High by-pass ratio turbofan

0001The invention relates to a jet engine, in particular a turbojet with high bypass ratio, including at least a compressor, a combustion chamber, a turbine, a blower mounted upstream the compressor and rotated by the turbine, and means defining, downstream of the blower, a flow annulus air to create a secondary stream around the housings of the compressor, the combustion chamber and turbine, which is added to gas combustion of the primary flow to increase thrust.

0002Turbojets modern commercial aircraft are characterized by a high bypass ratio, ie a high-speed connection / flow primary that is greater than 5 and up to 9 or 10. This results by a reduction in transverse dimensions of the body of the turbojet between the fan and the turbine (effect "wasp waist") and reduction these transverse dimensions causes a decrease in resistance to bending said body.

0003The bending deformations of the body of the turbojet cause themselves deformations of the casing around the rotor, and the housing is ovalis, which reduces play-rotor casing in some areas and increases at other locations (effect "distortion carcass").

0004The present invention is intended to provide a solution simple, effective and inexpensive these size effects of problems wasp and carcass distortion in turbojet engines, especially in turbojets with high bypass ratio.

0005It proposes for this purpose a turbojet engine, comprising at least one compressor, a combustor, a turbine, a blower mounted upstream of the compressor and rotated by the turbine, and means defining, downstream of the fan, an annular space air flow to create a secondary stream around the crankcases compressor, combustion chamber and turbine, wherein that said means comprise a substantially envelops cylindrical fixed surrounding the housings of the compressor, the chamber combustion and turbine and defining a surface substantially internal cylindrical guide the secondary flow, this envelope being formed of a single rigid piece and attached at its upstream end on a casing structural, for example an intermediate casing and at its downstream end on an exhaust casing and providing a force transmission between the structural casing and the exhaust casing.

0006This envelope, which surrounds away the body of the jet engine and which stiffens it, opposes the bending deformations of the body turbojet and forms a force transmission structure between front and rear portions of the body of the turbojet.

0007Its realization in one piece makes it possible to increase its rigidity and thus reduce the bending deformations of the body of the jet engine.

0008Advantageously, the downstream end of said envelope is fixed to the exhaust casing by means allowing at least one degree of freedom corresponding to the thermal expansion of the turbojet body operation.

0009In a particularly simple embodiment, the ends said shell are fixed by bolting to the intermediate casing and to the exhaust casing.

0010This method of fixing is simple and inexpensive and allows the disassembly of the casing if necessary.

0011Thanks to the rigidity of the shell and its attachment to the housings intermediate and exhaust, it becomes possible to remove the bars receiving thrust that power in general turbojets.

0012Furthermore, the doors are provided in the casing for allow access to equipment located within this envelope, such as especially fuel injectors, rings control of variable pitch blades and a gearbox training accessories.

0013According to another characteristic of the invention, said envelope comprises in its downstream portion, hinged flaps and means to move them between a rest position where they are in the extension of the casing and an operative position where they are projecting from said envelope and form obstacles to the flow of secondary flow, the flap moving means comprising jacks mounted on said housing and acting on the flaps or on a control ring of shutters.

0014This feature of the invention has a notable advantage when the operability of the turbojet necessary to increase the speed flight idle during the descent phase and the aircraft approach. This diet increase increases the thrust of the jet engine becomes too high. The shutters provided on the envelope used to break the thrust provided by the secondary flow during descent phases and approach and thus to bring the total thrust at an appropriate level.

0015This makes it possible during delete, on a turbojet high rate of dilution, the traditional system of "reverse" or against-thrust.

