Patent Publication Number: US-2011056055-A1

Title: Member for locking ring sectors on a turbine engine casing, including radial passages for gripping same

Description:
TECHNICAL FIELD 
     The present invention generally concerns a locking member for fastening ring sectors on an aircraft turbine engine casing, for example a turbine casing. 
     The invention also concerns a turbine engine for an aircraft comprising such locking members, this turbine engine being able to assume the form of a turbo-prop or a turbojet engine. 
     BACKGROUND OF THE INVENTION 
     Known from the prior art are rings circumferentially fastened on the casing around mobile vanes of the turbine of a turbojet engine, these sectors jointly forming a continuous cylindrical enclosure outwardly defining the gas passage stream in the turbine. The ring sectors are mounted on an inner casing of the turbine using casing elements, called intermediate casing elements or spacers, on which they are hooked by their front ends and maintained at their back ends by C-shaped or sideways U-shaped locking members. The latter parts are axially/longitudinally engaged from the rear on circumferential rims of the back ends of the ring sectors and the intermediate elements of the casing, to keep them radially pressed against each other. 
     This fastening of the ring sectors on the intermediate elements of the turbine casing allows them to follow the heat expansions and contractions of the turbine casing, in which hot gas or cold gas is injected to control its heat expansions and contractions in order to keep as little radial play as possible between the inner surfaces of the ring sectors and the ends of the mobile vanes of the turbine, and thereby increase the turbine&#39;s efficiency. 
     In a known manner, the locking members jointly form an annular locking device centered on the axis of the turbine engine, each member therefore only forming one angular sector of that device. Each member comprises two longitudinal clamping arms extending axially/longitudinally toward the back and connected at their back ends by a connection arm, while their front ends are intended to press at least one ring sector between them against at least one casing element. The latter two elements radially pressed against each other are effectively provided to be housed in the space formed between the two longitudinal arms, longitudinally open towards the front. 
     The locking members are designed, in particular concerning the elasticity and separation of the two longitudinal arms, so that the applied radial gripping is high performance. Yet in such a case, the removal of these locking members, required for example during maintenance operations of the turbine, is extremely difficult, due to the significant radial gripping force exerted by the longitudinal arms on the circumferential rims. Because of this, the removal usually requires the operator to use a tool, which generally has a shape that is not adapted, likely to damage the locking members, as well as the surrounding elements. Such a situation arises for example during the use of a screwdriver, which the operator tries to slide between one of the longitudinal arms of the member and the circumferential rim in contact with that arm. In fact, the screwdriver is then used as a lever arm, likely to damage both the concerned longitudinal arm and circumferential rim, or to injure the operator. 
     As a result, the design of current locking members does not allow quick and easy removal, and also creates significant risks of damaging the clamping arms during such a removal. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The invention therefore aims to at least partially resolve the abovementioned drawbacks, relative to the embodiments of the prior art. 
     To do this, the invention first concerns a locking member for a device used to fasten ring sectors on the casing of an aircraft turbine engine, said member extending along a circumferential direction between a first circumferential end and a second circumferential end, said member having, in cross-section along the plane orthogonal to said circumferential direction, two clamping arms connected together at the rear end thereof by a connection arm extending substantially parallel to the general spacing direction between the two clamping arms, the front ends of the two clamping arms being intended to press at least one ring sector against at least one casing element between them. 
     According to the invention, said member is provided, on either side of a fictional median plane orthogonal to said circumferential direction, with a passage for gripping said member, each passage being formed as a through-passage in said connection arm, emerging in an inter-arm space defined between the clamping arms. 
     Thus, the member according to the invention originally provides for means for its gripping, intended to facilitate its removal after it has been placed on the ring sectors, for example using a suitable tool. 
     Moreover, the particular positioning of the passages through the connection arm, i.e. away from the front ends of the clamping arms ensuring the pressing of the ring sectors, implies that they can easily cooperate with a removal tool without risking damaging the functionalities of that locking member, in particular therefore due to the absence of direct contact between the tool and the aforementioned front ends. In other words, gripping these passages with a tool does not create any direct mechanical stress on the clamping arms, which therefore do not risk being damaged by the pressure from the tool, the stresses in fact being concentrated on the connection arm offset towards the back of the sensitive area. This advantage is also found in the preferred case where the tool is intended to pass through the passages to penetrate the inter-arm spaces, so that the ends of that tool abut against the inner surface of the connection arm, near these same passages. 
     Thus, it is contemplated for the tool to cooperate with the walls of the passages, and/or with the inner surface of the connection arm. 
