Abstract:
A method for assembling an actuating ram of air bleed valves, which ram is placed between low pressure and high pressure compressors of a turbomachine, the ram including a piston rod surrounded by a spacer extending from the piston cylinder and configured to be connected to an end of the transmission mechanism linked to the bleed valves, the method including: deploying the piston rod such that it projects from the spacer; connecting the projecting piston rod to the end of the transmission mechanism; retracting the piston rod to bring the cylinder closer to the case wall; and attaching the spacer to the case wall.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of actuating rams of air bleed valves placed between a low pressure compressor and a high pressure compressor of a turbomachine, preferably an aircraft turbomachine. 
         [0002]    These bleed valves, also designated by the acronym VBV (Variable Bleed Valves) are indeed intended to be actuated under some circumstances in order to enable part of the air from the stream to switch from the primary flux to the secondary flux, in particular to avoid pumping phenomenon. In other words, these valves are intended to control the flow rate at the inlet of the high pressure compressor in order to limit in particular the pumping risks of the low pressure compressor by enabling part of the air to be discharged out of the annular flow space of the primary flux. Furthermore, in case of an accidental penetration of water into this flow space, in particular as rain or hail, or even of various debris, which are likely to be detrimental to the turbojet engine operation, these valves allow the recovering of this water or these debris which are centrifuged into the aforesaid flow space and their ejection outwardly from the same. In the case of turbofans, these valves can also be configured to enable fragments or debris to go from the flow space of the primary flux to an annular flow space of a secondary flux. 
         [0003]    The invention more precisely relates to the method of assembling an actuating ram of such bleed valves, to a case wall, in particular when the access conditions offered to the operator are restricted. 
       STATE OF PRIOR ART 
       [0004]    As illustrated in  FIG. 1  which is an axial cross-section schematic view of a twin-spool turbojet engine  10 , such a turbojet engine generally includes, from upstream to downstream along the gas flow direction, a low pressure compressor  12 , a high pressure compressor  14 , a combustion chamber  16 , a high pressure turbine  18  and a low pressure turbine  20 , which define a gas primary flux  22 . The high pressure turbine  18  is integral to the high pressure compressor  14  so as to form a high pressure spool, whereas the low pressure turbine  20  is integral to the low pressure compressor  12  so as to form a low pressure spool, such that each turbine drives the rotatably associated compressor about a turbojet engine axis  24  under the thrust of the gases from the combustion chamber  16 . 
         [0005]    An intermediate case  26  is usually sandwiched between the low pressure  12  and high pressure  14  compressors. 
         [0006]    In the case of turbo fans, which comprise a fan  28  ducted by a nacelle  30  to generate a secondary flux  32 , the intermediate case  26  generally includes arms  34  passing through the flow space of this secondary flux  32 . These arms, generally four of them and distributed at 90°, define between each other spaces wherein are arranged outlet guide vanes (OGV) (not shown). 
         [0007]      FIG. 2  illustrates at a greater scale the hub  36  of the intermediate case  26  of a turbojet engine of a known type analogous to that described above. 
         [0008]    This hub  36  includes an inner shroud  58  bounding the flow space of the primary flux  22 , an upstream flange  40  and a downstream flange  42  which are connected to the aforesaid inner shroud  38 , as well as an outer shroud  44  linking said flanges  40 ,  42 . 
         [0009]    The hub  36  supports intermediate case arms  34  attached to the radially outer ends of the flanges  40  and  42 . It also carries outlet guide vanes. 
         [0010]    Besides, this hub  36  is equipped with an annular row of bleed valves  48 , one of which is visible in cross-section in  FIG. 2 . In this figure, there appears more specifically the gate  50  of the valve  48 , which is pivotably mounted about an axis  51 , so as to be movable between an opening position and a closing position of a corresponding port formed in the inner shroud  38  of the hub  36 . 
