Patent Abstract:
An accessory gearbox for a turbomachine, the gearbox being equipped with a pump and including intermeshing pinions, one of which is formed as a single piece with a coaxial shank for driving a rotary part of the pump, wherein said rotary part is directly mounted on the shank.

Full Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an accessory gearbox for a turbine engine, this accessory gearbox, also referred to as an AGB, being provided with an apparatus and in particular a pump such as a centrifugal pump. 
       PRIOR ART 
       [0002]    The continuous search for performance in an aeronautical engine leads to integrating an accessory gearbox in a more and more constrained environment. The overall size of an accessory gearbox contributes to the overall performance of the engine. It therefore becomes necessary to reduce the size of the accessory gearbox and the apparatuses thereof. 
         [0003]    An accessory gearbox for a turbine engine is intended to transmit mechanical power originating from the turbine engine to apparatuses such as a pump, an air/oil separator, an electricity generator, etc. The accessory gearbox comprises intermeshing pinions, at least some of which are rigidly connected to coaxial shanks intended to rotate the moving parts or rotors of the apparatuses. 
         [0004]    In the prior art, the aforementioned shank of each pinion in the gearbox passes through an orifice in the casing of the accessory gearbox and is connected outside the gearbox to a shaft of the rotating part of the apparatus. 
         [0005]    When the apparatus is a centrifugal pump, for example a fuel pump, this pump comprises a wheel that is constrained to rotate with a shaft that is intended to be rotated by the shank of the pinion. The shaft is rotationally guided by bearings mounted in the centrifugal pump. This centrifugal pump is of the volute type, this volute forming part of the fixed part or stator of the pump and allowing the pressure necessary for the correct functioning of the pump to be generated. The fixed part-moving part assembly of the pump is connected to the accessory gearbox by means of the shank of the pinion and is then fixed to the casing of this gearbox. 
         [0006]    However, this technology is not satisfactory since the gearbox and the apparatus are too bulky, which makes it difficult to integrate them in the turbine engine. 
         [0007]    The invention provides a simple, effective and economical solution to this problem. 
       DISCLOSURE OF THE INVENTION 
       [0008]    The invention proposes an accessory gearbox for a turbine engine, this gearbox being provided with a pump and comprising intermeshing pinions, one of which is formed integrally with a coaxial shank for driving a rotating part of the pump, characterised in that this rotating part is directly mounted on the aforementioned shank. 
         [0009]    According to the invention, a part of the pump is integrated in the accessory gearbox and in particular in the space defined by the casing of the accessory gearbox. This is made possible by the fact that the rotating part of the pump is directly mounted on the shank of a pinion of the accessory gearbox. In other words, as opposed to the prior art, in which the rotating part was carried by a shaft intended to be driven by the shank of a pinion of the gearbox, the rotating part is in this case directly carried by the shank of the pinion. This makes it possible to eliminate both the shaft of the pump from the prior art and its guide bearings, and results in a saving in mass and a significant reduction in the axial size of the gearbox and of the pump (the axis in question here being the rotation axis of the pinion shank and of the rotating part of the pump). Moreover, the rotating part of the pump may be rotationally guided by the guide bearings of the shank of the pinion, which improves the reliability of the assembly. 
         [0010]    In a preferred embodiment of the invention, the pump is a centrifugal pump and its rotating part is a wheel that is directly mounted on one end of the aforementioned shank. 
         [0011]    The wheel may be mounted between a first and a second casing of the centrifugal pump, which are fixed to a casing of the gearbox. 
         [0012]    The shank is preferably rotationally guided by a bearing carried by the first casing. The first casing may be in the form of a disc. It may comprise a central orifice for the shank to pass through. The first casing may comprise at its internal periphery a cylindrical rim for mounting the bearing for guiding the shank. 
         [0013]    The second casing may comprise at its external periphery a flange for fixing for example to a fixing flange of the first casing or of the casing of the gearbox. 
         [0014]    The centrifugal pump may comprise a volute defined by the second casing or the casing of the gearbox. 
         [0015]    The first casing may define, together with the wheel, an annular space for housing sealing means, for example dynamic ones. 
         [0016]    The present invention also concerns a turbine engine, such as a turbojet engine, a turboprop engine or a turboshaft engine for an aeroplane or helicopter, characterised in that it comprises a gearbox as described above. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0017]    The invention will be understood more clearly and other details, features and advantages of the invention will emerge upon reading the following description given by way of non-limiting example and with reference to the accompanying drawings, in which: 
           [0018]      FIG. 1  is a highly schematic view of a turbine engine accessory gearbox on which two apparatuses are mounted; 
           [0019]      FIG. 2  is a highly schematic partial view in axial section of an accessory gearbox equipped with a centrifugal pump, and represents the art prior to the invention; 
           [0020]      FIG. 3  is a highly schematic partial view in axial section of an accessory gearbox equipped with a centrifugal pump, and represents the invention, and 
           [0021]      FIGS. 4 and 5  are schematic partial views in axial section and in perspective of an accessory gearbox and of a centrifugal pump according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Reference is made first of all to  FIG. 1 , which depicts highly schematically an accessory gearbox  10  for a turbine engine, such as a turbojet engine, a turboprop engine or a turboshaft engine for an aeroplane or helicopter, this gearbox  10  being equipped with accessories or apparatuses  12 , of which there are two in the example depicted. 
         [0023]    The accessory gearbox  10  is intended to transmit mechanical power originating from the turbine engine by means of a radial shaft emerging therefrom, and to transmit it to the apparatuses, including pumps, air/oil separators, electricity generators, etc. The transmission takes place through a kinematic chain consisting of successive pinions  14 ,  16 ,  18 ,  20 , of which there are four in the example depicted. 
