Abstract:
The present invention relates to an accessory gear box driveshaft ( 125 ) in a turbojet engine with intermediate casing ( 119 ), designed to be mounted in a radial arm ( 119   c ) of the intermediate casing ( 119 ), said shaft being connected, at a first end, to a means ( 126 ) of mechanical transmission to an engine shaft of the turbojet engine, and, at a second end, to a means of mechanical transmission to said box and comprising a bevel gear ( 125   a   1 ) between the two ends, to provide mechanical transmission to an additional accessory ( 128 ). This shaft is notable in that, together with said gear ( 125   a   1 ), it is contained in a case ( 131 ) forming an oil circuit sealed against said arm ( 119   c ). The invention also relates to an accessory ( 128 ) comprising a drive shaft ( 128   a ) collaborating with the gear ( 125   a   1 ) of the transmission shaft ( 125 ) and forming a modular assembly ( 130 ) therewith.

Description:
BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE Prior Art 
       [0001]    The present invention relates to the field of multispool and multiflow turbojet engines, particularly twin spool bypass turbojets. It is aimed at mounting an accessory and at the mechanical transmission between this accessory and a shaft of the engine. 
         [0002]    To drive the accessories mounted on the engine, such as electric generators, oil pumps or fuel pumps, which are necessary to the operation of the engine or that of the aircraft on which it is mounted, the required power is generally taken off the main shaft. A twin spool turbojet engine has two coaxial shafts, one of them, known as the low-pressure or LP shaft, connecting the low-pressure compressor to the low-pressure turbine and together forming the LP spool and the other, known as the high-pressure or HP shaft, connecting the high-pressure compressor to the high-pressure turbine and together forming the HP spool. In the case of such an engine, transmission of power to the accessories is generally provided by a radial shaft, housed in an arm of the intermediate casing, one end of which has a bevel gear collaborating with a gear secured to the high-pressure spool. The other end is mechanically connected to a box containing a number of gears and forming a support for the accessories while at the same time providing them with drive. When the engine is a bypass engine, the radial transmission shaft passes through both the primary flow and the bypass flow streams, respectively, because the accessory gear box, also known by its English-language acronym AGB, is mounted on the casing of the fan that generates the bypass flow. 
         [0003]    Because of evolutions in engine design and engine operating conditions, proposals have been made to mount additional pieces of equipment on the primary flow casing to engage with the radial accessory driveshaft between the two ends thereof. Such pieces of equipment may, for example, consist of a motor for driving the radial transmission shaft, to supplement the drive from the HP spool. Such supplementing is actually useful when the engine layout means that a great deal of power is demanded when this engine is running at idle, in order to drive certain accessories such as electric generators. At idle speed, the HP spool may be unable satisfactorily to supply all the power required in such a design. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention is therefore concerned with mounting an accessory or additional piece of equipment on the engine casing, in a position somewhere between the two ends of the radial transmission shaft, and with the arrangements relating to the radial transmission shaft. 
         [0005]    According to the invention, a turbojet engine comprising an intermediate casing with an accessory gear box driveshaft mounted in a radial arm of the intermediate casing, said shaft being connected, at a first end, to a means of mechanical transmission to an engine shaft of the turbojet engine and, at a second end, to a means of mechanical transmission to said box and comprising a bevel gear between the two ends so as to provide mechanical transmission to an additional accessory, is notable in that the shaft, with said gear, is contained inside a case that forms an oil circuit that is sealed against said arm. 
         [0006]    The driveshaft structure according to the invention has the advantage of avoiding oil leaks and thus limiting fire zones. This is particularly advantageous when the structure of the intermediate casing comprises an attached outer shell ring, the number of bolted components generally increasing the risks of oil leaks. 
         [0007]    According to a preferred embodiment, the case comprises a casing for the gear and two sheaths for those parts of the shaft that lie one on each side of the gear. 
