure (14), and - a device (22) for fastening the mast (20) to the panel (16), this device (22) comprising a fitting (24) which is fastened by first screws (26) to the mast (20) and by second screws (28) to the panel (16), the first screws (26) being screwed into nuts (32) which are mounted inside at least one internal cavity (40) of the mast (20), this internal cavity (40) being situated radially at the duct (18).

Description

[0001]DESCRIPTION TITLE: PROPULSION ASSEMBLY FOR AN AIRCRAFT Technical Field of the Invention The present invention relates to a propulsion assembly for an aircraft and, more particularly, to the connection of the engine of the propulsion assembly to an engine support structure. Technical Background The technical background includes, in particular, documents US-A-5,224,341, US-A1-2013 / 115051 and US-A1-2013 / 115057. A propulsion assembly is attached to an aircraft by a rigid connection that is likely to cross a gas flow duct. It is therefore important to minimize as much as possible the aerodynamic impact of this connection on the duct and on the gas flow. Figure 1 schematically shows the arrangement of an engine 12 of a propulsion assembly 10 with respect to a support structure 14 which is intended to be attached to the aircraft (not shown). The engine 12, of the turbomachine type, has an elongated shape or extends along a first axis A and an annular panel 16 extends around theengine 12 and the first axis A. The rib 18 extends around the engine 12 and the first axis A and is radially interposed between the panel 16 and the structure 14. A connecting strut 20 from the panel 16 to the structure 14 extends radially through the rib 18. As seen in Figure 2, the connection of the strut 20 to the panel is achieved by a fastening device 22 which is relatively bulky in the radial direction and therefore results in a significant radial spacing between the panel 16 and the engine 12. The invention proposes a solution to reduce and minimize this spacing as much as possible and therefore the bulk of the fastening device 22. Summary of the invention The invention relates to an aircraft propulsion assembly, comprising: - an engine extending along a first axis, - an annular panel extending around the engine and the first axis, - an engine support structure, - an annular flow channel of gas that extends around the engine and theThe first axis, the rib being radially interposed between the panel and the structure, - a connecting mast of the panel to the structure, the mast extending radially through the rib, and - a device for fixing the mast to the panel, this device comprising a fitting which is fixed by first screws to the mast and by second screws to the panel, characterized in that the first screws are screwed into nuts which are mounted inside at least one internal cavity of the mast, this internal cavity being located radially at the level of said rib. The location of the nuts at the level of the rib makes it possible to limit the radial bulk of the first screws and therefore of the fixing device as a whole. The turbomachine according to the invention may include one or more of the following features, taken individually or in combination with each other: - the first screws are of the countersunk type, each of the first screwsbeing engaged radially from the inside of a hole in the fitting and comprising a frustoconical head engaged in a recess of complementary shape to said hole; the invention thus proposes using special screws for fixing the device to the mast, namely countersunk screws. These screws have the particularity of being compact because their heads are adapted to be engaged in recesses of the holes in which they are mounted so that the ends of these heads are flush with the surface on which these recesses are formed; − the fitting has a generally flat or curved shape and is applied radially against the panel; − the second screws are of the countersunk type, each of the second screws being engaged radially from the outside of a hole in the panel and in a hole in the fitting and comprising a frustoconical head engaged in a recess of complementary shape to said holethe opening in the panel, and in that the second set of screws is screwed into nuts that are tightened against the fitting; said nuts are barrel nuts that are mounted inside the mast and have at least one degree of freedom within the mast; the invention further proposes using barrel nuts for tightening these screws. The advantage of barrel nuts is that they retain one or more degrees of freedom and allow the screws to be tightened blindly. The barrel nuts are housed inside the mast and therefore do not create any particular bulk on the outside of the mast; in the present application, a barrel nut is understood to be a nut that has a generally cylindrical or part-cylindrical shape and that includes a threaded bore that extends transversely with respect to the cylindrical or part-cylindrical surface. The thread axis, and therefore the screwing axis, is thus perpendicular to the axis of revolution of the surface.cylindrical or in the form of a portion of a cylinder; a barrel nut is