         [0024]    The pinions  16  and  20  each comprise a coaxial shank  22 , which is formed integrally with the corresponding pinion, and which passes through an orifice in the casing  24  of the accessory gearbox. The end part of the shank  22  of the pinion, situated outside the gearbox  10 , is engaged with a shaft  26  of the rotating part of the corresponding apparatus  12  in order to rotate this rotating part. 
         [0025]      FIG. 2  is a highly schematic view to a larger scale of the region where a pinion shank  22  is connected to a rotor shaft  26  of an apparatus  12 , which in this case is a centrifugal pump  30  having a volute. 
         [0026]    The shank  22  of the pinion is centred and rotationally guided by bearings  32  that are mounted in the casing  24  of the accessory gearbox  10 . The shaft  26  of the apparatus  12  is connected by one end to the part of the shank  22  situated outside the casing  24  and is centred and rotationally guided by bearings  33  mounted in a fixed part, such as a casing  34 , of the pump (apparatus  12 ). 
         [0027]    The centrifugal pump comprises a wheel  36  that is carried by the shaft  26  and is constrained to rotate with the shaft. The casing  34  of the pump defines a fluid inlet  38  upstream of the wheel  26 , a volute  40  and a fluid outlet downstream of the wheel, i.e. at the external periphery thereof. 
         [0028]    The technology depicted in  FIG. 2 , which represents the prior art, has the drawback of being axially bulky (axis A). The invention, depicted schematically in  FIG. 3 , makes it possible to overcome this problem by integrating a part of the apparatus  12 , namely the centrifugal pump in the aforementioned example, in the casing  24  of the accessory gearbox. 
         [0029]    This is made possible by the direct mounting of the rotating part of the apparatus on the shank of the pinion. In  FIG. 3 , the wheel  36  of the pump is in fact fixed to one end of the shank  22 . Part of the casing of the pump is housed inside the casing  24  of the accessory gearbox  10  and further serves as a support for a first bearing  32   a  for guiding the shank  22 , another bearing  32   b  for guiding the shank being carried by the casing  24  of the accessory gearbox  10 . 
         [0030]    Reference is now made to  FIGS. 4 and 5 , which depict a more concrete embodiment of the invention, and in which the elements already described above are designated by the same references. 
         [0031]    The casing  24  of the accessory gearbox  10  comprises an opening  44  having a circular contour that has the shank  22  of the pinion  18  passing through it axially. As can be seen in the drawings, the pinion  18  and the shank  22  are formed in a single piece, the shank having a roughly tubular cylindrical shape in this case. The shank  22  is rotationally guided by the bearings  32   a ,  32   b , the bearing  32   b  being carried by the casing  24  and the bearing  32   a  being carried by a first casing  34   a  of the pump. 
         [0032]    This first casing  34   a  is in the form of a disc and is intended to be applied and clamped against the casing  24  of the gearbox  10  in order to close off the aforementioned opening  44 . This first casing  34   a  comprises a central bore for the shank  22  to pass through and comprises at its internal periphery a cylindrical rim  50  extending inside the gearbox  10  and inside which the external cage of the bearing  32   a  is fixed, which is of the ball type in this case. The internal cage of the bearing  32   a  is fixed to the shank  22 . 
         [0033]    In a conventional fashion, the wheel  36  of the pump comprises a central hub surrounded by an annular wall and connected to this wall by blades, the hub and the wall defining therebetween a centrifugal stream having an axial inlet and a radial outlet. 
         [0034]    The wheel  36  of the pump is formed integrally with a rim  52 , as opposed to being mounted on the end of the shank  22 . In the example depicted, the rim  52  is connected to the hub of the wheel  36  and extends axially on the opposite side to the inlet of the centrifugal stream. 
         [0035]    The rim  52  has an internal diameter slightly greater than the external diameter of this end of the shank. In the mounting position, the rim  52  passes axially through the opening in the first casing  32   a  and the opening  44  in the casing  24  of the accessory gearbox  10 . 
         [0036]    The end of the shank  22  of the pinion, which passes through the opening  44  in the gearbox  24 , comprises a radially internal annular rim  56 , the internal periphery of which defines a passage orifice for a screw  60  for fixing the wheel  36  to the shank. The hub of the wheel  36  comprises a tapped axial hole  54  which, in the mounting position, is aligned with the orifice thereof. The screw  60  is engaged inside the shank and is then screwed in the hole  54  of the wheel  36  through the orifice in the end of the shank  22 . This screwing ensures axial holding of the wheel  36  on the shank  22 . This assembly between the wheel  36  and the shank  22  must be supplemented by means of a form-locked connection (type P3G or similar), constraining the parts to rotate with respect to each other. 
         [0037]    The external periphery of the wheel  36  defines, together with the first casing  34   a , an annular space  61  in which dynamic sealing means of the type consisting of a carbon contact gasket or separation gasket for example can be housed. In the case of a fuel pump, a double dynamic sealing having an intermediate drain may be used in order to prevent oil/fuel mixing. 
         [0038]    A second casing  34   b  is attached and fixed to the first casing  34   a  and defines, together with this first casing, a chamber for housing and rotating the wheel  36 . This second casing  34   b  comprises at its external periphery a flange  62  for fixing by means of the screw and nut type on a corresponding annular flange (not visible) of the casing of the gearbox  10 , the external periphery of the first casing  34   a  being interposed between these flanges and intended to be clamped between these flanges by screw clamping. In a variant, the casing  34   b  may be fixed directly to the casing  34   a.    
         [0039]    The second casing  34   b  defines a substantially cylindrical tubular inlet  38  for supplying fluid to the pump, and an annular peripheral space  64  for the fluid to emerge from the pump, this space comprising a volute (not visible).

Technology Classification (CPC): 5