FR2940359A1 - Exhaust casing for turbine engine of engine assembly of aircraft, has structural unit passed through exterior shell in manner to locally authorize relative displacement of unit between integrated assembly and shell - Google Patents

Abstract

The casing has a connection arm (24) extended from a hub towards an exterior shell (6). An effort passing bracket (20) is located radially with respect to the exterior shell. The connection arm has a structural unit (28) e.g. structural bar, which is extended in given direction between an internal radial end and an external radial end (36). The structural unit is passed through the shell in a manner to locally authorize a relative displacement of the structural unit between an integrated assembly and the shell, where the assembly is formed by the structural unit and the effort passing bracket. An independent claim is also included for an engine assembly of an aircraft comprising a turbine engine.

Description

1 EXHAUST CASE FOR TURBOMACHINE, COMPRISING A DISSOCIATE FASTENING FASTENER OF THE EXTERNAL VIROLE

DESCRIPTION TECHNICAL FIELD The present invention relates generally to the field of turbomachines, and more particularly to the exhaust casings fitted to these turbomachines. The invention is preferably applicable to aircraft turbomachines, for example of the turbojet or turboprop type. STATE OF THE PRIOR ART With reference to FIG. 1, a turbojet exhaust casing can be seen, according to a conventional embodiment known from the prior art. The exhaust casing 1, of axis 2 corresponding to the longitudinal axis of the turbomachine within which it is intended to be integrated, comprises a hub 4 and a concentric outer shell 6. In addition, connecting arms 8 connect the hub 4 and the ferrule 8 to ensure the attachment to one another. To do this, the hub is made in one piece with radial protuberances 10 each forming the end of an arm 8, and the ferrule 6 is made in one piece with radial protuberances 12 each forming another end of an arm 8. In addition, two protuberances 10, 12 are connected by a profiled solid piece 14 constituting the central portion of an arm 8. These connections are usually made by welding. In addition, the exhaust casing 1 comprises one or more force passage fittings 16, made in one piece with the ferrule 6, for example by molding. These fittings 16, usually clevis-shaped as shown in FIG. 1, are situated radially outwards with respect to said ferrule 6. They are intended for fastening the casing 1 to an element external thereto, preferably on the attachment mast of the turbojet engine. In this respect, the fittings 16 generally bear, in an articulated manner, connecting rods of the attachment pylon.

Usually, the casing 1 is subjected to high thermal stresses, with significant gradients in the radial direction, increasing outwards. These thermal stresses result from the passage, through this casing, of the flow of gas escaping from the turbine of the turbojet engine. In addition, it must be able to withstand high mechanical loads, encountered for example following the impact of a turbine blade, after the loss thereof. In addition, this housing must be able to withstand the passage of the forces used for the attachment of the engine, which pass in particular by the fittings 16 in the direction of the attachment pylon. If the design shown in Figure 1 is a solution that satisfactorily satisfies the requirements / constraints mentioned above, it is still perfectible. In particular, the junction zone between each fitting 16 and the ferrule 6 can be problematic because it is highly stressed, mainly because of the significant thermal stresses it undergoes. This highly stressed junction area therefore requires a very specific design, negatively impacting production costs. In addition, despite its specific design, the junction zone has a limited life, still due to its high fatigue stress essentially caused by the variation in thermal stresses it undergoes. DISCLOSURE OF THE INVENTION The object of the invention is therefore to remedy at least partially the disadvantages mentioned above, relating to the embodiments of the prior art. To do this, the invention firstly relates to an exhaust casing for a turbomachine comprising a hub, an outer shell being arranged concentrically, connecting arms extending from said hub in the direction of said outer shell , as well as at least one force-passing fitting intended for the attachment of said exhaust casing to an element external to the casing, said fitting being located radially outwards with respect to said outer shell. According to the invention, one of said connecting arms comprises at least one structural member extending in a given direction between an inner radial end fixedly mounted on said hub and an outer radial end fixedly mounted on said force-passing fitting said structural member 4 passing through said outer shroud in a manner allowing locally a relative displacement, at least in said given direction, between, on the one hand, the integral assembly formed by the structural member and said effort-passing fitting, and on the other hand said outer shell. The originality of the present invention is therefore essentially to provide one or more degrees of freedom between the force-passing fitting, and the outer ferrule portion through which the structural member integral with this fitting. This makes it possible to lower substantially the level of stress in the fitting, compared to the level observed in the prior art with this same fitting made in one piece with the ferrule. Indeed, the relative displacement allowed by the present invention is particularly advantageous in case of differential thermal expansion between the structural member and the shell, since it can then move locally relative to the member, in the direction of this last. The casing according to the invention therefore makes it possible to cope better with the thermal stresses it undergoes, resulting from the flow of gas passing through it. The design constraints of the force transfer fitting are then less important than before, so that it no longer requires complex shapes. The production costs are advantageously reduced. In addition, this results in a gain in terms of overall weight, which can be further accentuated by the fact that the dissociation between the ferrule and the fitting allows the use of different materials for the respective achievements of these elements. This dissociation also greatly facilitates the manufacture of the outer shell, and, more generally, simplifies the overall manufacturing process of the exhaust casing. If the casing according to the invention makes it possible to have a longer lifetime compared to the embodiments of the prior art, it also has the other advantage of strongly limiting, or even completely eliminating, the transmission of charges coming from the connecting arm, towards the outer shell. In fact, the proposed arrangement makes it possible to create a very privileged force path, starting from the hub, passing through the structural member, then reaching the effort-passing fitting dissociated from the outer shell. It is therefore less prone to deformations.