         [0011]    For actuating the bleed valves  48 , actuated rams  62  are provided, usually two of them arranged at 180°, as well as a transmission mechanism (not represented in  FIG. 2 ) sandwiched between these rams and the bleed valves. These transmission mechanisms are usually of the actuating ring, or twist cable type. 
         [0012]    In this embodiment, both rams are mounted to the downstream flange  42 , but could alternatively be mounted on any case wall, preferably located in proximity to the bleed valves they actuate. 
         [0013]      FIG. 3  shows an exemplary assembly of the actuating ram  62  to a case wall  60 , which thus corresponds herein to the aforesaid downstream flange. In this example, the ram  62  is attached to the case wall  60  using a spacer  64  extending from the ram cylinder  66 . The spacer therefore has a diameter substantially identical to that of the cylinder, and extends from the cylinder end from which projects the piston rod  68 . Besides, the spacer  64  surrounds the external end of the piston rod  68 , that is that opposite to the end carrying the piston. 
         [0014]    The spacer  64  has a downstream end integral to the cylinder, for example fastened by screwing. It then extends upstream to end with a collar  70  for bearing on the downstream surface of the wall  60 . It is this collar  70  which is mounted by screwing to the case wall  60 , for example using screws and inserts. 
         [0015]    The design of this exemplary embodiment of prior art has essentially been dictated by access difficulties for the operator which, here, can only intervene on the downstream side of the wall  60 , that is on the side of the so-called “core zone” located downstream of the fan zone, from which it is separated by the intermediate case. 
         [0016]    Thus, the transmission mechanism is provided to include an end  74  arranged projecting from the wall  60 , to downstream. This end  74  is for example integral to an outlet connecting rod  76  passing through an opening of the wall  60 , this connecting rod  76  being usually provided to be actuated by the ram for the purpose of bringing the bleed valves from the opening position to the closing position, and reversely. 
         [0017]    The end  74  is connected to the free end of the piston rod  68 , as can be seen in  FIG. 3 . The mechanical junction  78  between the piston rod  68  and the end  74 , for example of the ball-jointed connection type, thus lies inside the spacer  64 , provided with one or more side openings  80  enabling the operator&#39;s fingers to go through to access the junction  78 . 
         [0018]    For assembling the ram  62 , the spacer  64  is first attached to the downstream surface of the wall, with the piston rod in a retracted position. The operator, who here only has access from the core zone, then passes his/her fingers through the side openings  80  lying facing the end  74  and the piston rod end, in order to link them to form the mechanical junction  78 . For disassembling the ram carried out in particular during maintenance phases, the abovementioned operations are implemented in the reverse order. 
         [0019]    The openings should thus have a sufficient length to enable the operator&#39;s fingers to go through. This results in providing a large length for the spacer, which is necessarily accompanied by a high weight. This problem is all the more restricting that in order to provide the fire prevention function described below, the spacer generally is made of steel, and can make up more than half the overall weight of the ram. The extra length of the actuating ram due to the attachment spacer besides creates installing constraints as well as vibration amplifications. The cost is also impacted, since the spacer must undergo machinings for forming these openings. 
         [0020]    Furthermore, it is noted that the side openings of the spacer are closed upon operating the turbomachine, for example by suitable removable metal sheets. This can be explained by the need to have available a spacer having a fire prevention function throughout its length. In particular, this fire prevention barrier is provided to avoid that a fire breaking out in the core zone spreads in the fan zone by passing inside the spacer. 
         [0021]    Of course, the fire prevention function complicates the design of these metal sheets, because it requires expensive technologies due in particular to the low manufacturing tolerances permitted and to maintenance constraints, in particular the possibility of assembling and disassembling the ram in a limited period of time, for example in the order of fifteen minutes. 
       DISCLOSURE OF THE INVENTION 
       [0022]    The object of the invention is to overcome at least partly the abovementioned drawbacks, relative to implementations of prior art. 