     Preferably, each passage extends along a guideline substantially orthogonal to the circumferential direction and the spacing direction. Preferably, this line is a straight line, for example extending substantially axially, therefore with the aforementioned spacing direction corresponding to the radial direction. 
     In other words, each straight line is preferably parallel to an axis of the turbine equipped with a plurality of these members to ensure the pressing of the ring sectors against the casing elements. Of course, the orientation of the guidelines of the passages could be different from the axial/longitudinal direction, without going beyond the scope of the invention. 
     Preferably, the two passages are arranged on or near said first circumferential end and said second circumferential end, respectively. These ends correspond to the portions of the member that are the least stressed when the member is in the gripping condition of the ring sectors, such that the presence of the passages at these locations only creates a negligible mechanical weakening of the member, not requiring any overdimensioning of the surrounding areas. 
     Preferably, each passage is substantially cylindrical, with an axis corresponding to said guideline. 
     According to one preferred embodiment, each passage assumes the form of a slot extending along the guideline, i.e. the bottom of said slot extends substantially parallel to the radial direction. Preferably, it is provided that each slot is formed so as to open in said circumferential direction. 
     Preferably, each slot has, seen from the outside in relation to the member and along said guideline, a substantially semi-circular or substantially semi-oblong shape. 
     Whatever the contemplated case, each slot allows the connection arm to be passed through by a tool, the ends of which can then cooperate with the inner surface of said arm, near the slots. The aforementioned inner surface therefore constitutes a stop surface for the tool, substantially oriented towards the inter-arm space it defines. This stop surface can indeed serve as a bearing surface for a removal tool, which can then be stressed in the longitudinal direction towards the back in order to cause the desired removal. 
     According to another preferred embodiment of the present invention, each passage has, seen from the outside in relation to the member and along said guideline, a closed delimiting line. In this respect, this may involve a delimiting line with a general oblong or circle shape, of the bore type. 
     Preferably, the locking member forms an angular sector of an annular locking device, intended to be centered on the axis of the turbine equipped with such a device. 
     The invention also concerns a device for fastening ring sectors on an aircraft turbine engine, comprising casing elements formed with first circumferential rims on which second back circumferential rims of the ring sectors are applied, the fastening device also comprising a plurality of locking members as described above, engaged on said first and second circumferential rims to keep them pressed against each other. In such a case, the first and second circumferential rims, extending towards the back in the longitudinal direction, therefore penetrate through the front opening of the members defined between the clamping arms, in order to be kept radially pressed against each other there. 
     The invention also concerns an aircraft turbine engine turbine comprising a device for fastening ring sectors as described above, and/or at least one locking member as described above. It may alternatively involve a turbine engine compressor, without going beyond the scope of the invention. 
     Lastly, the invention concerns an aircraft turbine engine comprising a turbine as described above, and/or a device for fastening ring sectors as described above, and/or at least one locking member as described above, this turbine engine being able to be a turbojet engine or a turbo-prop, indifferently. 
     Other advantages and features of the invention will appear in the non-limiting detailed description below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This description will be done in light of the appended drawings, which: 
         FIG. 1  is a partial longitudinal cross-sectional view of a device for fastening ring sectors on a turbine casing of an aircraft turbine engine, according to one preferred embodiment of the present invention, this view also corresponding to a cross-sectional view along plane P 1  of  FIG. 3 , orthogonal to the circumferential direction and passing through one of the passages for gripping the member; 
         FIG. 2  is an enlarged partial view similar to that shown in  FIG. 1 , this view also corresponding to a cross-sectional view along plane P 2  of  FIG. 3 , constituting a fictional median plane orthogonal to the circumferential direction; 
         FIG. 3  shows a perspective view of a locking member belonging to the device for fastening ring sectors shown in  FIGS. 1 and 2 ; 
         FIG. 4  shows, enlarged, the locking member shown in  FIG. 1 ; 
         FIG. 5  shows the member shown in  FIGS. 3 and 4 , in cross-section passing through the two clamping arms, and orthogonally to the guidelines of the two passages; 
         FIGS. 6   a  to  6   c  diagram a method for removing the locking member shown in  FIGS. 1 to 5 , with  FIG. 6   b  corresponding to a view along line VIb-VIb of  FIG. 6   a;    
         FIG. 7  shows a view similar to that shown in  FIG. 3 , the locking member respectively assuming the form of an alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In reference jointly to  FIGS. 1 and 2 , it is possible to see a device for fastening ring sectors on a turbine casing of an aircraft turbine engine, according to one preferred embodiment of the present invention. 