also called a barrel nut or cannon nut; - the barrel nuts are each oriented so as to have one degree of freedom in rotation about a second axis parallel to said first axis; - the barrel nuts each have degrees of freedom in a plane perpendicular to an axis radial to the first axis; - the barrel nuts are arranged one behind the other along the first axis; - said at least one cavity is located in an oversized or thickened radially internal end of the mast; - the barrel nuts are carried by at least one nut support which is mounted inside said at least one cavity; - the nut support or each nut support is engaged in said at least one cavity by axial translation in a direction parallel to the first axis; - the nut support(s) has a shape complementary to that of said at least one cavity, and has, for example, a general shapecylindrical or circular in cross-section; - the nut support(s) comprise at least one lug capable of cooperating by elastic snap-fit ​​with at least one hole of complementary shape in the mast to ensure that the support(s) are held in position within the mast; the snap-fit ​​ensures the axial and circumferential positioning and retention of the support within the mast bore; - the nut support(s) comprise a body having several adjacent recesses in which the barrel nuts are mounted respectively, each of these barrel nuts comprising a nut movably mounted in a ring in the form of a cylindrical portion, the ring itself being movable in the corresponding recess of the body; - each nut comprises an external annular flange extending around a screw axis and slidably mounted in an annular groove of the corresponding ring, radial clearance being provided between the flange and a baseof the groove so as to allow degrees of freedom of the nut in the ring in a plane perpendicular to the screw axis; -- each ring comprises an external surface in the form of a portion of a cylinder and is rotationally movable in the housing of the body around an axis of revolution of this external surface, the ring being able to cooperate by means of a stop with the body to limit its travel around this axis of revolution. Brief description of the figures Other features and advantages of the invention will become apparent during the reading of the detailed description that follows, for the understanding of which reference should be made to the accompanying drawings in which: [Fig. 1] Figure 1 is a very schematic partial axial cross-sectional view of an aircraft turbomachine; [Fig. 2] Figure 2 is a very schematic partial cross-sectional view of an aircraft turbomachine; [Fig. 3] Figure 3 is a very schematic partial cross-sectional view of a turbomachineof an aircraft and illustrates an embodiment of the invention; [Fig. 4] Figure 4 is a very schematic partial axial cross-sectional view of the aircraft turbomachine of Figure 3; [Fig. 5] Figure 5 is a larger-scale and more detailed view of Figure 4; [Fig. 6] Figure 6 is a cross-sectional view along line AA of Figure 5; and [Fig. 7] Figure 7 is a cross-sectional view along line BB of Figure 5; [Fig. 8] Figure 1 illustrates an axial cross-section of an example of a propulsion assembly according to the invention. Detailed description of the invention Figures 1 and 2 have been described above. Figure 8 represents a propulsion assembly 10 in which the engine 12 is a turbomachine comprising an unducted propeller 62. Such a turbomachine is a turboprop and is known by the English terms "open rotor" or "unducted fan" or "open fan". Within this category of turbomachine, there are those with two unfaired propellers andCounter-rotating (known by the English acronym UDF for "Unducted Dual Fan") or those having a single unducted propeller and an unducted stator comprising several stator blades (known by the English acronym USF for "Unducted Single Fan"). Of course, the invention applies to other types of turbomachinery such as turbojets, and in particular twin-spool and twin-spool turbojets. In the present invention, and generally, the terms "upstream," "downstream," "axial," and "axially" are defined with respect to the gas flow within the turbomachine and with respect to the longitudinal axis A of the turbomachine 1. Similarly, the terms "radial," "radially," "internal," and "external" are defined with respect to a radial axis perpendicular to the longitudinal axis A and with respect to the distance from the longitudinal axis A. In Figure 1, the turbomachine comprises, from upstream to downstream, a low-pressure compressor or ("booster").