Preferably, said force-passing fitting is arranged without contact with said outer shell, ie away from it radially outwards, in order to further limit the transmission of forces between these elements. elements.

Preferably, said connecting arm comprises a plurality of structural members each extending in said given direction between an inner radial end fixedly mounted on said hub and an outer radial end fixedly mounted on said force-carrying fitting, said members structural members traversing said outer shell 6 in a manner allowing locally a relative displacement, at least in said given direction, between on the one hand the integral assembly formed by the structural members and said force-passing fitting, and on the other hand from said outer shell. Of course, the number of organs can be adapted according to the needs met. It is further noted that the members could extend in different directions, without departing from the scope of the invention. Preferably, each structural member takes the form of a bar, with ends adapted for their attachment to the hub and the fitting, for example by screw connections.

Preferably, said given direction, in which each structural member extends, is the radial direction, namely passing through the axis of the exhaust casing. Preferably, said connecting arm comprises an aerodynamic fairing arranged around each structural member. This fairing makes it possible to minimize the aerodynamic losses of the flow passing through the housing. In addition, it makes it possible to straighten this flow of gas. In this regard, it is noted that said aerodynamic fairing is connected to the outer shell and the hub by means of sealed connections to the flow of gas passing through the housing, always with the aim of limiting the disturbances of this flow. Preferably, said force-passing fitting defines a yoke, even if other designs can be envisaged, without departing from the scope of the invention. Preferably, a plurality of said connecting arms are respectively associated with force transfer fittings, as described above. Several of said connecting arms may also not cooperate with the fittings, but simply perform an aerodynamic role of recovery of the flow. In such a case, the structural members are not necessary, and these arms can then be constituted by simple aerodynamic fairings arranged between the hub and the outer shell. The invention further relates to an aircraft turbomachine comprising an exhaust casing as described above. The invention also relates to an engine assembly for an aircraft comprising such a turbomachine and an attachment pylon for securing the turbomachine on the fuselage or a bearing surface of the aircraft. In a first case, it can be provided that said outer member cooperating with said force-passing fitting is an integral part of a motor attachment fitted to said attachment pylon.

In a second case, it can be provided that said outer member cooperating with said force-passing fitting establishes a connection between said exhaust casing and a force-absorbing ring on which is mounted said attachment pylon.

