FIELD OF THE INVENTION

This invention relates to an assembly located at the rear (downstream end) of an aircraft turbojet engine to optimize the flow of hot gases expelled by the turbojet engine, and possibly absorbing at least part of the noise generated by [the interaction of these hot gases, coming from the internal engine parts (combustion chamber, turbine(s)), with the ambient air and with the flow of cold air expelled by the turbojet engine fan]

Specifically, the invention relates to the connection between what is often referred to as an “exhaust cone” and, located just upstream, a gas outlet of the turbojet engine.

Typically the exhaust cone is completed (surrounded) by a part called “primary nozzle”; these elements are commonly referred to as “plug” or “tail cone” for the exhaust cone and “nozzle”, and as “primary nozzle” for the nozzle.

The “exhaust cone” is intended to be positioned downstream turbine (part) of the turbojet engine, around which the primary nozzle is concentrically placed. Both the exhaust cone and the primary nozzle are attached to a turbojet engine casing by a flanged fastening system.

An aircraft turbojet engine assembly is thus already known per se, comprising:a central gas-exhaust element (which means: central element for exhausting gas), annular about an axis (X) and adapted for gas to be ejected by the turbojet engine around it, from upstream to downstream, anda connecting flange interposed between, upstream, one said metallic outlet of a turbojet engine and, downstream, the central element, to connect them together.

The above-mentioned X-axis is the longitudinal axis, or axis of rotation, of the turbomachine (in particular of the following fan20and moving blades of the engine12). In this context, ‘axial’ means the direction along (or parallel to) the X-axis; ‘radial’ means radially with respect to the X-axis and ‘circumferential’ means around the X-axis.

The central gas-exhaust element may correspond to the above-mentioned exhaust cone (marked1below), or at least to the upstream part1abelow.

A conventional exhaust cone1is shown inFIG.1, in which the upstream (AM) and downstream (AV) of the structure along a engine axis (X axis above) are located respectively to the left and to the right of the figure.

More generally, illustrated inFIG.1, is an aircraft gas turbojet engine10whose centre section, forming the gas turbine engine(s)12, is mounted inside an engine nacelle assembly14, as is typical of an aircraft designed for subsonic operation. The nacelle assembly14generally consists of a nacelle engine, known as a core16and a fan nacelle180surrounding a fan20located axially upstream of (or from) the engine12.

Axially downstream, the engine12comprises at least one turbine (which may be a low-pressure turbine) and, further downstream, an exhaust casing22comprising an inner annular shell22aand an outer annular shell22bdelimiting between them a downstream part of the primary vein24in which the combustion gases from the combustion chamber of the engine12circulate.

Axially, the inner annular shell22ais connected to the exhaust cone1, which may comprise an upstream portion1a(commonly referred to as the front plug), which is substantially cylindrical in shape, and a downstream portion1b(commonly referred to as the rear plug), which is conical in shape.

Connecting (joining) together the aforesaid metallic outlet of the turbojet engine, which may be said inner annular shell22a, and said central element, which may be said upstream part1aof the exhaust cone1, is difficult. In fact, as shown inFIG.2, it can be difficult to fix together axially, at the level of a bulb7, the aforementioned metallic outlet of the turbojet engine, which can be the said internal annular shell22aand the central element (generally identified as3) which, in the example of implementation of the following invention, will be assimilated to the exhaust cone1, the bulb7being a zone, swollen radially outwards, which the central element3can be present.

In particular, problems can arise in this regard:to manage the inlet diameter of the central element for the passage of flexible supports,complicated connection,and inclined connections (not parallel to the X-axis) in the bulb.

A proposed solution to at least some of these problems is that the connecting flange include:an annular part, and,circumferentially, flexible lugs having individually, axially:a first end at which the lug is connected to said annular part, anda second free end to which said lug is attached with the central element.

This makes it possible, in particular, to absorb differential expansions between the said central element and the said annular part which may respectively belong to, or define, the metallic exhaust casing and the non-metallic exhaust cone.

In this regard, it is further proposed that the flexible lugs extend radially outwards from the first end and/or from openings formed in the annular part.

This allows the mounting areas to be radially offset and combines flexibility and ease of installation

In addition, and in particular in this case, two possibilities have been more precisely defined:firstly, it is proposed that one said lug could be connected to said annular part, at one said first end, by means of tabs extending downstream and which would be integral upstream with said annular part;then, alternatively, it is proposed that one said lug could be connected in one piece to said annular portion, at the location of a portion of said annular portion forming a downstream edge of one said opening.

In the second case, by cutting locally, at the location of a rectangular area for example, the annular part on three sides and bending the cut part to form a so-called flexible lug, we avoid adding weight and make it easy both to manufacture and to achieve the desired flexible fixation.

In the first case, if such tabs are provided, integrated in a crenellated shape of the said annular part, the weight will also be limited, having in fact lightened this annular part in another way.

In this text, the word ‘connected’ means either ‘held in place by mechanical means’ (e.g. screwed, welded) or it means ‘part of’. If doing so creates a one-piece connection, this is specified.

Preferably, said annular part will be coaxial with said central element.

Preferably, the second free end of each said lug shall be located axially upstream of (or from) the first end of that lug. This may be important.

Indeed, by ensuring flexibility from downstream to upstream in the fixings via the said flexible lugs, it will be possible to bring the attachment of the central element/exhaust cone closer upstream (i.e., towards the connecting flange), thus favouring an attachment zone located axially outside one said bulb and an acoustic treatment zone which could be provided.

In this respect, it is also proposed that said central element have a peripheral wall having an upstream end portion where the central element will be fixed with said flexible lugs at their said second free ends.

In particular, said peripheral wall could usefully:be provided locally with a sound-attenuating structure (which may be honeycombed), andpresent its said upstream (attachment) end portion upstream of (or from) the sound-attenuation structure.

It may even be possible for the sound-attenuating structure to extend axially to the right of (which means: just around, at the same axial level than) the said lugs.

Thus, it was possible to fix the said central element, including a central element made of CMC (ceramic matrix composite, known per se), without impacting the acoustic treatment and without being located in the bulbous aerodynamic profile. The connecting flange can then be made of metal without difficulty. And, all the more so, this will maximise the acoustically treated surface of the central element.

The above should preferably be done:with one said upstream end portion for fixing the central element extending parallel to the said axis (X) (thus avoiding the above-mentioned inclined connections),likewise for said lugs towards their said second ends, so that these lugs and said upstream end portion of the central element/exhaust cone are attached together by screws passing through them.

It may also be useful to provide for the above-mentioned peripheral wall to extend:axially upstream, andradially outwardly with respect to said upstream end portion which it covers except at radial passage locations for said screws.

With said flexible lugs ensuring flexibility from downstream to upstream in the attachments, we will be able:to become more compact,thus limiting the mass of the solution compared to other flexible media,integrate, including with metallic connecting flanges, central element architectures/exhaust cones (CMC or metallic) provided with acoustic treatments in relation to a gas vein (see primary vein24above) equipped with upstream and downstream stiffeners.

The invention will be better understood, if need be, and other details, characteristics and advantages of the invention will appear upon reading the following description given by way of a non restrictive example while referring to the appended drawings wherein:

