Abstract:
A turbo engine comprises a driving shaft and a driven shaft actuated by the driving shaft being coupdriven to this driving shaft by means of a torsional coupling. The torsional coupling is integrated at least into one of the driven and driving shafts comprising a zone that is rotationally flexible, in such a way as to constitute the torsional coupling.

Description:
BACKGROUND 
       [0001]    Embodiments of the present invention relate to turbo engines, for example integrated motor-driven compressors. However, of course one does not go outside the framework of embodiments of the present invention merely because it relates to another type of turbo engine, namely a turbo alternator. 
         [0002]    An integrated motor-driven compressor group comprises a leakproof housing which contains an engine, for example an electric motor, and a compressor group, for example a multi-stage unit, which comprises one or several wheels with blades for compression carried by a driven driven shaft and actuated by a driving driving shaft consisting of the rotor of the motor or actuated by the latter. 
         [0003]    One coupling solution for the driving shaft and the driven shaft consists in a coupling of the driven shaft and the driving shaft by means of a rigid coupling, with bearings provided for supporting the ends of the line of shafts of the motor-driven compressor group, as well as its median portion. 
         [0004]    This solution poses in a certain number of cases manufacturing problems and problems related to the dynamic of the rotor. 
         [0005]    Therefore, it is proposed to couple the driving shaft and the driven shaft by means of a flexible coupling in order to avoid the problems related to the alignment. In this respect, one can refer to the document WO 2004/083644 which describes such a layout. 
         [0006]    The currently used flexible couplings, which are generally of the type with a membrane, increase the axial dimension of the motor-driven compressor group, typically of the order of 35 to 40 cm, compared to a rigid coupling with a flange. In addition, they present a fragility zone because they can be subjected, for example, only to tensile or compression forces that are limited in the axial direction. 
         [0007]    However, during the functioning of the layout described by the document WO 2004/083644, the gas feeding the compressor is extracted in full or in part after the compression stage and is used for cooling the motor. The flow of the cooling gas in the motor takes place in the direction of the compressor. 
         [0008]    The motor-driven compressor has a single abutment on the rotor of the compressor, on the opposite side of the coupling. Due to this fact, an axial thrust is generated in the motor and is absorbed by the coupling prior to being taken over by the axial abutment. 
         [0009]    Therefore, in order to alleviate these inconveniences, it has been proposed to use a torsional coupling placed in a hollow shaft of the compressor. Such a layout is described in the document FR 2 969 722. Although it is effective in alleviating the inconveniences related to the use of a flexible coupling between the driving shaft and the driven shaft, such a layout complicates the structure of the shaft assembly. 
       BRIEF DESCRIPTION 
       [0010]    In view of the preceding discussion, the aim of the embodiments of the present invention is to mitigate the inconveniences related to the layouts according to the state of the art and, in particular, to enable the axial efforts generated during the functioning of the levels of compression to be supported and this in a simple layout. 
         [0011]    Therefore, the object of an embodiment of the present invention is a turbo engine comprising a driving shaft and a driven shaft actuated by the driving shaft being coupled driven to this driving shaft by means of a torsional coupling. 
         [0012]    In addition, the torsional coupling is integrated at least into one of the driven and driving shafts which comprise a flexible zone in torsion so as to form the torsional coupling. This can be, for example, a motor-driven compressor group comprising a motor driving a compressor, comprising a set of wheels with blades for compression mounted on the driven shaft. 
         [0013]    The set is mounted in a common housing which is impermeable to the gas generated by the motor-driven compressor group. Because the torsional coupling is integrated in the driving and/or the driven shaft, the problems, namely in terms of design and manufacturing, in the assembly, which exist in the case of a torsional coupling assembled to a driving or driven shaft, such as described in the above-quoted document FR 2 969 722, are resolved. 
         [0014]    The shaft, in which the torsional coupling is integrated, comprises, in an embodiment, an external peripheral zone which constitutes a means for supporting the functions performed by the rotor. 
         [0015]    This torsional zone, existing at least in one of the driving and driven shafts, is formed, for example, by a cylindric part with a diameter that is smaller than the remaining part of the shaft in which the torsional coupling is integrated. It has, more particularly, a length selected in relation to the diameter in a way to confer to the coupling a torsional capability. Thanks to the presence of this reduction of the diameter, the shaft assembly comprises an internal shaft with reduced dimensions, through which the driving and driven shafts are coupled, permitting a localized deformation of the shaft assembly by the torsion. 