         [0023]    To do this, the object of the invention is to provide a method for assembling an actuating ram of at least one air bleed valve placed between a low pressure compressor and a high pressure compressor of a turbomachine, said ram comprising on the one hand a cylinder intended to be attached to a case wall from which projects an end of a transmission mechanism linked to said air bleed valve, said cylinder being extended by a spacer being used to attach it to said case wall, and including on the other hand a piston rod surrounded by said spacer and intended to be connected to said end of the transmission mechanism, the method comprising the following successive steps of:
       deploying the piston rod such that it projects from the spacer;   connecting the projecting piston rod to the end of the transmission mechanism;   retracting the piston rod so as to bring the cylinder closer to said case wall; and   attaching the spacer to the case wall.       
 
         [0028]    The invention provides a simple, low cost and low weight solution, in particular thanks to the possibility of removing the spacer side openings made in prior art. 
         [0029]    Indeed, since the side openings are no longer required, even when the operator has a restricted access available, the overall length of the spacer can be reduced. As a result, there is a weight and cost gain, the latter is also decreased thanks to the absence of metal sheets for sealing the openings, which besides makes it easier to achieve the fire prevention function at the spacer for attaching the actuating ram. 
         [0030]    Preferably, the step of retracting the piston rod is implemented such that the mechanical junction between the piston rod and the end of the transmission mechanism lies, at the end of this step, inside said spacer. 
         [0031]    However, in particular depending on the means used to retract the rod, it is possible that the mechanical junction is no longer inside the spacer at the end of this step. By way of example, this step is made either by using a pump to actuate the ram and cause the retraction of its rod, or the ram cylinder is pushed, for example manually, which could possibly result in changing the kinematics and moving the mechanism junction out of the spacer. In this regard, it is indicated that the fact of having the mechanical junction in the spacer at the end of this specific step is not essential, because upon starting the engine, the position of the ram rod is controlled by the calculator thanks to position sensors, and automatically brings this mechanical junction back to the position desired by the calculator, for example inside the spacer. 
         [0032]    Preferably, the step of attaching the spacer through the case wall is carried out by screwing, for example using inserts equipping the case wall, and screws inserted and screwed from the side where the actuating ram lies, that is in the “core zone”. 
         [0033]    Preferably, the step of deploying the piston rod is carried out such that in a ram position enabling its piston rod to be connected to the end of the transmission mechanism, the case wall and the spacer define between each other an access enabling an operator&#39;s fingers to go through. 
         [0034]    Preferably, the space is made so as to have no side opening. It is fixedly secured to the ram cylinder, or alternatively made as a single piece with this cylinder. 
         [0035]    Preferably, the step of connecting the projecting piston rod to the end of the transmission mechanism is performed using a ball-jointed connection or a hinged connection. It is for example provided to place an axis between both these elements to be connected to achieve the ball-jointed/hinged connection. The process specific to the present invention thus turns out to be particularly adapted to provide the assembly of this connection type, requiring the intervention of the operator as close as possible to the two elements to be connected. 
         [0036]    Such a connection enables in particular a non-linear movement of the end of the transmission mechanism to be allowed. This is in particular the case when the mechanism connecting rod carrying this end is intended to describe a complex trajectory, with for example at least one arc of circle component. 
         [0037]    Preferably, the method comprises a prior step of dimensioning the ram, respecting the following condition: 
         [0000]      ( C−M )/2= Y;  with 
         [0038]    “C” corresponding to the theoretical maximum stroke of the piston; 
         [0039]    “M” corresponding to the mechanical stop margin in a retracted position of the rod; 
         [0040]    “Y” corresponding to the distance between the wall and the centre of the mechanical junction between the piston rod ( 68 ) and the end, with the centre of the mechanical junction arranged in the spacer attached to the wall, and bringing on the one hand each valve into a closing position and bringing on the other hand the piston rod into a retracted position. 
