Cylindrical keyed coupling for composite propulsion shafting

Abstract

A coupling for a torsional drive includes a rotatable shaft, an outer surface of which has a keyway comprising a half-round groove. A rotatable hub disposed around the shaft and coaxial with the shaft has an inner surface provided with a second keyway, the second keyway also having a half-round groove. The two keyways are alignable so as to form a cylindrical keyway between the hub and the shaft. A cylindrical key is insertable into the cylindrical keyway between the shaft and the hub to prevent relative rotation therebetween. A plug disposed inside the rotatable shaft prevents radial deformation of the shaft. The material of the hub and the shaft may differ, in which case the material of the key is optimized to reduce stress concentrations and stiffness differentials between the hub and the shaft. The cylindrical key and the cylindrical keyway also may be conically tapered. The formed keyway and key may also be elliptical.

What is claimed is: 
     
       1. A coupling for a torsional drive, the coupling, comprising: a rotatable hollow shaft made frown a shaft material and having therein an axial bore and further having an outer surface provided with a first keyway, said first keyway comprising a half-round groove;   a rotatable hub made of a hub material and disposed around said shaft and coaxial with said shaft, said hub having an inner surface provided with a second keyway, said second keyway comprising a half-round groove, said first keyway and said second keyway being alignable upon appropriate rotational alignment of said hub and said shaft to form a cylindrical keyway between said hub and said shaft;   a cylindrical key made of a key material and insertable into said cylindrical keyway between said shaft and said hub, to prevent relative rotation therebetween; and   a bore plug made of a plug material and disposed in said axial bore substantially axially aligned with said cylindrical keyway for preventing radial deformation of said shaft by said key.   
     
     
       2. The coupling of claim 1, wherein said hub material and said plug material are metal. 
     
     
       3. The coupling of claim 2, wherein said shaft material is a fiber reinforced resin matrix composite material. 
     
     
       4. The coupling of claim 3, wherein said key material is selected so as to minimize a stiffness differential between said shaft and said hub. 
     
     
       5. The coupling of claim 4, wherein said key material has a stiffness that is intermediate between a stiffness of said shaft material and a stiffness of said hub material, so as to control the stiffness differential between said shaft and said hub. 
     
     
       6. The coupling of claim 1, wherein said cylindrical key and said cylindrical keyway are conically tapered. 
     
     
       7. The coupling of claim 1, wherein said first keyway has a keyway length measured in an axial direction of said shaft and said key has a key length measured in said axial direction and wherein said keyway length is substantially the same as said key length. 
     
     
       8. A coupling for a torsional drive, the coupling, comprising: a rotatable hollow shaft having therein an axial bore and further having an outer surface provided with a first keyway, said first keyway comprising a half-elliptical groove;   a rotatable hub disposed around said shaft and coaxial therewith, said hub having an inner surface provided with a second keyway, said second keyway comprising a half-elliptical groove, said first keyway and said second keyway being alignable upon appropriate rotational alignment of said hub and said shaft to form an elliptical keyway between said hub and said shaft;   an elliptical key insertable into said elliptical keyway between said shaft and said hub, to prevent relative rotation therebetween; and   a bore plug disposed in said axial bore substantially axially aligned with said elliptical keyway for preventing radial deformation of said shaft by said key.   
     
     
       9. A coupling for a torsional drive, the coupling, comprising: a rotatable hollow shaft made of a composite material and having therein an axial bore and further having an outer surface provided with a first keyway, said first keyway comprising a half-round, closed-ended groove;   a rotatable hub made of said composite material and disposed around said shaft and coaxial therewith, said hub having an inner surface provided with a second keyway, said second keyway comprising a half-round, open-ended groove, said first keyway and said second keyway being alignable upon appropriate rotational alignment of said hub and said shaft to form a cylindrical keyway between said hub and said shaft;   a cylindrical key made of metal and insertable into said cylindrical keyway between said shaft and said hub, to prevent relative rotation therebetween; and   a bore plug made of metal and disposed in said axial bore substantially axially aligned with said cylindrical keyway for preventing radial deformation of said shaft by said key.