         [0016]    In other embodiments, the torsional cylindrical part can be mounted either in the driven shaft or in the driving shaft, or in the two shafts—both driving and driven. 
         [0017]    The torsional cylindrical part can be entirely in projection starting from the shaft, into which the coupling is integrated, or can be partially or totally situated in the interior of a hollow part, in the form of a hollow shaft, enabling the hollow shaft to support one or several functions carried out by the rotor. When the torsional cylindrical part is located inside the hollow shaft, it is thus in cantilever around the torsional part. This solution can be realized eventually by means of a throat r or by reducing the diameter and of the assembly. 
         [0018]    The realization of the torsional part partially or completely inside a hollow part enables the length of the shaft assembly to be limited and thereby the dimensions, the weight and the cost of the turbo engine. This can have also a beneficial effect on the dynamics of the rotor. 
         [0019]    It has to be noted that the cylindrical part(s) can be obtained by using various techniques. 
         [0020]    One embodiment, comprises an axial cylindrical throat, which delimits in the shaft another internal shaft coupdriven to the other driving or driven shaft and one external shaft. For example, the axial cylindrical throat is formed by means of electroerosion. 
         [0021]    Alternatively, this torsional coupling is obtained by providing at the manufacturing stage a reduction of the diameter (for example by means of forging and by machining) in the driven and/or driving shaft. 
         [0022]    In this case, at least one of the driven and driving shafts comprises in its torsional coupling zone one axial cylindrical throat delimited by an internal shaft and one external shaft assembled around the internal shaft. 
         [0023]    In one embodiment mode, the external shaft is extending till the connection zone of the driving and driven shafts. 
         [0024]    According to another embodiment, the free end of the shaft, into which the torsional coupling is integrated at a diameter that is greater than the diameter of its median part, forms a coupling zone of the internal shaft with the other driving or driven shaft. 
         [0025]    Alternatively, it is also possible to ensure that that the free end of the shaft, to which the torsional coupling is integrated, has a diameter that is less than those of the coupling zone corresponding to the other driving or driven shaft, with which it is coupled, forming a flange that ensures the coupling of the driving or driven shafts. 
         [0026]    Other objectives, characteristics and advantages of the invention will become apparent from a reading of the following description, which is provided solely as an example without limitations and refers to the attached drawings in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  is a synoptic diagram illustrating the general structure of a motor-driven compressor group according to embodiments of the present invention; 
           [0028]      FIG. 2  illustrates a first embodiment of the motor-driven compressor group according to  FIG. 1 ; 
           [0029]      FIG. 3  illustrates another embodiment of a motor-driven compressor group according to the invention; 
           [0030]      FIG. 4  illustrates another example of the realization of compressor group according to an embodiment of the present invention; and 
           [0031]      FIG. 5  illustrates another implementation mode of the torsional zone. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Referring first to  FIG. 1 , a motor-driven compressor according to an embodiment of the present invention, designated by the general reference G, comprises essentially a motor  1 , for example an electric motor with high rotational speed, for example between 6,000 and 16,000 revolutions/minute, powered by a frequency converter and comprising a stator  2  and a rotor  3  forming a driving shaft for the motor-driven compressor group, and a compressor group  4  comprising a set of wheels with blades  5 ,  6  and  7 , here three in number, mounted on the driven shaft  8 . As it can be seen, the driven shaft  8  is supported by the radial bearings  9 . 
         [0033]    The arrangement is mounted on a base (not shown) and is located in a common casing  10 , which is impermeable to the gas generated by the motor-driven compressor group. The casing  10  comprises an input “INPUT”, through which the gas to be generated is drawn by suction into the compressor and an output “OUTPUT”, through which the compressed gas is delivered when it exits from the compressor group  4 . 
         [0034]    In the embodiment shown, the compressor group  4  comprises three wheels with blades mounted on the driven shaft  8 . Obviously, the compressor group  4  can comprise any number of such wheels with blades or comprise a different layout of wheels with blades. 