In both cases, said outer element is preferably a connecting rod. Other advantages and features of the invention will become apparent from the detailed non-limiting description below. BRIEF DESCRIPTION OF THE DRAWINGS This description will be made with reference to the appended drawings among which; - Figure 1, already described, shows a perspective view of a turbojet exhaust casing, according to an embodiment known from the prior art; FIG. 2 represents a perspective view of a turbojet exhaust casing, according to a first preferred embodiment of the present invention; - Figures 3a and 3b show sectional views taken along the lines IIIa-IIIa and IIIb-IIIb of Figure 2, respectively; FIG. 4 represents an enlarged perspective view of a portion of the exhaust casing of FIG. 2; - Figure 5 shows a perspective view similar to the previous, taken at another angle; - Figure 6 shows a sectional view taken along the plane P of Figure 5; FIG. 7 represents an engine assembly for an aircraft integrating the turbojet exhaust casing shown in FIGS. 2 to 6; Fig. 8 is a perspective view of a turbojet exhaust casing 9 according to a second preferred embodiment of the present invention; and FIG. 9 represents an aircraft engine assembly incorporating the turbojet exhaust casing shown in FIG. 8. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 2, an exhaust casing 100 for a turbojet engine can be seen. of aircraft, according to a first preferred embodiment of the present invention. The exhaust casing 100, axis 2 corresponding to the longitudinal axis of the turbojet engine within which it is intended to be integrated, comprises a hub 4 and a concentric outer ring 6. The latter has, at its upstream and downstream ends, assembly flanges 6a, 6b, the upstream flange 6a being intended for the assembly of this casing 100 on a turbine casing of the turbojet, while the other flange 6b allows connection to downstream equipment of the turbojet engine. In addition, the casing 100 comprises connecting arms extending from the hub 4 in the direction of the outer shell 6, as well as force transfer fittings 20 for fastening the casing 100 on elements external to this case. Here, these elements outside the casing 100, referenced 22, are preferably components of an attachment pylon, and in particular connecting rods 22 forming an integral part of an engine attachment belonging to the attachment pylon. These connecting rods 22 are preferably mounted articulated on their respective fittings. The fittings 20, here taking the form of screeds, are arranged radially outwardly relative to the ferrule 6, preferably without contact therewith. Among the connecting arms that equip the exhaust casing 100, two types are provided. The arms of the first type, referenced 24, are those associated with fittings 20. They are essentially designed to allow the passage of forces, and thus fulfill a structural role. The arms of the second type, referenced 26, have, on the other hand, no structural function, but make it possible to fulfill an aerodynamic function of rectifying the primary flow passing through the annular space between the ferrule 6 and the hub 4. In this respect, it is noted that that these arms 26 are optional, the aerodynamic function of recovery of the primary flow can indeed also be filled by the arms 24 of the first type. In this first preferred embodiment, there are provided two arms 24 each associated with a force recovery fitting 20, all the other arms being of the second type.