         [0008]    The invention applies in particular to the case where the transmission shaft is made in three cylindrical parts fitting one into the next, with a first cylindrical element on which the gear is mounted and two cylindrical shaft elements extending the first cylindrical element one on each side thereof. 
         [0009]    According to another feature of the invention, the accessory comprising a drive shaft collaborates with said gear of the shaft and is designed to form a modular assembly therewith. This layout is particularly advantageous because it simplifies factory assembly of the accessory and maintenance thereof, and allows the accessory to become interchangeable. The tricky assembly and adjustment of the bevel pair can thus be performed accurately outside the turbojet engine where space is tight and generally cluttered. When it is mounted on the turbojet engine, all that remains to be done is for the various cylindrical elements of the radial transmission shaft to be plugged together. An operation such as this does not require the use of precision tooling. 
         [0010]    More specifically, the modular accessory comprises a support on which the gear is mounted. 
         [0011]    The invention also relates to a bypass turbojet engine also having an intermediate casing with an auxiliary gear box driveshaft housed in a radial arm of the intermediate casing, and an additional accessory, wherein said gear is housed in a space in the radial arm that forms a boundary separating the primary flow duct from the bypass flow duct. 
         [0012]    More specifically, the case is formed of a casing for the gear housed in said space in the radial arm and of two sheaths for those parts of the shaft that are located one on each side of the gear. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    One nonlimiting embodiment of the invention is now described with reference to the attached drawings in which: 
           [0014]      FIG. 1  shows, in axial section, an overview of a twin spool bypass turbojet engine to which the invention may be applied, 
           [0015]      FIG. 2  shows, in axial section, a view through a radial arm of the intermediate casing in which an AGB driveshaft is housed with an additional accessory according to the invention, 
           [0016]      FIGS. 3 to 6  show a sequence in the mounting of the shaft according to the invention comprising an additional accessory. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0017]      FIG. 1  schematically depicts a twin spool bypass turbojet engine with its various main components. It comprises a first shaft  3  connecting, to the left in the figure, a fan rotor  5  and the first compressor stages  7  to the low-pressure turbine  9 ; the assembly forms the low-pressure or LP spool. Coaxial with the first shaft, a drum-shaped second shaft  11  connects the high-pressure stages  13  of the compressor to the high-pressure turbine  15 , this assembly forming the high-pressure spool HP with the combustion chamber  17 . The shaft  3  is supported, at the upstream end, by the bearing  3   a  mounted on the casing  19  that is termed intermediate casing and, at the downstream end, by the bearing  3   c  mounted on the exhaust casing  21 . The HP shaft here is supported by the bearing  3   b  of the intermediate casing  19  and at the rear by the shaft  3 , via the inter-shafts bearing  3   d.    
         [0018]    The intermediate casing is made up of a hub  19   a supporting the bearings  3   a  and  3   b , of an outer shell ring  19   b , provided with forward means of attachment to the aircraft and supporting the fan casing, and of radial arms  19   c  connecting the hub  19   a  to the shell ring  19   b . This intermediate casing at least partially consists of a casting to which radial arms may have been attached. The accessories, such as generators and fuel or oil pumps, are mounted on a gear box  23 , as is known, and which is known in the art as the AGB. This box is mounted on the outside on the fan casing at a location that allows it to be accessed for maintenance. The gears are mechanically connected to a shaft of the engine via a radial driveshaft  25  which is housed in a radial arm  19   c  of the intermediate casing. This driveshaft is connected to a first bevel gear at its inner radial end. This gear is in mesh with a bevel gear secured to the HP spool. The shaft  25  is also connected to a second gear at its outer radial end and this gear is in mesh with an input shaft for the set of gears in the AGB. 
         [0019]    In operation, an engine such as this draws in air via the fan which compresses it into a primary flow which passes through the compression stages, the combustion chamber and the turbine stages, and a bypass flow which is discharged into the atmosphere having bypassed the combustion chamber. The turbines drive the compression means via the LP and HP shafts respectively. 
