Abstract:
A turbomachine including an annular combustion chamber is disclosed. The combustion chamber includes a radially inner wall and a radially outer wall exhibiting symmetry of revolution. An annular chamber end wall equipped with a fuel injection device connects upstream ends of the inner and outer walls. A suspension device suspends the upstream end of the combustion chamber from an outer casing.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a turbomachine, such as an airplane turbojet or turboprop, equipped with an annular combustion chamber. 
     A turbomachine annular combustion chamber comprises two, an inner and an outer, coaxial walls exhibiting symmetry of revolution, which are connected at their upstream ends by a rigid annular chamber end wall and at their downstream ends have flanges for attaching to inner and outer casings. It also comprises an upstream annular cowling fixed to the chamber end wall and intended to direct the air flow into or around the combustion chamber. The chamber end wall and the cowling have openings to allow air to enter the chamber and to allow for the insertion of injectors that spray fuel into the combustion chamber. 
     At the downstream end, the chamber is connected by the outer flange to an outer casing of a turbine section positioned on the outlet side of the combustion chamber. 
     The way in which this chamber is mounted in the inner and outer casings and the way in which it is attached present a certain number of disadvantages which degrade turbomachine performance. 
     Specifically, the injectors cannot be positioned relative to the chamber in the optimum way needed for good combustion because of the way in which the chamber is attached. Specifically, the successive fixings of the various parts of the chamber, namely the fixings of the inner and outer walls of revolution to the chamber end wall, then the attaching of the inner and outer flanges to the casings of the turbomachine, lead to a build-up in manufacturing and assembly tolerances of each of the parts and therefore to imprecision in the positioning of the chamber within the casings. As a result, the injectors cannot be attached accurately to the casing and their tips cannot be aligned accurately along the axis of the combustion chamber, which means that the fuel injected into the chamber cannot undergo ideal combustion and turbomachine performance is diminished. 
     DESCRIPTION OF THE PRIOR ART 
     In the prior art, a distinction is made between two types of combustion chamber according to whether the combustion chamber is divergent or convergent, that is to say according to whether, from the upstream and downstream, the chamber diverges from or converges toward the axis of the turbomachine. 
     The combustion chamber is generally mounted in the outer casing from the downstream end and this does not present any particular difficulty in the case of divergent chambers. 
     In some instances, convergent combustion chambers may be preferred over divergent chambers because they occupy a smaller amount of space in the axial direction. Mounting such chambers in the outer casing from the downstream end means that the downstream diameter of the outer casing of the chamber has to be increased, thus leading to an increase in the radial dimension, in the mass and in the cost. The increase in the downstream diameter of the casing also causes misalignment between the outer casing of the chamber and the outer casing of the turbine section, thus reducing aerodynamic performance. Finally, attaching the chamber from the upstream end in order to avoid the aforementioned problems might not be feasible because it would entail recourse to inner and outer flanges attached to the upstream part of the combustion chamber in the bypass flow, with points of attachment in the regions of attachment of the injectors, and this would create mechanical difficulties and problems with airflow around the chamber. 
     In operation, the difference in temperature between the chamber and the outer casing may also lead to the injectors being misaligned relative to the axis of the chamber as a result of axial expansion of the chamber which may be by as much as several millimeters. 
     SUMMARY OF THE INVENTION 
     The subject of the present invention is a turbomachine, particularly one with a convergent annular chamber, which avoids the aforementioned disadvantages of the prior art in a simple, effective and economical way. 
     To this end, it proposes a turbomachine comprising an annular combustion chamber comprising two, a radially inner and a radially outer, walls exhibiting symmetry of revolution, all with respect to the axis of the turbomachine, and which are connected at their upstream ends by an annular chamber end wall equipped with fuel-injection means, which turbomachine comprises suspension means for suspending the upstream end of the combustion chamber from an outer casing, these means comprising at least one link rod articulated at its ends to a wall of the combustion chamber and to the outer casing, the downstream end of the combustion chamber being connected to an inner casing or outer casing by flexible connections or mounts. 
