Abstract:
An annular connector for connecting a rotor and shaft, has an axial cross sectional profile which approximates a serpentine form. The shape defines only obtuse angles and curves, so that during rotation of the assembly, stress variations in the connector are reduced, as are stress peaks.

Description:
FIELD OF THE INVENTION 
     Power generating means such as gas turbine engines, generate power by passing air through a compressor, burning some of the compressed air with fuel in a combustion chamber, and expelling the resulting gases to atmosphere via a turbine system. The operation becomes self sustaining, in that the turbine system drives shafting to which a rotor or rotors are connected, the or each of which has a plurality of compressor blades spaced about its rim in known manner, for the purpose of compressing the air which flows therethrough, to the combustion chamber. 
     BACKGROUND OF THE INVENTION 
     It is known, to connect a rotor to a shaft, via a drive arm consisting of an annular member, the axial cross sectional shape of which likens a hairpin, which is a term of art. However, such a shape as is described immediately hereinbefore, when absorbing the stresses imposed on the assembly of rotor and shafting during rotation, does so in a manner which results in a non uniform distribution of those stresses, which in turn, results in high value peak stress loads in local places. This adversely affects the life of the components of the assembly. Therefore, the present invention seeks to provide an improved rotor shaft connector. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a rotor and shaft connector comprises an annular drive arm for interconnecting said rotor and said shaft, a radially outer portion of said drive arm being fixable to said rotor and a radially inner portion of said drive arm and being fixable to said shaft, so that said rotor and shaft are operationally maintained in radially spaced apart relationship, said drive arm including a portion that is so configured as to be semi-toroidal in configuration to define a radially outer rim of said drive arm that is fixable to said rotor, said drive arm additionally including a radially inner flange that is fixable to a corresponding flange provided on said shaft, the arrangement being such that variation in stress distribution throughout said drive arm is minimized with consequent reduction in the magnitude of stress peaks therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention will now be described, by way of example, and with reference to FIGS. 1 to  3  of the accompanying drawings, wherein 
     FIG. 1 is a diagrammatic axial cross sectional part view of a gas turbine engine rotor system incorporating the present invention. 
     FIG. 2 is an enlarged part view of a rotor in FIG.  1 . 
     FIG. 3 depicts an alternative arrangement of the rotor in FIG.  2 . 
     FIG. 4 is an example of prior art. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a gas turbine engine compressor casing  10  supports a plurality of stages of stator blades  12 ,  14  and  16 , in known manner. Stages of rotor blades  18  and  20 , are positioned in known manner, between adjacent stages of stator blades  12 ,  14 , and  14  and  16 . Rotor blades  18 ,  20  are carried on respective rotors  22  and  24 . 
     Each rotor  22  and  24  is fastened to a common shaft  26 , via respective drive arms  28  and  30  which, as depicted, are integrally formed with their respective rotors  22 ,  24  and respective annular flanges  32  and  34 . The flanges  32  and  34  are fastened, by any suitable means such as bolts (not shown), to respective annular flanges  36  and  38 , which are formed integrally with the rotor shaft  26 . 
     Referring now to FIG. 2, in this example, which represents all of the rotors in the compressor casing  10 , the drive arm  28  has a portion  28   a  which is turned radially outwardly of, and over the drive arm, to join a face of the rotor  22 , adjacent the rim of a bore  42  which passes therethrough. 
     The shape of the curved portion  28   a  defines a part-elliptical cross-section, semi-toroid which, on operational rotation of the rotor  28  and the associated shaft  26 , by virtue of its curvature, distributes the working stresses which the drive arm  28  experiences, substantially evenly throughout its length, from flange  32 , to rotor  22 . It follows, that local stress peaks of any significant magnitude are avoided. 
     Referring now to FIG. 3, this example of the present invention differs from FIG. 2, firstly in that the semi-toroid  28   a  is truly part-circular in cross sectional profile, and the flange  32  joins the straight portion of drive arm  28  via a further curved portion  44 . This form also distributes stress loads more evenly than hitherto, with consequent reduction of local stress peaks. In both cases, a longer component operating life is thus achievable, compared to the life which is achieved by the prior art component depicted in FIG.  4 . 
     A further alternative form (not shown) of the present invention consists of curving that portion  46  of the drive arm  28 , which joins the flange  32  and the semi-toroid. Such a curve would have a relatively large radius of curvature, so as to avoid having to reduce the magnitude of the radius of curvature of the semi-toroid, in order to achieve tangial blending of the two radii. Moreover, no part of the curved portion  46 , if adopted, should dip below the maximum diameter of the flange  32 , so as to avoid effectively forming an acute angle therebetween. In FIGS. 1 to  3 , the portion  46  is frusto conical, and its small diameter end joins the flange  32  or  34  so that between them, the flanges  32  or  34  and portion  46  define an obtuse angle. As stated hereinbefore, the arrangement ensures a reduction in stress peaking areas, as the stresses move along the drive arms  28  and  30 . It follows that, forming the curved portion portion  46  in the manner described hereinbefore, will provide an identical advantage. 
     A rotor and drive arm in accordance with the present invention, can be manufactured in a number of ways, as follows. Firstly, the whole can be produced as a forged blank. This is the preferred method. The blank is then profile turned so as to form the totally finished article. Such a method of production is well known. It does have a drawback, in that if an error is made during the turning operation, the whole is scrapped. 
     An alternative mode of manufacture, is to form the rotor and drive arm from separate pieces. Referring again to FIG. 3, the rotor  22  has been produced and machined, during which process, a recess  48  has been cut in the face of that side to which the associated drive arm  28  is connected for operation. The drive arm  30  has been produced separately, and has a further flange  50  formed thereon, which fits into the recess  48  in the rotor  24 . When so fitted, the flange  50  and rotor  24  are welded together, about their external joint lines  52  and  54 . 
     The rotor  24  and drive arm  28  could be bolted together, but such a fastening would create weight, windage and balance problems.