Abstract:
Device for mechanically decoupled retention of components perfused by hot gas in an aircraft, with a coupling member for coupling to a component emitting hot gas and to a component accepting hot gas, with a holder, with a flange, and with a bellows, the holder being fittable to a housing or frame connected to the component emitting hot gas, the bellows being fastened by one end to the flange and by the other end to the holder, and the coupling member being fastened to the flange. By virtue of the device, both an angular misalignment and radial and axial positional misalignment can be equalized.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a §371 national stage patent application of PCT/EP2008/009462, filed Nov. 10, 2008, which claims priority from German Patent Application No. 10 2007 061 995.4, filed Dec. 21, 2007 and claims the benefit of U.S. Provisional Patent Application No. 61/015,870, filed Dec. 21, 2007, each of which is incorporated herein by reference. 
    
    
     FIELD OF THE APPLICATION 
     The invention relates to a device for mechanically decoupled fastening of an aircraft component perfused by hot gas to a housing or frame. 
     BACKGROUND 
     Hot gas in an aircraft arises, for example, in the course of operation of an auxiliary aggregate (in the following also called “Auxiliary Power Unit” or APU, respectively) which generates hot gas in the form of waste gas having a temperature of up to 730° C. A waste-gas system that cools and conducts away waste gas has to be mechanically connected to the structure of the aircraft and simultaneously be capable of equalising relative movements due to operation, thermal expansions, tolerances of manufacture and assembly. 
     In the case where use is made of ducts or channels for transporting gases, relative movements or production tolerances are ordinarily preferably compensated through the use of elastic rubber elements. By reason of the high temperatures arising in the case of pipes perfused by hot gas, the use of temperature-sensitive rubber—such as, for example, a rubber bellows—alone is no longer possible. 
     Furthermore, bellows made of metal are employed in addition which, although temperature-resistant, require certain minimal dimensions in order to be able to equalise predetermined relative movements. The minimal dimensions conflict with a requisite compact and effective structure in an aircraft, so that bellows made of metal are disadvantageous for the desired field of application. 
     In an aircraft, for instance, when conducting away APU waste gases, devices for positional equalisation are frequently used that can be compared with a piston/piston-ring combination. In the case of an APU arranged in the tail of an aircraft, such a technical solution is adequate for compensating the static and dynamic dimensional deviations between the APU, by way of system generating hot gas, and the waste-gas system. In this connection the APU and the waste-gas system are fastened to the same structural section. In the case where the APU and the waste-gas system are not fastened to the same structural section, both dynamic and static dimensional deviations that arise between the structural sections involved have to be taken into account. For instance, in the case of the military transporter of the AIRBUS A400M type the waste-gas system is fastened to the wing/fuselage fairing, and both the APU and an associated firewall are fastened to the fuselage. The dimensional deviations of the various structural sections therefore have to be taken into account in addition to the dimensional deviations between the system generating hot gas and the waste-gas system. Compensating the additive dimensional deviations between the APU and the waste-gas system and also, in addition, the dimensional deviations between the two structural sections by means of the proven piston/piston-ring combination could only be realised with an appropriately high piston-ring height. Associated with this, a correspondingly distinct increase in the restoring forces of the piston ring in the installed state would occur, resulting in increased friction. By virtue of the larger relative movements, in addition the forces due to the mass accelerations would increase. By reason of the thermal loading by the hot gas the structural members for conducting hot gas would be unable to support the high friction forces, as a result of which damage may arise. 
     DE 690 19 36012 relates to a flexible coupling device for a waste-gas or exhaust pipe manifold system of an internal-combustion engine, which serves to connect a first manifold section to a second manifold section. Formed on the first manifold section is a flange extending radially outwards, to which a first end of a flexible bellows is fastened by means of a first retaining ring. At its end facing towards the first manifold section the second manifold section likewise exhibits a flange projecting radially outwards, which forms a flat fastening surface. A second retaining ring is connected to the flange formed on the second manifold section and further secures a guide ring as well as a second end of the flexible bellows. 
     DE 20 2004 019 988 U1 discloses a connecting element for non-rigid connection of the end regions of two pipelines, which comprises a heat-protection element consisting of a mounting-pipe part and a protecting-pipe part for protection of a bellows element from hot gases flowing through the pipelines. Between end regions of the mounting-pipe part and the protecting-pipe part a flexible-spring arrangement may be provided. 
     SUMMARY 
     The object underlying the invention is to propose a device for mechanically decoupled fastening of an aircraft component perfused by hot gas to a housing or frame, which is of compact construction and, in addition, capable of compensating static and dynamic dimensional deviations, and also of withstanding the thermal loads placed upon them. 