         [0020]    It has been proposed for an additional accessory to be positioned in the space in the casing between the two, primary and bypass, flows. One example of such an accessory is a top-up motor which contributes to the driving of the radial transmission shaft  25  when the HP spool will not suffice. This is the case in engines in which the number of driven accessories and the power required are high at idle. A top-up motor such as this may be an air turbine, supplied with air from the primary flow. 
         [0021]    Extending beyond this particular example, the invention applies to any additional accessory, whether this is a receiving or driving machine, housed in this space. 
         [0022]    The problem that is encountered in this case stems in part from the lubrication the oil flow requirement for which easily exceeds the means already in place for the accessory driveshaft. The present invention aims at an arrangement to alleviate this problem. 
         [0023]      FIG. 2  depicts, in axial section, a partial view of the engine at the radial transmission shaft, according to the invention. 
         [0024]    Those components that correspond to those of  FIG. 1  bear the same references increased by  100 . Thus, we have an intermediate casing  119  in a radial arm  119   c  of which is housed the radial accessories driveshaft  125 , the accessories not being visible in  FIG. 2 . The shaft  125  passes through the shell ring  119   b  of the intermediate casing and its outer radial end is mechanically connected, for example via a splined connection, to a pair of bevel gears that have not been depicted. 
         [0025]    The arm  119   c  is hollow and formed of three radially distinct parts:  119   c   1 ,  119   c   2  and  119   c   3 . 
         [0026]    The part  119   c   3 , which is aerodynamically profiled, passes through the duct for the primary flow P on one side of which can be seen part of the LP compressor  107 , and on the other side of which there is the HP compressor  113 . The part  119   c   3  of the arm  119   c  is adjacent to the hub  119   a  of the intermediate casing. 
         [0027]    The radial arm  119   c  comprises a part  1   l   9   c   2  passing through the duct for the bypass flow S. The part  119   c   2  is adjacent to the shell ring  119   b.    
         [0028]    The arm comprises a part  119   c   1  between the first two. This part delimits a sector of the annular space which, on one side, extends the nose separating the primary and bypass flows and on the other side is itself extended by an annular space  129  between the two flows. 
         [0029]    In the hub  119   a , the bearing  103   a  supports the shaft  103  of the LP spool and the bearing  103   b  supports a journal  111  forming the upstream end of the compressor  113  of the HP spool. 
         [0030]    The shaft  125  is housed in this radial arm of the intermediate casing. The arm  125  is made in three elements:  125   a ,  125   b  and  125   c . The central first element  125   a  is of cylindrical shape, and hollow, and is secured to a bevel gear  125   a   1 . 
         [0031]    The second element  125   b  is push-fitted, from the radially inner side, onto the first element  125   a  and is held there by a splined connection. At its inner end, it is connected by a splined connection to a bevel gear pair  126  in mesh with the journal  111  of the HP spool. Thus, the element  125   b  is driven by the HP spool. 
         [0032]    The third element  125   c  is push-fitted, from the radially outer side, onto the first element  125   a  and is held there by a splined connection. As has been seen, the radial end of this element is not visible in the figure. It is connected mechanically by a pair of bevel gears to the input shaft of the AGB. The rotational movement of the HP spool is thus transmitted via the transmission means, consisting of the bevel gear pair  126  and the shaft  125 , to the input shaft of the AGB. 
         [0033]    An additional accessory  128  is housed in the space formed by the engine casing between the primary flow duct and the bypass flow duct. The accessory has a movement transmission shaft  128   a  ending in a bevel gear  128   a   1 . The accessory  128  is bolted onto the flank of that part  119   c   1  of the radial arm  119   c  which extends the previous annular space. 
         [0034]    This accessory may be any accessory; it may be a motor, an air turbine, a hydraulic motor, for top-up drive to the transmission shaft  125  where necessary. It may equally be an additional receiving accessory driven by the shaft  125 . 
