Abstract:
An engine includes a first element, a second element, an exhaust duct which extends from the first element into the second element, a connecting element which connects the first element to the second element and delimitates the exhaust duct at the transition between the first and second elements, the connecting element being flexible to allow relative movements between the first and the second elements. The connecting element includes a ring whose fastening to the first element is offset radially relative to its fastening to the second element.

Description:
[0001]     The present application is a continuation of International Application No. PCT/SE2005/000664, file May 4, 2005, which claims priority to SE 4041500-4, filed Jun. 4, 2004, both of which are incorporated by reference. 
     
    
     BACKGROUND AND SUMMARY  
       [0002]     The present invention relates to an engine, comprising a first element, a second element, an exhaust duct which extends from the first element into the second element, a connecting element which connects the first element to the second element and delimitates the exhaust duct at the transition between the first and second elements, the connecting element being flexible to allow relative movements between the first and the second element.  
         [0003]     The invention also relates to a vehicle provided with such an engine, the engine being situated with the second element vertically above or below the first element and under a floor of the vehicle.  
         [0004]     In addition, the invention relates to a connecting element for absorbing thermal movements between a first element and a second element connected to it, whereby an exhaust duct extends from the first element into the second element.  
         [0005]     The field of the invention comprises in particular engines for vehicles, particularly load-carrying vehicles, e.g. trucks or buses, although other applications are also conceivable.  
         [0006]     The first and second elements are exhaust duct constituent elements in or close to the engine of a vehicle. In particular, the invention relates to such elements in cases where thermal effects arising for example from exhaust gases flowing through the elements concerned cause relative movements between the elements as a result of their differing thermal expansion. The elements may be separately suspended relative to, or fastened to, one and the same frame and thereby be to some extent positionally fixed relative to one another. A connecting element provided at the transition between the elements therefore needs to be both flexible and sealing with respect to the exhaust gases which may be expected to flow through the elements concerned.  
         [0007]     The invention applies in particular to engines where a gas turbine is arranged in or forms part of the first element, and where a heat exchanger is arranged in or forms part of the second element, exhaust gases from the gas turbine being led away from it via the exhaust duct. The heat exchanger is preferably a stationary heat exchanger in which heat exchange takes place between exhaust gases and combustion air which is supplied to the gas turbine. In such cases the first element may take the form of a housing which surrounds the gas turbine, while the second element may take the form of a housing which surrounds or forms part of the heat exchanger.  
         [0008]     The connecting element comprises preferably a so-called compensator, preferably of the type called fabric compensator and which comprises a flexible fabric which either in itself or by being coated with suitable material can be substantially gas-tight. It may be mentioned in this context that the second element, which surrounds or forms part of the heat exchanger, is thermally insulated outside, whereas the first element, the gas turbine housing, is thermally insulated inside, which means that a substantial temperature difference may occur between these components, resulting in relative movements between the elements.  
         [0009]     In the development of modern vehicles there is a constant need to reduce the space required for the engine. In vehicles where the engine is situated under the floor, there is a need to reduce the engine&#39;s height requirement to a minimum.  
         [0010]     Heat exchangers, so-called recuperators, for gas turbines are generally so designed that their outer casing assumes a temperature close to that of the hot gas. Insulation is applied on the outside of the recuperator to reduce temperature effects on the surroundings. This means that the temperature of the outer casing and connection flange on the inlet portion of the gas side may vary from cold start to maximum operating temperatures up to 700° C.  
         [0011]     In contrast, the outer housing parts of the actual engine, i.e. those of the gas turbine, are insulated inside to make it possible to use conventional nodular iron housings or, in certain cases, aluminum housings. In such cases endeavors are made to ensure that the temperature of the outer housing is relatively low, preferably below 150° C.  
         [0012]     Connecting the outlet housing of the engine/gas turbine to a recuperator therefore requires a connection which can absorb the relative movements which occur between the parts as a result of thermal expansion. The connection also needs to be gas-tight. In most cases this can be achieved by some kind of fabric compensator or metal bellows, which usually has a preferably axial extent. For an automotive gas turbine, however, it is necessary for considerations of space to try to minimise the distance between the recuperator and the engine. The state of the art could be improved in this respect.  
         [0013]     It is desirable to provide an engine of the kind mentioned in the introduction, with a compact design, in particular with an overall height as low as possible, whereby the first and second elements are for example disposed vertically above/below one another and whereby the engine is situated under a floor or the like of the vehicle in which it is installed.  
         [0014]     It is also desirable to propose a connecting element between a first element, which advantageously surrounds or forms part of a combustion engine, preferably a gas turbine, and a second element, which preferably surrounds or forms part of a heat exchanger connected to the first element, the connecting element being intended to facilitate a compact engine design and be of simple construction and advantageous to produce from the cost point of view.  
