Patent Abstract:
A lock for constraining blades in a hub includes a flexible ring for constraining the blades from moving axially in the hub, a finger attached to the hub for preventing the ring from rotating relative to the hub and whereby the ring flexes about at least a partial circumference thereof if urged axially by the blades.

Full Description:
FIELD 
     This application relates to blade retention in gas turbine engines and the like. 
     BACKGROUND 
     Typically, a rotor assembly for an aircraft engine has a rotor disk and one or more arrays of rotor blades. The rotor blades extend outwardly into a working medium flow path such as air. The rotor blades engage the outer periphery or rim region of the rotor disk. The rim region of the rotor disk is defined generally by axially oriented slots that receive the roots of the rotor blades. 
     The working medium gases exert a tangential force and an axial force on the blades as the gases flow through the rotor assembly. The axial force on the rotor blades urges the rotor blade bases axially forward relative to the movement of aircraft carrying the engine and out of the axially oriented slots. Lock means are provided to lock the rotor blades against this forward axial movement. These locks add to the rotational mass of the rotor assembly and must be carried by the rotor disk. 
     If a rotor blade suffers a foreign object strike, however, the rotor blade tends to rotate about the points where the foreign object strikes sending the rotor blade&#39;s root forward relative to the movement of aircraft within the rotor disk. For this reason, to protect the integrity of the rotor and the rest of the engine, lock means are also provided to lock the rotor blades from moving axially forward. 
     SUMMARY OF THE INVENTION 
     An exemplary embodiment of a lock for constraining blades in a hub includes a flexible ring for constraining the blades from moving axially forward in the hub, a finger attached to the hub for preventing the ring from rotating relative to the hub and whereby the ring flexes about at least a partial circumference thereof if urged axially by the blades. 
     A further exemplary method for mounting a blade on a hub includes inserting a blade root into a slot in the hub, placing a flexible ring against the blade root, placing a finger within the ring to prevent its rotation and wherein the ring flexes axially about at least a partial circumference thereof if urged by the blade root. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an aircraft hub, a lock ring and an anti-rotation ring. 
         FIG. 2  is a perspective exploded view of the aircraft hub, a lock ring and an anti-rotation ring of  FIG. 1 . 
         FIG. 3  is a schematic view of the aircraft hub, a lock ring and an anti-rotation ring of  FIG. 1 . of  FIG. 1 . 
     
    
    
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1-3 , a hub  10  for an aircraft engine (not shown) or the like, with a lock ring  15  and an anti-rotation ring  20  is shown. The hub  10  has a plurality of splines  25  for attaching to a shaft (not shown). The hub has a plurality of mounts  30 , such as slots, for holding a fan blade root  35 . The mounts  30  have a trapezoidal cross section  40  that runs from the front  45  of the hub towards a back  50  of the hub. The trapezoidal cross section securely traps the fan blade root  35  therein. Other shapes of such mounts are contemplated herein. 
     A circular ring mount  55  is disposed about a front  45  of the hub. The ring mount  55  has a plurality of outer diameter tabs  60  that are separated by gaps  65 . The hub also has a plurality of inner diameter tabs  70  extending radially inwardly towards the spline  25 . Each inner diameter tab  70  at an end  75  thereof has an axial flange  80  extending outwardly therefrom. The inner diameter tab also has a hole  85  through which a bolt  90  is designed to extend. 
     Referring to  FIGS. 2 and 3 , each lock ring  15  has an inner surface  95 , an outer surface  100 , a front edge  105 , a back edge  110 , and internal diameter tabs  115  extending around the inner surface  95  of the lock ring. 
     The anti-rotation ring  20  has a circular body  120 , fingers  125  that extend towards the back end  50  of the hub, inner diameter tabs  130  that depend inwardly towards the splines and an axial flange  135  extending radially towards a front of the hub  45 . The axial flange  135  sits upon and cooperates with axial flange  80  of the hub. The inner diameter tabs  130  have a hole  140  extending therethrough. 
     During assembly, the lock ring  15  inner diameter tabs  115  are aligned with and disposed within the gaps  65  of the hub  10  and pushed axially towards the mounts  35  into the circular ring mount  55 . Once the inner diameter tabs  115  clear the gaps  65 , the lock ring is rotated as shown in  FIG. 3  so that the lock ring inner diameter tabs  115  are disposed behind the hub  10  outer diameter tabs  60 . Bolts  90  are threaded through holes  140  in the anti-rotation ring  20  and holes  85  in the hub  10  after which nuts  145  (see  FIG. 3 ) are threaded on the bolts and secured thereupon. In this arrangement, the axial flange  135  and the inner diameter tabs  130  of the anti-rotation ring  20  are seated against the inner diameter tabs  70  and axial flanges  80  of the hub  10 . The fingers  125  extend through the gaps  65  and prohibit the lock ring from rotating relative to the hub  10 . 
     If there is foreign object damage or bird strike against the blade  155  (see  FIG. 3 ), the strike or damage will cause a moment of inertia to move the blade root forward towards the front end  50  of the hub  10 . Because the lock ring  15  is designed to flex torsionally behind the outer diameter tabs  60  of the hub  10 , impact of the blade strike will be shared along a circumference of the lock ring  15  such that the anti-rotation key fingers do not shear and the blade lock does not shear and the blade root is retained within the hub  10 . 
     By allowing movement, such as deflection, in the lock ring  15  about a circumference thereof, split rings of the prior art (not shown) may be eliminated and the weight of the lock ring will be minimized to allow a more efficient arrangement. 
     Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Technology Classification (CPC): 8