         [0035]    A support casing  128   b  is secured to the accessory casing  128 . This casing  128   b  supports the central element  125   a  of the transmission shaft  125  via two bearings  128   b   1  and  128   b   2  such that the bevel gear  128   a   1  meshes with the bevel gear  125   a   1  of the element  125   a  to transmit rotational movement from one to the other. To facilitate assembly, the support casing  128   b  comprises a cover  128   b ′ on which the bearing  128   b   2  is mounted. 
         [0036]    The accessory  128  with the shaft  128   a , the support casing  128   b  and the element  125   a  of the shaft  125  together form a module  130  in that this assembly can be assembled separately and mounted on the turbojet engine as a unit as will be explained later on. 
         [0037]    The module  130  associated with the shaft  125  is isolated from the interior space of the arm  119   c  by a case  131 . 
         [0038]    This case consists of a casing  131   a  and of two sheaths  131   b  and  131   c . The casing  131   a  surrounds the support casing  128   b  of the accessory  128  and the element  125   a  that this casing supports. It has three openings, one for the passage of the accessory  128  and two for the shaft elements  125   b  and  125   c  respectively. 
         [0039]    The sheath  131   b  surrounds the element  125   b  of the shaft  125  and the sheath  131   c  surrounds the element  125   c . Appropriate seals provide sealing between the casing  131   a  and the two sheaths  131   b  and  131   c . Likewise, seals are provided at the other two ends of the two sheaths. 
         [0040]    The casing  128   b  is bolted onto the wall of the arm  119   c.    
         [0041]    By virtue of this case, the oil needed to lubricate the accessory and the mechanical transmission elements can be introduced along a circuit which does not interfere with the radial arms of the intermediate casing. For example, the oil already used to lubricate the pair of bevel gears  128   a   1  and  125   a   1  is collected in the space formed between the shaft elements  125   b  and  125   c  and the sheaths  131   b  and  131   c , respectively, so that it can be recycled. 
         [0042]    For more effective recovery, a specially dedicated device may be installed at the lowermost point of the casing  131   a , so as to return directly to the engine recovery circuit most of the oil that has been used to lubricate the bevel gear pair and its rolling bearings. A device such as this would avoid having to return to the AGB this flow of oil which may be contaminated with debris from the mechanical components of the module. 
         [0043]    The assembling of the assembly is now described in conjunction with  FIGS. 3 to 6 . 
         [0044]      FIG. 3  depicts the assembly of the module  130 . The support casing  128   b  is fixed to the accessory  128  the shaft  128   a  of which cannot be seen here. Next, the element  125   a  of the transmission shaft  125  is introduced and the casing is closed using the cover  128   b ′. The bearings between the element  125   a  and the support casing  128   b  have not been depicted. 
         [0045]    In  FIG. 4 , the module  130  is assembled. It will be understood that this operation can be performed in a workshop separate from the engine assembly workshop or at the supplier&#39;s. The module can be supplied assembled, this being a certain advantage because the tricky operations of adjusting the pair of bevel gears need to be carried out by specialist personnel using specialist equipment. 
         [0046]      FIG. 5  shows the fitting of the casing  131   a  of the case  131  into the intermediate casing  119  in the housing  119   c   1 . The radial arms  119   c  have not been depicted. The next step is to introduce the sheath  131   b  fitted with its seals from the outside through the radial openings in the casing  131   a , followed by the sheath  131   c  equipped with its seals. 
         [0047]    In  FIG. 6 , the module  130  is being introduced into the casing  131   a  through the axial opening of the intermediate casing  119 , after the sheath  131   b  has been fitted. The module  130  in place prevents the sheath  131   b  from leaving its housing. The module  130  is then bolted onto a radial wall of the casing  119 , then the mounting of this assembly is completed by fitting the two shaft elements  125   b  followed by  125   c.