(English) 63, a high-pressure compressor 64, a combustion chamber 65, a high-pressure turbine 66, and a low-pressure turbine 67. The rotors of the low-pressure compressor 63 and the low-pressure turbine 67 are mechanically connected by a low-pressure shaft 68 to form a low-pressure housing. The rotors of the high-pressure compressor 64 and the high-pressure turbine 66 are mechanically connected by a high-pressure shaft 69 to form a high-pressure housing. The low-pressure shaft 68 extends inside the high-pressure shaft and is coaxial with the longitudinal axis A. The propeller 62 is mounted upstream of the low-pressure compressor 63 (and preferably on its upstream portion). The propeller 62 comprises a plurality of movable blades 70 arranged around the longitudinal axis A and extending radially from an internal housing 71 forming the hub of the propeller 62. A straightener 72 is disposed downstream of the propeller 62. The straightener 72 comprises aA plurality of stator blades 73 (or fixed blades) known by the English acronym "OGV" for Outlet Guide Vane. In the present invention, the term "stator blade" or "fixed blade" refers to a blade that is not driven in rotation about the longitudinal axis A of the turbomachine. The stator blades 73 are distributed around the longitudinal axis A and are arranged downstream of the moving blades 70 of the propeller 62 so as to straighten the airflow generated by the latter. The airflow F passing through the propeller 62 is split into a primary flow F1 and a secondary flow F2 by a separation nozzle 74. The primary airflow F1 flows in a primary flow channel 75, while the secondary flow F2 flows radially outside the primary flow channel 75. In particular, the secondary flow F2 flows radially outside the casings and sweeps the unshod stator 72. In the case of a turbofan engine comprising shod movable blades 70, theSecondary flow F2 circulates in a secondary flow channel. In Figure 1, the primary flow F1 splits into a radially internal flow F11 and a radially external flow F12. This split is achieved by means of an annular splitting nozzle 76. This nozzle is advantageously, but not exclusively, positioned downstream of the separation nozzle 74. The radially internal flow F11 circulates within the primary flow channel 75 and, in particular, within the splitting nozzle 76. The primary flow channel 75 extends downstream, opening into a primary nozzle 77 through which the gases from the combustion chamber 65 are ejected. The radially external flow F12 circulates radially outside the dividing spout 76 in an external flow channel 18. In other words, the external flow channel 18 is arranged at least partially radially outside the primary flow channel 75. The radially external flow opens atThe turbomachine is exhausted by an ejection nozzle 79. The propulsion assembly 10 further includes a support structure 14 for the engine 12. The structure 14 can be, for example, a mast or a pylon for attaching the engine to the aircraft. In the case of Figure 1, it can be seen that the duct 18 is radially interposed between the panel 16 and the structure 14. Alternatively, it could be another duct. Depending on the configuration of the engine 12, the duct 18 could indeed be a secondary or tertiary flow duct, for example. The propulsion assembly 10 also includes a mast 20 for connecting the panel 16 to the structure 14. The mast 20 extends radially through the channel 18. Area W in Figure 1 is an example of the integration area of ​​the mast 20. Reference is now made to Figures 3 to 7, which illustrate one embodiment of the invention. The propulsion assembly 10 further includes a device 22 for attaching the mast 20 to the panel 16. This device22 comprises a fitting 24 which is fixed by first screws 26 to the mast 20 and by second screws 28 to the panel 16. According to the invention, the first screws 26 are of the countersunk head type. Each of the first screws 26 is engaged in an opening 30 of the fitting 24 radially from the inside and comprises a frustoconical head 26a which is engaged in a recess 30a of a shape complementary to the opening 30. In addition, the first screws 26 are screwed into barrel nuts 32 which are mounted inside the mast 20 and which have at least one degree of freedom inside the mast 20. The fitting 24 is advantageously as compact as possible. For this purpose, it can have a generally flat or curved shape and be applied radially against the panel 16. In the example shown, the radially internal end 20a of the mast 20 passes through a slot 34 in the panel 16, and this slot 34 is covered by the fitting 24, which is attached from the inside.on panel 16. The fitting 24 is supported by its outer periphery on panel 16 and in particular an internal surface 16a of panel 16. The second screws 28 for fixing the fitting 24 to panel 16 are preferably also of the countersunk head type, as seen in the drawings. Each of the second screws 28 can be engaged radially from the outside into an opening 36 in the panel 16 and into an opening 38 in the fitting 24, for example from the channel 18. Each of the second screws 28 comprises a frustoconical head 28a which is engaged in a recess 36a of complementary shape to the opening 36 in the panel 16, such that the ends of the screws 28 are flush with the external surface 16b of the panel 16 and do not disrupt the flow of the flux F12 in the channel 18. The second screws 28 can be screwed into nuts 39 which are tightened against the fitting 24. These nuts 38 can thus be radially interposed between the fitting 24 and the motor 12.The barrel nuts 32 are preferably each oriented so as to have one degree of freedom in rotation about an axis B parallel to the first axis A. The barrel nuts 32 may each have degrees of freedom in