In FIG. 3a, it can be seen that each arm 24 has one or more structural members 28 spaced in the axial direction, these bar-shaped members, for example of circular section, being wrapped in an aerodynamic fairing 30. This fairing 30, allowing the straightening of the primary flow through the exhaust casing, is preferably without contact with the structural bars 28, although contact could be provided without departing from the scope of the invention. The arms 26 have only aerodynamic fairing 30, and are therefore devoid of structural members, as can be seen in FIG. 3b. For both types of connecting arm 24, 26, the aerodynamic fairing 30 is connected to the inner surface of the outer shell 6 and to the outer surface of the hub 4 via sealed connections to the flow of gas passing through the housing 100 , in order to limit the disturbances of this flow. Preferably, these connections are made by welding, so as to allow their flexibility. Indeed, these connections can be solicited in case of differential expansion leading the outer shell 6 to move away from the hub 4 in the radial direction. Referring now to Figures 4 to 6, one can see in detail one of the connecting arms 24, and its cooperation with the other elements of the housing 100. First, it is noted that the structural bars 28 extend parallel in a given direction, preferably the radial direction, each from an inner radial end 32 fixedly mounted on the hub, preferably by screwed elements 34, as shown in Figure 4. They traverse the space annular borrowed by the primary flow, and each end with an opposite end called said outer radial end 36, fixedly mounted on the force transfer fitting 20, as shown in Figures 5 and 6. In this regard, it is noted that the assembly can also be achieved by screwed elements (not shown). To bring its end 36 beyond the outer shell 6, each structural bar 28 has the characteristic of crossing the outer shell 6, which has a through passage 38 provided for this purpose, shown in Figure 5. Thus, this passage 38 , preferably common to all the bars 28 of the arm, locally allows a relative displacement, at least in the radial direction of the bars 28, between on the one hand the integral assembly formed by these bars 28 and the fitting 20, and of the other hand the outer shell 6. The relative movement allowed to address the problem of differential thermal expansion between the structural bars 28 and the ferrule 6, likely to be encountered during the operation of the turbojet, because of the temperature gradient within primary flow through the exhaust casing 100. Indeed, the ferrule 6 can then move locally relative to the bars, at least in the radial direction corresp waving to that of the bars. In this regard, another degree of freedom is also released when the structural bars 28 are not directly in contact with the passage 38, but a clearance is provided between these elements. With reference to FIG. 6 showing the casing 100 which is not thermally constrained, it can be seen that a minimum clearance is preferably provided between the ferrule 6 and the force-retaining fitting 20, this clearance being for example provided sufficiently important for 13 during the operation of the turbojet creating differential thermal expansion, it is not consumed entirely, even under the most unfavorable thermal stress conditions. Thus, this design has the particularity of strongly limiting, or even completely eliminating the transmission of loads from the connecting arm 24 and the fitting 20, to the outer shell 6. Indeed, the proposed arrangement allows to create a path very privileged efforts, from the hub 4, through the structural bars 28, then reaching the fitting 20 dissociated from the outer shell 6, to finally spread through the connecting rods 22. The ferrule 6 is therefore less prone to deformation . As an indication, in the differential thermal expansion phases, the circumferential clearance possibly provided between the bars 28 and the passage 38 may also be partially or completely consumed. Preferably, the hub and the outer shell are made of Inconel 718 or any other material having a high temperature resistance, while the bars and the fitting are for example made of steel with thermal protection or Inconel. With reference to FIG. 7, it is possible to see an engine assembly for an aircraft comprising a turbojet engine 104 equipped with the exhaust casing 100 described above, the assembly 102 also comprising an attachment pylon 106 intended to ensure the attachment 14 of the turbojet engine under a wing of the aircraft. The attachment mast comprises a rigid structure 107, for example box-shaped as shown, as well as a plurality of engine attachments connecting the turbojet engine 104 to the box 107. Among these fasteners, there is for example a front attachment 108 connecting one end of the casing to the fan casing 110, a system of connecting thrust forces 112, and a rear attachment 114 connecting the casing to the exhaust casing 100. It is therefore this rear engine attachment 114 which comprises the rods 22 articulated on the yokes 20 of the exhaust casing. Naturally, the mast 106 is here described only as an indication, and could be designed in any other way known to those skilled in the art, so as to cooperate with the yokes 20 of the exhaust casing 100 specific to the present invention. Referring now to Figure 8, an exhaust casing 100 for an aircraft turbojet can be seen in accordance with a second preferred embodiment of the present invention. It has great similarities with the housing 100 described above. Moreover, the elements bearing the same numerical references correspond to identical or similar elements. Thus, it can be seen that the only difference lies in the number of structural arms 24 and yokes 20 cooperating with them. Indeed, it is no longer two arms 24 which are provided, but six, for example evenly distributed in the circumferential direction. Four aerodynamic arms 26 of the casing previously described have thus been replaced by structural arms 24. This second preferred embodiment is retained in particular for an implantation in the motor assembly 102 shown in FIG. 9. In this assembly, the mast of FIG. attachment 106, of which only its engine fasteners have been shown, is provided to ensure the lateral attachment of the turbojet engine 104 on a rear part of the aircraft fuselage. It has for example two front engine attachments 108, and a rear engine attachment 114 mounted on a force recovery ring 116, centered on the axis 2 and located in the rear continuity of the fan casing 110. This ring 116 of the turbojet engine is mounted on the exhaust casing 100 via link rods 122, one end of which is hinged to this ring, and the other end of which is hinged to one of the clevises 20 of the housing 100. Thus, as shown in Figure 7 where an aerodynamic cover 118 freely traversed by the rods 122 covers the casing 100, there are six connecting rods 122 which are provided between the ring 116 and the yokes of this housing 100, even if their number could be modified according to the needs met. Finally, it is noted that in the two preferred embodiments described, the rods 22, 122 are preferably arranged to be arranged in a substantially tangential direction relative to the outer shell 6.