         [0041]    This dimensioning is particularly optimal to enable a satisfactory access for the operator, while having a reduced overall space. However, other values are possible for Y, the aim being in particular to bring the mechanical junction sufficiently far from the wall to enable an easy manipulation for the operator ensuring the connection. 
         [0042]    Preferably, the distance “C−M” is equal to about 40 mm. This distance “C−M” also corresponds preferably to the access enabling an operator&#39;s fingers to go through, when the piston rod is placed in the deploying position. 
         [0043]    Another object of the invention is also to provide an actuating ram of at least one air bleed valve for being placed between a low pressure compressor and a high pressure compressor of a turbomachine, said ram comprising on the one hand a cylinder extended by a spacer being used to attach the ram to a case wall of a turbomachine, and including on the other hand a piston rod surrounded by said spacer and intended to be connected to the end of the transmission mechanism. According to the invention, said spacer is free of side openings. In other words, it is made in a single piece, by being solid and continuous on 360°. This enables it in particular to ensure a very satisfactory fire prevention function. 
         [0044]    Further advantages and characteristics of the invention will appear in the detailed non-limiting description below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]    The invention will be better understood, and further details, advantages and characteristics thereof will appear upon reading the following description made by way of non-limiting example and in reference to the appended drawings wherein: 
           [0046]      FIG. 1 , already described, is an axial cross-section schematic view of an airplane twin-spool turbojet engine of a known type; 
           [0047]      FIG. 2 , already described, is an axial cross-section partial schematic view at a greater scale of a turbojet engine of a known type substantially of the same type as that of  FIG. 1 ; 
           [0048]      FIG. 3 , already described, is a cross-section schematic view for assembling an actuating ram of bleed valves, to a case wall; 
           [0049]      FIGS. 4   a  to  4   d  represent different successive steps for mounting an actuating ram of bleed valves, according to a preferred embodiment of the invention; and 
           [0050]      FIGS. 5 and 6  are schematic views illustrating dimensioning of the actuating ram. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0051]    A preferred embodiment of the assembling method according to the invention is represented in  FIGS. 4   a  to  4   d . It aims at assembling, to the case wall  60 , the ram  62  actuating the VBV bleed valves  48 , through the transmission mechanism. For the implantation of the invention, the elements described in reference to  FIGS. 1 to 3  remain identical or similar, except for the spacer  64  which is free of side openings. It thus has a fully solid side wall extending between its upstream collar  70  and its downstream end integral to the ram cylinder  66 . Thus, in the figures, the elements bearing identical reference numerals correspond to identical or similar elements. 
         [0052]    Here again, the spacer  64  can be fixedly fastened to the ram cylinder  66 , or be made as a single piece with the same. In the first case, steel will be preferentially chosen, whereas in the second case, it would rather be aluminium or an alloy thereof. 
         [0053]    For the implementation of the method, first the end  74  of the connecting rod  76  should be projecting with respect to the wall  60 , to downstream, that is on the side where the ram should be assembled. The projection distance has to be such as to then allow handling by the operator, as will be described hereinafter. This position of the connecting rod  76  can correspond to any position of its stroke along its axis, at the end of which it places the VBV valves respectively in the opening position and in the closing position. However, preferentially, this position of  FIG. 4   a  is close or identical to that placing VBV valves into the closing position. 
         [0054]    In parallel, the deployment of the piston rod  68  is carried out, such that it projects from the spacer  64  also on a suitable distance so as to then allow handling of the end of the rod by the operator, as will be described hereinafter. This deployment of the piston rod  68  is also schematized in  FIG. 4   a.    