a plane P perpendicular to an axis radial to the first axis A. In the example shown, the barrel nuts 32 are arranged one behind the other along the first axis A. In the aforementioned case where they are free to rotate, their axes B of rotation coincide, as can be seen in the drawings. The barrel nuts 32 are preferably mounted in at least one internal cavity 40 of the mast 20, which may be located at the radially internal end 20a of the mast 20. This end 20a may be oversized or thickened in order to provide this internal cavity 40. Advantageously, the barrel nuts 32 are supported by at least one nut support 42 which is mounted inside the mast 20, and in particular in the aforementioned cavity 40.The nut support 42 is advantageous for several reasons. First, it facilitates the mounting and securing of the barrel nuts 32 in the mast 20. It also prevents the barrel nuts 32 from accidentally coming out of the mast 20, thus making them captive. Furthermore, it can be configured to allow or permit varying degrees of freedom of the barrel nuts 32 relative to the mast 20. In the example shown, the number of screws 26 is four, although this example is not exhaustive. And the number of supports 42 is two, each support 42 carrying two barrel nuts 26. Naturally, a single support 42 could be used for all four barrel nuts 26. In the drawings, it is further shown that each of the supports 42 is engaged in an internal cavity 40 of the mast 20, which therefore comprises two cavities 40. The cavities 40 are formed one after the other, and eachfrom an opposite end of the mast 20. For example, one of the cavities 40 is formed from an upstream end of the mast 20, and the other cavities 40 are formed from a downstream end of the mast 20 (with reference to the flow of flux F12 in the channel 18). The nut support(s) 42 can be engaged in the corresponding cavity 40 by axial translation in a direction parallel to the first axis A. The nut support(s) 42 preferably have a shape complementary to that of the corresponding cavity 40. In the example shown, the nut support(s) 42 have a generally cylindrical shape or a circular cross-section. As can be seen in Figures 5 and 6, the nut support(s) 42 may include at least one lug 44 adapted to cooperate by elastic snap-fit ​​with at least one hole 46 of complementary shape in the mast 20 to ensure that the support(s) 42 are held in position within the mast 20. The support(s)The nut support 42 may, for example, include two lugs 44 of this type diametrically opposed with respect to axis B, and engaged in separate holes 46 in the mast 20. It is therefore understood that, to remove the nut support 42, it will be necessary to move one or both lugs 44 to extract them from the corresponding hole 46. This will allow the nut support 42 to be moved again in translation parallel to axis A. Figures 5 to 7 show an example of an embodiment of a nut support 42. The nut support 42 may include a body 48 which has several adjacent recesses 50 in which the barrel nuts 32 are mounted respectively. Each barrel nut 32 has a nut 32a mounted in a ring 32b in the form of a cylindrical portion. Preferably, the nut 32a is movable relative to the ring 32b, and the ring 32b is movable in the corresponding housing 50 of the body 48. Each nut 32a may include an external annular collar 52 extending around an axis C and which isThe nut is mounted slidingly in an annular groove 54 of the corresponding ring 32a. The axis C is the screwing axis of the corresponding screw 26. A radial clearance J is preferably provided between the flange 52 and a bottom 54a of the groove 54 so as to allow degrees of freedom of the nut 32a in the ring 32b in the aforementioned plane P perpendicular to the screwing axis C. The nuts 32 are thus of the floating type in the rings 32b. Each ring 32b may comprise an external surface 56 in the form of a portion of a cylinder and be rotatable in the housing 50 of the body 48 about the axis of revolution of this external surface 56, which is the axis B in the example shown. The ring 32b is preferably adapted to cooperate by means of a stop with the body 48 to limit its displacement stroke around this axis B. Stop elements 58 of the ring 32b and the body 48 are schematically represented for this purpose in Figure 7. The fastening device 22 can be assembled and used in this way.Next, the nuts 32a are mounted in their respective rings 32b to form the barrel nuts 32, which are then mounted in the recesses 50 of the body 48. The nut holder(s) 42, fitted with the barrel nuts 32, is then mounted in the corresponding cavity 40 until the lug(s) 44 cooperate with the corresponding hole 46. The fitting 24 is applied against the panel 16, and then the screws 26, 28 are mounted. The screws 26 pass through the holes 30 of the fitting 24 and are blindly mounted in the barrel nuts 32 which are aligned, here radially, with the holes 30. The degree(s) of freedom of the barrel nuts 32 facilitate the screwing and tightening of the screws 26. It is the cavity 40 of the mast 20 or the support 32 which prevents the rings 32b from rotating (and therefore the nuts 32a) during screwing.