     The object is achieved by a device for mechanically decoupled fastening of an aircraft component perfused by hot gas to a housing or frame, which comprises the features stated in claim  1 . 
     The device according to the invention is capable of eliminating the disadvantages that have been described. It reduces or prevents stresses as a consequence of thermal expansion, relative movements of the connecting components, deformations of the structure due to operation, and vibrations. In addition, deviations of position and geometry of the connecting components can be compensated with the device according to the invention. 
     Through the use of a bellows, an angular misalignment and an axial positional misalignment of the device fitted to the housing and of a source of hot gas can be effectively equalised. In an advantageous further development of the device according to the invention a sealing connection to a firewall can be established, with a simultaneous possibility of compensation of positional and angular misalignments. The combination with a hollow conical shielding element is furthermore similarly advantageous, since the bellows is protected by the heat emanating from the hot gas. In addition, in a further development of the device static radial positional deviations can be equalised already in the course of assembly by means of a variably attachable force-fitting connection of a collar fitted to the coupling member. 
     The device according to the invention exhibits a number of advantages in comparison with known devices from the state of the art. The device according to the invention prevents or reduces, on the one hand, strains in the housing, in the pipes perfused by hot gas, in a firewall and in other structural members arranged in the immediate vicinity, both in the course of assembly and in flying operation. Moreover, the device according to the invention compensates static and dynamic dimensional deviations between the components involved and, in the case of use for a waste-gas system, so thermal expansions between the waste-gas system, a firewall and the surrounding structure in accordance with EASA Certification Specification CS 25A1123. The device according to the invention additionally allows the tight routing of a waste-gas channel through a firewall, so that the waste-gas channel complies with ISO Standard 2685 under all operating conditions and in the case of fire. 
     By virtue of the mechanical decoupling, vibrations between a waste-gas system and a firewall are reduced or prevented. By virtue of a force-fitting connection of the coupling member between the flange and the brace plate by means of a screw connection, a constant quality of connection is made possible, with a very flexible radial adjustment option. Lastly, the device according to the invention exhibits a very small installation-space requirement and a low weight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be elucidated in more detail in the following on the basis of the Figures. In the Figures the same objects are labelled by identical reference symbols. Shown are: 
         FIG. 1  top view of the device according to the invention, 
         FIG. 2  lateral sectional view of a waste-gas system with the device according to the invention, and 
         FIG. 3  lateral sectional view of the device according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     For the purpose of better comprehension, in the following an exemplary embodiment of the device according to the invention will be described which is integrated in exemplary manner into a military transport aircraft of the AIRBUS A400M type. The device according to the invention is not restricted to the mechanical decoupling of APU waste-gas pipes but may also be used in other aircraft systems in which a hot gas is to be conducted away through a pipe. 
       FIG. 1  shows a waste-gas system  2  wherein a housing cover which is fitted during operation has been dismantled for the purpose of better representation. The waste-gas system  2  comprises a housing  4  formed from a sheet-metal tank, reinforcing members, holders and fittings, and a waste-gas channel consisting, in exemplary manner, of three consecutive waste-gas pipes  6 ,  8  and  10 , which extends into the housing  4 , starting from a waste-gas inlet  12 . Waste-gas pipe  6  introduces the waste gas of an APU from the waste-gas inlet or interface  12  into the waste-gas system  2 , where it enters waste-gas pipe  8  and from there is finally routed into the environment via waste-gas pipe  10  situated at a waste-gas outlet  14 . The housing  4  is fastened to the mounting location via housing interfaces  16  and  18 , via which the loads of the waste-gas system are conducted away. For example, in the case of the aircraft of type A400M, interface  16  represents the wing/fuselage fairing, and interface  18  represents the firewall. 
     In  FIG. 2  the waste-gas system  2  with the integrated device according to the invention is represented in section. The waste-gas channel which is established by the three waste-gas pipes  6 ,  8  and  10  is perfused with waste gas of an APU from the waste-gas inlet or interface  12 . Waste-gas pipe  8  is fastened in the housing  4  by screws, waste-gas pipe  10  is welded in exemplary manner in a housing cover  20 . Waste-gas pipe  6  is fastened in the housing  4  by the device  22  according to the invention for mechanical decoupling, in order to be able to compensate relative movements and thermal expansion effects and, equally under all operating conditions, to guarantee a tight connection of the waste-gas inlet or interface  12  of waste-gas pipe  6  to the APU. 
       FIG. 3  shows the device  22  according to the invention in more detail on the basis of an enlarged portion identified in  FIG. 2  by dashed lines. In this connection let it be noted that the structural members that have been presented are preferentially of rotationally symmetrical construction and are arranged centrically in relation to the dash-dotted line in  FIG. 3 , with one separately specified exception. 