     The chamber is suspended from the outer casing at the upstream end of the chamber, thus allowing the chamber to be mounted in the outer casing from the upstream end and avoiding having to increase the downstream diameter of the outer casing. Alignment of the outer casing of the chamber and of the outer casing of the turbine section improves the aerodynamic performance of the turbomachine. Suspending the chamber from its upstream end improves the position of its upstream part and therefore allows the tips of the injectors to be aligned precisely with the holes in the chamber end wall, thus optimizing the combustion of the fuel. The elimination of the flanges that connect the downstream part of the chamber to the outer and inner casings makes it possible to reduce the mass of the turbomachine. 
     This link rod can be incorporated perfectly into the mechanical surroundings of the injectors and of the upstream part of the combustion chamber and does not disrupt the airflow that flows around the combustion chamber. Connecting the chamber to the outer casing using one or more link rods makes it possible to eliminate the operational radial stresses that are applied to the chamber. 
     Advantageously, the link rod lies in a plane that passes through the axis of the turbomachine. 
     According to another feature of the invention, one end of the link rod is articulated to the upstream end of the outer wall of revolution, its other end being housed and articulated in an outwardly projecting boss belonging to the outer casing. Each end of the link rod is articulated about a transverse axis on a cylindrical pin mounted in holes in a clevis belonging to the outer wall of the chamber or of the outer casing, respectively. 
     The articulation between the link rod and the chamber is positioned at the upstream end of the outer wall of revolution because this part is cooler than the other parts of the chamber, making it possible to limit clevis deformation as the chamber heats up during operation and thus optimizing the position of the injectors relative to the chamber. 
     Guide bushings may be set into the holes in the clevises to ensure correct positioning of the pins in the clevises belonging to the outer wall of revolution and thus guaranteeing optimal positioning of the chamber on the outer casing. 
     According to another feature, the ends of the link rod are articulated on the cylindrical pins by means of ball swivels through which these pins pass. 
     Inserting fixed ball swivels into the clevises allows the pins to swivel in the clevises, thereby making it possible to compensate for any defects in the shape of the components and any shortcomings in the fitting of the chamber relative to the outer casing. 
     In a preferred embodiment of the invention, the combustion chamber comprises three link rods distributed over the upper half-circumference of the outer wall of the chamber, one link rod lying in a vertical plane that passes through the axis of the turbomachine, the other two link rods being positioned symmetrically on each side of this vertical plane. 
     The link rods may be substantially parallel to the axis of the turbomachine, thus making it possible to limit the axial movements of the combustion chamber and optimizing the positioning of the injectors relative to the chamber as the latter heats up in operation. 
     According to another feature of the invention, the link rods may comprise means, for example screw means, for adjusting length, allowing the position of the chamber to be optimized within the casings. 
     The link rods are advantageously connected to the outer wall of the chamber between fuel injectors so as to improve the precision with which the injectors are positioned relative to the chamber. 
     According to another feature of the invention, at least one of the walls that are the outer wall and the inner wall of the combustion chamber comprises at its downstream end a flexible piece for connecting to or resting against an outer or inner casing. The flexible connecting piece is welded or brazed to the chamber and rests substantially radially against a casing. 
     The use of flexible components makes it possible to limit the vibration at the chamber outlet during turbomachine operation. Such components can be made of materials that are lighter in weight than the flanges of the prior art because most of the mechanical work is performed by the suspension means upstream of the combustion chamber. 
     The downstream end of the inner wall of the chamber may be connected by a flexible annular flange to an inner casing. 