Claims

CLAIMS 1. Propulsion assembly (10) for an aircraft, comprising: - an engine (12) extending along a first axis (A), - an annular panel (16) extending around the engine (12) and the first axis (A), - a support structure (14) for the engine (12), - an annular gas flow channel (18) extending around the engine (12) and the first axis (A), the channel (18) being radially interposed between the panel (16) and the structure (14), - a mast (20) connecting the panel (16) to the structure (14), the mast (20) extending radially through the channel (18), and - a device (22) for attaching the mast (20) to the panel (16), this device (22) comprising a fitting (24) which is fixed by first screws (26) to the mast (20) and by second screws (28) to the panel (16), characterized in that the first screws (26) are screwed into nuts (32) which are mounted inside at least one internal cavity (40) of the mast (20),1. Turbomachine (10) according to claim 1, wherein the first screws (26) are of the countersunk head type, each of the first screws (26) being engaged radially from the inside in an orifice (30) of the fitting (24) and comprising a frustoconical head (26a) engaged in a recess (30a) complementary in shape to said orifice (30).

2. Turbomachine (10) according to claim 1 or 2, wherein the fitting (24) has a generally flat or curved shape and is applied radially against the panel (16).

4. Turbomachine (10) according to any one of the preceding claims, wherein the second screws (28) are of the countersunk head type, each of the second screws (28) being engaged in an orifice (36) of the panel (16) and in an orifice (38) of the fitting (24), radially from the outside and comprising a frustoconical head (28a) which is engaged in a recess,(36a) of a shape complementary to the opening (36) of the panel (16), and in that the second screws (28) are screwed into nuts (39) which are tightened against the fitting (24).

5. Turbomachine (10) according to any one of the preceding claims, wherein said nuts (32) are barrel nuts (32) which are mounted inside the mast (20) and which have at least one degree of freedom inside the mast (20).

6. Turbomachine (10) according to claim 5, wherein the barrel nuts (32) are each oriented so as to have one degree of freedom in rotation about a second axis (B) parallel to said first axis (A).

7. Turbomachine according to claim 5 or 6, wherein the barrel nuts (32) each have degrees of freedom in a plane (P) perpendicular to a radial axis (C) with respect to the first axis (A). 8.

1. Turbomachine (10) according to any one of claims 5 to 7, wherein the barrel nuts (32) are arranged one behind the other along the first axis (A).

9. Turbomachine according to any one of claims 5 to 8, wherein said at least one cavity (40) is located in an oversized or thickened radially internal end (20a) of the mast (20).

10. Turbomachine (10) according to any one of claims 5 to 9, wherein the barrel nuts (32) are carried by at least one nut support (42) which is mounted inside said at least one cavity (40).

11. Turbomachine (10) according to claim 10, wherein the nut support or each of the nut supports (42) is engaged in said at least one cavity (40) by axial translation in a direction parallel to the first axis (A). 12.Turbomachine (10) according to claim 10 or 11, wherein the nut support(s) (42) has a shape complementary to that of said at least one cavity (40), and has, for example, a generally cylindrical shape or a circular cross-section.

13. Turbomachine (10) according to any one of claims 10 to 12, wherein the nut support(s) (42) comprises at least one lug (44) adapted to cooperate by elastic snap-fit ​​with at least one hole (46) of. complementary shape of the mast (20) to ensure that the support or each support (42) is held in position within the mast (20).

14. Turbomachine (10) according to any one of claims 10 to 13, wherein the nut support or each nut support (42) comprises a body (48) having several adjacent housings (50) in which said barrel nuts (32) are respectively mounted, each of these barrel nuts (32) having a nut (32a) movably mounted in a ring (32b) in a cylindrical portion, the ring (32b) itself being movable in the corresponding housing (50) of the body (48). 15.Turbomachine (10) according to claim 14, in which each nut (32a) comprises an external annular collar (52) which extends around a screw axis (C) and which is slidably mounted in an annular groove (54) of the corresponding ring (32a), a radial clearance (J) being provided between the collar (52) and a bottom of the groove (54) so ​​as to permit degrees of freedom of the nut (32a) in the ring (32b) in a plane perpendicular to the screw axis (C).

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