         [0055]    Then, the ram with its deployed rod is brought closer to the end  74 , as shown in  FIG. 4   b . In this closer position of the ram  62  enabling its rod  68  to be connected to the end  74 , the case wall  60  and the collar  70  of the spacer define between each other an access  84  enabling an operator&#39;s fingers to go through. Typically, this access has an axial length in the order of the value of the ram stroke, for example about 40 mm. This access  84  can be increased by tilting the axis of the ram  62  with respect to the axis of the connecting rod  76 , as has been schematized in  FIG. 4   b . The access  84  is then defined by the most extended part of the opening between elements  60  and  70 , herein the radially outer part, the most accessible to the operator from outside the turbojet engine. 
         [0056]    The connection of the piston rod  68  to the end  74  of the transmission mechanism can then be performed via this access  84 , using conventional means resulting in obtaining the mechanical junction  78 , for example of the ball-jointed connection type. 
         [0057]    Once the mechanical junction is obtained, the partial or full retraction of the piston rod  68  is carried out so as to bring the cylinder  66  closer to the wall  60 , as schematized in  FIG. 4   c . This retraction is preferably carried out by moving the cylinder  66  without moving the rod  68  relative to the wall  60 , after the connecting rod  76  and the rod  68  have been realigned. It is manually implemented or using a suitable tooling, preferably a pump or the like. During this retraction of the piston rod  68 , the latter as well as the connecting rod  76  thus remain substantially static with respect to the wall  60 . The retraction is completed when the collar  70  comes to bear against the downstream surface of this wall  60 , as is shown in  FIG. 4   d . At this stage, the mechanical junction  78  then lies inside the spacer  64 , within which it can remain confined during the connecting rod stroke aiming at switching from the opening position of the VBV valves to their closing position, and reversely. Alternatively, during this stroke, the junction  78  can go through the opening of the wall  60 , and thus go on the other side thereof. 
         [0058]    The attachment of the collar  70  to the wall  60  can then be carried out, for example by assembling screws on inserts (not represented) equipping this wall, this screwing being performed from the downstream side where lies the ram. Finally, the ram  62  is thus embedded into the case wall  60 , cantilevered. 
         [0059]    The invention thus allows an easy assembly of the ram even with a restricted access to the operator, in particular limited to only the downstream side of the wall  60 . 
         [0060]    For the disassembly of the ram  62  carried out during maintenance phases, the abovementioned operations are implemented in the reverse order. 
         [0061]    In reference now to  FIGS. 5 and 6 , an exemplary embodiment of the actuating ram  62  assembled to the case wall  60  is illustrated, with several preferred dimensioning criteria. 
         [0062]    In  FIG. 5 , the configuration is that placing the VBV bleed valves  48  into the closing position. The piston rod  68  is thus retracted into the regulated stop position. Only a margin “M” is then observed between the piston  68  and the mechanical stop formed by the cylinder bottom. In this configuration, the distance “Y” is defined between the wall  60  and the centre of the mechanical junction  78 , along the direction of the connecting rod  76  and the piston rod  68 . The distance “X” is in turn defined between the centre of the mechanical junction  78  and the end of the cylinder  66 , still along the same direction. Finally, the distance “C” corresponds to the theoretical maximum stroke of the piston, that is the distance separating both bottoms of the cylinder  66 . 
         [0063]    Thus, the length of the spacer  64  corresponds to the sum of the values X and Y. The length C−M, referenced in  FIG. 6 , here corresponds substantially to the access  84 , without taking into account a possible tilting of the ram  62 . This length therefore is preferentially sufficient to let an operator&#39;s fingers pass through. Finally, though not apparent in the figures, it is preferentially provided that the distance Y corresponds to about half the length C−M. The distance C−M is for example in the order of 40 mm, with M usually set to about 2 mm. 
         [0064]    It is besides noted that when the spacer  62  is attached to the wall  60 , as in  FIG. 5 , respecting distance Y leads not only to place each valve  48  into the closing position, but also leads to place the piston rod  68  into the retracted position, wherein the aforesaid margin M is observed. 
         [0065]    Of course, various modifications could be made by those skilled in the art to the invention just described, only by way of non-limiting examples.