Turbine module assembly device
DESCRIPTION 
     1. Technical Field 
     This invention relates to multi-stage gas turbine engines and particularly to two rotor stage turbine rotor assemblies. 
     2. Background Art 
     In twin spool gas turbine engines, working medium gases are compressed within a low pressure compression section and subsequently a high pressure compression section and used as an oxidizing agent in the production of a high temperature effluent. The high temperature effluent is subsequently expanded through a high pressure turbine section and subsequently through a low pressure turbine section. The high pressure turbine drives the high pressure compressor by way of a high pressure shaft and the low pressure compressor is driven by the low pressure turbine by way of a low pressure shaft disposed within the high pressure shaft. Within the turbine section rotor stages attached to the shaft are comprised of a hub, a disk and blades disposed about the peripheries of the disk. The flowpath shape is defined and maintained by a circumferential air seal between the two rotor stages. Blades extend outwardly across the flowpath for working medium gases to extract energy from the gases flowing thereacross. The energy is transmitted to the shaft by way of the disk and hub. High pressure turbines usually comprise two rotor stages with approximately equal amounts of work extracted from each rotor stage. Modern turbofan engines can generate over 60,000 pounds of thrust. The torque transmitted by each rotor stage of the high pressure turbine to the high pressure shaft in a large turbofan engine is approximately 500,000 inch pounds. 
     A major design goal of complicated turbofan engines is ease of assembly and disassembly while still maintaining structural integrity and limiting the weight of the engine. Limiting the size and weight of the disk portion of the turbine rotor stage while maintaining the structural integrity of the turbine rotor assembly is extremely beneficial. Eliminating holes and flanges for connecting the two turbine rotor stages together is also beneficial for preserving material strength in the face of high centrifugal loads and vibrations. 
     It is known in the field to attach the two rotor stages of the high pressure turbine together using either bolts or a more permanent means such as welding. It is further known to bolt or weld rotor stages to the shaft. These methods of attaching the two rotor stages to each other results in a gas turbine engine that is more complicated and more difficult to assemble and disassemble than is desired. Furthermore, the use of bolt holes in a disk and the flanges required to attach adjacent rotor stages together requires beefed up disks and heavier rotor stages. Bolt holes reduce the stress capability and structural integrity of the disks. Flanges increase the weight of the rotor stage and contribute to vibration problems that must be designed around. Prior art such as U.S. Pat. No. 3,997,962 to Kleitz et al. entitled &#34;Method and Tool for Removing Turbine from Gas Turbine Twin Spool Engine&#34; teaches the use of a spline to attach the two rotor stages to a single shaft. U.S. Pat. No. 4,004,860 to Gee entitled &#34;Turbine Blade with Configured Stalk&#34; shows the hub of the first rotor stage splined to the shaft, and the hub of the second rotor stage splined to the hub of the first rotor stage so that the shaft, the first rotor stage hub and the second rotor stage hub are all concentric. We have discovered that this type of design has difficulty maintaining concentricity between the hubs and the shaft. This means of attachment causes excessive wear of the splines thereby diminishing structural integrity of the hub to hub and the shaft to hub connections. It is also desired to be able to hold the turbine rotor assembly together so that it can be easily and safely transported for later installation in an engine. 
     DISCLOSURE OF THE INVENTION 
     One object of the present invention is a turbine module containing at least two rotor stages and a stator vane stage which can be transported and assembled onto a turbine shaft as a unit. 
     Another object of the present invention is a device for holding together a two stage turbine rotor assembly to permit transporting the assembly and disposing the assembly, as a unit, onto a turbine shaft. 
     A further object of the present invention is means for securing together the elements of a two stage turbine rotor sub-assembly which assures proper circumferential alignment between the two stages. 
     According to the present invention a gas turbine rotor assembly includes a first rotor stage with a first hub having a plurality of radially inwardly extending first lugs, a second rotor stage with a second hub having a plurality of radially inwardly extending second lugs which are equal to in number and cooperate with the first lugs to form projections, and a ladder lock overlaying the projections comprising a resilient split metal band having circumferentially disposed apertures through which the projections are radially disposed thereby securing the two turbine rotor stages to each other. 