0016Other features and advantages of the invention will appear reading the following description given by way of nonlimiting example and in reference to the accompanying drawings in which:<ul><li>Figure 1 is a highly diagrammatic view in axial section of a turbojet with high bypass ratio according to the invention;</li><li>Figures 1a and 1b are enlarged views of details of the Ia and Ib figure 1 ;</li><li>the Figure 2 is a schematic perspective view of the envelope of this turbojet;</li><li>Figure 3 is a schematic perspective view of the downstream portion the envelope of Figure 2, illustrating the components of the displacement means articulated; </li><li>Figure 4 is an enlarged schematic view of the means of displacement components of Figure 3.</li></ul>

0017Figure 1 schematically represents a turbojet 1 turbofan comprising a front fan 2 comprising a wheel 3 which rotates inside a nacelle 4. The air flow sucked by the fan 2 is divided downstream of the fan into a primary flow as it passes through a engine comprising a compressor 5, an annular chamber combustion 6 and a turbine 7, and a secondary stream that flows around of the engine as indicated by the arrows 8 and which provides thrust further in addition to that provided by the ejected combustion gas 7 of the turbine.

0018The passage for the secondary flow 8 is delimited externally by the internal wall 9 of the nacelle and internally by a casing 10 of substantially cylindrical shape which surrounds the motor and which extends from a such as a structural casing intermediate casing 11 to a housing exhaust 12 at the turbine outlet. The intermediate casing 11 is connected rigidly by radial arms to the nacelle of the fan.

0019According to the invention, this casing 10 is rigid and fixed at its upstream and downstream ends of the motor body to stiffen and prevent its bending deformations and the carcass distortion.

0020Increasing the dilution ratio of a turbojet engine, that is to say the increased flow ratio of secondary flow / flow of the primary stream, results in a reduction of the engine between the cross section compressor and turbine (effect "wasp waist"), this reduction section favoring carcass distortions as described above. The fastening the rigid casing 10 at its ends to the motor housing prevents bending deformations of the body, even when the rate of dilution is important, for example when it is between 5 and 10.

0021The casing 10 is one piece. As best shown in Figures 1a and 1b, the casing 10 is fixed at its upstream end by means an annular flange 13 on the intermediate casing 11, and at its end downstream by a support piece 14 of the exhaust casing 12, at motor fastening means on the attachment pylon to the wing of the plane. The fasteners are made preferably by means of bolts 15, 16, 17, 18. The attachment of the downstream end of the casing 10 on the housing exhaust 12 is designed to retain at least one degree of freedom corresponding to the thermal expansion of the engine in operation. To impart an axial degree of freedom to the shell 10, the support part 14 has a configuration affording it an axial deformation capacity elastic.

0022The section of the casing 10 increases from its upstream end to its median portion at the rear end of the nacelle 4, then decreases to its downstream end, the general shape of the casing being biconical.

0023As shown in Figure 2, the upstream portion 19 of the casing 10 comprises access openings to equipment which are at inside this casing, and in particular holes 20 for access to vane control rings with variable pitch which are located on a casing of the compressor 5, a hole 21 for access to a gear box control accessories and ports 22 for access to injectors fuel from the combustion chamber.

0024These access ports 20, 21, 22 are closable by doors or removable panels 23, 24, 25 respectively which is fixed on the casing 10 by any suitable means, for example by screwing.

0025The downstream portion 26 of the casing 10, which is downstream of the neck of the the secondary flow nozzle 8, has hinged flaps or panels 27 which are circumferentially provided and which are pivotable about axes transverse tangent to a circumference of the casing 10 between a position shown in Figure 2 where they are projecting outwardly the casing 10 and a retracted position or rest position where they extend in the surface of the casing 10, as shown in Figure 3.

0026Position output, flaps or panels 27 obstruct the flow downstream of the secondary flow 8 and break the thrust provided by the fan 2. This proves interesting when operability turbojet does not sufficiently reduce the engine revs during the descent and approach phases. One can thus keep adequate diet while reducing engine thrust.

0027The flaps or panels 27 may include herringbone reduce noise.

0028They are actuated by small jacks 28, directly or by via a control ring 29, as shown in Figures 3 and 4.

0029In these figures, a control ring 29 of the flaps or panels 27 is mounted within the downstream portion 26 of the envelope 10 and is moved by means of at least one jack 28 whose cylinder is carried by the casing 10 and whose piston rod acts on the ring 29 connected by connecting rods 30 to the flaps or panels 27.

0030This flap system or panels 27 to delete a Motor high bypass ratio means to "reverse" or against-thrust which are usually provided on this type of engine. It results in a reduction of the number of parts and cost.