         [0015]     According to an aspect of the present invention, the engine mentioned in the introduction can include a connecting element that forms a ring whose fastening to the first element is offset radially relative to its fastening to the second element. Ring-shaped in this context means not only a ring shape with circular inner and outer peripheries, but also other geometries which may be applicable, depending on, for example, the geometry of the recuperator. A preferred ring shape with respect to the shape of the second element, since the latter takes the form of a so-called recuperator, as will be described below, is therefore substantially rectangular or square inner and outer peripheries. This is a substantial difference from the tubular bellows used by the state of the art as flexible connecting element, and requires significantly less space.  
         [0016]     As the connecting element has bulk in a radial direction relative to the exhaust duct rather than in an axial direction from the first element towards the second element, the elements can be placed closer together in the exhaust flow direction while maintaining the possibility of absorbing thermally related movements between the elements concerned.  
         [0017]     The connecting element has preferably an inner periphery at which it is fastened to the first element, and an outer periphery at which it is fastened to the second element. The inner periphery of the connecting element may be said to face towards the exhaust duct and its outer periphery may be said to face towards the second element. In other words, the second element extends radially externally relative to the exhaust duct in the region where it is adjacent to the connecting element, and the connecting element is a flexible connecting element which extends in a radial direction outwards from the duct towards the second element. The connecting element preferably takes the form of a flexible disc with a thickness which is substantially less than its extent in its propagation plane. Flexibility of the connecting element in the exhaust duct direction is thus promoted.  
         [0018]     The disc including by the connecting element propagates preferably transversely to the longitudinal direction of the exhaust duct at the transition between the first and second elements.  
         [0019]     The second element has preferably, in the region where it is fastened to the compensator, an inside circumference which is substantially larger than the circumference of the exhaust duct at corresponding cross-sections. The first element takes preferably the form of a relatively thin-walled pipe in the region in which it emerges into the second element, whereby the inside circumference of the second element in the region is larger than the outside circumference of the first element, and also conceivably overlap the latter in the exhaust duct direction. The invention comprises thermal insulation applied externally to the first element and internally to the second element in the region and protecting the connecting element from the actual exhaust duct and the hot gas which may be expected to flow through it.  
         [0020]     An aspect of the invention comprises a gas turbine disposed in or forming part of the first element, a heat exchanger disposed in or forming part of the second element, and exhaust gases from the gas turbine being led away from it via the exhaust duct. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     The invention is described below by way of examples with reference to the attached drawings, in which:  
         [0022]      FIG. 1  is a cutaway schematic diagram of part of an engine according to the invention, with a connecting element according to the invention between a first and a second element of the engine,  
         [0023]      FIG. 2  is a cross-section of part of a connecting element according to the invention,  
         [0024]      FIG. 3  is a cross-section of an alternative embodiment of a connecting element according to  FIG. 2 , and  
         [0025]      FIG. 4  is a view from above of a connecting element according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]      FIG. 1  shows schematically a part of an engine  1  according to the invention. The engine  1  is a gas turbine engine and comprises a recuperator  2  and an engine housing  3 , i.e. a housing which surrounds the gas turbine of the engine. Exhaust gases are led from the engine housing  3  to the recuperator via an exhaust duct  4 . In accordance with the invention, the engine housing  3  is an example of a first exhaust duct constituent element and the recuperator  2  is an example of a second exhaust duct constituent element. The engine housing  3  and the recuperator  2  are normally suspended in a frame (not represented in detail) in such a way that they are to some extent positionally fixed and need a flexible connection to absorb thermally induced relative movements.  
         [0027]     The second element, here the recuperator  2 , takes the form of a stationary heat exchanger (unlike movable, e.g. rotating, heat exchangers) in which heat exchange takes place between the hot exhaust gases supplied to the recuperator  2  from the engine housing  3  and combustion air delivered via the recuperator  2  to a combustion chamber (not showed). It should be noted that the engine may comprise one or more compressors, intermediate coolers and further components which may normally form part of a gas turbine engine.  
         [0028]     As may be seen in  FIG. 2 , the recuperator  2  is provided externally with thermal insulation  7 , which means that the temperature of the recuperator plates closest to the exhaust duct will vary between the ambient temperature and exhaust temperatures which may be about 700° C. The first element, here the engine housing  3 , is provided with thermal insulation  8  on the inside to make it possible to use engine housing material of lower heat resistance, e.g. aluminium or nodular iron. The temperature of the engine housing walls may thus vary between ambient temperature and about 150° C. Thermal expansion will result in relative movements between the recuperator  2  and the engine housing  3 . To absorb these movements, a compensator  9  is arranged between and is connected to the engine housing  3  and the recuperator  2 .  