     In accordance with a preferred embodiment of the invention the first and second rotor stages are a part of a larger turbine module which includes a stage of stator vanes disposed between the rotor stages. 
     A principal advantage of the present invention is the ability to secure the two turbine hubs of a turbine rotor assembly together thereby facilitating the assembly, disassembly, transporting, and mounting onto a turbine shaft of the turbine rotor assembly. An additional advantage is to be able to effectively axially trap and radially support an interstage seal between the two turbine stages of the turbine rotor asembly without having to bolt or weld the two rotor stages together. 
     The foregoing and other objects, features and advantages of the present invention will become more apparent in the light of the following detailed description of preferred embodiments thereof as shown in the accompanying drawing. 
     Coaxial non-concentric thrust bearing relationship allows the hubs to be disposed on the engine shaft either individually or as part of an entire rotor assembly, or as part of a turbine module which includes the static structure. If the two disks are to be disposed on the shaft as a unit, such as a rotor assembly or turbine module, means are provided to hold such assembly together as it is installed, such as a fixture or other type of locking apparatus to be further described herein. 
     A principal advantage of the present invention is the ability to easily mount the individual rotor stages or a two stage rotor disk assembly to the engine shaft while maintaining an effective connection between the rotor stages and the shaft. An additional advantage is to be able to effectively trap and support an interstage seal between the two turbine rotor stages without having to bolt or weld the two rotor stages together. Yet another advantage of the invention is a turbine module, including both rotating and static structure, which is easily and effectively disposed on a shaft. 
     Other features and advantages will be apparent from the specification and claims and from the accompanying drawings which illustrate an embodiment of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a cross-sectional view of a gas turbine engine high turbine section incorporating the features of the present invention. 
     FIG. 2 is a view of part of the high turbine section of FIG. 1 with the turbine shaft removed. 
     FIG. 3 is a perspective view of a lock ring used to hold the turbine rotor stages together during installation of the rotor assembly in the engine. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A turbine module 5 constructed according to the present invention is shown mounted on the high rotor shaft 20 of a gas turbine engine in FIG. 1, and is shown separate from the shaft in FIG. 2. The module 5 includes a turbine rotor assembly 10 and a stator assembly 94. The rotor assembly 10 includes a first rotor stage 30 and a second rotor stage 40. The first rotor stage 30 comprises a first hub 32 and a first disk 34 cantilevered off the hub 32. The second rotor stage 40 comprises a second hub 42 and a second disk 44 cantilevered off the hub 42. A first disk rim 36 supports a first plurality of turbine blades 38. A second disk rim 46 supports a second plurality of turbine blades 48. An annular interstage seal 92 is disposed between, is supported radially by, and rotates with the disks 34, 44. 
     The stator assembly 94 includes a stage of stator vanes 102 disposed between the blades 38 and 48, a first annular outer air seal 96 surrounding the blades 38, and a second annular outer air seal 98 surrounding the blades 48. An inner stator shroud 104 supports a seal land 105 which cooperates with the rotating interstage seal 92. The seals 96, 98 and the vanes 102 are secured by suitable means to a turbine case section 106, which is also part of the stator assembly. More specifically, the first outer air seal 96 and the front end of the outer shroud 100 are attached to a first flange 108 of the turbine case section 106, and the second outer air seal 98 and the rear end of the outer shroud 100 are attached to a second flange 110 of the turbine case section 106. 
     The turbine blades 38 and 48 extract energy from the working fluid. The energy is transmitted to the shaft 20 by way of the first rotor stage 30 and second rotor stage 40. The shaft 20 has a first external spline 54 and a second external spline 64 which are axially displaced from each other and have the same diameter. The first hub 32 has a first internal spline 52 which is coaxial with and non-concentric to a second internal spline 62 on the second hub 42. The internal splines 52, 62 also have the same diameter. The first internal spline 52 on the first hub 32 engages the first external spline 54 on the shaft 20 for transmitting torque from the first rotor stage to the shaft. The second internal spline 62 on the second hub 42 engages the second external spline 64 on the shaft 20 for transmitting torque from the second rotor stage to the shaft. The large torque transmitted to the shaft 20 by each rotor stage is about 500,000 inch pounds in a large turbofan engine. Because the external splines 54 and 64 are of equal diameter, the hubs 32 and 42 can be easily slid forward onto shaft 20. This also makes machining of the splines on the shaft and on the hubs simpler. 
     Although preferred, equal diameter splines are not required for this invention. As long as the inside diameter of the first internal spline 52 is as large or larger than the inside diameter of the second internal spline 62, the first and second hubs 32 and 42 can be slid onto shaft 20 individually, or attached to each other as part of a sub-assembly or turbine module. 
     A cylindrical ridge 72 forms an annular recess 74 in the rear of first hub 32 to receive the front end 73 of the second hub 42, thereby preventing radial displacement between the first and second hubs. The front end 73 of the hub 42 also bears axially against the hub 32 such that the hubs 32, 42 are in thrust bearing relationship. A nut 120 having internal threads 122 screws onto screw threads 26 located near the rear of the turbine shaft 20 and aft of the second external spline 64. The nut 120 is in thrust bearing relationship with the second hub 42 and is used to tighten up the turbine rotor assembly 10 against a stop 24 which, in this preferred embodiment, is the bearing seal face of a bearing (not shown) located just forward of the turbine. An annular lock 130 has a third external spline 134 which engages a third internal spline 124 on nut 120. The lock 130 also has a plurality of tangs 132 circumferentially disposed about its forward end which engage a plurality of notches 28 in the rear end of shaft 20, thereby preventing the nut 120 and the lock 130 from rotating relative to shaft 20. Lock 130 has a plurality of rear tabs 136 which extend radially outwardly into an interior groove 126 on the nut 120. A first lock ring 140 and second lock ring 142 disposed in the groove 126 on either side of tabs 136 prevent axial displacement of the lock 130. 
     Referring to FIGS. 2 and 3, a first plurality of radially inwardly extending lugs 35 are circumferentially disposed about the rear end of the first hub 32 and a second plurality of radially inwardly extending lugs 45 are circumferentially disposed about the front end of the second hub 42. The two sets of lugs are mirror images of and abut each other to define radially inwardly extending projections 80. The sets of lugs 35 and 45 are arranged so that when they align axially, internal splines 52 and 62 also align axially, the teeth of the and the turbine blades 38 and 48 are in the desired circumferential relationship with respect to each other. 
     If the rotors 30, 40 are to be disposed on the shaft 20 as a unit such as a rotor assembly or a turbine module, or if such rotor assembly or turbine module is to be transported, a ladder lock 60, comprising a resilient metal band having circumferentially disposed rectangular apertures 61 therethrough and a split 63, is used to axially secure the first hub 32 to the second hub 42 for transporting the turbine rotor assembly 10. 
     The uninstalled diameter of the ladder lock 60 is larger than its desired assembled diameter so that, when in position with the projections 80 extending through the apertures 61, the ring will spring radially outward to rest against the inside diameters of hubs 32 and 42. The projections 80 fit closely within the apertures 61 to prevent any significant relative axial or circumferential movement between the rotor stages 30, 40. The interstage seal 92 is also held tightly in position between the stages. 
     Once the turbine module 5 is assembled onto the shaft 20 (FIG. 1) the splines 52, 62, nut 120, and lock 130 maintain the proper angular and axial position of the rotor stages 30, 40. The ladder lock 60 therefore serves no operational function during engine operation. It does, however, allow the turbine module 5 to be removed as a unit when servicing the engine. 
     Although the invention has been shown and described with respect to a preferred embodiment thereof, it should be understood by those skilled in the art that other various changes and omissions in the form and detail thereof may be made therein without departing from the spirit and the scope of the invention.