         [0035]    In the embodiment illustrated in  FIGS. 1 and 2 , the driven shaft  8  is equipped, at the level of its end zone, with a shoulder E, with which this shaft is bolted on the one end with respect to the driving shaft  3  of the motor  1 . 
         [0036]    In any case, the coupling between the driven shaft and the driving shaft consists of a torsional coupling. This torsional coupling is obtained by the implementation in at least one of the driven and driving shafts of a torsional zone, i.e. flexible in the rotation. 
         [0037]    In the embodiment shown in  FIGS. 1 to 4 , this torsional coupling is obtained by machining an axial cylindrical throat  11  in the driven shaft  8 , in order to form in the driven shaft  8  an internal shaft  12 , through which the driven shaft  8  is coupled to the driving shaft  3 , and an external shaft  13 , through which the driven shaft  8  is guided by the radial bearing  9 . The length of the throat will be selected in relation to the diameter of the shaft, in which it is mounted, with a length chosen in such a way as to confer to the coupling a torsional character. 
         [0038]    In this way, by mounting the cylindrical throat in the driven shaft  8 , the useful diameter of the shaft  8 , which transmits the actuation efforts is locally reduced, and its resistance to torsional and radial deformations can be reduced, while retaining an important radial rigidity. The driven shaft and in particular the internal shaft  12  remain notably capable of withstanding the axial force created during the operation of the wheels with compression blades  5 ,  6  and  7 . 
         [0039]    The presence of the torsional part enables because of the localized reduction of the useful section of the shaft assembly, the driven shaft  8  to be endowed with the characteristic that it can be deformed by bending and by elastic torsion so that on the one hand, defects in the angular alignment, on the one hand, and on the other lateral defects, on the other, between the driven shaft and the driving shaft can be compensated, either during the installation of the motor-driven compressor or while it is in operation. 
         [0040]    This flexibility also enables the flexural vibrations between the driving shaft and the driven shaft to be filtered. Furthermore, the torsional zone enables a gradation to be achieved of the efforts transmitted during the rapid changes of the torque transmitted by the motor or the resistive torque produced by the compressor. In addition, the mounting is largely simplified since the shaft assembly is constituted simply by two portions of the shafts, namely the driving shaft and the driven shaft. 
         [0041]    It is to be noted that in the embodiment illustrated in  FIGS. 1 and 2 , the torsional part is mounted in the driven shaft  8 . In addition, the driven shaft  8  comprises an external shaft  13 , whose end is behind in relation t to the free end of the internal shaft  12 , with which this shaft  12  was fixed to the driving shaft  3 . In other terms, in this embodiment, the internal shaft  12  has a diameter that is smaller than the diameter of the end formed by the shoulder E. 
         [0042]    In addition, the torsional coupling is obtained, as can be seen in  FIGS. 1 and 2 , by obtaining, at the manufacturing stage, for example by means of forging and by machining of the driven shaft  8 , a localized reduction of the diameter in order to form the end zone  12  of the driven shaft of reduced diameter, the cylindrical throat being then realized in order to form the external shaft  13 . 
         [0043]    The torsional coupling obtained in the embodiment shown in  FIGS. 1 and 2 , by arranging a throat in the driving shaft can of course be formed by arranging this throat in the driving shaft or in the two shafts—driving and driven. 
         [0044]    In another embodiment, which can be seen in 3, the external shaft  13  extends over a substantial part of the internal shaft  12 , which here does not have an end shoulder. Therefore, the mounting of the internal shaft  12  on the end of the driving shaft  3  employs a flange  14  fixed by being bolted onto the free end of the driving shaft  3  and connected in rotation to the internal shaft  12 . Axial throat could be provided, for example, in the internal peripheral surface of the flange  14 , destined to engage with the corresponding ribs mounted at the free end of the internal shaft  12 . 
         [0045]    In this respect, a flange with a general conical form or endowed with an end shoulder as can be seen in  FIG. 3  can be used. This embodiment is beneficial insofar as it enables the distance between the ends of the shafts to be reduced, i.e. the distance between the free end of the external shaft  13  and the free end with respect to the driving shaft  3 , this distance being fixed by the length of the flange  14 . 
         [0046]    According to a third embodiment, shown in  FIG. 4 , the driving shaft  3  and the driven shaft  4  both have an axial cylindrical throat  11  and  11   a . The throat  11  is similar to the throat used in the embodiment in  FIG. 3 . 