     In the case of an annular combustion chamber that converges toward the axis of the turbomachine, this can be mounted from the upstream end inside the outer casing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood and other details, advantages and features of the invention will become apparent from reading the following description, which is given by way of nonlimiting example, with reference to the attached drawings in which: 
         FIG. 1  is a schematic half view in axial section of a turbomachine combustion chamber according to the prior art; 
         FIG. 2  is a schematic half view in axial section of a turbomachine combustion chamber according to the invention; 
         FIG. 3  is a schematic exploded view, in perspective viewed from the downstream end, of a system for suspending a combustion chamber according to the invention; 
         FIG. 4  is a schematic part view, in perspective from the upstream end, of part of a combustion chamber and of its suspension system according to the invention; 
         FIG. 5  is a schematic partial side view on a larger scale of the system for suspending a combustion chamber according to the invention; 
         FIG. 6  is a view in section on A-A of the upstream part of the combustion chamber of  FIG. 5 ; 
         FIG. 7  is a view in section on B-B of the upstream part of the combustion chamber of  FIG. 5 ; 
         FIG. 8  is a schematic view in cross section of a combustion chamber showing the angular distribution of the link rods. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference is made first of all to  FIG. 1  which depicts a convergent annular combustion chamber  10  according to the prior art and in which a centrifugal diffuser  12 , mounted on the outlet side of a high-pressure compressor (not depicted) supplies air to an annular space  13  delimited by two coaxial casings, one of them,  14 , a radially inner casing with respect to the axis  16  of the turbomachine and the other of them,  18 , a radially outer casing, and which contains the combustion chamber  10 . This combustion chamber  10  is mounted upstream of a turbine section  20  surrounded by an outer casing  22  and comprises two, an inner  24  and an outer  26 , substantially cylindrical and coaxial walls of revolution and an upstream annular chamber end wall  28  to which there is attached an annular cowling  30  which extends in the upstream direction. The downstream ends of the walls  24 ,  26  are connected to the casings  14  and  18  respectively by annular flanges  32  and  34 . The upstream ends of the radially inner  24  and outer  26  walls of revolution are attached to radially inner and radially outer rims of the chamber end wall  28  and of the cowling  30 , respectively, by bolts  36 . 
     The chamber end wall  28  supports injector tips  38  which open into the combustion chamber  10  and which are directed along the axis  40  of this chamber  10 . Each injector  38  extends through a hole in the cowling  30  and has a cranked part which fits around the upstream outer edge of the cowling  30  and is connected to fuel supply means  42  borne by the outer casing  18 . These supply means  42  are attached to a boss  44  belonging to the outer casing  18 . 
     During operation, the air flow provided by the high-pressure compressor and leaving the diffuser  12  is guided by the cowling  30  and splits into a part (arrows A) which passes through air inlet orifices in the cowling  30  and through corresponding holes  46  in the chamber end wall  28  to feed into the combustion chamber  10 , and into two parts (arrows B) which bypass or flow around the combustion chamber  10 . 
     In the known art, the combustion chamber  10  is mounted from the downstream end and is attached by its downstream flanges  32 ,  34  to the outer  18 ,  22  and inner  14  casings. When the chamber is a convergent chamber  10  as depicted in  FIG. 1 , it is not possible to insert the chamber between the inner  14  and outer  18  casings unless the downstream diameter of the outer casing  18  is increased so that the downstream diameter R 1  of the outer casing  18  is greater than the diameter R 2  of the chamber end wall  28  thus leading to an increase in mass, size and cost. This increase in diameter also introduces misalignment between the outer casings  18  and  22 , thus disrupting the flow of air in the stream formed between the outer wall  26  and the outer casings  18 ,  22 . 
     Upstream attachment of the combustion chamber, whether this be a divergent combustion chamber or a convergent combustion chamber, cannot be performed using a flange similar to the one used for downstream attachment. This is because attaching it in this way would assume the availability of a flange in the region bypassing the chamber  10 , and the presence of such a flange would disrupt the air flow, and would entail attaching such a flange in the region of attachment of the injectors  38 , something that could be achieved only with difficulty. 
     According to the invention, these disadvantages together with those already mentioned, are avoided by virtue of the fact that, as depicted in  FIG. 2 , the combustion chamber  48  is connected at its upstream end to the outer casing  18  by suspension means. 
     These suspension means comprise at least one link rod  50  lying in a plane that passes through the axis  16  of the turbomachine, the ends of the link rod being articulated to the outer wall  26  of the combustion chamber  48  and to the outer casing  18 . The use of link rods  50  upstream of the chamber  48  makes it possible to reestablish alignment between the outer casings  18  and  22  thus allowing a considerable weight saving. In addition, the link rods  50  do not disrupt the flow of air (arrows B) bypassing the chamber  48 . 
     Each link rod  50  comprises a hole  52  at each of its ends, and into each hole is inserted a ball swivel  54  comprising a bore and held in position in the hole  52  by rotating it through 90°. 