         [0029]     The compensator  9  includes a flexible connecting element between the recuperator  2  and the engine housing  3  in that it is arranged to allow axial movements of the recuperator  2  towards and away from the engine housing  3 . To make a compact design possible whereby the distance between the recuperator  2  and the engine housing  3  is as small as possible, the recuperator plate in the region where it is intended to be fastened to the compensator  9 , is wider, i.e. it has an inside circumference which is greater, than the portion of the engine housing  3  to which the compensator  9  is intended to be fastened. Preferably, the recuperator extends radially externally relative to and at a distance from the portion of the engine housing  3  to which the compensator  9  is fastened. The compensator  9  extends mainly radially, i.e. its radial component is greater than its axial component in one or more vectors which describe its extent from the engine housing  3  to the recuperator  2  and relative to the exhaust flow direction (denoted by an arrow in  FIG. 2 ) or the exhaust duct  4 . It thus includes a disc or cone, with a cone angle which is preferably greater than 90° and, still more preferably, greater than 140° and, most preferably of all, close to 180°, i.e. a largely flat disc, in order to have as little bulk as possible in an axial direction.  
         [0030]     The compensator  9  takes the form of a flexible disc or plate, or a brim extending round the outlet of the engine housing  3 . In the version depicted in  FIG. 2 , it is fastened by bolts  10  to a flange  11  which starts from the engine housing  3 , and by bolts  12  to an end of the recuperator  2  which is situated radially externally relative to the flange  11 . As may be seen in  FIG. 4 , the compensator  9  is provided with means  5 ,  6  for fastening to the engine housing and the recuperator respectively, the means  6  for fastening to the recuperator being disposed radially externally relative to the means  5  for fastening to the engine housing, the means taking the form of holes to accommodate the bolts  10  and  12  respectively. The radially inner bolted connection including the first-named bolts  10 , and the radially outer bolt connection including the latter bolts  12 , are largely situated in the same radial plane and therefore contribute only to a small extent to the amount of distance between the recuperator  2  and the engine housing  3 . The flange L 1  is made of thin sheet metal and is bent back towards the engine housing  3  in the region radially outside the region in which it is fastened to the engine housing  3 . The overall height is thus further reduced.  
         [0031]      FIG. 3  shows an alternative version in which the compensator  9  is fastened directly to the engine housing  3  without any intermediate flange. This is a possible solution if the engine housing  3  exhibits low enough temperatures as to be sustained by the compensator material.  
         [0032]     Reverting in particular to  FIG. 2 , a thermally insulating cushion  13  is arranged between the engine housing  3  and the recuperator  2  to protect and thermally insulate the compensator  9  from the exhaust gases in the exhaust duct  4 .  
         [0033]     A first annular guide plate  14  for guiding the exhaust gases past the compensator  9  is fastened to the engine housing  3 , and a second annular guide plate  15  for guiding the exhaust gases past the compensator  9  is fastened to the recuperator  2 . The guide plates  14 ,  15  together form the portion of the exhaust duct  4  which extends from the engine housing  3  to the recuperator  2  in the region where the compensator  9  is arranged radially externally relative to them.  
         [0034]     The guide plate  14  fastened to the engine housing  3 , and the guide plate  15  fastened to the recuperator  2 , overlap one another in the longitudinal direction of the exhaust duct  4 . The first and second guide plates  14  and  15  respectively together overlap and protect the thermally insulating cushion  13  from the exhaust gases in the exhaust duct. The guide plate  14  fastened to the engine housing  3  extends, in the region where it overlaps the second guide plate  15 , radially within the latter with a clearance which allows for thermal movements arising from the sometimes great differences in temperature of the components to which they are fastened. The contact surface of the guide plate  14  relative to the engine housing  3  needs to be minimised in order to minimise heat conduction from the guide plate  14  to the engine housing  3 .  
         [0035]     The compensator  9  further comprises seal means  16  for sealing it relative to the engine housing  3  or the recuperator  2 . The seal means  16  take the form in this case of a string of seal material, preferably Teflon or some other suitable material such as silicone rubber, which is applied between the compensator  9  and the component the recuperator  2  and the engine housing  3  respectively, to which the compensator is fastened.  
         [0036]     It should be noted that a number of alternative embodiments of the invention would be obvious to a person skilled in the art. The features indicated above for the example where the first element comprises a housing for a gas turbine and the second element comprises a recuperator are not limited to such an application but may with advantage occur in other applications where the first and second elements form quite different exhaust duct components of an engine.  
         [0037]     In the present application, the use of terms such as “including” is open-ended and is intended to have the same meaning as terms such as “comprising” and not preclude the presence of other structure, material, or acts. Similarly, though the use of terms such as “can” or “may” is intended to be open-ended and to reflect that structure, material, or acts are not necessary, the failure to use such terms is not intended to reflect that structure, material, or acts are essential. To the extent that structure, material, or acts are presently considered to be essential, they are identified as such.  
         [0038]     While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims.