Abstract:
A fabricated torque shaft is provided that features a bolt-together design to allow vane schedule revisions with minimal hardware cost. The bolt-together design further facilitates on-site vane schedule revisions with parts that are comparatively small. The fabricated torque shaft also accommodates stage schedules that are different one from another in non-linear inter-relationships as well as non-linear schedules for a particular stage of vanes.

Description:
This invention was made with Government support under Contract No. DE-FC21-95MC31176 awarded by the Department of Energy. The Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a torque shaft assembly and, more particularly, to a torque shaft assembled from easily machined parts, with arms that are oriented one to another so that they move different stages of vanes in an optimal fashion. 
     The key to increased engine performance is increased engine overall pressure ratio. Engine overall pressure ratio is established in the compressor. The key to increased pressure ratio in an advanced compressor is to provide numerous stages of movable compressor vanes whose angles may be varied as the compressor is brought up to speed in order to prevent a condition called “stall”. Compressor “stall” is detrimental to the service life and condition of the compressor. Each stage of vanes may have optimal angle schedules that are different one from another, often in non-linear interrelationships. Furthermore, the vanes must replicate the desired angle schedule in both the opening and closing direction, which means that deflection of the moving system under actuation loads must be minimized. 
     Stage  2  is typically termed the master vane stage. The engine controller is typically programmed to monitor Stage  2 , and move the torque shaft so as to move Stage  2  in accordance with a program keyed to engine speed during startup or to effect power turndowns at constant speed when required. A power turndown is used when the power demand on the grid drops such as during lunch time, for example, and the plant operator wishes to keep the turbine-generator set running and synchronized to the grid. The generators cannot be permitted to generate any more power than the amount of power being used by the grid. 
     When the vane schedule is changed, because of performance requirements or optimization tests, radical changes are usually made to the kinematics of the Variable Guide Vane linkage (VGV) system (referred to by some engineers as Variable Stator Vane (VSV) system). Usually, this means a new torque shaft. Typically torque shafts are cast and then machined to define the torque shaft arm clevis locations. 
     BRIEF SUMMARY OF THE INVENTION 
     Certain new engines feature compressors with several stages of movable vanes that have non-linear schedules which necessitate out-of-plane torque shaft arm clevis locations. The out-of-plane torque shaft arm clevis locations make a cast one-piece torque shaft impractical. In addition, the axial spacing of the torque shaft arm clevis locations leave insufficient room to machine a cast torque shaft even if the torque shaft arm clevis locations are in-plane. 
     Furthermore, the Critical-to-Quality (CTQ) of the VGV system is vane angle accuracy. Accordingly, the present invention provides a torque shaft that addresses the problems associated with VGV systems, and particularly systems in which vanes have non-linear schedules and/or which otherwise preclude or inhibit the manufacture and use of cast, one-piece torque shafts. 
     The present invention provides a fabricated torque shaft that features a bolt-together design to allow vane schedule revisions with minimal hardware cost. The bolt-together design of the invention further facilitates on-site vane schedule revisions with parts that are comparatively small. The fabricated torque shaft of the invention also accommodates stage schedules that are different one from another in non-linear inter-relationships as well as nonlinear schedules for a particular stage of vanes. The invention also eases machining so as to prevent sag of a long shaft during machining. 
     Thus, the fabricated torque shaft of the invention is embodied in an assembly comprising a torque shaft main body having a forward end and a rearward end, bearings defined adjacent each end of the shaft main body, and a plurality of arm structures provided at spaced locations along said torque shaft main body for operatively coupling said torque shaft to a plurality of vane stages of a compressor; wherein at least one of the arm structures is detachedly secured to the torque shaft main body so that the at least one arm structure can be removed and replaced with another arm structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a fabricated torque shaft in a variable guide vane system; 
     FIG. 2 is a perspective view of a fabricated torque shaft comprising a first embodiment of the invention; 
     FIG. 3 is an enlarged view of the area identified in FIG. 2 with the retainer and bolt parts omitted; 
     FIG. 4 is a top plan view of the fabricated torque shaft of FIG. 2; 
     FIG. 5 is a rear elevational view of the fabricated torque shaft of FIG. 1; 
     FIG. 6 is a view taken along line  6 — 6  of FIG. 5; 
     FIG. 7 is an enlarged view of the area identified in FIG. 6; 
     FIG. 8 is a cross—sectional view taken along line  8 — 8  of FIG. 5 with the arm side wall portion omitted for clarity; 
     FIG. 9 is a cross-sectional view taken along line  9 — 9  of FIG. 5 with the arm side wall portion omitted for clarity; 
     FIG. 10 is a side elevational view of an input arm provided in the embodiment shown in FIG. 2; 
     FIG. 11 is a top plan view of the input arm shown in FIG. 10; 
     FIG. 12 is a side elevational view of an inlet guide vane (IVG) arm provided in the embodiment of FIG. 2; 
     FIG. 13 is a cross-sectional view of an exemplary arm provided: for Stages  0 - 4  in the embodiment of FIG. 2; 
     FIG. 14 is a top plan view of the arm shown in FIG. 13; 
     FIG. 15 is a perspective view of a fabricated torque shaft comprising a second embodiment of the invention; 
     FIG. 16 is a top plan view of the fabricated torque shaft shown in FIG. 15; 
     FIG. 17 is a side elevational view partly in cross-section of an input arm provided in the embodiment of FIG. 15; 
     FIG. 18 is a cross-sectional view of a stage  4  arm provided in the embodiment of FIG. 15; and 
     FIG. 19 is a cross-sectional view of a stage  3  arm provided in the embodiment of FIG.  15 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a schematic perspective view of fabricated torque shafts  10 ,  12  provided in accordance with a first embodiment of the invention mounted to a compressor case, generally designated with reference number  14 . Other key components of an exemplary Variable Guide Vane (VGV) system are shown in FIG. 1, to illustrate the component inter-relationships. More specifically, the first and second fabricated torque shafts  10 ,  12  are mounted on diametrically opposite sides of the compressor case  14 . Each shaft  10 ,  12  is mounted to a respective forward torque shaft mount  16 ,  18  and aft torque shaft mount  20  (only one of which can be seen in FIG.  1 ). The inlet and inlet guide vanes are omitted from FIG. 1 for clarity and the inlet guide vanes are instead schematically shown as a dash dot circle  22  at the forward end of the compressor case. As a result, the Stage  0  vanes  24  are visible in FIG. 1 at the forward end of the compressor case. 
     As described in greater detail below, the torque shaft includes a main body  26  having a four sided, generally square coupling  28  at a forward end thereof for being received in a complementary receptacle  30  of an inlet guide vane arm  32 , which is in turn coupled to an inlet guide vane turnbuckle  34  as shown in FIG.  1 . In the illustrated embodiment, the IGV arm is secured to the square coupling  28  with a wire locking insert  36 , a screw  38  and a retainer member  40 , although other known end coupling and retention assemblies may be provided in their stead. 
     In the presently preferred embodiment, the torque shaft main body  26 , best seen in FIGS. 2,  4  and  5 , is generally rectangular in cross-section, most preferably square as illustrated, to allow for planar support during machining of its features, thereby to preclude sag and consequent inaccurate geometry. Adjacent the forward end of the torque shaft main body, a bearing  42  is provided for being received in the forward torque shaft mount  16  of the compressor case (FIG.  1 ). Another bearing  44  is likewise provided at the opposite longitudinal end of the torque shaft main body  26  for being received in the aft torque shaft mount  20  of the compressor casing. 
     In the illustrated embodiment, an arm structure such as an arm clevis is detachably secured to the torque shaft main body for each stage of the VGV system as well as for the actuator input. In a conventional manner, each particular stage of vanes includes a unison ring for shifting the vanes of the stage in unison. Each unison ring is linked to a respective arm clevis of the torque shaft with a turnbuckle. Thus, as illustrated in FIG. 1, there is a Stage  0  arm  46  pivotally interconnected to a Stage  0  turnbuckle  48  which is in turn pivotally coupled to a Stage  0  unison ring  50 . Adjacent to and downstream of the Stage  0  arm, an input arm  52  is provided for being mechanically linked to an actuator mount  54  in a conventional manner. Downstream from the input arm there are respectively Stage  1 - 4  arms  56 , 62 , 68 , 74  pivotally interconnected to respective Stage  1 - 4  turnbuckles  58 , 64 , 70 , 76  which are in turn pivotally coupled to a respective Stage  1 - 4  unison ring  60 , 66 , 72 , 78 . Accordingly, a respective arm structure is provided for each of the Stages for translating movement of the torque shaft via the respective turnbuckle to the respective unison ring. As illustrated and as discussed in greater detail hereinbelow, in the presently preferred embodiments of the invention a bolted on arm clevis structure (hereinafter referred to simply as arm or arm structure) is provided for each movable stage of the compressor. It is to be understood, however, that one or more of the arm structures could be cast and machined with the torque shaft main body. Therefore the invention is embodied in its broadest respect in a fabricated torque shaft having at least one detachable arm structure, although it is preferred that all arms provided as a part of the torque shaft, including the input arm, be detachably secured to the main body thereof. 
     As mentioned above, two torque shafts  10 ,  12  are provided, one on each diametrically opposite side of the compressor case  14 . In the illustration of FIG. 1, only the IGV arm  80 , IGV turnbuckle  82  and forward torque shaft mount  18  of the second torque shaft  12  can be seen. It is to be understood, however, that an assembly generally corresponding to torque shaft  10  would be provided on the opposite side of the compressor case. 
     The specific links, torque shaft interface features and turnbuckle hole location of each arm combined with the arm interface features on the torque shaft determine the specific characteristic location of each vane stage as the torque shaft rotates. Thus, as illustrated in particular in FIG. 4, in an exemplary embodiment of the invention, the receptacles  84 , 86 , 88 , 90 , 92  provided for receiving the respective arms are machined to different depths in the torque shaft main body such that the receptacle  84  for the Stage  0  arm is most shallow of the arm receptacles with the receptacles  86 , 88 , 90 , 92  for,the Stage  1  arm, the Stage  2  arm, the Stage  3  arm and the Stage  4  arm, respectively being progressively more deeply defined in the torque shaft main body  26 . A receptacle  94  is also provided for the input arm  52 . In the illustrated embodiment, the receptacle for the input arm is at a minimal depth, provided substantially to determine the proper location for the input arm along the length of the torque shaft main body and its proper orientation with respect to the axis of the shaft. 
     The features controlling the placement of the arms in the torque shaft can be better appreciated from FIGS. 6,  7 ,  8 , and  9 . A shear bushing  96  is press-fit into shear bushing receptacle  98  defined in each arm receptacle and interfaces precisely with the intended arm. 
     A counter bore  100  is also defined in each receptacle to receive the shear bushing that is press fit into the torque shaft. 
     First and second bolts  102 , 104  and nuts  106 , 108  provided to secure each arm to the torque shaft. The nuts and bolts provided solely to clamp the arm to the torque shaft and thus do not produce positional errors. Pins  110  as shown in the detail of FIG. 7 are associated with each arm and its respective receptacle to ensure that the arm is installed in its intended position. 
     As illustrated in FIG. 6, the pin bores  112  respectively defined in the torque shaft main body and in each arm structure are uniquely disposed. This ensures that an arm structure adapted to, for example, the 4 th  Stage will only be mountable to the 4 th  Stage receptacle due to the mating pin  110 / 112  configuration. Thus, in the illustrated embodiment, the Stage  4  pin/receptacle  110 / 112  is disposed on the rearward end side of the receptacle and arm respectively. The location of the pin is progressively shifted towards the forward end of the torque shaft for each respective receptacle and arm sequentially disposed along the length of the torque shaft so that the Stage  2  pin  110  is disposed generally centrally of the receptacle and arm whereas the Stage  0  pin is disposed on the forward end side of the Stage  0  receptacle. As shown in detail in FIG. 7, one end  111  of the pin  110  is generally domed for being aligned and received in the respective pin bore  112  of the arm. The pin is preferably fixedly secured to the torque shaft main body  26  to be maintained within the respective arm receptacle. 
     As stated above, the receptacles for each of the arms may be machined to different depths depending upon the vane schedule. The arms themselves are desirably provided in shapes determined by the respective vane schedule. In the embodiment illustrated in FIG. 2, the arms provided for each of Stages  0 - 4  have generally a same or similar shape except that the thickness of the base of certain of the arms is varied in this embodiment. Thus, for example, the base  114  of the Stage  4  arm  74  is less thick than the base  116  of the Stage  0  arm  46 . 
     As illustrated in FIGS. 10 and 11, the input arm  52  defines a profile that includes a first generally flat portion  118  projecting generally from a plane of the top surface  120  of the torque shaft main body  26 , an inclined portion  122  on each of the two side wall portions  124  thereof and rounded tips  126  to minimize potential interference with other components during the angular adjustment of the torque shaft. 
     As mentioned above, the inlet guide vane arm  32  in the embodiment of FIG. 2 includes a receptacle  30  having generally flat planar surfaces  146  for respectively engaging generally flat planar surfaces  148  of the square coupling  28  of the torque shaft main body. Thus, rotation of the torque shaft main body according to displacement of the input arm is translated to a displacement of the inlet guide vane arm. The configuration of the IGV arm is determined according to the vane schedule and in the presently preferred embodiment, the IGV arm can be removed and replaced as necessary or desirable. 
     An exemplary arm structure of the type provided for Stages  0 - 4  is illustrated in FIGS. 13-14. Each such arm includes a base  130  by which the arm is secured e.g., as by bolting, to the torque shaft main body and first and second side walls  132  each of which projects in a respective plane that is generally perpendicular to a plane of the base. The bolts for securing the arm to the torque shaft main body  26  are inserted through respective bores  134 , 136  in the base of the arm. To accommodate the enlarged heads of the respective bolts, scarf cuts  138 , 140  are defined on the inner side of each arm side wall. Further, in the illustrated embodiment, a counter bore  142  is defined for receiving the head of the lower bolt so that the bolt will, be disposed entirely within the profile of the arm. A bore  144  is further defined in the base for receiving the pin that determines the proper position of the arm with respect to the torque shaft main body. As will be appreciated, the arms are respectively shaped to achieve the desired vane schedule of the respective stage and so that the torque shaft assembly will not strike another part while it is moving. 
     As is apparent from an examination of FIG. 2, in particular, in one exemplary embodiment, the Stage  0 - 4  arms have a generally similar configuration although the thickness of the base of certain of the arms may differ and the arms are mounted to receptacles of varying depth according to the vane schedule. The arms, however, can and will generally vary in shape according to the vane schedule of the compressor to which the torque shaft is mounted. Thus, an advantage of the fabricated torque shaft assembly of the invention is that one or more of the arms can be removed and replaced either due to potential failure, or because of a change in vane schedule according to which arm(s) of a different shape is determined to be necessary or desirable. 
     Thus, FIG. 15 illustrates an alternate embodiment of the invention in which certain of the arms of the fabricated torque shaft  210  have been removed and replaced as compared to the embodiment of the FIGS. 1-2. In the embodiment illustrated in FIG. 15, the input arm, the IGV arm and the S 0 , S 3  and S 4  arms have all been removed and replaced with arms of a different shape to accommodate a new vane schedule. As can also be seen from FIG. 15, the IGV arm is rounded at the attachment end as compared to the IGV arm of the FIG. 2 embodiment. Also, as illustrated, the input arm  252  is more truncated to receive its respective turnbuckle at a point closer to the torque shaft main body  26  than the input arm  52  of the FIG. 2 embodiment. As shown in FIG. 17, the more truncated side wall portions  232  alters the disposition of the turnbuckle receptacle  248 ; for receiving the respective turnbuckle, thus changing the amount by which the torque arm  210  rotates on actuation. 
     The S 0  arm  246  and the S 3  arm  268  are each substantially modified in the embodiment of FIGS. 15 and 19 so as to depend downwardly substantially below the elevation of the turnbuckle receptacle of :the corresponding arm of the FIG. 2 embodiment. As in the FIG. 2 embodiment, however, the S 3  arm  268  is received in a receptacle  90  that is deeper than the receptacle  84  of the S 0  arm  246 . Also, the depth or thickness of the base  250  of the S 3  arm  268  is less than the base  216  of the S 0  arm  246 . 
     Finally, as illustrated in FIG. 18, the shape of the S 4  arm  274  has been modified so as to be disposed with its turnbuckle receptacle  276  displaced downwardly relative to the turnbuckle receptacle  176  of the FIG. 2 embodiment. As can also be seen, the recess  254  along the bottom surface of the arm  274  is less pronounced in the FIG. 18 embodiment than in the embodiment of FIG.  2 . As will be understood, the arms are fastened to the common torque shaft main body  26  using nuts and bolts as in the FIG. 2 embodiment. Only certain of the arm structures selected for attachment to the torque shaft main body have been changed to accommodate the particular vane schedule of the compressor. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.