     An annular holder  24 , which is preferentially manufactured from sheet metal, is arranged on the housing  4  by means of a riveted joint, a welded joint or any other joining method. The holder  24  has a substantially U-shaped profile cross-section with an outer belt  26  and an inner belt  28 . On the outer belt  26  of the holder  24  a bellows  30  is fastened, for example by a clip which is not represented in detail. A conical shielding element  32 , which is likewise preferentially manufactured from sheet metal, is, together with several riveting nuts  34 , arranged on the periphery, riveted or welded to a rotationally symmetrical flange  36  made of sheet metal with an angled profile cross-section. 
     The flange assembly  38  formed from the components constituted by flange  36 , shielding element  32  and riveting nuts  34  connects the housing  4  and a firewall  40 , which has been cut out in rotationally symmetrical manner, to one another and forms a part of the fastening of a coupling member  42  which is of cylindrical construction. In the course of assembly, the flange assembly  38  with the shielding element  32  is pushed over the inner belt  28  of the holder  24 , and subsequently the bellows  30  is fastened to the flange assembly  38  by means of a clip, as a result of which the flange assembly  38  is similarly fastened to the housing  4  by the bellows  30 . 
     The flange assembly  38  is axially guided by the shielding element  32  on the holder  24 . As a result, the flange assembly  38  is axially mobile and can be inclined in any direction. The shielding element  32  serves to hold back the waste gas of the APU, in order to protect the bellows  30  from heat. The housing  4  is inserted into the lining of the wing/fuselage fairing and fastened at the interfaces  16  and  18 , so that it is positioned in fixed manner, the flange assembly  38 , however, firstly bears loosely against the outside of the firewall  40 . In the region of the waste-gas system the firewall  40  consists of a refractory wall which is reinforced with riveted stringers. In the region of the bushing of the waste-gas inlet or interface  12  for attaching to the APU the firewall  40  is recessed in circular manner. From the inside of the firewall  40  the coupling member  42  is inserted and screwed together with the flange assembly  38 , with a brace plate  44  and with the firewall  40  via the riveting nuts  34  by means of screws  46  which are radially distributed over the brace plate  44 . The radial position of the coupling member  42  arises when the waste-gas inlet or interface  12  of the component conducting away waste gas is oriented centrically in relation to the interface of the system generating waste gas (e.g. APU). 
     By virtue of the arrangement that is shown, various technical properties can be realised. Firstly, axial static and dynamic dimensional deviations between the firewall  40  and the waste-gas system  2  are compensated by a displacement of the shielding element  32  on the lower belt  28  of the holder  24 . Deviations in angularity between the housing  4  and the firewall  40  can be compensated by the flange assembly  38  being capable of being inclined arbitrarily in all directions. For instance, an obliquely-standing firewall  40  or an obliquely-situated waste-gas system  2  could be equalised by an appropriate inclination of the flange assembly  38 . 
     Generally, static and dynamic dimensional deviations are compensated in this manner in such a way that strains between individual structural members and components do not occur and both the flange assembly  38  and the brace plate  44  always rest parallel to the respective sealing surfaces. 
     Static radial dimensional deviations at the waste-gas inlet or interface  12  between the waste-gas system  2  and the APU can easily be compensated by appropriate adjustment of the coupling member  42 . In this connection the radially variably positionable coupling member  42  is pushed radially into a desired position (see reference symbol  48 ). As a result of screwing-in and tightening of the screws  46 , the coupling member  42  is fixed and fastened in the appropriate position. 
     Dynamic radial dimensional deviations can be resiliently intercepted via the holder  24  and the shielding element  32 . The dimensional deviations to be compensated can be enlarged by extending the inner belt  28  of the holder  24  and/or the shielding element  32 . Moreover, additional slots in the shielding element  32  and/or in the lower belt  28  of the holder  24  likewise have a positive effect on the magnitude of the dimensional deviations to be radially compensated. In order to guarantee fire resistance of the connection between the holder  24  and the shielding element  32  in accordance with ISO 2685, such slots should be covered. In this connection, two slotted conical shielding elements  32  made of thin sheet metal will have to be laid on top of one another and will preferentially have to be connected by means of a spot-welding process. In this connection, care is to be taken to ensure that the slots of both shielding elements  32  are arranged in slightly offset manner, so that the slots are covered and guarantee tightness. With the same method it is possible for a slotted lower belt  28  of the holder  24  to be sealed. 
     The device according to the invention enables a particularly effective mechanically decoupled retention of components perfused by hot gas in an aircraft, in order to eliminate thermal stresses as far as possible and to equalise positional misalignments between the pipes and sources of hot gas. The technical design that is shown is to be understood merely as an exemplary embodiment, which is to be understood only for the purpose of clarifying the technical features according to the invention, and not as a restriction of the scope of protection.