     In the figures, direction A corresponds to the longitudinal or axial direction, parallel to the longitudinal axis  2  of the turbine of the turbine engine. Direction B corresponds to the radial direction of the turbine, and direction C to the circumferential direction. Moreover, arrow  4  diagrams the main direction of the flow of gas within the turbine engine, parallel to direction A, the terms “front,” “upstream,” “back,” “downstream” used in the continuation of the description being used in reference to a direction of forward movement of the aircraft under the effect of the thrust from the turbine engine, this direction of forward movement being opposite the direction of arrow  4 . 
     In  FIG. 1 , reference  10  designates the mobile vanes of a high-pressure turbine stage of a turbine engine, which rotates in a turbine casing  12  inside which the casing elements  14  are fastened, called spacers or intermediate casing elements. The elements  14  support ring sectors  16  arranged circumferentially around the axis of rotation  2  of the turbine, along direction C, the inner surfaces of these ring sectors forming a continuous cylindrical surface that outwardly defines a gas passage stream in the turbine. 
     The ring sectors  16  have an angular scope around the axis of the turbine, in direction C, of about 10 to 20° , and there are for example around thirty of them. 
     Each ring sector  16  comprises, at its upstream end or front end, a circumferential rim  18  in cylinder portion form, by which it is hooked or fastened on a spacer  14 , and also comprises at its back end or downstream end a circumferential rim  20  in cylinder portion form that is applied against a corresponding circumferential rim  22  in cylinder portion form of the spacer  14 . Hereinafter, the circumferential rim  22  is called first circumferential rim, and the circumferential rim  20  is called second circumferential rim. 
     The two circumferential rims  20  and  22  extending in direction A are kept pressed against each other in direction B in which they are superimposed, by a C- or sideways U-shaped locking member  24  that is engaged from the back on the circumferential rims  20  and  22  and that keeps them radially pressed against each other. 
     Jointly, the locking members  24  form an annular locking device centered on the axis  2 , which is an integral part of the fastening device of the ring sectors. Thus, each member  24  assumes the form of an angular sector of the annular locking device, extending for example over about 10 to 20° , in direction C. To form a complete, preferably continuous ring, they are provided adjacent in direction C, for example around thirty of them centered on the axis  2 . 
     In this respect, it is noted that although the angular area of the members  24  around the axis  2  of the turbine can be of the same order as that of the ring sectors  16 , this area can alternatively be higher, without going beyond the scope of the invention. Thus, depending on the case, it is possible to provide one locking member  24  per ring sector  16 , or one locking member  24  for several ring sectors  16 . 
     The ring sectors  16 , the spacers  14  and the locking members  24  are metal, made of a metal matrix composite (CMC), or of other materials, and the locking members  24  are elastically mounted clamped on the circumferential rims  20  and  22 , to press them against each other with a certain pre-stress in the radial direction B, as will be detailed below. 
     As diagrammatically shown in  FIG. 2 , the second circumferential rim  20  of the ring sector  16  ends at its back end with radial teeth  26  oriented outwardly, and engaged in corresponding notches of the first circumferential rim  22  of the spacer  14 , so as to immobilize each ring sector  16  in rotation around the axis  2  of the turbine on a spacer  14 . 
     Generally, each locking member  24  comprises, in cross-section along a plane orthogonal to direction C as is the case in  FIG. 2 , two clamping arms  28  and  30 , called radially outer and radially inner longitudinal arms, respectively, that are rigidly connected to each other at their back end by a connection arm  32 , and the front ends of which are applied on the outer cylindrical face of the first circumferential rim  22  of the spacer  14  and on the inner cylindrical face of the second circumferential rim  20  of the ring sector  16 , respectively. Globally, the circumferential arms  28 ,  30  extend longitudinally in direction A, and are spaced away from each other in a general spacing direction, here preferably corresponding to radial direction B. The circumferential arm  32  extends substantially in this spacing direction, i.e. in radial direction B, to connect the two back ends of the arms  28 ,  30 . These last two arms therefore jointly form an inter-arm space open towards the front in direction A for the passage of the rims  20 ,  22 , and closed towards the back in this same direction A by the connection arm  32 , and more specifically by an inner surface  33  thereof. 
     While  FIG. 2  shows that the member  24  assumes, in cross-section orthogonal to direction C, a C or sideways U shape, it must be understood that the member extends under this form over a given angular sector along direction C, between a first circumferential end  24   a  and a second circumferential end  24   b,  as shown in  FIG. 3 . 