Of course, various modifications can be made by those skilled in the art to the invention which has just been described, by way of non-limiting examples only. 10

Claims (14)

REVENDICATIONS1. An exhaust casing (100) for a turbomachine comprising a hub (4), an outer shell (6) concentrically disposed therein, connecting arms (24) extending from said hub towards said outer shell, as well as at least one force-passing fitting (20) for catching said exhaust casing on an element (22, 122) external to the casing, said fitting being situated radially outwards with respect to said outer shell characterized in that one of said connecting arms (24) comprises at least one structural member (28) extending in a given direction between an inner radial end (32) fixedly mounted on said hub and an outer radial end ( 36) fixedly mounted on said force-passing fitting, said structural member (28) passing through said outer shroud (6) in a manner allowing a relative displacement locally, at least in said given direction, between a part the integral assembly formed by the structural member (28) and said force-passing fitting (20), and secondly said outer shell (6). 2. Exhaust casing according to claim 1, characterized in that said force passage fitting (20) is arranged without contact with respect to said outer shell (6). 18 3. An exhaust casing according to claim 1 or claim 2, characterized in that said connecting arm comprises a plurality of structural members (28) each extending in said given direction between an inner radial end (32) mounted fixedly on said hub and an outer radial end (36) fixedly mounted on said force-passing fitting, said structural members (28) passing through said outer shell in a manner which allows a relative displacement locally, at least in said given direction, between on the one hand the integral assembly formed by the structural members (28) and said force-passing fitting (20), and on the other hand said outer shell (6). 4. Exhaust housing according to any one of the preceding claims, characterized in that each structural member (28) takes the form of a bar. 5. Exhaust housing according to any one of the preceding claims, characterized in that said given direction, in which each structural member extends, is the radial direction. 6. Exhaust housing according to any one of the preceding claims, characterized in that said connecting arm comprises an aerodynamic fairing (30) arranged around each structural member. 19 7. An exhaust casing according to claim 6, characterized in that said aerodynamic fairing (30) is connected to the outer shell (6) and the hub (4) via sealed connections to the flow of gas through the housing . 8. An exhaust casing according to any one of the preceding claims, characterized in that said force passage fitting (20) defines a yoke. 9. An exhaust casing according to any one of the preceding claims, characterized in that a plurality of said connecting arms (24) are associated with force passage fittings (20), respectively. 10. A turbomachine (104) for aircraft comprising an exhaust casing (100) according to any one of the preceding claims. 11. Engine assembly (102) for an aircraft comprising a turbomachine (104) according to claim 10 and an attachment pylon (106) for securing the attachment of the turbomachine to the fuselage or a bearing surface of the aircraft. 12. Engine assembly according to claim 11, characterized in that said outer member (22) cooperating with said force-passing fitting (20) 20 is an integral part of a motor attachment (114) fitted to said attachment pylon ( 106). 13. Engine assembly according to claim 11, characterized in that said outer member (122) cooperating with said force-passing fitting (20) establishes a connection between said exhaust casing (100) and a recovery ring. forces (116) on which is mounted said attachment pylon (106). The engine assembly of claim 11 or claim 12, wherein said outer member is a connecting rod (22,122).