         [0047]    As in the embodiments described above, as regards the driven shaft, the axial cylindrical throat  11  creates an internal shaft  12  and an external shaft  13  which are extended along a substantial part of the internal shaft  12 , with this internal shaft  12  extending in a projection starting from the external shaft  13  along a length that is sufficient for the mounting of a flange  15 . 
         [0048]    As regards the driving shaft  3 , the axial cylindrical throat  11   a  creates in this shaft  3 , an internal shaft  16  and an external shaft  17  which are extended along a substantial part of the internal shaft  16 , with the latter extending in a projection beyond the free end of the external shaft  17  along a length that is sufficient for the mounting of the flange  15 . Thus, in this embodiment, the torsional zone of the shaft assembly is formed in the driving shaft  3  and in the driven shaft  8 . In other terms, with respect to the previously described embodiments, the shaft assembly comprises a torsional zone with increased length. 
         [0049]    It is to be noted that the embodiments shown in  FIGS. 3 and 4 , in which the mounting of the driven shaft and the driving shaft is performed by means of a fitted flange, enabling the torsional zone to be created at the manufacturing stage namely by means of forging and then by machining. 
         [0050]    The implementation of the torsional zone consists, in particular, in the realization of the internal shaft within the driven shaft  8 , through which the driven shaft  8  is coupled driven to the driving shaft  3 , and of an external shaft  13 , which is then assembled to the driven shaft  8  and through which the latter is guided by the radial bearing  9  in a way as to form a cylindrical throat between the two internal and external shafts. In other terms, and as this is illustrated with a dotted line in the figures, the external shaft is assembled around the zone of the shaft which has a reduced diameter. 
         [0051]    Such an assembly can be obtained with various means. The hollow part can be assembled on the rotor, for example close to the torsional zone, for example by bolting and/or through the diameter of the abutment and/or by means of a toothed hirth and/or by using many other assembly modes. 
         [0052]    The embodiments shown in the  FIGS. 3 and 4 , in which the driven shift comprises an internal shaft  12  and an external shaft  13 , are also beneficial since the external shaft can then be used for the implementation of functions carried out by the rotor. In particular, a bearing support and/or a support of one or several wheel(s) with blade(s) can be realized ( FIG. 3 ). 
         [0053]    It is also possible, in a variant, to arrange the axial cylindrical throat driving shaft and in the driven shaft and to make sure, regarding both the driving shaft and the driven shaft, that the distance between the ends of the shafts, namely between the ends of the two exterior shafts  13  and  17 , is equal to half of the torsional length or, in other terms, to ensure that the length of the interior shaft, which extends outside the exterior shaft, is equal to the length of the exterior shaft, as in the embodiment described in the reference to  FIG. 2 , both as regards the driving shaft and the driven shaft. 
         [0054]    Therefore, in the embodiment shown in  FIG. 5 , the torsional zone can be formed by the realization, during the manufacture of the driven shaft, of a zone  18  with diameter that is reduced in a such a way as to confer on the coupling a torsional character. As in the previously described embodiment modes, the coupling with the driving shaft can be realized both by providing a shoulder E at the end, as shown, or by using a fitted flange. 
         [0055]    The reduced diameter zone can also be realized independently from the rest of the driven shaft and can be assembled, as previously indicated in the reference to the  FIGS. 2 to 4 , to the driven shaft. 
         [0056]    Obviously, as it was previously indicated, as an alternative the reduced diameter zone can be formed in the driving shaft or in the two driven and driving shafts. It is to be noted that, as in the embodiments shown in  FIGS. 1 to 4 , the length of the reduced diameter zone is chosen in relation to the diameter of this zone in a way as to confer a torsional character on the shaft. 
         [0057]    For example, for a shaft diameter of the order of 50 mm, the torsional zone can be realized over a length between 600 and 700 mm. 
         [0058]    And finally, it is to be noted that in the different embodiments the axial cylindrical throat produced in the driven shaft and/or in the driving shaft, can be formed by means of electroerosion or by EDM (“Electrical Discharge Machining”), which is a machining procedure consisting in the removal of material in one piece by using electric discharges. 
         [0059]    This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.