     More specifically in reference to this figure, one of the particularities of the present invention lies in the installation, preferably at the circumferential ends  24   a,    24   b  or near them, of means allowing the gripping of the locking member  24 , globally arranged towards the back thereof, i.e. on the connection arm  32 . 
     This means assumes the form of two passages, each in slot form, respectively provided on either side of the plane P 2  constituting a fictional median plane orthogonal to direction C. More specifically and as mentioned above, the two slots  42  are respectively arranged at the ends  24   a,    24   b,  and have the particularity of each extending along a straight guideline  44 , preferably positioned axially, parallel to the arms  28 ,  30  and orthogonally to the connection arm  32 . For information, the two straight lines  44  are therefore substantially parallel, and spaced circumferentially apart from each other. 
     In reference jointly to  FIGS. 3 to 5 , it is possible to see that each slot  42  extends cylindrically along its straight guideline  44 , while being formed through the arm  32 , to emerge in the inter-arm space  40 , at the inner surface  33 . 
     In the illustrated preferred embodiment, each slot  42  is formed only through the arm  32 , away from the two arms  28 ,  30 . Nevertheless, each arm could extend more significantly in radial direction B, for example to the two clamping arms  28 ,  30 , without going beyond the scope of the invention. 
     Each slot  42  opens in the circumferential direction C, i.e. its bottom  46  is oriented in that same direction, towards the outside of the member. Preferably, seen outwardly in relation to the member and along the guideline  44 , like that of  FIG. 5 , the slot  42  assumes a substantially semi-oblong shape, with the corresponding circle half-diameter at the bottom  46  of the slot. 
     This bottom  46  forms a gripping surface for a removal tool. Nevertheless, the gripping of the member with the tool is preferably done using the inner surface  33  of the arm  32 , forming a stop surface for the ends of a tool having passed through that same arm  32 , through the slots  42  provided to that end. This stop surface  33  can indeed serve as a bearing surface for a removal tool  24 , which can then be stressed in the longitudinal direction towards the back in order to cause the desired removal. The particular positioning of these slots, offset towards the back on the member  32 , implies that the removal tool can easily cooperate with the member without risking damaging the functionalities thereof, in particular therefore due to the absence of direct contact between the front end of the arms  28 ,  30 . 
     In reference now to  FIGS. 6   a  and  6   c , a method is diagrammed targeting the removal of a locking member  24  initially situated in its gripping position of the ring sectors  16 , shown in the preceding figures. To do this, a tool  50  of a suitable shape is used, this tool globally having a stirrup-shaped head having two arms respectively provided with two ends  52  opposite each other, capable of being moved in direction C. The two opposite ends  52  are respectively inserted in the two slots  42  until they penetrate the inter-arm space  40 , for example by moving the tool in relation to the member  24  in direction A. Then, as shown diagrammatically in  FIG. 6   b , the two ends  52  are brought closer to each other along direction C, so as to be brought opposite the inner surface  33  of the arm  32 , near the two slots  42 , respectively. At that moment, the two arms of the stirrup head pass through the two slots  42 , respectively. The tool  50  is then stressed in the longitudinal direction A towards the back, manually or automatically, which results in putting the ends  52  in contact with the inner stop surface  33 , as shown in  FIG. 6   a . Continuing this action on the tool  50 , diagrammed by arrow  56  in  FIG. 6   c , results in gradually moving the member  24  in direction A by sliding towards the back of the arms  28 ,  30  on the rims  20 ,  22 , until complete removal of the member  24  releasing the ring sectors. 
     Other designs can be provided for the locking member according to the invention, like that shown in  FIG. 7 , in which the passages  42  are substantially recentered, i.e. spaced away from the circumferential ends  24   a,    24   b,  while remaining positioned on either side of the fictional median plane P 2 . 
     The embodiment that is shown here also differs from the preceding one in that the two passages no longer assume the form of slots, but are like bores. Indeed, each passage  42  has, seen (not shown) outwardly in relation to the member and along guideline  44 , a closed delimiting line  60 , for example circular or oblong. The passages  42  formed in the arm  32  are naturally through-passages, in particular to allow, as in the first preferred embodiment, the introduction of the ends of a removal tool into the inter-arm spaces, for their cooperation with the inner stop surface of the clamping arm  32 . 
     Of course, various changes can be made by a person skilled in the art to the invention just described, solely as non-limiting examples.