     The upstream end of each link rod  50  is inserted between two clevises  56  belonging to the outer wall of revolution  26 , which clevises run substantially radially ( FIGS. 3 and 4 ). Each clevis  56  has a transverse hole aligned with the hole in the adjacent clevis  56  used for attaching the link rod  50 . The radially inner part of each clevis comprises a flat-surfaced rim  55 . A bushing  58  is mounted in each hole and is inset in such a way as to form a rim  60  on those faces of the clevises  56  that face one another. The link rod  50  is attached using a pin  62  inserted through the holes in the clevises  56  and the bore in the ball swivel  54  belonging to the link rod  50 . The pin  62  has a threaded end  64  to take a fastening nut  66 , the other end having a head  68  with two flats, one of which collaborates with the rim  55  of the clevis so as to prevent any rotation of the pin  62  and any unscrewing thereof while the turbomachine is in operation. 
     The downstream end of each link rod  50  is inserted in a boss  72  belonging to the outer casing, which boss projects outward and is L-shaped. The boss  72  has two coaxial holes into which bushings  58  are set in such a way as to form rims  60  on the inside of the boss  72 . In a similar way to the clevises  56 , the boss comprises flat parts  74 , one of which is intended to engage with a flat  70  belonging to the threaded pin  62 . A locknut  66  holds the threaded pin  62  in position in the holes in the boss  72  and the bore in the ball swivel  54  belonging to the link rod  50 . 
     As depicted in  FIG. 3 , the boss  72  extends between two successive injectors  38 , allowing the link rod  50  to be sited as close as possible to the injectors  38  in order to allow the injectors  38  to be positioned very precisely relative to the combustion chamber  48 . It is thus possible to have good control over the penetration of the injectors  38  in order to optimize combustion of the fuel. 
     The ball swivels  54  are immobilized on each side by the cramping skirts  60  of the bushings  58 . These bushings  58  allow the pins  62  to be positioned very well in the holes. The bushings  58  belonging to the boss  72  also provide sealing against the air bypassing the combustion chamber  48  ( FIGS. 5 to 7 ). 
     The link rod  50  is directed substantially parallel to the axis  16  of the turbomachine, thus making it possible to limit the movements of the combustion chamber  48  in the axial direction. The use of an articulated link rod  50  makes it possible to absorb the radial stresses applied during operation to the chamber  48 . 
     Attaching the link rods  50  to the upstream end of the outer wall  26  that corresponds to the coolest region of the combustion chamber  48  limits the effect of thermal expansion of the chamber  48  on the clevises, thus making it possible to maintain alignment between the injectors  38  and the axis  40  of the chamber  48  and to optimize combustion of the fuel. 
     In order to limit vibration at the outlet from the chamber  48 , a flexible piece  76  is mounted between the downstream end of the outer wall of revolution  26  and the outer casing  18 . This piece  76  comprises an annular rim  78  at its inner end, welded or brazed to the outer wall  26 , and branches  80  extending outward and connected at their outer ends to rims  82  resting against the inner surface of the outer casing  18 . 
     When the turbomachine is not running, the flexible piece  76  is slightly prestressed between the outer wall of revolution  26  and the outer casing  18 . When the turbomachine is running, the flexible piece  76  at least partially absorbs the vibration at the chamber outlet. The special shape of the flexible pieces  76 , with disconnected outer ends, ensures permanent contact between the outer casing  18  and the outer wall  26 . 
     In the embodiment depicted in the drawings, the inner wall of revolution  24  is connected to the inner casing  14  via an annular flange  32 . 
     In an alternative form of the invention, the two, inner  24  and outer  26 , walls of revolution are connected by flexible pieces  76  to the inner  14  and outer  18  casings respectively. 
     In one particular embodiment of the invention that is depicted in  FIG. 8 , the chamber is connected to the outer casing via three link rods  50  distributed about the upper half-circumference of the outer wall  26  of the chamber  48 . One link rod  84  is positioned in a vertical plane passing through the axis  16  of the turbomachine, while the other two link rods  86 ,  88  are positioned symmetrically with respect to this vertical plane. The two symmetric link rods  86 ,  88  are approximately 80° from the link rod  84 , so as to perform their suspension function optimally. 
     Advantageously, the link rods  50  may comprise length-adjustment screws so as to ensure an optimum fit of the chamber into the casing. 
     In an alternative form, the upstream attachment of the link rod  50  is onto the outer casing  18  and the downstream attachment of the link rod  50  is onto the outer wall  26  of the chamber  48 . 
     The invention is particularly beneficial for use in a turbomachine with convergent combustion chamber so as to allow it to be inserted from the upstream end, but can also be used with a divergent combustion chamber in order to improve the precision with which the injectors can be positioned relative to the chamber.